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L OWE NE RGYBUI L DI NGS Wh y a n dH o w?




P I CT URE S : I S OVE R2 0 1 0


TITLE PAGE BATCoM Bachelor of Architectural Technology and Construction Management

DISSERTATION TITLE: Low-energy buildings. Why and How?

CONSULTANT: Hanne Ælmose Iversen AUTHOR: Ralitsa Yordanova Yordanova DATE/SIGNATURE: November 2012 /Ralitsa Yordanova/ VIA Student number: 123818

Number of copies: 2 Number of pages: 25 (2400 characters per page) Number of characters: app. 63000 Font: Arial 12 pt. All rights reserved – no part of this publication may be reproduced without the prior permission of the author.

NOTE: This dissertation was completed as part of a Bachelor of Architectural Technology and Construction Management degree course – no responsibility is taken for any advice, instruction or conclusion given within!

Abstract Low-energy concept is widespread topic nowadays. There are different strategies for achieving low-energy buildings, even numerous standards in the various countries – reaching even for the nearly zero-energy house. This report tries to underline and examine the most common principles in the building design of lowenergy houses. It will introduce several points that will significantly decrease the energy demand of a building regardless of its geographical location. The points covered will be: insulation and cold bridges, airtightness and ventilation. It will also clarify the reasons behind the idea of using the aforementioned components and present different methods of implementing them.

Key words: low-energy building, passive house, insulation, thermal bridge, airtightness, ventilation.

Problem Statement ................................................................................................. 1 Introduction............................................................................................................. 2 Insulation ................................................................................................................ 3 Saving Energy ..................................................................................................... 3 Saving Money ..................................................................................................... 8 Measures on a higher level ............................................................................... 10 Prevents Structural Damage ............................................................................. 11 Thermal Mass ................................................................................................... 12 Thermal Comfort ............................................................................................... 13 Thermal Bridges ................................................................................................ 14 Airtightness........................................................................................................... 17 Ventilation............................................................................................................. 19 Reflections............................................................................................................ 24 Conclusion............................................................................................................ 25 References ........................................................................................................... 26

Figure 1: Up - thermographic image of a renovated building; down – photograph of the same building, (Passivhaus Institut, 2002) ........Error! Bookmark not defined. ...............................................4 Figure 2: Wall constructions from left to right: brick-insulation-brick; concreteinsulation-plaster; concrete-insulation-fiber cement cladding; wooden post and beam structure with insulation and wooden cladding; wooden main frame with steel c-profiles in between, insulation and wooden cladding; Trombe wall. ............ 6 Figure 5: Foundation details. .................................................................................. 7 Figure 6: Mold and damage on a ceiling. ............................................................. 11 Figure 7: PCM inserted on a ceiling.(ClimateTechWiki, n.d.) ............................... 13 Figure 8: T thermographic image of construction with thermal bridge (up) and without (down). (Passivhaus Institut,n.d.) ............................................................. 15 Figure 10: Construction details of roof to wall connection (up) and balcony connection (down) without thermal bridges. ......................................................... 15 Figure 9: Typical details where thermal bridges may occur. ................................. 15 Figure 11: The principle of the pen - The airtight layer should surround the whole building envelope in every cross-section. ............................................................. 17 Figure 12: Two step seals from up to down: Mastic seal and polyethylene backing; round rubber profile; multi rubber profile; impregnated self-expanding seal; mortar joint. .................................................................................................. 18 Figure 13: Diagram for ventilation. ...................................................................... 20 Figure 14: Principle drawing of mechanical ventilation with heat recovery and subsoil heat exchanger (optional). ........................................................................ 21 Figure 15: Principal drawing of heat exchanger with cross channel counter flow concept from PAUL Wärmerückgewinnung. (PAUL Wärmerückgewinnung, n.d.) 22

Table 1: Table showing popular construction materials, their thermal conductivity and thickness needed for an U-Value of 0,13 W/m2K. (Генчев, Здравко, 2010) ... 5 Table 2: Reference between the energy performance of a house with car and oil consumption.(Isover, n.d.) ...................................................................................... 8 Table 3: Showing a connection between the U-Value, the annual heat losses and the cost of these losses.Passivhaus Institut,n.d.) ................................................... 9 Table 4: The per cent CO2 from the volume of the air in the room depending on the time the windows are closed.(Passivhaus Institut, n.d.) ................................. 20

Problem Statement I remember not a long time ago the sustainable approach was not the most popular one. Of course there were always people that care for the environment and I definitely see myself as one of them. “Everybody can make a difference and make the world greener, cleaner and more sustainable!” was what they taught me. And this is true! I believe that as architects we must carry that mission, “infect” the others with this attitude and influence the world with our sustainable design. Of course sustainable is broad concept – it covers economic, social and ecological problems. “Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” 1 Low-energy buildings are one of the most common and straight-forward ways of doing so. The report focuses on the principles and practices behind lowenergy concept in the building industry and especially on the methods that could be implemented in every weather conditions and do not depend on the plot. Renewable energy sources, such as PV, solar panels or wind turbines are not prior to this report but only the “rules” that should be followed in order for a lowenergy building to be built. The dissertation is written from strictly architectural and technical point of view and does not cover the management issues around lowenergy buildings or the procedures for certifying as such. It examines the most common principles and practices needed to be kept in mind when designing lowenergy buildings and it will try to answer the following research questions: 1. What properties does the insulation have? Why is insulation important in low-energy concept? What are the advantages of the usage of insulation? 2. What is a thermal bridge? Why is it important that the constructions in lowenergy buildings should be thermal bridge free? What are the advantages of thermal bridge free construction? 3. Why is airtightness important in low-energy concept? What are the advantages of an airtight building? 4. What is the importance of ventilation in low-energy buildings? What are the advantages of the mechanical with heat recovery? This dissertation is written as part of my final semester of the education as Bachelor of Architectural Technology and Construction Management in VIA University College, Horsens, Denmark. The report is based on a secondary research and the methodology used is analytical.


World Commission on Environment and Development’s (the Brundtland Commission) report Our Common Future (Oxford: Oxford University Press, 1987).


Introduction It is well-known fact that the Earth is facing a lot of serious problems nowadays concerning the environment – polar caps are melting, hurricanes and tornadoes occur more often, floods and draughts take their victims every year, pollution is in its highest peaks. It is also not a secret that the people should have acted towards a drastic change a long time ago. We as architect have the luxury to play one of the most significant roles in this change – our opinions, reflecting in our design can make a difference. Cradle to cradle design was invented in response to the waste treatment issue. Using new materials, dibbling trees before cutting them was the answer the architects gave to the world when deforestation began. Once presenting the embodied energy as a problem – life-cycle calculations started to be made by the architects. Ever since the Industrial Revolution the emission levels of CO2 had drastically increased – and they will not be stabilized for another 100300 years2 after the measures taken today, so we need to act quickly. This is why “sustainable” is a word that we use often today and not just in the architectural circles. The sustainability changes the core principles of the architectural design; therefore it changes the design itself and its practices, so the logical step is to be included in students’ education everywhere. Low-energy construction is a really big part of the sustainability issue in architecture. Around 40% of the energy consumption in Europe and the USA is consumed directly of the building industry – for planning, construction and maintenance. It is estimated that in the European Union countries the saving potential in this field is almost 29% making the nowadays 40% to the future 11%, or in other words reducing the energy input and energy waste from a building with 70%. The average CO2 emission decrease from one Passive house is 2,4 tons per year. It also consumes 80% less energy than a average house. Also in the European Union countries about 70% of the household energy demand is associated to ambient heating 3. The ambient heat is heat available for free from environmental sources like the sun, building materials, or air. Heat can also be stored, or conserved, by using insulation methods. So, it can be gathered when it is freely available and used when it is needed. There are a lot of different ways of saving energy in the building – from the construction principles to the everyday habits of its occupants. The Passivhaus standard is the pioneer in its field – trying to set criteria for a low-energy house. Of course the idea was not new, but it was one of the first times to act on it and the first certified house was built in 1990. The basic concept is to try to minimise the use of energy in every way – for heating, electricity, ventilation, etc. So in order to 2

