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

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

In other words, the lack of "it's been done before" information on mud-storage solar heating systems didn't keep Joseph Orr and family from building what now appears to be the only such system in existence!

But why? Why wet dirt instead of the more traditional water or rock storage? Joe cites three reasons: "First, because dirt is handy . . . it's already on the building site. Second, wet earth has surprisingly good heat-holding characteristics. (It has a capacity of 30 to 44 Btu's per cubic-foot-degree, versus about 20 for rocks and 62 for water.)

"What really convinced me to go the mud route, though," says Joe, "is its low cost compared to other storage mediums. On a cost-per-Btu-of-storage-capacity basis, you just can't beat mud for heat storage." Mr. Orr figures the cost breakdown for different systems of equivalent heatstorage capacity to be something like this:

WET DIRT

WATER

ROCK

To sum up: Wet dirt is inexpensive (dirt cheap, you might say). It's handy. It holds heat well. It's abundant. And now—thanks to the Orrs—it's also proven!

HOW THE ORR SYSTEM WORKS

To look at Joseph Orr's 420-square-foot glasshouse from a distance, you"d think it was "just another lean-to greenhouse". And in fact, certain aspects of the design are highly conventional. For instance, the conservatory (which is built onto the south side of a 28' X 40' workshop building) utilizes standard wood-frame construction. And its layout is entirely in line with state-of-the-art design principles. Unlike other "attached" greenhouses, however, Joe Orr's mudstorage unit is both actively and passively solar heated and can operate in any one of at least four different modes.

In the first mode, the greenhouse is warmed solely by the direct entry of solar radiation through the single-glazed (with Tedlar-coated Filon fiberglass) south wall. Thanks to the fiberglass glazing's heat-trapping properties—and to the use of up to 13" of fiberglass insulation in the conservatory's ceiling and walls—this mode alone suffices to keep the grow room's interior at or above its minimum design temperature of 58 °F on all but the cloudiest days.

Mode two comes into play whenever Ole Sol shines down on the greenhouse through a cloudless, fogless sky. Under such "clear air" conditions, the conservatory can quickly accumulate more warmth than the plants inside need . . . or can tolerate. For this reason, Joseph Orr installed a thermostat that—at 75°F or above—activates a wall-mounted fan which can—in turn—suck hot air out of the greenhouse and push it into the adjoining workshop. (This part of the system serves as the workshop's only source of heat . . . which—of course—means that on sunless days the shop stays cold. "We simply don't use the shop on those days," Joe Orr reports. "Instead, we find something else to do . . . such as work in the greenhouse.")

RSS | Comments | E-mail | Print