Marta Piñeiro _ Master Thesis

Aiming for Zero Emissions in a high-rise building Methodological analysis of an Integrated Design Process Marta PiĂąeiro Lago

Master’s thesis in Sustainable Architecture Supervisors: Luca Finocchiaro and Gabriele Lobaccaro Trondheim. June 2018

Acknowledgements I would like to express my special thanks and appreciation to my supervisors, Luca Finocchiaro and Gabriele Lobaccaro, for their patience and constant support throughout the whole process. This master thesis would not have been possible without your advice. I would also like to thank to the rest of the teachers in the Master in Sustainable Architecture for their implication and all the priceless knowledge.

I want to express my gratitude to Kristian Edwards and Snøhetta, for providing me with all the information that I needed from the case study building. Thanks to Nils Erik Anders Rønnquist and Bendik Manum for your advice regarding the implementation of the structural system. I am also especially thankful to Aitor Almaraz, for his highly appreciated help with the structural calculation and honest advice.

I would like to give a heartfelt thanks to my parents, Carlos and Josefa, for their education, support and understanding. Thanks to you I have been able to experience this unique opportunity not only to study, but to grow surrounded by such an amazing international group of people.

I am also veru thankful to my second family here in Trondheim: Raquel, Anxo, Borja, Rubén, Mi Chi, Roberto, Giorgia, Juan, Luca, Camilo, Marilú, Carmen, María and Alexis, for all the dinners, parties, ski trips and so much fun together. Home does not fell so far away when I am surrounded by all of you.

Special mention to my awesome classmates from the Master in Sustainable Architecture at NTNU. I could not have been luckier to share these two years with all of you. Special thanks to my inseparable colleagues, Juanma Cruz, Irene Hutami and Nikita Chhajer, for all the moments shared together and friendships that do not care about cultural differences.

Finally, I could not end this work without thanking my companion in life, Jairo Rúa, for your patience in reviewing this thesis and the constant jokes to make me laugh during stressful moments.

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Abstract The majority of the population lives in cities, which have been steadily growing due to the continuous increase of inhabitants. In this socio-economic context, population condensation has proven to be the most sustainable urbanism approach,and high-rise buildings emerge as the architectural typology that has been most utilized in order to achieve a sustainable urban model of development.

In the current global situation, 32 % of total global ďŹ nal energy use and 19 % of energy-related GHG emissions are due to the building sector. Thus, ďŹ nding a way to build more sustainably is not a possibility, but an urgent need. This thesis develops a methodology that will allow to design high-rise buildings aiming to achieve the Zero Emission Building Standard (ZEB).

The methodology is developed through a Case Study High-Rise Building with a climate-adapted design.

Parametric tools are implemented towards optimizing the shape and structure of the building and maximising on-site energy production. In addition, Life Cycle Assessment preliminary data and the use of passive strategies are taken into consideration in order to assure a sustainable design.

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Index

1.

3.

Introduction Motivation _ 10

Climate-adapted built form Optimisation parameters _ 30 Design of the geometries to be tested _ 30 Wind optimisation _ 32

State of the art _ 1 1

Solar optimisation _ 38

Aim of the thesis _ 12

Selected geometry _ 42

Methodology _ 13

References _ 49

References _ 15

2.

Case study analysis _ 1 1 Climate analysis _ 12 References _ 27

Preliminary analyses

-6 -

5.

Envelope design Envelope characteristics _ 64 Perforation _ 65 Transparency_ 66 Insulation _ 70 Environmental impact _ 72 Final envelope design _ 73 Variability _ 76 References _ 79

6.

Preliminary considerations _ 52 Structural core _ 53

4.

Structural system selection _ 55 Design and calculation of the deiagrid system _ 58 References _ 61

Structural system

-7 -

Process overview _ 82 Adopted design solutions: Findings and conclusions _ 82 Methodology implemented: Findings and conclusions _ 84 Further work _ 84

Conclusion & discussion

1.

Introduction

Aiming for ZEB in a High Rise Building

1. Introduction

1.1. Motivation Urban densification has motivated the development of tall building structures as a socio-economic solution for the population growth. Large amounts of greenhouse gas emissions are associated to the construction increase of this architectural typology. Hence, designing sustainable yet functional high-rise buildings has become a major need in the last decades.

According to the Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), in 2010 alone, the building sector accounted for 32 % of the total global energy use and 19 % of energy-related greenhouse gas (GHG) emissions. Those emissions added up a total of 49 gigatonnes of CO2 equivalent (Gt CO2 eq) released to the atmosphere (Fig. 1) [1], meaning that 9.31 Gt CO2 eq were directly related to the building sector.

In the case of the United States of America, the third most populated country in the world behind China and India [2], 39 % of the total

In China, the biggest pollutant country in the world, the building sector is becoming the second largest carbon emitter [4]. In 2012, China building sector’s emissions of CO2 equivalent raised up to 1600 million tonnes of carbon dioxide, 1200 millions of them due to indirect emissions and 400 million tonnes to direct emission [5].

When it comes to Norway, the building sector consumes around 50% of the total electricity production. The GHG emissions depend on the primary energy source for electricity and heat, which is hydropower in the case of Norway. Thus, embodied emissions related to this sector are lower than in most industrialised countries [6]. Despite its low GHG emissions in the building sector, Norway’s greenhouse gas emissions accounted for 52.8 million tonnes of CO2 equivalent in 2013, meaning that in order

50%

2050

75%

to fulfil the Paris Agreement, Norwegian overall emissions must be further reduced to 45-47 million tonnes of CO2 equivalent in 2020 [7].

In this international agreement, 195 United Nations member states agreed to limit the global temperature rise below 2 degrees’ Celsius in respect to pre-industrial levels by 2100.

According to scientific consensus documented by the IPCC, this implied to decrease the emissions in 1000 billion tons of CO2 equivalent worldwide starting in 2011 [8].

32% Industry 25% Emissions CO2 eq

2017

Fig. 2: Global population distribution (data from the Food and Agriculture Organisation of the United Nations -FAO-, 2016).

In 2010, a total of 49 Gt CO2 eq were emitted to the atmosphere

19%

Urban population

Rural population

emissions of GHG are due to this building activity, followed by the 33% of transportation and 29% of industry [3].

In the particular case of Norway, the creation of the Norwegian Climate Act constitutes a commitment to reduce GHG emissions by 40% from pre-industrial levels by 2030, and aims for a further reduction targeting 80-95 % by 2050, in line with EU aspirations [8].

In light of the Food and Agriculture Organisation of the United Nations (FAO) statistics, in 25 years, 75 % of the population will live in cities, while the rural population will be decreased up to a 25 % (Fig. 2) [9]. Moreover, 100 billion people are currently homeless, and 1 billion

AFOLU*

Buildings

3 billion people in the next 20 years

40%

Economic sectors

of the current population

*Agriculture, forestree and other land use

Fig. 1: Emissions of CO2 eq by economic sector (data form the IPCC, 2014).

Fig. 3: Future global population scenario.

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Aiming for ZEB in a High Rise Building

1. Introduction

The role of high-density development for a more sustainable growth

Low density

vs.

High density

Fig. 4: Comparison between high and low development models.

live in slums [10]. It is expected that in the next 50 years a considerable percentage of people in developing countries will have access to adequate housing, electricity, and improved cooking facilities. According to the IPCC “The ways in which these energy-related needs will be provided will significantly determine trends in building energy use and related emissions” [1].

Furthermore, as stated by the Canadian architect Michael Green [11], in the next 20 years, world population is expected to be increased by 3 billion people, which represents the 40% of the current global population (Fig. 3). When thinking about such a large number, a highdensity urban model of development seems like the only feasible solution (Fig. 4).

High-rise buildings are defined as the architectural typology in which the dimension on its vertical axis (height) is dominant over the horizontal dimension [12]. This implies a reduction on the footprint and therefore, a higher

embodied emissions may double or potentially triple by the next half of the century” [1]. In either case, the new construction activity in developing countries has promising mitigation opportunities albeit the associated significant risk [1].

most common candidates to replace concrete or steel. This tendency relies on the fact that , due to their carbon sequestration capacity, massive wood products combine the advantages of a sustainable material with those of industrialised processes.

Recent improvements in building’s technology and know-how have enabled construction and retrofit of very low or even zero energy buildings in developed countries. These retrofitting works have sometimes a high initial investment cost but are cost-effective within the building’s lifetime.

In existing buildings, energy savings between the 50 to 90 % of the initial energy consumption have been achieved through deep retrofits [1].

Besides, the use of energy-efficient appliances in lighting and information communication can reduce the substantial increases in electricity use that is expected due to the proliferation of different types of equipment and electronic gadgets used in every day’s contemporary lifestyles.

As an illustration, the carbon storage capacity of a single tree can reach up to 150 Kg of CO2 during its lifetime [15], just by the simple process of photosynthesis. It is estimated that forests could potentially globally sequester up to 2000 million tonnes per year [16]. When using a negative accounting method for the carbon stored in the material, this storage capacity allows compensating the CO2 embodied emissions of the end of life phase. The actual rate of carbon sequestration may vary among the different species. However, younger and fastergrowing trees have higher annual sequestration rates [16]. These are precisely the most suitable kind of species for the fabrication of massive timber products since they allow to increase the production while maintaining a sustainable forest exploitation.

Cities, as we know them nowadays, are predominantly made from steel and concrete.

These main construction and structural materials have great embodied emissions due to fabrication and production processes.

For instance, in a cradle to gate scope (A1 to A3 according to the System Boundary EN 15804:2012), one cubic meter of in-situ concrete may account for up to 188,23 kg CO2 eq [13], while the embodied emissions for a single cubic meter of structural steel may account for up to 10.68 kg of CO2 eq [14].

density ratio. Due to a lower per capita energy use, which is mainly caused by a reduction in transportation energy, compact or high-density urban models are identified by the IPCC as an important sectoral climate mitigation measure [1]. In this kind of development models, highrises play an important role. However, there is no international agreement on a minimum height for this architectural typology, as if a building might be considered or not a high-rise depends on its urban context. In Norway, buildings higher than six storeys may already be considered as high-rise buildings in most urban fabrics.

Accordingly, research in the architectural field is being oriented towards more energy efficient buildings and the use of more sustainable materials. There is a clear tendency in the current architectural scenario in developing structural prototypes and alternative solutions to conventional structural materials using timber-based products. Industrialized massive wood products such as cross-laminated timber (CLT), laminated veneer lumber (LVL) or glued laminated timber (glulam) are nowadays the

1.2. State of the art According to this aforementioned report, “the key trends that constitute population growth, migration to cities, household size changes, and increasing levels of wealth and lifestyle changes will contribute to significant increases in the building‘s energy use. This energy use and its

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In a cradle to gate scope, the use of CLT can suppose up to -601.77 kg CO2 eq per cubic meter of material [17], while a cubic meter of Glulam can suppose up to -629.76 kg CO2 eq [18]. Nevertheless, the embodied emissions in an A1 to A3 phase (production of the materials) for timber-based products can widely vary depending on the Environmental Product Declaration (EPD) database utilised and the accounting method. As a common practice, timber products from sustainably grown forests tend to be considered as carbon neutral since the CO2 emissions released during its combustion at the end-of-life stage are assumed to be resequestered in the growing phase [19].

Due to their minimum footprint and high compactness, high-rise buildings are the most common architectural typology in contemporary cities. The reduction of CO2 embodied emissions due to materials in a high-rise building can be specially noticed in the case of its structure, since

Aiming for ZEB in a High Rise Building

it represents the highest percentage of material in a building. This fact can make a net difference of thousands of kg CO2 eq per structure built.

In order to measure the carbon footprint of a building, the life cycle assessment (LCA) was introduced in the architecture field in the ‘60s.

This concept emerged as a consequence of the increasing concerns over the limitations of raw materials and energy resources. There was an increase of interest in finding ways to cumulatively account for energy use and to project future resource supplies and use [20].

Today, this method is utilised in the architecture field as a tool for decision-making support to assess the environmental impact of a building through its lifetime [19].

In order to encourage the reduction of GHG emissions due to the building sector activities, official certifications for sustainable and energy efficient buildings were introduced in the ‘90s.

Widely known examples of these certifications are the Building Research Establishment’s Environmental Assessment Method (BREEAM) or the Leadership in Energy and Environmental Design (LEED) [21].

1. Introduction

When considering the LCA of a building from a cradle to cradle scope (which means through all the stages of a building’s lifespan within the system boundary EN 15804:2012), operational energy use has traditionally been identified as the main contributor to the GHG emissions [26]. Nevertheless, due to the increase in the regulations’ requirements regarding buildings’ energy efficiency, this stage of the LCA has considerably reduced its environmental impact during the past years [26, 27]. As a result, embodied emissions related to materials from the production and replacement stages are gaining significance [28]. A careful choice of materials can significantly help to achieve a Zero Emission Building standard and consequently, an active reduction in the embodied emissions.

However, this approach is not enough if it is not combined with additional energy saving measures such as passive strategies or a climateadapted building design.

Within the Zero Emission Building concept, five different ambition levels are defined. The lowest ambition level is ZEB-O-EQ, which is achieved when the building’s energy production through renewable energy sources compensates for the embodied emissions of the building’s operation (O), excluding the energy use for appliances and equipment (EQ). The second level, ZEB-O, is similar to the previous one but including

nmental pe viro rfo n E r

e ac m

Moreover, in order to prevent an increase of the global warming effect, national and international initiatives and regulations play an important role.

For instance, at the European level, the revised directive on Energy Performance of Buildings (EPBD) of 2010 establishes the nearly Zero Energy Building (nZEB) as the building target from 2018 for all public buildings, and from 2020 for all new buildings [22].

A holistic approach to the architectural design process for high-performance building design and construction is called Integrated Design Process (IDP). It relies on the idea that every decision on the initial stages of the design will have an impact on the performance of the final architectural result (Fig. 5). In order to do that, every member of the team is supposed to shear a common vision of sustainability and work collaboratively to implement the sustainable goals. To apply this complex design process, wide multidisciplinary teams are often required.

Since its first application in the 1990’, IDP has been proved to produce more significant results than investing in capital equipment upgrades at

Envir on m

m

and inte gra sign de ti

on

ct impa tal en

Energy s yst e

During the past decades, the concept of ZEB has also been widely spread. However, this acronym is linked to a certain degree of confusion since it has two possible significances. The first one is Zero Energy Building, which is probably the most popular interpretation. This term makes reference to the total building’s energy balance which is supposed to be equal to zero, meaning that the energy demand is balanced with the energy production of the building by means of renewable energy sources.

the energy use for appliances and equipment.

The third level, ZEB-OM, compensates for the emissions due to the operation and materials (M). In the fourth level, ZEB-COM, construction (C), operation and embodied emissions due to materials are taken into consideration. Lastly, the highest ambition level is ZEB–COMPLETE, which takes into account all the previous stages, with the addition of the demolition and recycling phases [24, 25].

The second one makes reference to the Research Centre on Zero Emission Buildings (ZEB), which was funded by the Norwegian Research Council in 2009 [6]. The scope of this definition for the Zero Emission Buildings goes beyond the conventional definition of Zero Energy Buildings since the research carried out by the ZEB Centre is mainly focus on the overall CO2 eq emissions, minimising the building’s global warming potential through the assessment of its life cycle analysis (LCA). In other words, the aim of this research centre is to create buildings with zero GHG embodied emissions related to their production, operation and demolition [23].

Fig. 5: Integrated energy system concept.

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later stages [29].

1.3. Aim of the thesis In this master thesis, an Integrated Design Process will be applied to the design of a highrise building, creating a methodology that may allow achieving a Zero Emission Building.

Departing from the assumption that massive timber products have lower embodied emissions than any other frequently used structural material, the possibilities of timberbased structural systems will be explored within the case of a high-rise building.

Rather than focus on the final optimal solution, the main purpose of this master thesis will be to design a methodology for the integrated design process of this building typology in a cold climate with the support of parametric design tools and available simulation software.

Thus, of the whole integrated design process of a Zero Emission Building, this thesis will only focus on the stages previous to the balance of the CO2 emissions with renewable energy sources, which would later allow achieving this zero emission standard. Henceforth, the direction of this thesis will be towards the reduction of the energy consumption and embodied emissions by the implementation of a climate-adapted built form, passive strategies and optimisation of materials.

Research question According to the previously explained, the research question of this master thesis will be: what methodology should be followed and which parameters should be selected for an Integrated Design Process to minimise the environmental impact of a high-rise building?

Aiming for ZEB in a High Rise Building

1.4. Methodology The recent diffusion of advanced simulation software has modified the creative process through which architecture is conceived. This software offers an estimation of the environmental behaviour of different built forms, conditioning the canons on which the aesthetics of the project is based. This simulation and computational software can be utilised throughout the design process, ensuring a meaningful basis for the production of sustainable forms.

In an ordinary building design process, the task flow has been traditionally a linear and sequential set of activities [30]. However, the Zero Emission objective requires an iterative process that embraces the integration of sustainable goals early in the design process through energy performance and emissions accounting calculations (Fig. 6) [31]. Experience

1. Introduction

and materials of the building, the parameters addressed in this case will be: maximise energy efficiency, ensure an optimal production of on-site renewable energy, and minimise the embodied emissions due to materials.

with constructed nearly Zero Energy Buildings, shows that their design process is based on cyclic iterations and simulation-based decision making that effectively integrates, in early stages of the process, all aspects of building design, energy efficiency, daylight autonomy, comfort levels, and innovative solutions related to energy production and technical equipment [32].

A possible approach that would allow solving this complex optimisation problem is a multiobjective optimisation through parametric design [25]. In comparison with a conventional approach where alternative design solutions are modelled and tested, parametric models made it possible to generate forms where the solution to a specific numerical problem is already embedded [34]. However, the results of these machine-driven optimisations are usually far from a rational design in terms of conventional standardised elements for construction. Thus, instead of relying solely on the machines’ mathematical capacity to solve this complex optimisation problem, a balance between a scientific method and an intuitive approach will be implemented throughout the design of this proposal, combining numerical analysis and literature review with the intuition of the educated architect. The manual optimisation of these three parameters will be achieved by conducting trial-and-error analysis with the help of parametric tools and simulation software to analyse the environmental behaviour of the proposed solution.

As a matter of fact, 80% of all design decisions taken subsequently are influenced by the 20% of design decisions in early design phases [33].

Henceforth, choosing the key parameters to consider in order to achieve a sustainable highrise, as well as the methodology implemented to analyse those parameters, are decisive factors towards achieving a Zero Emission Building.

Assuming that the main drivers on the GHG emissions will be those related to the operation

In order to create a precise design based on a particular location, Snøhetta’s Gullhaug Torg project in Nydalen, Oslo, is selected as a case study in order to set the boundary conditions that will serve as the starting point for a new design.

The methodology that will be implemented is divided in four stages. Firstly, the method departs from a preliminary analysis of this case study building and the climate analysis from its location (Chapter 2). Secondly, it is followed by the design of a climate-adapted built form (Chapter 3). Thirdly, the analysis and decision on the structural system (Chapter 4). Lastly, the design of the exterior envelope of the

Fig. 6: Iterative design process.

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building (Chapter 5). As a consequence of the whole design process, an energy demand and embodied CO2 emissions would be obtained (Fig.7). This data would be used to achieve a Zero Emission standard in a further development of the design, which will not be assessed in this thesis.

For the case of the climate-adapted built form, the main drivers towards the selection of the building’s shape will be the wind pressure due to prevailing winds and solar radiation.

The former aims to minimise the drag force over the building´s envelope, while the study of the latter will allow maximising both solar exposure and solar heat gains. The design of the structural system will rely on the selection of construction and structural materials with lower embodied emissions and the minimisation of those materials. Lastly, the main objectives of the envelope design phase will be to achieve good daylight levels and a satisfactory natural ventilation inside the living spaces of the building.

As previously mentioned, since these kind of design processes are iterative, some considerations that otherwise would not be addressed until the next chapter must be taking into account when dealing with the previous parameter. As an example, when addressing the issue of the location for the structural cores, daylight and natural ventilation strategies that will be addressed in the following step of the design will be affected by this decision.

Therefore, some previous considerations on these passive strategies must be applied in this phase of the process. This reciprocity during the design process is what makes this kind of projects both complex and interesting.

Aiming for ZEB in a High Rise Building

1. Introduction

4. Envelope Daylight & Natural ventilation

3. Structural system Environmental performance & program distribution

2. Climate-based built form Wind pressure & Solar radiation

1. Preliminary analysis Case study & Climate

5. Energy Energy production & Energy demand

Fig. 7: Scheme of the methodological process and software that will be implemented in this master thesis.

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Aiming for ZEB in a High Rise Building

1. Introduction

References eprint/13467/1/WorldEnergyOutlookSpecialReport2016EnergyandAirPollution.pdf.

[6] T. R. C. f. Z. E. B. (ZEB), C. f. E.-F. E. R. (CEER/FME), Ed., ed. Beijing, 2009, p. 21.

[7] A. A. Are Lindegaard, Andreas Andersen, Stian Rein Andresen, Torgrim Asphjell, Ellen Bruzelius Backer, Kenneth Birkeli, Katja Ekroll, Helene Frigstad, Henrik Gade, Eilev Gjerald, Hege Haugland, Britta Maria Hoem, Nina Holmengen, Isabella Kasin, Hans Kolshus, Maria Malene Kvalevåg, Hanne Birgitte Laird, Christine Maass, Elisabeth Møyland, Hege Rooth Olbergsveen, Tone Sejnæs Pettersen, Simen Helgesen Ramberg, Bente Rikheim, Audun Rosland, Sissel Sandgrind, Odd Kristian Selboe, Svein Grotli Skogen, Fredrik Weidemann, Elin Økstad, “Knowledge base for low-carbon transition in Norway. Summary,” Norwegian Environment Agency2014, Available: http://www.miljodirektoratet.no/Documents/ publikasjoner/M287/M287.pdf.

[8] E. S.F., “Towards a low-emission Norwegian industry,” Enova S.F.ISBN 978-8292502-99-9, 2017, vol. Enova report 2017:5.

[9] U. Fao, “How to Feed the World in 2050,” in Rome: High-Level Expert Forum, 2009.

[10] F. Magrinyà Torner, “The Challenge of Slums. Global Report on Human Settlements 2003,” Cuadernos Internacionales de Tecnología para el Desarrollo Humano, 2005, núm. 3, no. United Nations Human Settlements Programme, p. 345, 2005.

[11] M. Green, “Why we should build wooden skyscrapers,” T. Talks, Ed., ed. Youtube, 2013.

[12] Z. Strelitz, Tall Buildings: a strategic design guide. RIBA, 2005.

[13] N. AS, “B20 M90 D22, 205000, Vibrerbar betong. Environmental Product Declaration,” ed: The Norwegian EPD Foundation, 2014, p. 6.

[14] S. P. SIA, “Steel Structure. Environmental Product Declaration,” ed: The Norwegian EPD Foundation, 2014, p. 7.

and K. B. Lindberg, “A Norwegian zero emission building definition,” Passivhus Norden, 2013.

[24] A. H. Wiberg et al., “A net zero emission concept analysis of a single-family house,” Energy and buildings, vol. 74, pp. 101-110, 2014.

[15] K. R. Richards and C. Stokes, “A review of forest carbon sequestration cost studies: a dozen years of research,” Climatic change, vol.