IPCC, 2001: Climate Change 2001: Synthesis Report. A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Intergovernmental Panel on Climate Change [Watson, R.T. and the Core Writing Team (eds.)]. Cambridge University Press, Cambridge, United Kingdom, and New York, NY, USA, 398 pp. (on-line edition) 3 Passive Home Training Module for architects and Planners, Passive-on Project, 2007


achieve that, energy saving methods must be used of course – or passive methods. These are the clever ways of saving on energy – through exploiting the well-protected building envelope and the hidden reserves of energy in the building; through implementing smarter technologies in the house. Naturally, all of these are different from project to project. No certain formula is developed so that it can insure a low-energy dwelling or even Passive house standard approved one, but there are some simple steps, which if followed will definitely lower the energy demand of a building and could be realised in every weather conditions. In some cases such building may in fact produce more energy than they actually use. Naturally nowadays the Passivhaus standard is not the only one and almost every country in Europe has developed one on its own. Of course the basis of these concepts is minimising the energy waste in buildings and utilising low-energy constructions. This report covers the common methods used in low-energy buildings.

Insulation Of course when speaking of low-energy houses the first thing that comes to mind is insulation. Indeed, the usage of insulation was difficult to acknowledge in some countries, especially where the climate is warm and the people and mainly looking for affordable housing. Fortunately, nowadays it is really common to use insulation when designing a house and more and more architects from all over the world are using it. The greatest thing when adding insulation to a construction is that it can give positive outcome in more than one ways and the benefits will be not just for the same of the construction but also directly for the owners and last but not least for the environment. The benefits of using insulation are several:  Saves energy and reduces energy waste in buildings.  Cuts on heating costs.  Together with the properties of the thermal mass could even be used as an energy source.  Prevents structural damage.  It is a measure the governments’ policies promote too, so sooner or later every building should comply with it.

Saving Energy We cannot talk about insulation and not mention the U-Value factor or the overall heat transfer coefficient (formerly known as K-Value). This is actually what defines the insulations as such. The U-Value is the energy transferred (“lost”) in Joules by 1m2 of surface when the temperature difference is 1K (1°C) for one second. Or in other words the rate of heat transfer in Watts for 1m2 with temperature difference 1K. The U-Value is measured either of surfaces, collection of surfaces or components – roof, walls, floors, even doors and windows. The smaller the UValue – the better level of insulation the component has and less energy is wasted 3

(Fig. 1). Comparison could be made between the renovated building in the right and the non-renovated behind in the left. It is easy to see that the temperature of the latter one is higher; therefore more temperature is transferred to the environment. But then again the U-Value is for components, which means that depending on the combination of materials and their thicknesses the U-Value will change. This is why every material is characterized by thermal conductivity factor [W/mK] – the rate of heat transfer per linear meter when the difference in the temperatures is 1K. And one more time – the better the thermal conductivity (usually indicated by λ) – the better insulation properties the material has.

Figure 1: Up - thermographic image of a renovated building; down – photograph of the same building, (Passivhaus Institut, 2002)

Hence this presupposes that the entire building envelope must be very well insulated, thus separating the inside from the outside forming a so to speak barrier between the climate in the house and out of it. Typically from October to April the temperatures outside are lower than the inside. During this time of the year the insulation will keep the rooms in the building warm and cosy. On the other hand in hotter climates, especially nowadays, in the summer the temperatures may rise above 43-45°C and surviving inside will become almost impossible and the thermal comfort is out of reach. But when the building envelope is well insulated the temperatures inside will be a lot lower than on the outside in these cases. So basically the insulation also works both ways – it keeps us warm in the winter and chill in the summer. Our ancestors, as a matter of fact, used insulating material a long time ago – straw and actually their houses were a lot better, as far as the energy demand is concerned, than some of the houses built later with only bricks or concrete. Fortunately, the insulation was rediscovered in the recent decades. And still a straw bale wall of thickness about 500mm is also sufficient for low-energy house, since the U-Value usually should be between 0,1W/m2K and 0,15W/m2K. Of course this means that materials with good (low) thermal conductivity should be used, so the walls for example will not be that thick.


The first part of the Table 1 is for comparison only – it is obvious that too much of the materials must be used in order a low heat transfer to be ensured. The second part on the other side is showing very good insulation materials. Some of them are Material Reinforced concrete Solid brick Perforated brick Soft wood Porous brick/concrete Straw Insulation High-quality insulation Air (stagnant) Nano porous superinsulation material normal pressure Vacuum insulation material (silica) Vacuum insulation material (high vacuum)

Thermal Conductivity [W/mK] 2,30 0,80 0,40 0,13 0,11

Thickness needed for 0,13 W/m2K [m] 17,3 6,02 3,01 0,98 0,83

0,055 0,040-0,034 0,025 0,024 0,015

0,41 0,3 0,19 0,19 0,11





Table 1: Table showing popular construction materials, their thermal conductivity and thickness 2 needed for an U-Value of 0,13 W/m K. (Генчев, Здравко, 2010)

for common use – as the insulation for example. This is because using normal insulation (usually 0,37 W/m2K) is the most economically advantageous solution – or you do not pay so much and still you get a wonderful quality. But the polyurethane foam insulation for example has better λ value but is also more expensive. The vacuum insulation is relatively new solution on the market and still under development, since even small damage could destroy the vacuum and the thermal bridges at the joints are hard to avoid. These isolations are usually silicic acid in envelope of glass, metal or metal coated synthetics and evacuated, so there is no heat transfer. The fixing is done on the edges of the panels, so additional harder protective layer is installed as extra precaution. Of course the panels must be made with tolerances but this leads to weakness in the joints of the panel. So at this spots the panel is covered with the common insulation material, but since the panel is not thick enough – the insulation thickness is also not enough. For this reason the whole panel is covered with conventional insulation, which protects its surface too. Therefore the vacuum insulation is primarily used in renovations where the necessary height of the room will not be sufficient if normal insulation is used; in restorations of historical buildings or patios above heated place with a barrier-free transition between the in- and outside. 5

Of course the thermal protection of the building envelope is achieved by combination of materials in the different constructions. At the moment good UValue is a must in all types of construction, regardless of the component or the choice of construction – brick, concrete, wood and/or steel post and beam structures. On Fig. 2 there are shown different solutions that could be used in a

Figure 2: Wall constructions from left to right: brick-insulation-brick; concrete-insulation-plaster; concrete-insulation-fiber cement cladding; wooden post and beam structure with insulation and wooden cladding; wooden main frame with steel c-profiles in between, insulation and wooden cladding; Trombe wall.

low-energy house, even a passive ones, where the energy requirement for space heating is smaller than 15kWh/m2*year and the maximum energy consumption as a whole not more than 120kW/m2K*year. Other low-energy standards where these details could also be used are the Swiss Minergie (38kW/m2K*year), French Effinergie (50kW/m2*year) and the Danish Klass 2015 (30 + 1000/A kW/m2K*year where A is the heated floor area of the building). The right most detail in Fig. 2 is the so called “semi-translucent” technique or Trombe/solar wall – where glazing is installed in front of the insulation. In this way some of the sun radiation is captured in the wall construction and rises its temperature. When this is done the actual U-Value is not so low, but the temperature difference between the inside and the outside is smaller, therefore the heat transfer is less. This solution works better in chillier climates – northern Europe, Scandinavia included. But trying to integrate this concept in warmer countries may be fatal, since it may lead to irreversible overheating. Therefore this “insulation” layer does not work in hot weather. Similar technique uses the translucent/transparent insulation. It is installed in front of a solid wall and the solar radiation is able to go through it and be collected by the solid wall and then released inside. The same as the Trombe wall this decreases the heating transfer and demand for the building. Nevertheless, using transparent insulation is not so widespread since the transparent protective layer inside is rather expensive and due to a probable overheating problems louvers, blinds or translucent coating must be bought, which also adds to the price. The transparent insulation also does not work in cold climates, since it is

Figure 3: Honeycomb insulation, (Barsmark A/S, 2010)


insufficient to achieve positive energy balance for the wall as a whole. Similar to the transparent insulation is the honeycomb insulation panels (Fig. 3). Both of them look alike but the difference is that the honeycomb does not allow the light to reach the interior. It absorbs the heat and acts like a buffer to the solid wall behind. Hence depending on the season and weather conditions the honeycomb could be more or less heated and also the horizontal elements prevent convective heat losses. Another great advantage is that is it fully recyclable.

