Passive House, or Passivhaus as it is known in Europe, is both a building energy performance standard and a set of design and construction principles used to achieve the standard. Buildings that meet the standard are ultra-low energy buildings that use 80 to 90 percent less energy for heating and cooling than conventional equivalent buildings, while providing superior air quality and comfort. As of 2014, there are approximately 30,000 Passive House buildings in the world.
A Passive House project maximizes the energy efficiency of the basic building components inherent in all buildings: roof, walls, windows, floors and the utility systems: electrical, plumbing & mechanical. By minimizing a building’s energy losses, the mechanical system is not called to replenish the losses nearly as frequently, saving resources, operational costs and global warming related pollution. Unlike any other structures, Passive House buildings maintain occupant comfort for more hours of the year without the need for mechanical temperature conditioning of the indoor air. The opposite has been the norm in this country with a history of cheap fuel and construction techniques with little consideration for energy losses through thermal bridging, air-infiltration, let alone being conscious of using some, or even any insulation. Thus, to minimize losses, Passive House focuses on insulation.
Strategic Design and Planning:
Passive House building projects are carefully modeled and evaluated for efficiency at the design stage. A Certified Passive House Consultant (CPHC) is trained to use computer modeling tools that allow designers to test “what-if” scenarios before construction begins.
Specific Climate Siting and Sizing:
Passive House design uses detailed, specific annual weather data from the home’s location in modeling a structure’s performance. Orientation of the windows can maximize or minimize solar gain and shading and affect the home’s heating and cooling needs.
To keep the heating and cooling in, wall assemblies require greater insulation values to stop the conditioned air from leaving. Walls are typically twice as thick as today’s standard construction, for good reason. Wall assemblies are analyzed to allow for proper water and moisture management to make a long lasting and an exceptionally healthy building.
Thermal Bridge-Free Detailing:
Breaks in the insulation layer usually caused by structural elements and utility penetrations in the building envelope create “thermal bridges,” allowing undesirable exterior temperatures to be transmitted through to the interior. Passive House design attempts to eliminate thermal bridges via progressive mindful architectural detailing.
Air-Tight Envelope (But Diffusion Open):
Anyone who has been in an older drafty home understands how stopping cold air from leaking in and heated air from leaking out, affects comfort and the efficiency of the mechanical systems. Passive House takes great care in designing, constructing and testing the building’s envelope for an industry-leading control of air leakage. Blower door testing is a mandatory technique in assuring high performance. Walls are designed to be virtually air tight, while allowing water vapors to dry out providing an excellent strategy to maintain a healthy mold-free environment.
Advanced Windows and Doors:
Historically windows and doors are the weak link of a building’s thermal defense system and Passive House places significant emphasis on specifying highly insulating products. To meet the high performance needs of various climate zones, windows must meet strict performance standards regarding: component insulation, air tightness, installation and solar heat gain values.
Energy Recovery Ventilation:
The “lungs” of a Passive House come from an appliance called a heat (or energy) recovery ventilator (HRV/ERV). It provides a constant supply of tempered, filtered fresh air 24/7. The heat from outgoing stale air is transferred to the unconditioned incoming fresh air, while it is being filtered, providing a huge upgrade in indoor air quality and consistent comfort, especially for people sensitive to material off-gasing, allergies and other airborne irritants.
One of the best benefits to implementing Passive House design is the high performance shell and extremely low annual energy demand. This allows owners to save on heating and cooling costs as they can now significantly downsize a building’s mechanical systems. Passive solar gains, plus heat from occupants and appliances supply much of the needed heat.
By installing efficient appliances, hot water distribution, and energy efficient lighting, a Passive House’s electricity consumption is also slashed by 50% compared to the average housing stock, without any loss of convenience.
Considering solar panels on your project? Passive House’s significant reduction in energy use allows solar energy to power a greater percentage of a building’s demands. Likewise smaller demand equates to smaller and more affordable photovoltaic systems providing higher cost-benefit value. Passive House design puts a project within reach for achieving true Net Zero performance, where the building generates as much energy as it consumes over the course of a year.
(Adapted from Passive House Alliance US, phaus.org)