Wednesday, March 25, 2009

Limits on the overall heat transfer coefficient through the building envelope

I've mentioned before that the first step in reducing energy consumption is to invest in a well-insulated building shell. Just like choosing a thick and warm winter jacket. I've also stated before that in the end what is important for the Minergie specification is that the weighted (I'll talk about this weighting very soon) energy consumption per unit area be less than 0.38 kWh/m2 per year. It is possible to achieve this by adjusting the different factors that play into this equation and to simplify the matter the Minergie group has come up with a set of "standard solutions". The limits given in the table below are those for the building elements. It is possible to build a Minergie house with components that exceed these values but make up the difference in other ways. In fact, not only it is possible, it seems to be often the case. This clarifies some of the confusion I had in earlier posts.

Table 1. Limits on the total heat transfer coefficient for building components.
Separation from exterior Separation from unheated interior Separation from ground
W/(m2·K) W/(m2·K) W/(m2·K)
Roof 0.15 0.20 -
Wall 0.15 0.20 0.20
Floor 0.15 0.20 0.20
Window 1.00 1.60 -
Door 1.20 2.00 -

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