Renewable propane

As for cooling, that is of course simply running a heat pump in reverse, extracting heat from the inside air and dumping it into outside air. So either way, the heat pump efficiency follows the same thermodynamic formula. (It also turns out to be the same formula as in a heat engine, but inverted). For a heat pump theoretical efficiency is Thot/(Thot-Tcold) and for air conditioning it is Tcold/(Thot-Tcold) where T is absolute temperature. Since Thot-Tcold (also known as delta T) is a much smaller number than the absolute hot or cold temperature itself we can get phenomenally good efficiencies out of heat pumps and air conditioners. 

The numbers get better the smaller that temp differential is. And, the differential is much smaller for summer cooling than it is for winter heating. If say it's 100 degrees out and you have your tstat set at  say 80 that's only 20 degrees delta T. Compare that to a typical winter heating scenario where it's 20 degrees out and your tstat is set at 70, a 50 degree spread. 

You see where this is heading? The point is that the benefit in reducing the temp you're pumping heat to is much less  in summer than the benefit in raising it is in winter, because the summer delta T is not very large to begin with. So, if it doesn't pay to install geothermal for winter heating it won't pay to install it for summer cooling either. 

For me personally living in the mountains  the summer cooling requirement is negligible. Propane is expensive, I have no access to natural gas  and don't want to be spending money on or burning fossil fuel anyway.  I would still personally consider installing a "geothermal" water source heat pump for winter if I had a nearby pond that was big enough to act as a heat source/sink for the system. Then it's just a matter of tossing a big coil of plastic pipe in the pond to act as a heat exchanger. Although water source heat pumps are more expensive than air source ones at least you don't have all the expense of burying the ground source loop, and the loop is much shorter because the heat exchange between it and water is much better than with soil. But lacking a large pond I'm going with a hybrid solar powered mini split/wood heat solution . Mini splits look fine to me. I don't have to heat or cool rooms I'm not using. What I don't like are noisy air handlers and compressors in centrdl systems.  Both the inside and outside mini split units are very quiet.