THERE'S A SOLAR HEATED HOUSE ALIVE AND WELL IN PRESCOTT ARIZONA

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We designed the collector to heat air-rather than water because we figured that such a system would
[1] be simpler, and
[2] neatly bypass the problems with freezing that seem to plague some other solar installations. A sheet metal supply manifold at the lower end of the glassed bays distributes air into the heating chambers, and the warmed air is then drawn off at the top by an intake manifold. Manual dampers in the sheet metal ducts can be adjusted to direct and "even out" the circulation through the collector. Last January, the average temperature of air introduced into the bottom of the roof mounted furnace was 80° F and the temperature of air drawn off at the top averaged 120° F.

Once we had settled on air as our heat transfer medium, it seemed simplest and most natural to store the warmth collected in the Grieve's solar system by blowing the heat-laden air through a bin filled with rocks.

This heat storage unit is actually two shoebox-shaped bins (each three feet high, seven feet wide, and eighteen feet long) set end to end under the house in an area previously designated for the stowage of odds and ends. We particularly liked the idea of using unbreakable, rust-free, tarnish-proof, no moving-parts rocks (32 tons of river rock in pieces three to five inches in diameter) as our heat sink, because we knew the storage bins would be inaccessible to maintenance once the construction of the house was completed.

The floor of the storage chambers is a concrete slab which is insulated around its perimeter to prevent heat loss. Walls and roof of the bins are wood stud construction with six inches of insulation throughout.

Hot air, as you know, tends to rise when left to go its own way. As might be expected, then, we found we had to use fans to force the warmth collected on the roof of the Grieve house down to the heat storage bins under the building.

This proved to be somewhat more difficult than we had anticipated. Due to the length of the duct runs from the roof to the basement and the static pressures within the storage bins themselves, we've found that our fans move only 1,500 cubic feet of air per minute instead of the 2,000 cfm we originally planned.

This means we're circulating just 75% of the volume of air we'd like to move which, in turn, means we're transporting less heat down to the basement than our bins are designed to hold. Besides that, the hot air we do force into the storage chambers stratifies as it moves through the bins although this doesn't seem to be a significant problem. As the air's pushed through the storage boxes, the rocks within have a natural tendency to diffuse and break up the stratification layers. On the average, last January, the temperature difference between air coming into the bins and air emerging eighteen feet later for return to the collector was 40° F.

Despite all the compromises we've built into the solar collector and heat storage bin, they've worked quite satisfactorily. Last December, for example, we were capturing and storing nearly 440 Btu per square foot of collector. That's just over 50% of what an optimum system should be able to do which, under the circumstances, isn't bad. As a matter of fact-again, this was last December-we found we could shut down one whole bay of the collector without noting any temperature drop on the air going into the bins. This indicates to us that, once we're able to move more heated air to the basement (as we originally planned), our system should catch and store at least 60% of the heat energy that an optimum system can capture.

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