KTH Byggvetenskap
Kungliga Tekniska Högskolan
Low‐Energy and Passive Buildings Economics of New Technologies
Nízkoenergetické a pasivní domy Ekonomika nových technologií
Master’s Thesis No 418
Civil and Architectural Engineering Building Technology
2011 05 30 Martina Spurná
Supervisors
Folke Björk, KTH Building Technology Lubomír Krov, CTU Building Technology
Preface
This Master’s thesis was written during my exchange studies at the Royal Institute of Technology in Stockholm provided by the International exchange program Erasmus.
I would like to express my thanks to Folke Björk, supervisor of my thesis from the department of Building Technology, for the time he devoted to the consultations and his useful comments to my work.
I would also like to thank my supervisor Lubomír Krov from my home university, the Czech Technical University in Prague, for his help.
Furthermore, my thanks go to the Slovakian passive house institute “Inštitút pre energeticky pasívne domy” in Bratislava for providing me the project documentation that I worked with as well as all other contact persons mentioned in the list of references for their valuable contribution.
Stockholm, May 2011 Martina Spurná
Abstract
The thesis is concerned with the theme of energy savings in the Building industry. It describes passive house development in detail with a focus on the construction part of buildings with low energy consumption.
At first, there is an overview of the actual situation concerning the new European Union’s restrictions and a basic classification of energy efficient buildings is introduced. Further, construction compositions in two energy standards are designed for a few selected construction systems suitable for a passive house. They are evaluated from different points of view and compared to each other. Finally, an estimate of the passive house value is given as well as return of extra investments with regards to energy price increase.
Key words
passive house energy consumption construction system thermal insulation ventilation
Abstrakt
Diplomová práce se zabývá tématem šetření energií ve stavebnictví. Podrobně popisuje výstavbu pasivních domů se zaměřením na konstrukční část budov s nízkou energetickou spotřebou.
Nejprve je představena aktuální situace s ohledem na nové požadavky Evropské unie a představena základní klasifikace energeticky úsporných domů. Pro několik vybraných konstrukčních systémů vhodných pro výstavbu pasivních domů jsou navrženy konkrétní skladby konstrukcí ve dvou energetických standardech. Systémy jsou hodnoceny z několika různých hledisek a vzájemně porovnány. Na závěr je vyjádřena hodnota celého pasivního domu a návratnost víceinvestice s ohledem na růst cen energií.
Klíčová slova
pasivní dům spotřeba energie konstrukční systém tepelná izolace větrání
Contents
1 Introduction ... 7
1.1 Energy consumption and the European Union ... 8
1.2 Definitions and standards ... 10
1.3 The Passive House Planning Package (PHPP) ... 11
2 The passive house ... 13
2.1 Location and orientation of the building... 13
2.2 Shape of the building ... 14
2.3 Building envelope ... 15
2.3.1 Construction systems ... 16
2.3.2 Windows and doors ... 21
2.4 Technical building systems ... 22
2.5 Methods of quality control ... 24
3 Presentation of available construction systems ... 26
3.1 Sand‐Lime Bricks ... 26
3.2 Ytong ... 28
3.3 Medmax ... 29
3.4 Timber construction ... 30
3.4.1 Novatop system ... 31
4 Study of details of available systems ... 34
4.1 Description of the designed compositions and elements ... 36
4.1.1 External walls ... 36
4.1.2 Floor on the ground ... 37
4.1.3 Roof ... 37
4.1.4 Windows and door ... 37
4.1.5 Other structures ... 38
4.2 Calculations of the unit costs ... 39
4.3 Basic comparison of chosen construction systems ... 40
4.4 Costs of the construction part ... 45
4.4.1 Extra investment to the construction part of a passive house ... 46
4.5 Construction time ... 47
5 Evaluation of the whole concept of energy efficient houses ... 49
5.1 Building services in the passive house ... 49
5.2 Building services in the classical house ... 50
5.3 Energy demands for heating and hot water preparation ... 50
5.4 Extra investments to the passive house standard and its return ... 52
6 Conclusion ... 56
References ... 58
List of appendixes ... 61
1 Introduction
The theme of energy saving seems to be quite popular nowadays, but there are many serious reasons for thinking about it. With regards to the environmental aspect it is known that traditional energy sources are not unlimited. It is important to reduce the dependence on mineral resources and look for possibilities to replace them effectively with renewable alternatives and to decrease energy consumption overall as well.
There is a big potential in the building sector to reduce energy consumption representing a significant amount of global energy use. Due to new restrictions of the European Union together with the ongoing increase of energy prices the development of low‐energy and passive buildings is more and more discussed.
Based on my calculations, the energy savings of a passive house compared to an ordinary house built in accordance with recommended values of technical standards could reach 9 300 kWh per year just on heating energy. With regards to a number of houses built in the Czech Republic per year (18 346 in 2009) [43], it gives a significant amount 170 GWh in total. Given a value of nuclear power plant Temelín’s unit capacity 1 GW it amounts 7 days of its operation. In case of a coal‐
fired power plant it is 170 000 tonnes of coal which would have to be burnt. [52]
These numbers show a considerable potential of savings in the building sector.
This thesis is focused on newly built energy efficient residential buildings, especially family houses in the passive standard. The aim of the work is to compare different construction systems available in the Czech Republic which are suitable for building of a passive house. Four construction systems are chosen to be evaluated from various points of view with a focus on their costs and influence on construction process.
