The Passive house, or Passivhaus Standard as it was originally named, is an energy efficient building model developed by the Germans in 1988. Today, it offers the highest energy standard for buildings with the ability to slash the heating energy consumption of a house by a whopping 90%! The houses are able to provide such savings because their high degree of insulation eliminates the need for a conventional heating system. Instead of relying on active systems and renewable technologies to bring a building to “zero energy,” the Passive House design utilizes natural resources, such as solar energy, to produce a highly efficient and healthy home. In addition to super insulation, Passive Houses require specific design components with respect to:
• Design without thermal bridges
• Air tightness
• Ventilation with heat recovery
• Comfort windows
• Innovative heating technolog
Super insulation
In order to meet the standard, Passive Houses are encased in ultra-thick insulation, which reduces heat loss during the winter and heat gain during the summer. This super insulation generally results in high R-Values (normally between 38 and 52) on all external walls, slab foundation and roofs. Such high values help to ensure that the home is kept at a comfortable temperature year round with very little energy use.
Design without thermal bridging
In addition to super insulating, it’s necessary to eliminate thermal bridges within a Passive House. Thermal bridges are created when two poor insulators come into contact allowing external air to flow into a home. This is a common problem in home construction, but can be a more serious issue in Passive Houses as it negates the investment in extra insulation.
Air tightness
Elaborate airtight seals around all doors and windows help produce a thermal envelope around the house. This envelope ensures the energy savings and longevity of the building by eliminating gaps that could allow moisture to enter, raise humidity levels and, over time, damage the structure of the home.
Due to these various structural requirements, the Passive House standard is applied more often to new buildings rather than retrofits. Still, a home can be retrofitted in the Passive House style and the model can be used on both residential and commercial constructions.
Ventilation with heat recovery
All these steps to keep air within the home may have you wondering about ventilation throughout the house. Indeed, proper ventilation is a crucial component to a Passive House and is quite easy to achieve. All that is required is a mechanical ventilation system in the form of a Heat Recovery Ventilator (HRV) or Energy Recovery Ventilator (ERV). Both systems work by passing the warm exhaust air past the incoming cold air in a way that does not allow the two streams to mix. This method also manages to recover 75% to 95% of the heat and makes sure that only fresh air is entering. As a result, no air is recirculated and the air quality is generally superior to that of normal homes.
Comfort windows
The windows in a Passive House must be extremely efficient so as to complement the insulation requirements and to reduce the flow of heat and cold. In Europe, they use triple pane windows with low-e coatings and Argon gas to achieve an R-value of just over 7. They also seek a low U-value of less than 0.20 (a very good Energy Star window in the US would be closer to 0.30).
Innovative heating technology
As a result of all the other requirements, the heating needs within a Passive House are extremely low. In fact, a Passive House can usually be heated by simply heating the fresh air that is brought in by the mechanical ventilation system. Various methods can be used to heat the incoming air, including a small heat pump, small condensing gas burner, small combustion unit for biomass fuel or a compact until for all in one heating, ventilation and hot water. All these options also eliminate the need for additional ducting in the home.
The Passive House model may seem extreme to some, and it does require rather strict standards to be met, but is offers extraordinary reductions in energy use, carbon emissions and heating costs. It is also gaining considerable recognition and exposure as the new administration in Washington brings more attention to green building and energy efficient homes. Today, there are about 150,000 Passive Houses around the world, the majority of which are located in Germany,Danmark and Austria. This number, however, is expected to grow in the coming years, especially in the USA as green building goes vogue.