63, no. 1-2, pp. 1-48, 2004.

[16] N. Y. S. D. o. E. Conservation. (9 May 2018). Trees: The Carbon Storage Experts.

Available: https://www.dec.ny.gov/lands/47481. html

[25] G. Lobaccaro, A. H. Wiberg, G. Ceci, M. Manni, N. Lolli, and U. Berardi, “Parametric design to minimize the embodied GHG emissions in a ZEB,” Energy and Buildings, vol.

167, pp. 106-123, 2018.

[17] S. H. e.V., “Cross-laminated timber (X-Lam). Environmental Product Declaration,” ed: Institut Bauen und Umwelt (IBU), 2016, p.

10.

[26] I. Sartori and A. G. Hestnes, “Energy use in the life cycle of conventional and lowenergy buildings: A review article,” Energy and buildings, vol. 39, no. 3, pp. 249-257, 2007.

[18] S. AS, “Standard limtrebjelke,” ed: The Norwegian EPD Foundation, 2014, p. 7.

[19] M. De Rosa, M. Pizzol, and J. H. Schmidt, “A comparison of LCA approaches accounting for CO2 emission and sink of forestry products: The case of Timber as a construction material,” 2013.

[27] A. Rønning and A. Brekke, “Life cycle assessment (LCA) of the building sector: strengths and weaknesses,” in Eco-Efficient Construction and Building Materials: Elsevier, 2014, pp. 63-83.

[28] M. K. Wiik, S. M. Fufa, T. Kristjansdottir, and I. Andresen, “Lessons learnt from embodied GHG emission calculations in zero emission buildings (ZEBs) from the Norwegian ZEB research centre,” Energy and Buildings, vol.

165, pp. 25-34, 2018.

[20] S. A. I. C. (SAIC), “A Brief History of Life Cycle Assessment,” in Life Cycle Assessment: Principles and Practice, M. A. Curran, Ed., ed.

Cincinnati, Ohio: National Risk Management Research Laboratory. Office of Research and Development. U.S. Environmental Protection Agency., 2006 p. 3.

[29] A. Zimmerman and P. Eng, “Integrated design process guide,” Canada Mortgage and Housing Corporation, Ottawa, 2006.

[21] A. A. Stephanie Vierra, LEED AP BD+C. Vierra Design & Education Services, LLC. (9 May). Green Building Standards and Certification Systems. Available: https://www. wbdg.org/resources/green-building-standardsand-certification-systems

[30] A. Mahdavi, “Computational decision support and the building delivery process: a necessary dialogue,” Automation in Construction, vol. 7, no. 2-3, pp. 205-211, 1998.

[31] S. Attia and A. De Herde, “Early design simulation tools for net zero energy buildings: a comparison of ten tools,” in Conference Proceedings of 12th International Building Performance Simulation Association, 2011, 2011.

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[32] S. Hayter, P. Torcellini, R. B. Hayter, and R. Judkoff, “The energy design process for designing and constructing high-performance buildings,” 2000: Citeseer.

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2.

Preliminary analyses

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

2.1. Case study analysis As mentioned in the previous chapter, the project developed by Snøhetta for the current parking slot in Gullhaug Square 2A (Nydalen, Oslo) has been selected as a case study. Moreover, its boundary conditions have been used for the design of a new project in this location. These boundary conditions are the urban context, architectural program and local climate.

Urban approach The area of Nydalen (Oslo) was established as an industrial area around the middle of the 19th century. Today, about 30000 people live and study in Nydalen. The scale and density of the building structure has evolved from an industrial area into an urban environment [1]. This area is located in the intersection of the transversal axis given by the Akre river and the belt around the centre of Oslo. In this suburbia area is where the city possesses the biggest potential for growth and expansion. Nydalen district is well connected

Fig. 8: Nydalen Plus master plan. MAD Arkitekter. 2015.

with the city centre and surrounding areas by bus, subway and train, having an excellent potential for accommodating more people without compromising the environmental impact resulting from increased traffic. In addition, the area is also very well suited for cyclists.

The Gullhaug Torg project, also called Nydalen Vy, is the “hub” of the master plan Nydalen Plus developed by Avantor towards the horizon of 2030 (Fig. 8). This master plan is based on the implementation of three strategies: connect, activate and densify. By their implementation, Nydalen Plus aims to unify the area of Nordre Aker district with the rest of the city, focusing on the user rather than the infrastructures in order to create a greener Oslo [2]. Avantor assures that all traffic increase in Nydalen will come from cycling, walking and public transport. Moreover, a separated master plan for converting large areas of the city centre car-free has been developed.

Fig. 9: Gullhaug Torg. Snøhetta and MIR. 2015 (available at: https://snohetta.com/projects/269-gullhaug-torg).

Program analysis

In a local context scale, the proposal developed

by Snøhetta is based on the plot unification, including the bridge as part of the square, as well as on the reinforcement of important connecting lines between different city spaces and service functions in the area. Gullhaug Square will be the district’s most important public space and central meeting point. In this space, different user groups’ needs will be taken care of, and several opportunities to experience and move throughout the plaza at all times of the day during the four seasons of the year will be provided. In this proposal, the Aker river is considered as the focal point and central element of attraction by treating both banks of the river and transforming them into an attractive public space. Moreover, it proposes low parking coverage to promote public transport and ensure efficient utilization of the urban spaces.

In Gullhaug Torg, additional parking spaces will be included through underground facilities to release outdoor areas for public use [2]. This urban context developed by Snøhetta will be preserved in the new design proposed in this master thesis (Fig. 11).

Normal

Terrase

Basement

Totals

Housing

4674

280

451

5405

Offices

4280

351

-

4635

Commercial

1115

-

-

1115

Technical services

343

-

-

343

10416

631

451

11498

Totals

total m2 without basement and terrases total m2 with basement and terrases

10416 m2 / 16 storeys = 651 m2 / storey

Fig. 10: Program analysis of functions and square meters (data from “Gullhaug Torg. Sluttrapport skisseprosjekt”, 2015).

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Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Architectural principles The shape and expression of the building is the result of the interaction between several parameters, considering the importance of the urban level, ground floor in terms of footprint, as well as building volume and height. In addition to optimise the needs of daylight and solar gains, the interdisciplinary cooperation around the climatization concept has been of crucial importance for geometry and façade’s design. Lastly, the architecture is characterized by choices related to the goal of reducing greenhouse gas emissions from materials.

The project will contain a mix-program of housing, offices and commercial spaces with a total surface of more than 10000 m2 (Fig. 10).

The building volume, with a tall and a low tower combined with a “glass bridge”, comes from the desire to take care of sight lines across the square and the different needs of the façade area (Fig. 9).

Gullhaug Square 2A

On the ground level there will be commercial activities with a café and restaurant with a direct visual connection to the river, as well as a public square oriented to the southwest. This commercial area will have large rooms that extend over two storeys with high openable windows facing the “sun wall” and the public areas.

On the east side, towards the main street Nydalen Allé, there will be a lobby for the office section as well as shared bicycle facilities. The residential entrance is added in the northwest corner.

Fig. 11: Situation plan. Nydalen area. Snøhetta’s urban proposal. Own elaboration.

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Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Design according to wind directions

The “glass bridge”, which fills the space between the two towers, is arranged for a cross-sectional passage where the flooring between the towers extends uninterruptedly. At the ground level, the passage offers a shortcut for people in the area, while serving as an entrance and dining area for the restaurants.

“Triple - Z “ concept: zero energy purchased for ventilation, heating and cooling

The differentiation in height between the two towers is made to create variation in the built shape, customize program and circulation, create better views for the apartments and relate to two different heights: existing buildings and the newly planned altitude of the towers in Nydalen Plus (Fig.13).

The 42 apartment units are assembled on the 12 upper floors and organized around a compact core. The tower’s faceted and tapered shape provides a slim volume with a lot of window area and good sun and daylight conditions (Fig. 12), while the lower housing levels are relatively large and area-efficient.

The office program requires large, coherent and flexible areas. They are located on the floor plans where the tower volumes meet in the “glass joint”. Here the slabs are interconnected from north to south with two communication cores, the main access being via the low southern tower.

In the new building’s proposal developed in this master thesis, the same program distribution will be implemented.

Fig. 12: Wind analysis over the building’s geometry. Snøhetta. 2015 (available at: https://www.futurebuilt. no/content/download/11951/85065).

Energy concept Gullhaug Torg will use innovative environmental technology and, as one of the FutureBuilt pilot projects and part of the “Natural Climatization of Office Buildings” research project, it will become the first building in Norway to be naturally ventilated. It applies a Triple-Z energy concept that has been inspired by the natural climatization strategy of the “22-26” office building in Austria [3]. This triple-Z concept means zero energy purchase for ventilation,

Fig. 13: Gullhaug Torg west elevation with the new towers as part of the future development plan.

Snøhetta. 2015.

- 20 -

heating or cooling.

The project’s Triple-Z ambition is groundbreaking in the Norwegian context and challenges many established truths around energy-efficient environmental buildings, that have been assumed by today’s construction industry. This focus has required a thorough understanding of principles and strategies and a solid interdisciplinary project team. The team integrates members with different backgrounds and across disciplines, such as architecture, interior architecture and landscape, construction and geotechnics, building physics, plumbing and electrical, acoustics and fire technicians.

It also included experts in the field of natural ventilation, energy efficient heating and cooling systems, daylight and materials. In addition, FutureBuilt has also contributed with expertise in area development in terms of climate-friendly transport and other parameters that ensure a reduction in overall greenhouse gas emissions from the project as a whole [2].

The building’s geometry, material use and programming are optimised for a climatization concept based on natural ventilation with automated façade shutters (Fig. 14) and a highly efficient thermal energy system (LowEx) cast into the slabs (Fig. 15). Relatively small volumes are required to achieve cross-ventilation in the open zones with offices and common areas.

Thus, external pressure differences around the building can be utilized to create air flow. This is achieved by opening hatches on opposite façades.

Closed volumes, like cellular offices, are added to areas without high solar load where the temperatures are more stable. Features like meeting rooms, with a higher density of people, are added to the corners of the building to get two accessible façades in the room and thus achieve an effective air change rate. This premise has been a driver of the design and led to a building body with many facets [1].

Natural ventilation of indoor environment

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Ventilation concept in the housing

requires a significantly greater factorization of person and equipment load. The load or number of people with associated equipment per m² is important for ventilation, heating and cooling. The ventilation strategy must provide adequate thermal comfort and air quality as in a regular office building with a corresponding m2 per workplace. Future rental terms are intended as an entire or a half floor per tenant. In order to maintain sufficient flexibility, it is considered a one-way cross-ventilation strategy [2].

cross ventilation In summer via vertical openings During the night and winter via top shutters

To ensure a good and stable indoor climate based on natural climatization, the net floor height is set at 3.5 m (gross 3.8 m). Along with the utilization of concrete slabs as thermal mass exposed to the indoor air, the volume helps to equalize temperature fluctuations, as well as provide greater robustness against the accumulation of polluted (used) air. Standard projects need an average of 70-100 cm of room height for technical installations. This project’s strategy reclaims these valuable centimetres which are used in a stratification strategy, increasing light levels in the façade and giving positive results regarding acoustics. The floor height is necessary to allow cold outside air to flow through horizontal hatches up under the deck and allow it to mix with the warm interior air in the room. In zones with higher density of people, this strategy is supported by the assembly of a chamber that regulates the thermal air jets [1].

Exhaust ventilation through bathrooms and kitchens

Fig. 14: Natural ventilation strategy. Snøhetta. 2015 (available at: https://snohetta.com/projects/269-gullhaugtorg).

Thermal mass effect in the offices Summer _ night cooling through exposed thermal mass

Horizontal opaque openings are used for ventilation during winter. They are placed high above the external walls to ensure minimal drag in winter and night cooling of exposed thermal mass in summer. Vertical openings are used for ventilation during most of the year.

These opening have the possibility of manual override (Fig. 14). Due to potential glare challenges, workplaces are drawn from the façade at a distance of 60-100 cm. This gives an improved transport area around the workplaces and reduces the glare at workplaces near the windows [2].

Winter _ low sun angle heats the exposed thermal mass (solar heat gains) Fig. 15: Thermal mass effect. Snøhetta. 2015 (available at: https://snohetta.com/projects/269-gullhaug-torg).

- 21 -

For about. 10% of the year, at peak summer and coldest winter days, there is a need for some degree of heating or cooling. The high-efficiency low-energy or exergy (LowEx) solution systems provide low-temperature radiant surfaces. The required areas for radiant surfaces in offices consist on the 25% of the useful floor area (BRA) and are located in both horizontal and vertical elements that serve as zone sections (Fig. 15).

For flexibility reasons, horizontal exergy surfaces are laid in a one-meter band in the floor around the façade [2].

Exergy surfaces should transport hot water and function in principle as an active thermal mass that circulates low-temperature water (3 degrees above the room temperature). Exergy surfaces have a constant temperature as opposed to a classic thermostat-controlled system. In the housing program, the heating surface area is increased to 50% of the useful floor area due to lower personal heat loads. In this part of the program, the system is considered more robust with an increased proportion of vertical active surfaces. A 60-80 cm band in the longitudinal direction of the façade ensures a gentle atmosphere in the living area, giving a special aesthetic quality to the floor of the home. Placement of furniture and carpets has an impact on the effectiveness of this system. In the remaining period of the year where no radiant cooling or heating is required, these surfaces act as exposed thermal mass (Fig. 15) [2].

In order to achieve this building’s zero heating or cooling standard, the building is dependent on exposed surfaces with high thermal inertia.

Vertical and horizontal exposed surfaces are positioned to utilize solar heat gains in winter, and a night cooling strategy ensures that the daytime temperature does not exceed the comfortable levels in summer. Temperature fluctuations on a 24-hour basis are highly smoothed by a lightweight construction system.

Exposed thermal mass that does not require additional heavy masses with associated negative LCA is an essential component of the building strategy (Fig. 15) [2].

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

2.2. Climate analysis Climate adaptation of buildings is probably the oldest and most effective energy-saving measure. Since the ancient times, regional climatic adaptation has always play an important role as an essential principle of architecture [4].

According to I. Andersen, of all the design measures that must be implemented in the design process of a Zero Emission Building, the location, orientation and form of the building are within the most efficient ones. This is due to the fact that they do not involve any extra investment cost, yet they have highly significant effects on the final result [5].

The Three-tier Approach to the Sustainability Design established by N. Lechner, enunciates the importance of basic building design as the base of the pyramid for the design of sustainable buildings, emphasizing the importance of building’s climate adaptation [6]. This same idea is also illustrated in the Trias Energetica pyramid,

Psychrometric chart in Nydalen, Oslo

developed by the ZEB centre as a crucial strategy for the Integrated Design Process (IDP) [5]. Thus, the importance of a thorough climate analysis is crucial in order to implement the most efficient passive strategies and an adequate building’s shape climate adaptation.

In this master thesis, the climate analysis has been carried out by means of Ladybug, a parametric tool for Rhinoceros that allows to easily visualize the different climatic parameters and their possible impact on the architectural form.

Comfort zone

Temperature ranges As previously mentioned, the location of the project is to be set in Nydalen, located in the Nordre Aker district of Oslo. According to the Köppen climate classification [7], the climate in the Norwegian capital belongs to the subtype Cfb (Warm Summer Continental Climate).

Fig. 17: Psychrometric chart from Nydalen area (weather data analysed with Ladybug).

Psychrometric chart with passive strategies

Monthly diurnal averages in Nydalen, Oslo Köppen climate classification _ Cfd Warm Summer Continental Climate

Thermal mass + night ventilation

Comfort thermal neutrality Temperatures range

Direct solar radiation

Diffuse solar radiation Internal heat gains

Fig. 16: Monthly diurnal averages values for temperatures range, direct and diffuse solar radiation. (data extracted from local weather file and analysed with Weather Tool).

Fig. 18: Psychrometric chart from Nydalen area (weather data analysed with Ladybug).

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Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Comfortable hours with no passive strategies

+

=

Comfortable hours due to internal heat gains

Total comfortable hours with internal heat gains

Fig. 19: Yearly comfortable hours for three different scenarios (weather data analysed with Ladybug).

Tempered by the proximity of the Atlantic Ocean and the Gulf Stream, the average temperature in Oslo is 6.9 °C. Winters are cold, with temperatures below 0 °C from September to April, with an average temperature of -4.3 °C in December and January, the coldest months of the year.

As shown in Fig. 16, only a small percentage of the temperature ranges of the months from

Passive strategies implementation

April to August are inside the temperature ranges considered as comfort thermal neutrality.

Moreover, due to the continental character of this climate, hot temperatures above the comfort thermal neutrality range can also be registered during the summer months of June, July and August. Henceforth, the application of passive or active systems for heating and cooling will be necessary to achieve the thermal comfort condition.

In order to assess the importance of the implementation of passive strategies, the psychrometric chart has been utilised. This chart is a graphic representation of the air properties in a specific climate such as relative humidity, wet bulb temperature, dry bulb temperature and dew point temperature. It allows to graphically analyse different types of psychrometric

Monthly average precipitations. Oslo airport observation site Data for 2017 (mm) 208.4

125.6 100.6

102.3 82.7 38.5 MAR

47.2

APR

50.0

MAY

JUN

79.6

63.7

JUL

54.3

AUG

SEP

OCT

NOV

DEC

37.5 JAN

17.9

FEB

Fig. 20: Monthly average precipitations. Oslo Airport observation site, Ullensaker. 2017 (data available at: https://www.yr.no/place/Norway/Akershus/Ullensaker/Oslo_Airport_ observation_site/statistics.html).

- 23 -

processes in order to find solutions related to temperature and humidity problems, avoiding the architect to carry out long and tedious mathematical calculations.

In Fig. 17 and 18 it is possible to observe that the majority of temperatures throughout the year are quite cold and close to the saturation limit, which also means that the annual precipitations are quite abundant. In Fig. 17, the comfort zone is marked inside a black polygon. It can be observed that only a few temperature ranges are within this comfort zone.

In order to improve the temperature and humidity conditions of the air, the effectiveness of different passive strategies has been assessed. The strategies tested are Evaporative cooling, thermal mass + night ventilation, internal heat gains, dehumidification, desiccant dehumidification and humidification. In Fig.18, the effect of the most effective passive strategies for this climatic conditions are illustrated with grey polygons. These resulted to be the use of internal heat gains and thermal mass combined with night ventilation strategies, from which the crucial one is the use of internal heat gains.

The improvement consequences of using this passive strategy can be clearly observed in Fig. 19, where a comparison between the yearly hours inside the comfort zone (marked in yellow) with and without the use of internal heat gains

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Wind rose for the whole year

Wind rose for the hot season

(Each closed polyline shows frequency of 1.7% = 151 hours)

(Each closed polyline shows frequency of 1.7% = 151 hours)

Frequency (%) Average wind velocity (m/s)

Fig. 21: Wind rose with frequencies and average wind velocities for the whole year (weather data analysed with Ladybug).

has been carried out.

Nevertheless, in this same figure it can also be observed that this measure alone is not enough to situate the whole set of annual temperatures inside the comfort zone. Therefore, during the months of January, February, March, April, October, November and December (marked with a predominantly greenish blue

Fig. 22: Wind rose with frequencies and average wind velocities for the hot season (from June to September) (weather data analysed with Ladybug).

colour), additional heating systems must be implemented.

months with higher amount of precipitations in 2017 were August (with an average of 208 mm), October (with an average of 125 mm), and September and January (with an average of 100 mm). In contrast, the months with less amount of precipitations were February and March, with an average of less than 40 mm (Fig. 20).

Precipitations As mentioned before, the amount of annual precipitations in the city of Oslo is quite significant. According to data from the Oslo Airport observation site in Ullensaker [8], the

- 24 -

Prevailing winds Due to the increase of pressure over the building associated with the height, the wind is a highly significant factor when designing a high-rise building. As can be observed in Fig. 21, 22 and 23, for the case of Oslo, the prevailing wind directions can reach significant values of over 10 m/s throughout the year.

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Wind rose for the cold season

Wind proďŹ le. Prevailing wind average velocity

(Each closed polyline shows frequency of 1.7% = 151 hours)

Fig. 23: Wind rose with frequencies and average wind velocities for the cold season (from October to May) (weather data analysed with Ladybug).

The prevailing wind directions for the entire year (Fig. 21) are from the south, with an average wind velocity of 2.82 m/s and a frequency of 11.23 % of the year; south-southwest, blowing during 10.13 % of the year with 2.93 m/s as average velocity; and the north-northwest during 9.97 % of the year with an average wind velocity of 3.13 m/s. Fig. 22 shows the prevailing winds for the hot months of the year (from June to September),

where the north-northwest direction is the prevailing with an average wind velocity of 2.87 m/s and a frequency of 13.66 % of the time.

Regarding the cold part of the year (which in the case of Oslo can be considered from October to May), the two prevailing directions for the wind are south-southwest (with an average speed of 2.95 m/s and a frequency of 12.33 %), and south (with a frequency of 12.33 % and an average

Fig. 24: Wind proďŹ le for prevailing wind average velocity (weather data analysed with Ladybug).

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Aiming for ZEB in a High Rise Building

2. Preliminary analyses

speed of 2.95 m/s).

Prevailing winds in the context of Nydalen

Despite the prevailing wind speeds being very low with respect to the maximum wind velocity, a maximum wind speed of 20 m/s is too significant to be ignored. Thus, the new proposal for this high-rise building must take the pressure associated with this maximum wind speed into consideration, at least for the prevailing wind directions.

N

Solar radiation Due to its location in the north hemisphere, the orientation with a higher exposure in Oslo will be towards the south. This fact can be clearly appreciated in Fig. 26 and 27.

E

W

In Fig. 26, the annual mean values for the total radiation in every direction are depicted. When referring to the total solar radiation, both the diffuse and direct radiation are included in the definition. It is observed that the maximum value corresponds to 700 kWh/m2 for the south orientation, while surfaces oriented to the north can received up to 100 kWh/m2 due to diffuse radiation caused by the reflection of the solar rays in the clouds and other surfaces.

The last figure (Fig. 27) shows the mean values for the direct and diffuse solar radiation. The values for the direct radiation refer to the energy transfer by the solar rays reaching the earth surface on a straight line. In the case of the orientation with higher solar exposure (towards the south), this values can reach up to 500 kWh/ m2, whereas for the northwest and northeast directions the mean values are less tan 100 kWh/m2. Due to the natural sun path, surfaces oriented towards the north will not receive direct solar radiation.

S

Fig. 25: Yearly wind rose overlapped with the context for the intervention (weather data analysed with Ladybug).

- 26 -

Regarding the diffuse solar radiation, also shown in Fig. 27, this term refers to the energy transferred by the solar rays that have been scattered by molecules and particles in the atmosphere and reached the ground after being deviated of their initial trajectory. For orientations

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

References Radiation rose

towards the south, this values can reach up to 400 kWh/m2, while for the north orientation the mean values are around 150 kWh/m2.

Total solar radiation for the whole year

The values for the total solar radiation will be used to analyse the solar heat gains of the building proposed.

[1] Naturligvis, “Passiv klimatisering av fremtidens.

Energieffektive bygg.

Erfaringsrapport,” 2018, Available: https://www. futurebuilt.no/content/download/11951/85065.