Figure 4: Roof constructions from left to right: concrete-insulation-asphalt; steel trapeze platesinsulation-steel covering (with ceiling); wooden trusses-insulation covered with OSB plates, on top roof tiles (with ceiling).

On Fig. 4 are shown typical roof constructions and it is obvious that they are very well insulated. Actually the design heat flow resistance (which is inversely proportional to the λ) of the roofs with a pitch up to 30° is the lowest from all the other building components. This means that more heat is transmitted from the roof than from the walls or floors. This comes naturally since the heated air rises and is more likely to escape from up than down. Roof also appears to be the most complicated part of a house construction because for example the majority of building mistakes in Denmark are mainly in the roof area – around 90%. This is why the attachment of insulation in the roof must be done very carefully and if the roof is ventilated the insulation (as in the rightmost detail in Fig. 4) must be very well covered so it does not get wet and damaged, since this will destroy its insulating qualities. On Fig. 5 up is shown typical ground supported floor and foundation construction used in Denmark. The depth of the foundation is 900mm – it is below the 750mm set as frost free depth. The upper part of the foundation is executed with two blocks of Leca term 450mm. 4 In this way the heat transfer is minimized since the blocks are made with 195mm insulation in the middle and the concrete is light and porous. The Figure 3: Foundation details. 4


total U-Value of the Leca term is 0,15W/m2K. The idea behind Fig. 4 down is that the house together with the inner flange of the foundation is staying on a concrete layer. The latter is casted together so different movement is avoided and the air penetration is more unlikely, which means that the building is more protected against radon. This solution is developed by Sundolitt A/S and is leaning towards principles used in south Sweden for some time now. The foundation depth is definitely lower – just 400mm and the soil above the perimeter drain respectively 600mm. Hence it is highly possible for the foundation and drain to freeze. This is why the outer flange of the foundation is casted in an U-shape EPS insulation than the front part of the insulation is taken and put down to lay as shown in Fig. 4 down. In this way the outer leaf of the foundation is totally separated with insulation from the inner one, so the building envelope is better thermally protected. Also the cut piece of insulation with a length of 500mm protects the perimeter drain of being frozen. Sometimes in countries with hot climate the ground supported slab is not insulated, because in the winter the building does not “loose” much energy from it – since the soil temperature is around 10-12°C and in the summer the house can cool down better. This is due to the fact that the soil temperature during the whole year is actually really close to the average air temperature a year. Of course there are multiple other solutions of insulating the building components. Some are easy to execute, others a little more complicated but it is true that in the contemporary architecture and construction there are numerous principles of solving one detail, proven over time. Nevertheless now and then they should make room for new, innovative solutions. Anyway the main point is that insulating the building envelope is a concept worth implementing.

Saving Money Sometimes the idea of just helping the environment or improving the building as a whole is not enough for the public to be convinced in using insulation. A better translation of the insulation properties is in money. In Table 2 5 it is shown the

Old Building Building Regulations Low-energy house Passive house/ Komfort husene

Car Gasoline Litre/100km 20 8-10

House kWh/m2a 200 80-100

House Heating Oil Litre/m2/yr 20 8-10







Table 2: Reference between the energy performance of a house with car and oil consumption.(Isover, n.d.) 5

Information from Isover brochure


principle of saving money in low-energy (Passive house) buildings. Here the difference between the buildings is obvious. If we assume that there is a singlefamily house with a perimeter of 40m (10x10m – area 100m2), wall height 2,5m and 22% of the heated floor area is glazing then the wall area is 78m2. For these 78m2 then the difference between 200kWh/m2a and 15-50kWh/m2a is enormous. Similar example with the same area is presented in Appendix 1. There are two types of wall – with and without insulation. The U-Values have a big difference and the kWh per annum even more. And imagine that this difference in the heat transferred loss comes out of the consumer’s pocket. On Table 3 6 is shown another example of the cost saving capabilities of the well-insulated building component. Even that the insulation material is relatively expensive the investment in it is repaying fast enough not only for the environment but for the user also. After all saving 591 € a year just from the external wall is not bad at all. And a U-Value of 0,10W/m2K is not difficult at all to achieve – it will for example work for any construction and probably even be lower with and insulation of 400mm and λ value around 0,037W/mK. U-Value [W/m2K]

1,25 1,00 0,80 0,60 0,40 0,20 0,15 0,125 0,10

Heat Loss Rate [W] 4125 3300 2640 1980 1320 660 495 412 330

Annual Heating Losses [kWh/yr] 9750 7800 6200 4700 3100 1600 1200 975 800

Annual Cost External Wall Only [€/yr] 644 515 409 310 205 106 79 64 53

Table 3: Showing a connection between the U-Value, the annual heat losses and the cost of these losses.Passivhaus Institut,n.d.)

The insulation is a powerful tool for saving. Even though the investment is quite big for some people at the beginning, it is definitely paying off and fast. Let us not forget that on Table 3 it is shown how much can be saved from the wall and not surprisingly it becomes even more if the other building components, such as roof, floors are well thermally protected too. If the thermal protection of the building envelope was not financially beneficial then the energy service companies (ESCO) will not be so interested in it. ESCO have developed a financial model for supporting the implementation of energy saving projects, which is beneficial as 6

According to calculations of Passivhaus Institut, assuming a gross price for heating of 6,6€cents/kWh


much for the company as for the clients. The principle of the ESCO business model is that the company covers every cost in connection with the energy renewal of the building and the client pays them with the money he saved from bills in the next few years. This means that ESCO comes with a proposal to renew the house, then does it, but just for the couple of next years the owners continues to pay the same amount of money for the bills, that he used to. Then after the contract has expired the owner of the house has a renewed home for free and smaller energy bill, due to the energy savings. As we can judge from this business model – improving the thermal protection of the building envelope definitely pays off and fast too.

Measures on a higher level From what we see above the demands are really harsh. This actually means that nowadays instead of heating up one house we could heat up ten and more (referring to Table 3). The good news is that the requirements will get stricter and stricter in the future. For example the Danish Building regulations 2010 set the line for the total demand of energy supplied to a building (house, hotel) to cover heat losses, ventilation, cooling and domestic hot water to a 52,5+1650/A kWh/m2 per year, where A is the heated gross floor area. For offices, schools, institutions, etc. the demand is 71,3 + 1650/A kWh/m2 per year but it also includes the energy for lightning. In the energy frame for 2015 this demand lowers down to respectively 30 + 1000/A kWh/m2 per year and 41 + 1000/A kWh/m2 per year. In 2020 they will be 20kWh/m2 and 25kWh/m2. Also the standard BOLIG+ stands for energy neutral building (year to year) or a zero-energy building that produces the same amount of energy or even more than it consumes. All this is due to the fact that the European Union aims to reduce the domestic greenhouse gases with 80% by 2050 compared to the levels in 1990. Since the building industry is responsible for the major part of the greenhouse gas it should have an even higher reduction coefficient of 0,88-0,91 7. More than one quarter of the building stock in 2050 is still not built, which means that exactly this 25% of the future 2050 buildings will compensate in relation to the greenhouse gasses for the other approximately three quarters that are already here. It is also no coincidence that more and more developed countries have their own standards for low-energy houses or even nearly zero-energy buildings (NZEB). It is true that even though there has been literature covering this topic from the 70ties until recently there was not a uniform explanation of the NZEB concept. In 2010 recast of the Energy Performance in Building Directive (ERBD) the European Parliament and Commission stated that by the end of 2020 all new buildings must be nearly zero-energy and all public owned new buildings must be NZEB from the end of 2018. According to the EPBD a nearly zero-energy building is:


COM(2011) 112 final, A Roadmap for moving to a competitive low carbon economy in 2050.


