Brrrr … It’s Cold, but ‘Green’ in the Ice Box

ice boxesWashington, D.C. in the summertime is typically hot and humid — many might even say swampy. In other words, it’s the perfect place to demonstrate Passive House design principles using massive blocks of ice.

The #IceBoxChallengeDC, which ended Friday, tested how well ice could hold up inside two shed-sized “ice boxes.” The red box was built to standard building and energy code requirements (the 2013 DC Building Codes are locally amended versions of multiple 2012 codes). The blue box was built to Passive House certification requirements.

Each ice box — fitted with a small viewing window and a thermometer so spectators could read the indoor temperature — was filled with a 1,800-pound block of ice and left out in Farragut Square in downtown D.C. for two weeks in the middle of July.

Originally developed in Germany, the Passive House program focuses on limiting the amount of energy needed to operate the building. To be certified, the home must embody a set of specific best practices, such as continuous insulation without any thermal bridging, high-performance windows (typically triple-pane) and doors, and an airtight building envelope.

The thicker walls, floor and roof of the blue Passive House Ice Box enable it to hold temperature well: On the mid-July day that NAHB staff went to see the boxes — when the sun was bright and the temperature hovered in the 90s — the interior temperature of the blue box was 40 degrees and the ice block was visibly larger than the block in the red box. The red box was about 12 degrees warmer and there was a puddle around the front of the box.

Friday’s big reveal showed that the ice block in the code-built box was significantly smaller than the one in the Passive box, weighing 463 pounds and have lost 74% of its mass during the course of the demonstration. The Passive House ice block lost 53%, weighing in at 838 pounds.

While the voluntary, above-code National Green Building Standard focuses on whole-house sustainability including land design, water use and resource efficiency, it’s instructive to see the building science takeaways from the Ice Box Challenge, said NAHB sustainability and green building program manager Michelle Diller.

“We are seeing the impacts of building to above-code insulation and air-sealing requirements and how this could translate into a home that uses significantly less energy, needs a smaller HVAC-R system, and can cost less to operate,” Diller said. “I have found that many people working with the Passive House system agree there is generally 5-12% cost premium to build to the program.”

However, she noted, a recent study from the Pennsylvania Housing Finance Agency, which has embraced Passive House through its state allotment of federal Low Income Housing Tax Credits, showed the construction budget of awarded projects to be less than that of conventional ones. Additionally, Passive House construction realizes 40-90% energy savings over standard design, providing payback for the initial investment.

Next stop on the East Coast Ice Box Challenge: Pittsburgh.

To get additional information about NAHB’s sustainable and green building programs, contact program manager Michelle Diller. To stay up to date on happenings in the high-performance residential building sector, follow the Sustainability and Green Building team on Twitter.


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