[2] A. Danielsberg et al., “Gullhaug Torg sluttrapport skisseprosjekt 2015,” Oslo: Avantor.

2015.

[3] B. Eberle, “2226 building Lustenau (Austria) 2013: Climatización natural mediante regulación de flujos,” A+ T: revista trimestral de Arquitectura y Tecnología, no. 44, pp. 96-101, 2014.

[4] K. Yeang, A. Balfour, and I. Richards, Bioclimatic skyscrapers. Ellipsis London, Limited, 1994.

[5] A. G. Hestnes and N. L. Eik-Nes, Zero Emission Buildings. Fagbokforlaget, 2017.

[6] N. Lechner, Heating, cooling, lighting: Sustainable design methods for architects. John wiley & sons, 2014.

[7] M. Kottek, J. Grieser, C. Beck, B. Rudolf, and F. Rubel, “World map of the KöppenGeiger climate classification updated,” Meteorologische Zeitschrift, vol. 15, no. 3, pp.

259-263, 2006.

Fig. 26: Radiation rose for the total solar radiation throughout the year (weather data analysed with Ladybug).

Radiation rose

Direct solar radiation for the whole year

Radiation rose

Diffuse solar radiation for the whole year

[8] Oslo Airport Observatory Site. (2017).

Weather statistics for Oslo Airport. Available: https://www.yr.no/place/Norway/Akershus/ Ullensaker/Oslo_Airport_observation_site/ statistics.html

Fig. 27: Radiation rose for the direct and diffuse solar radiation throughout the year (weather data analysed with Ladybug).

- 27 -

3.

Climate-adapted built form

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

3.1. Optimisation parameters

3.2. Design of geometries to be tested

According to the aforementioned Threetier Approach to the Sustainability Design developed by N. Lechner, decisions on the initial design stages can reduce the energy consumption of buildings up to 80 %. This approach sets the basic building design on the base of the three-tier pyramid as the main contributor to the effectiveness of the final result, with passive systems on the middle of the pyramid, and mechanical equipment on the top [1]. In this basic building design, the decision on the building’s shape can be considered a crucial stage.

It is important to point out that the optimisation of the building’s shape to minimise wind pressure loads may seem to be in contradiction with the fact that wind is one of the main driving forces for natural ventilation. According to T. Kleiven, the two passive strategies associated with natural ventilation are thermal buoyancy and wind. As explained by this author, “thermal buoyancy will typically be the driving force on a calm cold day with practically no wind, whereas pressure differentials created by wind will typically be the dominating driving force on a windy hot day” [6].

Besides, in his book “Bioclimatic Skyscrapers”, K. Yeang points out the importance of building’s climate adaptation in order to reduce its energy consumption [2]. In “Design with Climate”, V. Olgyay understands this climate adaptation as a consequence of the natural forces acting on the shape of living organisms. Thus, every natural form can be read as a balance of forces [3], which may be also applicable to architectural forms.

These passive strategies are commonly utilised in combination but they can also occur separately [6]. The aforementioned scenario of a calm cold day will be the prevailing situation for Nydalen throughout the year, as shown in the previous climate analysis. Accordingly, for this particular location, the optimisation of the building’s shape to be exposed to a minimum wind pressure will not be detrimental for the implementation of an efficient natural ventilation system.

In order to achieve the harmony between shape and natural forces, the climatic parameters previously analysed will be implemented in a geometry study to find out the most suitable shape to this particular climate and architectural typology.

In addition to this, in a cold climate like the one in Norway, taking maximum advantage of the solar heat gains during winter can make a significant difference on the overall energy consumption for heating. Such approach becomes specially relevant if today´s construction systems are considered, as they are mainly focused on the air-tighness of buildings in order to reduce their thermal losses.

At this step of the design, it is important to remember that the biggest driver on the overall GHG emissions of a high-rise building is the amount and type of materials utilised on its structure, representing the largest amount of materials in the whole building [4]. Moreover, the main factor that drives the amount of materials needed in a high-rise building typology is the stress on the structure due to the wind pressure [5]. Thus, optimising the building’s shape in order to bear the minimum wind pressure seems like the most logical approach, in order to pursue the goal of reducing the GHG embodied emissions from materials to the minimum, as established in the introduction of this thesis.

In order to select the geometry that will be developed further on the next chapters of this thesis, a sensitivity analysis of the previously mentioned parameters has been carried out.

This approach is based on the simulation of several geometries under different wind and solar radiation conditions. As a result of the broad range of possible combinations, a trade off between wind and solar performance is selected as ultimate design.

Six different geometries have been chosen to be analysed in relation to the selected parameters.

Three of them are four-sided polyhedrons, while the other three have rounded shapes (Fig. 28).

The four-sided polyhedrons have been designed in a way that they have the maximum possible area exposed to the south. This has been done in order to maximise both its solar heat gains and its potential for energy production through a photovoltaic system, which will be important in order to achieve the Zero Emissions balance.

The shape shown in Fig. 29 is a combination of two simple rectangles. One aligned with the main street Nydalen Allé, and the second one aligned with the bank of the river. The second shape is a simple offset of the plot perimeter (Fig. 30). Finally, the third one has been designed with the optimum angle for maximising the solar radiation that the south-oriented façades are receiving (Fig. 31). This angle is 67.5º with the

1.

2.

4.

5.

3.

6.

Fig. 28: Selected geometries to be tested

- 30 -

The round shapes have been designed in order to create minimum resistance to the wind pressure and therefore to minimise the horizontal forces over their envelopes.

Shape number 4 has a circular footprint (Fig. 32). This is to create a geometry that reacts in an equal manner to wind blowing from every direction. Shape number 5 is an elliptical shape (Fig. 33). The base ellipse of this geometry has been aligned with the natural directionality of the plot which, as a matter of fact, coincides with the prevailing wind directions. Lastly, geometry number 6 has the shape of a water drop (Fig. 34).

To make a precise comparison of these six geometries, all of them have been scaled to have the same floor area (650 m2) and the same height (65 m).

The selection criteria utilised for the election of the most adequate geometry will be the following, enunciated in this order of priority: 1. Minimum force on the envelope due to prevailing winds.

2. Maximum mean power per exposed area during the cold season.

Selected geometries

As a conclusion, wind pressure and solar radiation will be the selected natural forces to be analysed as driving parameters for the design of the built form.

horizon line according to the research published in “Boosting solar accessibility and potential of urban districts in the Nordic climate: A case study in Trondheim” [7].

3. Maximum energy production potential for the future installation of photovoltaic solar panels.

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

3. Solar angle shape

1. Combined shape

650 m2

650 m2

67.5º

Fig. 29: Roof plan and axonometry of the first selected geometry.

67.5º

Fig. 31: Roof plan and axonometry of the third selected geometry.

2. Plot shape

4. Circular shape

650 m 2

650 m2

650 m2

Fig. 30: Roof plan and axonometry of the second selected geometry.

Fig. 32: Roof plan and axonometry of the fourth selected geometry.

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Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

3.3. Wind optimisation 5. Elliptical shape

650

The load on a surface due to the wind action is directly proportional to the wind pressure over the surface integrated over the affected area (Fig. 35).

This force due to the wind action is called drag force. The drag force is a horizontal force, perpendicular to the envelope of the building.

This horizontal force multiplied by the distance from the base of the building cause a bending moment applied at the base. Therefore, the higher the distance, the greater the moment.

Wind speed increases with the height.This behaviour arises from the viscous forces that the uid, in this case air, experiences against the Earth surface, other buildings, trees and other elements. These facts explain why wind force is detrimental when designing a high-rise building.

m2

force consequence of the combination of these individual pressures.

The vortexes on the back façade have signiďŹ cant importance, as they are created alternately in a clockwise and counter clockwise direction due to the variation on the ow speed on the side façades. This produces vibrations in a cross-wind direction, that the structure of the building will have to handle. In order to reduce the vortexes on the back side it is important to reduce the distance between both wind ows from the side façades (distance between dashed lines in Fig. 36) , so-called separation area [5].

Drag force Fig. 33: Roof plan and axonometry of the ďŹ fth selected geometry.

6. Water drop shape

đ??šđ??š =

đ??šđ??š =

đ?‘ƒđ?‘ƒ ∗ đ?‘‘đ?‘‘đ??´đ??´

đ?‘ƒđ?‘ƒ ∗ đ?‘‘đ?‘‘đ??´đ??´ đ??šđ??š đ??´đ??´

Drag coefďŹ cient Cd = * , ∗ - + +

đ??šđ??š đ??´đ??´ Cd = * + , ∗ -

+

Fig. 35: Formulas for the drag force and drag coefďŹ cient.

65 0m

2

According to the Eurocode-1, there are 5 terrain categories associated with different roughness degrees. For the case of Nydalen, category 4 applies, belonging to an area in which at least 15 % of the surface is covered by buildings with an average height of more than 15 m [8].

Wind does not affect uniformly to the different façades of a building (Fig. 35). As a general rule, the façade facing the wind direction will receive a positive pressure, while the side and back façades will handle vortexes and underpressures (Fig. 36). The drag force is the overall

Fig. 34: YRoof plan and axonometry of the sixth selected geometry.

- 32 -

Fig. 36: Common wind ow in a rectangular building.

An efďŹ cient way to reduce the separation area is by creating elongated geometries. The optimal geometry is the shape of an airfoil [5]. However, this kind of shapes may be optimal for one prevailing wind direction but detrimental for others.

The behaviour against the wind is measured by the drag coefďŹ cient, which is directly proportional to the drag force divided by the area, and indirectly proportional to the product of the air density divided by two and the squared wind speed. In other words, the drag coefďŹ cient shows us how aerodynamic a geometry is. The smaller the number, the more aerodynamic the geometry will be.

In order to test which geometries better behaves with respect to the prevailing wind directions, the six geometries designed on the previous chapter have been tested in a virtual wind tunnel.

This wind tunnel has been simulated by means of Flow Design, a user-friendly simulation tool that helps to test ideas in early design stages of

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Wind analyses with Flow Design (wind coming from the south)

1. Combined shape

2. Plot shape

3. Solar angle shape

4. Circular shape

5. Elliptical shape

6. Water drop shape

Fig. 37: Wind tunnel simulations with Flow Design for the six geometries designed.

- 33 -

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Summary of analyses (wind coming the south) Summary of from analysis

Summary of analyses Summary oftheanalysis (wind coming from north-northwest)

(wind coming from the south)

Shape

1. Rectangular shape

2. Plot shape

3. Solar angle shape

4. Circular shape

5. Elliptical shape

6. Water drop shape

Wind direction

w

w

w

w

w

w

(wind coming from the north-northwest)

2 / Climate-based build form

Testing time (minutes)

Positive peak pressure (Pa)

Negative peak pressure (Pa)

Highest wind velocity (m/s)

25:00

0

-295.00

31.99

1.67

895049.9

0.1197

35:00

0

-254.25

31.49

1.60

858627.0

0.1147

45:00

0

-237.26

29.59

1.54

826264.8

0.1105

55:00

0

-215.19

30.06

1.50

803931.6

25:00

349.33

-303.40

31.63

1.91

1068719.0

35:00

351.60

-277.24

31.35

1.85

1037190.0

45:00

352.87

-262.84

31.52

1.78

55:00

351.03

-236.88

31.83

25:00

171.76

-593.60

35:00

171.44

45:00

Drag coefďŹ cient (Cd)

Drag Froce (N)

Mean Force (kN/m2)

Shape

đ??šđ??šđ??šđ??š = đ??šđ??šđ??šđ??š =

0.1351

1.72

35.74

0.71

309202.1

0.0389

-573.61

35.27

0.70

304712.1

0.0384

177.82

-558.36

33.50

0.66

290117.7

0.0365

55:00

180.73

-539.92

33.50

0.64

279262.4

0.0351

25:00

328.59

-182.60

41.00

1.05

474584.1

0.0728

35:00

343.16

-155.76

40.85

1.03

466644.4

0.0714

45:00

353.50

-152.51

40.17

1.02

461191.7

0.0707

55:00

364.37

-108.40

40.00

1.02

459559.0

0.0705

25:00

263.40

-540.30

34.27

0.71

291361.7

0.0428

35:00

263.78

-513.32

34.83

0.71

292448.8

0.0430

45:00

267.60

-498.42

34.58

0.67

275844.5

0.0406

55:00

278.76

-423.84

31.78

0.62

253215.9

0.0372

25:00

275.67

-389.44

40.51

0.55

173530.0

0.0235

35:00

280.30

-387.31

40.49

0.50

160603.2

0.0219

45:00

285.25

-378.57

40.37

0.48

152676.3

0.0208

55:00

288.77

-372.11

40.53

0.46

147481.0

0.0199

Negative peak pressure (Pa)

Highest wind velocity (m/s)

Drag coefďŹ cient (Cd)

w

25:00

307.03

-487.11

31.26

1.77

723468.4

0.0967

35:00

302.42

-476.76

31.01

1.70

695692.7

0.0931

45:00

316.36

-405.20

30.01

1.69

693538.9

0.0928

55:00

315.24

-404.00

29.99

1.68

688087.6

0.0920

25:00

317.07

-198.84

39.98

1.49

587686.1

0.0766

35:00

329.38

-168.77

39.99

1.45

572904.9

0.0745

45:00

338.38

-147.07

39.99

1.43

562707.9

0.0733

55:00

228.47

-139.93

40.00

1.40

553613.9

0.0722

25:00

308.35

-372.08

40.00

1.48

552908.0

0.0696

35:00

318.27

-350.13

40.07

1.46

546708.9

0.0688

45:00

323.79

-334.19

40.11

1.42

531003.1

0.0668

55:00

341.13

-315.75

41.09

1.39

521034.8

0.0655

25:00

328.59

-182.60

41.00

1.05

474584.1

0.0728

35:00

343.16

-155.76

40.85

1.03

466644.4

0.0716

45:00

353.50

-152.51

40.17

1.02

461191.7

0.0707

55:00

364.37

-108.40

40.00

1.02

459559.0

0.0703

25:00

266.68

-375.20

40.55

0.47

166655.7

0.0246

35:00

269.08

-385.82

39.94

0.47

168204.2

0.0247

45:00

270.42

-392.45

39.96

0.46

164368.5

0.0241

55:00

268.02

-399.06

39.94

0.46

161973.0

0.0238

25:00

279.24

-591.02

39.97

0.81

315249.5

0.0428

35:00

281.24

-577.12

39.97

0.76

298466.7

0.0495

45:00

285.18

-560.03

39.98

0.72

283124.2

0.0385

55:00

285.18

-560.03

39.99

0.72

283124.2

0.0385

đ?‘ƒđ?‘ƒđ?‘ƒđ?‘ƒ ∗ đ?‘‘đ?‘‘đ?‘‘đ?‘‘đ??´đ??´đ??´đ??´ đ?‘ƒđ?‘ƒđ?‘ƒđ?‘ƒ ∗ đ?‘‘đ?‘‘đ?‘‘đ?‘‘đ??´đ??´đ??´đ??´

đ??šđ??šđ??šđ??š đ??´đ??´đ??´đ??´ Cd = *đ??šđ??šđ??šđ??š đ??´đ??´đ??´đ??´+ , ∗ - Cdshape = * 2. Plot + +

0.1393 0.1299

Positive peak pressure (Pa)

1. Rectangular shape

0.1076

996744.7 963789.6

Wind direction

Testing time (minutes)

, ∗ -

+

0.1256

w

w

3. Solar angle shape

w 4. Circular shape

w 5. Elliptical shape

w 6. Water drop shape

48 /110

49 /110

Fig. 38: Results from the simulation in Flow Design for the south wind direction.

Fig. 39: Results from the simulation in Flow Design for the north-northwest wind direction.

- 34 -

Drag Froce (N)

Mean Force (kN/m2)

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

2 / Climate-based build form Drag coeffi cientforforevery everygeometry geometry for for the south wind directions Drag coeffi cient south and andnorth-northwest north-northwest wind directions

1.

2.

3.

4.

5.

Drag force in every geometry for the south and north-northwest wind directions Drag force in every geometry for the south and north-northwest wind directions

1.

6.

(KN) 1.8

NNW

1.6

S

1.4

1.50

1.68

1.2

NNW 1.40

0.6 0.4

700

1.39

1.0 0.8

800

NNW

S

NNW

1.02

1.02

600

S

0.64

0.62

0.2

NNW NNW 0.46

S

3.

803

688

300 200

0.46

5.

6.

NNW NNW

NNW

322

554

400

0.72

4.

964

S

500

S

2.

S

1000 900

S 1.72

2 / Clim

S

S

NNW

460

521 NNW

S

279

253

100

NNW

S

162

147

283

0

0

Fig. 40: Comparison of results from the drag coefficient values obtained on the last interval of every geometry.

Scenario: south (S) and north-northwest (NNW) wind directions.

Fig. 41: Comparison of results from the drag force values obtained on the last interval of every geometry.

Scenario: south (S) and north-northwest (NNW) wind directions.

51 /110

50 /110

the design process.

The simulations with Flow Design have been carried out for the four prevailing wind directions (south, north-northwest and south-southeast) according to the climate analysis in Chapter 2. In addition, the simulations have also been carried out for the west wind direction in order to to test its performance when the wind flows from a perpendicular direction to the prevailing ones.

On all these simulations only the maximum wind speed has been input on the wind tunnel in order to simulate the worst case scenario.

Accordingly, a wind speed of 20 m/s has been used for the south, north-northwest and south-

southeast directions and 15 m/s for the west direction.

the values for the last interval are utilised for the comparisons.

These simulations allow to simultaneously visualize a large amount of information, such as pressures distribution over the envelope of the building, wind velocities, drag force and drag coefficient. Among those, the values that will allow to make a decision over the best shape to develop further are the drag force and drag coefficient, as previously explained.

Analysis of the results The simulations have been first carried out for the cases of the south and north-northwest wind directions, as these are the two most frequent ones throughout the year. It can be observed in Fig. 40 and 41 that the geometries that better behave against these two directions are number 3 (solar angle shape), number 4 (or circular shape), number 5 (elliptical shape) and number 6 (water drop shape).

The values for four different intervals in every simulation are shown in Figs. 38, 39, 42 and 44, corresponding to a simulation time of 25, 35, 45 and 55 minutes. In Fig. 40, 41, 43 and 45 only

As expected, all the curved shapes react better

- 35 -

to these two opposite wind directions. Their drag coefficients range from 1.02 in the case of the circular shape, to 0.46 in the water drop shape, corresponding with drag forces that range from 521 kN to 147 kN for the same geometries respectively. It is not surprising that the lowest drag force and drag coefficient belong to the water drop shape for the south wind direction, as that is the optimal geometry for that wind flow.

Shape number 3 reacts the best to these winds with respect to the other two polygonal shapes.

However, despite the values for the south direction are similar to the ones achieved with the curved geometries, for the case of the north-

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

2 / Clima Drag force most aerodynamic geometries south, north-northwest Drag force onon thethe most aerodynamic geometries forfor thethe south, north-northwest and south-southeast wind directions and south-southeast wind directions

Summary of analyses (wind coming from the south-southeast)

Summary of analysis (wind coming from the south-southeast)

Shape

1. Rectangular shape

Wind direction

w

2. Plot shape w

Testing time (minutes)

w

4. Circular shape

w

5. Elliptical shape w

6. Water drop shape

w

3.

Positive peak pressure (Pa)

Negative peak pressure (Pa)

Highest wind velocity (m/s)

Drag coefďŹ cient (Cd)

Drag Froce (N)

Mean Force (kN/m2)

25:00

0

-325.16

27.38

1.02

417769.6

0.0559

35:00

4.47

-263.67

27.50

0.98

400277.6

0.0535

45:00

1.66

-266.05

27.19

0.93

381236.5

0.0509

55:00

13.33

-247.11

27.21

0.90

368903.6

0.0494

25:00

283.08

-339.43

39.66

0.89

352024.4

0.0459

35:00

282.55

-350.13

39.71

0.84

331650.2

0.0433

45:00

290.16

-354.15

39.90

0.80

316837.3

0.0413

55:00

295.21

-348.80

40.18

0.79

312826.0

0.0408

300

0.0547

200

25:00 3. Solar angle shape

2 / Climate-based build form

296.25

-335.04

39.95

1.16

435036.9

(KN)

4.

5.

6.

800 700 600

NNW

500

521

400

35:00

305.38

-321.68

39.99

1.12

417028.2

0.0525

100

45:00

314.17

-303.64

39.93

1.06

395028.8

0.0497

0

55:00

330.25

-291.37

39.96

1.03

383881.8

0.0483

25:00

328.59

-182.60

41.00

1.05

474584.1

0.0728

35:00

343.16

-155.76

40.85

1.03

466644.4

0.0716

45:00

353.50

-152.51

40.17

1.02

461191.7

0.0707

55:00

364.37

-108.40

40.00

1.02

459559.0

0.0705

25:00

266.68

-375.20

40.55

0.47

166655.7

0.0246

35:00

269.08

-385.82

39.94

0.47

168204.2

0.0247

45:00

270.42

-392.45

39.96

0.46

164368.5

0.0241

55:00

268.02

-399.06

39.94

0.46

161973.0

0.0238

25:00

288.60

-426.48

41.09

0.72

282466.4

0.0383

35:00

290.78

-429.23

41.16

0.67

260239.8

0.0353

45:00

292.40

-407.74

40.28

0.61

239562.9

0.0325

55:00

292.85

-403.44

40.25

0.59

232056.3

0.0315

S

SSE 384

S

NNW

SSE

460

460

460

279

NNW

S 253

NNW

SSE

S

162

160

147

283

SSE 232

Fig. 43: Comparison of results from the drag force values obtained on the last interval of the four best geometries. Scenario: south (S), north-northwest (NNW) and south-southeast (SSE) wind directions.

northwest these values are considerably high.53 /110 To sum up, the shape with the best performance respec to these two wind directions is number 5 ( elliptical shape). When compared with the rest of geometries, it provides the lowest relative value of drag force and drag coefďŹ cient.

This behaviour could also be expected due to its symmetricity and the fact that the shape is elongated along the direction of these winds.

The analysis has been repeated for the third most frequent wind direction (the south-southeast), and the results have been compared with the previously obtained (Fig. 43). In this case, the comparison only considered the shapes selected in the previous simulation, discarding shapes number 1 and 2.

52 /110

Fig. 42: Results from the simulation in Flow Design for the south-southeast wind direction.

- 36 -

Once again, the most optimal shape is number 5. Its maximum drag force (of 253 kN corresponding to the southern winds) is lower than the maximum drag forces obtained for other geometries. This result could be expected since this geometry is aligned with the northnorthwest and south-southeast.

The second better result is for the case of geometry number 6 (the water drop shape), with a maximum drag force of 283 kN for the northnorthwest direction. Finally, the third better result is for the circular shape, with a maximum drag force of 460 kN. However, this shape will be discarded and take instead shape number 3 for the last comparison. The reasoning that follows this selection is that shape number 3, with a maximum drag force of 521 kN for the

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

2 / Clima Summary of analyses (wind coming from the west)

Drag force on the most aerodynamic geometries for the south, north-northwest, Drag force on the most aerodynamic geometries wind for thedirections south, north-northwest, west, and south-southeast west, and south-southeast wind directions

Summary of analysis (wind coming from the west)

Shape

Wind direction

Testing time (minutes)

w

25:00

188.49

-233.18

25.09

35:00

187.55

-161.56

45:00

189.52

55:00

195.54

1. Combined shape

w 2. Plot shape

w 3. Solar angle shape

w 4. Circular shape

w 5. Elliptical shape

w 6. Water drop shape

2 / Climate-based build form

Positive peak pressure (Pa)

Negative peak pressure (Pa)

Highest wind velocity (m/s)

Drag coefficient (Cd)

3.