“(...) a building that has very high energy performance (...) and the nearly zero or very low amount of energy required should to a very significant extent be covered by energy from renewable sources, including renewable energy produced on-site and nearby”. In Denmark, Norway and the United Kingdom there are already research centres on the NZEB. A lot of countries in the EU had make a commitment (including the aforementioned three) to reduce the energy output from the buildings, even France’s goal is more ambitious – to make by the year 2020 all new buildings energy-positive. An energy positive building could even sell back electricity to the electricity companies is some countries which makes in more attractive to the public. Also the Swiss standard Minergie recently develop the Minergie-A, standard for NZEB. Every year there are numerous presentations held in Europe with representatives from almost every country, which share knowledge and exchange ideas in the field of low-energy architecture and nearly zero-energy buildings. Referring to these excessive measures the governments and the EU takes it is to conclude that reducing the energy usage of the buildings is really important. Instead of waiting for the change to overtake us, we can be the beginning of the change. In this way of thoughts investing in insulation is good move since the governments` policies promote it too.

Prevents Structural Damage The good thermal protection also prevents form structural damage. When outside the temperatures drops the wall without insulation becomes cold too. This means that the inner surface on the wall will be cold too. When the hot air from the inside reaches the cold surface of the wall condensation begins, or in other words there is a dew point. The steam in the air Figure 4: Mold and damage on a ceiling. (or the vaporized water in the air) when in contact with the wall becomes water, since its temperature drops when exchanging energy with the wall. This means that during the chillier months of the year there will constantly be moisture build-up on the wall, combining this with the low temperatures of the wall itself and there are the perfect conditions for growing mould (Fig. 6), especially behind counters and fixed furniture. The moisture is able to ruin the construction fast or at least accelerate its aging process, shorten considerably its life-cycle or increase the maintenance cost. Condensation and moisture build-up are particularly fatal when talking about wooden constructions, since they are highly susceptible to decoy.


On the other hand mould and moss are dangerous and could cause a lot of allergies or even asthma. Having them in the house is particularly risky when there are children in the house. Combining this with neglected radon protection (radon is responsible for about 2% all deaths from cancer in Europe8) and there is a high chance of lung illness. If concrete is used as a material for the external walls then again not using insulation hides a high chance of structural damage. The concrete is a really strong material and can withstand a great value of pressure (compression), but its weakness is when submitted to tension. When concrete is expanded it usually cracks – especially if this happens numerous times during its life-cycle. Having insulation in the construction changes the situation, especially if the insulation is on the outer side of the wall. In this way the concrete is able to maintain an almost constant temperature during the year, resulting in fewer cracks in the concrete, less costly maintenance and longer life-cycle.

Thermal Mass Another key factor in the thermal protection of the building is the thermal mass capacity of the elements in its construction. This is the ability of the building to store and regulate internal heat. Houses with low thermal mass heat up really fast but also cool down fast. This means that every little change in the temperature affects the indoor temperature of the building and it is subject to wide variables in the internal temperature. On the other hand, materials with high thermal mass result in steady indoor temperatures. Every material inside the house contributes to its thermal mass. The ability of material to store and absorb heat is called thermal capacity of specific heat capacity (as known in physics). Brick, concrete and stone have high thermal capacity, but air has low, so the only way for the air to stay warm longer is if the building components surrounding it have warmed up. For low-energy house the high thermal mass is advantageous, because in this way the heat gain during the day could be used for night time heating. This is why a technique where the South facing façade and floors are solid and in dark colour could be applied, in order to maximize the solar radiation gains. The high thermal mass also equals the daily fluctuations in temperature. If of course also works when the building needs to be cooled down – in the night time ventilation takes the heat off the components during dark, then when in the day they can absorb the heat, instead of transferring it to the interior. Different approach could be used with light external wall construction and design relying on the thermal storage capacity of the interior. Unfortunately, when the thermal protection of the building is really good then overheating problems may arise. Of course this extra heat could be ventilated out or just prevented at the first place (shades, louvers, etc.). But in this way the heat 8

Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies, S. Darby 2004


is “lost”, since usually if collected could be used afterwards. This is when the thermal capacity comes to the rescue, but it cannot always absorb the full amount of solar radiation. This is why phase change materials (PCM) could be used. These heat storage components absorb heat while changing the aggregate state of the material (liquefaction) and in the same time maintaining its temperature. When the temperature drops the PCM crystalizes and therefore releases the stored heat. The water is an example of a phase changing material. In the PCM the change in aggregate conditions happens within the range of room temperatures. They can be used for heating up or cooling down the interior. Usually the PCM are organic (made form carbon) or salt and paraffin are used and they come in a wide range of formats – pouches, containers or double-webbed panels. They could be implemented as a form of napped sheeting in floors or ceilings (Fig. 7) and their micro-encapsulation makes it possible to add the material to plaster. For example in the Rotterdam floating pavilion that bears resemblance with the Eden project uses PCM in their conference room. If absorbs energy (liquid phase) when the temperature is above 21°C and heats up the space (fixed phase) when the temperature is below 21°C. The PCM have also a great storing capacity even when minor changes in the temperature occur. It could also reduce the weight and thickness of the construction – 20mm of gypsum plaster with 30% content of PCM admixture equal the average daily thermal storage capacity of 180mm concrete. However, usually the domestic building have the necessary thermal mass even without the usage of PCM, though in office building the PCM may prevent overheating issues during the day and the Figure 5: PCM inserted on a ventilation in the night can then drop down the ceiling.(ClimateTechWiki, n.d.) PCM temperature.

Thermal Comfort Using insulation in the building or thermally protecting a building creates more comfortable environment for the users – it improves the thermal comfort of the inhabitants. The thermal comfort is the state of the mind, which expresses satisfaction with the thermal environment. Due to individual differences it is impossible to specify a thermal environment that could content everybody at any time given, but it could definitely predict an environment that can be acceptable by the major percentage of the occupants. Comfort models describe to what range of conditions people will feel thermally contented in buildings. One of them is the Adaptive Model. It proposes a correlation between the comfort temperature of the occupants and the outside temperature. The idea behind this is that the human body adapts and makes changes in its metabolic rate, so people will feel different temperatures as comfortable in relation to the season. 13

Another model is the Fanger model, named after the Danish scientist Povl Ole Fanger (ISO 7730). According to him optimal thermal comfort is present when the heat the human body produces is equal to the heat it releases. Obviously, there is a relationship between the thermal comfort and the activities of the occupants – since different heat is produced if the person in sleeping or running for example. The clothing also matters, but factors from the indoor climate count too – like the air temperature, the temperature of the surroundings (radiant temperature), the air speed and turbulence and the air humidity. There are number of combinations between these factors that need to be followed.  The relation between the steadiness of the air and its humidity  For air speed under 0,8m/s the displeased from draughts must be maximum 6%  The difference between the room temperature and surface temperature is small  The difference in radiant temperature ( or the radiation temperature asymmetry) is less than 5°C  The difference between the temperatures of the air next to the head and ankle of sitting person in no more than 2°C  The variance in temperature in the different corners of the room is not higher than 0,8°C Apparently, the better the insulation level is in the building the better will be the thermal comfort. Of course the air humidity depends on the room temperature – the higher the temperature – the lower the humidity rate. Also the heat flow from outside is reduced and if the heat from inside wants to escape it has to overcome the thermal resistance of the surface, therefore the difference in temperature between the surfaces and the air in the room is smaller. Good levels of insulation is prerequisite for heating through the thermal mass storage of the building components and interior object, consequently that the room will be heated from multiple sources in different directions and the radiant temperature asymmetry will be small and the variance in temperatures in the different locations of the room also small. The insulation also reduces the noise pollution from outside, again improving the comfort of the inhabitants. Hence using and increasing the insulation levels in a building also improves our own perception of the home we live in or the office we go to work in. Then maybe it is not exaggerated to say that insulation makes us happier.

