Passive House is an energy efficiency standard for buildings, originally developed as “Passivhaus” by Professors Bo Adamson Wolfgang Feist in Germany in the late 1980s and early 1990s. It is the most rigorous building standard for energy efficiency, and the most effective path to achieving net-zero energy buildings.
While there are many other “green building” standards in the marketplace today, Passive House is notable for its singular focus on operating energy, while others may also focus on aspects such as water use, material sourcing, transportation infrastructure, and more. The original standard as developed in Germany is still administered today around the world by Passivhaus International (PHI), and is a performance-based standard with three key metrics.
≤ 1.4 kWh/ft2 or ≤ 4.75 kBTU/ft2 annual heating and cooling demand
≤ 11.1 kWh/ft2 or ≤ 38.1 kBTU/ft2 annual total primary energy demand
≤ 0.05 CFM50 and 0.08 CFM75 per square foot of gross envelope area
Since the founding of Passive House Institute United States, (PHIUS) in 1997, the standard has been revised to account for the variability of the domestic climate. In 2015, the new US standard, PHIUS+ 2015 was introduced with its own set of performance metrics. These metrics set limits on airtightness according to building envelop area and on annual heating and cooling demand and peak heating and cooling loads, specific to the climate where the project is located. There is also an overall source energy limit, and in line with the 2030 Challenge, must be source net-zero by y2030. In addition, new projects certified under PHIUS must qualify for the US DOE Zero Energy Ready Home program and the US EPA Indoor airPLUS program. Project performance must be verified by a rater pre- and post-occupancy.
There are hundreds certified Passive House buildings in the US today, both under the PHI standard and the PHIUS standards. For both standards, Certified Passive House Consultants use the advance Passive House Planning Package (PHPP) modeling software to model building energy performance, and the results of these models form the basis for verification and certification.
The metrics of either standard can represent overall energy usage reductions of 60 – 80% (and space heating and cooling energy demand reductions of approximately 90%) compared to traditional buildings. Such performance is achieved through several core principles:
Infrared Image exterior of a Passive House.
- Thermal insulation – minimizes heat transfer through opaque elements of the building envelope’s surface.
- Reduction of thermal bridges – prevents conductive heat transfer through structural elements.
- High-performance windows – minimizes conductive and convective heat transfer through building glazing, as well as window frames, while allowing control of visibility and radiative heat gain.
- Airtightness – prevents convective heat transfer from uncontrolled air movement between the interior and exterior of the building.
- Balanced ventilation with energy recovery – provides 100% fresh outdoor air, preconditioned through high efficiency heat exchange.
- Efficient mechanical systems – decrease energy demand and internal heat gains.
- Passive elements – utilize building orientation and shading to optimize natural light and solar heat gain.
- Readiness for renewable integration – allows building to achieve net-zero energy by way of photovoltaics, solar thermal, geothermal, wind power, etc.
Besides the obvious advantage of reduced operating costs through lower energy use, Passive House buildings offer a number of additional benefits:
- Increased occupant comfort – by eliminating drafts and minimizing temperature differentials between indoor surfaces.
- Improved indoor air quality – through a constant, controlled supply of filtered, fresh outdoor air.
- Little to no marginal cost – increased costs to achieve the Passive House standard can be offset by downsized HVAC equipment.
- Passive resilience – because of their low-energy design, Passive House structures can maintain superior comfort over traditional buildings in the event of power outages or other unforeseen circumstances.
- Potential for carbon neutrality – low energy demand, integrated with renewable energy technologies, can lead the way to a sustainable, carbon-free future.