Passive House design

You may have started to hear the term Passive House turn up on television and in architectural design articles and be wondering what’s so different between passive house design as it can apply to any building and these particular buildings.

Passive house (German: Passivhaus) is a voluntary standard for energy efficiency in a building that looks at the entire building’s ecological footprint. It results in ultra-low energy buildings that require little energy for space heating or cooling. While some techniques and technologies were specifically developed for the “passive house” standard, others, such as superinsulation, already existed, and the concept of passive solar building design dates back to early house building.

The design is not an attachment or supplement to architectural design, but a design process that integrates with architectural design. Although it is generally applied to new buildings, it has also been used for retrofits and is not limited to houses or residential properties since office buildings, schools, kindergartens, and a supermarket have and can also be constructed to the standard. The first Passivhaus residences were built in Darmstadt in Germany in 1990 and occupied by the clients the following year. The Passive House Institute (PHI) in 1996 was established as an independent research institute.

Even in its earliest technological form, early passive houses saw the requirements for space heating at 90% less than that required for a standard new building at the time, and the Economical Passive Houses Working Group was created. If a building meets the passivhaus standards, it does not need conventional heating systems, though some heating will still be required and most passivhaus buildings include supplemental space heating. This is normally distributed through a low-volume heat recovery ventilation system that is required to maintain air quality, rather than by a conventional hydronic or high-volume forced-air heating system.

Heat recovery ventilation (HRV), also known as mechanical ventilation heat recovery (MVHR), is an energy recovery ventilation system that operates between two air sources at different temperatures. By recovering the residual heat in the exhaust gas, the fresh air introduced into the air conditioning system is preheated (or pre-cooled), and the fresh air’s enthalpy is reduced before it enters the room, or the air cooler of the air conditioning unit performs heat and moisture treatment. The heat recovery system helps keep a house ventilated while recovering heat being emitted from the inside environment.

The Passive House standard defines globally consistent performance metrics for buildings. The certification is carried out by a PHI-approved Passive House Certifier, and there are certifiers working throughout the world. The PHI administers a certification scheme that allows a building to be called a Certified Passive House. To obtain certification, a building must meet the following criteria:

• Thermal comfort must be achieved during winter (20°C minimum) as well as in summer (this can be adjusted in extreme climates), with not more than 10% of the hours in a given year over 25°C.
• Heating demand 15kWh/m2/yr or heating load 10W/m2.
• Cooling demand 15kWh/m2/yr (in humid climates this allowance increases to allow for dehumidification) or cooling load 10W/m2 (if installed)
• Humidity must not exceed 12g/kg for more than 20% of the year (~60%RH at 25°C).
• Airtightness must be 0.6ACH50 or lower and be verified on site.
• Overall energy use (Primary energy renewable must not exceed 60kwh/m2/yr. When calculating overall energy use, Passive House includes whole-of-building energy; this includes heating and cooling, hot water, lighting, fixed appliances and an allowance for consumer electronics.

There are 3 levels of Passive House certification available: classic, plus, and premium. Classic does not require the installation of renewable energy generation. Passive House Plus buildings are more efficient (maximum PER of 45kWh/m2a) and will produce about as much energy as they consume over a year. Passive House Premium certified buildings are more efficient again (maximum PER of 30kWh/m2a) and will produce a significant excess of energy over the year.

For more details head to YourGov or get in touch with some of the designers on our directory who specialise in passive house buildings