At first, this subject is introduced in context with the current situation in the European Union followed by a basic classification of buildings according to their energy heating demand. Further, to explain the whole conception of the passive energy standard, general requirements, recommendations and options of the building elements are described.
The comparison of the construction systems aims at design, evaluation and price comparison of the main structures and elements of the building envelope. That includes external walls, roof and floor compositions, windows and entrance door.
These structures and elements are created for both passive and “classical” standard and follow thermal demands for these categories determined in the Czech technical standard ČSN 73 0540 about thermal protection of buildings. Further, there is a list of main advantages and disadvantages of the particular construction systems and the comparison of their influence on the building‐up.
In addition, estimations of technical building systems costs were made for both the passive and the classical house to evaluate the passive house concept overall and to express return of extra investments.
In the thesis the passive house standard is analyzed in detail, but every methods and new recognitions are worth for buildings in low‐energy standard as well. The low‐energy houses are considered as a halfway between the passive and classical standard. Therefore they can be easily evaluated using all information here mentioned.
1.1 Energy consumption and the European Union
Figure 1 The energy consumption of the European Union in 2007 [33]
Figure 1 shows the deployment of energy consumption of the European Union in different sectors in 2007. It is startling that the main part of the energy need is not spent in industry or transport as it could be expected. Almost 40 % of the entire energy need comes simply under the use of buildings. It is possible to find large reserves relating to the energy savings in this sector. That is why the energy efficient buildings are built more and more often.
There is a new Directive on the energy performance of buildings (2010/31/EU), which was adopted by the European Parliament and the Council of the European Union in May 2010. It is a recast of the previous one (2002/91/EU) from 2002. The impulse for the new ordinance is connected with the above mentioned significant energy consumption of buildings in the European Union. The expected extension of the buildings sector brings fears of endless increase of the Union’s energy dependency together with greenhouse gas emissions.
There are two main targets given by the directive:
o after 31 December 2018 new buildings occupied and owned by public authorities are nearly zero‐energy buildings, and
o by 31 December 2020 all new buildings are nearly zero‐energy buildings. [34]
Furthermore, the energy need should be considerably covered by energy from renewable sources. There is no further explanation of the term “nearly zero‐energy building”, and the member states are asked for to draw up national plans to determine the numerical demands according to their climate conditions. The European Union emphasizes that the requirements should be cost‐effective.
According to the experts, this is a good first step to extend the energy efficient development together with saving the environment. The problem could be the lack of specialists familiar with this subject both in projection and realization, but the situation is nowadays improving and the further development is expected. They are not unified in the opinion which level should be determined for a nearly zero‐
energy building. [39]
Together with preparations of the national plan the Czech technical standard ČSN 73 0540 about thermal protection of buildings will be recast this year. One of
the main parameters the U‐value is expected to be lowered again. Figure 2 shows that this main parameter indicating the thermal properties of the building envelope has been significantly reduced during last 50 years.
3,70 3,70
2,70
1,80 1,70 1,70 1,45 1,45 1,50
0,89
0,46 0,38 0,38 0,38 0,30 1,25
0,93
0,51 0,32 0,30 0,24 0,24
0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0
U‐Values [W/(m2.K)]
Windows External wall Roof
Figure 2 Progress of the U‐value demand of external walls, roof and windows during last 50 years; in accordance with ČSN 73 0540 [35, 36, 37, 38]
The diagram shows demanded U‐values and in the case of external walls they hold for heavy constructions. In addition, the recommended values are a little lower. It is 1,2 W/(m2.K) for windows, 0,25 W/(m2.K) for external walls and 0,16 W/(m2.K) for roof. [35]
1.2 Definitions and standards
Energy efficient buildings are generally divided into a couple of categories according to their energy performance expressed as an annual energy need for heating per a square metre of the building. For this, unit kWh/(m2.a) is used. It means how many kilowatt hours we need for heating one square metre of floor space per year.
There are three categories used in the central Europe: the low energy buildings, which record an energy requirement of less than 50 kWh/(m2.a), passive buildings with an energy requirement of less than 15 kWh/(m2.a) and zero‐energy buildings, which are almost self‐sustaining and have an energy requirement of less than 5 kWh/(m2.a). [1]
However, the above mentioned value is not the only one requirement of the passive standard. In the Central European climate following basic demands have to be fulfilled.
o Specific space heat demand max. 15 kWh/(m2.a) o Pressurization test result n50 max. 0,6 h‐1
o Entire specific primary energy demand max. 120 kWh/(m2.a) [32]
The specific space heat demand expresses annual energy need for heating as already explained above and the pressurization test indicates the air tightness of the building envelope which ensures right function and efficiency of mechanical ventilation system. Finally, the required maximal amount of primary energy is connected with usage of non‐renewable energy sources including also the production, transformation and delivery of the energy carrier. [1]
To achieve these demands it is necessary to design the house as a whole thermal bridge free concept with preciseness related to the utilization of passive solar and indoor gains, minimization of thermal losses and a suitable solution of technical equipment. To support the way of the design a couple of additional demanded values are determined. For instance, the non‐transparent structures of the building envelope should not exceed U‐value 0,15 W/(m2.K), and windows of high quality should have the maximum Uw‐value 0,8 W/(m2.K). Further, ventilation with a thermal recovery system of minimal efficiency 75 % has to be installed. These demands and components will be onwards described in detail. [9]
1.3 The Passive House Planning Package (PHPP)
Passive houses have to fulfil above introduced requirements. For verification of the energy consumption of the passive house a tool called The Passive House Planning Package was developed. It is software based on a Microsoft Office Excel spreadsheet which is intended not only for the certification, but also as a support during the whole process of passive house design. It offers to the designer an accurate setting of construction elements and used technologies, and possibilities for their flexible changing during searching the best option and assessment of more variations.