Drag Froce (N)

Mean Force (kN/m2)

1.75

586766.3

0.0785

23.51

1.53

515031.2

0.0688

-138.88

22.95

1.46

489946.3

0.0655

-137.86

22.64

1.41

474942.3

0.0635

(KN)

5.

6.

800 W

700 600

25:00

170.76

-262.69

26.59

1.10

317299.6

0.0413

35:00

172.57

-154.30

23.19

1.18

342559.9

0.0447

45:00

174.32

-130.58

22.18

1.15

332506.9

0.0434

400

55:00

176.53

-128.23

21.51

1.11

321856.2

0.0419

300

212. 74

-186.89

29.64

1.95

769496.4

0.0967

200

35:00

207.08

-167.29

30.37

1.77

700286.5

0.0880

100

45:00

216.55

-194.45

30.34

1.76

695160.3

0.0874

55:00

233.77

-166.64

30.28

1.76

696843.8

0.0876

0

25:00

171.52

-159.67

22.92

1.01

255393.8

0.0391

35:00

177.19

-109.15

21.19

1.00

253779.0

0.0389

45:00

178.22

-104.66

21.63

0.96

243108.7

0.0372

55:00

181.15

-98.28

21.95

0.94

237571.0

0.0365

25:00

180.02

-265.08

25.27

1.38

416744.9

0.0614

35:00

184.14

-133.56

24.55

1.37

414704.8

0.0611

45:00

186.38

-126.77

22.42

1.36

411346.8

0.0605

55:00

191.06

-122.89

22.77

1.32

399302.2

0.0587

25:00

219.66

-249.80

30.09

2.71

836125.9

0.1136

35:00

223.10

-164.52

29.94

1.91

737679.6

0.1003

45:00

236.41

-142.11

29.87

1.84

711097.8

0.0967

55:00

256.87

-110.77

29.86

1.80

695838.3

0.0946

696

NNW

500

25:00

W

697

521 S 279

W

SSE 384

399

NNW

S 253

NNW

SSE

S

162

162

147

283

SSE 232

Fig. 45: Comparison of results from the drag force values obtained on the last interval of the three best geometries. Scenario: south (S), north-northwest (NNW), south-southeast (SSE) and west wind directions (W).

54 /110

north-northwest wind direction, has a higher 55 /110 potential for the cases of the south and southsoutheast directions than the circular shape.

shape number 3 and 696 kN for the case of shape number 6, both for the wind coming from the west).

Lastly, the west wind direction has been simulated for the six geometries summarising the results on a bar chart, in order to check what would happen when the wind is flowing on a perpendicular direction to the aforementioned ones (Fig. 44 and 45).

This result may be explained due to the rounded edges of this geometry, which help to maintain a laminar wind flow and consequently, opposing a lower resistance.

It can be observed in Fig. 45 that the shape opposing the least resistance to the analysed wind directions is number 5 (elliptical shape).

This geometry handles a maximum drag force of 399 kN for the west wind direction, which is almost half of the drag forces handled by the other two geometries (697 kN for the case of

Fig. 44: Results from the simulation in Flow Design for the west wind direction.

- 37 -

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

3.4. Solar analysis Solar radiation is an important design analysis in cold climates because of its potential for both passive solar heating and energy generation from renewable sources.

The benefits of passive solar heating are numerous. Passive systems allow to heat interior spaces in buildings with little or no additional initial cost, lower maintenance and higher reliability than traditional active heating systems [1]. Moreover, while active collectors supply only heat, the use of passive solar heating creates a more pleasant indoor environment for the use, specially during winter [1].

However, there are two considerations worth mentioning when implementing passive solar heating. Firstly, a very high exposure to solar radiation can lead to overheating problems during summer, even in cold climates like Norway.

Secondly, an efficient use of solar heating is not achieved solely by letting the sun light come inside the building. The implementation of a

heat storage and heat retention system is also needed [1].

For heat storage, materials with high thermal inertia such as concrete are conventionally used. In addition, the evolution of material technologies in the last years has led to the creation of alternative solutions, as for example, the phase changing materials (PCM) [9].

Despite Norway’s high latitude, it has been proven through different Zero Emission Building pilot projects that the use of active solar energy, such as photovoltaic or solar thermal collectors, can make a significant difference in the total emission balance of a building [10].

In order to analyse the performance of the six different geometries in terms of their active and passive solar energy potential, two types of analyses have been carried out.

The first analysis is based on measurements of

the solar radiation over the building’s envelope during both the hot and the cold seasons. In the case of Norway, the cold season has been assumed to last from October to May, while the hot one is considered to be from June to September. Each geometry has a different envelope surface, so the mean power per exposed area (w/m2) has been measured in order to figure out which geometry is receiving the higher solar radiation per square meter.

The analysis has been carried out by means of Honeybee (a parametric analysis tool for Rhinoceros), and Diva for Rhinoceros (a plug-in for solar analysis) (Fig. 46, 47, 48, 49, 50, 51).

Therefore, these surfaces directly exposed to the solar radiation on the envelope’s façades will lead to different solar radiation measurements.

This analysis has been carried out through Diva for Rhinoceros, as this tool allows to achieve more precise results. For the analysis of these surfaces, the sensors have been distributed every 2 m with a distance of 0.5 m from the surface of the façade.

The second analysis assesses the potential of each geometry for energy production. The surfaces that are directly exposed to the sun path during the largest part of the year have been analysed, including the roof area. As mentioned at the beginning of this chapter, all the geometries have the same footprint area, but a different total envelope’s surface.

In Fig. 53 and 54 it is possible to observe a comparison of the results obtained from the simulations and collected in Fig. 52. Cold season results (from October to May) are considered to be more relevant in the mean power analisys due to the high demand of thermal energy in this period of the year. Hence, these values are

1. Combined shape North façades

The results of both analysis are collected in Fig. 52.

Analysis of the results

2. Plot shape South façades

North façades

South façades

Hot Season

Hot Season

Cold Season

Cold Season

Fig. 46: Analysis with Honeybee of the mean power per exposed area for shape Nº 1.

Fig. 47: Analysis with Honeybee of the mean power per exposed area for shape Nº 2.

June - September

June - September

October - May

October - May

- 38 -

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

5. Elliptical shape

3. Solar angle shape North façades

North façades

South façades

South façades

Hot Season

Hot Season

Cold Season

Cold Season

Fig. 48: Analysis with Honeybee of the mean power per exposed area for shape Nº 3.

Fig. 50: Analysis with Honeybee of the mean power per exposed area for shape Nº 5.

June - September

June - September

October - May

October - May

North façades

4. Circular shape

North façades

South façades

Hot Season

Hot Season

Cold Season

Cold Season

6. Water drop shape

South façades

June - September

June - September

October - May

October - May

Fig. 51: Analysis with Honeybee of the mean power per exposed area for shape Nº 6.

Fig. 49: Analysis with Honeybee of the mean power per exposed area for shape Nº 4.

- 39 -

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Shape

1. Rectangular shape

Sun path

Parameter

8125

m2

Area with energy production potential (epp)

4064

4064

m2

18000000

16200000

597

346

698393

328404

Envelope area

8324

8324

m2

Area with energy production potential (epp)

3772

3772

m2

18300000

16600000

763

280

660689

317680

Envelope area

8600

8600

m2

Area with energy production potential (epp)

5386

5386

m2

19000000

16500000

767

333

943396

453614

Envelope area

7175

7175

m2

Area with energy production potential (epp)

3594

3594

m2

15700000

14100000

760

341

626622

292260

Envelope area

7443

7443

m2

Area with energy production potential (epp)

4159

4159

m2

16600000

14600000

774

341

66132

296619

Envelope area

8006

8006

m2

Area with energy production potential (epp)

5612

5612

m2

18000000

15300000

781

332

983051

472681

Energy received on the whole envelope

Energy received on the whole envelope Mean power per area Average solar radiation on area with epp

Energy received on the whole envelope Mean power per area Average solar radiation on area with epp

4. Circular shape

Energy received on the whole envelope Mean power per area Average solar radiation on area with epp

5. Elliptical shape

Energy received on the whole envelope Mean power per area Average solar radiation on area with epp

6. Water drop shape

Units

8125

Average solar radiation on area with epp

3. Solar angle shape

Cold season

(October to May)

Envelope area

Mean power per area

2. Plot shape

Hot season

(June to September)

Energy received on the whole envelope Mean power per area Average solar radiation on area with epp

66 /110

Fig.52: Results from the analysis of the mean power per exposed area and potential for energy production during the hot and the cold seasons.

- 40 -

KWh W/ m2 KWh

KWh W/ m2 KWh

KWh W/ m2 KWh

KWh W/ m2 KWh

KWh W/ m2 KWh

KWh W/ m2 KWh

2 / Climate-based build form

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

2 / Climate-based build form Mean power per exposed surface during the hot and cold seasons

Mean power per exposed surface during the hot and cold seasons

1.

(W/m2)

2.

3.

4.

5.

6.

800

H

H

H

H

H

700

769

763

767

774

781

600

H

500

560

400

C C

346

300

281

200

the main guideline for assessing the adequacy of the different geometries respect to the power captured by the exposed area.

In Fig. 53 can be observed that the geometries with a higher mean power per exposed surface are shapes number 1, 4 and 5. Of those, the geometry showing the best result is shape number 1 (or combined shape), with an average of 346 w/m2 during the cold season, and 769 w/ m2 during the hot one. Shapes 4 and 5 have the same average value for the mean power during the cold season (341 w/m2), and an average of 560 and 774 w/m2 during the hot season respectively.

C

C

C

C

333

341

341

332

2/

100 0

Fig. 53: Comparison of results from the analysis of the mean power per exposed area during the hot (H) and the

Energy received on the surface with potential for energy production during the hot and the cold seasons cold (C) seasons.

Energy production potential during the hot and the cold seasons

1.

2.

673. /110

(MWh) 1000

700 600

H

300 200

983

H

H

661

328

C

454

318

Figure 54 shows the results comparing the energy received on the exposed surfaces to direct solar radiation, which highlight the geometry’s potential for future solar energy production.

661

627

C

C C

An important observation is that the elliptical shape’s performance sits between the three best geometries in both wind analysis and mean power per exposed surface analysis.

H

H

698

The variation on the mean solar radiation during the cold season is not really signiďŹ cant across these six geometries. The biggest difference is shown between shapes 1 (combined shape) and 2 (solar angle shape), with a difference of 19 % on shape 2 in relation to shape 1.

6.

943

500 400

5.

H

900 800

4.

C

C

292

297

473

As it can be seen, the three best geometries in this regard are number 1, 3 and 6. Unexpectedly, the geometry with higher energy production potential is shape number 6 (water drop shape)

100 0

Fig. 54: Comparison of results for the energy received on directly exposed surfaces with potential for energy production during the hot (H) and the cold (C) seasons.

68 /110

Moreover, all the geometries excluding the circular shape have similar values on the mean solar radiation during the hot season. This Climate-based build form implies that the circular shape is the most suitable geometry to avoid future overheating problems. However, it is also possible to solve this problem with a well-designed ventilation system and, most of all, with the implementation of dynamic shading devices.

- 41 -

with a total of 983 MWh during the hot season and 473 during the cold one. In contrast, the geometry designed with an optimal angle with the horizon line regarding solar exposure [7] (shape number 3 or solar angle shape) occupies the second place in the ranking. This shape receives a total of 943 MWh during the hot season and 454 MWh during the cold one.

Shape number 5 (elliptical shape), which was among the best geometries in the previous analysis, has the second lowest energy production potential, just after the circular shape. The total energy received in the exposed surface of this geometry during the hot season is 661 MWh (33 % lower regarding the value from shape 6), while the total energy received during the cold season is 297 MWh (37 % lower regarding shape number 6).

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

3.5. Selected geometry Multi objective desgins are characterized by solutions where a trade off between several parameters is achieved. For the case of the previous analyses, the elliptical shape has proven to be the best solution in the wind analysis, and the third best for the passive solar heat gains analysis. Moreover, these two where the most important parameters in the established set of priorities at the beginning of this chapter. This good performance respect to the wind and solar gains outbalances the low energy production potential which,in turn, was considered the least important priority. Moreover, this feature may be improved by slightly reshaping the geometry, as it will be shown further on this chapter.

As a conclusion, shape number 5 (elliptical shape) has proven to be the optimal compromised solution for the overtaken analyses (Fig. 55).

Thus, this geometry is the selected for the further development of the project.

Selected geometry. Shape Nº 5

Fig. 55: Selected geometry placed on its context.

Thus, the shape alteration possibilities that have been tested are the followings:

This geometry has another important quality: its compactness. It has been demonstrated that in cold climates compact shapes are an effective solution to passively reduce the energy consumption of buildings [1]. Compact shapes have less exposed surface to the exterior environment, reducing the thermal losses through the envelope.

•

•

Option 2 (Fig. 58) implements the same porosity strategy, but though a horizontal opening combined with a vertical one.

These are communicated in the middle as a combination of a central atrium and a sky lobby.

•

Option 3 (Fig. 59) is based on the width variation strategy, reducing the width of the building with its height.

•

Option 4 (Fig. 60) varies the cross-section of the geometry, rotating its floor plan along its height.

Further wind optimisation So far, the variation of the geometries affected only to their floor plan, being linearly extruded to create a volume. However, much more can be done at the basic design level in order to further improve the behaviour of the building.

Vortex shedding is one of the major issues in high-rise buildings. The bigger the drag force is, the bigger the vortices. As seen in the previous wind analysis, the drag force over the elliptical shape was higher from the west wind direction.

Several strategies can be applied to reduce this phenomena. (Fig. 56).

One way is to increase the porosity through openings across the building that allow the air flow to pass through and release the pressure on the envelope [5]. Another strategy is to vary the width of the building along the height, which leads the vortices to shed in different frequencies, reducing the associated fluctuations [5]. A similar effect can be achieved varying its cross-section shape [5]. For instance, by rotating the floor plan of the building through its height.

Finally, other possible solution would be to create a structural element to counterbalance the wind force, such as a sided structural core.

Option 1 (Fig. 57) applies the porosity strategy, creating horizontal openings in alternated floors communicated in the middle in order to alter the wind flow and release the wind pressure.

•

Option 5 (Fig. 61) is a combination of the previous one with a variation of the floor plan geometry, trying to create a bigger alteration on the wind flow.

The results of the simulations have been compiled in a table for comparison (Fig. 62).

The values of four different intervals for each geometry have been collected (25, 35, 45 and 55 minutes since the simulation stated). These intervals are chosen as the wind flow is stabilised after 25 minutes of simulation.

How to develop the geometry further (Solve the problem of the drag force due to west wind)

1. Holes

These improvement possibilities have been modelled with Grasshopper, a parametric tool for Rhinoceros, and tested once again in the wind tunnel simulated with Flow Design (Fig. 57, 58, 59, 60 and 61). The last possibility of creating an exterior structural element has been left out of the simulations as it would alter the first simulation results.

2. Holes + roof opening

3. Vary section

Fig. 56: Possible ways to improve the behaviour against the wind coming from the west.

- 42 -

4. Sided core

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Option 3. Vary section

Option 1. Holes in the envelope

Fig. 57: Possibility number 1 to reduce the drag force from the wind coming from the west.

Fig. 59: Possibility number 3 to reduce the drag force from the wind coming from the west.

Option 4. Twisting the geometry

Option 2. Sky lobby with roof opening

Fig. 58: Possibility number 2 to reduce the drag force from the wind coming from the west.

Fig. 60: Possibility number 4 to reduce the drag force from the wind coming from the west.

- 43 -

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Summary analysis Summary of of analyses (windcoming coming from the west) (wind from the west)

Option 5. Twisting the geometry

Shape

1. Holes on the envelope

2. Sky lobby + roof opening

3. Varying the section

Fig. 61: Possibility number 5 to reduce the drag force from the wind coming from the west.

Analysis of the results From Fig. 65 can be observed that option 4 (twisted geometry) produces the best results respect to the drag force originated by the wind from the west. Option 3 (varying section) leads to similar drag forces in this direction, however, its behaviour against wind from the south is superior to any of the other proposed geometries. Geometry 1 (holes on the envelope) also performs adequately respect to the wind from the south, but the high drag forces originated by the western wind make this option less attractive. The remaining two alternatives present worse results for both wind directions.

The drag force due to the west wind direction in the original elliptical shape was 399 kN, and the mean force over the envelope is 0.05864 kN/ m2. In Fig. 64 the percentages of improvement with respect to this initial mean force are shown.

Compared to the new proposed geometries, this means that in option 4, a reduction of 48% with respect to the initial drag force has been achieved (twisting the floor plan along the height). The second best option for this wind direction is option 1 (creating holes on the envelope façades), with a reduction in the drag force of 28 %. The third place is for option number 3 (varying the cross-section of the geometry, with a reduction of 26 % in the drag force. This is only a 2% lower than the previously alternative, so they can be considered equally good.

4. Twisting the geometry

5. Modifying and twisting the geometry

Shape axonometry

Testing time (minutes)

Positive peak pressure (Pa)

Negative peak pressure (Pa)

Highest wind velocity (m/s)

Drag coefficient (Cd)

25:00

165.50

-291.13

26.40

0.98

295300.5

35:00

166.93

-148.51

26.49

1.06

320378.9

45:00

170.21

-168.80

25.18

1.06

320676.1

55:00

173.27

-150.61

25.16

1.03

311954.7

25:00

175.28

-269.34

24.59

1.27

383846.9

35:00

179.15

-221.52

23.60

1.30

393851.7

45:00

181.19

-207.80

23.63

1.26

382019.1

55:00

185.80

-196.50

23.38

1.21

366026.2

25:00

162.92

-214.66

23.36

1.23

288592.0

35:00

158.95

-207.78

22.81

1.16

272030.2

45:00

160.90

-183.59

22.12

1.06

249490.1

55:00

163.41

-170.42

21.94

1.05

246077.9

25:00

137.19

-205.82

29.88

0.97

244605.8

35:00

135.78

-144.51

21.91

0.98

247078.8

45:00

135.91

-147.58

21.67

0.93

234335.6

55:00

135.66

-134.53

21.86

0.88

220641.7

25:00

186.47

-173.04

29.75

1.32

378458.5

35:00

194.24

-152.40

29.73

1.23

352595.3

45:00

197.02

-187.91

29.84

1.15

329867.1

55:00

206.34

-143.44

29.95

1.14

325599.0

Fig. 62: Results from the simulation in Flow Design for the west wind direction.

The effect of this change in the geometry has also been calculated regarding to the south wind direction. The percentages of improvement with respect to the original mean force are also shown in Fig. 64. In this case, it can be observed that the best result is obtained with the third option (varying the cross-section along the geometry’s

79 /110

- 44 -

Drag Froce (N)

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Summary analysis Summary of of analyses (windcoming coming from the south) (wind from the south)

Shape

1. Holes on the envelope

2. Sky lobby + roof opening

3. Varying the section

4. Twisting the geometry

5. Modifying and twisting the geometry

Shape axonometry

Testing time (minutes)

Positive peak pressure (Pa)

Conversion of units for the results of the last interval

2 /Conversion Climate-basedof build form for the results of the last interval units

Negative peak pressure (Pa)

Highest wind velocity (m/s)

Drag coefďŹ cient (Cd)

Shape axonometry

Drag Froce (N)

25:00

141.03

-240.28

25.49

0.63

144832.7

35:00

141.49

-267.41

25.16

0.65

149676.5

45:00

145.21

-252.42

25.24

0.62

142397.5

55:00

145.04

-256.14

25.14

0.60

137762.4

25:00

151.20

-205.21

21.11

0.89

205266.7

35:00

152.73

-174.72

19.95

0.89

205943.8

45:00

155.34

-126.82

19.68

0.87

201186.1

55:00

157.50

-120.58

19.60

0.85

196332.1

25:00

131.72

-319.02

29.10

0.59

105426.0

35:00

131.29

-284.40

29.48

0.57

102785.6

45:00

128.86

-277.89

29.67

0.54

97471.0

55:00

131.09

-271.33

29.73

0.53

95183.4

25:00

131.03

-181.55

31.41

1.03

269956.4

35:00

130.94

-132.25

21.35

0.99

259845.1

45:00

131.85

-124.35

19.59

0.94

246844.4

55:00

132.51

-106.97

19.10

0.91

237380.5

25:00

153.57

-197.88

22.96

0.90

187733.6

35:00

155.74

-161.86

22.61

0.97

201085.4

45:00

159.72

-154.05

22.45

0.93

193393.9

55:00

164.20

-120.96

22.52

0.93

193163.8

Total envelope’s surface (m2)

Total drag force (kN)

Mean force (kN/m2)

Improvement with respect to the elliptical shape

West

South

West

South

West

South

7443

312

138

0.04

0.02

28 %

50 %

7443

366

196

0.05

0.03

16 %

29 %

5640

246

95

0.04

0.02

26 %

55 %

7196

221

237

0.03

0.03

48 %

12 %

7081

326

193

0.05

0.03

22 %

27 %

1. Holes on the envelope

2. Sky lobby + roof opening

3. Varying the section

4. Twisting the geometry

5. Modifying and twisting the geometry

Fig. 63: Results from the simulation in Flow Design for the south wind direction.

82 /110

80 /110

Fig. 64: Calculation of the mean force over the envelope for the west and south wind directions.

- 45 -

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Comparison of the effect of modifying the shape in the west and south wind directions

2 / Climate-based build form

Comparison of the effect of modifying the shape in the west and south wind directions

1.

(KN)

2.

3.

Design of the final geometry according to the results of the simulations

4.

5.

800 700 600 500 400 300

W W

W

366

312

S

200

S

100

138

196

W

W

246 S

221

S 237

326

Fig. 66: Modification of the geometry in order to improve its behaviour against solar exposure.

S 193

Proposed final geometry

95

0

Fig. 65: Comparison of the results obtained for the drag force in the west (W) and south (S) wind directions.

height), with an improvement of 55 % in the mean force obtained for this wind direction. The second best result obtained is for the first option (creating horizontal holes across the building), with an improvement of 50 %. Surprisingly, the fourth option achieves the lowest performance of only a 12%, in contrast with the fact that it was the best alternative for the previous wind direction.

South is the prevailing wind direction, so the improvements for this case scenario have a higher relevance than for the west one (which occurs only for around 5 % of the whole year according to the weather data). Moreover, due to the geometry’s symmetricity, the effect in the other prevailing wind directions (southsoutheast and north-northwest) will be very similar to the behaviour in the south one. That

is the reason why the simulations for these other wind directions have not been repeated. As a result, the third option (varying the section) has been selected as the optimum alternative to implement.

81 /110

Further solar optimisation Once the strategy to reduce the wind force has been settled, the next step is to further optimise the solar exposure. The main goals are to achieve maximum solar exposure in winter, as well as to increase the energy production potential through the use of solar power.

