Hello geo folks I am putting together a water supplied domestic hot water heater from a ex-window a/c of 7500 btu, as a warmup maybe for a whole house heating cooling system. Drilled a 4 -5" well to 100' , hit water at about 22' and marine clay about 2 ft later, stayed in that til about 80' then alternating layers of marine clay and black sand to where i quit at 100'. Put down 3/4" hdpe utube and was going to fill it with the bentonite chips as grout but noticed it stayed full of water at about 20' for a couple days so filled it with sand up to about 10' then sealed it with the chips and ran it about 30' into the house in a 2' trench. I measured the amt of sand going in so i think i got a good continuous fill. Amazing how easily the utube went down in that slick clay once it was full of water and had a couple of old window weights taped on the end! I thought it would be adequate for the 7500 btu water heater but wondered if i could maybe also hook it to a bigger unit for heatin/cooling? So i guess my question is what you can get out of 100' of utube in a sand filled 4-5" hole in marine clay when its flooded about 3/4 of the way?? It occurred to me that it might be way more than the normal 200 ft/ton norm we seem to use here on the non rocky east coast!
Groundwater movement would have a very strong influence on the heat transfer. If you have no groundwater movement, you have nothing better than a standard borehole that is 100' deep in saturated sands/clays. So about 1/2 ton capacity in our area. By the way, the bentonite is code (sealing the borehole) in just about every area I'm aware of. It is to prevent vertical cross contamination of aquifers.
But if i can't load the system fully (pull BTUs in or out til) how can i measure it with just a pump and thermometer? I haven't finished the 7500 btu unit yet but, if it was, measuring the delta t would only tell me it could handle the 7500 unit but not how much more
I doubt there's much water movement in the marine clay - could only be from the strata where the water was sitting on top of the marine clay at about 25' thru the sand down to the black sand (or vice versa but i doubt it) So, you're likely right - i'll be lucky to get enough transfer to run the 7500 btu compressor.
I second the 1/2 ton. It will support the 7500 BTU/h load, since the window units are likely not very efficient. A COP of 2 would get half of the energy from the compressor heat, and half from the borehole.