The calculation of an energy balance is too complicated to be counted without any software. The Excel file includes many sheets which contain a lot of formulas. For a user the important cells are signed to fill in. Each sheet of the excel file is focused on a part of information needed to express the energy balance of the house such as characteristics of the building size, U‐values of external structures, window types and shading, ventilation, heating, electricity demand and many others. [30]
There are a number of software tools made for energy calculations, but the methods of calculating differ to each other. Therefore it is important to know which one was used because otherwise the results are not comparable. Most of the tools are simpler and some are used on a national level as an attestation for a possible financial support or just for a general notion of the building energy consumption.
The PHPP was systematically developed by the Passive House Institute in Darmstadt and it is used mainly in the Central Europe.
2 The passive house
Energy performance of a passive house is influenced by many factors. The most important of them are:
o climatic conditions
o choice of building lot (location and dispositions)
o orientation of the building on the lot (exposure to effect of sun and wind) o size and shape of the building
o size of fenestration on particular sides of facade o properties of building envelope
o amount of indoor thermal incomes o option of ventilation
o choice of heating system, water heating and electrical appliances o real way of usage of the building [9]
2.1 Location and orientation of the building
It is important to consider already the location of the building. In case this consideration is skipped, it can occur that the building is built with high energy performance, but there are not enough civic facilities and possibilities of the public transport in the neighbourhood. It could mean that the commutation, e.g. to the city nearby, represents higher energy consumption and air pollution than the building itself. This is sometimes problem of new districts, which are by developers presented as “living in the nature”.
When the suitable location is chosen, the building should be placed on the lot in the best way. It relates right orientation to the cardinal points which includes also the size and the deployment of windows in the building envelope. Here the main role of the designer begins. Of course, most of the lots do not have the optimal position and options. We do not build without connections, therefore some regional rules or influences of surrounding build‐up area are usually necessary to be solved. Despite of it, the designer should find the best possible way.
The main facade of the house ought to be situated to the south (south‐east, south‐
west) direction. Size of windows should be bigger in the south and there ought to
be just small windows in the north side. But everything has to be appropriate, too big windows can lead up to the overheating of the house in the summer. It is necessary to make the calculation to verify the passive solar incomes which can help to precede this undesirable effect.
Figure 3 Function of shading in different seasons: a) summer, b) spring and autumn, c) winter [4]
Figure 3 shows correctly designed shading according to the incidence angle of sun shine. The horizontal construction protects against the sun shine in the summer when the sun is high, whereas, in the winter transmits to the room passive solar gains.
2.2 Shape of the building
The next important issue of the essential conception is shape of the building. In case the energy efficient level is expected, the shape should be as compact as possible.
The sphere is considered to be the ideal shape with the best rate of surface to volume. Of course, it is an inapplicable shape in the building industry. Therefore, the cuboid with the longer side seated to the south and the roof slightly inclined to the north is optimal for nowadays built passive buildings. [4] In the process of proposal and also ensuing assessment the ratio A/V [m‐1] is used. A [m2] is the surface of the building envelope and V [m3] is the volume of the building. This ratio should be as low as possible. Generally, the shape without needless corners and niches has smaller surface exposed to the exterior. The same relates to the number of designed storeys. A two‐storey house will have better basic conditions to achieve the passive standard than bungalow with large surface area exposed to the exterior.
The irregularity then influences the thermal losses, what more, it relates to the number of complicated details and thermal bridges in construction.
However, the above mentioned does not mean that the passive house is always a simple rectangular cuboid or even a cube. Passive houses are built in many different forms. Figure 4 shows different examples emphasizing the varying forms of already built passive houses. The type of the roof takes the main role in case of the final appearance of the house.
Figure 4 Examples of different shapes of detached houses built in passive standard [8, 13]
The size of the house depends on its investor, but it should not be either small or big, it should follow its supposed purpose. As the samples show, the passive house is not any blockhouse as we can hear from some unknown people. It is not only insulation what creates the passive house as in next chapters is described.
2.3 Building envelope
Basic demands on the building envelope are maximal allowed thermal transmittance U‐values [W/(m2.K)] of external walls, floor slabs, roof areas and windows.
Demands used in the Czech Republic are shown in table 1. They come out of requirements used in Central Europe and are adopted in the Czech technical
standard ČSN 73 0540‐2 from 2007. It is expected that an additional rise in the requirements will be adopted this year.
Table 1 U‐values of the building envelope components demanded and recommended for all houses in the Czech Republic in accordance with ČSN 73 0540‐2 and recommended for passive houses [8]
Construction element
Demanded by ČSN 730540‐2 [W/(m2.K)]
Recommended by ČSN 730540‐2 [W/(m2.K)]
Recommended for passive houses [W/(m2.K)]
External wall (heavy / light‐weight) 0,38 / 0,30 0,25 / 0,20 0,10 ‐ 0,15
Roof ≤ 45⁰ 0,24 0,16 0,08 ‐ 0,12
Floor on the ground 0,45 0,3 0,08 ‐ 0,12
Windows and entrance door 1,7 1,2 0,8
2.3.1 Construction systems
There are many options how to build a house. The construction systems of a passive house are not much different from classic houses, but some are more suitable and some of them we should avoid. Above all, it is important to do everything correctly according to the well prepared contract documents with elaborate details.
