Wednesday, 24 August 2016

It's a Passive House, not a passive solar house

Here's another thing I didn't fully appreciate until taking the Passivhaus course last summer. The windows don't need to be that big.

I guess I started off with the idea of getting all our energy from the sun, so that we wouldn't need to get any heating energy from anywhere else. This is known as passive solar design. It was a popular idea in the 1970s, but by the early 1980s it was clear that super-insulation was a better approach. Trying to meet heating needs by making the south-facing windows as big as possible was the wrong approach for two reasons: it would end up being much more expensive, and on a sunny day the south facing rooms would get far too hot.

At least this was clear to those involved in those discussions in the 1970s and 1980s, but there have since been generations of house builders clinging to the dream of putting in enough windows so that heat is free.

This doesn't mean we should live in caves. Windows in houses are a very good idea, and it's also important to put most of the windows to the South where they will get solar gain in the winter and will be easier to shade in the summer. Also it's a good idea to have few windows east and west where there will be little heat to gain in the winter when you need it, but a significant amount in the summer when you don't.