Thermal Bridges Not just the thermal protection of the components is crucial in a project but also the connection between them. The heat does not transfer always perpendicular to the surfaces. The heat transfer obeys the simple rule of physics that for example electricity satisfies too – they both follow the path of least resistance. Or the heat 14

“chooses” to transfer through the materials with higher λ value (Fig. 8). Thermal bridges in traditional structures lead to 10-15% of the heat loss9. This is why the insulation ought to surround the whole building envelope (Fig. 9) but this is not always so easy. Sometimes the connection details are tricky. Typically thermal bridges are found in the connection with:       

Foundations Recesses in the wall for windows and doors Fastening with metal through the insulation Floor divisions Assembling of elements Balconies Railings, parapets.

Figure 6: T thermographic image of construction with thermal bridge (up) and without (down). (Passivhaus Institut,n.d.)

If a thermal bridge plays a significant role in one construction or is a part of it, in cases of floors, walls, roofs, etc. then it is calculated in the UValue. For example in a cavity brick wall (brickinsulation-brick) the wall ties connecting the loadbearing with the non-loadbearing leaf are a constant thermal bridge all across the wall. This is why their influence is taken into account in the correction of the U-Value. On Fig. 9 are shown one of the common details which require attention when designing, since it is essential that the insulation layer is not Figure 8: Typical details where thermal broken. Every time there is a connection the bridges may occur. detail must be designed, carried and executed with precision. Of Fig. 10 are shown typical connection details. The first one (up) is a roof to an external concrete and brick wall connection. It is a standard detail and has many variations – with different roof pitches and with or without overhang. The important thing is that the insulation layer in the Figure 7: Construction details of roof to wall connection (up) and roof overlaps the one in the balcony connection (down) without thermal bridges. 9

By Isover


wall, so basically it has the same thermal protection as the other building components. On Fig. 10 down is a principal construction of a balcony connection to the building. Here the tactic used is to make the balcony a separate construction from the main one (the building). So in this way the balcony will not have to lean on the loadbearing inner leaf of the external wall. This also gives some flexibility to the building, in case later the balconies have to be enlarged, closed, turned into bay windows maybe or removed. Otherwise, this is the solution used when the balcony is cantilevered. If the balcony is supported to two columns in each end then again it is a separate construction and the thermal bridge could be avoided (maybe together with some water problems also). Recent development of technology came with a lot of solutions even if the balcony is cantilevered. One of them is to have a piece of hard insulation with reinforcement coming out and when the balcony and the slab inside are casted their reinforcements connect to this one (solution by Halfen and Isokorb). Other idea is to bolt short steel beams to the inner leaf of the construction, perpendicular to the wall. They penetrate the outer leaf and then are connected to steel frame on which the balcony is built on site. Similar solution is with brackets connected to the inner leaf and a balcony prefabricated slab with such a shape that several small pieces go through the inner leaf of the external wall and lay on the brackets. Of course there is a still a thermal bridge in these cases, but it is reasonably smaller. Actually, if a construction is carried out with a thermal bridge of 0,01W/mK or less it is automatically assumed that the detail does not have any thermal bridges. In lowenergy houses due to the big thickness of the insulation layers the construction is relatively warm, so even if a thermal bridge is present it will not cool down the surroundings so much, since basically all the construction is relatively warm. Even though this should not underrate the importance of a thermal bridge free construction details for low-energy buildings. Thermal bridges could be caused by circulating cold air in the insulation. This is why cracks in the insulation layer are taken into account when correcting the UValue – done during the U-Value calculation. This issue could be avoided in several effective ways:  The insulation is attached in an airtight way to the warm part of the building (when the insulation is on the outside).  Openings in the decks or walls connected to the outside are air tightened, so no cold air could penetrate.  The insulation is protected by the wind from the outside.  The insulation is laid in several layers.  Granulated insulation is blown into the cavity walls. These few points open the topic of another common practice in the low-energy buildings.


Airtightness Another common practice in the low-energy buildings is making them airtight. The airtightness in important for several reasons:  The prevention of structural damage  The prevention of heat escape  Cleanliness and comfort – the cold air entering the room causes inconvenience. Figure 9: The principle of the pen - The Airtightness is the building’s envelope airtight layer should surround the whole resistance to inward or outward air leakage. building envelope in every cross-section. Excessive air leakage results in increased energy consumption and a draughty, cold indoor climate. Making the whole building airtight is mainly dependent on the planning. The airtight layer should surround the whole building envelope in every cross-section as the red line on Fig. 11. The architect should design details which achieve continuity between each part of the construction and the next. He should also communicate his intentions clearly to the builder. An undisturbed airtight layer is hard to be made by the craftsmen if the planning and details of it are not thorough, simply enough because the construction is done by many people but the airtight layer should be one whole (permanently connected). Two “nearly” airtight layers will serve no purpose – leakage will still take place.

The airtightness is also the best way to avoid damage due to condensation because of the high temperature inside. As a result of wind or high pressure outside the leakage may come from exterior. The insulation is not an airtight layer (except for the foam glass panels) so the constructions must be protected otherwise. Commonly used is a membrane – it protects from air leakage and from condensation. The damp proof membrane is described by Z-Value – the higher the Z-Value the higher the protection against damp in the construction. The ZValue shows the relation between the thickness of the layer and its permeability. The air barrier should closely follow the line of the inside face of the insulation. This is why the DPM is usually put on the warm side of the insulation or maximum 1/3 in it, in cases when screwing or similar could damage it. It must also be accessible, since once the building is finished repairing the airtight layer should not be impossible. The brickwork is not airtight too. This is why the walls must be plastered and the plaster must continue to the floor. OSB and watertight gypsum panels are used again as s wind-barrier when it comes to external cladding wall. Most of the producers also offer their own solutions, so choosing the material is due to the designer. Specific danger is the window and door placement. In these cases sealants are used (Fig. 12).


Airtightness must not be mistaken with insulation. The latter slows the energy transfer in form of heat; the former slows the matter transfer in form of air leakage. Again not every airtight material can prevent condensation. Typically DPM is used, since it fulfils both demands, is affordable, easy to work with – flexible and does not take almost any space. Of course there are some innovative materials that are even more suitable to use. They can adapt to the weather conditions, which makes them perfect for every construction type. In the cold months it blocks the moisture diffusing into the Figure 10: Two step seals structure. The humidity is relatively low in winter and from up to down: Mastic seal and polyethylene backing; then the molecular structure of the material changes round rubber profile; multi and increases its diffusion resistance to an air layer rubber profile; impregnated seal; mortar equivalent to 5m.10 In the warm months the material self-expanding joint. allows any moisture that is trapped to diffuse back to the inside. Then again its molecular structure changes and the diffusion resistance drops to an air layer equivalent to 0,2m or 0,3m.11 Thus the moisture that has already penetrated is able to escape. In this way damp building elements in the construction can dry out during the summer and remain dry, avoiding mould formation and damage to the construction due to moisture. All subject to careful and effective bonding of overlapping seams in the membrane and sealing of junctions with components and around all penetrations, such as chimneys, pipes and services. The practice in designing good air barrier usually consists of the following steps:  Keep it simple – the simpler the design is, the more likely it is to be built right. For example complex forms increase the number of junctions, therefore the probability of discontinuities if higher. This of course does not mean that the design must be simple, but just that care must be taken in the design process and things should not be made unnecessary complicated.  Once decided which layer is going to be the airtight protection, it is better to stick with it. The airtight layer must be able to be tracked without lifting the pen in every cross section.  When minimising the number of different type of constructions helps, since every time two different constructions meet there is a high chance of problems arising.