The basic dividing is into the light‐weight (wooden) constructions and the massive constructions, which involve the masonry and permanent shuttering systems. It is not possible to say, which system is the best one. Each of them has some advantages and disadvantages. The final choice depends always on investor and tradition plays often one of the main roles in his decision.
2.3.1.1 Massive constructions
The masonry systems are formed by the load‐bearing structure made from any kind of bricks or blocks and by the insulation layer. The bricks can be ceramic, sand‐lime, concrete or aerated concrete, etc.
All these types are, claimed by producers, suitable for building passive houses. But some of them have so many disadvantages, that it is better to avoid the risk of using them. I mean above all the ceramic blocks. According to Ing. arch. Josef Smola, who is active in the field of wooden constructions and energy efficient buildings, the perforated ceramic blocks are really unsuitable for passive houses. The walling from them is demanding that the technological process has to be fulfilled precisely. But there is also another problem. While the blocks are made more and more concave,
they lose strength. Transportation and manipulation with these are problematic.
There is a risk of fracture of thin structure forming the block. If the blocks are not unbroken, they cannot fulfil the demand of air tightness (figure 5). Air can fluctuate through the concave structure and also wall chases weaken the wall. Regarding to policy of energy efficient houses is the production process of these bricks really unfriendly to the environment, because of huge energy consumption during its burning. [11]
Figure 5 Fractures in the structure of ceramic block originated in manufacturing are obvious [11]
Despite of the opinion of experts, this material is the most frequently used in the Czech Republic concerning "classical" buildings. The producers make huge advertisement and the bricks can be bought quite cheaply.
The masonry system can be single‐layer, but it is more used to be equipped with insulation. This structure is called ETICS (External Thermal Insulation Composite Systems) and consists from adhesive material, thermal insulation and facing.
The systems based on permanent shuttering derive benefit from saving labour due to making the load‐bearing construction and thermal insulation in one step. At first, prefabricated thermal framework is set together and sequentially it is filled with reinforced concrete.
There are two main types of this system. The framework is formed either of polystyrene or of cement‐bonded boards made of wooden chips. The Velox system, which represents the second type, is shown by figure 6. Properties of the surface are similar to wood, because wood makes 89 % of content of the board.
Figure 6 System Velox ‐ cement‐bonded boards made of wooden chips are equipped with thermal insulation and joined by steel clips [14]
Medmax system, which belongs to the first type, is in detail described in chapter 3.3. The main advantage of this type made of polystyrene is that plastic clips for joining two sides are used. This protects the risk of thermal bridges in the wall structure.
2.3.1.2 Timber constructions
There are a considerable number of alternatives for timber construction systems, but for energy efficient houses mainly two of them are used. These are both based on a composite structure. In the first type the load‐bearing construction is made of wooden balks or I‐beams and the space between them is filled by thermal insulation. The construction is closed by wooden boards. This structure goes from traditional American system called “Two by Four”. It can be made as prefabricated in a factory building or set together on the building site. The load‐bearing construction of the second type is made from massive wooden boards. They are fit together on the site and after that equipped with insulation layer.
There is a big difference in the building time among these opportunities. It takes much more time to set constructions from several elements together directly on the building site. The big advantage of the prefabrication is that everything is being prepared in heated hall with a help of machines and the construction elements are set together without any influence of weather conditions. The assembly is then very fast both in the hall and on the building site. A disadvantage of this way is the need of an equipped manufacture hall together with higher demands on the transport of the structural components, and also costly mechanization for their assembly has to be used. These already prepared constructions can be transported to the building site in different phases of its assembly; from load‐bearing walls prepared for inserting insulation and completion to whole prepared walls including windows, installations and wiring.
Wood is fully renewable and natural material. It is the only one material, which has a positive CO2 balance. It means that during the growing of a tree more CO2 is absorbed than it is produced afterwards during its processing and utilization. Wood supports the environmental benefit during whole life cycle of the construction. Even the disposal of it in the end of the usage is simple in this case. It does not have any high demands on transport and the construction is almost fully recyclable.
2.3.1.3 Position of timber constructions in building industry
In time when the first concept of a house is made, investor stands before the question which material to use. The basic decision is between massive and timber construction. The situation is various in different countries. The number of wooden houses and its proportion in whole development is in the Czech Republic much lower than in other countries in spite of good presumption and needful conditions for it. The forest coverage is 34 % (in comparison, it is 31 % in the USA) and the current felling makes just 75 % of annual increase of timber resources.
However, the Czech Republic is, regarding the timber production in building industry, deep under the average. According to the Czech Statistical Office there was built about 2,9 % dwellings out of timber in 2008. In comparison, its proportion
in Germany is 7 %, in Austria, Switzerland and Great Britain 10 %, and in Scandinavian countries, USA and Canada even over 60 %. [15]
The problem has roots in the history when at the turn of 18th and 19th century the build‐up of wooden constructions was forbidden because of low fire resistance.
