The idea of the Passive house was first developed by Professors Bo Adamson of Lund University in Sweden and Wolfgang Feist from the Institute for Housing and the Environment in Germany. The idea was hatched in May 1988 and by 1990 the first Passivhaus (German for ‘Passive house’) was built in Darmstadt in Germany.
In September 1996 the Passivhaus Institute was set up in Darmstadt to help develop standards and improve techniques for building Passive houses. Since the inception of the Passivhaus Institute more than 25,000 Passive houses have been built, mostly in Germany, Austria and Scandinavia.
The main idea behind the Passive house is to reduce space heating to as near minimum as possible. So far Passive houses have managed to reduce heating and cooling by 90% compared to standard new buildings. Passive houses don’t have central air systems or other types of central heating. They only have small back-up heating systems.
How does the passive house work? The method for reducing the need for heating to as close to zero as possible can be broken up into parts:
❶ Thick insulation is used. Wall insulation and roof insulation in particular are focused upon. Typically Rip40 walls and Rip60 roofs are used. It is normally the case that such high specification walls and roofs are designed prior to the construction of a house but they can also be retro-fitted. (Rip40 and Rip60 refer to R values or the thermal resistance of a material – namely its ability to resist transferring heat).
❷ The places where walls meet roof and where walls meet foundations and flooring are made as airtight as possible.
❸ Windows and doors are made as air-tight as possible.
❹ Large windows are avoided and windows with triple panes are used with a double low e glazing. The insulated windows and low e glazing minimizes heat loss through windows.
❺ Forced air (air-conditioning or central air) and hydronics heat systems are not used. Instead a dual purpose 800 to 1,500 watt heating and/or cooling element integrated with the supply air duct of the ventilation system is used. This can be powered by solar energy or other sources of alternative energy; and as a last resort by utility company electricity.
❻ Hot water is generated by passive solar gain on the roof.
❼ The main source of heating comes from waste heat from appliances (such as lighting and white goods) and from human body heat. Because the house losses very little heat this heat effectively builds up keeping the interior warm.
The cost of the air ventilation system is kept low by using natural ventilation (opened windows) when the weather outside is clement. And when it is cold outside mechanical heat recovery ventilation systems, with a heat recovery rate of over 80% and high-efficiency electronically commutated motors (ECM) are employed to maintain air quality. Because the house is virtually air-tight the rate of air change can be optimized and carefully controlled at about 0.4 air changes per hour. All ventilation ducts are insulated and sealed against leakage. The notion of high grade insulation and making a house air-tight as possible is called superinsulation. Superinsulation is amazingly efficient: a passive house typically loses less than 0.5 °C (1 °F) per day (in winter), stabilizing at around 15 °C (59 °F) in the central European climate.
Although the technology used for making Passive houses has been developed with the colder climes of central and Northern Europe in mind, there are a few certified Passive houses in hot and tropical climates. For example in Lafayette, Louisiana, USA, there is a Passive house which uses Energy Recovery Ventilation instead of Heat Recovery Ventilation. This removes excess humidity and transfers excess heat to the hot water tank.
The cost of building a Passive house is 14% more expensive than building a standard house. However, that extra cost is off-set by the vast reduction in heating/cooling costs.
A Passive house is different to a Zero Energy Building in that a Zero Energy Building focuses more on renewable energy technologies (such as photovoltaic) to off-set the building’s primary energy consumption. However the two approaches are complimentary and both use the same principles of thermal energy transfer and storage.