[Greenbuilding] Drilled well to heat Greenhouse

[Niko Horster]

Hi Speireag,

Hope you are well.
This will work in theory. You will have to do a heat loss calculation or
estimate and see at what rate you have to pump the water to obtain enough
BTU's from the delta T  water to environment.
If the water is at 45F (this would be the April temp (usually the lowest of
the year from a deep well, or a safe assumption from a shallow well) and
your rock bed (I would bed your pex in wet sand for optimal low cost heat
exchange) is at maybe 40F after running your pump all day long (solar pump
is a neat idea, however you will have most BTU demand on the system when
there is prolonged periods of little or no sun, so maybe an small battery
butter and a couple of El-cid pumps in parallel would do it)
Your night time low goal is 33F (and even that is on the chilly side for
some plants) what is your heat loss. 

In my opinion you will have to supplement that with some solar hot water.
Swimming pool type collector within the greenhouse then run into a gravel
bed under the floor insulated with 4" of blue foam would work well here. 

There are a few precedents of your idea, I have links if you are interested.


Niko

niko at oharagercke.com