Study claims "Energy saving homes often use more energy." Than what?

passive house
© Peter Aaron/ A passive house in the country with a lot of glass.

An attention-getting but grossly misleading title

There is a fascinating post in The Conversation with a misleading title: Why energy-saving homes often use more energy. It's based on a study by André Stephan and Robert Crawford, A comprehensive assessment of the life cycle energy demand of passive houses. One is only allowed a 5 minute scan of the study without paying, but you can see a careful analysis of the materials that go into the passive house, and the embodied energy of those materials. The authors write:

A closer look shows that the low-energy house requires much more embodied energy than a standard house because of the additional insulation and triple glazed windows it uses. So even though the low-energy house has much lower energy bills for heating (and cooling), that’s offset by a similar increase in embodied energy, negating any benefits offered by the additional materials.

bill of materials, Passive House/Screen capture

Looking at the bill of materials in the case study passive house, it appears that the single biggest difference between it and a normal house is the huge amount of polyurethane insulation, all 122.9 cubic meters of it. There are other insulations (like cellulose) that have a far lower embodied energy. It has a terra cotta tile roof and clay brick and block exterior, crappy choices from an embodied energy point of view. As far as the triple glazed windows go, Passive house windows are expensive and in most cases, designers use a lot less of them than in a conventional house. Finally, embodied energy is an element of design that frankly, people have not paid a lot of attention to until recently. It clearly wasn't an issue of concern for the designers of the case study passive house analyzed here.

How to bury the lede.

However, the real point of the study is completely missed by this focus on the embodied energy in the passive house, which can go up and down by huge amounts simply by careful selection of materials.

© The Conversation

The authors appear to be saying that there is no point in building a big passive house in the suburbs or the country and calling it green and sustainable, because compared to an apartment in the city, it's not. Without even taking into account the energy required to build the roads and supply the ambulances and schools that support the lower density, in the bigger picture, the passive house is not a whole lot better than a standard one. It's all a convoluted way of coming to this conclusion:

The current preoccupation with improving energy efficiency for heating and cooling means that the significant indirect energy requirements of houses are often overlooked. This is why we need more comprehensive regulations and schemes that take into account other factors, including house size, the materials used within them, and where they are located.

Trying to reduce our heating and cooling bills is a good start. But there is even greater potential to save energy by considering the materials used to build our homes and the way we move around. Now is the time to look beyond individual homes, and start building better, more affordable, more energy-efficient neighbourhoods and cities.

I don't know why they just didn't say this in the first place.

All their data show that the Passive house uses a lot less operating energy than the standard one. Their embodied energy calculation is a distraction as it is a complete variable depending on the designer's choices and preoccupations. However their fundamental conclusion is still valid: Living in a smaller apartment in the city is, in every way, more energy efficient than living in a big detached house in the suburbs or the country. Dissing on the Passive House may be attention-getting, but it buries the point. That's a shame.

And as a thought exercise, take a passivhaus made of cross-laminated timber, insulated with cellulose, with modestly sized windows, put a big PV array on the roof to charge your electric car or bike. Run the numbers again. Toss entire study in garbage.

Tags: passive house

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