Earlier this week, I posted about my solar furnace project. I can’t take all the credit for the idea of a solar furnace as they have been around for a long time. Most of them seem to be passive – relying on natural motion from the warm air rising through the system. This sort of air flow is not typically very strong (though it can be), so cannot open a louver or check valve. Just leaving the hot air pipe open is an option though physics will bite back at night or when it is not sunny outside. Just as hot air rises, cool air sinks so at night, warm air will syphon from the house backwards through the system. Some folks drape a piece of plastic over the warm air output so that the warm flow blows the plastic open a little. Cool air cannot flow back through the plastic, supposedly.
All that sounds nice, but I cannot be satisfied with simplicity when I can further complicate things with technology. Being interested in saving a buck and doing the right thing energy-wise, I replaced our old thermostat with a digital programmable one a couple of years ago. I noticed that the old thermostat had a mercury switch so I didn’t want to just throw it in the trash – instead I kept it in my stash of junk…and lucky I did. This project is prime for my sort of junk. I stripped the mercury switch and the bi-metallic temperature wire from the thermostat and connected it to an old computer fan. I am building a box that will contain the thermostat and the computer fan. The fan will pull warm air from the furnace across the thermostat. While the air is warm, the mercury switch will turn on the fan which will blow open the dryer vent (that will prevent cold-air backflow) and send warm air into my room.
Initially, I had planned to power all of this with a solar panel. My fan is a 12 volt, 0.62 amp fan (though I ran it just fine with a 9-volt battery). To drive the fan directly from the solar panel (at 9 volts), I would need a 5.58 watt panel (watts = volts * amps). I may be able to get away with a little less but the cost of a 4-6 watt solar cell would still cost somewhere around $50. I have various 9 volt wall-wart transformers from old gadgets that I no longer need.
For now, I will just drive this system from wall power. At 9 volts, when the fan is on, it will draw around 4-5 watts – about the same as a nightlight. I can live with that.
My plan is to get all of this hooked up and running this weekend. I will post again with the final project. It is supposed to be cool this weekend so I guess the timing will be right!
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