THE ROLE OF VOIDS IN THE OVERALL PERFORMANCE OF TALL BUILDINGS

THE ROLE OF VOIDS IN THE OVERALL PERFORMANCE OF TALL BUILDINGS ASSESSING THERMAL PERFORMNACE, DAYLIGHT AND NATURAL VENTILATION IN COMMERCIAL BUILDINGS IN LONDON

September 2019

Justina Vazquez Caputo UNIVERSITY OF WESTMINSTER, COLLEGE OF DESIGN, CREATIVE AND DIGITAL INDUSTRIES SCHOOL OF ARCHITECTURE AND CITIES MSC ARCHITECTURE AND ENVIRONMENTAL DESIGN 2018/19 SEM 2&3 THESIS PROJECT MODULE

ABSTRACT Nowadays, the search for iconic tall office buildings have become the latest trend for large firms all around the world, and it comes along with an environmental agenda that drives the popularity and success of the designs. However, can tall buildings be sustainable? Although there are some successfully built examples that claim to have reduced energy consumption by almost 50%, there is hardly any published data about it.

Buildings account for over 45% of UK energy use and carbon emissions, thus, the need to improve building’s performance. As buildings get higher, structure demands more space, making the floor plate grow in order to maintain its spatial efficiency. To overcome this, a common factor in most environmentally responsive tall buildings refer to the use of voids, which have the capacity to bring daylight, visual communication and the possibility of natural ventilation into the building

by shortening the distance façade-usable area.

Therefore, voids are a powerful resource in these buildings to comply with actual policies and the global sustainable agenda.

This thesis will explore the effects of introducing voids in a high-rise building, first in three built examples: The Commerzbank Headquarters, 30 St. Mary Axe and 110 Bishopsgate, and then performing a generic analytical study in order to understand their performance. It will quantify its improvements in daylight, airflow rates and thermal performance, giving a general overview of the role they undertake in the overall performance of the building. Moreover, highlighting their potential towards generating not only more climate responsible buildings, but also high quality spaces that create a sense of community within the building and relate to the outdoor environment.

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TABLE OF CONTENTS Acknowledgements Chapter 1: Introduction 1.1 General Background and Problem Statement 1.2 Hypothesis 1.3 Methodology and Thesis Collaboration 1.4 Summary of Main Findings 1.5 Structure Chapter 2: Literature Review: Tall Commercial Buildings 2.1 Historical Overview 2.2 Definitions and Limitations 2.3 Impacts on the City 2.4 Arguments against and in favour of Tall Buildings 2.5 Sustainable Tall Buildings 2.6 Potential of Voids in Tall Buildings: Benefits and Possibilities 2.6.1 Natural Ventilation in Tall Buildings 2.6.1.1 Segmentation 2.6.1.2 Wind and Tall Buildings 2.6.1.3 Double Skin Facades 2.6.2 Daylight 2.6.3 Buffer Zones Chapter 3: Context and Precedents 3.1 Climate Analysis and Climate Change Scenario 3.2 Case Studies 3.2.1 Commerzbank Headquarters 3.2.2 The Gherkin 3.2.3 The Heron Tower 3.2.4 Area Comparison Study 3.3 Research Questions Chapter 4: Analytical Work 4.1 Case Studies Evaluation 4.1.1 Methodology and Inputs 4.1.2 Twelve Storey Void Case 4.1.3 Six Storey Void Case 4.1.4 Three Storey Void Case 4.1.5 Summary Chart Comparison 4.1.6 Loads comparison 4.2 Generic Analysis 4.2.1 Methodology and Inputs 4.2.2 Thermal Performance Analysis 4.2.3 Daylight Comparison 4.2.4 Natural Ventilation Studies 4.2.5 Climate Change Scenario 4.2.6 Summary Chart Comparison 4.2.7 Loads comparison Chapter 5: Addition of Vegetation 5.1 Benefits of Introducing Vegetation in Workspaces 5.2 Evapotranspiration Rate 5.3 Analytical Work 5.3.1 Methodology and Inputs 5.3.2 Outcomes Chapter 6: Conclusions and Recommendations

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ACKNOWLEDGEMENTS This thesis project idea would not have been possible without Dr. Joana Carla Soares Goncalves, my tutor. I am very grateful for her support and encouragement.

In addition, Dr. Rosa Shiano-Phan, as well as all the course professors’ contributions, whom have inspired me throughout this entire postgraduate course.

Without their classes and knowledge, I would, perhaps, still think tall buildings as “glass boxes”.

A special thanks to Hilson Moran and Professor Amedeo Scofone for offering this thesis topic and for

his guidance in the process, I am very grateful for this collaborative opportunity.

I am very thankful to Dr. Juan Vallejo, with his helpful guidance I was able to narrow the scope of the research and find the best path to develop the study.

I would like to express my gratitude to my fellow classmates, from whom I have learnt a lot. Also, my family that have supported me so much the entire year.

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CHAPTER 1 INTRODUCTION

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CHAPTER 1: INTRODUCTION

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1.1 GENERAL BACKGROUND AND PROBLEM STATEMENT The IPCC has set a global target that pushes buildings to reduce energy consumption by 60% by 2050. That target will be hard to achieve if tall buildings are not designed with an environmental approach in mind. This means incorporating climatic and cultural context into the design, researching the main aspects of its occupation, what the internal environmental conditions mean in terms of energy consumption, how the envelope relate to external climate, understanding the building’s performance and informing future designs. In addition to this, tackling performance and quality by reviewing the current design criteria and taking advantage of environmental conditions to achieve comfort. In this way, more flexible, adaptable tall buildings can be designed, in which occupants are given the chance to control their environments, leading to users’ satisfaction.

Moreover, environmental design sets a new methodology and tools to redefine the design of tall buildings, stimulating the shift from the artificially controlled sealed glass box, into environmentally responsive new structures. In this context, iconic tall buildings such as The Commerzbank Headquarters in Frankfurt, can encourage this shift by establishing new exciting architectural responses to look up to.

In commercial architecture, an environmental approach is crucial since new developments and designs are driven exclusively by market law (Soares Gonçalves, 2010). Even though markets are tending to consider environmental issues, which boost their popularity, as well as environmental targets are incorporated into legislation and politics, it will only necessarily change when market forces shift completely towards sustainability and environmental quality is properly valued. The truth is that if there are economic interests involved, tall commercial buildings will continue to exist, highlighting the importance to strive towards sustainability.

In this sense, there are many new high-rise building proposals that use alternative technologies and claim to be energy efficient. However, very few have been built and are in operation. Nevertheless, in most of these buildings, the needed environmental quality is not achieved, reinforced by the limited access to their energy consumption data, which draws a barrier to improving building design (Soares Gonçalves, 2010).

Taking into consideration that there were at least 76 new tall buildings planned for London in 2019 (Kollewe, 2019) by the time of this writing, it is crucial that these new buildings contribute to environmental and energy performance, leading to less environmental impact of

these buildings in operation, and more quality spaces with the potential to enhance productivity and mental health.

Soares Gonçalves (2010) notes that, on top of environmental design, the achievement of sustainable tall buildings relies on the precision of design-related decisions, building forms capable of adapting to changes without compromising performance, skilful facility management operation, and conscious and participatory users, which handle adaptive opportunities to achieve comfort. Alongside with stricter energy regulations and codes on performance, buildings with better environmental performance, quality spaces, and in compliance with energy consumption, can be built. By considering geographical and climatic context, buildings can minimise demand for energy, water, and other resources.

Introducing voids into these types of designs can help achieve these goals. Atria cut deep floor plans providing daylight, environmental quality and performance, creating spaces more aligned to external conditions, which allow fluctuations and are more flexible. This quality is extremely powerful, even more in office buildings, which need to adapt to new ways of working, and global sustainability.

1.2 HYPOTHESIS This thesis will strive to narrow the gap on published data about environmental responsive tall buildings, by quantifying how the introduction of voids can boost the overall performance of the building and minimise energy consumption. It is based on the belief that tall buildings can be environmental when they take climatic context into account and incorporate voids as a powerful strategy to optimize daylight, allow natural ventilation and reduce annual loads. By bringing views out and connecting offices to outer conditions, performance can be enhanced alongside with wellness and psychological benefits to its users.

Figure 1.1.1: Design of voids in a new tower. Source: Archinect

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1.3 METHODOLOGY AND THESIS COLLABORATION The thesis is based upon literature review on tall buildings, natural ventilation, daylight and vegetation to validate the hypothesis. A study on built precedents, which have proven to have reduced energy consumption with a void strategy and built in cold temperate climates, was carried away first. These case studies serve as examples to compare by means of analytical work, the effectiveness of the strategy to improve thermal performance, daylight and annual loads. In this sense, these precedents support and back up the hypothesis.

The analysis is performed by ESLD TAS dynamic thermal simulations to study performance and comfort under the EN 15251:2007 Adaptive Comfort Model, and Rhinoceros with Grasshopper plug-in alongside DIVA daylight simulations to evaluate useful daylight illuminance levels. Comfort is observed also in detail by selecting a winter and a hot summer day to analyse hourly performance and get a clear understanding of the building’s behaviour under different climatic conditions. The aim is to compare the results of using voids against not doing so.

Second, a generic analysis was conducted to provide a theoretical study to investigate the strategy in depth.

The same methodology was employed to compare two different distributions in the plan of the same void-tofloor area. This way, quality is considered not only in the office spaces the voids are meant to serve, but also for the voids themselves. Besides testing both buildings against thermal performance and daylight, a wind flow analysis was included to examine how natural ventilation is executed under the introduction of voids.

CFD analysis using Autodesk CFD software was performed to study natural ventilation by comparing both plans alongside a no void version of the building.

Lastly, the thesis contains input from Hilson Moran, that suggested adding vegetation into these spaces. More specifically, the cooling effect greenery could provide to enhance not only wellness, but also natural cooling strategies. To accomplish this, a CFD was conducted testing the contribution of adding trees and living walls to cooling down the village’s offices of the generic building. Following the FAO Penman-Monteith formula and the methodology provided by Gkatsopoulos (2017), the cooling in watts for both was determined and inputted in the simulation. Methodology and inputs for each part of the analytical work will be further explained in each corresponding section.

1.4 SUMMARY OF MAIN FINDINGS The main findings upon studying the cases showed that for climates such as London’s, where heating is the predominant necessity, voids do not impose a big difference by enhancing natural ventilation. However, big changes can be noted in terms of daylight and wellbeing. What is more, it shows the buffer capacity and potential for cross ventilation the voids can offer when distributed among the floorplate even in cellular plans. The generic analysis displayed two possible arrangements of these voids in a circular building form: one with six voids, each one with limited area, and another one distributing the same area into half the number of voids. This manoeuvre showed little difference between each other, evidencing the possibility to add spatial quality into the voids for them to be enjoyed more than just as environmental enhancers. Furthermore, it reinforced the usefulness of the strategy upon imminent climate change and opened the possibility of further reducing the void’s area without compromising performance. Further studies should be carried away to support this new hypothesis.

1.5 STRUCTURE The thesis is divided into two main components: literature review and analytical work.

Literature review is based on research on high-rise buildings, their challenges and opportunities, and how incorporating environmental design in their development can enhance their performance. This includes the acknowledgment of voids as a useful resource to comply with the required sustainable standards. Research on wellness, daylight, natural ventilation strategies and vegetation id developed upon the hypothesis that voids can enhance and potential all of them.

Before moving on to analytical work, a climate analysis and precedent study is approached to give the analysis the proper context upon which the study will be focused on. This section is contained in chapter two, where information about tall buildings and their strategies can be found, chapter three for precedent and context analysis, and chapter five for research on vegetation and the benefits of including it in these designs.

The analytical section takes chapter four and five, and seeks to quantify, by the means of environmental modelling and simulations, the rewards of introducing voids in tall buildings. First, taking built references as an example, then deepening the evaluation in a theoretical generic building, and finally assessing the contribution of greenery in these spaces.

Figure 1.1.2: Sketch of London’s skyline. Source: Wikipedia

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CHAPTER 2 LITERATURE REVIEW

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CHAPTER 2: LITERATURE REVIEW

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2.1 HISTORICAL OVERVIEW Tall buildings can be associated with economic and industrial change and with advances in technology which led to the continuous search to overcome the limits imposed by engineering restraints through the development of new construction technology.

Throughout architecture history, tall buildings’ main reasons to be have been economic and political issues orchestrated by corporations’ desire for economic power which brought iconic forces and spectacular views along with them.

Tall building typology was born in European cities after the Second World War, when it was already a widespread arrangement in important cities of America such as Chicago and New York. In fact, modernism society’s tall building was achieved due to the incentive of these cities to have the tallest building, pushing to break the first height restrictions. These towers followed the “form follows function” modernist concept in which modern office culture emerged. Modernism embraced the idea of rationalism, structural clarity, transparency and total control of the internal environment, conforming the international style “glass box office” which disregarded completely environmental considerations.

However, this international style which relied almost exclusively on air conditioning and artificial lighting, was challenged in the 1970s with the world energy crisis, categorizing this model as an energy waster. The Brundtland Report, among other organizations, raised questions about the environmental role of architecture and how to build more sustainable cities. Tall buildings’ approach was shifted towards a more “sustainable” one: the “intelligent building”.

In the 1990s, Europe’s tall commercial buildings started to emphasize energy efficiency by redefining the environmental quality of the indoor environment considering environmental performance as one of the main driving forces in the design. The intention to create iconic buildings pursued the idea of producing inviting, productive and energy efficient tall buildings that consider the impacts on its surroundings rather than focusing only on being taller than the rest.

Nevertheless, the environmental performance of tall buildings has been a widely discussed matter, being that they represent one of the most energy consuming structures in the built environment of the 20th century.

Figure 2.1.1: Seagram Building in New York. Source: The New York Times

Figure 2.1.2: Sears Tower in Chicago. Source WTTW

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2.2 DEFINITIONS AND LIMITATIONS The CTBUH (Council on Tall Buildings and Urban Height) (https://www.ctbuh.org/) defines a tall building as “whether or not the design, operation or urban impact are influenced by the quality of tallness and require special measures in planning, design and construction when compared with buildings representative of ordinary construction” (Beedle 1978, p7). Tall buildings can also be referred to as high-rise, towers or skyscrapers. Skyscrapers are defined by Yeang (1999, p24) as “essentially a tall building with a small foot print and small roof area with tall facades”. He also defines tall buildings with special structural and engineering systems needed due to their height. It is also a relative concept, since a building will be tall if it exceeds its surrounding buildings’ heights (Soares Gonçalves, 2010).

A height of five storeys set a limit for vertical circulation without lifts for occupant’s safety, and for many years, the definition of tallness was determined by a 20 storey high building which required special vertical circulation strategies. Today, the barrier has been pushed to over 60 storeys, a height that imposes great challenges for design and operation of the building. This can be overcome by new technologies such as double decker and triple decker or express lifts which need considerably space, making it difficult to maximise netto-gross area ratios.

In addition to vertical circulation, another challenge faced by tall buildings is spatial efficiency which carries economic aspects, but if structure and services are integrated into one combined design solution, the building will be more efficient. Therefore, the main design challenges are finding the right balance between form and spatial efficiency and the interaction with the urban morphology: the way that a tall building encounters ground floor can have a profound impact on the street level microclimate.

Although height is not a limit factor for structures, the taller the building, the larger the structure it will need in its design. Wind is the most important parameter to consider, as it greatly influences its shape. Curvilinear, triangular and cylindrical shapes are known to be structural efficient forms and when combined with strategies such as setbacks, terraces or openings through the mass, they reduce wind loads and pressures and prevent uncomfortable turbulences at pedestrian level. Other challenges of tall buildings consist on fire and safety design and how internal spaces are environmentally controlled, affecting greatly on energy consumption.

Figure 2.2.3: Example of how tall buildings encounter the ground floor.

Source: CNN

Figure 2.2.4: Example of how tall buildings encounter the ground floor. Source: The Silicon Valley

Figure 2.2.1: The Shard, London.

Figure 2.2.2: 8 Canada Square, London.

Source: Wikipedia

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Figure 2.2.5: Tallest buildings in UK. Source: Wikipedia

Since the 1990s, the discussion related to tall buildings has revolved around the need for density and that it represents the ideal typology for modern cities to accommodate the intense growth in population.

Nevertheless, tall buildings’ typology is rather used to build commercial buildings rather than residential ones.

High-rise buildings can revitalize degraded urban areas, bringing density, value and profitability to its surrounding neighbourhood. Usually, clusters of tall buildings over an area make businesses benefit from their proximity while rising the area’s socioeconomic difference in scale, and continuity of the urban fabric, ensuring vitality and communication between its functions and the street life. Strategies such as marquises, columns or podiums can help contribute to vitality, fostering greater development in a virtuous cycle.

The latent growth in the construction of tall buildings preoccupies and raises questions on their environmental performance, their social integration and their impact on surroundings. Can tall buildings be sustainable? There have been many examples around the world that challenge the common belief that they cannot by integrating the design to the urban fabric, enhancing the public realm, minimising energy consumption and integrating passive strategies. In other words, they follow an environmental approach directed by planning regulations to control their environmental impact and the environmental quality of its surroundings.

Figure 2.2.6: Leadenhall Building, London. Source: Wikipedia

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2.3 IMPACTS ON THE CITY One of the main contributions of tall buildings to cities is the ability of creating higher densities over small portions of land, with the potential to free space for open, public spaces. What’s more, if combined with the proximity of mix-used activities, they can bestow a considerable decrease in the city’s energy consumption.

Tall commercial buildings often reflect signs of progress and financial prosperity, loudly illustrated on most of the world’s financial leading cities’ skylines. However, cluster of tall buildings require a huge demand in city infrastructure, and when it is not enough to cope with this claim, commercial towers fail to bring urban development.

Urban mobility can be enhanced by the proximity between towers in mix-use neighbourhoods, even contributing to more sustainable means of transportation such as cycling or walking. In fact, closeness to public transportation and the provision of public spaces can create the basis for a walking and energy efficient city. On the contrary, without the support from an optimal infrastructure and mobility, tall buildings can generate traffic congestions, pollution and noise, compromising the quality of open spaces and the city altogether (Soares Gonçalves, 2010). Therefore, clusters of high-rise buildings can affect the built environment in a positive way, but only when introduced with carefully planned public policies that contemplate uses, densities, influence on surroundings, the capacity of the local infrastructure.

With regards to contextualization, there are three main issues to consider before introducing a tower in a city: its image and presence on the urban morphology, how its first levels interact with its surrounding fabric, and the design’s approach towards the local climate and environmental performance. London, among other European cities, has developed strict public policies that encourage the construction of tall buildings only in specific areas, such as the financial district where the most extensive infrastructure is available. Furthermore, reports such as “The Strategic Guidance for London Planning Authorities” intend on protecting historical buildings’ visual space from being blocked by new tall buildings.

How this typology touches the ground remains one of the main design challenges, as it needs space around it to be able to avoid negative impacts on the street level’s quality. To bring appropriate conditions, they must provide inviting public spaces that manage the

Figure 2.3.1: London’s financial district with its cluster of tall buildings. Source: CNN

Figure 2.3.2: London’s skyline. Source: Profab

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difference in scale, and continuity of the urban fabric, ensuring vitality and communication between its functions and the street life. Strategies such as marquises, columns or podiums can help contribute to bringing the building closer to the human scale.

In addition to this, the height, form and position in the urban form can deeply alter microclimatic conditions of the city, its environmental performance and its open spaces’ quality. At the same time, the microclimate that a tall building creates will have a mayor influence on its own performance.

In this context, the most relevant aspects include shadow casting, wind turbulence (not negative when aiding in pollution dispersal) and the reduction of the surrounding’s and street level’s sky-view factor, minimising solar access. This is crucial especially in cold, temperate climates such as London, where overshadowing of public and green spaces is mostly undesirable. Moreover, when clustered conforming urban canyons, it can lead to increasing urban heat island effects.

Regarding solar access, UK policies have adopted since the Second World War new solar access indicators based on the availability of sky-view factor. The use of reflective glass in tall building’s facades can cause glare and discomfort by reflecting unwanted direct solar radiation to its surroundings.