In order to achieve such improvements, the cross-section of the building is varied so that the widest area is located in the middle, reducing its

Fig. 67: Visualization of the geometry on its context.

- 46 -

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Summary of analysis (wind coming from the south) 2 / Climate-based build form

Summary of analysis (wind coming from the west) Summary of analyses (wind coming from the west)

Shape

1. Elliptical shape

2. Modified elliptical shape

3. Final shape

4. Final shape with openings

Shape axonometry

Testing time (minutes)

Positive peak pressure (Pa)

Negative peak pressure (Pa)

Summary of analyses (wind coming from the south)

Highest wind velocity (m/s)

Drag coefficient (Cd)

Drag Froce (N)

Shape

Shape axonometry

Testing time (minutes)

Positive peak pressure (Pa)

Negative peak pressure (Pa)

Highest wind velocity (m/s)

Drag coefficient (Cd)

Drag Froce (N)

25:00

263.40

-540.30

34.27

0.71

291361.7

35:00

263.78

-513.32

34.83

0.71

292448.8

45:00

267.60

-498.42

34.58

0.67

275844.5

399302.2

55:00

278.76

-423.84

31.78

0.62

253215.9

1.23

288592.0

25:00

131.72

-319.02

29.10

0.59

105426.0

22.81

1.16

272030.2

35:00

131.29

-284.40

29.48

0.57

102785.6

-183.59

22.12

1.06

249490.1

45:00

128.86

-277.89

29.67

0.54

97471.0

163.41

-170.42

21.94

1.05

246077.9

55:00

131.09

-271.33

29.73

0.53

95183.4

25:00

116.12

-154.18

20.48

1.02

417014.6

25:00

130.60

-228.68

25.84

0.61

188794.7

35:00

120.85

-148.67

20.46

1.01

412695.2

35:00

132.79

-224.97

25.36

0.60

186384.1

45:00

124.44

-142.96

20.46

1.00

410905.2

45:00

130.22

-226.51

24.98

0.60

187232.7

55:00

127.81

-137.61

20.44

1.00

410644.7

55:00

130.34

-226.16

25.21

0.60

187309.5

25:00

158.47

-198.46

26.84

1.02

418111.9

25:00

130.60

-228.68

25.84

0.61

188794.7

35:00

160.67

-208.96

23.17

1.02

415506.4

35:00

132.79

-224.97

25.36

0.60

186384.1

45:00

165.44

-201.54

22.94

1.01

414089.9

45:00

130.22

-226.51

24.98

0.60

187232.7

55:00

166.63

-197.98

22.07

1.01

414081.9

55:00

130.34

-226.16

25.21

0.60

187309.5

25:00

180.02

-265.08

25.27

1.38

416744.9

35:00

184.14

-133.56

24.55

1.37

414704.8

45:00

186.38

-126.77

22.42

1.36

411346.8

55:00

191.06

-122.89

22.77

1.32

25:00

162.92

-214.60

23.36

35:00

158.95

-207.78

45:00

160.90

55:00

1. Elliptical shape

2. Modified elliptical shape

3. Final shape

4. Final shape with openings(closed for this wind direction)

Fig. 68: Results from the simulation in Flow Design for the west wind direction.

Fig. 69: Results from the simulation in Flow Design for the south wind direction.

width towards the upper and the bottom part. façade inclined towards the solar rays in order to This approach leads to tilted surfaces in the86 /110increase its solar exposure, while in the bottom south façade of the buildings, which enhances part the opposite effect is achieved. the solar exposure as this orientation is optimal in the north hemisphere.

As a result, this design protects the offices, where high internal heat gains may be expected As mentioned in Chapter 1, the building from the use of appliances, from a possible proposed in this thesis has the same program overheating effect during summer. This strategy distribution than the design proposed by has been proven to work in such a renowned Snøhetta. Therefore, the commercial and building as the London City Hall designed offices areas are located on the lower half of

by Foster and Partners. Moreover, a possible the building, while the apartments are located overheating effect in the housing upper section on the upper part. This upper part has its south has also been taken into consideration and its

the virtual wind tunnel. Fig. 68 and 69 display preventing solution will be explained in Chapter 87 /110the results of these simulations for the south 5. and west wind directions in comparison with the values obtained for the previous geometries.

In addition, the roof surface has also been tilted, with an inclination of 30º, as observed in Fig. 66 In addition, a fourth option has also been tested. and 67. This design choice relies once again in This alternative proposes two vertical openings the maximisation of its solar exposure, ensuring in symmetrical locations of the building with the a higher energy production potential on the purpose of releasing the wind pressure caused roof surface. by the west wind direction.

To check that the new design has the same Moreover, the mean force values for these two improvement effect in relation to the wind directions have been calculated and compared pressure, the geometry has been simulated in

- 47 -

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Conversion of units for the results of the last interval

Scheme of the wind flow and pressures distribution

Conversion of units for the results of the last interval Shape axonometry

Total envelope’s surface (m2)

Total drag force (kN)

Mean force (kN/m2)

2 / Climate-based build form

Improvement in relation to the elliptical shape

West

South

West

South

West

South

7443

399

253

0.06

0.04

0.00 %

0.00 %

5640

246

196

0.04

0.02

19 %

35 %

1. Elliptical shape

2. Modified elliptical shape

Fig. 71: Wind flow, pressures and under-pressures distribution for the south wind direction.

with the original values. They are shown in Fig. 70.

3. Final shape

Analysis of the results 9286

411

187

0.04

0.02

18 %

Fig. 70 shows that the improvement achieved with this geometry is even bigger for the case of the south wind direction. This is probably due to the fact that this geometry is even more elongated on its longitudinal axis than the previously analysed (option 1 and option 2 in this table). Thus, an improvement of 41 % regarding the initial elliptical shape has been achieved for this wind direction. This means an improvement of a 6 % with respect to option 2. The wind flow and pressures distribution around the building for this wind direction have been represented in Fig. 71.

41 %

4. Final shape with openings

9286

414

187

0.04

0.02

17 %

41 %

However, in the west wind direction, the improvement is 1 % less than the 19 % achieved with option number 2. This is due to an increase in the perpendicular surface to this wind direction, which causes a higher resistance to the wind flow.

88 /110

Fig. 70: Calculation of the mean force over the envelope for the west and south wind directions.

- 48 -

Fig. 70 shows that a fourth option has been considered in the wind tunnel simulations.

This option is a variation of option 3, with the addition on two vertical openings located in opposite sides of the building. This measure aimed to reduce the wind pressure due to the wind blowing from the west. However, the results are almost identical to option number 3, showing no improvement achieved due to its utilisation.

With the aim of checking the improvement effect regarding the solar exposure, this final geometry has been analysed with Honeybee.

The results of this analysis can be observed in Fig. 72 and 73.

As shown in Fig. 73, this new geometry allows an improvement on the mean solar power per exposed area of 3 % during the cold season (from an initial value of 341 W/m2 achieved in the initial elliptical shape to the 351 w/m2 achieved in this final geometry. On the other hand, it also allows to increase in a 1 % the solar exposure during the hot season (form 774 W/m2 achieved in the original shape to 785 W/m2 achieved in

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

References Solar analysis of the final shape North façades

this final one). This small improvement during the hot season is due to the double inclination of the south oriented façade, which protects the lower part from the solar rays when those have their highest elevation angle. This fact will be further explained in the following chapters.

South façades

From the previous approach a compromised solution between different design parameters has been shown, proving the potential of multi-objective design.

Optimization of several parameters might encounter opposite tendencies in many design variables. Therefore, a balance that allows to achieve a good result for all the design parameters is indispensable.

Hot Season

June - September

[1] N. Lechner, Heating, cooling, lighting: Sustainable design methods for architects. John Wiley & Sons, 2014.

[2] T. Kleiven, Natural ventilation in buildings: architectural concepts, consequences and possibilities. Institutt for byggekunst, historie og teknologi, 2003.

[3] K. Yeang, A. Balfour, and I. Richards, Bioclimatic skyscrapers. Ellipsis London, Limited, 1994.

[4] M. Piñeiro Lago, “High-rise Buildings in Contemporary Architecture,” NTNUMay 2017 2017, Available: https://issuu.com/ marta.pineiro.lago/docs/high_rise_wooden_ buildings_in_conte.

[5] P. Vongsingha, “Adaptive Façade for Windload reduction in High-rise,” 2015.

Cold Season

October - May

2 / Climate-based build form

Summary of solar radiation analysis

Fig. 72: Analysis with Honeybee of the mean power per exposed area for the final geometry.

[7] G. Lobaccaro, S. Carlucci, S. Croce, R. Paparella, and L. Finocchiaro, “Boosting solar accessibility and potential of urban districts in the Nordic climate: A case study in Trondheim,” Solar Energy, vol. 149, pp. 347-369, 2017.

Summary of solar radiation analysis Shape

Sun path

Parameter

2. Final shape

Cold season

(October to May)

7443

7443

16600000

14600000

KWh

Mean power per area

774

341

W/ m2

Envelope area

9286

9286

m2

21000000

18800000

KWh

785

351

W/ m2

Energy received on the whole envelope

Energy received on the whole envelope Mean power per area

[8] C. E. de Normalisation, “Eurocode-1: Basis of design and actions on structures-Part 2–4: Actions on structures ‘‘Wind actions’’,” European Committee for Standardisation, Brussels, 1995.

Units

(June to September)

Envelope area

1. Elliptical shape

Hot season

[6] V. Olgyay, Design with climate: bioclimatic approach to architectural regionalism. Princeton University Press, 2015.

m2

[9] R. Baetens, B. P. Jelle, and A. Gustavsen, “Phase change materials for building applications: a state-of-the-art review,” Energy and buildings, vol. 42, no. 9, pp. 1361-1368, 2010.

[10] A. G. Hestnes and N. L. Eik-Nes, Zero Emission Buildings. Fagbokforlaget, 2017.

Fig. 73: Calculation of the mean power per exposed area with the results obtained from Honeybee.

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4.

Structural system

Aiming for ZEB in a High Rise Building

4. Structural system

4.1. Preliminary considerations Integrated Design Processes imply that some considerations that otherwise would not be addressed until further stages of a project are evaluated in the early design. This is the case of natural ventilation and daylight strategies during the design of the builiding´s structure.

It is a well-known fact that the energy budget for cooling in tall buildings has considerably increased during the past decades. This is especially remarkable for office buildings due to the intensive use of appliances in working spaces, which increases in a great manner the internal heat gains. As an illustration, according to the U.S. Department of energy, heating, ventilation and air conditioning systems (HVAC) account for the 33 % of the total building energy consumption [1].

Another factor that greatly contributes to the need of cooling is the air-tight design of contemporary buildings due to regulation compliance. The increased efficiency in these HVAC systems by passive means is one of the most important steps in making tall buildings more sustainable [1].Thus, the design of an efficient and effective natural ventilation system can significantly reduce the energy used for cooling.

The efficiency of this passive strategy is tightly related with the floor to ceiling height, as well as with the distance between air inlet and outlet openings. Therefore, the location of the structural core of the building, the height of the floors or the use of design strategies such as atria affect directly to the building’s structure.

As mentioned in Chapter 3, there are three natural forces that can be used for natural ventilation: thermal buoyancy, wind or a combination of both [2]. Thermal bouyancy over wind force was justified for the case of Oslo´s climate (see Chapter 3) Moreover, a good natural ventilation system relies on the knowledge and correct selection of the natural ventilation principles. There are three

Single-sided ventilation

ventilation principles: single-sided ventilation, cross ventilation and stuck ventilation [2] (Fig. 74).

H

A single-sided ventilation principle consists on a common air inlet and outlet placed on one side of the analysed thermal zone. This principle allows and efficient natural ventilation in a room depth equal to the double of the floor to ceiling height.

2H As a rule of thumb, single-sided ventilation is effective to a depth of about 2 to 2.5 times the floor to ceiling height.

Cross-ventilation allows to increase the room’s depth up to five times the floor to ceiling height without losing effectiveness. This is due to the fact that in these systems the air inlet and outlet are placed in opposite sides of the thermal zone, creating a wind current across it that helps to remove air pollutants.

Cross-ventilation H

Lastly, a stuck ventilation principle relies on the density of the hot and cold air inside a room.

According to this principle, the air inlet located in one side of the thermal zone forces the natural convective currents inside it. The hot or exhaust air, that has lower density than the cold and fresh one, is evacuated through an air outlet located on the top part of the thermal zone. When combined with a cross-ventilation principle, stuck ventilation allows room depths up to 5 times the distance from the air inlet to the air outlet in both sides of the thermal zone.

5H As a rule of thumb, cross-ventilation is effective up to 5 times the floor to ceiling height.

Stuck ventilation

These ventilation principles are implemented in a building through characteristic ventilation elements [2]. For the case of high-rise buildings, atria and double façades are the most common ventilation elements used for natural ventilation purposes [2]. Both elements have their benefits and drawbacks. In addition, the use of double glass façades creates a direct impact in the emissions due to materials, as well as an increase of the embodied emissions due to the building’s maintenance. Commonly used triple-glass windows with low conductivity have large associated embodied emissions on their production phase (A1 to A3), of the order of 110.2 kg CO2 eq for a single window of 1.23 m x 1.48 m [3]. The implementation of this

H

5H

5H

As a rule of thumb, single-sided ventilation is effective across a width of 5 times the floor to ceiling height from the inlet to where the air is exhausted.

Fig. 74: Natural ventilation principles.

- 52 -

characteristic ventilation element requires less space than atria. However, since one of the goals in this thesis is the reduction of emissions due to materials, the implementation of double façade as characteristic ventilation element should be avoided.

Nevertheless, natural ventilation is not the only passive strategy that can be used to reduce the energy demand of high-rise buildings. In cold climates, an efficient use of solar and internal heat gains can make a significant difference in the total energy budget. Moreover, providing adequate daylight levels inside the building will not only have repercussions on the health and well-being of the building’s inhabitants, but also on the electricity use.

Aiming for ZEB in a High Rise Building

4. Structural system

4.2. Structural core The position of service cores is of central importance in the design of a high-rise building.

The service core not only has structural implications, but it also affects the building’s thermal performance and views [4]. In Fig. 75, representations of the location possibilities for the structural core can be observed. There are basically three possibilities: central core, double core and single-sided core.

In order to check the direct implications regarding daylight levels of this structural element’s location, the three possibilities have been simulated with Diva for Rhinoceros. As it can be observed in Fig. 76, the mean daylight factor (DF), mean daylight autonomy (DA), and Daylit area have been calculated for each possibility. It is worth noting that this particular simulation does not show accurate values but a rough estimation of the daylight levels that could be achieved in every possible distribution.

This is due to the fact that, in order to simplify the calculation, the whole envelope area with access to solar radiation has been considered as glass, and the structural cores as opaque materials. The adequate proportion of windows in relation to the floor area will be calculated in Chapter 5.

According to European Standards, the mean DF should be higher or equal to 2 % [5]. However, these standards are sometimes considered too low, and hence a minimum Df of 2% and mean DF of 5% are more adequate standards.

The daylight autonomy makes reference to the percentage of sensors with illuminance values with a daylight factor equal or higher than 2 % during the whole occupant schedule, which has been set to a normal office schedule from 8:00 to 18:00. Thus, a DA of 100 % means that all the sensors in the room fulfil the minimum requirement of 2 % as DF. The percentage of the room with a DA larger than 50 % for active occupant behaviour is called daylit area.

As it can be observed in Fig. 76, option 1 (central core) allows to achieve evenly distribute daylight values in the whole room. In this option, all the

Location of the cores. Three possibilities

sensors have a DA of 60 % or higher, being the mean DA 75 % of the occupied hours and the daylit area the whole room. Option 2 (double core), has a good DF near to the window area, but it considerably decreases towards the centre of the space, being the lowest DA 50 % of the occupied hours. Moreover, the daylit area does not reach the 100 % like in the previous case.

Finally, option 3 (single-sided core) shows, as the previous one, a high DF near the windows, but some darker areas near the core. However, this option considers the entire room as daylit.

1. Central core

It is also important to mention that all the core possibilities that have been tested are interior cores. This has been done in order to avoid any kind of negative effect of the structural core in the optimised building geometry in relation to the wind. Moreover, every option has its own implications, not only regarding daylight distribution, but also in relation to its thermal behaviour, natural ventilation and space efficiency. In order to analyse every possible implication in relation to these parameters, a table of comparison has been done (Fig. 77).

The table has been divided into two parts: environmental performance and functionality.

Within the environmental performance category, the natural ventilation, solar accessibility and sun shading implications have been analysed.

Whereas, the category of functionality has been divided into the two predominant functions of this building: offices and housing.

2. Double core

3. Single-sided core

Fig. 75: Location possibilities of the structural core. Bioclimatic Skyscrapers. Ken Yeang, 1994

Daylight simulations for three core possibilities 1. Central core

Regarding the natural ventilation of the interior spaces, the central core possibility is the only one that allows to easily ventilate the whole space just by single-sided ventilation. This is due to the fact that the maximum distance from the window area to the core is 7.5 m and the floor to ceiling height has been set up to 4 m, following the previously introduced rule of thumb. For both the double core and the single-sided core options, the distance from the window area to the central space exceeds 8 m, which makes it necessary to introduce either cross-ventilation or stuck ventilation.

2. Double core

Mean DA: 75.18% Mean DF: 8.4% Daylit area: 100%

3. Single-sided core

Mean DA: 67.10% Mean DF: 5.1% Daylit area: 98%

Mean DA: 72.54% Mean DF: 7.2% Daylit area: 100%

Scanned

Fig. 76: Daylight simulations for the location possibilities of the structural core.

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Aiming for ZEB in a High Rise Building

4. Structural system

3 / Structural sys

the structural core’s location Impact ofImpact theofplacement of the structural core

Parameter

Natural ventilation

Environmental performance

Solar accessibility

Sun shading

Central core

Double core

Single-sided core

Easier to naturally ventilate on the minor axis direction through single-sided ventilation

More difficult to naturally ventilate in the minor axis direction (need for cross or stuck ventilation)

More difficult to naturally ventilate in the minor axis direction (need for cross or stuck ventilation)

Easier to achieve adequate daylight levels in the four sides of the core

More difficult to achieve adequate daylight levels in the central area

More difficult to achieve adequate daylight levels in the central area

Does not cause any overshadowing effect (need of additional measures to avoid overheating)

Creates overshadowing effect in both southern and northern areas ( beneficial in the north avoiding thermal losses and in the south avoiding overheating)

Creates overshadowing effect where the core is placed ( may be beneficial when placing it right, for instance avoiding glare coming from the east)

Does not allow an open floor plan concept.

Allows an open floor plan concept.

Allows an open floor plan concept.

Allows to allocate cell offices in one of the sides without affecting the efficacy of natural ventilation

Does not allow to allocate cell offices in one of the sides due to the need of cross ventilation.

Does not allow to allocate cell offices in one of the sides due to the need of cross ventilation.

Allows to evenly distribute apartments with the same daylight and natural ventilation conditions.

Allows to evenly distribute apartments with the same daylight and natural ventilation conditions.

Does not allow to evenly distribute apartments with the same daylight and natural ventilation conditions.

Offices Functionality

Housing

Fig. 77: Summary of possible implications for the core’s location possibilities

96 /110

- 54 -

Aiming for ZEB in a High Rise Building

4. Structural system

4.3. Structural system selection As previously explained, in relation to solar accessibility, the option with central core is the one that allows to achieve good daylight levels across the whole useful area and more evenly distributed illuminance values.

However, in regard to sun shading, both the double core and single-sided core options are better possibilities, since they allow to protect interior spaces from direct sunlight, avoiding possible glare problems and overheating.

Moreover, the double core allows to protect from both the thermal losses from the north façade and the overheating from the south.

Referring to offices’ functionality, the central core option is the only one that does not allow an open floor plan concept. However, to apply an open floor plan concept also implies that no cell offices will be placed in the office layout. In order to provide as maximum flexibility as possible for the future stakeholders, considering the implementation of cell offices

as well this assumption. It consists of various existing culverts from the district heating network located underneath the plot (Fig. 78), which makes it impossible to allocate the structural cores on top of them.

is also important. This kind of singular offices are normally placed along one or more façades to provide them with natural light. When this occurs, a cross-ventilation concept is no longer possible, since at least one entire façade will be obstructed. For this reason, the double and single-sided core options are not appropriate in this particular situation.

Once the location of the structural core has been decided, the structural system associated to the core has to be selected. Due to the curve geometry of the building, a bidirectional system is the most appropriate option in relation to the slabs. Moreover, another important factor to have in mind is the structure’s material.

Finally, regarding the housing program, both the central and double core allow to design apartments with similar daylight, natural ventilation and view conditions. This is possible in either the four sides of the building for the case of the central core, or in two sides of it for the double core. Whereas, the asymmetric location of the single-sided core makes this more difficult to achieve.

“Size and scale have important implications environmentally and functionally. Engineering for efficiency is not the last and only determinant; it is possible to make a choice for several efficient schemes because of architectural, aesthetic, and environmental reasons. The human needs must give the directions” [6]. These words written

by M. Goldsmith in “Buildings and Concepts” are the basis for the selection of the structure’s material in this master thesis.

From the previous discussion, it is considered that the central core would be the best option to implement. Moreover, an additional difficulty related to the boundary conditions confirms

It was previously mention in Chapter 1 that, due to its great possibilities to reduce embodied emissions due to materials, a timber-based structural system would be considered (Fig.

Location of the core Additional problem: culverts of the district heating network

Emissions due to different structural materials (kg CO2 eq/m2)

7.5 7.5

m

m

200 150 100 50 0 -50 -100 -150 -200 -250 -300 -350 -400 -450 -500 -550 -600 -650

Concrete 188 Steel 11

-602

-630

CLT

Glulam

Fig. 79: Embodied emissions associated to the production of some structural materials. Data from EPD Norge and ibu-epd.com.

Fig. 78: Footprint and core’s location of Gullhaug Torg building and the proposed building in this thesis in relation to existing underground culverts.

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Aiming for ZEB in a High Rise Building

4. Structural system

Slab system Concrete Jointed Timber Frame (CJTF) _ SOM

79). Some other advantages of timber are small dead weight (allowing to reduce concrete required in the building’s foundations), good thermal characteristics, durability, and good resistance to fire of massive timber components.

Moreover, the intention of research on timberbased structures’ possibilities was also previously mentioned.

There are several systems with these characteristics available in the market. Most of them have been design and tested by recognised international architectur offices.

Some of these examples are Finding the Forest Through the Trees (FFTT), developed by the Canadian architect Michael Green, or Concrete Jointed Timber Frame (CJTF), developed by Skidmore, Owings & Merrill (SOM) [7, 8].

Due to its bidirectional slab system, CJTF developed by SOM was finally chosen. This structural system is composed by 70 % of timber and 30 % of concrete for the case study in which it was applied, including the foundations.

Mass timber is utilised for the main structural elements, and reinforced concrete at the highly stressed locations of the structure, which are the connecting joints. The result of its application is an efficient structure that combines the strength of both materials. This allows to reduce the building’s carbon footprint by 60-70 % with respect to a traditional concrete structure.

