Modify a mini split to get heat from ground water or air

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ThermallyDynamic

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Hi, I'm new to this forum so hello.

I have a house across the street from a lake in Western MA so we have ground water which is governed by the lake height. Our basement has a french drain with pumps that run for months sometimes in the winter and spring, seemingly more often due to climate change. Warm winters with more rain than snow, and larger downpours in rainstorms lately. The pumps have run for 6 weeks continuously now even though they are running less often.

OK, so now I'm thinking there's a lot of heat in that ground water, how can I get it into a mini split system? For a month and a half it was pumping and estimated 10+ gallons a minute to the outside. That's a lot of H2O and heat at 50F.
The last few weeks have had night time temps from 5 to 20F, right where HP COP go down near 1 or below.

I have 2 ideas.

1. Modify the heatpump(s) to add a switchable H2O to freon heat exchanger to work alternately with water or outside air. Lot's of difficult tech work, I would think, and I'm wondering if anyone has done that.

2. Build an insulated enclosure or box around the heat pump and pump in the ground water thru a car radiator w/fan inside the box so that heats the air inside the box to 50deg F on days below 50. The box would also have a removable panel for warm season use above 50F. No modification of the heatpump needed. I've seen a Utoob vid with someone burying 4" plastic pipe and running air through it, not water.

To keep the radiator clean and from freezing make a Cu or plastic coil inside the french drain pump basin to pick up heat and circulate water/antifreeze mix from the pump basin to the radiator in the outside box. Or something like that, a holding tank, perhaps.

Has anyone done that? It's a part-time geothermal heat boost.

Right now we don't have heat pumps but we're looking into it due to the Mass Saves rebate programs.

Thanks
Thermally yours,
GK
 

Fitter30

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For get about it. The main problem is oil return. Then refrigerate charge it won't be the same from water to air cooled. Minis use micro channel condensers and evap coils that is why their refrigerate charge are so small. Ground source heat pumps use between 2-3 gpm per ton of cooling or heating ( will gain more btu's from the compressor).They are the most efficient way to heat or cool. Indoor swimming pools have package units that use air and water don't come in that small of tonage and the cost very high. Contact your electric company see if they offer a energy audit that includes a blower door test ( test for how air tight the house is) see rebates and another set of eyes. Windows, doors and insulating save money.
 
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ThermallyDynamic

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For get about it. The main problem is oil return. Then refrigerate charge it won't be the same from water to air cooled. Minis use micro channel condensers and evap coils that is why their refrigerate charge are so small. Ground source heat pumps use between 2-3 gpm per ton of cooling or heating ( will gain more btu's from the compressor).They are the most efficient way to heat or cool. Indoor swimming pools have package units that use air and water don't come in that small of tonage and the cost very high. Contact your electric company see if they offer a energy audit that includes a blower door test ( test for how air tight the house is) see rebates and another set of eyes. Windows, doors and insulating save money.
Thanks. We've had the energy audit and Mass Saves did a blown in insulation job in 2x4 walls, foamed air leaks in the basement, blown in and foam board in the attic. In any sub freezing weather the house interior drops 10 degrees overnight. Right now we're wrapping the house in 3" polyiso foam board to cut down the heat loss followed by siding. Maybe we can cut the loss to 5 degrees overnight with that.

Thanks for the technical info about heat pumps not really suited to doing dual air-water duty. I don't have that extensive knowledge of the fine details that make them work well.

That said, we're pumping hundreds of gallons a day of 50F groundwater to the outdoors. Seems a shame to waste it. It will stop in the summer and it costs $50/month/electric to do. I'll give up on modding the heat pump but it seems like heating the air around it during winter wouldn't hurt as a non contact way to transfer heat. Fully reversible and no heat pumps would be harmed doing so.

Has anyone done anything like that? It's cheap geo thermal and it would not hurt the compressors which would think it's a lot warmer than it is. I thought this would be a good place to ask as it's DIY and pros here.

From what I've seen a car radiator is capable of a lot of BTUs with a good fan.

My calculations show about 495K BTUS of heat would be available per hour in heated air if I could get them all to the condenser. Right now there is about 5Kbtu per flush in ground water. It frequency has varied from 1 per every 40 sec to 1 per 2 minutes. And I have 2 sets of pumps running too.

I'll draw a sketch and post it.

Again, thanks.
GK
 
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