Hell Alec,
 
> Jd> First, lower the greenhouse slightly, to reduce the amount of
> Jd> glazing, plastic, etc.
 
> Most heat losses are through the walls [surprise! most people think roof.
> Not so]. So a squat building makes sense, thermally.
 
> Jd>  I am thinking that three feet would do.
> ^^^^^
> Are you a Vertically Challenged very small person? How will you work
> inside such a tiny house??
 
No, I stand over six feet.   I do not intend to begin the roof at
ground level, only lower the floor about three feet, this will allow for
more than six feet of side wall between outside ground level and eave.
 
> Technical problem- how to make a good pattern for your "coil". At the
> feed end the water will be hottest. At the drain end the water will be
> quite cool.
 
One "coil" should do, first around the perimeter, then probably beneath
the raised beds and under the walkways last. Data from alpine locations
support this theory. Of course they only extend the growing season, two
months, May and September.  We are planning an eleven month, possibly a
year around operation.
 
Don't forget the solar gain, even at the Winter Solstice, we have eight
hours of dependable sunlight; central Colorado is not Alaska. 
 
> Three or four scrap auto radiators, sprayed black and boxed/glazed
> would be more appropriate than plastic pipe.
 
This may be the best idea yet!  However, the cost of rodding, cleaning
and repairing used radiators is probably about a hundred dollars each,
the piping, etc. they  may not be as cheap as first imagined, though.
 
> Put the storage tank under the greenhouse! Use a hi temp cutout to block
> water flow to storage, if greenhouse overtemp thermostat operates.
 
Completely underground tanks have their own special problems. Maintenance
is difficult to impossible, the EPA gets into the act also, remember. ;)
 
> I'm no gardener, but think that your problems will include the need for
> accurate temp control.
 
Not a critical as might be thought,  remember that plants normally grow
outdoors with as much as forty degrees  difference between the noon and
midnight temperatures. A greenhouse is simply a large "cold frame" with
some heat added to extend the growing  season to as near year around as
possible.
 
>  Commercial greenhouses use quick response automation and heater units I
> guess. So the gardener can take a short vacation at times. But maybe you
> plan to be there every day?
 
They use fans to control the air temperature in the summer,  and overhead
heaters, the same as those used in factories when heat is needed. Propane
is expensive, sunlight is cheaper and the delivery is dependable.
 
> Second thoughts about auto radiators- if you use these with 12v thermatic
> fans, these could be roof mounted to your glazing bars, and the fans
> controlled by master thermostat. [These fans come with relays.]  The
> radiators/ fans mounted in shallow double glazed boxes, to recirculate
> greenhouse air NOT introduce fresh air.
 
This is a thought,  I wonder how this would work instead of circulating
the hot water under the floor. I also wonder if the water would have to
be hotter. It will add to the power load as pumps will still be needed,
apart from the fans. Hmmmm back to the drawing board and the books.

 
TTYL
 
James 
--- DB 1.58/003790
---------------