In CJFT there is a band of reinforced concrete at every floor’s perimeter and all wall to floor intersections. Supplementary reinforcement is provided at perimeter beams. The floor system consists of CLT panels that spam between timber shear walls at the centre of the building, as a central core. It is complemented with glulam columns and the reinforced concrete spandrel beams. The system works in a very similar manner to a reinforced concrete slab, where the ends of the floor panels are rotationally restrained through the rebar reinforcement connections.

This system stiffs the floor and enhances the deflection and vibration characteristics.

Fig. 80: Concrete Jointed Timber Frame (CJTF). Hybrid structural system developed by SOM.

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As explain in “The Case of Tall Wood Buildings” and “The Timber Research Project” reports, heights up to 30 storeys can be achieved with an all-timber-based system [7, 8]. However, the addition of concrete to achieve a hybrid system has additional advantages, being one of them the reduction in production cost.

In a posterior report published in 2017, SOM explored the possibility of adding a concrete tapping slab to their CJTF system (Fig. 80) [9].

This 10 cm concrete addition allows to improve not only the acoustic insulation properties of the structural system, but also its thermal behaviour.

This is due to the fact that in a daily basis, a 10 cm layer of exposed concrete is enough in order to stabilise the temperature fluctuations inside a room due to its thermal mass property.

Therefore, this system will act as a heat storage from the solar and internal heat gains, releasing the hot during the night and helping to reduce the heating energy consumption.

Traditionally, the use of timber-based structural systems in high-rises have been oriented towards replacing traditional forms of conventional construction in steel and concrete. Therefore, the result is the use of timber-based structures implemented as framing systems. Rather than focusing in this traditional alternative, this thesis aims to compare this application with the possible implementation of a not that conventional structural typology for timber high-rises: the diagrid system.

Diagrids are often built in steel. This material can be recycled and up to 97 % can be reused, making it an excellent choice in a “design for disassembly” approach [10]. Moreover, the amount of energy needed to produce a tonne of steel has been reduced by 50 % in the past 30 years, making it a more sustainable choice for building structures [10].

However, very few architects and engineers have explored the possibility of implementing a diagrid system in timber. Nonetheless, it is not a new concept either. A clear example is the

Aiming for ZEB in a High Rise Building

4. Structural system

Comparison of two different structural systems

Diagrig system + structural core

Framing system design and diagrid system

Housing 8 floors 3.60 m height

Framing system + structural core

Offices 7 floors 4 m height Commercial 2 floors 5 m height

Allow to reduce materials on the structure.

Higher amount of materials need in the structure.

Difficulty of designing windows in combination with the diagrid system.

Easier to design windows in combination with the diagrid system.

Impossible to design floors with different floor to ceiling heights.

No columns that may hinder the distribution of the program.

Housing 9 floors 4 m height

Easy to design floors with different floor to ceiling heights.

Columns may be an obstacle for the program distribution.

Offices 7 floors 4 m height Commercial 2 floors 4 m height

Fig. 81: Drawbacks and benefits of selecting a diagrid or a framing structural systems

Fig. 82: The building with a framing structural system versus a diagrid system.

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Aiming for ZEB in a High Rise Building

4. Structural system

4.4. Design and calculation of the diagrid system In traditional rectangular-shaped wooden highrise buildings (such as Murray Grove in London, Moholt 50/50 in Trondheim or Västerbroplan in Stockholm) framing systems are a very suitable structural option. However, in more organic geometries such as the proposed elliptical building, other structural solutions seem to be more appropriated. As different scales require different structures [6], different geometries

Unipol Tower designed by the Italian architect Cucinella for the city of Milan (Fig. 83). In this tower, a diagrid system is implemented to support the weight of the exterior curtain wall envelope. In this master thesis, the feasibility to push this structural system to the next level will be explored.

Column´s location is one of the main issues when designing and calculating the structure of high-rise buildings. As can be observed in the comparison carried out in Fig. 81, these structural elements are normally a big obstacle to the program distribution. Moreover, diagrid systems not only allow to get rid of the columns location problem. When well designed, they also allow to reduce the overall amount of structural material.

Fig. 83: Unipol Tower. Cucinella. Milan.

Fig. 84: Mock up of a diagrid joint. The Autodesk BUILD Space: 1, 75, 500”. Available at: http://blogs. autodesk.com/.

required different systems. For all these reasons the diagrid system was finally chosen to be developed.

The diagrid in combination with the central core behaves as a tube in tube system composed by core and structural façade. The material chosen for the core is CLT, acting as a continuous solid material, while the diagrid elements will be

Parametric design of the diagrid system

Nevertheless, this system also has some drawbacks. When designed to substitute interior columns, it becomes impossible to design floors with different heights, since all the intersections between the diagrid elements are at the same distance. The implementation of this system also creates some difficulties with the window’s design. When an all-glassed envelope is not desired, the combination between opaque and translucent envelope components becomes more complex, since the diagrid elements have to be avoided on the window’s location.

In order to take advantage of the stuck effect in high-rise buildings, the addition of an atrium has been decided. This characteristic ventilation element can be observed in Fig. 82. The thermal behaviour of this characteristic element through the seasons will be explained on the following chapter. In Fig. 82 it can also be observed that both a prototype with a framing system and a diagrid system were tested. However, due to the eccentricity on the columns’ location between the housing and the office parts, the cross-section of the columns in the lower floors of the framing system was not sufficient.

The dimension of these columns had to be considerably increased, leading to very thick elements that made it difficult to distribute the program.

Fig. 85: Parametric design of the diagrid structure with Grasshopper.

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Aiming for ZEB in a High Rise Building

4. Structural system

Structural calculations with Cype 3D Bending moments Y

glulam discrete elements joined together. The horizontal deck system will be composed by the previously mentioned hybrid combination of concrete beams and CLT panels with the 10 cm concrete tapping slab.

Bending moments Z

The diagrid system was first conceived in Grasshopper (Fig. 85). After testing several options, the 55º angle between its elements was finally chosen, as it significantly improved the vertical transmission of loads. In order to check the feasibility of this structural model, it was pre-dimensioned with the software Cype 3D (Fig. 86 and 87). The loads assumptions for

the calculation of this pre-dimensioned structure were: • Dead loads of horizontal structural elements: 1.5 kN/m2 • Finishing materials and partitions: 3 kN/m2 • Use loads (for residential and office use category): 2 kN/m2 • Wind load. Previously calculated value through the wind tunnel for the worst case scenario (west wind direction): 0.04 kN/m2 multiplied by the exposure and pressure coefficients [11].

To achieve a reasonable sizing of the elements

Tensions distribution

Fig. 86: Diagrams of efforts in the diagrid structure obtained from the Cype 3D calculation.

Fig. 87: Pre-dimensioned diagrid system through Cype 3D.

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Aiming for ZEB in a High Rise Building

4. Structural system

is important to correctly model the transmission of deck loads to the diagrid structure. The slabs together with the central core play the role of stabilizing elements to horizontal loads such as the wind pressure. Therefore, they have to lean on the horizontal elements of the diagrid structure. Rubber bearing connection elements are then utilised so that the momentum is not transmitted to the diagrid, modelled as pin joints.

Visualization of the building within its context

The joints between the diagrid elements are assumed to be rigid, materialised in a similar way to the joint shown in Fig. 84.

In order to avoid unnecessary load transmission from the slabs to the diagrid, some of the connections between these two structural elements are modelled with the connecting rubber bearing placed vertically, so that the load from the deck system are not transmitted to the diagrid system at every joint. This is especially important in those parts where the structure is not vertical, such as the south facing elements, where the transmission of loads would not be achieved in the most efficient manner, resulting in an over-sizing of these elements. As a result, vertical loads from the deck system are transmitted to the diagrid in three points: the north façade and both sides of the protuberance facing south.

In the initial design phase of the structure, an alternative system with intersecting elements every other slab was also taken into consideration.

However, this option was discarded due to the generation of significant eccentricities on the forces over the diagrid, which may have resulted in an unacceptable increase of the elements’ cross-section.

Another important assumption to be mentioned is that, in order to achieve thinner elements in the diagrid structure, the timber material has been considered as class 1, or protected from the humidity and exterior environment [12].

This means that the envelope of the building has to be placed on the exterior , covering the

Fig. 88: Structure of the building’s proposal on its location at Gullhaug Square 2A.

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Aiming for ZEB in a High Rise Building

4. Structural system

References structure.

The final diagrid structure

[1] A. Sev and G. Aslan, “Natural Ventilation for the Sustainable Tall Office Buildings of the Future,” World Academy of Science, Engineering and Technology, International Journal of Civil, Environmental, Structural, Construction and Architectural Engineering, vol. 8, no. 8, pp. 897909, 2014.

It can be observed in Fig. 87 and 89 that the diagrid elements vary in their dimensions throughout their location in the building’s structure. This is due to the optimisation of the structure materials in relation to the structure’s loads.

[2] T. Kleiven, Natural ventilation in buildings: architectural concepts, consequences and possibilities. Institutt for byggekunst, historie og teknologi, 2003.

Once the structural section for the different elements is determined, there are two possible ways of proceeding. One way is to homogenise the dimension of each and every element to the equivalent readily available on the market, unifying the dimension requirements of the most stressed elements. That way, pre-cast elements could be utilised and the overall structure’s cost reduced. Another approach is to maintain the different elements with their optimised dimensions. The result of this procedure is a more complex execution of the structure’s construction, but an optimisation of the material used.

[3] H.-v. M. AS, “H-window, 1.23 x 1.48, type AT200E. Environmental Product Declaration,” ed: The Norwegian EPD Foundation.

[4] K. Yeang, A. Balfour, and I. Richards, Bioclimatic skyscrapers. Ellipsis London, Limited, 1994.

[5] S. Norge, “NS-EN 12464-1: 2011,” Lys og Belysning. Belysning av arbeidsplasser., in, 2011.

Nowadays, thanks to mass-customisation processes, it is a feasible possibility to think about structures with bespoke elements as an efficient structural system. For this reason, and once again with the intention to push the limits of the timber structure, this possibility will be implemented.

[6] M. Goldsmith, Buildings and Concepts.

Rizzoli International Publications, 1987.

[7] M. G. Architects, “The Case for Tall Wood Buildings,” February 22, 2012.

[8] Skidmore, Owings & Merrill, LLP, “Timber Tower Research Project,” Skidmore, Owings & Merrill, LLPMay 6th, 2013, vol. Final Report.

[9] Skidmore, Owings & Merrill, LLP, “Physical Testing Report #1. Composite Timber Floor Testing sst Oregon State University,” December 4th, 2017.

[10] T. M. Boake, Diagrid structures: systems, connections, details. Walter de Gruyter, 2014.

[11] S. Documento Básico, “Seguridad Estructural Acciones en la edificación,” Código Técnico de la Edificación, p. 13, 2003.

Fig. 89: Mock up of the final building’s structure.

[12]

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C.

SE-M,

“Código

Técnico

de

la

Edificación. Documento Básico de Seguridad Estructural: Madera,” ed: Libro.

5.

Envelope design

Aiming for ZEB in a High Rise Building

5. Envelope design

5.1. Envelope characteristics In the book “Architecture and Natural Energy”, R. Serra defines the envelope of a building as the skin that physically separates interior from exterior environment [1]. This author classifies the building’s envelope in relation to 10 parameters that define the building’s permeability to the exterior environment.

These parameters are: settlement, attachment, weight, perforation, transparency, insulation, smoothness, texture, colour and variability [1].

Settlement and attachment define the relative situation of the building in relation to the terrain and other buildings. The other parameters are characteristics related to the envelope and its relation to the exterior climatic conditions.

For the scope of this thesis, those parameters that define the relation of the building with the terrain and surrounding buildings will not be considered, since they are already fixed

Some envelope characteristics Perforation

Transparency

Insulation

Fig. 90: Perforation, transparency and insulation envelope characteristics. Rafael Serra. Architecture and Natural Energy. 2001.

through the boundary conditions. However, those parameters that define the relation of the envelope with the exterior environment may be relevant for achieving the Zero Emissions goal.

relation to this parameter. On the one hand, part of the envelope can be transparent and let the solar radiation pass through. On the other hand, even if the envelope in its totality is opaque, part of the calorific radiation can still reach the interior due to absorption and re-emission processes.

From this last group, four envelope characteristics will be analysed and optimised in this chapter.

These parameters have been chosen due to their direct implication with aspects such natural ventilation, daylight quality and comfortability levels. These parameters are perforation, transparency, insulation and variability. Three of them are represented in Fig. 90.

The transparency coefficient is defined by the glass surface in relation to the total envelope’s surface. There is a direct relation between the degree of transparency and the quality of the interior illumination. However, depending on the orientation, glare probability must be also studied. Moreover, glasses surfaces with high exposure degree to solar radiation can cause greenhouse effect, which must also be controlled. As contradistinction, big glass surfaces protected from solar radiation may cause big heat losses, unless its degree of transparency can be controlled depending on the solar radiation that reaches the surface.

The perforation concept is an envelope characteristic that refers to the degree of permeability to the pass of the air . This parameter depends on both the perforation surface as well as the dimension and position of the openings.

The perforation is not a static quality. It normally varies in relation to the exterior temperature.

Thus, during winter, the perforation degree is smaller than during summer.

A building with big glass surfaces will have significant heat gains through solar radiation, but also great thermal losses through conduction.

Moreover, glass is not a good acoustic insulation material. Therefore, a high transparency degree is strategy that should be carefully utilised.

The perforation coefficient is given by the relation between the perforated surface and the total envelope’s surface. This parameter is not necessarily related to the amount of light that passes through the envelope. However, it can coincide with this parameter depending on the kind of openings designed.

The insulation characteristics define the resistance of the building’s envelope to the heat transmission through conduction. This energy flux is produced when the interior temperature differs from the exterior. The insulation degree is established by the global heat transfer coefficient, measured in W/m2K. Values of 0.5 W/m2K correspond to well insulated surfaces, while values higher than 4 W/m2K are synonym of little insulation degree.

The climatic repercussion of a high perforation degree relies on the fact that the temperature inside the building tends to match the temperature from the outside. This assures the air renovation, which is a good solution for hot and humid climates, but not for extreme climatic conditions. Therefore, the building’s air tightness is tightly related to its permeability, which is given by the infiltrations due to the joints on the envelope. The air tightness coefficient is the relation given by the surface of joints and the total envelope area.

There is a direct relation between the insulation material and its acoustic properties. In general, porous materials with big pores are bad acoustic insulation and good acoustic absorption materials. When the insulation material is combined with an air chamber, its acoustic behaviour is different, since the air inside

The transparency concept is defined by the behaviour of the building’s envelope towards the solar radiation. Two situations can occur in

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performs as an acoustic barrier.

Its climatic repercussion relies on the fact that a very insulated building has little interior-exterior energy exchange. This implies that the building will lose very few heat during the heating season.

However, the insulation efficiency also relies on the orientation, being recommendable to increase the insulation thickness in those areas where the climatic conditions are more extreme.

Generally speaking, high insulation thickness are needed in cold climates, being also a good strategy under hot and dry climatic conditions.

Finally, the variability parameter makes reference to the envelope’s ability of modifying its characteristics. It is necessary to distinguish here between “modifiable envelopes” and “operable envelopes”. Modifying the openings in relation to the envelope refers to the ability of transforming transparent openings into opaque and vice versa, while modify the insulation refers to transform no-insulating elements into insulating ones. The term operable refers to the ability of eliminating sections of the envelope in order to let the air pass through.

Varying the transparency degree has both a direct interior lightning and thermal repercussion. Varying the envelope in order to achieve a higher transparency degree lets more natural light pass through, but it also decreases its insulation properties. This fact can greatly vary the building’s thermal behaviour.

Aiming for ZEB in a High Rise Building

5. Envelope design

5.2. Perforation The perforation concept is directly related with the application of natural ventilation. The rise of concerns about global warming in the past decades has resulted in an increased interest in naturally ventilated buildings. Openings through windows can be enough to cool the buildings during most part of the year [2]. Moreover, the energy consumption of a naturally ventilated building is normally 40% lower than an airconditioned building [3].

Different research have proven that sufficient day and night ventilation rate can be reached by window’s opening, even if wind characteristics are unfavourable [2]. The size, shape and location of the window apertures to reach sufficient ventilation rates have been studied in different papers [2]. It has been proved that, for northern European climates, natural ventilation can be considered for cooling loads in the range 10–35 W/m2 [4].

In addition, natural ventilation is not only a good strategy when it comes to reducing the building’s energy consumption, some aspects of comfort can also be improved with this passive strategy. For instance, equipment from mechanically ventilated buildings are likely to be associated with noise, while natural ventilation is usually silent [2]. Another advantage is that the control over the decision of opening or closing the windows increases the comfortability level of the user. Furthermore, studies of sick building syndrome (SBS) have shown that perception of greater control over ventilation, temperature and lighting is associated with decreased probability of developing the symptom [2].

In relation to this, users are also believed to be more tolerant of draughts in naturally ventilated buildings. The explanation relies on the fact that they appreciate the cause of the air movement, and this air is perceived as fresh. On the other hand, in an air-conditioned building, any draught sensation will be perceived as uncontrollable and therefore uncomfortable [2].

It is also important to point out the relative

to have openings that can provide enough fresh air even with small driving forces, such as in climatic conditions with little wind or low insideoutside temperature differences.

psychological sensation of the same temperature under different exterior climatic conditions.

Thus, the same refreshing breeze that can be appreciated in summer may be perceived as cold draught in winter [2].

Therefore, an opening type will be a top window that helps to easily remove the exhausted air situated on the upper part of the room. This design using high located outlet openings helps winds to complement buoyancy forces. The second opening type will be vertical windows that provide a greater driving height increasing airflows during the summer. The final proposed window module will therefore be very similar to the one proposed by Snøhetta for this same project.

When referring to natural ventilation, it is also important to distinguish between air quality ventilation and ventilation for cooling. Air quality ventilation is implemented to provide a clean, healthy and comfortable atmosphere for the building’s users [2]. However, ventilation for cooling aims to lower the building’s inner temperature [2]. This type of ventilation can occur during occupation hours as well as when the building is not occupied. The ventilation is qualified as natural when it has no related energy consumption due to the use of fans [2].

In the offices during the heating season, the natural ventilation will primarily rely on singlesided ventilation when moderate airflows are needed, while during the summer it can be complemented with cross ventilation, especially during periods when night cooling is necessary.

During the cooling period, air movement cools us by forced convection which is improved when we sweat. A maximum desirable speed of 0.8 m/s causes about 3ºC of perceived cooling. That is the limit air speed for day ventilation. On the other hand, for night ventilation, air speed can be increased to 1.5 m/s. Higher speeds can blow papers off the desks if the window openings are at the same level [2].

In addition, in order to take advantage of the stuck effect in a high rise building, a southeast oriented atrium will be introduced to help ventilation through buoyancy effect. This will be implemented with air inlets in the bottom part of the atrium and air outlets for the exhaust air at the top.

In Snøhetta’a proposal, a concentration of approximately 800 ppm (CO2) is considered, with 20% of dissatisfied users. Low-emitting materials are assumed to be used, which results in an airflow needed of 0.7 l/m² (2.5 m³/ hm²) [5]. For a typical office landscape with 10 m² per person a final airflow of 5 m³/hm² has been calculated. This is approximately half of a standard Norwegian airflow in an office building considering ventilation for cooling. However, this same value is considered as a normal airflow in other countries such as, for example, Sweden [5].

Design of the window module with 6 % of operable area 1.36

Necessary opening area to achieve efficient natural ventilation in offices varies from 6 % to 3 % of the floor area depending on the wind direction in relation to the envelope openings [2]. These percentages also coincided with the calculated ones for the case of the building proposed by Snøhetta for Gullhaug Torg. Thus, a total openable area of 6% of the floor area will be implemented in this project.

2.50 1.94

Moreover, due to the difference in ventilation needs and variation in comfortable air temperatures perception through the seasons, two different types of openings area needed.

This is due to the fact that for the case of natural ventilation openings there are two contradictory goals. The first one is to have openings that release exhausted air with the minimum risk of draft during the heating season. The second is

0.30 1.50

Fig. 91: Window module according to final calculated percentage for window area and openable area.

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Aiming for ZEB in a High Rise Building

5. Envelope design

5.3. Transparency The envelope characteristic of transparency has a direct repercussion on daylight levels. Different research have shown that energy savings between 10 % and 40 % could be achieved by an adequate use of daylighting depending on the shape of buildings and climate zones [6].

Daylight metrics such as daylight factor (DF) are used to evaluate daylight levels in a space.

Daylight factor is the ratio of the internal illuminance due to daylight from the CIE standard overcast sky to the external illuminance due to an obstructed hemisphere of the sky above [7].

The DF can be calculated by the sum of the three different daylight components: the Sky Component (SK), which is the light that comes directly from the sky; the Outside Reflected Component (ORC), which is the fraction of the daylight that meets the point inside the room after being reflected by shielding buildings; and the Inside Reflected Component (IRC), which is the light that meets the point after being reflected from indoor surfaces in the room.

These three daylight components are illustrated in Fig. 92.

The component with a higher contribution to

the DF is the SK. This component depends on several parameters, such as how big the floor to ceiling height is, how tall the window is and how obstructed is the light coming from the outside.

Therefore, the higher a room in a building is located, the more natural light will reach the interior due to less obstruction from exterior elements. Consequently, less floor to ceiling height or smaller windows will be needed in order to have the same DF than lower floors.

The floor to ceiling height in this project has been set to 4 m, assuming that some of this height will be covered with technical installations behind a false ceiling. A big floor to ceiling height will also allow a bigger gradient of temperature difference inside the rooms, easing natural ventilation processes.

while a DF between 4% and 6% is classified as medium, and between 2 % and 4 % as low. For DF lower than 2%, the daylight availability is classified as none [9].

windows obtained from the parametrization can be observed.

In addition to calculating the average daylight factor (mean DF), calculations of mean daylight autonomy and continuous daylight autonomy have been performed. This gives an estimation of daylight utilization for lighting during occupied hours.

The sky conditions used for the simulations are “CIE overcast sky”, which is used in the standard daylight factor calculation. Reflection factors for interior surfaces are set according to standard values in NS-En 12461-1. For the windows, a 3-layer low-emission and argon filled glassing with a light transmission factor of 0.5 has been used. The analysed grid mesh has a dimension of 1 x 1m between sensors, with a height of 0.80 m above the floor, representing the work plane according to NS-EN 12461-1. Ambient bounces have been set up to 4 for a more accurate simulation. The occupancy schedule chosen corresponds to a working schedule from 8:00 to 16:00.

In order to assess the required window area to meet the daily requirements, different options varying the window to wall ratio were parametrically designed and simulated later on with Diva for Rhinoceros. A single floor was analysed in these simulations corresponding to the third floor of the building. This is due to the fact that, due to shielding from neighbouring buildings and its proximity to the ground level, this floor will be the worst case scenario for the office program. In Fig. 94 it can be observed the parametric design for the four options tested, which correspond to 20, 30, 40 and 50 % window area from the total surface of the façade.

In Fig. 93, the different areas and number of

The regulations are not very restrictive regarding daylight factor levels inside habitable spaces.

The British Standard, for example, recommends a daylight factor of minimum 2% in a room [8].