Before that it was the mostly used material, but the opinion that wood as a building material is inferior and that wooden houses are unsafe remains, unfortunately, up to now. Although most of the old wooden buildings built long time ago are still used and admired. [12]
It takes long time to get familiar with this “new construction”. The mistrust of it brakes its expansion and the other countries are ahead of us. The development of energy efficient buildings helps to break the space. More and more people are turning to timber technologies, because of their environmental sentiment. And this is the opportunity. There are many companies offering low energy and passive timber houses and also the progress of the systems is fast.
So should we build massive or timber houses? In brief, it is not possible to say that one option is the best. Each project is unique. The important thing is to find the best solution for concrete conditions, possibilities and investor’s requests.
Another advantage of timber constructions is, in addition to above mentioned ecological aspect, the possibility for a rapid construction process. Opposite of the massive constructions, the dry technique is not dependent on weather and does not include any technological breaks and after the end of the building process it is possible to occupy the building immediately. Concerning the light‐weight, transport of complements is easier and also the wall thickness is used to be more slender.
However, these issues depend on concrete structure chosen for the wall.
Disadvantages of timber constructions are before all shorter building life‐span and lower fire resistance. This can be protected by a suitable surface treatment against weather conditions or facing of fire‐proof material. Another problem is the worse acoustic properties of the construction, but the compositions of the structures, especially the floor structure, are designed with regards to this weakness.
2.3.2 Windows and doors
Windows still constitute the weakest parts of the building envelope. These are the places, where major thermal losses and gains can appear. The fenestration has to be considered. In addition, the windows create also the aesthetic aspect of the whole building. Window’s frames are made of plastic, wood or wood‐aluminium (figure 7). Choice of material depends on investor. Every material used for window frames can fulfil required parameters. For passive houses triple glazed windows are used.
Figure 7 Sectional view of triple glazed windows: a) plastic, b) wooden, c) wood‐aluminium frame [16, 17, 18]
The required Uw‐value of windows for the passive houses is 0,8 W/(m2.K). It includes both glazing and frame. We can see really fast current development in quality in the field of windows. It is no problem to get windows with nowadays demanded value, whereas, few years ago windows with such low Uw‐value did not exist yet. The thermal loss coefficient of windows on the market (Uw‐value) has been reduced significantly during the last 30 years.
To build passive houses, highly efficient windows have to be used. However, the type of glazing and frames will depend on climate. In the Central European climate, there are three essentials:
Triple glazing with two low‐e‐coatings (or another combination of panes giving a comparable low heat loss)
"Warm edge" ‐ spacers, Super‐insulated frames. [19]
Spaces between each two glass panes are filled by inert gases, which improves thermal insulating properties of the window. Further, the joint between the frame and the window jamb has to be perfectly made. The window is placed to the insulation layer and the insulation covers main part of its frame. Figure 8 shows two alternatives of setting to the jamb and its influence on the course of temperature.
The course of temperature in the exterior wall shows that the left one results in much lower surface temperatures than the other one on the right side. Thus, the right alternative is the better one without a thermal bridge.
Figure 8 The wrong and the right window setting and its influence on the course of temperature in the exterior wall [9]
For entrance doors the same demand is accepted. It means U‐value 0,8 W/(m2.K) is required. Regarding entrance door, the doorsill is a problematic point. It is not possible to cut out this thermal bridge, but a door of high quality ought to be used to minimize the thermal bridge and keep the air tightness on high level.
2.4 Technical building systems
The most important issue for an occupant is comfort and healthy indoor environment. A sufficient amount of fresh air is for people essential. In the super insulated and air tight buildings such as a passive house there cannot be expected any gap ventilation through leaks in the construction and also the opening of windows is not enough. The ventilation has to be ensured by a mechanical means which replace the “used” air by the fresh one automatically and regularly. If the air is not being changed the air humidity and an amount of air pollutants are increasing
and even mildew can appear. Further, for the energy efficient buildings this means a controlled way of air exchange without thermal losses.
Therefore, an air conditioning system is installed which always includes also a heat recovery system. It transmits the warmth of the exhaused air to the fresh air entering the building without their mixing. The warm used air is removed from kitchen, bathrooms and toilets and the fresh air is coming to the rooms of living.
Due to the thermal recovery the energy for heating is saved. The fresh air is already preheated and it is not necessary to heat it much. This is appreciated especially when outside temperature is very low. The recovery system of a passive house should exceed efficiency of 75 % and the process can be supported also by a subsoil heat exchanger. This is placed in the ground in depth 1,5 ‐ 2 m under the surface where the stable temperature around 4⁰C is and the incoming air is there during winter preheated as freeze protection of the recovery system and during hot summer days it is cooled.
In the system there are filters which ensure the new air to be clean. Furthermore, the filtration is welcomed by allergic people to protect the incoming air also against pollen and dust elements and keep the indoor environment harmless.
There are two options of heating used in the passive house. It can be joined with the ventilation system as a warm‐air heating system or it can work separately. In the case of a warm‐air heating system the air is being heated in connection with hot water preparation and the heat is consequently distributed by the air conditioning to the rooms. There is an advantage that the heating system does not need its own heating piping and bodies. The second option needs the classical heating system as well as a gas, solid fuel or electric medium. However, the heating systems are used only during the coldest days of the year because the heating period is cut down due to low thermal losses and positive passive gains of the building.
