How is a passive house built?

Transcription

1 How is a passive house built?

2 Passive houses A passive house stands out by having an incredibly warm and comfortable indoor climate, and by having very limited energy consumption. Each passive house thus actively contributes to the protection of the climate. The concept of the passive house is to build a house that can retain heat and use the heat from the sun, also known as passive heating, so that ultimately there is no need for heat supply or a heating system. By building in accordance with the passive house concept and adding the best principles of the building physics, we get a building that is warm, comfortable and healthy to live in. Hence the name COMFORT HOUSES. 2 The concept of the passive house is to build a house that retains heat and uses the passive heat generated in the house by its residents, food preparation, electrical equipment and sunlight so that ultimately there is no need for heat supply or a heating system. COMFORT HOUSES are built exclusively to well-known principles.

3 Passive heating Passive heating works like a thermos flask, in that the more heat is retained, the less energy needs to be used to produce new heat. The interaction between the individual building elements means that it is possible to construct a house which uses almost no energy for heating and has a fantastic indoor climate. Starting with the principle of passive heating, it is a relatively small step from a low-energy house to a passive house. A low-energy house needs very little heat supply a passive house needs no heat supply. By building the house as a passive house, you can do without district heating at all. This saving offsets the extra cost of construction. 3 Approx. 90% of energy is used to keep a condition stable, e.g. the coffee in a coffee machine. From active to passive!

4 Requirements To meet the requirements for passive heating in Germany, some criteria s have been defined for the energy consumption, building envelope and ventilation of a passive house. Heating energy demand max. 15 kwh/m²/a (m² = Treated floor) Criterium Airtightness max. 0,6 h -1 Criterium Thermal load max. 10 W/m² (m² = Treated floor) Recomandation Total primary energy demand max. 120 kwh/m²/a (m² = Treated floor) Criterium Overtemperature in rooms (temp. >25 C) max. 10 % Recomandation The above requirements can be verified in accordance with the Passivhaus Dientsleistung s calculation program PHPP (Passivhaus Projektierungs-Paket - Passive House Design Package). Heating energy demand 4 The energy demand is the raw number of kwh to be supplied to the air in the room to maintain an indoor temperature of e.g. 20 C. The figure applies whether the heating source is electricity, natural gas or bio-fuel. The energy demand is calculated all year round and allows for the local variations in outdoor temperature and sunlight. Ventilation To maintain a fixed temperature of 20 C, as much has to go in as out. In an ordinary house, the energy input represents a very substantial proportion of space heating. In a passive house, loss through structures and windows is minimised to such an extent that the combination of passive heating and heat recovery from ventilation air can provide almost all the heating. Windows Added energy Roof, walls, floor Bodies Equipment In an ordinary house the difference between heat loss and passive input is high. This leads to a high heat demand (columns 1 and 2). In a passive house the difference and therefore the heat demand are minimized (columns 3 and 4). Loss Gains Loss Gains Windows Ventilation Windows Roof, walls, floor Added energy Windows Ventilation Bodies Equipment

5 Requirements Airtightness Airtightness describes how airtight the structure is. In Germany, where passive house requirements have been defined, airtightness is defined as air changes per hour at 50 Pa pressure difference. In Denmark it is defined as l/s per m² gross floor area. Converted to Danish figures, the requirement of 0.6 h- 1 corresponds to l/s per m². Thus the requirement for airtightness is 4-5 times more stringent than Danish requirements for new buildings. The requirement for airtightness ensures reduced energy consumption, optimal control of ventilation functions and the elimination of damp problems in the structures within the building envelope. Heat load Heat load is the maximum permitted demand on the output of the space heating system. This is the heat that needs to be added to the room air on the coldest day of the year, unless there are visitors or you are baking a cake, washing and tumble drying clothes or doing something else that contributes high surplus heat. 5 The calculation is almost the same as for the energy demand. The difference is that rather than an annual average it calculates a one-day average on a cold winter s day. At the same time, it assumes a minimum of internal heat input from bodies and equipment: that is, the worst case. The test for airtightness is carried out in the same way as for other new buildings, but the requirement is 4-5 times stricter. The calculation needs to be carried out for both a cold sunny day and a cold, cloudy day. Windows Ventilation Added energy The heat load for heating a passive house is so low that it can be provided by a lightbulb; however, a passive house is not heated with lightbulbs unless it is the high-efficiency type. Roof, walls, floor Ventilation Bodies Equipment Windows Loss Gains Worst case: on the coldest day of the year the maximum demand on the heating system may be 10 W/m².

