Geothermal

[Kroeran]

All a geothermal system consists of, basically, is a heat pump, like the one in your refrigerator. Your fridge moves heat from a cold place (the inside) to a warm place (your kitchen). A geothermal system moves heat from dirt in your yard (or water from a well), to your house. In the summer it moves the heat the other way to cool your house.

There are different ways to get the heat to the heat pump such as glycol loops, wells that feed water to a heat pump and then drain on the ground and heat exchange loops in a lake or pond.

I still dont get how dirt that is cooler than the house provides heat

is it just an air conditioner/fridge in reverse? it dissipates cold in the ground more efficiently than a reverse heat sink to air?

 

[samclem]

is it just an air conditioner/fridge in reverse?

Yes. A "regular" heat pump and A/C unit works the same way as these geothermal units. When your AC unit is turned on, it (through a compressor that forces a change in state of the refrigerant) moves heat from the air in your home to the outside air. That's why the air being blown out from the outside unit is so hot--it has had heat added to it from your inside air. There are air-to-air heat pumps that are designed to run "backward", and they make the inside air warmer and cool off the outside air (actually they "take heat from" the outside air, but that's an academic distinction). So, in the winter time the air being exhausted from the outside unit is colder than the outside air.

There's nothing magic about these "geothermal" units. They are more properly called "ground source heat pumps" or "ground coupled heat pumps." Instead of exchanging heat with the air outside your home (which might be very cold in the winter) they exchange heat with the soil or water underground. This soil/water tends to stay at a fairly constant temp year round (much more than the outside air does), so these units can be very efficient compared to air-to-air heat pumps.

There have been folks who installed "earth tubes" to directly use the moderate ground temps underground. In the summer, when it might be 90 degF outside, they bring in outside air through several hundred feet of buried pipe, and the air comes inside the home at about 70 degrees. It sounds better than it works--lots of condensation inside the tubes as the hot, humid summer air contacts the cool walls of the pipe. This is a great mold-growing environment.

it dissipates cold in the ground more efficiently than a reverse heat sink to air?

There's no such thing as a "reverse heat sink." Heat flows only one way (hot to cold) through a heat sink. If we make it flow another way (through introduction of energy) then those processes each have specific names.