Passive House beats building code box in Ice Box Challenge

Ice box challenge
© Rob Bernhardt at the Ice Box Challenge unveiling

On July 27, members of Passivehouse Canada loaded a tonne (1000 kilograms, 1.1 American Tons) of ice into two boxes in Vancouver; one box was built to the Passive House standard of insulation, and one to the British Columbia building code standard for residential construction. This was the start of the great Icebox Challenge.

On August 14, Rob Bernhardt and his Passivehouse Canada team opened the boxes and found that "639 kilograms of ice remained in the Passive House box. Only 407 kg of ice remained in the B.C. Building Code box."

A high-pressure ridge had settled over the region soon after July 27, challenging each of the building standards to perform under heat-wave conditions. While the temperature inside each box varied by less than a couple of degrees on any day, it was clear when the boxes were opened that the extra insulation in the walls, floor and ceiling of the Passive House box, along with its northward-oriented window made a clear difference. The ice inside the Passive House box was still a solid, straight-edged block. The normal-insulated Code box had had absorb far more heat coming through the structure’s walls and roof—the top layer of ice was only about 5-10 cm thick, and the sides of the ice blocks had lost their sharp, straight edges as well as a lot of volume around the sides.

The Passive House people are excited, writing that "the biggest winners of the Ice Box Challenge are the Passive House community." And there is no question that the passive house entry did win a big victory, with more and prettier ice left after the challenge. But I cannot help but wonder if it was a pyrrhic victory, because the building code box did a lot better than I ever would have thought.

It takes a lot of energy to melt ice, 80 calories per gram or 80Kcal per kg. The difference in weight between the two blocks of ice, at the end of the challenge, was 202 kg; multiply that by 80 and you get 16,160 kilo calories, which converts to 21,585 Wh or 21.585 kWh, or about $3.15 worth of electricity. It's not a lot of energy over 18 days, and only 50 watts per hour.

Of course you cannot compare a little box to a house, but you can't just multiply those calories and dollars by the floor area either; the little box has a far higher surface area relative to the volume enclosed than a house-sized box. And though I was surprised, others in the field were not; as one expert told me:

The results were not surprising to many PH'ers. That design gave the code box a lot more help than it could have: same great form factor and a very small window. That's not how most code buildings are designed, yet PH box still came out ahead.

passive benefits© Passivehouse Canada

You also can't compare a Passive House design to a conventional design just on the basis of insulation; there are also air tightness and ventilation criteria that cannot be evaluated and compared on a little box.

BC Standard© British Columbia Insulation standards

From an ice box challenge point of view, I think that the BC building code box did surprisingly well, a solid second. But the challenge points out the real danger of looking at Passive House and just talking about energy efficiency; you have to talk about comfort and air quality too. In a long op-ed in the Vancouver Province, Rob Bernhardt described what it's like to live in a Passive House:

We don’t wear sweaters indoors during the winter. Or slippers. Or heavy socks. We do yoga in our ground-level living room without feeling chilled. We sit by the windows and watch storms whip the tops of nearby Douglas-fir trees and feel no cold or draughts. In winter, the house is warm and cosy. In summer, it’s comfortably cool. It’s also quiet.

If anything, I think the Ice Box challenge demonstrates that these are the issues that should be promoted, and that people care about.

Tags: passive house | Vancouver

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