This is similar to the Norwegian standard, TEK 17, which recommends an average DF of at least 2 % [9]. As a guideline, mean DF higher than 6 % classifies to have strong daylight availability,

Daylight components

Analysis of the results The results of the simulations can be observed in Fig. 95. A summary of the results from this analysis can be observed in Fig. 96.

Areas of different façade options

SK

ORC

Simulation parameters

Wall area

Window area

Total number of windows

20 % of façade area

288

72

24

30 % of façade area

252

108

36

40 % of façade area

216

144

48

50 % of façade area

180

180

60

Percentage of window area

IRC

Fig. 92: “The Graphical Tool for Sky Component, Solar Glare and Overheating Risk Prediction”. Barbara Matusiak.

Fig. 93: Windows and walls areas for the different window to wall ratio possibilities. Data from Grasshopper.

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Aiming for ZEB in a High Rise Building

5. Envelope design

Window area in relation to the wall area

Window area = 20 % of the wall area

Window area = 30 % of the wall area

Window area = 40 % of the wall area

Fig. 94: Design of different faรงade options regarding the window to wall ratio. Designed with Grasshopper.

- 67 -

Window area = 50 % of the wall area

Aiming for ZEB in a High Rise Building

5. Envelope design

The first parameters obtained with the simulations is the daylit area. This parameter indicates the percentage of the room with a daylight autonomy that corresponds to at least 50%, meaning that during 50% of the occupied schedule the daylight levels in the room will be above the target illuminance.

The daylight autonomy is directly related to the illuminance levels within a room. Therefore, when considering this kind of simulations it is important to understand the illuminance concept. This photometric measure refers to the intensity of the light received at a surface. It is stated in lumens/ square meter (lm/m2) or lux (lx). the minimum illuminance levels required to fulfil daylight autonomy are set to 300 lx.

The daylight autonomy values given by the simulations are an indicator of the need for electric lighting according to the user’s threshold specified. In order to make an estimation of the percentage of occupied hours in which artificial lighting will be needed, the values for the continuous daylight autonomy (cDA) have been used.

more).

As can be observed in Fig. 96, a mean DF higher than 2 % can be achieved in every of the four options proposed. This values would be enough to fulfil the TEK 17 regulation. However, as previously mentioned, other international standards such as the British, establishes that mean values of DF between 2 % and 4 % can be related with a low daylight availability, which is not the most favourable option for a working space.

In contradistinction to the mean daylight autonomy (mean DA), the cDA awards partial credit in a linear fashion to values below the user defined threshold. Thus, if 300 lux were specified as the DA threshold and a specific point exceeds 300 lux during 50% of the time on an annual basis, then the cDA might result in a value of approximate 55% to 60% (or even

Values of mean DF from 4 % to 6 % achieved in the 40 % and 50 % window area options are related with a medium daylight availability.

Moreover, the mean daylight autonomy for these two options is 69 % and 72 % respectively, which can be increased up to 77 % and 79 % by applying the mean continuous daylight autonomy parameter.

Daylight autonomy simulations Window area = 20 % of the wall area

Window area = 30 % of the wall area

Window area = 40 % of the wall area

Window area = 50 % of the wall area

According to these results, it is possible to make an estimation of the percentage of the working schedule in which artificial lighting will be needed. This value results in 23 % of the occupied hours for the case of a window area equal to 40 % of the façade. Whereas, for the option where a 50 % of the façade are windows, an estimated use of artificial daylight is reduced in a 2 % of the occupied hours with respect to the previous option. Having into consideration the reduced number of daylight hours during the Norwegian winter, these results are very good standards. Moreover, only these last two options qualify for the LEED-NC 2.1 daylighting credit 8.1.

Both the 40 and 50 % window area options would also fulfil the BREEAM-NOR criterion Hea 1 [10]. This criterion establishes that 80% of the office floor area has to be adequately daylit.

This means that the average daylight factor measured at a height of 0.8 metres according to the building’s latitude (which in this case is higher than 60º) for multi-storey buildings, has to be at least of 3.3 %.

Fig. 95: Diva simulations for the different window to wall ratio possibilities.

- 68 -

In addition, the analysed space in a multi storey buildings also has to achieve a minimum DF of 1.32 % or a view of the sky from desk height (0.7m). For the case of the 50 % window area this second condition is assured to be fulfilled, since the percentage of sensors with a minimum DF higher than 2 % is 100%. As for the case of the 40 % window option, considering that it has a useful daylight illuminance of 84% (meaning that the illuminance values range from 100 to 200 lux during more than 50 % of the time), and at the same time it has a high daylight autonomy (with a threshold of 300 lux), it can be said that this minimum DF is possibly fulfilled as well.

Both options have a view of the sky from the desk height.

To conclude, a difference of 2 % between the values for the mean cDA for these last two options (40 % and 50 % of window area) can be considered as low. Thus, the option of 40 % of window area in relation to the façade surface can be considered as the compromised solution between achieving good daylight levels and low thermal losses. This thermal losses parameter will be further studied in the following section.

Aiming for ZEB in a High Rise Building

5. Envelope design

3 / Structural system

Daylight levels in relation to the window area

Analysis

Window area equal to 20 % of wall area

30 % of wall area

40 % of wall area

50 % of wall area

Daylit Area

58 %

87 %

100 %

100 %

Mean Daylight Factor

2.4 %

3.7 %

4.9 %

6.0 %

Percentage of sensors with min. DF = 2%

44 %

70 %

89 %

100 %

50 %

63 %

69 %

72 %

67 %

74 %

77 %

79%

22 %

39 %

52 %

63 %

50 %

93 %

84 %

75 %

33 %

26 %

23 %

21 %

Mean Daylight Autonomy

(for active occupant behaviour)

Mean continuous Daylight Autonomy (for active occupant behaviour)

Percentage of sensor with max. DA > 5 % Useful Daylight Illuminance

(100 < UDI < 200 lx larger than 50%)

Estimated use of artiďŹ cial lighting during occupied hours

(According to continuous Daylight Autonomy)

Fig. 96: Summary of daylight levels for every simulated percentage of window area. Data obtained from simulations in Diva.

106 /110

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Aiming for ZEB in a High Rise Building

5. Envelope design

5.4. Insulation The insulation characteristic of an envelope is inversely proportional to its thermal losses. The thicker the insulation layer, or the smaller the heat transfer coefďŹ cient of the envelope materials, the less thermal losses will be produced.

As shown in the climate analysis, the use of

internal heat gains as a passive strategy makes of a considerable difference in the reduction the energy use for active heating. In order to take advantage of this passive strategy it will be extremely important to prevent thermal losses

through the buildingâ&#x20AC;&#x2122;s envelope.

In order to do that, a parametric study of the ratio between glassed and opaque components

of the envelope has been carried out, concluding that the 40 % glassed area was a good compromise solution. In order to prove this statement, the thermal losses associated with each of the envelope possibilities will be analysed in this section.

As shown in the following equation, the total heat losses of an envelope (or heat transmission) are equal to the product of the global heat transfer coefďŹ cient of the envelope (or Uvalue), the envelope area and the temperature

winter temperature is -10ÂşC. This makes a total temperature difference of 30ÂşC.

difference between inside and the exterior environment.

Heat transmission

The next step in the calculation is to determine the heat transfer coefďŹ cient of the envelope. The recommended values from the ZEB centre have been used [11]. This values can be consulted in Fig. 97.

đ??ťđ??ť" = đ?&#x2018;&#x2C6;đ?&#x2018;&#x2C6;%&'() â&#x2C6;&#x2014; đ??´đ??´ â&#x2C6;&#x2014; â&#x2C6;&#x2020;đ?&#x2018;Ąđ?&#x2018;Ą

Since only the heat transmission though the envelope of one building ďŹ&#x201A;oor is been calculated, the values that will be relevant for the calculation are the façade and windowâ&#x20AC;&#x2122;s heat transfer coefďŹ cients. From the range of 0.1 to 0.12 Wm2/K recommended for wall elements by the ZEB centre, the wall solution chosen has a global Uvalue of 0.1 Wm2/K. The materials that composed the constructive solution implemented will be analysed in the following section.

For a continental climate, like the one = đ?&#x2018;&#x192;đ?&#x2018;&#x192; â&#x2C6;&#x2014; đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ??´đ??´ differences can in Oslo theđ??šđ??š temperature signiďŹ cantly vary depending on the season.

Therefore, two different scenarios will be đ??šđ??š transfer đ??´đ??´ considered for the heat calculation.

Cd = 4will be

The ďŹ rst scenario the average 6 â&#x2C6;&#x2014; % 5 5 thermal losses throughout the year. The second scenario will be the average heat transfer during winter.

For the ďŹ rst scenario (average throughout the year) the average temperature is 6ÂşC. By setting the average inner temperature to 20ÂşC makes a total temperature difference of 14ÂşC.

Regarding the windows, a triple-glassed low emission window with argon ďŹ ll has been chosen, with an equivalent Uvalue of 0.6 Wm2/K, which is also between the recommended coefďŹ cients range.

The same procedure has been followed to calculate the temperature difference during winter. In this case, the average

These selected heat transfer coefďŹ cients multiplied by the temperature differences lead to thermal losses per square meter of 1.4 W for the case of the wall and 3 W/m2 for the case of the windows as an average during the year.

The calculated average winter thermal losses increase up to 8. 4 W/m2 for the wall and 18 W/ m2 for the windows.

Selection of heat loss coefďŹ cients according to ZEB Centre recommendations Recommended Uvalue (Wm2/K)

Selecteded Uvalue (Wm2/K)

Walls

0.10 - 0.12

0.10

Roof

0.07 - 0.10

-

Floors

0.06 - 0.09

-

Windows

0.40 - 0.80

0.60

Construction element

By multiplying these values by the total square meters of façade, the heat losses per constructive element are obtained. These heat losses range from 403.2 W to 252 W for the case of the wall, and from 604.8 W to 1512 W for the case of the windows during the entire year. These thermal losses are increased during winter, with an average for the wall that ranges from 864 W to 5640 W, and an average for the windows ranging from 1296 W to 3240 W.

Fig. 97: Recommended heat transfer coefďŹ cient values according to â&#x20AC;&#x153;Zero Emissions Buildindgsâ&#x20AC;? from the Norwegian ZEB Centre. 2017.

Finally, the total heat loss for every window to

- 70 -

wall ratio can be calculated by the sum of the thermal losses through the windows and through the wall in each case. The results show thermal losses that range from 1008 W, for the case of a 20 % window area, to 1764 W for the case of the highest window to wall ratio calculated. During winter, these thermal losses are increased up to 2160 W in the 20 % window ratio to 8880 W for the case of a 50 % window ratio.

As it can be observed in Fig. 98, the thermal losses increase in a linear way in relation to the increment of the window to wall ratio. This way, thermal losses are increased by 50 % with every increment of 10 % of the glassing ratio.

Aiming for ZEB in a High Rise Building

5. Envelope design

Thermal losses calculation Percentage of window area

Temperatures difference

Average of the whole year 20 ºC - 6 ºC = 14 ºC

Constructive element Walls

Heat transfer coefficient

Heat loss per square meter

Heat loss per constructive element

Total heat loss through the façade

Percetage of increment *

0.1 Wm2/K

14 ºC x 0.1 Wm2/K = 1.4 W/ m2

288 m2 x 1.4 W/ m2 = 403.2 W

Average during the whole year Walls + windows = 1008 W

100 %

Average during winter Walls + windows = 2160 W

100 %

Average during the whole year Walls + windows = 1260 W

150 %

Average during winter Walls + windows = 2700 W

150 %

Average during the whole year Walls + windows = 1512 W

200 %

Average during winter Walls + windows = 3240 W

200 %

Average during the whole year Walls + windows = 1764 W

250 %

Average during winter Walls + windows = 8880 W

250 %

Windows

0.6 Wm2/K

14 ºC x 0.6 Wm2/K = 3 W/ m2

72 m2 x 3 W/ m2 = 604.8 W

Walls

0.1 Wm2/K

30 ºC x 0.1 Wm2/K = 8.4 W/ m2

288 m2 x 8.4 W/ m2 = 864 W

Windows

0.6 Wm /K

14 ºC x 0.6 Wm /K = 18 W/ m

72 m x 18 W/ m = 1296 W

Walls

0.1 Wm2/K

14 ºC x 0.1 Wm2/K = 1.4 W/ m2

252 m2 x 1.4 W/ m2 = 352.8 W

Windows

0.6 Wm /K

14 ºC x 0.6 Wm /K = 3 W/ m

108 m x 3 W/ m = 907.2 W

Walls

0.1 Wm2/K

30 ºC x 0.1 Wm2/K = 8.4 W/ m2

252 m2 x 8.4 W/ m2 = 756 W

Windows

0.6 Wm /K

14 ºC x 0.6 Wm /K = 18 W/ m

108 m x 18 W/ m = 1944 W

Walls

0.1 Wm2/K

14 ºC x 0.1 Wm2/K = 1.4 W/ m2

216 m2 x 1.4 W/ m2 = 302.4 W

Windows

0.6 Wm /K

14 ºC x 0.6 Wm /K = 3 W/ m

144 m x 3 W/ m = 1209.6 W

Walls

0.1 Wm2/K

30 ºC x 0.1 Wm2/K = 8.4 W/ m2

216 m2 x 8.4 W/ m2 = 648 W

Windows

0.6 Wm /K

14 ºC x 0.6 Wm /K = 18 W/ m

144 m x 18 W/ m = 2592 W

Walls

0.1 Wm2/K

14 ºC x 0.1 Wm2/K = 1.4 W/ m2

180 m2 x 1.4 W/ m2 = 252 W

Windows

0.6 Wm /K

14 ºC x 0.6 Wm /K = 3 W/ m

180 m x 3 W/ m = 1512 W

Walls

0.1 Wm2/K

30 ºC x 0.1 Wm2/K = 8.4 W/ m2

180 m2 x 8.4 W/ m2 = 5640 W

20 % of façade area Worst case scenario: winter 20 ºC - (-10 ºC) = 30 ºC

Average of the whole year 20 ºC - 6 ºC = 14 ºC

2

2

2

2

2

2

2

2

2

2

30 % of façade area Worst case scenario: winter 20 ºC - (-10 ºC) = 30 ºC

Average of the whole year 20 ºC - 6 ºC = 14 ºC

2

2

2

2

2

2

2

2

2

2

40 % of façade area Worst case scenario: winter 20 ºC - (-10 ºC) = 30 ºC

Average of the whole year 20 ºC - 6 ºC = 14 ºC

2

2

2

2

2

2

2

2

2

2

50 % of façade area Worst case scenario: winter 20 ºC - (-10 ºC) = 30 ºC

Windows

0.6 Wm2/K

14 ºC x 0.6 Wm2/K = 18 W/ m2

180 m2 x 18 W/ m2 = 3240 W

*The percentage of increment has been calculated with respect to the same façade area completely opaque with average thermal losses 504 W and average thermal losses during winter 1080 W. Fig. 98: Calculation of average thermal losses through façade’s constructive elements during the winter and throughout the year.

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Aiming for ZEB in a High Rise Building

5. Envelope design

5.5. Environmental impact Every utilised material has an environmental impact on the overall GHG emissions of the building. Even if the selection of materials for the building’s structure plays a more important role in the total emissions accounting, the envelope of a high-rise building represents also a large surface. Furthermore, the materials selected for this constructive element will not only be relevant on the final environmental impact of the building, but also on its thermal properties and heat transfer with the exterior environment.

One of the most important variables when deciding the constructive composition of the building’s envelope is the location of the insulation layer. In order to avoid thermal losses, the insulation layer has to be continuous along the whole envelope. There are mainly two

Fig. 101. Moreover, by locating the insulation layer on the outside, the envelope will be more protected from extreme exterior conditions, meaning that a lower risk for condensation or frost problems will be achieved.

possibilities for placing the insulation layer: on the inside or on the outside. A simple sketch illustrating these two possibilities can be observed in Fig. 101.

As mentioned in Chapter 4, the glulam material of the diagrid elements has been calculated as protected. This means that the envelope should be placed outside this structure protecting it from exterior environmental conditions. Thus, along with the envelope, the insulation layer will be placed on the outside.

Another advantage is that this constructive solution allows to use the thermal inertia of the concrete topping slab for the chosen deck system, since there is no need to cover it with insulation to avoid thermal bridges.

In order to decide the best materials for the building’s envelope so as the desired heat transfer coefficient and low embodied emissions are achieved, a comparison of different material options have been carried out. The embodied emissions in the production stage of different

The decision of placing the building’s envelope outside the diagrid structure allows not only to reduce the section of the diagrid elements, but also to decrease the insulation material in the envelope. This fact can be clearly observed in

envelope materials can be observed in Fig. 99.

As shown in this figure, due to its composition of recycled glass, the glass wool is the insulation material with lower embodied emissions due to its production (with 7.4 Kg CO2 /m2 eq versus the 12.7 Kg CO2 /m2 eq of rockwool) [12]. Moreover, glass wool allows to achieve lower conductivity values (of the order of 0.31 λ in comparison to 0.35 λ for Rockwool), which means more than 10 % increment in the thermally efficiency [13]. This can be translated into a reduction of up to 10 % of material for the same thermal performance.

Consequently, it allows to achieve the same thermal performance at less than half of the weight. However, in a kilogram by kilogram comparison, glass wool is more expensive.

Nevertheless, for an equivalent thermal

Embodied emissions of different façade options Material Emissions due to different construction materials (kg CO2 eq /m2)

50 45

Keyboney pine

40

Triple glass Low E

35

38.6

44.6

30 25 20

Rock wool

15 10

12.7

5

7.4

0 -5 -10 -15 -20

Glass wool

-10.0 -14.6

Conifer solid panel

Termotre spruce

Fig. 99: Embodied emissions associated to the production (A1 to A3) of some construction materials. Data from EPD Norge and Pilklington.com.

20 % of façade area 30 % of façade area 40 % of façade area 50 % of façade area

Insulation: Glass wool 35 cm

2131 kg CO2 eq

1865 kg CO2 eq

1598 kg CO2 eq

1332 kg CO2 eq

Damp proof layer: Polypropylene

314 kg CO2 eq

275 kg CO2 eq

235 kg CO2 eq

196 kg CO2 eq

Interior cladding: Solid wood panel 15mm

- 2880 kg CO2 eq

- 2520 kg CO2 eq

- 2160 kg CO2 eq

- 1800 kg CO2 eq

Exterior cladding: Termotre spruce 15mm

- 4190 kg CO2 eq

- 3667 kg CO2 eq

- 3143 kg CO2 eq

- 2619 kg CO2 eq

Glass: Triple-glassed, Low Emissivity, Argon filled

2777 kg CO2 eq

4165 kg CO2 eq

5554 kg CO2 eq

6943 kg CO2 eq

Totals

- 1848 kg CO2 eq

118 kg CO2 eq

2084 kg CO2 eq

4052 kg CO2 eq

Fig. 100: Calculation of embodied emissions for one floor of the different window to wall ratio possibilities. Values for the production stage (A1 to A3). Data from EPD Norge and Pilklington.com.

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Aiming for ZEB in a High Rise Building

5. Envelope design

5.6. Final envelope design performance, glass is the most cost effective solution [13]. In addition, regarding the acoustic properties, the difference between rock and glass wool in terms of optimal performance is that the latter achieves the same decibel reduction than the former with less than half of the mass [13].

Regarding the glass choice for the windows, a global Uvalue of 0.6 has been chosen from the ZEB centre recommendations. The glass option that allows to achieve this heat transfer coefficient is a triple-glass with low emissivity and argon fill. This element has embodied emissions of 38.6 Kg CO2 eq/m2 [14], which means that the total embodied emissions due to the glass production for the option of 40 % of windows would be 5554 Kg CO2 eq for a single floor.

Lastly, regarding the interior and exterior cladding choices, Termotre spruce represents a good option for the exterior layer while a solid conifer panel could be applied in the interior layer. The selection has been

In Fig. 102 it is possible to observe the summary of results for the four window to wall ratio possibilities. These options, with a total window are of 40 % of the façades area, will be the perfect compromised solution, allowing to achieve good daylight levels as well as not too high thermal losses and embodied emissions.

based on their embodied emissions due to production. However, for materials in which CO2 sequestration accounting has been considered in this initial stage, the final LCA stage of demolition and recyclability should be also considered in the final embodied emissions calculation. Moreover, other parameters such as the maintenance and the materials lifespan should be considered in the final decision.

These additional considerations may cause some changes on the materials choice.

the diagonal elements of the diagrid system.

Therefore, in many occasions these timber elements coincide with the location of the window, occasioning not only lower levels of daylight reaching the interior, but also certain inconvenience for the users when operating the windows. Secondly, due to the location of the diagrid system on the inside part of the envelope, some discontinuities appear between the exterior envelope and the interior partitions, causing thermal and acoustic bridges. These two phenomena can be observed in Fig. 103 and 104.

However, when considering this 40 % of window area together with the program distribution in the floor plan two constructive difficulties appear. First, it is almost impossible to place that many windows and avoid at the same time

To conclude, the calculated embodied emissions for the envelope of a single floor will range from -1848 Kg CO2 eq to 4052 Kg CO2 eq, depending on the window to wall ratio. For the selected option of a window’s percentage equal to 40 % of the façade area, the calculated embodied emissions will be of 2085 Kg CO2 eq per building’s floor.

Summary table Parameters

20 % of façade area

30 % of façade area

40 % of façade area

50 % of façade area

Daylit area

58 %

87 %

100 %

100 %

Mean daylight factor

2.4 %

3.7 %

4.9 %

6%

Continuous daylight autonomy

67 %

74 %

77 %

79 %

Estimated use of artificial lighting

33 %

26 %

23 %

21 %

Yearly average thermal losses

1008 W

1260 W

1512 W

1764 W

Environmental impact

- 1848 kg CO2 eq

118 kg CO2 eq

2084 kg CO2 eq

4052 kg CO2 eq

Envelope’s insulation possibilities

Fig. 102: Summary of the analysed parameters for the four different window to wall ratio possibilities.

Fig. 101: Comparison of constructive solutions for a building insulated from the inside and from the outside.

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Aiming for ZEB in a High Rise Building

0 1

5

5. Envelope design

Office type floor plan.3rd floor

Housing type floor plan.10th floor

40% window ratio

40% window ratio

0 1

10

Fig. 103: Proposed layout for the office part corresponding to the 3rd floor. Application of the 40% window ratio.

5

10

Fig. 104: Proposed layout for the housing part corresponding to the 10th floor. Application of the 40% window ratio.

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Aiming for ZEB in a High Rise Building

0 1

5

5. Envelope design

Office type floor plan. 3rd floor

Housingtype floor plan. 10th floor

Double-skin façade

Double-skin façade

10

0 1

Fig. 105: Proposed layout for the office part corresponding to the 3rd floor. Application of double-skin façade.

5

10

Fig. 106: Proposed layout for the housing part corresponding to the 10th floor. Application of double-skin façade.

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Aiming for ZEB in a High Rise Building

5. Envelope design

5.7. Variability For these reason, a second alternative has been designed. This alternative consists on the implementation of a double-skin façade as a constructive solution for the envelope, placing the diagrid structure in the middle of the two layers (Fig.105 and 106). This system not only allows the continuity between envelope and interior partitions, but it also allows the diagrid system to be visible from the outside, which increases the aesthetic quality of the building.