For the hot water preparation and within connected reduction of primary energy need solar collectors are often used. These are connected to a water reservoir. The need of hot water is stable during the year but the solar energy gains are changing.
Therefore, the reservoir is joined also on an additional heating device.
2.5 Methods of quality control
Figure 9 The most frequent places of untightness in the construction [9]
For the right functioning of indoor environment of the passive house an air tight building envelope is needed. When the air goes through the construction outside and inside, the house is cooled and that means thermal losses of the object.
For ensuring of the air tightness of the building the implementation of a sealing plane is demanded. Although, this is ensured in the massive and concrete walls by continuous layer of plaster, or by the homogenous concrete layer, in light‐weight constructions the solution has to be settled in advance. The air tight layer is often made by a plastic foil, OSB boards or other suitable boards with sealed connections.
But there are still a lot of risk places in every kind of systems, especially where the construction elements are connected. The most often occurring places of leakages are shown in figure 9. The protection has to be designed in detail with using weather strips, foils, or mastics. [9]
To verify the demand of the air tightness (n50 ≤ 0,6 h‐1) the measurement called Blower door test is used. This is based on the difference in the air pressure value inside and outside of the house. When the test is being held, every opening has to be closed. In the entrance door a big ventilator is placed (figure 10) and the fan creates overpressure or underpressure with a differences from 80 to 20 Pa between indoor and outdoor pressure. Finally, it is evaluated as an average value for the pressure difference of 50 Pa. The amount of the changed air in the building is
measured. The value n50 means how much of the air volume of the building is changed during an hour expressed in percents.
The measurement is made two times; at first when the air tight layer is finished and for the second time during the usage of the house. The first test proves the air tight layer in time when it is possible to detect and repair faults founded by the measuring. The second one is used for verifying the properties required for the certification of the passive house efficiency. [9]
Figure 10 A ventilator placed to the entrance door during the Blower‐door test [29]
3 Presentation of available construction systems
These construction systems were chosen for the comparison:
o Sand‐Lime bricks o Ytong
o Medmax
o Timber construction – Novatop 3.1 Sand‐Lime Bricks
The sand‐lime brick is a natural building material made of lime, sand and water.
These ingredients are mixed in different proportions into a raw mixture that is poured and then pressed into moulds. The resulting compacted green body is hardened by steam at 203 °C to just below 16 bars. [20] After that are the products ready for distribution. There is just a very small amount of energy used during the manufacturing. Due to the process of compression and hardening the sand‐lime bricks have high level of bearing strength, density and sound‐transmission loss.
Figure 11 A mini‐crane used for assembly of walls made of sand‐lime bricks [20, 21]
The biggest advantages are the ecological aspect, excellent properties for acoustic insulation and thermal accumulation and high static load capacity while low thickness of the wall.
Disadvantages of this system are high demands to storing of the material. The bricks must be protected from damp, ice and snow. On the contrary, in hot weather
the bricks are drying up and have to be moistened. The bricks do not have stable colour which should be considered when the face masonry is designed. Further, the weight makes the need of machine (figure 11) and demanding arrangement of the site.
What more, there is a thermal bridge in the construction detail between exterior wall and foundation which has to be solved. This problem is protected when some additional insulation is designed. Next figures show two options of solution.
Figure 12 shows a detail of design and a photo from building site, where the wall is founded on a row of foam‐glass bricks. Figure 13 shows another option, where the insulation is laid under the whole area of foundation. The figure shows how the foam‐glass gravel is delivered to the building site. In the same way, expanded polystyrene can be used, but the foam‐glass gravel is cheaper and does not have requirements for the ground flatness.
Figure 12 Exterior wall founded on the foam‐glass bricks [10, 21]
Figure 13 Exterior wall founded on the foam‐glass gravel [10, 21]
3.2 Ytong
Ytong is a type of aerated concrete. The blocks are made from natural raw materials
‐ sand, lime, cement and water. Manufacturing of this material is low in energy demand and it utilizes all unused rests of the material. The material is fully recyclable.
Figure 14 Block of Ytong – in the bottom‐right hand corner is the straight‐up block with slip feather and formed holders [22]
Advantages: Ytong records high compressive strength when density is low. The straight‐up blocks are also really light and could be equipped with formed holders for easier work. The structure of the material is homogenous, therefore it has the same properties in all directions and it is possible to use almost each piece, which has been cut off. The material is possible to be cut in simple way.
Disadvantages: The Ytong blocks are brittle and need handling with care. By transporting, storing and assembling they should be protected. Further, the weather conditions influence the building process. It is a moisture‐absorbing material and the damp lowers its thermal properties.
This material has the best thermal insulating properties of all masonry construction systems. Thermal conductivity of the blocks achieves up to 0,08 W/(m.K), but it is still not enough to use single‐layer walling for passive buildings. As thermal insulation can be used expanded polystyrene (EPS), mineral wool or the special material developed by Ytong – Multipor.
Multipor is thermal insulation made on the same base as Ytong itself. The structure is similar to the aerated concrete. Combination of these two layers of walling ensures stability of size. It works well together with the adhesive developed especially for it.
There are not so many passive houses built in the Ytong system. Figure 15 shows terraced houses built in Židlochovice in the Czech Republic.