6 Requirements Total primary energy demand The total primary energy demand is the energy used for heating, domestic hot water, ventilation, cooling, electricity for running the building and household. In other words: it is the total amount of energy that needs to be supplied to the property. Including for example bio-fuels and electricity from wind power, from solar cells, but excluding earth and solar heating. any scope for cheating by heating the house with the aid of inefficient white goods and standby power loss. If you look at the passive houses built in the last 10 years, it looks as if the 120 kwh/m 2 per year is set very high. On average, existing single-family houses need 88.5 kwh/m 2, and none of them exceeds kwh/m 2. The 120 kwh/m 2 is not a target, but an absolute maximum. A criterion for the total energy consumption including housekeeping electricity exists in order to eliminate 6 The house must not be heated by an inefficient fridge or freezer. That is why there is also a criterion for the total power demand of the household.

7 Requirements Overtemperature in rooms The recomandation for overtemperature in rooms is max. 10%. The 10% is the calculated proportion of the time of usage when the room temperature exceeds 25 C. The calculation does not take into account whether you open windows yourself to let in cool air. In practice you would naturally adjust the room temperature in this way when you are at home. A recomandation for maximum overtemperature has been imposed so as to ensure that the house is not made unbearably hot to come home to in an attempt to build as much passive solar heating as possible into a design. Ventilation U-value 0,1 W/m 2 K 7 Airtightness Heating energy demand max. 15 kwh/m 2 a U-value 0,7 W/m 2 K U-value 0,1 W/m 2 K No thermal bridges U-value 0,12 W/m 2 K

8 Realisation The architect s options when building a house with passive heating are limitless. The architect s hands are free but, as always, there are some important, recommended steps to follow in the planning phase so that everything goes according to plan. 8 Planning The first step is to set out the house in the best possible position on the plot. - preferably with 40% of the windows area placed in the southfacing facade - out of the shade of other buildings, hills or woods - preferably with a compact layout The next step is to plan the method of building the house, its surface structure without unnecessary projections and the boundary of the heated area of the house. Finally, the principles should be checked which ensure that the house retains heat. Heat retention is first and foremost realised through: - increased thermal insulation - elimination of thermal bridges - airtight construction - energy-efficient windows - heat recovery and controlled ventilation

9 Realisation Attic unheated 1st floor heated Ground floor heated Garage unheated Basement heated Basemant unheated In black and white it can be hard to see where the heated boundary of the house is, so it is important to highlight the sections that are included in the heated area. 9 More thermal insulation To retain the heat, the insulation of the building envelope must be thicker than normal, and the insulation must as far as possible form an unbroken layer round the whole house so that thermal bridges are avoided. In a passive house, the insulation must be thicker than in normal structures, i.e. for single-family houses the U value should be under 0.1 W/m 2 K, corresponding to approx. 300 mm in walls and 450 mm in roof and floor. The insulation must envelope the house.

