Replies

We built an architect-designed passive solar in 1981, and lived in it until our family outgrew it.

There's really no "technology" or moving parts involved - that's why it's called "passive". No solar panels, no electricity, no water pipes. It is not meant to replace artificial means of heating and cooling - it supplements them.

It involves three important concepts that are really just common sense: the changing angle of the sun with the seasons; orientation of house and features (especially closets and other 'dead air' and windows); solar gain/ storage mass.

Here are the keys to making it work:

1. siting the house so that the long axis faces south or slightly east of south. If possible, the south side should be longer than the north. Our house was a symmetrical trapezoid.
2. minimizing glass on all sides but the south side, and placing 'dead air' like closets, hallways, etc. on the north.
3. design roof overhangs to shade the interior in the summer but allow light into the home in the winter(there's actually a calculation based on latitude). The equinox is the normal crossover point, but you can vary that depending on your local climate. In the South, we opted to have light enter the interior for a shorter period during the year.
4. build a "solar mass" (we poured a huge concrete cube that formed the dining room/ solarium floor) that will absorb heat during the day and radiate it at night
5. insulate like MAD - we framed up with 2x8s and 10s instead of 4s or 6s, and had additional R-MAX outside the studs as well. Roof was super-insulated, and ice dams are not a consideration here.

We had a conventional HVAC system, but it ran very little. Our total cooling costs for the hottest month in Georgia (the main consideration) hovered around $100 in the 1980s. We also had a manufactured fireplace and a whole-house ventilation fan that would pull the stripes off a pussycat.

So . . . in answer to your questions:

1. you let the furnace or the fireplace run a little more.
2. superinsulated roof helps a lot, shade helps a lot, you run the A/C a bit more but you don't need much.
3. there isn't any technology. That's the beauty of it.