Has anyone heard of this, or tries it?

Question

Using pipes in the ground to heat and cool you house.

http://mb-soft.com/solar/saving.html

Answer 1

it'd have to be a fairly large "cave".

too small, and it'd heat up over time.

Answer 2

This is quite common and is known as a heat pump.

Answer 3

The geothermal heat pumping process does work moderately well if done in a manner appropriate to local environment.

But we have had people from Arkansas go to Montana and do things the same way as they did in Arkansas... putting pipes 1.3 metres into the ground to extract heat that the sun had left there.

Well in Montana the ground freezes deeper than 1.3 metres without anybody pumping eat out of it. When they start pumping heat out of Montana ground, it is frozen solid down to the pipes before January starts. Trying to pump heat in summer into dry Montana soil takes a lot more energy than pumping it into wet soil anywhere.

We can pump heat into a small lake, just to cool the house, and it is moderately economical to do so. We can pump heat out of a small lake if the lake is very close to the house, if the lake will not freeze down as deep as the pipes.

Near my home there is a municipal building that is heated and cooled via a very deep well,  that  goes down into a crack in the rock that goes out under Lake Huron. That provides a constant 10C temperature to evaporate a refrigerant that falls down the pipe, so that the refrigerant gas comes to the surface, is compressed to give up heat.  The energy cost is about 1/4 what resistance electric heating would be, but it is still expected to cost about 3 years energy savings to recover the installation costs.

Critical to those economics are a building or group of buildings that need a volume of heating energy that justifies that installation cost.

This particular installation works even better for cooling. It takes less than 5% as much power to cool it as it would take with air to air AC systems.

It seems that when you pump heat from a place of high temperature to a place of lower temperature, the  heat will move itself if one just pumps the liquid refrigerant up the pipe.

They did not have that big a need for AC, so did not use it in savings projections.

The cost efficiency of that municipal building would not be expected if one were heating just a single house. But it would make a lot of sense for an Apartment complex.