What is a PassivHaus?
It started, by all accounts, in the USA during the energy crisis in the 1970s. The push to reduce energy consumption of buildings was a response to the high energy costs of the time and resulted in the development of tightly enveloped houses. A building envelope is all the components that separate the interior from the exterior. Low-energy buildings maintain comfortable indoor conditions by a building envelope that insulates and prevents air leakages keeping the exterior climate change from influencing the interior.
In Europe they continued the development and derived a set of design and construction principles governing the air quality and comfort, which if followed rigorously will result in certification to a standard of the Passivhaus Institute.
“A Passivhaus is a building in which thermal comfort can be achieved solely by post-heating or post-cooling the fresh air flow required for a good indoor air quality, without the need for additional recirculation of air.” – Passivhaus Institut (PHI)
To be a Passivhaus, a building must meet the following standards: an infiltration speed no greater than 0.60 air changes per hour @ 50 Pascals, a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all functions of 120 kWh per square meter (11.1 kWh per square foot).
The heating requirement in a Passivhaus is reduced to the point where a separate heating system is no longer required and cooling is also minimised by the same principles and through the use of shading and in some cases via the pre-cooling of the supply air. As well as being an energy performance standard Passivhaus also provides excellent indoor air quality by reducing the air infiltration rates and supplying fresh air which is filtered and post heated by the MVHR unit.
The advantages of a Passivhuas are:
- Energy savings of up to 90% compared with typical building and over 75% compared with average new buildings.
- High level of comfort.
- Recycle energy sources inside the building such as the body heat or entering solar heat.
- Good insulation of building shell – exterior walls, roof and floor slab which keep the heat in during winter and out during summer.
- A continuous supply of fresh air making for superior air quality through controlled ventilation without draughts by pre-heating or pre-cooling the air.
There is a separate standard that can be applied to retro-fits. EnerPHit is a slightly relaxed standard for retrofit projects, where the existing architecture and conservation issues mean that meeting the Passivhaus standard is not feasible.
What is needed to achieve a PassivHaus?
Highly insulated walls, floor and roof and special windows typically triple pane glass. This prevents heat exchange with the outside environment, keeping the house cooler in summer by preventing heat entering the house and warmer in winter by preventing cold entering and heat leaving. A ventilation system which continually supplies fresh air and a highly efficient heat recovery unit that harvest and heat leaving the building for re-use.
In order to claim the standard the house will need to designed and constructed in accordance with the quality controls and guidelines of the Passivhaus certification. This would usually require an architect and builder who have been trained and certified by an approved Passivhaus organisation.