Tall buildings with its different heights, can also add roughness to the urban fabric affecting wind patterns and urban ventilation. They can either enhance ventilation or cause blockages preventing air movement from entering inner parts of the city when there is not enough distance between buildings.

Figure 2.3.4: Glare from reflective glass facade. Source: Dallas Morning News

Figure 2.3.3: Relationship between density and urban form.

Source: Design Thesis Journal

Figure 2.3.5: Overshadowing by tall buildings. Source: City Hall Watch

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2.4 ARGUMENTS AGAINST AND IN FAVOUR OF TALL BUILDINGS There are many arguments against building tall exacerbated by this image of the glass box office with a total artificially controlled environment. According to Ijhe (2015), these buildings require important amount of energy for its operation, they do not have regards for changes in the urban life quality, they produce an overload in infrastructure, and they impact on the historic fabric. What’s more, the use of high amounts of glass (which allows for mayor heat losses through conduction) and the elevated concentration of people that inhabit them, account for excessive heating loads.

They are also susceptible to overheating, so they rely on technical systems for ventilation and cooling, as well as for lifts and shafts that generate great energy demands.

These common features usually found in tall buildings, contribute in excessive carbon emissions. Furthermore,

when not properly designed, they cast unwanted shadows to the neighbouring buildings and volatile streets microclimates.

However, projects such as The Commerzbank Headquarters, by Foster and Partners, show the potential of tall buildings for sustainability when environmental performance, urban impact and global sustainability are considered on their planning and design. They also exemplify that energy consumption depends on the use of the building and its pattern of occupancy rather than height itself (Soares Gonçalves, 2010). Moreover, they demonstrate an understanding of the local climate and the users’ needs by reviewing conventional standards for comfort and environmental quality.

Figure 2.4.1: Environmental design methodology. Source: Klaus Bode

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2.5 SUSTAINABLE TALL BUILDINGS The 1987 Brundtland Report defines sustainable development as one "that meets the needs of the present without compromising the ability of future generations to meet their own needs." This means promoting a way of living in which human activity can coexist with nature allowing every species to evolve in a safety environment while not jeopardizing the upcoming society's rights, resources and own development.

The recent growth in demand and need of land has created a noticeable rise in tall buildings' construction since the 90’s. Together with the increase in awareness for climate change and the need for more sustainable buildings, there is an upswing pressure for constructions to be “green". There is a strong belief to stop building the standardised commercial “glass box" office and start incorporating local climate and culture into the design of tall buildings to provide quality and reduce energy consumption.

Environmental responsive tall buildings are, as the architect Klaus Bode stated in his lecture for this module, those which are planned with a low energy design approach, considering environmental performance, urban impact and global sustainability.

This is by minimising energy demand by architectural design, maximising the efficiency of technical systems by applying them only when needed, tending to use renewable energy and, if possible, applying passive and technical solutions for its operation. In addition, how the building’s architectural features respond to different climatic conditions generating appropriate solutions for different contexts. In this matter, the building form will influence shape and the dimensions of its floorplate and façade-to-floor ratio, while its porosity will affect possibilities for natural ventilation and wind loads.

Orientations should be carefully considered to prioritise daylight, passive solar gains and the use of space, managing the amount of radiation received.

Environmental tall buildings’ façade should comprise daylight penetration and distribution among the floor area while successfully manage solar gains and glare discomfort (Soares Gonçalves, 2010). Lately, in most cold and temperate climate European cities, there has been a preference for double-skin facades which present the opportunity of natural ventilation for tall buildings by acting as a wind shield while providing a thermal buffer that mediates external conditions. Yet, they should not be considered as the only environmental performing façade component for this building typology (Soares Gonçalves, 2010).

Environmental design strives for the use of natural resources and passive strategies to reduce energy consumption and, thus, carbon emissions, changing solutions according to the local climate. Also, the use of

local source labour and materials that ensure durability and flexibility. This calls to rethink the tall building’s design strategy to one that considers form, facades, materials and internal layout in the context of its climate and the user’s perception of thermal comfort, maximising the use of its form and fabric to control the internal environment. By designing based on the adaptive comfort band model, great savings in energy can be made, as it gives occupants the opportunity to adjust to its optimal comfort temperature by making changes in clothing, activities, or by opening windows, adjusting shades or blinds. Occupants show more satisfaction when provided the chance to control its environment. But, efforts have to be made to educate users to use the building properly (Soares Gonçalves, 2010).

It can be said then, that height is no limit for sustainability. In fact, tall buildings carry along significant potential when environmental thinking and design are considered and drive the overall design from its start. In this sense, iconic new tall building examples such as the Commerzbank Headquarters or The Gherkin, are highly important as they set new standards and ideals for space efficiency, environmental performance, energy consumption, as well as new aesthetic, economic and environmental values with the potential of advanced technologies and unique design possibilities.

Figure 2.5.1:Commerzbank Headquarters in Frankfurt. Source: Wikipedia

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2.6 POTENTIAL OF VOIDS IN TALL BUILDINGS: BENEFITS AND POSSIBILITIES Environmental performance, from the architectural design perspective, revolves around the building’s different solutions to diverse contexts, especially by the building form and its envelope. Environmental performance can be enhanced using these parameters to provide passive strategies related to natural ventilation and daylight, which will contribute to the overall thermal performance of the project.

Environmental principles attempt to maximise the use of the form and the fabric to optimise the control of the internal conditions.

Voids are a common feature in environmentally responsive tall buildings which include them in the form of sky courts or sky gardens with multi-storey atriums.

In summary, these provide spaces for leisure and wellbeing, enhance daylight penetration, stimulate communication with the outdoor environment and with the rest of the building’s functions and, in some cases, work as a strategy for natural ventilation. Most of them do it in a mix-mode system that supplies ventilation when the external conditions (temperature, air speed and humidity) are not favourable for cooling by passive means. Hybrid designs reduce the risks produced by high wind pressure that vary over a wider range due to the elevated height, but they are usually accompanied by expensive and sophisticated façade systems (Etheridge and Ford, 2008). This strategy is mostly implemented coupled with a double-skin façade in landscape typology office buildings for their efficiency in cross ventilation. On the other hand, cellular-office layout buildings are usually approached with a singleskin façade with operable windows and wind shields, which work efficiently for a single-sided ventilation strategy (Soares Gonçalves, 2010).

According to Saxon, atria contributes to the cultural function of buildings and “appeal to the mind and the senses. They put people at the centre of things in a way lost in recent architecture. They encourage play: people-watching and promenading, movement through space, enjoyment of nature and social life. They provide a social antidote to the oppressive interiors and the formless external spaces of today” (1983, p5). In his book, he emphasises atria’s potential to provide impressive communal areas, which connect and bring people together, views and connectivity with the outdoor conditions bringing daylight and direct solar access to the deepest parts of the plan. In that sense, he compares atria to a “giant double-glazing” feature with its ability to capture daylight, preventing wind, rain and uncomfortable temperatures in the meantime. They also help with natural ventilation and acclimatization (which can be enhanced by the stack effect from its

Figure 2.6.1: Ford Foundation Garden. Source: Architectural Digest

multi-storey height), and act as buffer zones. Winter strategies should maximise solar gains through passive solar heating design and in summer prevent overheating by appropriate shading devices and an effective natural ventilation strategy. Overall, the atrium contributes as usable space that adds quality to the design.

In reference to wellbeing, lately, and even more after new building certifications systems started to focus on health and wellbeing such as the WELL Building Standard, a connection was set between environmental quality and occupant’s health, wellness and productivity. Alongside sustainability standards, it has been driving the market towards the introduction of

Figure 2.6.2: Ford Foundation Garden. Source: Archdaily

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Figure 2.6.3: Commerzbank Headquarters, Frankfurt Figure 2.6.4: The Gherkin, London Figure 2.6.5: The Heron Tower, London Source: Wikipedia

wellness features in the built environment.

Environmental qualities refer to specific physical parameters such as temperature and thermal comfort, air quality, light and lighting or noise, control of indoor climate, among others (Hanc, McAndrew, Ucci, 2019).

Concerning commercial buildings, it is important to consider that it has been proven that building energy costs are increased by a low in productivity whenever poor environmental conditions exist, highlighting the importance and close relationship between wellbeing, productivity and environmental performance, promoting healthy work environments and energy savings at the same time (McArthur, Jofeh, Aguilar, 2015). Wargocki et al. (2000) noted that doubling the ventilation rate in offices led to a 1.75% of improvement in productivity, and Wyon (20014) showed a decrease of 6% to 9% in productivity in poor indoor air quality offices (cited in Hanc, McAndrew, Ucci, 2019, p1173 and p1178). In addition to this, Heschong (1999) linked a rise between 7% and 26% in performance due to increased light quality, improving also behaviour, mental stimulation and wellbeing at schools, while classrooms with access to views resulted in a 15% to 23% improvement in the learning progress; these percentages increasing even more with operable windows (cited in the same article, p1178). These

authors concluded then that improving air quality and lighting are the main factors to achieve better productivity rates in offices, therefore, rising the company’s economic value.

Voids are included in buildings that will be studied in this project: The Commerzbank Headquarters in Frankfurt; 30 St Mary Axe in London, both by Foster and Partners; and 110 Bishopsgate designed by architects Kohn Pedersen Fox, at the same location. In the Commerzbank (figure 2.6.3), atria in the form of gardens enable air movement from different wind directions and give its occupants control over windows and shading devices, plus, adding alternative working spaces. 30 St Mary Axe (figure 2.6.4) contains voids in the periphery which spiral around the building’s height and are subdivided each six floors. Its floor plate has a star shape that allows more facade perimeter to improve daylight and natural ventilation. 110 Bishopsgate (figure 2.6.5) pushes the services to the South facade and places a central void connecting each three floors that not only enhances environmental quality but also enables the core and corridors to be day lit and ventilated too. Although this tower does not provide an operable façade, the atrium creates a ushape floor plate that optimises daylight access and views out.

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2.6.1 NATURAL VENTILATION IN TALL BUILDINGS Natural ventilation is a crucial factor for saving energy; it reduces internal air temperature and increases heat losses by convection. When external conditions are favourable, natural ventilation has the ability to increase thermal comfort, not only improving air quality through pollution dispersal, but also reducing the need for active cooling and therefore, carbon emissions. Although it is difficult to lower temperatures beyond the external one, previous studies demonstrate that the increase of indoor air movement produces a physiological cooling effect. In fact, an indoor air speed of 0.25 m/s can produce a cooling effect equivalent to a 1K reduction in resultant temperature.

Tall buildings’ façade design need to pay special attention to the site’s air speed, the noise generated by wind at higher levels, and the impacts of its shading devices in flow patterns. By providing operable windows, occupants achieve much more comfort and productivity as they are given the opportunity to manipulate them according to their needs, therefore, being more tolerant to a wider range of temperatures (notion of adaptive comfort).

2.6.1.1 SEGMENTATION Examples demonstrate that the use of atriums and voids are useful to make natural ventilation more efficient.

They deal with high wind velocities and pressures, making them more flexible. As Etheridge and Ford (2008) define, natural ventilation's aim is to allow flow rates in the fabric to maintain optimum internal conditions that can be controlled by its occupants, and it happens when pressure differences are generated across the building’s apertures. The effect of wind and gravity on temperature differences between indoor and outdoor air produce these pressure differences, which depend on air density, wind direction, height and shape of the building.

Tall buildings receive high wind pressures due to elevated wind velocities, and great buoyancy pressures because of differences in temperatures, operating with a wide range of pressures that need to be controlled. In this sense, aerodynamics play an important part to cope with high pressures. Naturally-ventilated-seeking towers, overcome high-pressure differences, dividing the building into segments that work independently from each other, isolated by large, connected internal open spaces (fig. 2.6.1.1.1). The use of atria generates inward flow of fresh air to the deeper part of the plan,

Figure 2.6.1.1.3: Stratification by ventilation top and bottom. Source: Baker, 2009 Figure 2.6.1.1.1: Segmentation. Source: Etheridge and Ford, 2008

Figure 2.6.1.1.2: Atrium stack ventilation (Barclaycard Headquarters).

Source: CIBSE, 2005

Figure 2.6.1.1.4: Annual heating energy consumption for abuilding with an atrium showing the impact of ventilation pre-heating. Source: Baker, 2009

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Figure 2.6.1.1.5: Stack effect.

Source: CIBSE, 2005

Figure 2.6.1.1.6: Division in villages, Commerzbank Headquarters.

Source: Wikipedia

and its height can create stack effect ventilation that can be combined with cross ventilation to achieve comfort in a more efficient way (figure 2.6.1.1.2). In this respect, the use of atria has the advantage of combining wind and buoyancy forces to act together when the internal temperature is above the external one and the outlets are situated in a low wind pressure area (Etheridge and Ford, 2008). Although wind driven ventilation’s design approach is to design horizontal flow paths, by careful design of the atrium and its stack effect, wind forces can be used to induce vertical flows through the building to combine both effects (CIBSE AM10, 2005). Figure 2.6.1.1.4 illustrates the possible energy consumption reduction in heating loads when the cold winter air is preheated through an atrium.

For natural ventilation driven by stack effect to be efficient, the atria’s temperature has to be higher than the adjacent spaces, making sure that the hot layer is confined above the surrounding occupied rooms by promoting a stratified layer as shown in figure 2.6.1.1.3 (CIBSE AM10, 2005). When atria serve several occupied storeys, the neutral pressure level has to be pushed above the last occupied floor to ensure that air enters through each level and is exhausted through the atria’s outlet at a higher level, and not through the last floor’s aperture reducing its comfort conditions (figure 2.6.1.1.5). This is achieved by varying the opening sizes of the inlet and the vent, or by raising the height of the stack (CIBSE AM10, 2005).

In the case of The Commerzbank, the building is

Figure 2.6.1.1.7: Division in villages, Heron Tower. Source: Wikipedia

segmented into four villages of 12 floors each (figure 2.6.1.1.6), whereas in 110 Bishopsgate, into 11 villages of three floors each (figure 2.6.1.1.7). Etheridge and Ford (2008) claim that each village can be designed in isolation by conventional procedures, the main challenge consisting on achieving the optimum flow rates for each segment and the correct aerodynamics around the outlets to perform under different wind directions.

While designing for natural ventilation, the parameters to be considered to cope with heat gains are not only the facade’s orientation and responses to wind and solar protection, but the plan’s depth, the rooms' floor to ceiling height, the building's density and occupancy patterns. The area and position of apertures are also a key feature to enhance natural ventilation, requiring different sizes and orientations for cooling or heating seasons. In the Commerzbank, this strategy is combined with chilled ceilings in the cellular offices for cooling, and with an underfloor heating system in the sky courts during winter for heating. It is often joined with internal thermal mass to help reduce energy consumption.

Nevertheless, as mentioned before, natural ventilation is applied to most tall buildings in mix-mode systems as a result of climate constraints and increasing internal gains in workspaces. Also, because of security, culture, noise and pollution. However, the recent energy crisis calls for natural ventilation to be considered as a genuine strategy, as it is a key factor towards reducing buildings' carbon emissions.

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CHAPTER 2: LITERATURE REVIEW

Figure 2.6.1.2.1: Wind velocity profiles. Source: Szokolay, 2008

Figure 2.6.1.2.2: Diagram of airflow around high-rise buildings. Source: Oesterle, 2001

Figure 2.6.1.2.3: London’s wind profile. Source: Meteonorm 6.1

Figure 2.6.1.2.4: Wind flow around high buildings. Source: Lecture on urban microclimate for Evaluation of the Built Environment Module

2.6.1.2 WIND AND TALL BUILDINGS Wind forms a boundary level which is generated by the slowing effect of the ground surface and its turbulent flow through it, and which depth varies according to the ground’s roughness and surfaces and objects sitting on its surface. In that way, it is different in open country where it can reach a height of 270m, than from a city area where it can go over 500m as illustrated in figure x 2.6.1.2.1 (Szokolay, 2008). Regardless, tall buildings are more exposed to wind, and having higher altitudes, receive higher wind magnitudes. Wind speeds increase with height, as there is less friction and less obstructions that retard wind near the ground.

Figure 2.6.1.2.3 illustrates London’s wind profile showing mean wind speed at different heights in a city terrain for summer season obtained from Meteonorm 6.1. At 10m from the ground the average wind velocity is 1.47 m/s; at a height of 160m, approximately around 50-storey height, the speed increases more than double to 3.33 m/s, and at a height equivalent to 60 storeys, to around 3.87 m/s. In this sense, it can be deduced that flats at higher altitudes can be ventilated with smaller apertures compared to lower flats since flow rates increase with wind speed. Yet, the time in which the aperture can be opened will be restricted to optimum velocities, as high wind magnitudes may cause elevated air changes in the room causing discomfort.

As wind hits a tall building (figures 2.6.1.2.2 and .4, it is pushed up, down and around the sides, and air forced downwards increases wind speed at street level. At the base of the building, the downdraught produces a horseshoe vortex, curling around the sides; over the middle section of the building, the airflow will go around it; and at the top, most of it will be pushed up over the roof producing a three-dimensional top flow airstream (Oesterle, 2001). Figure 2.6.1.2.5 shows the pressure distribution around a square building form high-rise building with two different wind directions. Pressure distribution around buildings will differ with the building form and wind direction. In angular building forms, such as the example shown in these figures, the airstream presents a breakaway behind the corners that are set at right angles to the wind direction, causing suction peaks and high negative pressures. On the contrary, curvilinear and round shapes present more aerodynamics, and less obstruction to the wind load.

Figure 2.6.1.2.5: Qualitative pressure distribution around a high-rise building with a square plan, where the wind direction is at right angles to one side. Source: Oesterle, 2001

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2.6.1.3 DOUBLE-SKIN FACADES Besides the inclusion of atria, another usual applicable strategy for tall buildings is the use of double skins to aid in natural ventilation, providing weather protection and wind sheltering. They are commonly found in cold and temperate climates and consist usually of two glass skins: an outer single skin glass and a double-glazed inner layer, with an air gap in between. The cavity is usually shaded with intermediate adjustable blinds, sealed or ventilated either mechanically or naturally.

When ventilated, the intermediate cavity acts as a wind shield promoting natural ventilation of the internal rooms by solar induced thermal buoyancy and the effects of wind (Oesterle, 2001). Figures 2.6.1.3.1 and 2.6.1.3.2 illustrate the reductions in wind pressure and temperature curve for a building with a double skin. It acts as a buffer, not only providing thermal and acoustic insulation, but also including the possibility of passive solar heating, solar control, increased daylight access, transparency, views and in-out communication. It can also be paired up with a heat recovery system using preheat air from the cavity to reduce heating loads. Cavities vary in depths, can link two or several floors, but need to be ventilated and shaded in hot periods to avoid overheating even in cold climates, reducing radiation and direct sunlight access. The height of the cavity is an important parameter to consider and it is linked to the building’s function, orientation and design of the façade, and the local climate’s characteristics (Soares Goncalves, 2010).

As mentioned before, double skin facades do not represent the only solution for tall buildings, there will exist as many strategies as different climates, functions and context possible. What’s more, environmental performance should not rely exclusively on facades, but on a combination of it with the building’s form, orientation and layout, among other parameters. In fact, for example, The Commerzbank Headquarters tower, which is proven to have a successful environmental performance, does not have a double skin façade. This building combines a reduced windowto-wall ratio with shading devices and wind shields for its operable windows, demonstrating that even in cold and temperate climates, the use of single skin facades coupled with a proper design, can achieve double skin’s effective performance.

Figure 2.6.1.3.1: Reduction of fluctuations in wind pressure by equalising effects in the double-skin facade (“wave-breaking effect”. Source: Oesterle, 2001

Figure 2.6.1.3.2: Temperature curve around sun shading in a double-skin façade. Source: Oesterle, 2001

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2.6.2 DAYLIGHT As Westfall (2001) indicates on his thesis, people feel more connected to the outside in the presence of natural light that denotes changes throughout the day, seasons and year, keeping people energized leading to more productivity and efficiency. Moreover, he explains how daylight triggers circadian rhythm, which keeps the body in synch with the progression from day to day. It signals the body when to wake up or sleep according to the earth’s revolution on its axis. When circadian rhythm does not correspond to sunlight hours, it can lead to psychological disorders and even depression, highlighting the importance to bring daylight into office spaces, where most of adult society spend most of the day.