10 11

Data taken for VARIO KM / VARIO KM Duplex. Data respectively for VARIO KM and VARIO KM Duplex.


 Details must be carefully designed to ensure continuous airtight layer. When doing that the construction sequence must be also kept in mind, to insure the build-ability. If construction details are not so good or the staff on site have better ways of doing them – it is better if they are revised.  Minimising the penetrations through the building envelope and airtight layer – regardless if by services, structure or construction. In the case of the pipes – a service space inside the air barrier might help, meaning to have a shaft or service room in the building. Of course some penetrations are unavoidable but then proper details must be made and the pipes for example have to be re-sealed to the airtight layer. The airtightness of a construction can be checked by “Blower-Door Test”. A ventilator brought in the building creates pressure of +/-50Pa. Depending on the tightness this ventilator has to work more or less in order to achieve the aforementioned pressure. With the help of artificial smoke the leak points could be detected. The n50 value indicates the amount of air, assuming that 1 is the whole air in the room that is changed in one hour at +/-50Pa. Or if the n50 is 3,5 this means that the air in the room changes completely 3,5 times per hour. If the n 50 is 0,5 this means that the whole air in the room will change in 2 hours, and so on. According to the EnEv (German standard for energy savings) the values for n50 without ventilation should be less than 3 h-1 and with ventilation system 1,5 h-1. In the Passive house this value cannot be more than 0,6 h-1 (corresponds usually to around 0,32-0,40l/s*m2 as commonly it is between 0,2 h-1 and 0,6 h-1. According to the Danish Building Regulations from 2010 the air change through leakage in the building cannot be more than 1,5 l/s*m2 of the heated floor area (at 50Pa pressure again), for low-energy buildings – 1,0l/s/m2. The result is the average between the measures at -50Pa (suction) and at 50Pa (overpressure). In case of buildings with high ceilings – when the area of the building envelope divided by the floor area is greater than 3, the air change must be less than 0,5l/s/m 2 of the building envelope and for low-energy houses 0,3l/s/m2. The airtightness is extremely important in the low-energy design. After all, even if the insulation layer is thick enough and the building is heated well with the leakage of the hot air out or the cold air in, so is the temperature dropping. Spending on good insulation does not make sense if the airtightness is not at its best too.

Ventilation It is a common misconception that a breathing building is better that airtight – meaning that investing in airtightness is not a good move, since the change in the air in the building is healthy. Unfortunately, this is not true because in cannot provide the necessary amount of fresh air and only excessive amount of heat is “lost”. Additionally this type of ventilation is highly dependent on the weather conditions – air speed, pressure, humidity, temperature, etc. Most of all it will also 19

not be satisfactory for the occupants, so the question comes to comfort and economy again. But then again if the necessary amount of fresh air is not let in then the CO 2 levels in the building become dangerously high (Table 5). The CO2 levels, measured as a per cent of the air volume in the room, where 0,1 volume per cent is considered as a limit value and is a factor of the indoor air quality, another indicator of the resident’s comfort. Time [h] 0 1 2 3 4 5 CO2 [vol. %] 0,036 0,140 0,240 0,336 0,428 0,516

6 0,600

7 8 0,691 0,758

Table 4: The per cent CO2 from the volume of the air in the room depending on the time the windows are closed.(Passivhaus Institut, n.d.)

It is obvious that there is an excessive need of ventilation because otherwise the air quality in the room will become extremely bad. Thus extremely decrease the comfort of the inhabitants. If ventilation is distributed by natural or passive means – large amount of heat is lost. And in order no heat it be transferred to the outside the building should be well sealed and then again the air exchange rate is insufficient (Fig. 13). So the ventilation is mandatory. For example if an air exchange of 0,33 h -1 is to be achieved, the windows should be open 5-10 minutes every 3 hours. And this is just unnecessary complicated, since nobody can follow up this schedule and on top of that great amount energy will be used to warm the air all over again (or cool it down in the summer). Many will add the point that nowadays the air outside is not hygienic enough, so purifying it is not a bad idea at all. Ventilation

Energy Consumption

Closed rooms require a regular supply of fresh air as a hygienic supply maintaining the air quality and ensuring inhabitants comfort.

With natural ventilation (through windows) a large percentage of the heat is transferred to the outside, therefore the cost for heating increases and the energy efficiency of the building decreases.



Due to the lack of ventilation the humidity in the air increases, which leads to mold, damp damage and bad air fatigue.

A tightly closed building and closed windows at all-time reduce the heating cost but also the air interchange rate.

Figure 11: Diagram for ventilation.


So when the air quality in an airtight building is to be maintained and no energy to be transferred to the outside, the logical step is to use mechanical ventilation with heat recovery (MVHR). It could be used in new or renovated buildings and not just to supply sufficient amount of air, but also as an energy saving method. MHVR will work all time of the year, regardless of the weather conditions outside. Of course the investment in MVHR is not small, but since it is very effective and saves money on energy bills it will pay back in few years. In an airtight building there must be a ventilation system anyway, but if it is with a heat recovery this means that it serves two purposes. Other advantage of this new generation of ventilation systems is that they also work silently, not disturbing the occupants in any way. The ventilation unit works as any other. It changes the air in the building – the rate is usually 0,5h-1. Usually in a Passive house for example it is 0,3-0,4h-1. Sometimes due to draught the air change could fall down to 0,25h -1 but not any further12. The humidity in the air in winter is rather low and if the ventilation rate in the house is big then the moisture produced inside will be exhausted to the outside fast and the average humidity inside will drastically drop, since the entering air is really dry. Anyway, the principle of the ventilation system is always the same. It takes the air from the polluted rooms (kitchen, bathroom, scullery, etc.) and the inlet is from the other rooms (Fig. 14). It is essential that the ventilation is balanced, so no vacuum or overpressure issues arise. The exhausted air taken from the polluted rooms must be added as a surplus in other rooms, so the internal airflow in the house is from the corridor for example to the kitchen. It is good to add the air in not so small Figure 12: Principle drawing of mechanical ventilation with room so the flow is not so heat recovery and subsoil heat exchanger (optional). perceptible. Big rooms such as bedrooms or teaching rooms in school for instance must have balanced ventilation. Once the pipes are out (usually from the roof) the distance between them should be taken into account – it must be at least 1m, which is a thumb rule. This is done because otherwise the fresh air inlet will not be so fresh, since it will just take back the dirty exhausted air, because the two pipes are in such a small proximity. 12

