[Greenbuilding] Drilled Well to Heat Greenhouse?

[Speireag Alden]

Sgrìobh Philip Proefrock:

>If you are wanting to do a DIY installation, you might also be able to cut
>trenches down below the frost line and run your PEX in there, rather than
>doing vertical bores.  That's a strategy GSHP installers use when space is
>not at a premium, since it is less expensive than vertical bores.

     An excellent suggestion, but site-dependent.  Around here, where 
the ground is extremely difficult to dig, thanks to jumbo rocks and 
their smaller cousins, drilling is actually less expensive.

Sgrìobh Niko Horster:

>Hi Speireag,
>
>Hope you are well.

     Hi, Niko!  Well enough, thank you.  Too busy, as usual, but 
learning to cut back and say "no" and get organized, so that I'm 
hoping to have life comfortably under control by next week.  (ha!)

>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)

     Not a bad assumption.

>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.

     During the winter, I think all of my solar hot water capacity 
will be going to heat demand water in the house.  At least it will 
until I get enough solar collectors hooked up (and then I'll have the 
problem of what to do with the excess heat in the summer - ah, the 
joys of a sauna which is always on...)

>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.

     Thank you, I am.  The real question is cost-effectiveness, I 
think.  If I drill an 8-inch well, I can stuff a fair amount of pipe 
down it, and with the water table only 20 feet down (roughly, judging 
by my other well), I'll have all kinds of transfer surface down in 
the ground.

     However, I don't know if it's worth the cost, so I guess I'll 
have to do some modelling.  Looking at a 15°F heat differential, I 
have to say I'm guessing that it's probably not worth the $1500 or so 
it would take to install it.  The greenhouse will be earth-bermed, 
with the house on one side, an active hot compost pile, and probably 
a few chickens.  Combine that with a few thousand buried 2-liter PET 
bottles filled with water, and I'll bet I can avoid most hard freezes 
without doing anything other than living life as usual.

     Thanks for the feedback, folks!

-Speireag.

-- 
Fill the molten glass.
Sit with singing summer frogs.
Think on Jack's wedding.