This $30 Solar Setup Heats a 30 X 40 Workshop for Five Hours or More Every Sunny Winter Day
(Page 8 of 9)
November/December 1977
By the Mother Earth News editors
Clearly, to be really effective, your controller needs some sort of temperature sensor. No, this sensor doesn't have to be expensive. As a matter of fact, almost every gas furnace made has just such a device somewhere in its innards and a little scrounging can probably get you one for nothing. (We removed ours from the same old furnace that supplied our blower.)
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It's easy to scavenge one of these temperature sensors from an old gas furnace. Open the panel that covers the pilot light and burning chamber. Inside you should see a small box with wires leading out of it. Cut or disconnect these wires and remove the box's cover. You should find a little gauge or dial inside with two movable pointers that can be set to turn the burner on and then off at whatever temperatures you choose.
Remove the screws that hold the box in place and pull it straight out. Surprise! You're now holding a box in your hand ... and that box has a long snout of a tube perforated with holes sticking out its back. If you can peer into this tube, you'll see a spiral strip of metal that expands and contracts as it's heated and cooled. It's this expansion and contraction that operates a simple switching mechanism inside the controller ... thereby making it possible for the controller to turn a gas furnace's blower—or, in this case, the blower for a solar furnace—on and off.
It's no trick to adapt one of these controller boxes to your sun-powered heating system. Just drill a hole through the wall that forms the back of your solar collector, stick the probe through the opening so that enough of the snout extends right into the collector to get a good temperature reading, and then electrically connect the "little black box" in series with the blower's motor in the same way that you'd hook up any other simple switch.
Now, at least, your solar furnace's blower can be set to turn on only when there's enough excess heat in its collector to make the operation of that blower worthwhile. But what if you don't want that warmth ... what if your room or shop is already up to—or higher than—the temperature you prefer?
No problem. When you hook your collector's temperature sensing device in series with the blower motor, just add an indoor high voltage thermostat (the kind used when electric heating cables are installed in a ceiling) as shown in Diagram 1. By adjusting the settings on both the collector sensor and the indoor thermostat (which you'll mount somewhere in the room being heated), you can now go away for days at a time ... always confident that the solar heater's blower will kick on-and will only kick on—when the collector is hot enough to do some good and the room is cool enough to need the collector's heat.
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