“One of the strongest contributions which atria can make to energy contributions in buildings is in allowing the use of daylight to be re-established” (Saxon, 1983. p77). Atria should be introduced with the right design to remove thermal cost and provide the right quality of light to the greatest plan-depth possible, avoiding glare and contrast. This is by achieving an optimum ratio between task and ambient light, where task light is the one needed to rightfully perform the work activity, and ambient is the background illumination. To avoid discomfort by contrast, a ratio of 1:3 between minimum

and maximum light levels is recommended between adjacent and transitional spaces (Soares Goncalves, 2010). For offices, the recommended illuminance levels are between 300 and 500 lux, which can be achieved with daylighting in a well-designed building (Saxon, 1983). Daylight availability depends on sky conditions, and in tall buildings’ higher levels is affected mostly by architectural aspects rather than by contextual ones.

The areas of a building’s plan with good daylight levels depend on a variety of parameters which include the site’s climate and its daylight availability, the building’s surroundings (which affects lower levels), its form and orientation. Also, the window-to-wall ratio, the floor-toceiling height, the treatment of the facades, the introduction of atriums and the internal layout including furniture and colours. The inclusion of voids is a good strategy to maximise daylight penetration. Reducing the need for artificial lighting, they act as “light ducts”, where its proportions will vary depending on sky conditions and the reflectivity of its walls play an important part in distributing the light. Landscaping can conflict with daylighting performance, vegetation should be carefully placed not to minimise daylight access, being the floor of the atrium an appropriate area without great penalties (Saxon, 1983).

Figure 2.6.2.1: The way light enters occupied spaces varies at different levels of the atrium. Source: Saxon, 1986

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Figure 2.6.2.2: Daylighting occupied space. Source: Saxon, 1986

Regarding the collection of light into the occupied spaces, Saxon (1983) claims that windows should ideally allow views out, directing much of its light upwards into the ceiling, to bounce further into the room and reduce contrasts. This can be achieved by reflection, and light shelves can be useful strategy in order to accomplish it.

Moreover, he notes that to gain full benefit from daylight, artificial lighting systems and the internal finishes of the room need to be considered together with it, giving occupants the possibility to adjust it according their own comfort levels.

Furthermore, the facade treatment of the building should be able to balance daylight penetration avoiding excessive daylight and illuminance levels that can cause glare. It should also prevent uncontrolled solar radiation from heating up the space, elevating temperatures above the comfort level. This is especially important in tall buildings for which higher levels are unobstructed and more exposed to sunlight, needing a proper shading strategy.

Figure 2.6.2.4: Sky-garden, Commerzbank Headquarters. Source: Wikipedia

Figure 2.6.2.3: The amount of reflected light available for lower storeys can be enhanced by selective design of the walls at each level. Source: Saxon, 1986

Figure 2.6.2.5: View from internal office, 110 Bishopsgate. Source: Wikipedia

Figure 2.6.2.6: View from internal office, Commerzbank Headquarters.

Source: Wikipedia

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CHAPTER 2: LITERATURE REVIEW

Figure 2.6.3.1: Buffer Thinking from The Guardian newspaper. Source: Saxon, 1986

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2.6.3 BUFFER ZONES

Figure 2.6.3.2: Buffer zones possibilities.

Figure 2.6.3.3: Types of atria and their thermal use. Source: Saxon, 1986

A buffer zone is meant to create a thermal bridge sheltering the building from weather variations and collecting solar gains to improve thermal performance by a protection layer from the outdoor environment during both winter and summer. In this way, radiation reaches this space in a direct way, and provides indirect gains and diffuse light to the workspaces. The intention of providing such areas are usually to control solar access in offices while supplying the building a useful area that connects the programme with itself and outdoors providing the opportunity for leisure and greenery (see figure 2.6.3.2). In cold and temperate climates such as London, the addition of buffer zones contributes to the reduction of heat losses by minimizing external influence and helps to create desirable microclimate conditions inside the rooms. In this sense, these buffer zones function as atria: open halls with glazed roofs or large windows, which tackle several storeys of the building providing light and ventilation to the interior. They also acts as double skin facades, as they are intended to preheat the air before entering in the workspace.

Saxon (1983) thinks of buffers as semi-external spaces, that in order to supply comfortable conditions to the spaces they intend to protect, they do not attempt to be comfortable throughout all the year. They get colder temperatures in winter and hotter in summer, therefore, activities in these spaces are seasonally appropriate, in order to reduce energy consumption.

Figure 2.6.3.1 illustrates Terry Fanel and Ralph Lebens (1980) thesis and thoughts on “buffer thinking”, highlighting its benefits and how these could be achieved. He then categorizes types of atria according to the site’s climate, distinguishing between the warming atrium, for climates that require heat for most of the year, the cooling atrium, for cooling-required locations, and the convertible atrium with the possibility of providing both (see figure 2.6.3.3).

The warming atrium, usually chosen strategy for climates such as London, should be designed to admit as much sunlight as possible and therefore, should be at least 5°C warmer than the external temperature in sunny conditions. In overcast conditions, it should also stay warmer due to the heat flow into it from its surrounding rooms, shortening the heating season.

Internal walls and floor should contribute to thermal storage, re-radiating heat over cloudy periods. In summer season, the atrium helps with ventilation to cope with the higher external temperatures (Saxon, 1983).

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CHAPTER 3 CONTEXT AND PRECEDENTS

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CHAPTER 3: CONTEXT AND PRECEDENTS

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3.1 CLIMATE ANALYIS AND CLIMATE CHANGE SCENARIO

Figure 3.1.1: Köppen-Geiger climate classification: Cfd - Oceanic climate.

Source: Wikipedia

Monthly Average Climate Data

oC

30.00 25.00

mean max/min

20.00

"Global Horizontal Radiation"

15.00

Wind Velocity

10.00

DBT mean average Adaptive Comfort EN 15251:2007 (Class II)

5.00 0.00

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Adaptive Comfort EN 15251:2007 (Class III)

Dec

Figure 3.1.2: Monthly average climate data, London.

Source: Meteonorm 6.1 Frequency of Sky Types (8am - 6pm) 100 90 80 70 %

60

Cloudy

50

Partly Cloudy

40

Sunny

30 20 10 0

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Figure 3.1.3: Sky types, London. Source: Meteonorm 6.1 Cumulative Rainfall 100

30

90

27

80

24

70

21

60

18

50

15

40

12

30

9

20

6

10

3

0

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

days

mm

The UK is categorized under oceanic climate as from the Köppen-Geiger climate classification (see figure 3.1.1) and typically features moderate climate with warm summers and cold winters. The city of London is located on 51.52º N, 0.15º W and presents average dry bulb temperatures of 5°C to 8°C in winter season, from December to March, and from 15°C to 21°C in summer, from June to September (see figure 3.1.2).

London’s sky is mostly overcast around 70% of the time during the months from September to March, decreasing this percentage to around 55% from April to August. Overall, it is approximately 60% cloudy, 10% partly cloudy and 30% sunny (figure 3.1.3).

Annual rainfall is around 700 mm total with more than 170 rainy days and more than 35 mm rainfall per month, an overall average of almost 60mm per month.

The monthly average relative humidity is considerably even through the year, featuring values between 75% from April to August and from 80% to 85% from November to January (figure 3.1.4). Regarding wet bulb temperatures, monthly mean averages record between 3.5°C to 7°C from November to April, and between 10°C and 15°C during the months of May to October. London is considered a windy city with prevailing wind direction from South-West, and the yearly average wind speed is around 3.3 m/s.

Its daily average global radiation falls between 2.14 kW/m2 and 0.53 kW/m2 during the months of October to March, being the highest in March and lowest in December, and between 4.92 kW/m2 and 2.84 kW/m2 from April to September, being the highest in July. Daily average diffuse radiation accounts for 1.39 kW/m2 to 0.37 kW/m2 in the months of October to March, and between 2.77 kW/m2 and 1.09 kW/m2 from April to September (see figure 3.1.5). Figure 3.1.6, illustrates the difference between the amount of radiations that hits each façade, showing a great disparity between North façade and the rest.

The constant ground temperature at depth -10m all year refer to potential for geothermal heat pumps and heating and cooling systems (see figure 3.1.6).

In order to provide thermal comfort, tall buildings, as well as all building typologies, need to adapt to its climate, maximising uses of each site’s natural resources. Temperate climate cities, such as London, require great architectural design adaptability; it has a predominant heating season, but needs natural ventilation and adjustable shading strategies in summer and mid-season to cope with solar gains. Natural ventilation strategy can be applied from mid-April to mid-October for cooling or pre-heating air as needed.

Rainfall RH mean AVERAGE (%) Days

0

Figure 3.1.4: Cumulative rainfall and mean average relative humidity, London. Source: Meteonorm 6.1

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CHAPTER 3: CONTEXT AND PRECEDENTS

Daily Average Horizontal Radiation 6.00 5.00

kW/m2

4.00 Global

3.00

Diffuse

2.00 1.00 0.00

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Figure 3.1.5: Daily average horizontal radiation, London.

Source: Meteonorm 6.1 Monthly Average Global Vertical Radiation 3.50 3.00

kWh/m 2

2.50 North

2.00

East

1.50

South

1.00

West

0.50 0.00

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Figure 3.1.6: Monthly average global vertical radiation, London.

Source: Meteonorm 6.1 Monthly Average Ground Temperature 30.00 25.00 20.00

0.00 m 1.00 m

15.00 °C

2.00 m 4.00 m

10.00

6.00 m 10.00 m

5.00 0.00

The use of thermal mass and insulation can be appropriate, accumulating solar gains and discharging them to the internal space in a few hours. In summer, it can absorb undesired solar gains, removing them later by ventilation and conduction through walls to avoid overheating.

Thermal comfort is a key parameter to reduce energy consumption: by attempting to maximise hours within comfort by environmental passive means, buildings can offer the maximum comfort conceivable while using the least energy possible. Thermal comfort refers to the interaction between environmental parameters such as air temperature, humidity, mean radiant temperature and air velocity, with people’s metabolic rate and clothing.

However, user’s perception of thermal comfort is not only about the physiological responses of their body, but also with their cultural background and the psychological conditions associated with adaptive opportunities to manipulate the surrounding environmental conditions. Adaptive comfort levels, such as the EN 15251:2007 model, relate to the behaviour of occupants to maintain their body temperature by changing their clothes or activity or by exercising control over indoor conditions, manipulating windows, fans, blinds, heating or cooling (Soares Gonçalves, 2010).

Taking into account adaptive models by tolerating variable indoor temperatures, can save considerably amount of energy in mechanically controlled buildings.

It also reduces consumption in mix-mode buildings as natural ventilation can be applied with a wider temperature range as long as occupants have good control over it.

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

-5.00

Figure 3.1.7: Monthly average ground temperature for London.

Source: Meteonorm 6.1

Figure 3.1.8: chart showing the temperature difference between the present and future climate. Source: Meteonorm 6.1

CLIMATE CHANGE SCENARIO The IPCC’s (Intergovernmental Panel on Climate Change) report on the impacts of global warming of 1.5ºC above pre-industrial levels and greenhouse gas emission pathways, calls for global awareness and response to the threat of climate change (https://www.ipcc.ch/).

The A1 scenario of the report refers to a future world with rapid economic and new technologies growth and global population that peaks by 2050 and then declines.

A1B scenario consists of a balance across fossil intensive and non-fossil energy sources. Taking into considerations the intermediate emissions scenario, A1B, and as figure 3.1.8 illustrates, by 2050, there will be an increase in air temperatures of up to 6K for at least 10% of the year, increasing their values in both summer and winter seasons. Although this shows more hours within comfort for 2050 (figure 3.1.9) due to higher temperatures in the future, clearer skies and increased radiation levels, it presents catastrophic repercussions worldwide. The report also forecasts a rise in sea levels and in the number of heavy

precipitation events all around the world, with the acceleration of water cycles and high CO2 emissions, causing irreversible impacts on population and ecosystems. London, for example, is predicted to increase annual rainfall by between 5% and 20% in almost all months of the year, as represented on figure 3.1.10.

In reference to solar radiation, the global radiation is expected to rise by 15% mostly in warm seasons, and figure 3.1.11 exposes the differences between vertical radiation for both present times and by 2050. The figure shows higher radiation for the future for most of the time in the year, in almost all orientations.

The IPCC report is reason to raise concern and rethink how cities should be built; reconsidering the ways in which designers could contribute towards shifting the built environment towards an architecture that incorporates an environmental approach, maximising natural resources and reducing energy consumption, including mitigation attributes in dense cities where needed, and minimising carbon emissions.

Figure 3.1.9: Psychometric chart for both present (left) and future (right), London. The future scenario shows more hours within comfort due to warmer air temperatures. Source: Meteonorm 6.1

VERTICAL RADIATION DIFFERENCE 20 50 X 20 17

50 % 40% 30 % 20 % 10 % 0% -10 %

Figure 3.1.10: Cumulative rainfall comparison between present and future 2050 climate, London. Source: Meteonorm 6.1

Figure 3.1.11: Vertical radiation comparison between both years’ climates, London. Source: Meteonorm 6.1

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3.2 CASE STUDIES Three buildings were chosen to perform the study of the role of voids in tall buildings. This references account for known successful built examples which incorporated voids in the form of sky-courts and atria in order to enhance their environmental performance.

These buildings are icons in their cities, having become part of their skylines as impotent structures which not only convey a symbol of power, but also references of status to the rest of the world. They proudly present new environmental, economic and aesthetic values, while setting new standards of energy consumption and environmental performance. They flaunt upon their new technological advances displaying new design possibilities, making environmental design more attractive and something to look for in new designs.

These buildings make use of different strategies, heights and form of voids in order to incorporate natural ventilation, daylight and connectivity to the deeper parts of their plans, while taking three basic geometric building forms, therefore, different aerodynamics. In this sense, they presented three distinctive and interesting examples to explore and study the implications of incorporating such strategy.

Figure 3.2.1.1: Ventilation strategies, Commerzbank Headquarters.

Source: Wikipedia

3.2.1 COMMERZBANK HEADQUARTERS The Commerzbank Headquarters building is located in Frankfurt, Germany (cold and temperate climate); it was designed by Foster and Partners and built in 1998. It has a triangular building form with a core in each vertex (part of the structural strategy), and consist of four villages of 12 storeys each. Each village has a 12th storey central void that is connected with three atrium gardens that are four storey high and rotate 120° across the plan, so that each one of them faces a façade orientation of the building. This enables air movement from different wind directions and cross ventilation between the voids from stack effect.

Among its environmental aspects, it provides natural ventilation for all working areas, visual communication, interaction and views out through the atria, and distribution of daylight and glare control coupled with façade design and form. At local scale, the building was designed considering its surroundings. It provides a transition from the mid-rise old city centre buildings into the tower in the middle, with a six-storey high block (see figures 3.2.1.2 and .3). In that way, it diminishes its impacts on the microclimate of its surroundings and on pedestrian comfort.

The building has a cellular office layout and the floor-

Figure 3.2.1.2: Commerzbank Headquarters, Frankfurt. Source: The skyscraper Center

32

Figure 3.2.1.3: Commerzbank Headquarters showing the two different scales of the building, Frankfurt. Source: Wikipedia

Figure 3.2.1.4: Summer ventilation (top) and winter strategy (bottom) of the sky-gardens, Commerzbank Headquarters. Source: Wikipedia

plate is divided into zones by the ventilation strategy for each one of them: an external zone facing the external faรงade, an internal zone, both designed for single sided ventilation; and an intermediate zone between the two.

The gardens provide fresh air for the internal zone and are connected to the middle void which articulates the whole village. This approach allowed a deeper, yet naturally ventilated floor-plate, and in consequence, a taller building was possible. Figures 3.2.1.1, 3.2.1.4, 3.2.1.6 and 3.2.1.7 display the different ventilation strategies for the village, and 3.2.1.5 the division of zones across the plan.

In some floors, changes in occupancy patterns have altered the working spaces joining some external zone offices with the intermediate corridor zone, and therefore, making these spaces open plan areas.

Changes in internal gains were negligible, without any increase in cooling loads. On the contrary, it boosted the overall performance of the building, reducing the need for mechanical cooling in the altered intermediate zones, while maintaining the independency of the internal offices.

When external climatic conditions are not favourable for natural ventilation, the building is mechanically ventilated in a mix-mode approach. Its control is set upon two sectorizations of the building: a vertical one, which accounts for the different microclimatic conditions of each village, and a horizontal one that separates the floor plate into the three different internal zones. When wind pressures and velocities are high, windows facing the wind orientation are closed, but the other two can be left opened to continue with natural ventilation. Regardless, occupants can operate windows in the internal offices, and overall ventilation by passive means is possible for 80% of the year (Soares

Figure 3.2.1.5: Division of internal zones, Commerzbank Headquarters.

Source: Wikipedia

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CHAPTER 3: CONTEXT AND PRECEDENTS

Gonçalves, 2010).

The façade of the external offices consist of a doubleskin façade formed by an external glass panel that acts as a wind shield, an intermediate blind, and internal double-glazed operable windows. Nevertheless, windows are closed to maintain internal temperatures below 26°C in summer, when there are high wind speeds, and when external temperatures go under 5°C or indoor temperatures under 17°C. In winter, underfloor heating helps keep indoor temperatures above 5°C. The gardens act as buffer zones mediating external conditions, as dynamic working areas, and as spaces for leisure and social interaction. They also provide communication between floors and a link with outdoors, by offering views out to all offices around the building, recreating microclimatic conditions that are comparable to the external climate. The central void, acts as a duct connecting and distributing air throughout the entire village.

The Commerzbank was one of the earliest naturally ventilated new tall buildings in Germany, becoming one of the most significant buildings in environmental design and architectural expression in the country.

Figure 3.2.1.6: Passive heating/cooling/ventilation systems in offices, Commerzbank Headquarters. Source: Davies, 1997

Figure 3.2.1.7: Active heating/cooling/ventilation systems in offices, Commerzbank Headquarters. Source: Davies, 1997

Figure 3.2.1.8: View to the atrium, Commerzbank Headquarters. Source: Wikipedia

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Figure 3.2.1.9:Vegetation in sky-garden, Commerzbank Headquarters. Source: Wikipedia

Figure 3.2.1.10: Passive strategies in Commerzbank Headquarters.

Source: Wikipedia

Figure 3.2.1.11: View to the atrium (top), central void (left) and garden’s façade window operation (right), Commerzbank Headquarters. Source: Wikipedia

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CHAPTER 3: CONTEXT AND PRECEDENTS

3.2.2 THE GHERKIN Commonly known as “The Gherkin”, 30 Saint Mary Axe was built in 2004 in London and its architect was also Foster. It has a round shape that reduces air turbulence at ground level and improves sky view at pedestrian level. What’s more, environmental assessment on the building has demonstrated the potential of the form to reduce energy consumption regarding the environmental control systems by 20% (Soares Gonçalves, 2010). Its design was inspired by Bukminster Fuller’s “climatroffice” concept (see figure 3.2.2.1), where the internal environment is totally protected from the outdoor conditions by a glass façade and characterised by internal gardens. The building consists of five villages with six atria across the plan’s periphery, which spiral around the building’s height and are subdivided each six floors, yet portraying a unified image through the building. The atria are highlighted in the building’s expression by a darker glazing, that although it contributes to the architectural expression of the building, it may reduce daylight penetration into

the voids (see figure 3.2.2.4). These, cut the floorplate into a star shape increasing the perimeter of the plan, improving daylight and adding the opportunity for natural ventilation. They also allow communication among floors, views out and social interaction, becoming especially important and helpful when companies take more than one storey.

