An Intro to Passive House Concepts

We talk a lot about what goes into designing a building to Passive House standards - both the physical parts that make the building airtight and super-efficient, as well as the labor on both the design and construction sides. But sometimes we get ahead of ourselves and forget that not everyone is familiar with what Passive House is, and how a Passive House building is different from a typical building. So we've put together this brief primer to help introduce people to the concepts.

To start, Passive House is an overall, holistic approach to the design of a building that focuses on energy efficient performance and user comfort. The first Passive House, “Darmstadt House” was completed in 1991 near Frankfurt, Germany by Wolfgang Feist. It was provided with “a highly precise data measurement and acquisition system to examine the achievements of the project’s objectives” (Passive House Academy 2017, 12). This eventually evolved into the PH standard for whole-building energy modeling and verification that is used today by the German based, Passive House Institute (PHI). PHI is an internationally focused organization which certifies that buildings meet their strict guidelines. The Institute continues to research and develop these guidelines as they apply the PH standard to projects in various programs and climate types around the world. (Note: The Passive House Institute United States - PHIUS - is an alternative certifying entity that uses slightly different criteria). Handel Architects’ experience focuses on the PH standard as set by PHI, the certifying body for all of our Passive House buildings to date.

Criteria for Certification

PHI establishes the performance criteria based on a project’s program and geographic location. The certified result is a project with a 50%-80% reduction in energy usage compared to a conventional building (Passive House Academy 2017, 12). While every project is unique, the guiding principles remain the same: to provide a comfortable and healthy interior environment without exceeding a maximum Source Energy Use Intensity (EUI), and the lowering of the heating/cooling demand by combining a tightly-sealed, robustly insulated envelope with an efficient MEP system that includes a continuous fresh air ventilation system with heat recovery.

These criteria illustrate how ambitious the PH standard truly is as applied to a multifamily building in NYC:

The estimated Source EUI for a building following the 2018 IECC is 130 kBtu/sf/yr (NYSERDA, 2018). A PH certified multi-family building in NYC is nearly three times better at approximately 50 kBtu/sf/yr, based on data analyzed from the House at Cornell Tech in New York City. Even with the 45% reduction required by the IPCC by 2030, a standard building will well exceed the EUI of a Passive House building built in 2019.

The R-value for a standard code minimum opaque wall is approximately 13.5, while for a PH project, the R-value hovers +/- 25. The PH wall is extremely well-insulated with minimal metal-to-metal connections (thermal bridges) interrupting the continuity of insulation.

Additionally the U-value for a standard code minimum window averages 0.38 and for a PH project the U-value is approximately 0.17 (typically a triple glazed window with a thermally broken window frame).

PH buildings provide 24/7 fresh air ventilation to each habitable room treated with a very tight, Merv 13 filter; typical buildings have a minimal mechanical fresh air ventilation requirement.

The façade is built to extremely tight standards, but still with operable windows, and is 7-10 times tighter than a typical building.

The well-insulated façade, as well as exceptional window construction and installation, leads to outstanding acoustical comfort.

Source Energy Use Intensity (pEUI) Distribution Comparison

The effort to design a superior enclosure, along with the specifying of energy efficient systems and equipment, lowers the overall Source Energy needed to operate a building by 50-80%. The chart below shows a 60% reduction of overall energy usage at the House at Cornell Tech – shrinking all loads, and dramatically reducing the heating load which is typically the biggest burden of a residential building.

Closing

The threat of climate change and the need for healthier interiors is building a strong case for implementing Passive House design in both our new and existing buildings. As precedent for PH is accumulating, the industry is maturing and embracing this proven pathway. Handel Architects is a global leader in the design of Passive House projects and we embrace any opportunity to apply our experience to any building type. Together with our enlightened clients and dedicated partners, we can make a difference.

We encourage you to explore our Passive House projects below.

The House at Cornell Tech, New York City

Sendero Verde, New York City

Winthrop Center, New York City

Student Residences at the University of Toronto Scarborough, Toronto

Passive House and Design Flexibility

Passive House buildings are energy efficient but how does this standard impact the design of a building?

It stands to reason that such stringent performance requirements could restrict the flexibility of a project to respond to specific design conditions. This is where the PH energy model plays a big role. By modeling every building component, the design team can experiment with how different variables impact building performance. Variables can be manipulated to meet specific project requirements allowing for a give and take between the individual building components resulting in a unique design that meets identical performance criteria, as is illustrated in the two case studies. The full project teams (architect, ownership, consultants, and contractors) meet specific demands by finding the right balance of the following variables:

• Site and Program (form factor, orientation, daylighting/shading, urban context, aesthetics)
• Exterior wall
• Air Sealing
• Window Performance
• Thermal Bridge Mitigation
• Mechanical System

These are just some of the many variables considered. The PH standard’s data-driven approach sparks innovation and allows each new project to find its own path. Through knowledge-sharing and increasing industry familiarity with the PH requirements and techniques, more variables are discovered, and the standard becomes more flexible and achievable. In each case study the design team had ongoing conversations with PHI to analyze and solve the unique challenges posed by high-rise applications, a relatively new application for the PH standard.

Learn more

View the next report in our series: Sustainability Report Issue #4: Bending the Curve - An Approach to Radically Cut Emissions From the Building Industry