JOSEPH ORR'S FABULOUS "MUD HEAT-STORAGE" SOLAR GREENHOUSE

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Mode three—the active collection (and storing) of Ole Sol's energy—is in operation whenever the sun shines on the system's 6' X 30' solar collector. As the collector's temperature passes the 100 °F mark, a thermostat-triggered fan begins to blow hot air through ductwork leading to the underground storage bin. There, a distribution manifold routes the heated air through 21 runs of mud-submerged plastic pipe, then to a second manifold that returns the air to the roof for another warm-up. (In the process, 878 cubic feet of wet earth in the storage bin becomes warmed to 90 °F or more.)

At night or in cold weather—or any other time that the temperature inside the conservatory begins to dip below 58 °F—still another thermostat kicks on yet another fan . . . this time, a blower that routes cold greenhouse air through the 21 mud-submerged"heat exchange" pipes and back into the nursery as warm air. Also, at night, Joseph and Amelia Orr place large, insulated "shutters" over the conservatory's main (south) wall, to trap heat inside the structure. (Note: These same shutters—laid flat in front of the greenhouse—serve as reflectors during the day to bounce more solar radiation into the grow room.) In this way (mode four), the greenhouse is kept at or above tomato-growing temperature at all times.

100%-SOLAR-HEATED

How well does the Orr system perform? So far—in three years of operation (including two particularly severe winters)—the temperature in the greenhouse has never fallen below 58° F . . . there's always been enough "reserve heat" in mud storage to keep the little conservatory warm night and day. In other words, the "mud storage" solar heating system actually provides 100% of the greenhouse's heating needs.

And it does more! Not only will the system meet the total space-heating demands of the greenhouse itself . . . it also heats (on a part-time basis) the former grocery store that now serves as the Orr family's workshop (see "mode two" above). In effect, then, the Orr conservatory is 100% solar-heated and then some!

Nonetheless, Joe Orr had originally hoped for more. "We didn't insulate the bottom of our wet-earth storage bin," Joe points out. "We figured that—since the bottom is only 17% of the bin's total surface area—heat losses there would be insignificant. We were wrong. Although air from the solar collector has topped 150 °F, the bottom of the storage bin has never gotten warmer than 90° F, and just slightly over 100 °F midway up the bin. So we've only got 20 to 25% of our intended storage capacity. We wish now that we'd added six inches of insulation to the bottom of the mud pit and three more inches around the sides, minimum."

Despite the fact that Joe had hoped for more heating capacity (his original plan was to convert the workshop area into an apartment that would get 100% of its space heat from the greenhouse), he still takes a great deal of pride in having achieved "100%-and-then-some" solar heating of his greenhouse. And rightly so . . . because many—if not most —"active" solar heating installations being built today end up costing their owners moremoney than the Orrs spent on their entire greenhouse setup (about $2,000) while performing lessefficiently. (Darn few solar installations even aspire to 100%plus efficiency!)

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