The implementation of this constructive solution will increase the CO2 emissions due to material. However, it has been proven that the optimisation of the window ratio to avoid unnecessary GHG emissions is not a suitable strategy for this particular project.

The variability concept refers to the building’s capacity to adapt its thermal behaviour to the pass of the seasons.

The solution for the possible overheating problems will be assessed in the following section. Regarding the prevention of the heat losses from the north-oriented spaces that do not receive direct solar radiation, a possible solution would be to combine opaque partitions such as sandwich panels with the glassing of the interior layer. By such approach, adequate daylight levels could be still achieved while preventing excessive thermal losses. This system must be implemented in combination with daylight availability simulations to estimate the new glassing area needed.

It has been mentioned that atria and doubleskin façades are typical characteristic ventilation elements in high-rises. However, their effectiveness depends on their variability in relation to the exterior weather conditions.

Both elements use the natural driven force of buoyancy, which can be used alone or in combination with the wind.

Both elements work well during winter conditions since they capture the energy provided from the solar radiation due to greenhouse effect. In both systems the greenhouse effect works the same way. When the solar radiation reaches the exterior glassing layer, part of the radiation is absorbed by the glass, while the rest is reflected or transmitted to the inside. The solar radiation that crosses the glassing heats the air of the atrium or the cavity of the double-skin façade and is again reflected, absorbed or transmitted by the second envelope layer. Some of the radiation reflected for the second time passes again through the first glassing layer to the exterior, while other fraction is captured inside.

This radiation trapped in between the exterior and interior layers are responsible for the increase of the air temperature inside due to convective heat exchange. This temperature increase has been represented with colour gradients in Fig. 107 and 109, showing the winter behaviour of the building for the case of the atrium and the double-skin façade.

In case that the increase of the final embodied emissions due to the use of this constructive system were too big to be compensated with renewable energy production, a reconsideration of the structural system utilised would be necessary. Combining the optimised 40 % window ratio with a framing system such as the one proposed in Chapter 4 would be a possible option. However, it is believed that due to the organic geometry of this building, a diagrid system is more appropriate in this case.

The Double-skin façade is a constructive technique specially developed for cold climates [15]. Allowing to take maximum advantage of solar heat gains during winter, this technique has been widely used during the past decades in commercial and office buildings across Europe [15]. The air cavity created between the two layers of the façade is used to collect the heat from the solar radiation, improving the thermal comfort and the indoor air quality while reducing energy demand for heating.

Two atria have been implemented in this building. The first one coinciding with the office space and the second one located just above the first atrium, corresponding with the housing area. In order to avoid the associated risk for overheating in these spaces during summer, a good ventilation strategy must be implemented.

In Fig. 108, this naturally driven ventilation strategy can be observed. Air inlets are located in the lower part of the atrium, while the outlets are situated on the upper part. These openings

However, this constructive solution has also some disadvantages. Different problems associated with the use of double-skin façades are the overheating risk during the summer and the excessive thermal losses in north-oriented spaces.

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force convective flows helping the exhaust air to leave and the fresh to come in through pressure differences. Moreover, if the wind direction is favourable, open windows in opposite sides of the atria can increase the ventilation efficiency through cross ventilation.

Due to high internal heat loads, the spaces with a higher risk for overheating correspond to the part of the building where the offices are located.

For this reason, these spaces are located in the lower part of the building, and the atrium façade in this area is tilted in the opposite direction to the solar rays. A natural protection of this space from the solar rays is achieved during summer, when the solar elevation angle can reach up to 54º in Oslo. During winter, with a mean sun’s elevation angle lower than 10º, this space still receives solar radiation.

In order to take advantage of the temperature gradient in the atria, the implementation of a heat recovery system with a rotatory heat exchanger could be a good solution. These systems are normally used for preheating the ventilation air, allowing to reduce the total energy consumption. The location of the heat recovery system must be set in the warmer area of the atrium, which is the upper part. Apart from this heat exchanger, and due to its high efficiency, a geothermal heat pump is also proposed to supply the domestic hot water and space heating demand, combined with a bioboiler for peak loads during the colder days of winter. All these technical systems can be observed in Fig. 107 and 108.

Regarding the overheating protection during summer for the double-skin façade, a typically used shading system is the installation of venetian blinds. The blinds are commonly located in the air cavity of the double-skin façade, protecting the building from solar heat gains [16]. In general, the temperature of the blinds rapidly increases with solar radiation, which is an advantage in the cold period but a disadvantage in the hot months. For this reason, an alternative shading system is proposed.

Aiming for ZEB in a High Rise Building

5. Envelope design

Winter behaviour

Summer behaviour

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Fig. 107: Variability of the buildingâ&#x20AC;&#x2122;s envelope during the cold season.

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Fig. 108: Variability of the buildingâ&#x20AC;&#x2122;s envelope during the hot season.

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Aiming for ZEB in a High Rise Building

5. Envelope design

In spite of traditional blinds, the use of plants is proposed in this project as a feasible alternative.

Vegetation has the ability to dissipate absorbed solar radiation into sensible and latent heat.

It has been proven that about 60 % of the radiation absorbed by plants is turned into latent heat [16]. Due to the latent heat transfer, temperatures reached on the leaves are much lower than that reached on the blinds.

The results of a research comparing plants with venetian blinds as shading systems for a doubleskin façade shows that the temperature increase of the blinds is about twice higher than in the leaves for the same solar radiation [16]. This decrease of temperature means lower amount of heat transferred to the air within the cavity, and therefore less heat transfer to the interior.

Moreover, the application of plants may bring additional benefits. Some of them are the improvement of thermal insulation; higher noise attenuation by absorption, reflection and diffraction; oxygen production, CO2 reduction and air filtering from dust and chemicals; or positive psychological effects as stress reduction and aesthetics stimulant to the people in the room [16]. Due to their beneficial effects, plants have also been included in the two atria of the building, as well as on the open roof terrace, allowing not only to improve the aesthetic qualities of the space, but also to naturally filter the air coming from the outside and stabilising humidity levels.

are related to maintenance and the difficulty of controlling the light transmission. In addition, the appropriate type of vegetation must be chosen to assure an effective sun shading effect. Some issues such as temperature and humidity conditions, permanent exposure to solar radiation and maintenance cost must be taken into consideration when selecting the appropriate specie for this purpose.

As it can be observed in Fig. 109 and 110, shedding plants are proposed in this project. In autumn these plants will shed leaves, creating a naturally adjustable shading system. During winter, the solar radiation will pass through the plants with no leaves obstruction, generating the solar heat gains needed. In summer, the leaves will stop most of the solar radiation, allowing

On the contrary, some disadvantages of applying vegetation in the double-skin façade

Winter behaviour. Double-skin façade

just for the necessary daylighting of the rooms.

The solution proposed is a double-skin façade composed by two layers of glassing for the south, west and east orientations. Whereas, for the north-oriented spaces, it consists of an exterior layer of glassing and an interior layer combining opaque insulated surfaces with the necessary glassing ratio to satisfy the required daylighting of interior rooms. However, through a detailed study of the daylight availability on each orientation it could be possible to adjust the interior layer on every orientation to be a combination of wall and windows, allowing to reduce heat transfer as well as emissions due to the glassing.

In these two figures it can also be observed

Summer behaviour. Double-skin façade

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Fig. 109: Thermal behaviour of the double-skin façade during the cold season.

Fig. 110: Thermal behaviour of the double-skin façade during the hot season.

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Aiming for ZEB in a High Rise Building

5. Envelope design

References the implications of the solar elevation angle variation throughout the year. During winter, the low solar elevation angle allows for more solar rays to reach the interior of the room, heating the exposed thermal mass of the slab system.

As mentioned in Chapter 4, this slab system with exposed thermal mass will allow to stabilise temperature variations in a daily basis. During the cold season, the air cavity of the double-skin façade will be ventilated just the necessary to maintain good indoor air quality, avoiding to lose the solar heat gains. During summer, this air cavity will be permanently ventilated, avoiding excessive heat to be store on it.

[1] R. Serra Florensa and H. Coch Roura, Arquitectura y energía natural. Univ. Politéc. de Cataluña, 2001.

In order to control air quality through natural ventilation, an innovative building automation system has been implemented. This system, based on the implemented in the “22-26” project in Austria, controls openings based on the internal carbon dioxide concentration, temperature levels, and occupant demands [17].

The system uses automated window openers, which in this case could be overridden by the users to manually control them and increase comfort feeling.

[2] E. Gratia, I. Bruyere, and A. De Herde, “How to use natural ventilation to cool narrow office buildings,” Building and environment, vol. 39, no. 10, pp. 1157-1170, 2004.

[3] C. Allocca, Q. Chen, and L. R. Glicksman, “Design analysis of single-sided natural ventilation,” Energy and buildings, vol. 35, no.

8, pp. 785-795, 2003.

[4] D. Dickson, Ventilation technology in large non-domestic buildings. Air Infiltration and Ventilation Centre, 1998.

Ventilation concept in the office area Meeting rooms in the corners for cross ventilation

[5] A. Danielsberg et al., “Gullhaug Torg - sluttrapport skisseprosjekt 2015,” Oslo: Avantor.2015.

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[6] T. Miyazaki, A. Akisawa, and T. Kashiwagi, “Energy savings of office buildings by the use of semi-transparent solar cells for windows,” Renewable energy, vol. 30, no. 3, pp. 281-304, 2005.

Single-sided ventilation in cell offices

[7] B. Matusiak, “The Graphical tool for sky component, solar glare and overheating risk prediction,” in Proceeding of the 26th CIE conference in Bejin, 2007, vol. 6, no. 8.

Single-sided ventilation in the open office layout

[8] J. Mardaljevic, M. Andersen, N. Roy, and J. Christoffersen, “Daylighting metrics: is there a relation between useful daylight illuminance and daylight glare probability,” in Proceedings of the building simulation and optimization conference (BSO12), Loughborough, UK, 2012, vol. 1011.

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Cross ventilation and stuck effect in the atrium

[9] S. Norge, “NS-EN 12464-1: 2011,” Lys og Belysning. Belysning av arbeidsplasser., in, 2011.

[10] BREEAM-NOR, “Technical Manual BREEAM-NOR ver. 1.1,” Norwegian Green Building Council2012, vol. SD 5066A: ISSUE

Fig. 111: Cross and single-sided ventilation in the office layout.

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1.1.

[11] A. G. Hestnes and N. L. Eik-Nes, Zero Emission Buildings. Fagbokforlaget, 2017.

[12] T. N. E. Foundation. Available: http:// epd-norge.no/ [13] K. E. I. LLC. (2018). Glasswool or Rockwool.

Available: http://www.knaufexeedinsulation.ae/ glasswool-or-rockwool [14] P. N. G. F. G. Business, “Pilklington energiKare Triple. Environmental Product Declaration.,” ed, 2012.

[15] J. Zhou and Y. Chen, “A review on applying ventilated double-skin facade to buildings in hot-summer and cold-winter zone in China,” Renewable and Sustainable Energy Reviews, vol. 14, no. 4, pp. 1321-1328, 2010.

[16] W. Stec, A. Van Paassen, and A. Maziarz, “Modelling the double skin façade with plants,” Energy and Buildings, vol. 37, no. 5, pp. 419427, 2005.

[17] L. P. Junghans, “Concept 22/26, A High Performance Office Building without Active Heating, Cooling and Ventilation Systems.”

6.

Conclusions and discussion

Aiming for ZEB in a High Rise Building

6. Conclusions & discussion

6.1. Process overview This master thesis departed from the desire of investigate the design process of a high-rise oriented towards the goal of a Zero Emissions Building. A thorough literature review was carried out to find out the driving parameters for the CO2 emissions of contemporary high-rise buildings.

Materials and energy consumption during daily operation were found to be the most significant parameters influencing the embodied emissions of this architectural typology.

6.2. Adopted design solutions: Findings and discussion The organic geometry obtained from the wind and solar radiation optimisation resulted in the application of a structural system adapted to the unconventional building’s shape. This structural system had to be bidirectional in order to transfer the loads in the most efficient manner to save materials in the building’s structure.

transparency, insulation, environmental impact and variability. The envelope was designed with a focus in optimising natural ventilation and daylight levels while minimising thermal losses and embodied emissions due to materials.

The chosen structural system was a combination of a diagrid structure and central core working as a tube in tube system. The organic behaviour of the diagrid allowed to transfer horizontal loads from the wind and vertical loads from other structural and construction elements directly to the foundations, avoiding the need of columns and achieving higher degree of flexibility for the program distribution.

The boundary conditions of a real project were utilised in order to propose a building design based in a specific climate and programmatic needs. This building was the Gullhaug Torg project designed by Snøhetta. A new design was proposed based on these boundary conditions. Through the investigation of the design process, a methodology was designed with the purpose of serving as a basis for future ZEB high-rise buildings. The methodology implemented is based on an Integrated Design Process approach. The objectives addressed through this methodology are: maximise energy efficiency, ensure an optimal production of on-site renewable energy, and minimise the embodied emissions due to materials.

The combination of structure and envelope presented however some difficulties. It was found out that the complexity of this structural system did not allow for direct application of a traditional envelope composed by walls and windows. Two reasons explain this fact. The first one is that discontinuities between the interior partitions and the exterior envelope were created due to the location of the diagrid structure between them, generating thermal and acoustic bridges. The second is that the calculated optimum glassing ratio of 40 % of the façade area did not allow to place windows avoiding the diagonal elements of the diagrid

The methodology has been divided in four steps, organised in four different chapters. A preliminary analysis of the climatic conditions and building’s requirements was carried out in Chapter 2. To maximise energy efficiency, a climate-adapted built form was designed in Chapter 3. The main parameters considered at this step were wind pressure and solar radiation.

In Chapter 4, the structural system and materials were decided. The assumption of utilising massive timber products as main structural components was made in order to reduce embodied emissions in the biggest contributor to the building’s materials. Massive timber products not only have very low embodied emissions, but they also allow to reduce the amount of concrete used in the building’s foundation due to their light weight. Chapter 5 was focused on the building’s envelope. Here, five different parameters were analysed: perforation,

system, generating undesirable shading and difficulties for the users in operating the windows.

The use of a double-skin façade makes possible to have a transparent exterior envelope showing the diagrid from the outside, improving the aesthetic qualities of the building. However, if this system is to be selected, the inner layer (behind the diagrid structure) must be optimised in terms of heat losses and solar heat gains through the glassing, as well as assure the implementation of an efficient ventilation and dynamic shading system. The first must be carried out by the optimisation of the window to wall ratio. The second should be implemented by the study of air temperature and quality in relation to different shading systems and ventilation solutions. These calculations were out of the scope of this project, but the author believes that such study could lead to further improvements in the proposed design.

The proposed structural system is a consequence of the initial assumption of utilising massive wood products to decrease the weight of the structure and minimise the emissions due to materials. However, it has also been mentioned that embodied emissions due to steel production have been dramatically decreased during the past decades. Moreover, recycling possibilities of these structural elements are much higher

Compatibility of structural and envelope systems

Diagrid system

Framing system

Conventional wall + windows envelope Double-skin façade Fig. 111: Conclusions of compatibility based on the analysis of different structural and envelope options.

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Aiming for ZEB in a High Rise Building

6. Conclusions & discussion

than those for massive wood products. As opposed to steel’s recycling possibilities, timber products are commonly burned at the end of their life time for energy production. The combustion of these materials generates GHG emissions to the atmosphere that can overcome the CO2 captured during their life time if CO2 sequestration is not implemented in the thermal power plant. Hence, in a complete life cycle overview, the total embodied emissions due to structural materials may be lower by utilising a steel-based system when the end-of-life phase of structural elements is taken into consideration.

in the calculation. However, for the design of a cost-effective system, the dimensions of the different elements must be adapted to commercialised sections. In addition, different dimensions must also be homogenised as much as possible to ease the construction and fabrication process. This goes in contradiction with material’s optimisation, yet facilitates the process and diminishes production costs.

The cost implication of the structure solution adopted was out of the scope of this work, but it is believed to be an important factor to take into consideration in future studies.

When the pre-dimension of the timber diagrid structure was calculated, the results showed the necessary dimensions for every element of the structure to support the loads considered

Another finding from this particular design process is that the complexity of building’s geometry may cause difficulties in the structure and construction systems, which may at the same

time increase cost and embodied emissions associated to them. Thus, a comparison between pros and cons of an organic climate-adapted shape versus a more conventional geometry should be assessed in terms of both cost and embodied emissions.

The cost parameter has not been taken into consideration for this master thesis. However, in real-life projects, cost is a decisive factor that usually drives design decisions. Throughout this discussion, cost and embodied emissions due to materials seem to be contradictory parameters, since what often implies less production costs is normally related with higher embodied emissions. This is the case, for instance, of timber and concrete products. Timber has very low embodied emissions on the production phase.

However, the associated cost of this material is normally higher than concrete, which has larger embodied emissions. On the other hand, timber products allow to speed up construction processes, which also decreases final costs.

A future study of this parameter may allow to implement more cost-effective solutions on the design.

Relation between daylight hours and the 24-hour schedule of an average person

The program distribution through the different building’s floors is found to be optimal in relation to the efficient use of solar and internal heat gains. To represent this conclusion, the diagram from Fig. 112 has been elaborated, representing the daily-basis activities of an average person in relation to the different sun paths in Oslo throughout the year.

At home Commuting Working Sleeping

It is important to note that higher daylight levels are achieved in the higher floors of the building. This is due to a lower obstruction of the sky component (SK), which has been proved to be the higher contributor in the calculation of daylight factor.

As it can be observed in this diagram, an average person normally spends 8 hours per day at the work place, usually in the mornings from 8:00 to 16:00 or 9:00 to 17:00. This time interval also coincides with a permanent solar exposure

Fig. 112: 24 hours representation of the daily basis activities for an average person in relation to the sun path during the equinox and the winter and summer solstice.

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throughout the year, being the shorter amount of daylight hours during the winter solstice, from 9:30 to 15:30 approximately. It has been said that office spaces have higher risk of overheating, caused by solar gains in combination with internal heat gains due to appliances’ use. The cooling demand in these spaces is dominating throughout the whole year even for cold climatic regions. For this reason, it is important to avoid excessive solar radiation that may contribute to higher internal heat gains.

On the other hand, the time spent at home is an average of 13 hours per day (5 in the afternoon, 7 sleeping during the night and 1 in the mornings) except for the weekends, when this amount can even reach 24 hours. The highest amount of time is spent at home, yet this time interval only coincides with the daylight hours from spring to autumn. Thus, it is important to locate the housing part of the program on the upper floors of the building in order to guarantee enough sun availability to take maximum advantage of the solar heat gains. This upper location of the apartments also guarantees a higher degree of privacy, a highly appreciated quality in a private home.

As a conclusion, a climate-adapted building has been designed in this master thesis, taking as main parameters the wind pressure over the envelope, and the solar radiation for energy production and solar heat gains. A structural system has been designed to suit the organic resulting form, focussing on reducing emissions due to materials. Finally, the building’s envelope has been designed based on ensuring good natural ventilation, daylight levels and variability throughout the seasons while minimising the embodied emissions due to materials and thermal losses. As a result, a building with good energy performance, low embodied emissions, and adequate ventilation and solar exposure has been designed.

6.3. Methodology implemented: Findings and discussion In a parametric optimisation like the implemented in this methodology, to find the optimum solution that satisfies all the parameters is not possible in most of the cases. As an example, the optimisation of the building’s geometry in order to support minimum wind pressure is contradictory with an optimal natural ventilation approach. This is due to the fact that wind is one of the main driving forces for natural ventilation.

Other examples are the aforementioned cost parameter in contradiction with emissions, or the maximisation of daylight levels and minimisation of thermal losses. In these cases, to choose the predominant parameter that will allow to achieve the final goal is key in the success of the design process. In most of the cases, a compromise solution is the proper answer to these contradictory situations.

There are factors that cannot be parametrised during the design process, and can only be assess through the critical thinking of the educated architect. Some examples of such factors are the integration of the building with the surroundings or the aesthetic qualities of it. The design of Zero Emission Buildings shows that the Integrated Design Process is not intuitive and simulations must be implemented to determine energy performance in early design stages. Thus, both a good critical thinking and energy simulations are complementary in an Integrated Design Process.

Due to the complexity of an IDP implementation, these kind of design processes are usually composed by interdisciplinary groups of experts in different fields. This complexity is reflected in every chapter of this master thesis, which could constitute a separated thesis on their own.

The interdependency among the factors to be parametrised is another difficulty added to the equation.

The parameters that have been taken into consideration for the design of the methodology proposed in this thesis are wind pressure, solar radiation for energy production and heat gains, embodied emissions due to materials,

6.4. Further work

thermal loses through building’s envelope and daylight levels inside the building. However, it is considered that for a future improvement of this methodology, other aspects such as cost implications must be introduced as driving parameters of the Integrated Design Process.

It has been shown that the design of organic shapes creates some difficulties in the selection of the structural system. An interesting study to complement this thesis would consist of comparing the CO2 emissions due to structural materials of a timber-based diagrid system versus a conventional framing system. Another interesting comparison would be the overall embodied emissions through the building’s life cycle comparing a diagrid system in timber versus the same system made out of steel, relating the results with the cost and maintenance associated to the different structural options.

For the estimation of the environmental impact of materials in this thesis, a production phase scope (A1 to A3) has been chosen. However, as seen in the example of the steel structures, it is important to take into account the materials’ lifespan in their entirety in order to have accurate results from the Life Cycle Assessment.

Optimise the heat transfer coefficient of the double-skin façade by studying the variation of the layer’s composition would be another interesting approach to complement this project. Some of the study possibilities could be: different dimensions for the air cavity layer, different glassing options for the exterior layer, or different glassing ratios for the interior layer in combination with opaque elements. This study must include the relation between the different options and their embodied emissions due to materials.

Sustainability is a call to include environmental concerns in the production of built forms. The importance of climate adaptation has been proved to be key in the design of sustainable buildings. The production of forms has to be based on the understanding of the forces from the physical environment. However, due to climate change, it is possible that in some decades climatic characteristics inherit to present climates will drastically change. For this reason, to assure robustness of the design towards this climatic uncertainty will be a good approach to implement in today’s sustainable constructions.

A deep study and optimisation of the dynamic shading system utilised in a double-skin façade could play an important role on the final energy consumption. This system could influence the daylight availability of the interior spaces as well as their internal heat loads through solar gains.

The relation between different dynamic system options with the maintenance cost would be an interesting study to complement this work.

In conclusion, a methodology based on the implementation of an Integrated Design Process has been designed in this master thesis. This methodology consists on an initial climate and boundary conditions analysis as a first step. Subsequently, the parameters that drive the climate-adapted built form are decided and the building’s geometry optimised in relation to them. For this particular project, wind pressure and solar radiation were found to be the most significant parameters. On a third step, the structure is designed driven by the selection of structural materials with low embodied emissions. As the final step, the building’s envelope is designed based on solar radiation, natural ventilation, heat losses and environmental impact as driving parameters for the design.

Regarding the methodology implemented, it would be interesting to analyse the cost impact in every decision made. Therefore, for a future improvement of the methodology proposed in this thesis, cost must be introduced as a driving parameter in the design process.

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Norwegian University of Science and Technology Faculty of Architecture and Design Department of Architecture and Technology