We finally had a sunny day yesterday and I was able to get some real results from my solar furnace . I had to make a few changes for success though…
First of all, I discovered that the mercury switch was not sensitive enough to really work. The cold air outside was messing up the way it functioned. I could not insulate the part of the air box where the switch was since the switch has to be able to move (if you’ve never seen the setup, a mercury switch is placed on a temperature sensitive metal coil which moves and allows the mercury to open or close the switch). I decided to experiment with wiring the solar panel straight to the fan which actually worked very well. The fan only came on when the sun was out and shining pretty brightly which was precisely when the best heat was being made.
The pipes that run from the furnace to the house were white originally but it seems that enough cooling took place in the pipes to make the system not work as well as I had hoped. I painted them flat black like the rest of the system and it worked like a charm. The pipes absorbed heat from the sun while transferring the heat through the system, thus helping with the whole “hot air rises” thing.
I also discovered that I had a few air leaks around the pipes and in the holes for the air pipes in the furnace. I used silicone caulking (which will actually cure in about any temp regardless of what the instructions say) to patch all of the holes/gaps/leaks.
Once I made those three changes, I took temperature measurements of the cool air pipe from my family room floor and the warm air pipe from the furnace. My floor air was 63 deg F and my warmed air was 84 deg F! Hee-haw! Eureka! Ding Dang, y’all!
Ok, so I was pretty happy with the results. The fan kicks on and off with the sun which manages the heat pretty well. I still need to boost the power to the fan to get a little more air flow. I did some experimenting and was able to get a better temperature rise with a bit more air flow. I will probably add another cheap-o solar panel to run the fan better. I also need to find a better way to prevent backflow. I really don’t like hanging a piece of plastic in front of the vent. For now, it is working but I don’t like it as a long term solution. I have glass to build one more furnace so I will probably build it out then figure out some way to deal with both systems. Anyhow, for now, I am pleased with the solar furnace!