The office’s façade is formed by a double skin with a ventilated cavity to the outside and internal blinds for solar control (depicted on figure 3.2.2.5). Natural cross ventilation is provided through the openings on the atria and across the open plan layout, hence, the offices have no direct openings to the outside. Although this may seem as occupants have less control on adaptive opportunities to maintain their thermal comfort levels, this strategy is useful in naturally ventilated tall buildings, since it aids in controlling high wind velocities and pressures due to height. In this sense, less opening areas, but strategically placed through the plan, make it easier to provide more opportunities for natural ventilation, widening the range in which it can be

Figure 3.2.2.1: “Climatroffice”, 1971 - A new synergy between nature and the workplace.

Source: Wikipedia

Figure 3.2.2.2: View form internal atrium (left). Figure 3.2.2.3: Window opening at the peripheral voids. Source: Wikipedia

Figure 3.2.2.4: 30 Saint Mary Axe, London.

Source: Wikipedia

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applied. Figure 3.2.2.3 portrays how windows are opened through the building’s façade. The mechanism is controlled by a mix-mode approach and is limited by a 5°C outdoor temperature in winter and an internal temperature of 24°C or 26°C (depending on the building management) in summer. It is predicted that natural ventilation goes from 40% to 75% of the year depending on external climate’s conditions (Soares Gonçalves, 2010).

Environmental consultancy predicted energy savings between 30 and 50 kW/m2/yr compared to the figure for a similar good-practice mechanically-cooled building in London, which is 250 kW/m2/yr (Foster and Partners, 1998). However, actual performance relies on occupation patterns and how windows are operated.

30 Saint Mary Axe constitutes one of the main tall buildings of the City of London’s financial district, and was the first environmentally responsive tall building of the new generation to be built in the cluster, boosting the next ones to follow its example.

Figure 3.2.2.5: Section of The Gherkin. Source: Archdaily

Figure 3.2.2.6: Passive strategies, 30 St. Mary Axe. Source: Wikipedia

Figure 3.2.2.7: Natural ventilation, 30 St. May Axe. Source: Archdaily

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CHAPTER 3: CONTEXT AND PRECEDENTS

3.2.3 THE HERON TOWER Located in London, 110 Bishopsgate building or Heron Tower, was designed by Kohn Pedersen Fox Architects and built in 2011. This building consists of a rectangular building form segmented in eleven villages of three floors each. Its floor plate has a u-shape with a central, North-facing atrium that optimises daylight from diffuse radiation, visual communication and views out of the city. The core and building services are placed on the South, blocking direct radiation and high-altitude suns, while allowing services to be day lit and ventilated (figure 3.2.3.4).

Its design brief included flexible layouts, good daylight, visual communication and energy efficiency. In this respect, the building achieved a reduction of between 25% and 30% in energy consumption by a mix-mode approach, compared to local good practice references (Soares Gonรงalves, 2010).

The atrium, which is three storeys high, is sealed and was designed exclusively for daylight and views, not contributing to natural ventilation. However, the East and West facades include a double skin with ventilated cavities each three floors. Besides providing natural ventilation, the double-skin manages heat losses and solar radiation by internal blinds, which moderate the surface temperatures across the glass envelope (see figure 3.2.3.6). The building is controlled by a mix-mode strategy so, when conditions are not appropriate for natural ventilation, windows are closed and the building is cooled by artificial means.

The Heron Tower is, together with The Gherkin, part of the cluster of office towers of the business district in the City of London, representing the new environmental design criteria approach, which produces buildings with high quality and low carbon footprint.

Figure 3.2.3.1: View from the void, Heron Tower in London.

Source: KPF

Figure 3.2.3.2: Heron Tower in London. Source: Flickr Figure 3.2.3.3: North-facing atrium. Source: The Architects' Journal

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Figure 3.2.3.5: 110 Bishopsgate. Source: Flickr

Figure 3.2.3.4: Plan and section of the building. Source: Wikipedia

Figure 3.2.3.6: Double-Skin strategy foe East and West facades. Source: KPF

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CHAPTER 3: CONTEXT AND PRECEDENTS

3.2.4 AREA COMPARISON STUDY

Figure 3.2.4.1 shows an evaluation of the Commerzbank Headquarters’ spatial efficiency in terms of gross-to-net area ratio. The study presents the Commerzbank as the building with highest void-to-floor area ratio, reaching almost to 26% of the total. Although office area is reduced from 35% to 49% by the inclusion of the voids, the gardens and communal areas have been proven to boost the environmental quality of the project, reducing carbon emissions and due to its energy savings, its operational costs are less compared to the conventional “glass box” building. In fact, these spaces have been known to be used as working environments, therefore contributing to the net area, gaining a 7% back, and increasing the overall net-to-gross ratio to 54% (a difference of 21% with the no void scenario).

40

Figure 3.2.4.2 shows an evaluation of the 30 St. Mary Axe’s spatial efficiency in terms of gross-to-net area ratio. The building presents a net-to-gross area ratio of 70% (by deduction of the core), and with the voids he net area is only reduced by 15%. If the area of the first floor of the voids is accounted as usable space, 3% is gained back, increasing the net-to-gross ratio to 63% and adding the possibility of introducing passive strategies to the building, enhancing its performance with minimized energy consumption. Overall, the void-to-floor area ratio is 9.55%.

Figure 3.2.4.3 shows an evaluation of the 110 Bishopsgate’s spatial efficiency in terms of gross-to-net area ratio. The Heron Tower has the greater ratio, the void accounts a reduction in net area of just 11% compared to a full usable floor plate, and 3% is gained back if voids are taken into account. This building has the lower void-to-floor area ratio and it may be due to the fact that it was not designed to contribute and work for natural ventilation, but for daylight penetration only. Overall, the void-to-floor area ratio is 8%.

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CHAPTER 3: CONTEXT AND PRECEDENTS

3.3 RESEARCH QUESTIONS Based on the literature review and precedents study, this thesis will explore upon the contribution that the addition of voids represent in the overall performance of tall buildings, as a useful tool to enhance environmental performance. It will strive to achieve a quantification of the increment in performance that this strategy brings, by comparing a building with voids to a scenario where the voids were not included, taking as a reference the buildings from the case studies.

Moreover, what are the changes they bring to these type of buildings? Are they an adequate strategy for London?

Improvements will be measured in terms of daylight, thermal performance and natural ventilation in the que to answer if these type of buildings can sincerely be called sustainable.

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44

CHAPTER 4 ANALYTICAL WORK

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CHAPTER 4: ANALYTICAL WORK

4.1 CASE STUDIES EVALUATION 4.1.1 METHODOLOGY AND INPUTS The case studies analysis consists of: First, dynamic thermal simulations using ESDL TAS to test three different building forms with three diverse void strategies against thermal performance and annual loads. The Commerzbank Headquarters, The Gherkin and the Heron Tower were taken as a reference to perform a comparison study between each of the mentioned buildings with a same version of the plan without voids (completely occupied floorplate). In this sense, the original building form, proportions and void strategy were taken into account, yet with some simplifications. As the aim of the study was not to quantify the actual performance of these buildings, but only the contribution of the voids to enhance environmental performance, the three cases were considered as if they had the same height of 60 storeys and same standard materials and conditions, taken from common practice. They were also thought to have equal floor-to-ceiling height and a good performing glazed façade, thus, a low u-value. Although they are originally situated in different locations, they were all tested in London without any surrounding urban fabric, to generate a theoretical scenario and avoid context’s external influence upon the buildings’ performance.

Figure 4.1.1.1 illustrates the buildings’ models, table 4.1.1.2 presents the inputs, conditions and constructions for the simulations and figure 4.1.1.3 display the buildings’ general characteristics. The middle

floor of the middle village of each building was tested, as shown in the previous figure, to obtain a representative case, which will indicate the average performance of the building. As one of the main functions of the void is to provide a semi-external zone, which will be more open to the outside, a second glazed façade was introduced between the void and the office spaces. By doing so, they create an enclosed buffer zone to provide the offices with more controlled temperatures and wind speeds for natural ventilation.

Both facades were provided with apertures that are controlled by internal and external temperatures (see aperture types in TAS inputs, figure 4.1.1.2).

Two different simulations were conducted for each scenario: a free-running mode alternative by which frequencies within and out of comfort were studied; and a mechanically ventilated option to evaluate cooling loads. For the free-running scenario, frequencies were measured as per the class 2 EN 15251:2007 Adaptive Comfort Model. Table 4.1.1.5 highlights the minimum and maximum temperatures that were contemplated. A different temperature was acknowledged for the voids, as they are not meant to be comfortable throughout all the year, but aid to provide comfortable temperatures to the workspaces, making them seasonally appropriate.

Furthermore, to have a deeper understanding of the buildings’ performance under diverse conditions, the results for a hot summer day and a cold winter day for

Figure 4.1.1.1: TAS models for the three buildings.

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CHAPTER 4: ANALYTICAL WORK

INPUTS FOR TAS SIMULATIONS FOR CASE STUDIES AND GENERIC STUDY *Occupancy and Internal Conditions are assumed to be only on weekdays

operable area

APERTURE TYPES Summer - Void Façade Summer - Void Internal Façade Summer - Office Façade Summer Weekends Mid Season - Void Façade Mid Season - Void Internal Façade Mid Season - Office Façade

0.2 0.5 0.1 0.2 0.1 0.5 0.08

Winter - Void Façade Winter - Void Internal Façade Winter - Office Façade Winter Weekends FEATURE SHADING

0.08 0.5 0.05 0.1 1

SCHEDULE Occupancy Occupancy Occupancy Summer Night Time Vent Occupancy Occupancy Mid Season Ventilation

FREE RUNING MODE BUILDING ZONE T° CONTROL EXTERNAL T° CONTROL T - C - R aperture starts to open when T-R: starts at 12°, fully open at 14° / C: starts at 16°, fully open at 18° adjacent zone exceeds 18°C T-R: starts at 14°, fully open at 16° / C: starts at 16°, fully open at 18° Weekday T-C-R and fully opens at 20°C T-R: starts at 14°, fully open at 18° T-R T C R Weekends T-C-R T-R-C: starts at 12°, fully open at 14° Weekday T-C-R T-R: starts at 10°, fully open at 12° / C: starts at 8°, fully open at 10° T-R aperture starts to open when T: starts at 10°, fully open at 14° / R: starts at 10°, fully open at 12° adjacent zone exceeds 18°C T: starts at 14°, fully open at 18° / R: starts at 10°, fully open at 12° / C: starts at 6°, fully open at T-C-R and fully opens at 20°C 12° Weekday T-C-R T-C: starts at 4°, fully open at 8° / R: starts at 6°, fully open at 8° T: starts at 14°, fully open at 18° / R: starts at 12°, fully open at 14° T-R Weekends T-C-R Summer - Summer Wknds T-C-R DAY TYPE

Occupancy Occupancy Winter Midday Ventilation Winter Night Time Vent Morning and Afternoon Shading *Buildings T: triangle form, 12 storey high void - C: circular form, 6 storey high void - R: rectangular form, 3 storey high void

MECHANICALLY VENTILATED MODE DAY TYPE (⁰C) Upper Limit Voids 27/26 COOLING Winter and Mid Season Upper Limit Offices 26/24 Set back 150 Upper Limit Voids 18.8 Summer and Mid Season HEATING Upper Limit Offices 20.8 Set back 5 *For Free Running Mode, Thermostat were set at: Upper Limit: 150⁰C and Lower Limit: -50⁰C. THERMOSTAT

CONSTRUCTIONS LAYERS

BUILDING ELEMENT

Concrete block, medium density Air cavity

EXTERNAL WALL

PUR Plasterboard

INTERNAL WALL (CORE)

Plaster

25

Clincker Concrete Block

75

Air cavity

50

Clincker Concrete Block

75 25 20 100 20 20 280 60 300 300 30

Plaster Lightweight Plaster

INTERNAL WALL (PARTITIONS)

Foamed Slag Concrete Part. Block Lightweight Plaster Carpet Air cavity

INTERNAL FLOOR -

INTERNAL CEILING

THICKNESS (mm) 150 25 75 20

Concrete Screed Concrete Air cavity Concrete Tiles Metalic Frame, no thermal break, aluminium spacer

WINDOW FRAME

Coated Poly

GLAZING - FAÇADE

Argon Cavity Low-E Glass Opitherm

GLAZING - VOID INTERNAL FACADE

Argon Cavity Clear Float

U-Value (W/m²·K) 0.289

1.231

0.924

DAYS SUMMER 115 to 292

MID SEASON 67 to 114 295 to 313

WINTER 1 to 66 316 to 365

different hours of the day were plotted upon the buildings’ plan and section. Conditions of the referenced days are expressed in table 4.1.1.6.

On the other hand, for the mechanically ventilated case, set points for active cooling and heating were adopted from general practice: 26°C and 24°C for cooling (to test the difference between more tolerable occupants and the usual practice) and 21°C for heating. The purpose of these simulations is not to state realistic loads, but to compare scenarios, hence, looking at results in terms of percentages of improvements rather than numbers.

Furthermore, the same feature shading input was implemented in all windows of the three buildings to try to replicate their adjustable shading devices, as most of them have internal blinds within its double-skin façade.

Lastly, the study will evaluate daylight performance of the buildings and its improvement compared to a novoid scenario, by means of UDI (useful daylight illuminance) simulations using Rhino, Grasshopper and DIVA software. For these simulations, the range within 300 lux to 2000 lux was adopted since the optimum levels for workspaces are between 300 to 500 lux, and more than 2000 lux results in glare discomfort. External windows were considered to have a transmittance of 0.6 and the void’s internal windows of 0.85.

For distinction of the different areas of each building’s plan, which are named after their orientation, see figure 4.1.1.4.

Overall, the study aimed to look, compare and analyse changes in thermal, daylight, ventilation performance, and changes in heat gains and losses attributed to the inclusion of a void strategy.

0.499

2.308 6 12 6 6 12 6

U-VALUE: 1.210 G-VALUE: 0.300 U-VALUE: 1.974 G-VALUE: 0.638

SCHEDULES Occupancy Lighting Equipment

9 to 18 9 to 10, 15 to 18 9 to 18

Winter Midday Ventilation Summer Night Time Ventilation Winter Night Time Ventilation Morning and Afternoon Shading Mid Season Ventilation

12 to 14 21 to 9 6 to 20 10 to 12, 13 to 16 13 to 16

Figure 4.1.1.2: TAS inputs, conditions and constructions.

Figure 4.1.1.3: TAS inputs, conditions and constructions.

Figure 4.1.1.4: Wind rose for orientation reference. Source: Meteoblue

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CHAPTER 4: ANALYTICAL WORK

UNIVERSITY OF WESTMINSTER 48

Adaptive Comfort EN 15251:2007

Ta (°C)

OFFICES

MONTH

VOIDS

mean max

mean average

mean min

Class II

neutral

Class II

max

min (-2)

Jul

21.32

17.40

13.03

27.54

24.54

21.54

27.54

19.54

Dec

8.18

5.18

2.65

23.51

20.51

20.80

23.51

18.80

Figure 4.1.1.5: London’s climatic conditions for July and December and class 2 EN 15251:2007 Adaptive Comfort Model. Source: Meteonorm 6.1

m

dm

dy

h

Ta

RH

1-12

1-31

1-365

1-24

°C

%

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

0 0.1 0.4 0.6 0.7 0.8 0.9 1 1.1 1.7 2.2 2.5 2.7 2.7 2.6 2.4 2 2.3 2.7 2.9 3.7 4 4 3.7

COLD WINTER DAY 89 92 91 93 90 98 95 97 95 93 92 93 89 93 92 95 94 93 91 91 87 85 88 94

m

dm

dy

h

Ta

RH

1-12 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6

1-31 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19

1-365 170 170 170 170 170 170 170 170 170 170 170 170 170 170 170 170 170 170 170 170 170 170 170 170

1-24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

°C 12.6 11.9 11.5 11.4 11.8 12.2 13 13.9 15.5 16.9 17.6 18.2 18 18.1 18.2 18.6 18.6 18.5 18.1 17.5 16.7 15.5 14.3 13.1

% 89 91 96 96 97 90 86 79 73 67 60 53 53 54 54 51 52 55 56 60 64 71 74 76

Td

Tp

°C -1.5 -1.1 -0.8 -0.4 -0.7 0.6 0.2 0.6 0.4 0.6 1 1.4 1.2 1.7 1.5 1.7 1.1 1.4 1.4 1.6 1.7 1.8 2.2 2.8

°C -0.6 -0.4 -0.1 0.2 0.1 0.6 0.6 0.8 0.8 1.2 1.7 2 2 2.2 2.1 2 1.6 1.8 2.1 2.3 2.8 3 3.2 3.2

DD G_Gh N RR degrees CW Wh/m2 oktas mm m/s 3.7 244 0 6 0 4.5 174 0 6 0.8 3.7 52 0 6 0.2 2.8 186 0 7 0 4.5 240 0 7 0.2 4 133 0 7 0 4.7 190 0 7 0.1 3.5 136 0 7 0 3 277 2 8 0.4 2.6 235 13 8 0 2.2 220 23 8 0 2.1 245 26 8 0.1 1.9 257 28 8 0.1 2.7 264 23 8 0.5 2.5 214 15 8 0.3 2.6 228 5 8 0.1 3.5 236 0 8 0.9 4.2 236 0 8 1.2 4.2 118 0 8 1.5 2.7 162 0 8 2 4 209 0 8 0.3 4.2 194 0 8 0.6 3.7 170 0 8 3 4 213 0 8 6.2

HOT SUMMER DAY Td

Tp

°C 10.9 10.5 10.8 10.8 11.2 10.6 10.6 10.4 10.8 10.7 9.6 8.6 8.2 8.8 8.9 8.3 8.5 9.3 9.1 9.6 9.8 10.2 9.8 8.9

°C 11.6 11.1 11.1 11 11.4 11.2 11.6 11.8 12.7 13.2 13 12.7 12.5 12.8 12.9 12.8 12.9 13.2 13 12.9 12.7 12.4 11.7 10.8

KEY

FF

FF

DD G_Gh N degrees CW Wh/m2 oktas m/s 5.7 274 0 8 5 242 0 8 6.7 237 0 8 5.7 245 0 8 4 242 23 8 3.8 214 53 8 3.5 240 128 8 3.7 249 206 8 3 178 388 7 2.8 249 438 7 2.8 272 349 8 3.8 246 384 8 3.2 319 173 8 1.6 310 275 8 1.9 306 275 8 3 296 387 7 3.5 300 259 8 4.7 280 228 7 4 282 124 5 3.2 318 61 5 3 319 0 6 2.6 294 0 6 3.5 329 0 6 2.6 265 0 6

RR mm 0 0.7 0 0 0 0 0 0.1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Ts

hs

Az

°C degrees degrees -1.6 0 -168.1 -1.3 0 -142.1 -1.2 0 -121.5 -1.4 0 -106.1 -0.7 0 -93.2 -0.7 0 -81.5 -0.4 0 -70.5 -0.7 0 -59.5 0 2.3 -48.1 0 8.6 -35.5 0 13.2 -22.3 0 15.8 -8.3 0 16 5.5 2.3 13.9 20 2.2 9.6 33.3 1.9 3.6 46 0.2 0 57.4 0.8 0 68.5 1.2 0 79.5 0.9 0 91.1 2.1 0 103.4 2.5 0 118.4 2.3 0 138 2.1 0 163.1

Ts

hs

m dm dy h Ta RH mx Td Tp FF DD

Month (1-12) Day of month (1-31) Day of year (1-365) Hour (1-24) Temperature (°C) Relative humidity (%) Mixing ratio (g/kg) Dew point temperature (°C) Wet bulb temperature (°C) Wind speed (m/s) Wind direction (degrees CW)

G_Gh Global radiation horizontal (Wh/m2) G_Bh Direct radiation horizontal (Wh/m2) G_Dh N RR Ts hs Az Sd Lg Ld

Diffuse radiation horizontal (Wh/m2) Cloud cover fraction (oktas) Precipitation (mm) Surface temperature (°C) Height of sun (degrees) Solar azimuth (degrees) Sunshine duration (h) Global illuminance (lux) Diffuse illuminance (lux)

Az

°C degrees degrees 11.5 0 -173.2 10.6 0 -159.2 10.6 0 -145.6 10.3 0 -133.3 11.5 4.9 -121.6 12.1 13.3 -110.6 13.6 22.4 -100 15.2 31.7 -88.4 18.6 41 -76 20.5 49.8 -60.5 20.3 57.1 -41.1 21 61.6 -15.2 19 61.7 13.5 20.4 57.4 39.5 20.4 50.2 59.5 21.6 41.5 75.2 20.4 32.2 88 19.9 22.9 99.3 18.6 13.8 110.2 17.5 5.3 121.2 16.2 0 132.5 13.5 0 145.2 12.6 0 158.3 11 0 172.3

Figure 4.1.1.6: Conditions for the typical days to analyse hourly plots. Source: Meteonorm 6.1

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CHAPTER 4: ANALYTICAL WORK

4.1.2 TWELVE STOREY VOID CASE This study refers to The Commerzbank Headquarters building, and figure 4.1.2.2 summarize the scenarios planned to evaluate this void and its ventilation strategies. As illustrated, the no void scenario was tested against three different layout alternatives: first as an open plan without internal partitions, then taking the same cellular layout as the void scenario, and the last one partitioning the plan in two (adding partitions were the void used to be). Figure 4.1.2.1, presents the division of zones and figure 4.1.2.3 set the conditions and zone characteristics for these cases.

