Solar Air Heater Proto

     Shortly after moving into our home on Canyon Road, winter rolled in. When our gas bill arrived in the middle of December (2005), Jeri Dawn wasn't impressed - it was around $150. She said, "We have to do something about this." It seemed to me we had terrible drafts from the ancient windows. So I went to Home Depot and purchased 5 or 6 sheets of 2" foam insulation boards (4'x8') that I cut to fit tightly into the window openings. This reduced the drafts and heat loss, so we also reduced the temperature settings. My wife thinks the sub-arctic temperatures at night were a little too low. The following month our bill went down around $20 while my friend Jake Sanchez's bill went up another 35%. I figure that we saved the $120 spent on foam in the first winter.
     By the time summer rolled around, Jeri Dawn asked me to leave the foam in quite a few of the windows to keep the heat out of the house and the light out of the kids' rooms for nap time. Other pieces have been removed and added each year, many of which may need to be replaced soon.
     The next winter, in an attempt to reduce costs even more, we bought electric blankets, allowing us to lower the temperature even more at night. The morning temperature setting usually kicked in when all my girls woke up. I usually got up about an hour before that - man, was it frigid. Most of the winter, we wore slippers and sweatshirts - it was kind of cozy.
     Last year I happened upon a website that showed a solar air pop can heater and started collecting cans. After more research I decided that the pop can idea seemed like too much work. I took a few discarded stencils (5-6 mil stainless steel sheets about 25"x25") from work, painted them black and stuck them in the south facing windows. During the day I removed the foam from the windows and attempted to heat the house with the sunlight. It would have worked better if the foam fight tightly back in the windows after each day, but wear and tear prevented it. I think we may have come out a little ahead, but not much.
     I hoped to have built doors (to match the room decor) for the south facing windows this year, but that hasn't happened yet. What? With all the other projects, who really thought that would happen? But I did build a prototype of the solar air heaters that I want to build before November. The picture only shows it partially complete, since in the excitement of completing a project, I set out to prove that it would work instead of documenting the completion. At this point there is a 2x4 frame with a 2'x4' sheet of osb on back. Inside is a 2'x4' sheet of 2" foam (leftover from the windows) covered by double foil, double bubble insulation. I cut two holes for air intake and exhaust, placed a fan at the intake, cut and placed 0.75"x0.75" wood strips to channel the air snake-like through the air-gap, covered it with a 5-6 mil sheet of stainless steel spray painted black and then mounted a piece of acrylic (polycarbonate) over the top of it all.
     To test it, I set thermocouples at the intake and exhaust and set it in the sun (at about 60° from horizontal and directly at the sun - similar to how it will be mounted in the winter but rotated 90°; this made for a pretty high angle of incidence which is a good worst case scenario for the winter.) The results are posted below. The temperature drops as the sun moves and the heater is no longer perpendicular to the sun. The temperature gain is over 100°F.


















     The plan is to make 3 solar air heaters, 4'x8' each with fans that move 10 times as much air as the proto; 4 times more air because they are 4 times larger than the proto, then more than double that because the lower temperatures in the heaters means that more of the heat has already been transfered into the house! Instead of using stencils (5-6 mil stainless steel), I am thinking about using aluminum foil. Aluminum is great for heat transfer and foil is about as cheap as I can get it. I don't know if this is the best idea, but haven't yet found a reason to use anything else. Instead of an acrylic glazing, I want to get Lexan ThermoClear Multiwall sheets for added insulation. They're expensive and shipping is worse. I'm trying to find a source in the Salt Lake area. As soon as I can find those, and a few fans, I'll get started on the final project. I still haven't figured out exactly where I'll mount these or what to do about ducting...