Crazy question, probably, about storage

[hoverwheel]

Ground source (geothermal) heat pumps are on the expensive side in my area even if I had the land for it.

Air sourced heat pumps can work in my climate, but could get questionable if it is super cold for a good stretch of time.

So what if I install 1000 gallons or so of water storage and use that as the source?

I'm the summer that storage would tend to get hot and maybe could be used to heat domestic water.

In the winter the storage would tend to get cold. If it got "too" cold, well I don't know, but the floor on a Mitsubishi hyper hear is 13 below. Unsure of a retasked ground source. Maybe a wood stove with a heart exchanger would add enough heat to the storage to keep it working?

I said it was a crazy question. Is it worthwhile even doing the math?

 

[maple1]

The storage needs to be heated by something. Storage isn't a source.

 

[cpeltier]

The storage needs to be heated by something. Storage isn't a source.

This method of using a tank for a geothermal source is actually common in hotel and apartment complexes. The building will have a large common loop and individual heat pumps in the units will heat and cool with this loop as a source. The loop itself is heated via a boiler or cooled using cooling towers. You can try the same thing with your storage tank but for heating you need to add as much heat to the storage as your removing. Since your using a heat pump you don't need to worry about your source being terribly hot since your just moving heat but it will cool the storage by the BTU amount that your removing. The warmer you can make the storage the more efficient the heat pump will be. The wood stove idea will work if it can provide enough heat. You will be able to take advantage of some huge delta Ts (cold storage vs hot wood stove) with this setup. Of course you have to make sure storage doesn't freeze by making it too cold with the heat pump. You could add glycol but it will derate heat exchange efficiency somewhat. It would be an interesting experiment!