Figure 4.1.2.1: Division of TAS zones for the 12 storey void case.

Figure 4.1.2.2: scenarios to be tested for the 12 storey void case.

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TRIANGLE - 12 STOREY VOID

*For the No Void Scenario, the same zones were all considered as offices.

EXTERNAL OFFICES

INTERNAL OFFICES ZONE CHARACTERISTICS Height area volume

2.7m 344.542m² 930.264m³

ZONE CHARACTERISTICS Height area volume

2.7m 210.149m² 567.403m³

INTERNAL CONDITIONS N. people 28 aprox 6.7 W/m² Occupancy Equipment 15 W/m² Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Light Work Ventilation (Mech. Vent. mode) 0.87 ach *Internal Gains are calculated as per CIBSE Guide

INTERNAL CONDITIONS N. people 17 aprox 6.7 W/m² Occupancy Equipment 15 W/m² Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Light Work Ventilation (Mech. Vent. mode) 0.86 ach *Internal Gains are calculated as per CIBSE Guide

**In Weekends, the zone is unnocpied and unconditioned

**In Weekends, the zone is unnocpied and unconditioned CORRIDOR

VOID 4 ST. - 1ST FLOOR ZONE CHARACTERISTICS Height area volume INTERNAL CONDITIONS N. people Occupancy Equipment

2.7m 423.069m² 1311.513m³, total: 5,246.052m³

11 aprox 6.7 W/m² 15 W/m²

Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Walking, Sitting, Light Work Ventilation (Mech. Vent. mode) 0.24 ach *Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unnocpied and unconditioned

ZONE CHARACTERISTICS Height area volume INTERNAL CONDITIONS N. people Occupancy Equipment

2.7m 253.224m² 683.704m³

10 aprox 2.36 W/m² 5 W/m²

Lighting 15 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Walking Ventilation (Mech. Vent. mode) 0.42 ach *Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unnocpied and unconditioned

Figure 4.1.2.3: TAS zones’ conditions and characteristics.

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CHAPTER 4: ANALYTICAL WORK

TAS RESULTS – HOURLY PLOTS Figure 4.1.2.4 displays TAS simulation resultant temperature outcomes at 11 am for all different scenarios on a cold winter day and a hot summer day: day 5 and 170, respectively.

For the partly cellularized plan (4.1.2.4 and 4.1.2.5), results portray no sign of ventilation either for the deepest part of plan, recording higher temperatures than the rest of the zones.

In the case of the open-plan non-void case, the greater difference between both plans is shown in the “Void 12” zone, recording a gap of around 3°C in summer and 6°C in winter. While this zone’s temperature in the non-void plan is almost reaching the outdoor temperature in summer, in the void scenario it shows one of the coolest (24.1°C) even though it is in the deepest area of the plan, evidencing a good ventilation strategy. In the cold day, both void zones act as buffers in the void scenario (although they display temperatures closer to the external one), while in the other scenario the respective zones record higher temperatures due to elevated internal gains and lack of ventilation. In fact, the nonvoid building presents temperatures that are mostly within comfort in summer, this may be because of internal gains being distributed across the entire plan and through an overall larger volume of air. In winter, due to less façade-to-floor ratio, heat gains are accumulated and elevate temperatures above 23.5°C, the adaptive comfort model limit for the January.

Regarding external offices, the “ESE offices” register around 1°C higher than the “NNW offices” due to solar gains. At 3 pm (see figure 4.1.2.5), this difference still shows probably as a result of internal and solar gains combined with thermal mass. Solar gains also raise temperatures at the voids in the void scenario in summer at 3 pm, increasing the “internal offices” temperatures as well, but managing to stay 5°C lower than the outdoor temperature. It also keeps temperatures in all zones that they serve within comfortable conditions, provided they can be ventilated throughout the entire year. Considering occupants to be more tolerable towards temperatures in the usable void (Void 4), the range within comfort could be widened to 18.8°C, thus, achieving comfort even in a cold day.

In case of the cellular non-void plan, shown in figures 4.1.2.4 and 4.1.2.5, the lack of ventilation is evident in the internal zones, reaching very high temperatures for both days, and recording a difference of 10°C between “internal offices” and outdoors. This scenario would probably need mechanical ventilation throughout all year for almost all zones.

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CHAPTER 4: ANALYTICAL WORK

NO VOID SCENARIO

CELLULAR PLAN PARTLY CELLULARIZED

DAY 5 AND 170 AT 11 AM

OPEN PLAN

VOID SCENARIO

Figure 4.1.2.4: TAS outcomes for resultant temperatures at 11 am for a cold and a hot day for all scenarios.

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CHAPTER 4: ANALYTICAL WORK

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CHAPTER 4: ANALYTICAL WORK

NO VOID SCENARIO

CELLULAR PLAN PARTLY CELLULARIZED

DAY 5 AND 170 AT 3 PM

OPEN PLAN

VOID SCENARIO

Figure 4.1.2.5: TAS outcomes for resultant temperatures at 3 pm for a cold and a hot day for all scenarios.

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CHAPTER 4: ANALYTICAL WORK

UNIVERSITY OF WESTMINSTER 56

WITHIN COMFORT 20.8-27.5 TAS RESULTS – FREQUENCIES AND COOLING LOADS Figure 4.1.2.7 displays overheating and hours within and below comfort for the void scenario against the openplan non-void scene. The void scenario achieves between 18% and 7% more hours within comfort, achieving the “internal offices” zone the higher percentage. In addition, although the non-void scenario records lower rates for below comfort in most of the zones, the opposite happens for overheating hours.

Besides, the difference in “below comfort” does not exceed 5% overall. Moreover, it is interesting to see that “internal offices” records a similar percentage of around 24% for this category in both scenarios, highlighting the buffer capacity of the voids to minimise heat losses in winter. Furthermore, the void scenario achieves 80% of hours within comfort in “internal offices”, decreasing overheating hours by almost 20% in internal zones.

When looking at cooling loads, it can be said that while loads for the “external offices” and “corridor” are lower in the non-void scenario because they are within the “passive zone” of the building, the situation is reversed for the inner zones. Besides, actual occupancy patterns have combined these two zones in some of the floors in the original building, and this would reduce loads for both zones, coming closer to the numbers for the nonvoid case. Regarding “internal offices”, loads were reduced by 30%, and for the “void 12” zone by 70% (see figure 4.1.2.6). For a set point of 24°C, loads were increased by more than 3 times for “internal offices”.

On the contrary, it does not increase loads for the void zones.

COOLING LOADS kWh/m2 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF

VOID 12.3

VOID 4.1

NO VOID

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF

VOID 12

VOID 4

VOID 12

VOID 4

VOID 12

VOID 4

NO VOID

BELOW COMFORT <20.8 40% 35% 30% 25% 20% 15% 10% 5% 0%

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF NO VOID

OVERHEATING >27.5 20% 18% 16% 14% 12% 10% 8% 6% 4% 2% 0%

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF NO VOID

Figure 4.1.2.7: Frequencies for void and non-void open plan scenario.

COOLING LOADS kWh/m2 10.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00

CORRIDOR

EXT OFF ESE EXT OFF NNW VOID

INT OFF

VOID 12.3

VOID 4.1

NO VOID

Figure 4.1.2.6: Cooling loads for void and non-void open plan scenario, a set point at 26°C (up) and 24°C (down).

UNIVERSITY OF WESTMINSTER 57

CHAPTER 4: ANALYTICAL WORK

WITHIN COMFORT 20.8-27.5 Figure 4.1.2.9 illustrates frequencies for the void scenario against the non-void cellular plan. As seen on the hourly profile, zones which are in the core of the plan and do not get any contact with outdoor conditions, are almost no time within comfort. They are most of the time overheating, not being able to cope with their high internal gains. “Corridor”, “internal offices” and “void 12” zones are between 90% and 95% of the time overeating, while for the void scenario the percentages are negligible for all zones.

Figure 4.1.2.8 shows cooling loads for the mentioned setting points. While there are hardly any loads for the void scenario at a set point of 26°C, for the non-void scenario, these figures are increased by almost 20 times. Comparing loads for both set points, loads are raised by 3.7 times for the void scenario, but only 1.4 times for the other one.

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF

VOID 12

VOID 4

VOID 12

VOID 4

VOID 12

VOID 4

NO VOID

BELOW COMFORT <20.8 40% 35% 30% 25% 20% 15% 10% 5% 0%

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF NO VOID

OVERHEATING >27.5 COOLING LOADS kWh/m2 25.00 20.00 15.00 10.00 5.00 0.00

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF

VOID 12.3

VOID 4.1

NO VOID

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF NO VOID

Figure 4.1.2.9: Frequencies for void and non-void open plan scenario.

COOLING LOADS kWh/m2 30.00 25.00 20.00 15.00 10.00 5.00 0.00

CORRIDOR

EXT OFF ESE EXT OFF NNW VOID

INT OFF

VOID 12.3

VOID 4.1

NO VOID

Figure 4.1.2.8: Cooling loads for void and non-void open plan scenario, a set point at 26°C (up) and 24°C (down).

58

WITHIN COMFORT 20.8-27.5 In the case of the partly cellularized plan, although the “external offices”, “corridor” and “void 4” zones get comparable percentages for hours within comfort, between 60% and 80%, a difference of 15% can be seen in “internal offices”. Even a greater one for the “void 12” zone, achieving the void scenario almost 40% more than the other does (see figure 4.1.2.11). The deepest part of the plan shows more than 75% overheating hours for the non-void scenario, while in the void scenario, there are hardly any hours above 27.5°C. Figure 4.1.2.10 displays cooling loads, and the greater difference is reflected in the inner zones of the non-void scenario, recording 6.5 times more loads than the rest of the zones for both cases. Moreover, setting a cooling set point of 24°C would raise the number by 2.85 times compared to a set point of 26°C.

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF

VOID 12

VOID 4

VOID 12

VOID 4

VOID 12

VOID 4

NO VOID

BELOW COMFORT <20.8 40% 35% 30% 25% 20% 15% 10% 5% 0%

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF NO VOID

OVERHEATING >27.5 80%

COOLING LOADS kWh/m2

70%

14.00

60%

12.00

50%

10.00

40%

8.00

30%

6.00 4.00

20%

2.00

10%

0.00

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF

VOID 12.3

VOID 4.1

NO VOID

0%

CORRIDOR EXT OFF ESE

EXT OFF NNW VOID

INT OFF NO VOID

Figure 4.1.2.11: Frequencies for void and non-void open plan scenario.

COOLING LOADS kWh/m2 25.00 20.00 15.00 10.00 5.00 0.00

CORRIDOR

EXT OFF ESE EXT OFF NNW VOID

INT OFF

VOID 12.3

VOID 4.1

NO VOID

Figure 4.1.2.10: Cooling loads for void and non-void open plan scenario, a set point at 26°C (up) and 24°C (down).

UNIVERSITY OF WESTMINSTER 59

CHAPTER 4: ANALYTICAL WORK

UDI RESULTS UDI results for both scenarios (see figure 4.1.2.12), show a noticeable difference for the triangular shape building form. The inclusion of voids to this building achieves an improvement of 35% in daylight access compared to the non-void scenario. Looking at the void case’s simulation outcomes, 62% of the plan achieves illuminance levels within the range by 45% of the time, and in the non-void case, only 28% does.

NO VOID SCENARIO – OPEN PLAN

VOID SCENARIO

Figure 4.1.2.12: UDI simulation results for within the range between 300 to 2000 lux for the non-void open plan case (up) and void case (down).

External windows’ transmittance was set to 0.6, and for internal windows to 0.85

60

Figure 4.1.2.13: Diagram of the studied village in the void scenario.

UNIVERSITY OF WESTMINSTER 61

CHAPTER 4: ANALYTICAL WORK

4.1.3 SIX STOREY VOID CASE Figure 4.1.3.2 summarize the scenarios planned to evaluate this void strategy and figures 4.1.3.1 and 4.1.3.3 illustrate the zone division and their internal conditions for TAS simulations, respectively.

Figure 4.1.3.1: Division of TAS zones for the 6 storey void case.

Figure 4.1.3.2: scenarios to be tested for the 6 storey void case.

62

CIRCLE - 6 STOREY VOID

*For the No Void Scenario, the same zones were all considered as offices.

OFFICES ZONE CHARACTERISTICS Height area volume

2.7m 220.542m² 595.464m³

INTERNAL CONDITIONS N. people 18 aprox 6.7 W/m² Occupancy Equipment 15 W/m² Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Light Work Ventilation (Mech. Vent. mode) 0.87 ach *Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unnocpied and unconditioned

VOID - 1ST FLOOR ZONE CHARACTERISTICS Height

2.7m 34.928m²

area

108.275m³, total: 649.65m³

volume INTERNAL CONDITIONS N. people

3 aprox

Occupancy Equipment

6.7 W/m²

Lighting

10 W/m²

15 W/m²

Infiltration

0.3

Minimum Fresh Air Activity Ventilation (Mech. Vent. mode)

8 L/s pp Walking, Sitting, Light Work 0.80 ach

*Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unnocpied and unconditioned Figure 4.1.3.3: TAS zones’ conditions and characteristics.

UNIVERSITY OF WESTMINSTER 63

CHAPTER 4: ANALYTICAL WORK

DAY 5 AND 170 AT 11 AM TAS RESULTS – HOURLY PLOTS Figure 4.1.3.4 plots resultant temperatures for 11 am for the same selected days as the 12 storey void case. Results show that for the void scenario in summer, temperature in the voids is higher than in the offices but lower than the external temperature, evidencing that they act as buffers mediating the external conditions. The office spaces achieve similar temperatures, and this could be due to effective cross ventilation. In winter, they also help provide a better microclimate for the offices, maintaining them in comfortable conditions and reducing heat losses.

Temperature in the different levels of the void show evidence of some stratification, this could mean that stack effect may be combined with cross ventilation, enhancing the performance of the building’s ventilation strategy. Overall, there is a delta T of 1°C in the voids and a 2°C difference between indoor and outdoor temperature for the offices in summer, and almost a 2°C difference in winter.

In the non-void scenario, the offices that have an operable façade (corresponding to the zones where there were voids in the previous case) record more than 1°C above the external temperature. The rest of the offices are also warmer than outdoors, evidencing that ventilation may not be enough to provide cooling.

Temperature differences between both scenarios’ corresponding zones are even more noticeable at 3 pm, when the external temperature is higher; especially in South-West oriented zones due to solar gains and lack of ventilation in the non-void scenario (see figure 4.1.3.5).

NO VOID SCENARIO

VOID SCENARIO

Figure 4.1.3.4: TAS outcomes for resultant temperatures at 11 am for a cold and a hot day for both scenarios.

64

DAY 5 AND 170 AT 3 PM NO VOID SCENARIO

VOID SCENARIO

Figure 4.1.3.5: TAS outcomes for resultant temperatures at 3 pm for a cold and a hot day for both scenarios.

UNIVERSITY OF WESTMINSTER 65

CHAPTER 4: ANALYTICAL WORK

WITHIN COMFORT 20.8-27.5 TAS RESULTS – FREQUENCIES AND COOLING LOADS When comparing the different scenarios against frequencies (figure 4.1.3.7), the non-void situation shows more comfortable temperatures in winter than the other case, as a result of high internal gains trapped inside the rooms. This heats up the space and makes the zone record even high temperatures in cold weather.

However, the void plot presents between 70% and 82% of hours within comfort for the offices. What’s more, the non-void scenario has almost more than 20% of overheating hours while the voids succeed in lowering the temperatures to have less than 3% of hours above 27.5°C. Figure 4.1.3.6 illustrates cooling loads for both scenarios. The greater difference between both cases is reflected in the void zones. The void scenario records almost 5.6 times less energy required for cooling for these zones than the other does. Concerning offices, the non-void workspaces document 1.6 times more than the other ones. On the other hand, cooling loads grow around 2.7 times when the setting point is lowered by 2°C.

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

VOID VOID VOID VOID VOID VOID OFF OFF SW WNW NNW NE ESE SSE WSW NW VOID

NO VOID

VOID VOID VOID VOID VOID VOID OFF OFF SW WNW NNW NE ESE SSE WSW NW

OFF NNE

OFF OFF SE OFF SSW ENE

OFF NNE

OFF OFF SE OFF ENE SSW

NO VOID

OVERHEATING >27.5

COOLING LOADS kWh/m2 COOLING LOADS kWh/m2

14%

5.00 4.00

12%

3.50

10%

4.00

3.00

8%

2.50 3.00

6%

2.00

2.00 1.50

4%

1.00 1.00

2%

0.50

0.00 0.00

OFF OFF SE OFF ENE SSW

BELOW COMFORT <20.8 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0%

VOID

6.00

OFF NNE

CORRIDOR EXT OFF ESE VOID EXT OFF INT OFF VOID VOID VOID VOID VOID OFF OFF SW WNW NNW NE ESENNWSSE WSW NW VOID

VOID

VOID VOID OFF 12.3 OFF OFF SE4.1OFF

NNE

ENE

SSW

NO VOID

NO VOID

0%

VOID VOID VOID VOID VOID VOID OFF OFF SW WNW NNW NE ESE SSE WSW NW VOID

NO VOID

Figure 4.1.3.7: Frequencies for void and non-void scenario.

COOLING LOADS kWh/m2 12.00 10.00 8.00 6.00 4.00 2.00 0.00

VOID VOID VOID VOID VOID VOID OFF OFF SW WNW NNW NE ESE SSE WSW NW VOID

OFF NNE

OFF OFF SE OFF ENE SSW

NO VOID

Figure 4.1.3.6: Cooling loads for void and non-void open plan scenario, a set point at 26°C (up) and 24°C (down).

66

UDI RESULTS As shown in figure 4.1.3.8, 77% of the void scenario’s plan is within the range almost half of the year, while in the other plan the percentage is 54. Therefore, voids reduce the need for artificial lighting by 23%.

NO VOID SCENARIO – OPEN PLAN

VOID SCENARIO

Figure 4.1.3.8: UDI simulation results for within the range between 300 to 2000 lux for the non-void case (up) and void case (down). External windows’ transmittance was set to 0.6, and for internal windows to 0.85

UNIVERSITY OF WESTMINSTER 67

CHAPTER 4: ANALYTICAL WORK

4.1.4 THREE STOREY VOID CASE Figure 4.1.4.2 summarize the scenarios planned to evaluate this void strategy, and figures 4.1.4.1 and 4.1.4.3 illustrate the zone division and their internal conditions for TAS simulations, respectively.

Figure 4.1.4.1: Division of TAS zones for the 3 storey void case.

Figure 4.1.4.2: scenarios to be tested for the 3 storey void case.

68

RECTANGLE - 3 STOREY VOID

*For the No Void Scenario, the same zones were all considered as offices.

