Solar Air Heater
Pictured above is my wood shop. A small out building 20*18 feet. The front of the building faces south making it perfect for a hot air collector. On a sunny day the collector will provide most if not all of the heat needed. My construction technique and materials are simple and low cost.
I stripped off the steel siding exposing the old 3/4 wood siding.
The siding is covered with aluminum flashing. A grid of 2*2 with a simple rabbet to hold in the glass is installed. My glass is 1/4 plate so I installed a 2*6 to hold all the weight. A few coats of high temperature paint are applied. 6" air intake and outlet installed. Fiberglass batts are installed behind the attic collector. Generally the shop is well insulated.
Simple rabbet joint cut on a table saw. Glass is held in place by points and silicone calk.
The collectors use separate intake and exhaust. Both take cold air off the floor and warm it before returning it to the shop. The attic collector is 50 square feet and the lower collector is 56 square feet. Both use a duct booster fan of 250 CFM running at .35 amps each. Dayton snap disk thermostat no. 2E245 turns on at 110 degrees and off at 90 degrees. The lower collector uses almost no duct work at all while the attic collector uses about 16'. Both use a simple flap type back draft preventer. After the sun goes down the flaps close keeping the cold air in the collector contained so it doesn't cool the shop. The valves are made from light weight shopping bags. The cold dense air pushes them closed along with gravity trapping the cold air in the collector.
Closed position.
Open.
Performance: In late fall early winter here in Minnesota we have a lot of cloudy days. The days get to be much more sunny the closer to spring we get. So I will burn more wood in the first part of winter. The collector produces heat late morning to mid afternoon in January. The closer spring comes and the days get longer and the sun has more power, the collectors work better. In summer the sun angle is so high the collectors really do not produce a lot of heat.
January 19 1:00 PM
-5 outside, wind chill -16 F
Attic collector temp rise of 50 degrees. 28 in temperature, 78 out temperature.
Lower collector temp rise of 76 degrees. 26 in temperature, 102 out temperature.
April 1 1:00 PM
Attic collector temp rise of 57 degrees 46 in temperature, 103 out temperature.
Lower collector temp rise of 89 degrees 46 in temperature, 135 out temperature.
I really wanted spring to get here, but April 1 we had another foot of snow. My daughter calles it "fake spring" as it starts to melt and then it snows again.
The attic collector is more efficient I believe due to the heat rises naturally and faster through it where the lower collector relies more on the fan to pull the air through. On a sunny day with a outdoor temperature around 0 the collectors will get the temperature in the shop up to +50 by 1 PM.
If it's windy the collectors will give up heat through the single pane glass. So windy days the output is less.
Many of my ideas and theory came from the book "Solar Air Heating Systems" by Steve Kornher. I think I have it about memorised ;-)