Figure 15 Example of a passive terraced house built in the Ytong system from Židlochovice in the Czech Republic [8]
3.3 Medmax
Medmax is a construction system based on the principle of the permanent shuttering. The shuttering is put together from shaped bricks, which are made from grey polystyrene, Neopor. Neopor is a special type of expanded polystyrene, in which elements of graphite are added. This improves its properties and lowers thermal conductivity of the material. Medmax was developed for low energy and passive houses. [23]
On the surface of the shaped bricks the lock‐system is made (figure 16). At first, the wall is build up from the bricks joined with the aid of the lock‐system and plastic spacing sticks, after that reinforced and finally filled with concrete. In this way is the load‐bearing structure built together with the thermal insulation. The surface of the completed wall can be protected by classical techniques such as coating, or wooden or ceramic facing.
Figure 16 Medmax – the wall from shaped bricks with the lock‐system and red plastic spacing sticks; filling‐up the shuttering with concrete [24]
Advantage of this system is above all the light‐weight bricks, which ensure simple mounting, manipulation and transport of the material. Also the lock‐system facilitates to build straight walls simply. The system is very variable due to the possibility to cut the bricks easily. These characteristics allow the realization on self‐
help in easy way. Neopor provides really good thermal properties of the wall while the thickness is still low. The concrete load‐bearing construction is always 150 mm thick. The U‐value of the 450 mm thick wall is 0,1 W/(m2.K). Furthermore, the monolithic core assures the tightness of the whole construction.
Among disadvantages can be count lower thermal accumulation ability. This problem is possible to compensate through the use of proper materials for ceiling and floor. The technologic procedure of filling‐up the shuttering has to be strictly observed. The concrete structure has to be monolithic in each part. Further, there is almost no chance to make later changes in the layout of interior.
3.4 Timber construction
To select one type of the timber structures for comparison is more problematic.
There are many structures available.
A view to the list of built passive houses has detected that there is something wrong with the common opinion that timber constructions are always really thin and that investor can save many square metres if he builds a wooden house. This is true in
case of timber houses in “classical” standard where the U‐value is much higher than mentioned 0.1 W/(m2.K). Really few introduced built passive timber houses have wall width being lower than 450 mm and this width can be reached also by massive construction. Thinner structures can be reached when the thermal insulation is inserted between wooden beams of timber framework or when massive wooden boards are equipped by insulation with high thermal properties, often with polystyrene. However, this structure does not agree with the opinion that timber house is fully ecological.
It is impossible to involve in this thesis the large amount of construction possibilities given by market. Therefore, a construction from Novatop system was chosen for the comparison, because this is the same system ETICS as it is used by massive constructions.
3.4.1 Novatop system
The load‐bearing construction of the Novatop systems is based on massive wooden components made from glued laminated multi‐layer wooden boards. The individual layers of the boards are always turned by 90⁰ to each other and glued together to create stable components with high strength. These boards are produced directly according to the design documentation in the manufactory. Their size is up to 12x3 metres. The Novatop system includes components for walls, floor structures and also roofs. These components together form a uniform construction.
Figure 17 The layers of the wooden board are glued together turned by 90⁰ to each other [27]
The boards are stored in horizontal position on a dry place and have to be protected against adverse climatic conditions also during the transportation to a site. There they are erected and the load‐bearing construction is set together by help of a crane at a fast rate. Sequentially, it is equipped by a thermal insulation layer.
The structure of the Novatop boards is diffusion open and air tight. It has also good acoustic properties and the really slender complements have high static characteristics and shape stability. [27]
The received information about Novatop system is not as detailed as about the other systems, especially concerning the costs. Therefore, the Novatop system was not included into all comparisons. The costs are not possible to calculate per a square metre as were in other cases. Each building is individual and the production costs depend a lot on its characteristics. According to the estimation of the producer the price of the load‐bearing construction of the sample house described onward would be expected around 1 500 CZK per a square metre by walls and 2 600 CZK per a square metre by the floor structure. The production of the boards would take 3 days and their assembly on the building site approximately 2 days. [48]
The composition of the external walls is considered by an installation layer on the indoor side and by an additional thermal insulation on the outdoor side of the walls.
Figure 18 shows two types of recommended structures which both reach U‐value 0,1 W/(m2.K).
Figure 18 Two recommended compositions of the Novatop external wall; on the left side with thermal insulation made of STEICO fibreboard and on the right side with polystyrene [27]
Both of the compositions in above figure have the load‐bearing construction made of two Novatop massive boards with total thickness 84 mm and are provided with an indoor installation skin wall made of a plaster board on a wooden crate filled with additional insulating material. The structure on the left hand side is equipped by ecological components of the Steico system. The thermal insulation of the Steico fibreboards is inserted between vertical wooden I‐beams. The second structure is insulated by expanded polystyrene.
4 Study of details of available systems
As a basis for the comparisons of the construction systems the project documentation of a sample passive house in Brnov les in Slovakia was used. The two‐storey house is rectangular shaped and has an aisle roof inclined to the north.
On the southern side of the house is a wooden balcony construction which serves also the role of shadowing. On the northern side is another wooden construction which forms and protects the entrance area in front of the house door. The illustrations below show the plans and a cross section of the house.
Figure 19 The ground‐floor plan of the sample house [7]
Figure 20 The second‐floor plan of the sample house [7]
Figure 21 The cross section of the sample house [7]
The structures of external walls were designed in four construction systems and two energy standards; “passive” and “classical”. The structures designed in passive standard reach demanded thermal properties for passive houses and the structures in classical standard have properties which follow the recommended U‐values for common development in the Czech Republic (table 1). Further, the structures of the floor on the ground and the roof were also designed in these two standards.
