This $30 Solar Setup Heats a 30 X 40 Workshop for Five Hours or More Every Sunny Winter Day
(Page 6 of 9)
November/December 1977
By the Mother Earth News editors
SINGLE VERSUS DOUBLE GLAZING AND OTHER SURPRISES
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We wondered just how much better our collector would work with two layers of plastic on its front instead of only one. So we operated the solar heating system with its collector enclosed by a single sheet of film for about a week before we applied the second. Surprisingly enough, the "double glazing" of plastic raised the temperature inside the collector by only about ten degrees ... which wasn't nearly as much as we had anticipated. There was, however, relatively little wind during the test of the single layer (although it was quite cold: 5 to 10 degrees above zero), and this undoubtedly made some difference. The single sheet would almost certainly lose far more heat on windy days than the double layer of film.
We were also surprised to learn that temperatures inside our collector did not directly reflect the differences in outside air temperature. In the middle of the winter, with the blower turned off, it didn't seem to matter much whether it was five or 40 degrees above zero outside. The temperature inside the double glazed collector usually hit 140 degrees by about 10:00 a.m., rose to 150 or 160 somewhere between 11:30 a.m. and 1:30 p.m., and then fell back to 140 by 4:00 p.m. With the blower running, these figures all dropped about 30 degrees right across the board. (Remember, too, that our collector is set up in Springfield, Missouri. Readings will be somewhat different for any unit you build if you live at a different latitude, your area experiences more or less cloud cover, etc.)
From our observations, then, we have concluded that the outside air temperature makes practically no difference in the performance of our vertically mounted collector. The angle of the sun, however, makes a great deal of difference in the unit's output ... and, interestingly enough, these variations in output work entirely to our advantage.
That is: During the coldest months of winter (outside air temperatures of five to 40 degrees Fahrenheit), when the sun is lowest in the sky, our collector—as we've already stated—hits a maximum internal temperature (blower off) of 150 to 160 degrees. In May, though (outside air temperature of 80 degrees), with the sun much higher in the sky, the collector warms up inside (blower off) to only about 120 degrees!
A vertically mounted collector, then, works just the way we'd all like a solarenergy trap to work. It catches a lot of the sun's rays in the winter (exactly when we want it to), and absorbs increasingly less of those rays as Ole Sol rises higher in the sky and the weather warms (which is precisely the time that we don't want a solar or any other kind of heating system to work well at all).
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