MIDDLE OFFICES

NW - NE OFFICES ZONE CHARACTERISTICS Height area volume

2.7m 458.572m² 1238.144m³

INTERNAL CONDITIONS N. people 38 aprox 6.7 W/m² Occupancy Equipment 15 W/m² Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Light Work Ventilation (Mech. Vent. mode) 0.88 ach *Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unoccupied and unconditioned

ZONE CHARACTERISTICS Height area volume

2.7m 82.843m² 222.705m³

INTERNAL CONDITIONS N. people 7 aprox 6.7 W/m² Occupancy Equipment 15 W/m² Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Light Work Ventilation (Mech. Vent. mode) 0.91 ach *Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unoccupied and unconditioned VOID - 1ST FLOOR ZONE CHARACTERISTICS Height area volume INTERNAL CONDITIONS N. people Occupancy Equipment

2.7m 122.88m² 380.928m³, total: 1,142.784m³

10 aprox 6.7 W/m² 15 W/m²

Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Walking, Sitting, Light Work Ventilation (Mech. Vent. mode) 0.76 ach *Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unoccupied and unconditioned Figure 4.1.4.3: TAS zones’ conditions and characteristics.

UNIVERSITY OF WESTMINSTER 69

CHAPTER 4: ANALYTICAL WORK

DAY 5 AND 170 AT 11 AM TAS RESULTS – HOURLY PLOTS The resultant temperature obtained at 11 am and 3 pm for days 170 and 5 are displayed in figures 4.1.4.4 and 4.1.4.5 for the rectangular, threestorey void building form. It can be deduced from these images that although the void also acts as a buffer, it is more effective in mediating external conditions in the middle office rather than the ones facing the facades. In addition, the “N and E offices” get a higher temperature due to direct radiation. This could mean that the void is less effective in this case than it is when it is distributed across the floorplate, or when it takes higher proportions. It also may indicate that it is too deep, with a reduced façade-to-floor ratio compared to the previous examples.

Nevertheless, compared to the non-void scenario, the void does help to ventilate the offices, which in this case records almost 4°C more than the outdoor temperature in summer at 11 am. In winter, it performs similar than the other, increasing the indoor temperature due to internal gains.

NO VOID SCENARIO

VOID SCENARIO

Figure 4.1.4.4: TAS outcomes for resultant temperatures at 11 am for a cold and a hot day for both scenarios.

70

DAY 5 AND 170 AT 3 PM

NO VOID SCENARIO

VOID SCENARIO

Figure 4.1.4.5: TAS outcomes for resultant temperatures at 3 pm for a cold and a hot day for both scenarios.

UNIVERSITY OF WESTMINSTER 71

CHAPTER 4: ANALYTICAL WORK

WITHIN COMFORT 20.8-27.5 TAS RESULTS – FREQUENCIES AND COOLING LOADS In this case, the void scenario also achieves more hours within comfort, between 10% and 20% more than the other does, and although it accounts for almost 20% more hours below comfort overall, it decreases overheating hours by 30% in almost all spaces (see figure 4.1.4.7).

Regarding cooling loads (see figure 4.1.4.6), the void scenario reduces loads by 25% in almost all zones. A difference of 1.8 times in energy consumption can be observed when active cooling is set to 24°C.

80% 70% 60% 50% 40% 30% 20% 10% 0%

VOID 1

NE OFFICES VOID

NW OFFICES

MIDDLE OFFICES

NO VOID

BELOW COMFORT <20.8 30% 25% 20% 15% 10% 5% 0%

VOID 1

NE OFFICES VOID

MIDDLE OFFICES

NO VOID

OVERHEATING >27.5

COOLING LOADS kWh/m2 30%

10.00 9.00

25%

8.00 7.00

20%

6.00

15%

5.00 4.00

10%

3.00 2.00

5%

1.00 0.00

NW OFFICES

VOID 1

NE OFFICES VOID

NW OFFICES

MIDDLE OFFICES

NO VOID

0%

VOID 1

NE OFFICES VOID

NW OFFICES

MIDDLE OFFICES

NO VOID

Figure 4.1.4.7: Frequencies for void and non-void scenario.

COOLING LOADS kWh/m2 14.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00

VOID 1

NE OFFICES VOID

NW OFFICES

MIDDLE OFFICES

NO VOID

Figure 4.1.4.6: Cooling loads for void and non-void open plan scenario, a set point at 26°C (up) and 24°C (down).

72

UDI RESULTS 58% of the plan’s area achieves 300 lux 45% of occupancy time in the void scenario, reducing the need for artificial lighting by 8% compared to the non-void scenario (see figure 4.1.4.8). This void is the less successful in providing natural lighting to most of its area.

NO VOID SCENARIO

VOID SCENARIO

Figure 4.1.4.8: UDI simulation results for within the range between 300 to 2000 lux for the non-void case (up) and void case (down). External windows’ transmittance was set to 0.6, and for internal windows to 0.85

UNIVERSITY OF WESTMINSTER 73

CHAPTER 4: ANALYTICAL WORK

4.1.5 SUMMARY CHART COMPARISON non-void scenario.

The building with the highest cooling loads is the Heron Tower example, recording 57% more than the Commerzbank example, and 55% more than the Gherkin building. The reason behind it could be due to the ventilation strategy not being enough to cope with its high internal gains. It is also the building that shows the smallest difference between void and non-void scenario in terms of daylight (8%), since it has the littlest void area compared to the others.

Overall, there is not much difference between void and non-void scenarios with regards to thermal performance, recording less than a 15% difference in terms of hours within comfort. This may indicate that for a climate such as London, where the heating season is predominant and natural ventilation not that much needed, voids may not be essential to provide natural cooling to reduce cooling loads. Nevertheless, a big difference is noted in terms of daylight, improving the performance of the building substantially, and recording improvements of between 221% and 116%.

Table 4.1.5.1 and figure 4.1.5.2 outline the main findings for the case studies evaluation. To summarize, the building form that achieves more comfort in office spaces is the circular shape due to a proper ventilation strategy and its form. It also delivers one of the less overheating hours, between 1% and 3%. The triangular building’s “internal offices” record similar comfort levels (around 70%) and benefit from the void’s buffer capacity regardless being on the deepest part of the floorplate, and without having any direct contact to the façade as in The Gherkin example. In the three buildings, offices facing Southern orientations achieve greater comfort, and voids are proven to mediate external conditions, especially in the 6-storey void building, where they decrease hours below comfort by 60%, and overheating hours by 20%.

Regarding daylight, the best performing shape is also the circular one having the core area in the centre and more façade-to-floor ratio, achieving 77% of the plan appropriate daylight levels during most of the occupied year. Nonetheless, the triangular shape shows the most improvement (221%) between void and

12 storey void

CASE STUDIES COMPARISON CHART VOIDS WITHIN 20.8-27.5 BELOW <20.8 OVERHEATING >27.5 DAYLIGHT - % OF PLAN THAT DOES NOT NEED ARTIFICIAL LIGHTING FOR 45% OF THE YEAR COOLING LOADS kWh/m2 THERMAL PERFORMANCE

75% 24% 1%

NO VOIDS NULL WALLS CELLULAR PLAN VOID PARTITIONS

57% 24% 19%

62% 1.7

6 storey void

5% 95%

60% 7% 33%

28% 2.5

21

3

3 storey void

VOIDS

NO VOIDS

VOIDS

NO VOIDS

68% - 78% 19% - 26% 1.8% - 3%

60% - 62% 27% - 30% 8% - 11%

68% - 72% 22% - 25% 5% - 9%

62% - 68% 13% - 15% 20% - 22%

77%

54%

58%

50%

2.2

4.3

4

8.3

Figure 4.1.5.1: Case studies summary chart.

Figure 4.1.5.2: Case Studies’ performance.

74

Figure 4.1.5.2: Case Studiesâ&#x20AC;&#x2122; performance.

UNIVERSITY OF WESTMINSTER 75

3 STOREY VOID CASE: Figure 4.1.6.2 shows heat balance for “middle offices” for both scenarios.

Similar conclusions can be drawn for this case, having the void scenario more heat losses by air movement and higher solar gains. Annual loads (figure 4.1.6.1) express the same pattern as the previous cases.

Figure 4.1.6.1: Annual loads for all scenarios.

20

solar

light

occup

equip

l+o+e

TRIANGLE – no VOID

80 60 40 20 0 80

CIRCLE - VOID

6 STOREY CASE: Figure 4.1.6.2 shows heat balance for “WSW offices” for both scenarios for this building form. In this case, there are more heat losses by air movement in the void scenario, and this could indicate the presence of natural ventilation supplied by the voids. It can be observed that it has more solar gains too, provided that voids help with daylight and sun access into the offices.

Overall, there are little losses through glazing conduction due to its low u-value and good performance. Figure 4.1.6.2 shows heat balance for “Void SW” and “SW offices”. In this case, the difference is more noticeable, showing the void case much more losses through ventilation (in midseason records higher numbers indicating that in summer apertures may be closed some days to prevent hot air entering the building). It also shows extra solar gains than the non-void scenario due to more façade-to-floor ratio. This pattern replays in the other two buildings too. The non-void scenario shows more loads overall, and this could be due to that loads in the void scenario are spread across a larger volume of air than the other does.

Annual loads for this case (figure 4.1.6.1) show a difference of around 15% in solar gains between both scenarios. In both cases, the highest gains are attributed to equipment, and the lower, to occupancy.

40

0

60 40 20

80

CIRCLE – no VOID

12 STOREY CASE: When comparing heat balance for “internal offices” of both scenarios (see figure 4.1.6.2), the lack of ventilation in the non-void scenario is evident. The non-void scenario losses heat mainly via building heat transfer to cope with its internal gains, while the void scenario does it mostly by natural ventilation. What’s more, the nonvoid scenario shows more infiltration, possibly due to higher temperature differences with its adjacent zones. Moreover, these offices get some solar gains, while in the other case they hardly get any. Overall, looking at annual loads (figure 4.1.6.1) the non-void plan records around 65 kWh/m2 for internal gains, and 10 kWh/m2 for solar gains. Loads for the void scenario are less than 60 kWh/m2 for internal and almost 15 kWh/m2 for solar gains (67% more).

60 40 20 0 80

RECTANGLE - VOID

4.1.6 LOADS COMPARISON

60 40 20 0 80

RECTANGLE – no VOID

CHAPTER 4: ANALYTICAL WORK

TRIANGLE - VOID

60

60 40 20 0

UNIVERSITY OF WESTMINSTER 76

CHAPTER 4: ANALYTICAL WORK

VOID SCENARIO

NO VOID SCENARIO HEAT BALANCE NO VOID - INTERNAL OFFICES

HEAT BALANCE - INTERNAL OFFICES 40.00

30.00

30.00 20.00

20.00 10.00

Loads W/m2

Loads W/m2

10.00

0.00

0.00

-10.00 -10.00

-20.00 -20.00

-30.00

TRIANGLE

Month of the year

Month of the year

HEAT BALANCE - VOID SW

HEAT BALANCE - WSW OFFICES

HEAT BALANCE - NO VOID SW OFF

HEAT BALANCE - WSW OFFICES

60.00

40.00

30.00

40.00

80.00

30.00

60.00

20.00

40.00

10.00

20.00

40.00

20.00

Loads W/m2

Loads W/m2

0.00

0.00

-10.00

0.00

0.00

-10.00

-20.00

-20.00

-40.00

-30.00

-60.00

-20.00

-20.00 -40.00

-30.00

Month of the year

Month of the year

Month of the year

CIRCLE HEAT BALANCE - MIDDLE OFFICES

HEAT BALANCE - MIDDLE OFFICES 40.00

30.00

30.00 20.00

20.00

10.00

Loads W/m2

10.00

Loads W/m2

Loads W/m2

10.00

Loads W/m2

20.00

0.00

0.00

-10.00 -10.00

RECTANGLE

-20.00

-20.00

-30.00

Month of the year

Month of the year

Figure 4.1.6.2: Heat balance for all scenarios.

UNIVERSITY OF WESTMINSTER 77

CHAPTER 4: ANALYTICAL WORK

UNIVERSITY OF WESTMINSTER 78

4.2 GENERIC ANALYSIS

4.2.1 METHODOLOGY AND INPUTS

Following the lessons learnt from the case studies evaluation, a generic, theoretical case was chosen to develop the analysis further. In this sense, the circular building form was elected not only because it achieved a good performance, but also because it showed the best aerodynamics, working better with wind.

Moreover, it was interesting to observe how with such a lower void-to-net area ratio than the Commerzbank reference (15% to 34%) and the fewer operable façade of the three, it attained efficient cross ventilation by cause of its voids strategically distributed across the plan. Therefore, the shape’s void strategy was also elected.

Furthermore, the study will maintain a 6-storey-high void, as it is the average height between the studied examples, the same building height, and will look at the results for the same floor level, at 123.1m.

Nevertheless, the dimensions of the plan will be altered in the pursuit to achieve a completely free-running building. For that, the average plan depth from façade to core between the case study plan and the rule of thumbs for daylight was considered. The depth for the case study consisted on 12 m, and the rule of thumbs establishes that the depth of the plan from the facade that will achieve good daylight is given by multiplying the floor-to-ceiling height by 2.5 times (6.75 m). Thus, the depth was resolved to be 9 m (see table 4.2.1).

Methodology, aims and inputs for the generic analysis followed equivalent steps as the case studies evaluation, refer to previous figures 4.1.1.2 and 4.1.1.3 to see heights, materials, and conditions for TAS simulations. Nevertheless, the study did not include a comparison between a void against a non-void scenario, since the difference was already established, but between different distributions of the voids among the plan (figure 4.2.1.1). The aim was to understand the changes in the building’s performance if instead of six voids across the floor plate, the same area was distributed in three, achieving spatial delight, and bigger, more quality spaces for them to be enjoyed rather than just included as performance-enhancers.

The equivalent days were tested to indicate daily and hourly performance for a winter and summer days (refer to table 4.1.1.6), against the adaptive comfort band mentioned in the previous study (table 4.1.1.5).

Zone naming also followed the same criteria (see figure 4.1.1.4).

Daylight was assessed by the same means and inputs, comparing the improvement between a void and nonvoid scenario.

In this case, an airflow study by virtue of rhino and CFD (computational fluid dynamics) software was conducted to enquiry the changes that voids bring in a design and to what extent they help with natural ventilation. The conditions and inputs for these tests will be displayed on section 4.2.4.

Depth of the plan: 9m

Average between: Rule of thumbs for daylight: room depth= 2.5 floor to ceiling height (2.5 x 2.7= 6.75m) Depth from core to façade in case study example: 12m

Table 4.2.1: Procedure to select the generic shape’s depth.

Figure 4.2.1.1: Plans of the generic’s study different scenarios.

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4.2.2 THERMAL PERFORMANCE ANALYSIS Figure 4.2.2.1 shows the models, 4.2.2.3 summarize the scenarios planned to evaluate these two void distributions, and figures 4.2.2.2 and 4.2.2.4 illustrate the zone division and their internal conditions for TAS simulations, respectively.

Figure 4.2.2.1: TAS village models for both scenarios.

Figure 4.2.2.2: Division of TAS zones for the 6 and 3 voids case.

Figure 4.2.2.3: scenarios to be tested in the generic study.

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GENERIC STUDY - 6 VOIDS OFFICES ZONE CHARACTERISTICS Height area volume

VOID - 1ST FLOOR 2.7m 120.104m² 324.281m³

INTERNAL CONDITIONS N. people 10 aprox Occupancy 6.7 W/m² Equipment 15 W/m² Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Light Work Ventilation (Mech. Vent. mode) 0.89 ach *Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unoccupied and unconditioned

ZONE CHARACTERISTICS Height area volume

2.7m 21.462m² 66.531m³, total:399.186m³

INTERNAL CONDITIONS N. people 2 aprox Occupancy 6.7 W/m² Equipment 15 W/m² Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Walking, Sitting, Light Work Ventilation (Mech. Vent. mode) 0.87 ach *Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unoccupied and unconditioned

GENERIC STUDY - 3 VOIDS VOID - 1ST FLOOR

OFFICES ZONE CHARACTERISTICS Height area volume

2.7m 242.523m² 654.811m³

INTERNAL CONDITIONS N. people 20 aprox Occupancy 6.7 W/m² Equipment 15 W/m² Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Light Work Ventilation (Mech. Vent. mode) 0.88 ach *Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unoccupied and unconditioned

ZONE CHARACTERISTICS Height area volume

2.7m 43.260m² 134.107m³, total:804.642m³

INTERNAL CONDITIONS N. people 4 aprox Occupancy 6.7 W/m² Equipment 15 W/m² Lighting 10 W/m² Infiltration 0.3 Minimum Fresh Air 8 L/s pp Activity Walking, Sitting, Light Work Ventilation (Mech. Vent. mode) 0.86 ach *Internal Gains are calculated as per CIBSE Guide **In Weekends, the zone is unoccupied and unconditioned

Figure 4.2.2.4: TAS zones’ conditions and characteristics.

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DAY 5 AND 170 AT 11 AM TAS RESULTS – HOURLY PLOTS Results show (see figure 4.2.2.5 and 4.2.2.6) the same pattern as The Gherkin reference: the voids help raise offices’ temperatures in winter and decrease them in summer. It is interesting to note that there is minimal difference between these two scenarios, and even though the distance between the voids is doubled, the building’s overall thermal performance is not harmed. In both cases, although temperature in the voids gets close to the outside temperature, the offices maintain almost a delta T of 1°C. Temperatures in all offices of the three void plan are quite similar, demonstrating that cross ventilation is still achieved.

A difference of less than 1°C can be seen at 3 pm between offices of both plans, especially in SouthWest oriented ones. This could be as a result of having more solar gains. This variation can be noted in “NNW void” and “ESE void” which in the three void case almost reach the same temperature as the “SW void”, regardless of not getting direct radiation. What’s more, the office’s temperatures in this scenario get closer to the ones in the voids, indicating that the distribution strategy may be even more efficient in the six voids plan. Nevertheless, temperatures in all zones are almost 1°C less than the external temperature.

6 VOIDS SCENARIO

6 VOIDS SCENARIO

3 VOIDS SCENARIO

3 VOIDS SCENARIO

Figure 4.2.2.5: TAS outcomes for resultant temperatures at 11 am for a cold and a hot day for both scenarios.

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DAY 5 AND 170 AT 3 PM 6 VOIDS SCENARIO

3 VOIDS SCENARIO

Figure 4.2.2.6: TAS outcomes for resultant temperatures at 3 pm for a cold and a hot day for both scenarios.

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TAS RESULTS – DAILY PROFILE Regarding daily profiles, figure 4.2.2.7 and figure 4.2.2.8 show similar behaviour in both cases for each day. For the cold day, the graphs illustrate the highest delta T of between 14°C and 18°C, due to internal gains and low u-value envelope materials. In mid-season, the difference with the outside temperature is lower, between 6°C and 4°C, as a result of the addition of ventilation. In summer, all zones reach similar temperatures to the external, evidencing an efficient natural ventilation cooling strategy.

Overall, temperature rises more at the end of the day due to the effect of thermal mass, which tends to mitigate temperature changes, absorbing heat and releasing it afterwards.

In the cold and temperate days, temperatures in the voids are in between the external and the one in the offices, proving their buffer capacity. It is interesting to see that this does not happen in the three void scenario during the cold day. This may be due to higher internal gains than the other case, heating up the space without ventilation.

Furthermore, resultant temperatures are lower than dry bulb temperatures in the winter day and the summer day for both cases due to probable lower solar gains than internal gains (in summer this indicates the effect of the application of a feature shading input).

Cold winter day - SW void and SSW office daily profile 25

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2.5

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External T (°C) Void SW Resultant Temp (°C) Off SSW Resultant Temp (°C) Off SSW Solar Gain (W/m²) Void SW Dry Bulb (°C) Off SSW Dry Bulb (°C) Void SW Solar Gain (W/m²)

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Cold winter day - SW void and SSE office daily profile 25

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5 0

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External Temperature (°C) Void SW Resultant Temp (°C) Off SSE Resultant Temp (°C) Off SSE Solar Gain (W/m²) Void SW Dry Bulb (°C) Off SSE Dry Bulb (°C) Void SW Solar Gain (W/m²)

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Figure 4.2.2.7: Daily profiles for both scenarios on a cold, winter day.

