What is a Passive House? fundamentals
The revolutionary energy performance of Passive House buildings demands a rigorous and scientific approach to design and construction. Energy performance savings of 80%+ in comparison to conventional Canadian construction do not happen by chance.
If a building is to achieve year-round comfort in a cold or cool climate zone with such minimal heating/cooling energy use, then it’s necessary to incorporate passive design fundamentals, including the following:
Pre-Planning
If you want to build a Passive House it’s important to get qualified professional advice on achieving this standard at the beginning of the design process. Unless this is a clearly defined goal from the start of a project, the building will likely not meet Passive House performance standards.
Efficient Building Shape
Since the amount of heat loss from any building envelope is proportional to its surface area, the building’s surface area must be minimized to achieve exceptional energy performance. Passive House designers use a ratio known as the ‘Shape Factor’ to assess buildings, this being the ratio of the building’s surface area divided by its volume. By this measure, buildings with sprawling designs, exposed floors, heated garages etc. have higher shape factors, and will therefore experience higher heat losses, even if their floor areas are identical.
Solar Exposure
Passive solar gains normally form an important component of the heating requirements in a Passive House. In most regions of Canada high solar gains though south-facing glazing are potentially available and need to be utilized on site through appropriate design if the Passive House Standard is to be achieved. At the same time, glazing on northern facades should be minimized. Skylights are almost always a poor design choice from an energy-efficiency viewpoint. Both winter and summer shading performance, as well as year-round comfort design requirements are determined in detail using the Passive House design software (PHPP).
Superinsulation
The insulation levels required for any building to achieve Passive House performance must be determined by modeling the building using the PHPP software and relevant climate data. To ensure accuracy this should be done (or supervised) by an experienced Passive House designer.
Depending on the climate zone, houses built in Canada will likely need between three and seven times better insulation performance than that provided by current national and provincial Building Codes, in order to achieve Passive House performance. The designer must ensure complete insulation coverage for all parts of the building shell.
Advanced Windows
As the thermally weakest part of a building envelope, windows are a critical component in Passive House design, often representing more than 50% of all heat losses in a building. Windows are also critical to interior comfort, and the interior glazing and frame surfaces need to remain warm enough on cold nights to minimize interior downdrafts in areas adjacent to the window. In all parts of Canada triple glazing is essential, with two low-e coatings and argon (or krypton) gas fill, as well as insulated spacers between each glass pane. It is also critical that window frames are insulated. Most windows currently sold in Canada meet few if any of these requirements.
Airtightness
Passive House buildings need to achieve very high levels of airtightness compared to conventional construction, in order to minimize heat loss from air infiltration, and also to protect the building structure against possible moisture damage.
Ventilation with Heat Recovery
All Passive Houses are fitted with a ventilation system which provides excellent indoor air quality and which has exceptional heat recovery performance.
Ventilation Air Pre-heating
A simple and inexpensive geothermal heat exchanger is often incorporated into the Passive House heat recovery ventilation system, which allows for pre-heating of the cold incoming airstream and ensures that the HRV unit can be kept frost-free without the need for energy-intensive defrosting. Such systems can also provide some active cooling and dehumidification during summer,
Thermal Bridge-Free Construction
In order to certify a Passive House, the designer must demonstrate that all parts of the building fulfill a strict thermal bridge criterion. This is typically achieved via an engineering heat loss analysis of various building components, such as wall-floor intersections. In practice, European Passive House designers have developed a large number of appropriate thermal bridge-free construction solutions, since most builders and architects cannot be expected to perform such calculations. Significant thermal bridging is found throughout all building envelopes in contemporary Canadian construction.