Border established by long-term tests by Passivhaus Insutut, Darmstadt, Germany


If all ventilation units work on the same principle how then the mechanical ventilation with heat recovery is better than the normal one? In ordinary ventilation unit the exhausted air from inside is of course warm and then it is released outside and all of its heat is wasted. And the air form the inlet is cold, so it must be heated again, which one more time is a waste of energy. In the MVHR the heat from the air which is about to be let outside is used to warm up the incoming air. This saving is welcomed, considering that usually the energy used by a ventilation system with average air exchange rates uses 20-30kWh/m2 per year13. And the MVHR can achieve an efficiency of 85-99%14, which means that it can recycle almost all of the energy used to warm up the first round of fresh air in the building. Then an exhausted air with a temperature of 20°C can warm up an incoming air with a temperature of 0° up to 18°C. And this unit uses just 2-7kWh/m2 per year. The secret of the MVHR is the heat exchanger. This is where the heat contained in the warm, extracted from the inside air is transferred to the cold air from the outside. The heat exchanger is using the so called cross channel counter flow concept invented by PAUL Wärmerückgewinnung GmbH (Fig. 15). The air flows through the heat exchanger in squaresectioned channels, which cross section (A-A) looks like chess board. In this way the heat exchange takes place across four surfaces instead of just two, this of course significantly Figure 13: Principal drawing of heat exchanger with cross improves the efficiency of the channel counter flow concept from PAUL Wärmerückgewinnung. (PAUL Wärmerückgewinnung, n.d.) MVHR. Subsoil heat exchanger could also be used. It takes benefit of the ground temperature, which 2-3m below the terrain level is always steady and between 1015°C. Hence in the winter the temperature of the ground is significantly higher that air’s temperature and in summer the opposite. This potential could be used in the ventilation system. A plastic or metal pipe with a diameter of 100-400mm (smoothwalled, rigid or semi-rigid) is placed under or close to the building with slope, so when condensation forms, it runs to an outlet or gulley. Of course the deeper it is the bigger the heating and cooling potential it has but also the excavation cost increases, so usually the heat exchangers are placed between 1,3m and 1,5m. There is an open subsoil heat exchanger, when the air form the outside is directly drawn through a screen intake in about 30m long tube and then is directly passed into the building. The closed loop one is when part of the air inside is taken, led through pipe with a length about 30-150m and then brought back to the building. 13 14

Нискоенергийната сграда, ЕнЕфект, 2010 PAUL Wärmerückgewinnung GmbH


Combination between open and closed could be made with unidirectional check valve dampers that allow open or closed operation depending on the season, fresh air requirements, humidity, etc. The subsoil heat exchanger could be very useful in low-energy houses in warmer climates, since in the summer excessive overheating is usually present and the heat exchanger could cut on energy consumption and bills. The overheating is a common problem even in not so hot climates. For example if the majority of the windows face south a lot of sun light will be entering the building. Also because of the insulation it will not be able to leave fast enough, causing overheating. An appropriate indication of overheating problem may arise is the criterion that the temperatures inside should be more than 26°C and less than 20°C just 100h per year and more than 27°C and less than 19°C just 25h per year. Usually this is rather tough to fulfil and care must be taken when designing. For example in the Danish projects Komfort Husene only 2 out of 10 houses met this conditions, which must all be met in the future low-energy class 2015 and building class 2020. Of course in houses where heating and air-condition unit are present this could be easily avoided, but in low-energy to passive houses the energy demand is low and strict so the overheating could be prevented in other ways. As mentioned before the subsoil heat exchanger is one of the options along with shading and louvers and natural ventilation. A lot of people believe that in passive house the windows should not be open, but this is not true. Natural ventilation must be an option in low-energy houses – during the day and during the night, making use of the “free” cooling effect available by opening the windows. In order to prevent breaking-ins the openings must be implemented since the beginning of the design process – for example as small windows in the upper part of a curtail wall. In addition to the natural ventilation the high thermal mass also has positive influence when it comes to cooling the building down. Here we are talking about the combination between high thermal mass and natural ventilation because otherwise with insufficient air change the thermal mass will only gain heat during daytime and release it at night, therefore increasing the overheating problems. The mechanical ventilation with heat recovery can even be the heating system of the building. With the ventilation preheated air could be let in the room. Anyway there is an air inlet in the living rooms, bedrooms, offices, etc. and with preheating this air it becomes easier to distribute the warmth in the building. Of course the air could not be heated much – just to 55°C, because otherwise it becomes dry and too hot. Anyway, a requirement established by the Passivhaus standard is that a passive house heating demand should not exceed 10W/m2K of the heated floor area. Therefore, heating with ventilation is available only in low-energy buildings, where the heating demand is low and could be satisfied this system. To sum up


the MVHR is very efficient and useful in low-energy buildings for the following reasons:  The MVHR can improve the energy efficiency significantly by recovering a heat that would otherwise be wasted.  The former also results in smaller heating bills.  Could be combined with heating, so no need to spend extra money on heating system.  Improves summer ventilation – if the system has summer bypass, which allows it to skip the heat exchanger, resulting in cooler, fresh filtered air entering the building.  Reduces condensation levels, which occur from everyday activities. High condensation levels lead to structure damage and mildew growth. The latter can cause diseases and lung problems.  Due to the low humidity levels there are no dust mites in the building.  Pollen and dust filter – the air entering the premises is filtered; hence this is in great help of the people suffering from hay fever or other airborne allergies. By reducing the dust in the air it also soothes the people with asthma. The filters also keep the insects out.  MVHR continuously extracts cigarette smoke and odours; kitchen smells and steam are quickly removed leaving the building fresh and pleasant.  The mechanical ventilation with heat recovery works silently and does not disturb the occupants at all.  Minimum maintenance – every couple of months the filters are replaced or cleaned.  Easy to operate.

Reflections The low-energy buildings are not just luxury but demand of the present, and the future of the architecture. They are eco-friendly because they have low CO2 emissions and almost no heat is transferred to the environment. Additionally, they cut the heating bills significantly and to build a passive house for example one must invest maximum 10% more than for a normal house. Usually this number is no higher that 8-9%. The low-energy buildings have longer life-cycle and better indoor climate and the advantages continue. There is no exact formula on how to build a low-energy house that will work in every situation, plot or climate. This is why the passive house standard is still experimental in a lot of countries. In the recent decade new low-energy building standards appeared and now almost every developed country in Europe has at least one and the requirements keep getting stricter and stricter. Of course there are many principles and practices of making a low-energy building. The building shape and orientation are one of them and they must be 24

thought trough since the beginning of the design process. But they are highly dependent on the specific location on the building, so there is no rule that could be applied every time. Energy-saving windows (usually with three layers) are used in low-energy buildings too, but their description is long and strictly technical, specific for the company producers. However, some measurements are common in every low-energy house regardless of the altitude and latitude, plot size, urban development, etc. Every low-energy building has well insulated components. This is cheap, easy and affordable way of improving the energy-demand in a building and could be implemented in every possible construction and detail. Avoiding thermal bridging is also a common practice in low-energy buildings. Doing that is a little bit trickier and desires individual attention to the detail, however the most common design solutions are already developed and preventing the thermal bridge in a building is not impossible mission, but a demand in low-energy architecture. The airtightness is also a requirement. Just as avoiding thermal bridges – making an airtight building is not hard but should be done carefully, since even small mistakes could damage the constructions, shorten its life-cycle and increase significantly the heating needs of the house. Fortunately, a lot of materials nowadays are developed to stop this from happening. All of the above methods are passive – meaning they save energy without using one at all. On the other hand the mechanical ventilation with heat recovery uses energy, but saves far more than that. It recycles the heat from the extracted air and with it raises the temperature of the fresh air from outside before releasing it inside. In this way the heating demand could be decreased less than 10W/m2 of the heated floor area. Furthermore, MVHR reduces the humidity in the air, preventing structural damage of the components and mildew and fungus growth, which cause allergies and bad odour. Naturally, for one passive house for example a combination or even all of the measures mentioned so far must be taken.

Conclusion I have investigated the common principles and practices in the low-energy architecture. I have analysed several ways of improving the building’s energy efficiency – through insulating the building components well; avoiding thermal bridges; improving the airtightness and using mechanical ventilation with heat recovery. All of the above could be used in various geographical locations and climates. I have pointed out the advantages and importance of implementing the measures described above and I have also shown several details explaining their application.