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Temperate day - SW void and SSW office daily profile 25

18

6 VOIDS

16

External T (°C) Void SW Resultant Temp (°C) Off SSW Resultant Temp (°C) Off SSW Solar Gain (W/m²) Void SW Dry Bulb (°C) Off SSW Dry Bulb (°C) Void SW Solar Gain (W/m²)

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Temperate day - SW void and SSE office daily profile 10

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9 External Temperature (°C) Void SW Resultant Temp (°C) Off SSE Resultant Temp (°C) Off SSE Solar Gain (W/m²) Void SW Dry Bulb (°C) Off SSE Dry Bulb (°C) Void SW Solar Gain (W/m²)

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Hot summer day - SW void and SSW office daily profile 25

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External T (°C) Void SW Resultant Temp (°C) Off SSW Resultant Temp (°C) Off SSW Solar Gain (W/m²) Void SW Dry Bulb (°C) Off SSW Dry Bulb (°C) Void SW Solar Gain (W/m²)

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Temperate day - SW void and SSE office daily profile Hot summer day External Temperature (°C) Void SW Resultant Temp (°C) Off SSE Resultant Temp (°C) Off SSE Solar Gain (W/m²) Void SW Dry Bulb (°C) Off SSE Dry Bulb (°C) Void SW Solar Gain (W/m²)

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Figure 4.2.2.8: Daily profiles for both scenarios on a temperate day and a hot, summer day.

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WITHIN COMFORT 20.8-27.5 TAS RESULTS – FREQUENCIES AND COOLING LOADS Focusing on frequencies for these two floor plans (see figure 4.2.2.10), the greater difference between the two lays in hours within comfort for the void zones. The three void scenario’s voids record almost 15% more hours within comfort, as a result of fewer hours below comfort. Regarding overheating hours, the six voids scenario shows less than 2% below the other, a negligible improvement.

On the contrary, cooling loads show a greater difference in the office spaces, needing the three void case higher energy consumption than the other. However, the difference is also minimal, just around 2 kWh/m2 for a setting point of 26°C (figure 4.2.2.9). Energy consumption increases by 2.63 times when the set point is changed to 24°C.

60% 50% 40% 30% 20% 10% 0%

VOID VOID VOID VOID VOID VOID OFF OFF SW WNW NNW NE ESE SSE WSW NW 6 VOIDS

OFF NNE

OFF OFF SE OFF ENE SSW

3 VOIDS

BELOW COMFORT <20.8 80% 70% 50% 40% 30% 20% 10% 0%

VOID VOID VOID VOID VOID VOID OFF OFF SW WNW NNW NE ESE SSE WSW NW 6 VOIDS

VOID VOID VOID VOID VOID VOID OFF OFF SW WNW NNW NE ESE SSE WSW NW VOID

OFF NNE

OFF OFF SE OFF ENE SSW

3 VOIDS

COOLING LOADS kWh/m2 10.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00

70%

60%

COOLING LOADS kWh/m2 5.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00

80%

OFF NNE

OFF OFF SE OFF ENE SSW

OFF NNE

OFF OFF SE OFF ENE SSW

3 VOIDS

OVERHEATING >27.5 5% 4% 3% 2% 1% 0%

VOID VOID VOID VOID VOID VOID OFF OFF OFF SW WNW NNW NE ESE SSE WSW NW NNE VOID

OFF OFF SE OFF ENE SSW

VOID VOID VOID VOID VOID VOID OFF OFF SW WNW NNW NE ESE SSE WSW NW 6 VOIDS

3 VOIDS

Figure 4.2.2.10: Frequencies for 6 voids and 3 voids scenarios.

3 VOIDS

Figure 4.2.2.9: Cooling loads for 6 voids and 3 voids scenarios, with a set point at 26°C (up) and 24°C (down).

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4.2.3 DAYLIGHT COMPARISON

VOID SCENARIO – 6 VOIDS

NO VOID SCENARIO

VOID SCENARIO – 3 VOIDS

UDI simulations were performed to compare daylight performance within and below the range between 300 to 2000 lux for the same plan with six and three voids, and against a non-void scenario (see figure 4.2.2.3).

Results for the “in the range” simulations are shown in figure 4.2.3.1. Simulations present hardly any difference between six and three voids scenarios, but an improvement of almost 25% compared to the non-void plan.

More than 90% of the plan’s area for the two first achieve the optimum illuminance levels for 45% of the year; the non-void scenario accomplishes it for 74% of the time.

Figure 4.2.3.2 illustrates UDI levels below 300 lux. The voids scenarios record between 2% and 5% hours below the range for 65% of the occupied year, and do not need artificial lighting for 65% of the time. In case of the non-void plan, the percentage increases to 26%.

98% of the of the plan is within the range 45% of the time

74% of the of the plan is within the range 45% of the time

95% of the of the plan is within the range 45% of the time

2% of the of the plan needs artificial lighting 65% of the time

26% of the of the plan needs artificial lighting 65% of the time

5% of the of the plan needs artificial lighting 65% of the time

Figure 4.2.3.1: UDI simulation results for within the range between 300 to 2000 lux for the 6 voids, non-void , and 3 voids case (up). External windows’ transmittance was set to 0.6, and for internal windows to 0.85 Figure 4.2.3.2: UDI simulation results for below the range between 300 to 2000 lux for the 6 voids, non-void , and 3 voids case (down). External windows’ transmittance was set to 0.6, and for internal windows to 0.85

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4.2.4 NATURAL VENTILATION STUDIES Figure 4.2.4.2 presents the different cases for wind-alone CFD simulations to test the effect of wind and the subsequent indoor ventilation flow path. These studies consist of three cases: .A base case with a total aperture of 14 m2 per floor in the voids’ external façade, and an aperture area of 9 m2 for the internal façade; .Case one, which reduces aperture areas by half; .Case two closes the connection between offices turning the layout as a cellular plan.

In all cases, the outdoor wind velocity is set to be 2 m/s, the wind direction is perpendicular to the SW void, and all voids are opened in every storey. For the base case, a second direction was also studied to test airflow patterns for a wind direction in between voids as illustrated in the previous figure. Figure 4.2.4.1 displays inlets and outlet distribution according to wind directions.

Figure 4.2.4.1: Inlet and outlet distribution according to simulation outcomes for each case and wind direction.

Figure 4.2.4.2: Scenarios to be tested against natural ventilation.

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BASE CASE Results show (see figures 4.2.4.3, 4.2.4.4 and 4.2.4.5) the effect of the shapeâ&#x20AC;&#x2122;s aerodynamics, increasing wind velocity to the sides, but pushing these high velocities away from the building. In general for all cases, the highest wind velocities are around the core near the main inlet, where in some areas go even higher than 2 m/s. Then, air experiences flow reversal and is diverted to the sides and to the West and East facing offices, which receive high wind speeds (around 1.5 m/s to 0.2 m/s). Offices at the North, opposite and further away from the flow direction, record average velocities between 0.15 m/s and 0.05 m/s.

On the other hand, the non-void case achieves cross ventilation across the entire plan due to no obstructions and high pressure on its apertures. However, it records the highest speeds of the three: above 2.5 m/s on almost 30% of plan. The rest of the area gets around 0.6 m/s close to the façade, and 0.1m/s near the core. The NE offices, opposite to flow direction get velocities around 0.3 m/s and 0.5 m/s.

Lastly, the three void plan displays the lowest speeds, 1.5 m/s around the core and in workspaces an average of about 0.7 m/s. This scenario shows air being more evenly distributed through the plan than the six voids scenario.

Overall, the average wind velocity of the void scenarios is less than the non-void plan, especially in the working area. This indicates that voids help minimize air velocity which is crucial in tall buildings. Nevertheless, wind speeds recorded are high and uncomfortable, evidencing the need to reduce the aperture area.

Results for the second wind direction, in between voids, showed lower indoor air velocities since air enters the building at lower speeds.

Figure 4.2.4.3: CFD base case results for 1st, 3rd and 6th floor, and section through WNW-ESE and SW-NE voids for 6 voids scenario.

Figure 4.2.4.4: CFD base case results for typical floor, and section through WNW-ESE and SW-NE voids for non-void scenario.

Figure 4.2.4.5: CFD base case results for 1st, 3rd and 6th floor, and section through WNW-ESE and SW-NE voids for 3 voids scenario.

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1st floor

3rd floor

6th floor WNW - ESE SW - NE

VOID SCENARIO – 6 VOIDS

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WNW - ESE

VOID SCENARIO – 3 VOIDS

SW - NE

NO VOID SCENARIO

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Figure 4.2.4.6: Models for CFD simulations.

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CASE ONE Reducing apertures by half help reduce velocities (see figures 4.2.4.7, 4.2.4.8 and 4.2.4.9). However, near the core there are still over 1.5 m/s, indicating that apertures should be further reduced in order to achieve comfortable indoor speeds. In this case, there is a bigger difference between 6 and 3 voids plans, recording the latter better conditions due to less operable area. The 6 void scenarioâ&#x20AC;&#x2122;s highest velocity in office areas is of 0.8 m/s, and contrary to the last case, the NE void, opposite to flow direction, shows more air movement and acts as an inlet, with air speeds around 0.25 m/s.

In the non-void plan, velocities raise to 2.3 m/s around the core and around 1.5 m/s to the West of the plan.

The wind is distributed in a clockwise direction, presenting some turbulence at the South part of the plan.

In the 3 voids scenario, the highest wind speeds around the core are around 1 m/s to 1.3 m/s, and air movement at the back offices is around 0.07 m/s.

Overall, the 6th floor of both void scenarios show better performance in terms of air distribution across the plan.

Figure 4.2.4.7: CFD case 1 results for 1st, 3rd and 6th floor, and section through WNW-ESE and SW-NE voids for 6 voids scenario.

Figure 4.2.4.8: CFD case 1 results for typical floor, and section through WNW-ESE and SW-NE voids for non-void scenario.

Figure 4.2.4.9: CFD case 1 results for 1st, 3rd and 6th floor, and section through WNW-ESE and SW-NE voids for 3 voids scenario.

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6th floor WNW - ESE SW - NE

VOID SCENARIO – 6 VOIDS

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WNW - ESE

VOID SCENARIO – 3 VOIDS

SW - NE

NO VOID SCENARIO

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Figure 4.2.4.6: Models for CFD simulations.

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CASE TWO When the plan is subdivided, air cannot move freely in the non-void scenario, showing the lowest speeds (0.25 m/s to 0.001 m/s) and most of the plan without almost any air movement (see figure 4.2.4.11). This is not the case for the other two scenarios, which still achieve cross ventilation. Regardless, these two scenarios keep recording velocities over 1 m/s (see figures 4.2.4.10 and 4.2.4.12). So, apertures should be reduced even more, or a second skin introduced in order to incorporate some resistance to the incoming wind, without harming the cross ventilation strategy.

In the 6 voids scenario, velocities in the two adjacent zones to the void that acts as an inlet record around 1.3 m/s, and the rest of the offices below 0.25 m/s.

Some areas of the NE offices in the 3 voids scenario show velocities lower than 0.03 m/s. This indicates that for a cellular plan, increasing the distance between voids may not be enough to provide ventilation, or that apertures in the external faรงade of the voids that are not facing the wind direction, should be increased.

Further studies should be carried away to understand this matter and get to deeper conclusions.

Figure 4.2.4.10: CFD case 2 results for 1st, 3rd and 6th floor, and section through WNW-ESE and SW-NE voids for 6 voids scenario.

Figure 4.2.4.11: CFD case 2 results for typical floor, and section through WNW-ESE and SW-NE voids for non-void scenario.

Figure 4.2.4.12: CFD case 2 results for 1st, 3rd and 6th floor, and section through WNW-ESE and SW-NE voids for 3 voids scenario.

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WNW - ESE

VOID SCENARIO – 3 VOIDS

SW - NE

NO VOID SCENARIO

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4.2.5 CLIMATE CHANGE SCENARIO To test how these buildings would perform under future circumstances, the weather file according to IPCCâ&#x20AC;&#x2122;s climate change prediction for the intermediate emissions scenario 1AB, was inputted in TAS simulations. Figure 4.2.5.1 and 4.2.5.2 show frequencies within and below comfort and overheating hours for the middle floor in the middle village for both buildings (3 and 6 voids), against climatic conditions at the present time and 2050. Inputs such as materials, internal gains and aperture types were the same as the ones for the previous cases (refer to section 4.1.1 in this chapter).

Simulation outcomes display that under imminent raises

Figure 4.2.5.1: Frequencies for 6 voids and 3 voids scenarios.

in temperatures, hours within comfort will decrease by less than 12% in both cases, due to a growth in overheating hours by between 7% and 10%. Hours below comfort are reduced by less than 3% for both cases. It can then be deduced that although temperatures will raise by up to 6K, these buildings will still be able to achieve comfort for at least 55% to 66% of the year, reinforcing the idea of voids as a powerful strategy to accomplish desirable thermal performance in tall buildings. Besides, results also show that heating season will still be predominant for most of the year.

Figure 4.2.5.2: Frequencies for 6 voids and 3 voids scenarios.

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4.2.6 SUMMARY CHART COMPARISON In summary, as presented in table 4.2.6.1 and figure 4.2.6.2, there is little to no noticeable difference between the six and three voids scenarios in terms of thermal performance and daylight. Offices achieve comfort for 60% to 72% of the time (a difference of 5% in hours within comfort and 1.5% for overheating between both scenarios), and between 98% and 95% of their floorplan does not need artificial lighting for almost half of the year.

Regarding ventilation, voids help reduce wind pressure and high velocities, especially in the 3 voids scenario where apertures have less area and are further away from each other. Voids also ensure natural ventilation in all cases. However, while the 6 voids plot achieves cross ventilation throughout all the plan even in a cellular layout, the 3 voids may not be enough if this is the case.

GENERIC STUDY COMPARISON CHART

15% 6 voids

WITHIN 20.8-27.5 THERMAL BELOW <20.8 PERFORMANCE OVERHEATING >27.5 DAYLIGHT - % OF PLAN THAT DOES NOT NEED ARTIFICIAL LIGHTING FOR 45% OF THE YEAR

64% - 72% 27% - 35% 0.8% - 1.1%

VENTILATION

no void

15% 3 voids 60% - 65% 31% - 36% 2.3% - 2.8%

98%

74%

95%

OPEN PLAN

ACHIEVES CROSS VENTLATION

AIR MOVES ACROSS ALL THE PLAN HIGHEST WIND SPEEDS

AIR MOVES ACROSS ALL THE PLAN LOWEST WIND SPEEDS

CELLULAR PLAN

ACHIEVES CROSS VENTLATION

DOES NOT ACHIEVE CROSS VENTILATION

70% OF THE PLAN ACHIEVES CROSS VENTILATION

COOLING LOADS kWh/m2 THERMAL PERFORMANCE CLIMATE CHANGE SCENARIO

Nevertheless, only a small area of this plan (30%) shows slow air movement. Overall, the highest velocities recorded are around the core, and not in the office spaces or near the façade area. Regardless, for outdoor velocities of 2 m/s or more, the aperture area should be less than the tested to achieve comfortable indoor velocities under 1 m/s, or a second skin introduced to slower the incoming winds.

The results indicate that the void-to-net area ratio could still possibly be reduced to gain more usable office space, without harming the overall performance of the building. Moreover, the 3 voids scenario also provides comfort while improving the void’s spatial quality: more area could provide further opportunities for views and social interaction. This means that these voids could be used not only as environmental enhancers but also as spaces to add quality and dynamism to the design.

WITHIN 20.8-27.5 BELOW <20.8 OVERHEATING >27.5

1.8

10.4

59% - 65% 27% - 34% 7.1% - 8.6%

52% - 57% 31% - 35% 12.7% - 12.8%

Figure 4.2.6.1 : Generic study summary chart.

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Figure 4.2.6.2: Generic Studiesâ&#x20AC;&#x2122; thermal performance.

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4.2.7 LOADS COMPARISON When comparing both scenario’s free-running mode heat balance for the “SW void” zone, a difference of 30% in solar gains can be noted in favour of the six voids case (see figure 4.2.7.2). The ventilation pattern is similar, and although air movement is mostly a loss in the 6 voids plan, in the 3 voids case it is often a gain (except for the months of January, March, May, October and December, when it acts as a loss for this scenario too). In addition, there are higher losses by ventilation in the 3 voids plan in cold and midseason, when loads range from between 50% to 65% more than the other, during the months of November to February. This may be as a result of higher temperatures in offices that may require more ventilation in this case. In both scenarios, the highest gains are from solar access, and most losses are through ventilation.

With reference to the offices, heat balance between both is quite similar, showing equivalent behaviour for ventilation and a lower difference for solar gains compared to the void zone: it shows less than a 10% difference between them. This may result from the same feature shading input.

Regarding annual loads (see figure 4.2.7.1), a similar and comparable pattern is shown between both scenarios.

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40

20

0 solar

light

occup

equip

L+O+E

solar

light

occup

equip

L+O+E

80

60

40

20

0

Figure 4.2.7.1: Annual loads for both scenarios.

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HEAT BALANCE - VOID SW 80.00

40.00

VOID SW Equipment Sensible Gain (W/m²)

20.00

VOID SW Occupancy Sensible Gain (W/m²) VOID SW External Conduction Glazing (W/m²) VOID SW External Conduction Opaque (W/m²) VOID SW Building Heat Transfer (W/m²) VOID SW Air Movement Gain (W/m²)

Loads W/m2

6 VOIDS SCENARIO

60.00

0.00

-20.00

VOID SW Inf/Vent Gain (W/m²) VOID SW Lighting Gain (W/m²)

-40.00

VOID SW Solar Gain (W/m²) -60.00

Month of the year

HEAT BALANCE - VOID SW 80.00

40.00

20.00

VOID SW Equipment Sensible Gain (W/m²) VOID SW Occupancy Sensible Gain (W/m²) VOID SW External Conduction Glazing (W/m²) VOID SW External Conduction Opaque (W/m²) VOID SW Building Heat Transfer (W/m²)

Loads W/m2

3 VOIDS SCENARIO

60.00

0.00

-20.00

VOID SW Air Movement Gain (W/m²) VOID SW Inf/Vent Gain (W/m²)

-40.00

VOID SW Lighting Gain (W/m²) -60.00

Month of the year

HEAT BALANCE - SSW OFFICES 40.00

20.00

SSW OFF Equipment Sensible Gain (W/m²)

10.00

SSW OFF Occupancy Sensible Gain (W/m²) SSW OFF External Conduction Glazing (W/m²) SSW OFF External Conduction Opaque (W/m²) SSW OFF Building Heat Transfer (W/m²) SSW OFF Air Movement Gain (W/m²)

Loads W/m2

6 VOIDS SCENARIO

30.00

SSW OFF Inf/Vent Gain (W/m²)

0.00

-10.00

-20.00

SSW OFF Lighting Gain (W/m²)

-30.00

-40.00

Month of the year

HEAT BALANCE - VOID SSE 40.00

20.00

VOID SSE Equipment Sensible Gain (W/m²)

10.00

VOID SSE Occupancy Sensible Gain (W/m²) VOID SSE External Conduction Glazing (W/m²) VOID SSE External Conduction Opaque (W/m²) VOID SSE Building Heat Transfer (W/m²) VOID SSE Air Movement Gain (W/m²)

Loads W/m2

3 VOIDS SCENARIO

30.00

0.00

-10.00

VOID SSE Inf/Vent Gain (W/m²) VOID SSE Lighting Gain (W/m²) VOID SSE Solar Gain (W/m²)

-20.00

-30.00

Month of the year

Figure 4.2.7.2: Heat balance of SW voids and SSW offices and SSE offices for 6 voids and 3 voids scenario.

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CHAPTER 5 ADDITION OF VEGETATION

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CHAPTER 5: ADDITION OF VEGETATION

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5.1 BENEFITS OF INTRODUCING VEGETATION IN WORKSPACES As Saxon claims, "let green plants into the space, as the most acceptable bridge between technological objectivity of any building and the subjective nature of people" (1986, p1). In this sense, he imagines atria as a metaphor for the outdoors, connecting people with external conditions and outside views.

