Quick Passive House Refresher

It’s so simple it’s elegant.

Passive House, or Passivhaus as it’s known in Europe, is not a brand name, but rather a design and construction method. It is a measurable approach to energy efficient design and construction that critically relies upon the following to be performed with precision:

  • Energy modeling the home during design-stage using the Passive House Planning Package software
  • Create an airtight building envelope
  • Insulate with super insulation, WAY more than is found in a typical building
  • Install extremely efficient doors and windows
  • Capture the heat that exists in ventilated air, and use it to heat fresh, filtered air which comes into the home constantly
  • Have third-party professionals verify the performance of the home

Passive Houses are mechanically very simple and exceptionally efficient. Due to careful energy modeling, the heating or cooling systems are tiny and are often not needed for much of the year. Also, heat from appliances, cooking and humans are often all that’s needed to keep a Passive House cozy!

That’s pretty much it… but, if you want to know more… please read on.

How is energy performance measured?

The Passive House Planning Package (PHPP) is a complex and proven modeling tool created by the Passivhaus Intstitut of Darmstadt, Germany. Based on hundreds of specific data points, the PHPP predicts energy consumption and performance of a Passive House prior to project ground-breaking. The PHPP considers localized climate data, solar orientatation, comfort criteria, seasonal shading conditions, as well as the internal heat gains mentioned above. The PHPP is empowering as a comprehensive design tool, allowing for the optimization of any project to its architectural design, specific site, building assembly components and budgetary constraints. A few examples, the specificity of the PHPP results calculate valuable information such as potential overheating periods in a given year; it offers the ability to model cross-ventilation or night-flushing to mitigate active cooling needs. We can also accurately determine the size of solar array required to make the project carbon neutral.

What does a Passive House Cost?

The cost to build a Passive House often saves a homebuyer money up front when compared to other methods of construction. In some cases it can add 5%-10% which typically pays back in less than ten years because of extreme energy cost savings. A Passive House is built usually with commonly available materials. The major differentiators of building a PH are in the detailing: no thermal bridging, order of materials in assemblies (consider the building science more thoroughly), super insulation and super efficient windows and doors. In response to the growing national interest in Passive House as the most cost effective, sensible solution to net-zero energy housing, the Washington State University Energy Extension Program has adopted the North Residence as a pilot project this year. They will be collecting data throughout the next year pertaining to energy usage, comfort and indoor air quality.

Required Performance Characteristics

To achieve Passive House Certification, a home must meet specific performance characteristics set forth by the Passive House Institute:

  • Annual heat requirement of 4.75 Kbtu’s per square foot per year
  • Primary energy demand under 38 Kbtu’s per square footage of treated floor area
  • Airtight building shell ? 0.6 ACH @ 50 pascal pressure, measured by blower-door test

In addition, the following are recommendations, varying with climate:

  • Window u-value 0.8 W/m2/K
  • Ventilation system with heat recovery with 75% efficiency with low electric consumption @ 0.45 Wh/m3
  • Thermal Bridge Free Construction 0.01 W/mK

Posted on September 13, 2010

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