Thermal Mass Anyone?

Reader Contribution by John Kosmer
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Any net zero-energy home (one that actually produces at least as much energy annually as it consumes) needs two things. The first is the sun, providing passive solar energy.

Needing the sun for energy is why some Passive House retrofit homes leave me baffled. In his lecture at The Cooper Union in NYC, Wolfgang Feist said that southern exposure is helpful in achieving Passive House energy efficiency requirements, but not essential. Not all homes you wish to renovate have a decent southern exposure.

But here’s the problem with that position. In its simplest form, we are discussing the heat you create for your home and how well the house is able to retain that heat. In a home without southern exposure (to provide external energy from the sun for passive solar heat and/or solar electric), you rely solely on the home’s insulation and on energy created by internal heat sources (like a heating unit or your family).

So let’s say you have two homes that are super insulated to the same degree. One home has negligible external heat or electric gain and the other has south-facing windows that allow passive solar heat gain and electric solar panels, which together provide anywhere from 50% to 100% of the home’s energy needs. Obviously, the passive solar home has a much better chance of being net zero energy or more, because it’s using external energy.

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