Passive House: New interest in an old idea.

The term Passive House is an internationally recognized building standard for energy efficiency. Despite what its name may suggest, the Passive House standard does not apply to houses alone. Any type of building can be designed and built to the Passive House standard. As I write this, there is a Passive House hospital being built in Frankfurt Germany. In German, where the standard originated, it is known as the Passivhaus standard.

The goal of the Passive standard is to produce buildings that are sufficiently energy efficient to allow them to rely almost exclusively on “passive” energy sources to provide their heating and cooling needs. Passive sources of heat are generally derived from sun light, appliances and occupant body heat. Passive cooling can be provided by window orientation in combination with natural ventilation aided by a building’s stack effect (air movement due to temperature/density gradient).

In Canada, exploration in “passive” building design goes back to the 70s. A good example would be the Saskatchewan Conservation House, which was built in 1977. Unfortunately, large scale adoption of these types of building techniques however have yet to gain significant traction on account of North America’s historic access to cheap energy. With the inevitable rise of energy costs, incentive to build energy efficient buildings will only increase with time.

(Fig 1 – slideshare.net, Fig 2 – Image credit: passipedia.org)

The Passive House standard can generally be defined by three stipulations.

1. The first stipulation relates to how much energy is required to heat and cool the building. The standard states that the building cannot use more than 15kWh/m2 of energy per year to provide ambient heating and/or cooling. This represents an energy consumption savings of up to 90% compared to conventionally built buildings. In order to achieve this high level of efficiency, passive house buildings rely upon supper insulated and airtight exterior walls, ceilings/roofs and floors. In other words, the entire building envelope is designed to impede heat transfer. One exception are windows which are designed to both allow and repel the Sun’s energy depending upon the season. This is accomplished through orientation, sizing and the use of exterior shades and canopies. Additionally, the windows themselves incorporate triple glazing to maximize their thermal resistance and various coatings to minimize/maximize heat gain.
2. Air tightness is the second stipulation. The Passive House standard requires that the buildings be extremely air tight in comparison to conventionally built buildings. The standard states that the building envelope must not leak more than 0.6 times the building’s entire volume per hour when subjected to a pressure difference across the envelope of 50 Pa.  To provide fresh air, Passive House buildings incorporate heat recovery ventilation systems. These highly efficient systems allow for the exchange of not only air, but its retained heat, and humidity as well.
3. Thirdly, the Passive House standard stipulates that the primary energy (the source energy) consumption for heating, hot water, electricity etc., be limited to less than 60kWh/m2 per year. This stipulation looks beyond the building envelope design to address larger issues of sustainable living. One can imagine that it will become more stringent in time with the advent of technological advances.

The standards first two stipulations result in walls, ceilings and floors that are essentially at room temperature, regardless of the exterior temperature. This results in a building that is very comfortable to be in due to the lack of radiated heat transfer between one’s body and the surrounding surfaces (interestingly, current building codes do not address at all occupant comfort due to radiated heat transfer).

As a Senior Project Manager for the Building Science & Sustainability (BSS) Group at Pinchin Ltd. I am excited to see some Passive House ideals and other technological advances making their way into new construction projects and the restoration of existing buildings. If you would like more information on the Passive house standard or are interested in preforming a building envelope condition assessment of your home to determine what energy efficiency improvement can be implemented, please feel free to contact me.