Holistic approach to energy efficiency
Within the European Union, Germany and Austria are ahead with respect to low energy building concepts. To date more than 5,000 dwellings have been constructed in accordance with the principles of PassivHaus design, which reduces energy use by up to 90% compared to existing building stock. The European PEP project aims to bring this experience to the UK.
Professor Wolfgang Feist of the PassivHaus Institut Germany, says: "Ten years ago, no-one believed us that houses can manage with less than a tenth of the heating energy used by average old buildings. Since then, the concept of PassivHaus design has spread around Europe, with several UK projects now in the planning stages.
The principles of low-energy design are simple and well known. Step 1 is to reduce the energy demand; Step 2 is to meet the remaining energy requirement as efficiently and cleanly as possible. These underpin the concept of PassivHaus design.
Building a PassivHaus is not just a case of specifying components elementally, it requires an holistic approach to energy efficiency and strong management on-site. The main technical differences between a dwelling built to UK Building Regs standards and the PassivHaus standard can be broadly described as follows:
- Intelligent use of passive solar gains and the specification of building features which limit risk of overheating in summer.
- Super-insulation: opaque fabric U-values must be less than 0.15 W/m2K, with U-values for windows and doors generally needing to be less than 0.8 W/m2K (for both the frame and glazing). Thermal bridges are also eliminated.
- Airtightness: 1 m3/(h.m2) at 50 Pa test pressure or less
- Whole house mechanical ventilation with heat recovery (75% efficient or better).
By specifying these features the design heat load is limited to the load that can be transported by the minimum required ventilation air. Thus, a PassivHaus does not need a traditional heating system or active cooling to be comfortable to live in - the heating demand can be met using a small electric heater within the ventilation system (although there are a variety of alternative solutions).
More information from: www.passivhaus.org.uk
