Heating buildings is one of the largest contributors to greenhouse gas emissions. The sun provides a significant opportunity for heating buildings with little greenhouse gas emissions.
Pure passive solar designs have the disadvantages of overheating the living space and/or not having enough thermal mass to maintain the temperature through many cloudy days.
Active solar designs usually involve many pumps, sensors, controllers, etc that add considerable construction expense and increase maintenance and repair.
The advantages of this simple design are:
- Heat is stored outside the living space
- Only one moving part (a fan)
- Only one piece of electronics (a solar panel)
- The energy storage is literally dirt cheap
- The solar collector is also a place to
1. dry cloths in all weather conditions
2. lounge or host meals without bugs on warm evenings
3. sunbath on the rare cold, but sunny winter days
The inside of the foundation is the sides of the heat storage area. Once the foundation has cured and the forms are removed use vapor barrier to make a liner around the inside of the foundation. Tape all the seams so it is a continuous barrier. If it rains it would fill up like a swimming pool.
Heat Storage - Insulation
Cut and fit foam insulation board around the bottom and sides of the heat storage area. Use 2" thick 25 PSI or better High Density Expanded Polystyrene Foam Board that's rated for below grade under slab and sidewall foundation use. Don't use Extruded Polystyrene, the blue, green or pink stuff, the blowing agents used to produce it have a high global warming potential. Consult with an architect or structural engineer for the PSI rating required for your structure.
Seal the insulation boards together with tape and/or expanding spray foam.
Heat Storage - First Layer of Rock
The heat storage medium in this house is #1 crushed limestone. The stones should be 4 inches in diameter. Ask for it washed. I didn't and it took a lot of effort to wash the grit off.