Remember those fruits and veggies for your vitamins, Hattie!
I'm going to take slight exception to the author and the builder of that greenhouse heated by compost. It seems to me that running cool water in tubes thru compost is just a good way to cool-off the compost rather than heat the interior of a greenhouse. I think it would take a fairly massive pile and a fairly small greenhouse to get very far down the road with this idea.
Glazing, of just about any type, loses heat at a fairly good clip. Insulating material can be spread across a greenhouse overnight when heat-loss is usually greatest, but that's another story. Double glazing helps but the additional material, decreases light to the interior. That light
is necessary for plant growth and makes a VERY important contribution to heating.
I feel that the very best things one can do is to
* maximize the penetration of light,
* cut down on air leaking from the greenhouse, and
* use something on north walls to retain heat within the structure.
A conventionally framed and insulted north wall and even north side of the roof will go a long way towards retaining heat from the daytime sun while protecting against heat loss at all times. Certainly, glass or plastic glazing material doesn't need to be on the northside.
Southside, the angle of the glass or plastic should be as close to perpendicular to spring/winter sunlight as possible. Obviously, the sun is moving in the sky (at least from our perspective
) and greenhouses don't usually pivot to follow the sun. But, especially if you are trying to maximize light inside the structure and minimize reflection - you would want light coming in at a right angle.
Back to the compost generated heat: I think we often over-estimate the amount of heat kicked-out by compost. 1000 Btu/hour per "active" ton of compost seems to be about maximum
Penn State U, Big Download! . Without any remarkable temperature difference, wind, leakage, etc. - greenhouse glazing will lose 1 Btu/hour per square foot
ag agency, New South Wales . Big pile - - little greenhouse.
To minimize the cooling of the pile while taking maximum advantage of the heat - I would put the compost pile INSIDE the greenhouse under the growing bench. You probably want to have a bench anyway and the space under the bench often has little use. A 4-foot wide bench, accessible from 2 sides would be very useful. Now, I'm not sure about interior air quality. Ventilation for the pile, may be very important.
Or, just do a better job with available solar energy. Pumps, water . . . I don't see the need.
Steve
] 
) and labor was cheap. Running air-filled pipes (you would not want *water*-filled, that seems like a bad idea in several ways) would be a bit of an improvement on the old systems in some ways, but you would not get as much heat out of it that way, and also it is susceptible to the same major problems that the old style things had.
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