References Books Gonzalo, R. and Habermann, K. J., 2002, Energy Efficient Architecture, Munich: Birkhäuser Moltke, I., 1990, Energi I arkitekturen (Energy in architecture), Taastrup: Energiteknologi, Dansk Teknologist Institut Д-р арх. Генчев, З., 2010, Нискоенергийната сграда, София: ЕнЕфект Център за енергийна ефективност

PDFs Boermans, Y., Hermelink, A., Schimschar, S.,Grözinger, J., Offermann, M., (Ecofys Germany GmbH) and Thomsen, K. E., Rose, J., Aggerholm, S. O., (Danish Building Research Institute Sbi, 2011, Principles for Nearly Zero-Energy Buildings: Paving the way for effective implementation of policy requirements: Executive Summary, [pdf]: Buildings Performance Institute Europe (BPIE) [pdf]. Accessed at: <>. [Accessed 2012]. European Council for an Energy Efficient Economy, 2011, Steering through the maze #2 Nearly zero energy buildings: achieving the EU 2020 target, [pdf]. Available at: < > [Accessed October 2012] Government of Ireland, 2008, Limiting Thermal Bridging and Air Infiltration Acceptable Construction Details, [pdf]: Comhshaol, Oidreacht agus Rialtas Áitiúil, Environmenr, Heritage and Local Government; HomeBond and SEI Sustainalbe Energy Ireland. Accessed at: < s/FileDownLoad,18749,en.pdf>. [Accessed October 2012]. Isover, 2010, Active for more comfort: The Passive House Association,1st Edition [pdf]: International Passive House Association, Darmstadt. Available at: < chure.pdf?-session=user_pref:42F9490C1b3982CE24xpuy174BAF>. Accessed October 2012. Isover, n.d., Live comfortably – Save natural resources. The Isover Milti-Comfrot House. [pdf]. Available at: <> [Accessed October 2012].


Isover, n.d., The Isover System for Airtightness and Moisture Protection, [pdf]. Available at: <>. [Accessed October 2012].

Larsen, T. S., Jensen, R. L. and Daniels, O., 2012, The Comfort Houses: Measurements and analysis of the indoor environment and energy consumption in 8 passive houses 2008-2011, [pdf], Ålborg University. Accesible at: < ements%20and%20analysis.pdf>. [Accessed October 2012]. Marszal, A. J., Bourrelle, J.S., Nieminen, J., Berggren, B., Gustavsen, A., Heiselberg, P. and Wall, M., 2010, North European Understanding of Zero Energy/Emission Buildings, [pdf] Trondheim: Ålborg University, Norwegian University of Science and Technology, VVT Technical Research Centre of Finland and Lund University. Accessed at: <>. [Accessed October 2012]. The Passive-on project, 2007, Passive-On: Marketable Passive Homes for Winter and Summer Comfort, Passive Home Training Module for Architects and Planners, [ppt]. Available at: <> [Accessed October 2012] Thomsen, K. E., 2011, Danish definition of “Nearly Zero-Energy Buildings”, [pdf] Danish Building Research Institute, Sbi, Ålborg University. Accessed at: <>. [Accessed October 2012]. Tommerup, H. and Svendsen, S., 2006?, Innovative Danish Building Envelope Components for Passive Houses, [pdf]. Kongens Lyngby: Technical University of Denmark Available at: < 20envelope%20components%20for%20passive%20houses_final_2006-0315.pdf> [Accessed October 2012]. World Commission on Environment and Development’s (the Brundtland Commission) report Our Common Future (Oxford: Oxford University Press, 1987). Available at: < >. [Accessed November 2012.]

Internet [Accessed October 2012]. [Accessed October 2012].

27 [Accessed October 2012]. [Accessed October 2012]. [Accessed October 2012]. s/UK/The%20significance%20of%20airtightness.pdf [Accessed October 2012]. [Accessed October 2012]. [Accessed October 2012]. [Accessed October 2012]. [Accessed October 2012]. mal_brigdes.html [Accessed October 2012].


Images Figure 1: Up - thermographic image of a renovated building; down – photograph of the same building, (Passivhaus Institut, 2002) tection_works/insulation_increases_comfort__evidence_no.3_outdoor_thermography [Accessed October 2012]. Figure 2: Wall constructions from left to right: brick-insulation-brick; concreteinsulation-plaster; concrete-insulation-fiber cement cladding; wooden post and beam structure with insulation and wooden cladding; wooden main frame with steel c-profiles in between, insulation and wooden cladding; Trombe wall. Figure 3: Honeycomb insulation, (Barsmark A/S, 2010) p=3&n=39 [Accessed October 2012]. Figure 4: Roof constructions from left to right: concrete-insulation-asphalt; steel trapeze plates-insulation-steel covering (with ceiling); wooden trusses-insulation covered with OSB plates, on top roof tiles (with ceiling). Figure 5: Foundation details. Figure 6: Mold and damage on a ceiling. Figure 7: PCM inserted on a ceiling.(ClimateTechWiki, n.d.) [Accessed October 2012]. Figure 8: Thermographic image of construction with thermal bridge (up) and without (down). (Passivhaus Institut,n.d.) mal_brigdes.html [Accessed October 2012}. Figure 9: Typical details where thermal bridges may occur. Figure 10: Construction details of roof to wall connection (up) and balcony connection (down) without thermal bridges. Figure 11: The principle of the pen - The airtight layer should surround the whole building envelope in every cross-section. Figure 12: Two step seals from up to down: Mastic seal and polyethylene backing; round rubber profile; multi rubber profile; impregnated self-expanding seal; mortar joint. Figure 13: Diagram for ventilation. Figure 14: Principle drawing of mechanical ventilation with heat recovery and subsoil heat exchanger (optional). Figure 15: Principal drawing of heat exchanger with cross channel counter flow concept from PAUL Wärmerückgewinnung. (PAUL Wärmerückgewinnung, n.d.) [Accessed October 2012]. Cover page - Examples of Passive houses (Isover, 2010) 29 hure.pdf?-session=user_pref:42F9490C1b3982CE24xpuy174BAF [Accessed October 2012]


List of Appendixes Appendix 1: …..………………………………………………………………………….1 U-Value Concrete Wall...………………………..…………………………………..1 U-Value with Insulation……………………………...………………………..……..3


Appendix 1 U-Value Concrete Wall

Figure 1: Concrete wall.

Figure 2: Graph for concrete λ value. (DS418, 2002).

Material Rsi Concrete Plaster Rse

d [m] 0,200 0,015

λ [W/mK] R=d/λ 0,130 2,540 0,079 0,200 0,075 0,040 0,324




3,089 W/m K

U=U`+ΔU ΔU=ΔUg+ΔUr+ΔUf U=2,703+0=


3,089 W/m K

kWh per year = U*3810Kd*24h*195m2 1000




3810 Kd in Copenhagen for 2011 according to, accessed October 2012


U-Value with Insulation

Figure 3: Concrete wall with insulation.

Figure 3: Correction for air-cracks. (DS418, 2002)

Material Rsi Concrete Insulation Plaster Rse

d [m] 0,200 0,300 0,015

λ [W/mK] R=d/λ 0,13 2,540 0,079 0,037 8,108 0,200 0,075 0,04 8,432 2


0,119 W/m K

U=U`+ΔU ΔU=ΔUg+ΔUr+ΔUf 2




ΔUg=0,01*(8,108/8,432) = U=0,119+0,009=

0,009 W/m K 2

0,128 W/m K



kWh per year = U*3810Kd*24h*195m2 1000




3810 Kd in Copenhagen for 2011 according to, accessed October 2012


Low energy buildings why and how  

Principles and construction practices in low energy buildings (nZEB & Passive houses) dissertation work.

Low energy buildings why and how  

Principles and construction practices in low energy buildings (nZEB & Passive houses) dissertation work.