Just for fun, I decided to build an insulated box to collect heat and pipe it into my unheated basement workshop. Like a miniature greenhouse, a glass layer facing south allows light in but prevents warm air from escaping.
The box is built from 1/2" thick plywood insulated with two layers of 3/8" sheet insulation left over from the residing of our house this summer. I used a spare storm window for the "glazing" The only thing I bought new for the project (at first) were 19 black ceramic tiles, each one foot square. They provide "thermal mass" to accumulate heat. There is a slit along the bottom to allow cold air in, and a 1" round hole at the top to let hot air out.
The box works fabulously at heating the air inside to more than 150 degrees Fahernheit after about 90 minutes of strong sunshine (with outdoor temperatures in the 30's). The problem has been getting the heat into the house. I have several small electronic indoor/outdoor thermometers equipped with sensors at the end of 10 foot cables. These allow me to measure the air temperatures inside the workshop, inside the solar box, and 2" into the mouth of the tube carrying air into the workshop.
I started off with a small diameter (0.75") plastic tube (running through a hole in the plastic window) because (a) I had some lying around from the water barrel project, (b) I thought the hot air would steadily flow up and out on its own and (c) because I did not want to let air flow through the box so quickly that it would not heat up. Very little airflow. Then I added a small 12 volt fan (from a dead computer) inside the house using a funnel to connect to the tubing. More airflow, but still very little. Temperature inside the box would be 140 degrees but the air coming into the house via the tube was only 60 degrees. (It WAS being heated, because the outside temperature would be 30 degrees and the workshop would be 45 degrees.) Then I mounted the fan inside two funnels and put it in the solar heat box itself, pushing the air instead of pulling. That worked a lot better -- but the incoming air flow was tiny in volume, and still was not close to the air in the box (like 80 degrees versus 150). Driving the fan with a 12 volt battery instead of a small solar panel got the incoming air flow fast enough that the air was around 90 to 100.
The newest phase, built on 2/1/2001, is the attachment of a 4" duct to the box. Hopefully the air flow rate will dramatically increase, even if the fan is powered by the solar panel (borrowed from a motion-sensing outdoor light fixture used in the garage) that probably only generates about 9 volts.
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