Detailed drawings of all compositions are in appendix I.
Although the design of the structure compositions is based on the values of thermal properties recommended for a passive energy standard, the conclusions are useful also with regards to the low‐energy buildings. The low‐energy standard has lower demands on the thermal properties and the whole concept is approximately in the middle of the two considered energy standards.
The compositions were designed for the passive standard and after that adjusted for the classical one by reducing of the thermal insulating layer. The design was simplified from the primary documentation. The external wall is in each case plastered and the green roof was replaced by the titanium‐zinc plate roofing. These parts do not have influence on the comparisons and depend just on investor’s subjective opinion and choice.
4.1 Description of the designed compositions and elements
4.1.1 External walls
For choice of the concrete structures of the external walls the U‐value 0,1 W/(m2.K) was determined. Next compositions reach this value:
o Sand‐Lime bricks 175 mm + EPS GreyWall 300 mm o Ytong Blocks 300 mm + EPS GreyWall 200 mm o Medmax 450N
o Novatop boards 84 mm + external thermal insulation + inside installation skin wall
4.1.2 Floor on the ground
The composition of the floor on the ground in passive standard follows the primary design. The damp and water‐proofing insulation is made of penetration coating and asphalt damp‐proofing strips glued to the concrete slab by fuse. Three layers of expanded polystyrene Isover of total thickness 260 mm make the thermal insulation. The polystyrene insulation is covered by separating PE foil and on it 70 mm thick concrete topping reinforced by steel meshes KARI is added. The U‐value of this composition is 0,131 W/(m2.K).
The classical composition differs in the thickness of the polystyrene insulation which is only 120 mm. The U‐value of the classical composition is 0,287 W/(m2.K).
4.1.3 Roof
The composition of the roof in passive standard was changed from the primary design as mentioned above. The load‐bearing structure is created by 400 mm high box beams which are made of OSB boards filled by insulation. This improves the thermal properties of the whole composition, because the insulation inserted into the beam reduces the thermal convection. The main thermal insulation layer lies between these beams and is made of blown cellulose. The titanium‐zinc roofing is placed on the top OSB boarding and the soffit is formed by plaster board with 50 mm mineral wool in a wooden crate. The damp‐proofing is ensured by Hofafest boards and the tightness of the construction by the layer of OSB boards with sealed joints fastened under the main beams.
The main structure in case of the classical composition is formed by simple wooden rafters with cross section 100x200 mm, between which is put thermal insulation of mineral wool. U‐value of the passive standard composition is 0,095 W/(m2.K) and the classical composition has U‐value 0,17 W/(m2.K).
4.1.4 Windows and door
The properties of the building envelope and also the price of the house are significantly impacted by the quality of windows and doors in the building envelope.
The windows and entrance door were also calculated in two already mentioned
energy standards. Two types of wooden windows were chosen from the offer of the company TTK CZ Eurowindows. Figure 22 shows a description of them.
Figure 22 “TTK Comfort” for classical on the left and “TTK Pasiv Plus” for passive standard on the right hand side [28]
The classical window “TTK Comfort” has standardly insulating double glazing and its total Uw value is 1,2 W/(m2.K) along the recommended level of the norm. The “TTK Pasiv Plus” has triple glazed sealed unit with Ug = 0,5 W/(m2.K). This window is suitable for low‐energy and passive houses and its Uw‐value does not exceed 0,8 W/(m2.K).
4.1.5 Other structures
The foundations of the house were left the same for each case, because it would need a special static check to change it for different construction systems. Because of this reason, it was not calculated with it. The house is founded on the concrete strip foundations and the reinforced 125 mm thick concrete slab is made on a gravel cushion of thickness 125 mm.
The structures which do not influence the envelope of the building were simplified and made identical for the three massive constructions. The floor structure of the second storey is designed as a composing structure of beams and tile fillers covered
with poured concrete and the partition walls are from Ytong blocks of thickness 100 mm.
For the comparisons only the shell construction of the main part of the house has been studied. The other components are not included, because they are for each case the same. Also the inside finishing work is not involved, because especially price of these elements is too individual and depends on the investor’s choice of particular materials and devices. If the increase of the costs between passive and classical building should be expressed as percentage, these prices would influence it subjectively. Therefore, the elaboration contents just the overhead construction without completion.
4.2 Calculations of the unit costs
There were conducted tables (appendix II.) with calculations of the wall structures which provide basic view of the properties of the particular designs and their costs.
The costs expression is based on the valuation of used materials and needed labour per a square metre of the structure of external wall, floor on the ground and roof always in the two energy standards. There is also the target value of the time needed for the build‐up of these elements. These tables can be efficiently used as a tool for primary decisions concerning the building systems.
The field of prices is changing all the time and the final price of the construction always depends on many various impacts, mainly on the actual situation of the market. Therefore, the comparison comes from the available information in the current time, but values can be later simply updated by actual prices or discount possibilities and also the choice of designed materials can be modified.
The prices of materials used in the calculations were selected according to the usage. The main materials (especially thermal insulations) were valued by pricelist prices of the producers, even if it was possible to find better prices in the market, to keep the comparability of them. By other components without this possibility values near average were chosen. In this way prices for all the construction types were produced in a way making them suitable for comparisons.