10 Realisation Avoid thermal bridges Wherever the insulation is interrupted or penetrated, or where there is a step in the insulating layer, a thermal bridge arises. Thermal bridges lead to 10-15% of the heat loss in a traditional structure. To ensure that the building needs no added heat at all, it is therefore necessary to avoid thermal bridges. The best way to locate thermal bridges is to review the floor plan, cross-sections and detail drawings to find possible gaps in the external insulation. Anywhere that a step occurs in the insulation thickness or where the insulation is broken, a solution must be found to reduce the cold bridge as much as possible. Geometrical thermal bridges can be avoided if the external insulation is appropriately designed and is continuous. Colour the insulation yellow, then every break in the yellow line thermal indicate a potential cold bridge. 10 At each thermal bridge, insulation should be inserted to give the heat as long a route out of the house as possible to eliminate heat loss at the thermal bridge.

11 Realisation Airtight construction Airtightness of the structure is a precondition for a good thermal balance and indoor climate. It is therefore necessary to avoid penetrating the damp-proof membrane and where necessary to ensure that any penetrations are made good and sealed. Air flows in a leaky house Air flows in an airtight house Airtightness of the structure also ensures that ventilation can be controlled correctly and that the air passes through the heat exchanger. This means that connections between various building elements, for example between wall and windows and between wall and ceiling, must be made airtight. 11 The red line indicates where the airtightness plane is located in the building. The line must enclose the heated area, and the line must be intact all the way round. Joints between materials must be planned at each detail point.

12 Realisation Energy-efficient windows The windows must retain heat and let as much solar energy enter the house as possible, so the windows must use low-energy glass and thermally insulated frames. To make the best possible use of passive solar heat gain, the sun s rays must hit the windows in winter when there is a need for heat input, but the windows should ideally not be directly affected by sunlight in summer. This is achieved by having the large glazed panels facing south and building them under a wide overhang. East-, west-, and north-facing windows should only be as large as necessary to achieve optimal light entry. External wall 18,5 C Windows 9,9 C Indoor temperature 22 C External wall 21,4 C Windows 19,1 C Indoor temperatur 22 C Traditional house Outdoor temperature -10 C Passiv house The requirement for a U-value of under 0.85 W/m 2 K for the built-in window ensures that there is always a thermally comfortable indoor climate in the room. Even without a heating system, the internal surface temperature of the window should not be less than 17 C on a cold winter s day. 12 Heat loss U-value Indoor Solar heat gain g-value Triple glazing which retains the heat in the room while solar heat is permitted to enter through the pane. Triple glazing with a thermally insulating window frame Orientation of the house and location of the windows in the building can be very significant to the total energy that can be supplied to the house.

13 Realisation Heat recovery and controlled ventilation The ventilation system ensures good, even air renewal in the house. Heat from the used indoor air is used to heat the new fresh air that is drawn in. For the ventilation to be correctly controlled, the house must be airtight. This means that all connections between the various building elements must be airtight. It is important at the planning stage to find the shortest duct runs. Schematic of venting in a passive house. Moist air from the kitchen, bathroom and toilet are extracted while fresh air is supplied to the living rooms. 13 Compact systems The system is available in several versions, in the form of compact units that resemble a cupboard. Hot water Hot water comes from a heat pump that uses waste heat from ventilation air, supplemented in some cases by earth heating and a solar collector. The heat pump can also provide the requisite additional heat.

14 Comfortable advantages Always warm and comfortable Well-insulated, airtight structures and energy-efficient windows result in an even surface temperature throughout the room, and it is possible to sit near the window all year round and enjoy the view and daylight without discomfort from draughts or cold. 14 Good indoor climate Controlled ventilation also has a number of advantages for the indoor climate: the air is purified of dust, pollen and particles and the automatic extraction reduces moisture and dust so that you do not need to spend time airing the rooms every day, but can open a window when you please.

15 Comfortable advantages Quiet Efficient insulation and good windows give the house better sound insulation so there is less noise pollution from the surroundings. 15 Cost Building in accordance with the passive house principle costs more than an ordinary house: experience shows that the cost is about 8% higher. However, it is cheaper than a low-energy house and eliminates the worries about rocketing energy prices.

16 KOMFORT HUSENE A collaboration between: Saint-Gobain Isover a/s Østermarksvej 4 DK Vamdrup Telefon