WARM YOUR SWINE WITH SUNSHINE

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That completed the collector part of the project. And, once back on solid ground, we haved a joint sigh of relief that everyone had survived hit or her strut on the treacherous ski slope of a roof.

MAKE-DO DUCTWORK

It was then time to turn our attention to building a manifold that would carry the heated air from the roof to the farrowing house. We used inexpensive pressed board for our ductwork and simply nailed and caulked the joints tight. The warmth was brought in through a window that had once housed one of two exhaust fans. We figured ducts about one foot square would be large enough to move the amount of air that our calculations had shown we'd be able to pull in from our rooftop heater at any given time.

The next step was to get a supply of fresh air into the collector. To do this, we went into the hay mow (the upper part of the barn) and sawed a series of 6- by 12-inch holes in the roof ... near its top but opening into the collector. Using air from inside the barn provided us with a double advantage: The outer surface of the collector stayed sealed and dry, and our system allowed us to reclaim any heat that rose from the farrowing house below.

Admittedly, that extra warmth was slight ... thanks to a lot of stored hay and nine inches of insulation that we'd put into the ceiling of the sow's quarters a year earlier. But, by this time we'd learned—as John stated in a rare poetic moment—that "solar energy is an efficiency game, and you have to play it all the way".

After the ductwork had been taken care at we dealt with the matter of how we'd pull the warmth down into the building. We realized that fan size was very important. (Obviously, the faster you move the air through a collector, the less temperature rise you'll get.)

With Engineer Rode's help, we learned that air movement at the rate of 5 to 10 feet per minute would be best. The formula for proper fan size is this: The fan's CFM rating should be 5 to 10 times the number of cubic feet that the collector occupies. In our case, we were talking about 200 cubic feet of collector (24 feet by 25 feet by 4 inches). Therefore, we installed a 1/4-horsepower, 16-inch-diameter fan rated at 1,760 CFM. That gave us an air movement of 8.8 feet per minute (1,760 divided by 200), (in later tests, we found that the single intake fan, placed below the middle of the collector, tended to evacuate the air from the center of the roof ... but it was unable to remove all the valuable warmth from the unit's corners. Slightly larger ducts should, we think, eliminate that problem.)

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