Biophilia relates to Saxon's idea of "the living atrium". It refers to the hypothesis that people have an inherent tendency to come in contact with Nature, plants and living things, as a consequence of evolutionary history, and considering that we are presumably adapted to live in a green environment (Grinde and Grindal Patil, 2009).

Biophilia research suggests that a close association with Nature improves psychological health and quality of life.

Moreover, theories claim that Nature can help with stress reduction and mental restoration much faster than urban environments, documented in the Health Council of the Netherlands in 2004. This effect, according to Grinde and Grindal Patil (2009), can be explained due to air being healthier around plants (less polluted and more humid), it may also be because they emit pleasant fragrances or as a result of a good visual experience. However, they note that findings show that indoor plants do not have such a concluding effect as outdoor Nature, and that more research needs to be done to come to defining conclusions. Nevertheless, they stress out upon the idea that as people tend to spend most of their time indoors, even a small difference shown by plants is helpful and therefore, should be taken into consideration. Besides, the effect

of having open Nature views has been thoroughly reviewed and acknowledged.

Furthermore, Cooper (20015) claims that biophilia design is the answer to increasing world population moving into urban environments. He introduces it as a way of re-connecting the places where people live and work with Nature, and in this way, boost people's wellbeing, productivity and creativity. In his study, he discovered that 67% of the people he interviewed felt more productive and enthusiastic when working at bright offices with accented yellow, green or blue colours. Coupled with the 33% of people that claimed to be influenced by workplace design, biophilic design's approach gets more alluring. The study also shows UK as one of the main countries in which less natural light was encountered in working environments, and therefore, desired by almost 44% of its employees. The second main element chosen by 20% of the people were indoor plants, paired up with natural colours and elements.

In his report, Cooper (2015) states that perceptions of wellbeing in workspaces can increase by up to 15% in the presence of natural elements and views of Nature by effect of the Attention Restoration Theory. This theory says that experiencing Nature allows concentration in a more effortless way, thus, leading to more productivity (6% higher) and less absenteeism.

The same rate of improvement was shown in the report for creativity levels under the presence of plants and bright colours, reinforcing the idea of biophilic design as a positive attribute to incorporate in working spaces.

Figure 5.1.1: Vegetation in workspaces. Source: Terrace outdoor living

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5.2 EVAPOTRANSPIRATION RATE Besides providing surface shading, humidification, air scrubbing, soil and water purification as well as psychological benefits, vegetation also affects urban and indoor spaces' microclimate by cooling through evapotranspiration. This process refers to water absorption and its further transpiration from the plant's leaves to the air in the form of water vapour, with the resulting heat being absorbed and bringing about a decline in air temperature (Gkatsopoulos, 2017). Gkatsopoulos also claims that as the combined effect of shading and evapotranspiration has been calculated to have reduced annual loads in the built environment by 53%, they cannot be measured separately. He stated that as vegetation density increases, there will be more evapotranspiration and, hence, more cooling.

This process depends on several factors such as radiation, vapour pressure, temperature, wind speed and the resistance from the specific plant's canopy, which varies with species. Canopy resistance, in turn, depends on its leaves' pores, their stomata, by which they control their transpiration.

Cooling by evapotranspiration can be calculated following the Penman-Monteith formula, which calculates the average evapotranspiration rate for an area of selected vegetation species, using meteorological data and crop specific coefficients.

Based on this formula, the Food and Agriculture Organization of the United Nations (FAO), has published in its Irrigation and Drainage Paper 56 (1998) data for calculating evapotranspiration from various crops.

What’s more, Akbari provided a method based on this formula to obtain the rate for single trees related to its own crown area (Gkatsopoulos, 2017).

The FAO Penman-Monteith formula is then:

Where ETo reference evapotranspiration rate [mm/day] Kc crop coefficient Δ slope of vapour pressure curve [kPa/°C] Rn net radiation at crop surface [MJ/m2 day] G soil heat flux [MJ/m2 day] es saturation vapour pressure [kPa] ea actual vapour pressure [kPa] (es - ea) saturation vapour pressure deficit of the air [kPa] γ psychrometric constant [kPa/°C] T mean daily air temperature at 2 m height [°C] U2 wind speed at 2 m height [m/s] Ac tree crown area [m2] The author explains that the reference evapotranspiration rate is then multiplied by Kc to determine the evapotranspiration rate for the specific species. Lastly, it is divided by the species' crown area to achieve the amount of cooling in watts they could provide. However, he notes that processes such as evapotranspiration are very difficult to simulate due to the chaotic nature of vegetation. Nonetheless, it could stimulate designers and clients to introduce vegetation as a genuine passive strategy to improve the building's performance, from early stages in the design.

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5.3 ANALYTICAL WORK 5.3.1 METHODOLOGY AND INPUTS In order to calculate the cooling effect that vegetation could provide by adding one tree per void space and living walls in all slabs facing them (see model in figure 5.3.1.1), the suggested methodology was followed. In this sense, a website version of the tool developed by FAO (http://www.fao.org/land-water/databases-andsoftware/eto-calculator/en/), which was used to calculate the reference evapotranspiration rate of crops according to London's meteorological data.

Results and inputs can be visualized in figure 5.3.1.3. Together with the information gathered from Gkatsopoulos' paper (2017) which specified the crop coefficient for Beech trees, common in London, and data about the crop coefficient of living panel wall systems calculated in Van de Wouw, Ros and Brouwers' paper (2017), the evapotranspiration rate for both was calculated (see table 5.3.1.4). This number was then divided by the crown area of each species and by the average sunlight hours in July to obtain the hourly average cooling in watts provided by both of these plants for the hottest month of the year.

Modelling these species in Rhinoceros and then feeding it with this data in a CFD software (Autodesk CFD) as negative heat gains, the effect of vegetation in the six voids plan building was simulated. Surface temperatures, as well as air temperature, were kept similar to highlight the effect of greenery. Inputs for the CFD simulations are displayed on table 5.3.1.2.

Figure 5.3.1.1: Model for CFD simulations

MATERIALS Air, variable Concrete Wood Soft Glass

GEOMETRY Building's envelope Slabs, Core Trees, Living walls Internal façade

BOUNDARY CONDITIONS SW + NE void Inlets velocity 2 m/s temperature 26.5°C WNW, NNW, ESE, SSE voids Outlets pressure 0 dyne/cm² film coefficient 0.6 W/m²/K Ceiling temperature 26°C film coefficient 0.6 W/m²/K Floor temperature 25°C film coefficient 1.2 W/m²/K Glass Façade temperature 26.5°C

INTERNAL CONDITIONS Building Element

Temperature

Glaze Façade Ceiling Floor Core Slabs

26.5 26 25 25 25

Internal Windows

26

Figure 5.3.1.2: CFD simulations’ inputs

Figure 5.3.1.3: Evapotranspiration rate was calculated using FAO’s web tool.

July's reference evapotranspiration rate in London ETₒ (mm/day) 4.9

plant species Beech Tree Panel system -Living wall

species' crop plant's evapotranpiratio conversion to w/m² coefficient crown area n rate Kc 0.8 1.46

Etc (mm/day) 3.92 7.15

/0.408 9.607 17.534

/0.0864 111.2 202.94

Ac (m²) 9.26 4.59

daily average cooling provided watts 1029.7 931

average sunlight hours in July h 6.3

hourly average cooling provided watts 163.45 147.78

Figure 5.3.1.4 : Calculation of the evapotranspiration rate for a beech trees and living walls

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5.3.2 OUTCOMES WIND ANALYSIS Figures 5.3.2.1, 5.3.2.2 and 5.3.2.3 display airflow analysis for both vegetation and no vegetation scenarios, showing that air is more evenly distributed across the plan in the first one.

On the first floor, velocities around the core record the highest speeds (tendency already seen in the wind alone past simulations), but are higher in the no greenery added scenario. With vegetation, the highest speed is around 0.25 m/s in the first floor; on the contrary, without it, speed goes above 0.5 m/s. Whatâ&#x20AC;&#x2122;s more, this plans present velocities over 2 m/s in offices around the inlets. Both NW and SE offices show less air movement in both cases being the lowest speed 0.02 m/s and the highest 0.06 m/s for the vegetation scenario, and 0.09 m/s for the other one. It could be said that vegetation help reduce high wind speeds in offices without harming the overall cross ventilation strategy. The voids, however, show more air movement in the greenery added simulation. Whereas in the first one the average for this floor is 0.1 m/s, in the other one it is 0.05 m/s, except for the inlets where it goes up to 0.25 m/s. This may be due to buoyancy forces induced by the cooling provided by trees and living

walls.

In the second floor there is even a bigger difference between both simulations, showing the no vegetation scenario higher wind velocities that range from 0.5 m/s to 0.2 m/s around the core, and 0.3 m/s on the offices.

The vegetation scenario displays little difference between offices, maintaining the speed quite similar in all workspaces, ranging from 0.03 to 0.15 m/s.

Plan 3 already shows increased velocities for the greenery case. This may indicate that the slowing capacity of the trees does no longer helps reducing speeds, and should be taller, apertures should be less opened or more vegetation introduced. Nonetheless, it still shows lower velocities compared to the other simulation. The highest speed recorded for the offices in the vegetation scenario is about 0.15 m/s and for the other 0.25 m/s.

The pattern is repeated in higher floors, presenting higher speeds for both simulations, recording the 6th floor the highest velocities. The NW offices record the highest, up to 0.3 m/s, and around the core it exceeds 0.5 m/s. In this floor, although the no vegetation's peak is lower, there are higher wind speeds in the offices overall.

WITH VEGETATION

SW - NE

WNW - ESE

NO VEGETATION

Figure 5.3.2.1: CFD results for both scenarios. Sections through WNW-ESE and SW-NE voids.

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CHAPTER 4: ANALYTICAL WORK

WITH VEGETATION

6th floor

3rd floor

1st floor

NO VEGETATION

Figure 5.3.2.2: CFD results for both scenarios: 1st, 3rd and 6th storeys.

Figure 5.3.2.3: CFD results for both scenarios.

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Figure 5.3.2.4: Atrium garden, Commerzbank Headquarters, Frankfurt. Source: Pinterest

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TEMPERATURE ANALYSIS Regarding temperatures (see figures 5.3.2.5, 5.3.2.6 and 5.3.2.7), a reduction of 0.5°C can be observed in the voids that act as inlets between both scenarios in the first two floors, only reaching a comparable temperature after the 4th floor. Moreover, an average reduction of almost 1°C can be noted in the 1.5 metres distance from the living walls in the rest of the voids reaching to 26°C only in the last floor, similar to the other simulation. A bigger difference is accomplished in the first floor of the voids, especially in the WNW and NNW ones, where the difference rises to 1.2°C, presenting an average temperature of 24.75°C, a difference of 2°C with the external temperature.

With reference to office spaces, the first floor shows the highest contrast between scenarios, recording between 0.8 and 0.5°C difference and a Delta T of around 1.5 to 1°C. In the vegetation scenario, SSW and ENE offices record the highest temperature of 25.8°C near the core due to the air flow direction from the inlets going their direction, bringing warmer air at 26.5°C. The second floor, aided by the cooling provided by the plants, shows a difference of around 0.4 to 0.5°C between the offices of both scenarios, where offices adjacent to the inlet voids record 0.4°C higher than the rest of the offices in the scenario with greenery, and presents a delta T of 1°C.

The third floor's offices with vegetation display a reduction of between 0.3 and 0.4°C compared to the other. In this plan, the action of living walls is more noticeable, lowering the temperature of SSW and ENE offices by 0.3°C, due to airflow movement, achieving a delta T of 0.7°C. By the 4th storey, the effect of vegetation is lower.

However, a reduction of 0.25°C is still achieved in most of this plan compared to the non-vegetation one. A difference of 0.5°C can be observed to the external conditions.

In the 5th and 6th floor, temperatures are quite similar between both buildings, accomplishing a reduction of only 0.1°C. Nevertheless, near the living walls this is increased by 0.4°C, reinforcing the cooling strategy vegetation can provide, combined with the improvements in productivity and wellbeing it brings to users.

In summary, vegetation not only help minimise high wind speeds, allowing also a better distribution of the air across the plan, but also help reduce temperatures up to 1.2°C. Proving office spaces with cooler and more comfortable air movement, the introduction of vegetation in the voids also improves their own comfort levels, while supplying the building with a quality space which connects users with outdoors.

WITH VEGETATION

SW - NE

WNW - ESE

NO VEGETATION

Figure 5.3.2.5: CFD results for both scenarios. Sections through WNW-ESE and SW-NE voids.

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CHAPTER 4: ANALYTICAL WORK

WITH VEGETATION

6th floor

3rd floor

1st floor

NO VEGETATION

Figure 5.3.2.6: CFD results for both scenarios: 1st, 3rd and 6th storeys.

Figure 5.3.2.7: CFD results for both scenarios.

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CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS

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CHAPTER 6: CONLUSIONS AND RECOMMENDATIONS

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Tall buildings have become a trend, and although they are highly questioned and their impacts upon its surroundings worry many people, that trend is starting to shift towards a sustainable goal, reducing energy demands and carbon footprint. Besides economic benefits, tall office buildings can revaluate urban areas, and when planned with appropriate public policies, adequate infrastructure, public mobility, and an environmental approach that drives the design, they can have positive impacts upon the city. Moreover, they can enhance the public realm and boost urban development, attracting people, creating social interaction possibilities, freeing up space for open-green spaces, and integrating the design to the urban fabric.

Tall buildings can be sustainable. In fact, height is not a limit for it. When this typology incorporates local climatic context and culture in its design, by designing its form, facades, materials and internal layout according to users’ perception of thermal comfort to maximise the control of the internal environment, tall buildings can provide environmental quality as well as a considerable reduction in energy demands.

Environmental performance relates to temperature and thermal comfort, air quality, daylight, and adaptive opportunities to control indoor conditions. This is especially important for businesses as recent studies have proven the connection between environmental performance, wellbeing and productivity. These studies have raised the importance of daylight and air quality as the main factors in achieving better productivity rates: they demonstrated that improvements in daylight can raise performance by 26%, while a poor indoor air quality, due to the lack of natural ventilation, can decrease productivity by almost 10%.

In this sense, voids are a powerful tool to enhance the performance of a tall building. Besides supplying the design with spaces for leisure and communication with the outdoor environment and within itself, the voids heighten daylight penetration opportunities by increasing the façade-to-floor ratio, and in that way, they also potentiate opportunities for natural ventilation. Thus, contributing to the overall thermal performance of the project, delivering buffer zones which maximise solar gains and reduce heat losses in winter, and in summer prevent overheating by minimising direct radiation coupled with a natural ventilation strategy. Atria act as “light ducts”. Besides giving external views and triggering circadian rhythm, which keeps the body in synch with the progression of the day, higher daylight levels play an important part in reducing energy consumption.

Tall buildings operate with a wide range of pressures, due to extra exposure to wind. If aiming for natural ventilation, an appropriate strategy is to divide the building into segments that work independently from each other, each of them connected by atria, to make

these pressures manageable. In addition, voids provide the opportunity to combine wind and buoyant forces to act together, making natural ventilation more effective, and bringing inward flow of fresh air to the deeper parts of the plan. However, most of high-rise buildings apply this strategy in mix-mode systems due to climate, security and noise constraints.

Furthermore, voids offer open spaces that can reestablish commercial buildings with Nature. Biophilic design strives to grant occupants with a close association with Nature so as to promote mental restoration, productivity, creativity and stress reduction, enhancing users’ perception of wellbeing by up to 15% and life quality.

For the case studies evaluation, three successfully environmental-performing built examples were chosen: The Commerzbank Headquarters, 30 Saint Mary Axe and 110 Bishopsgate, to perform a thermal analysis and a daylight comparison between the buildings with their original design against a non-void version. Results showed a difference between hours within comfort for the office spaces of around 15% for the first two, and 5% for the last one in favour of the void scenario.

Overheating hours presented a difference of 25% for The Commerzbank (the largest due to its 0.34 void-tonet area ratio), 7% for The Gherkin, and 14% for the Heron Tower. Initial hypothesis predicted the change would be more significant. However, outcomes indicated that for cold and temperate climates such as London, where the predominant need is for heating, voids providing natural ventilation as a cooling strategy may not be such a useful resource. Nonetheless, cooling loads showed around 48% to 56% improvement between scenarios.

On the contrary, daylight simulations exhibited a great difference between the two cases. In case of the 12storey-void building, an improvement of 221% was observed between the plans, recording 62% of the plan between 300 and 2000 lux for almost half of the year.

The 6 void case displayed a better performance, achieving 77% of the plan these levels for that time, and accomplished a 143% improvement. The rectangular building form showed the less daylight levels compared to the rest (58%), although the daylight was improved by 116%.

Overall, the circular shape showed the biggest difference between void and no void scenario, and was chosen to continue the study further, trying different articulations of the same void area (15%) as taken from the example, and with the average void height from the three case studies (6 storeys).

The generic analysis then compared a 6 void plan against one with three, adding spatial quality to the voids themselves and more opportunities for leisure and

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communication. Results showed hardly any difference in terms of thermal performance, recording a difference of 5% for hours within comfort and less than 1.5% for overheating hours. Moreover, there were no noticeable changes regarding daylight either between both plans, recording that more than 95% of them are within adequate daylight levels and therefore, not needing artificial lighting for almost half of the year. However, in terms of cooling loads, the 3 void scenario records loads over 5.7 times higher than the other one.

The ventilation study displayed that both buildings achieve cross ventilation even in a cellular plan (in the 3 void building only 30% of the plan does not achieve it).

In addition, it was demonstrated that voids help to reduce wind velocities and allow a better distribution of the airflow across the plan. Due to the building internal layout’s form, the highest speeds are around the core and not in the office spaces, indicating that perhaps some resistance such as vegetation should be implemented. However, the simulations indicated that for outdoor velocities of 2 m/s, the aperture area should be reduced to achieve comfortable indoor speeds.

Furthermore, results indicate that the void-to-net area ratio could still possibly be reduced to gain more usable office space, without harming the overall performance of the building. Further studies should be carried away in this matter.

Climate change scenario showed an increase in overheating hours of between 7.85 to 5.1 times.

Regardless, hours within comfort show a difference of only 6 to 8.5%, indicating that the voids can manage even higher temperatures without decreasing their performance in a noticeable way.

The addition of vegetation is useful not only because it enhances people’s wellbeing and quality of life, but also due to the cooling effect it can provide, reducing air temperatures in hot summer days, and hence, reducing energy consumption. It can also help reduce air speeds, and provide a better balanced airflow through the building, as demonstrated in the corresponding section’s simulations. The effect of trees and living walls in the voids was to reduce temperatures by up to 1.2°C, achieving a Delta T of 2°C. In case of the offices, the impact is mostly seen in the first two floors where both types of vegetation are working together, accomplishing an average difference of 0.6°C between a building with greenery and one without it, and a Delta T of around 1°C. In higher storeys, the effect of the living walls is reduced to the immediate area surrounding them, but still being able to reduce temperatures by 0.15°C.

In summary, although the aim of this thesis was not to provide a universal specific solution for a tall building’s void design, it can be established and demonstrated that that this type of design provides this building typology with opportunities to introduce passive strategies, boosting the project’s environmental performance. They do so by cutting the floorplate and bringing daylight and fresh air to the deeper parts of the plan. In this way, voids minimise energy consumption and carbon footprint while supplying the building with spaces for leisure, wellbeing, communication, and connection to the outdoor conditions and Nature. It also provides an opportunity for users to manage the room’s internal conditions by themselves, according to their needs and external climate. Nevertheless, the design of the void itself will vary according to the building’s form, envelope and context, and special attention has to be paid in order for the overall design not to affect its surroundings in a negative way. Tall buildings have to be designed under strict environmental policies, with an environmental design approach and in the appropriate context. If this is planned correctly, and climate and culture acknowledged in the design, tall buildings can carry great environmental potential.

Figure 6.1: Tall buildings + vegetation. Source: Wikipedia

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