A passive house is a building with extremely low annual heating energy requirement coming to less than 15 kWh/m² per annum (to compare – for a conventionally built detached house this factor is 120 kWh/m² per annum). Its’ comfortable interior climate is provided by passive energy sources, such as: inhabitants, electrical appliances, solar energy and heat recovery from ventilation. This effects the building does not require an additional, operating heating system. Heating energy needs are met thanks to heat recovery from the air circulating throughout the building. The main task when designing a passive house is to foresee a proper external wall insulation together with economical building structure and adequate routes for ventilation ducts and water & sewage installations.
A passive house is considered to be cost-effective when the overall cost of the development (construction cost plus project cost plus internal appliances cost plus 30-years running costs) do not exceed an average costs of the same type applied to newly built conventional house.
Passive house characteristic features:
1. Compact shape and proper insulation:
All external building elements should be insulated in a way where the U-factor does not exceed 0,15 W/m2.K.
2. Southern orientation together with taking into account an over shading issue:
Passive use of solar energy is a significant aspect in designing a passive house
3. Energy-efficient window glazing and frames:
Windows (glazing and frames – all together) should have U-factors not exceeding 0,80 W/m²K with solar heat-gain coefficients around 50%
4. Building envelope air-tightness:
Air escape through leaking joints should be lower than 0,6 times the house volume per hour.
5. Passive preheating of fresh air:
Fresh air may be supplied to the building by underground channels, in which the ground-to-air heat transfer process takes place. It will result in fresh air preheating to the temperature over 5°C even on cold days in winter period.
6. Highly efficient heat recovery from exhaust air using air-to-air heat exchanger:
Most of the heat present in the exhaust air is transferred to incoming fresh air (heat recovery efficiency over 80%)
7. Hot water supply using renewable energy sources:
Energy required for water heating is supplied by solar panels or heat pumps
8. Energy efficient appliances:
It is necessary to provide a passive house with low energy consuming appliances (refrigerators, cookers, freezers, lamps, washing machines, dryers etc.)
Recuperator is a “heart” of each ventilation with heat recovery system. This element is responsible for amount of recovered heat which means that its’ task is to recover the heat but also to reduce the system heat loss. Recuperator may be assembled in garage, wardrobe, convertible attic space or unused, insulated attic space as well as in the other technical room. Recuperator based mechanical ventilation system substitutes traditional gravity ventilation ducts meanwhile the gas flues and chimney flues remain unchanged.
15 reasons making heat recovery ventilation system worth heaving:
1. Reduction of heating costs (even by 50%)
2. Possible reduction of radiators size and boiler heat output (energy requirements to heat the building lower even by 45%)
3. The building is more energy efficient (better energy efficiency factor on BER Assessment)
4. Possibility of omitting the construction of expensive gravity ventilation ducts
5. Possibility of omitting the purchase of more expensive windows with air outlets and microvents
6. Increase of the house living standards (house easier to sell in the future)
7. Lack of unhealthy air draughts (there is no necessity to ventilate the house by opening opposite windows)
8. Building supplied with mechanical ventilation system is aerated regardless to weather conditions
9. Incoming air filtration (less allergens and dust in the internal air)
10. Better comfort throughout the day thanks to lower CO2 density
11. Lower CO2emission to atmosphere (environment protection)
12. We breath only with fresh air. Recuperation supplies the fresh air and removes the used one.
13. Recuperation lowers the level of moisture in the internal air
14. Possibility of assemblage of in-ground heat exchanger (additional cooling in the summer and even higher recuperator’s efficiency in the winter)
15. Continuous access of fresh air (even in the winter) without cooling the house
Bibliography: Polski Instytut Budownictwa Pasywnego i Energii Odnawialnej