TL;DR: It’s kinda like a watercooled heatpump that uses the earth as its heatsink.
It’s not actually using ground water though. Although such systems exist (open loop), mine is a closed loop.
They dug an 8 inch wide hole, 300ft down.
They then put a loop of polypipe that goes down to the bottom to a heat-fused U joint and then back up.
The free space in the “well” is then backfilled with bentonite (clay) to maximize thermal exchange between the loop and the ground.
The bentonite also swells when in contact with water, so it might help mitigate smaller leaks, but don’t quote meon that.
The pipe is filled with a mix of water and glycol to make sure it can’t freeze and a pump takes care of circulating that to the heatpump, but there’s no fluid exchange between the loop and the environment.
AKA Closed loop.
A traditional heatpump is an air-air heatpump, a geothermal heatpump is a water-air heatpump.
Basically, the advantage of the geo heatpump is that the liquid comes back out of the loop and into the heatpump at about 7 degrees C all year.
It is much easier for a heatpump to heat your inside air to 22C by extracting heat from a 7C liquid than from -30C outside air.
Similarly, cooling your inside air by dumping heat into a 7C liquid is easier than by dumping it into +30C outside air.
The heatpump itself is installed inside where the old furnace was, which means it’s also more protected than a traditional heatpump that’s installed outside, hopefully increasing its lifetime.
Don’t get me wrong, traditional heatpumps are also great and might a great fit on lots of places.
Having (some) pretty cold days up here, we went with the geothermal and it is more than sufficient year round. The only times the aux heat kicks in is when I test it manually.
TL;DR: It’s kinda like a watercooled heatpump that uses the earth as its heatsink.
It’s not actually using ground water though. Although such systems exist (open loop), mine is a closed loop.
They dug an 8 inch wide hole, 300ft down.
They then put a loop of polypipe that goes down to the bottom to a heat-fused U joint and then back up.
The free space in the “well” is then backfilled with bentonite (clay) to maximize thermal exchange between the loop and the ground.
The bentonite also swells when in contact with water, so it might help mitigate smaller leaks, but don’t quote meon that.
The pipe is filled with a mix of water and glycol to make sure it can’t freeze and a pump takes care of circulating that to the heatpump, but there’s no fluid exchange between the loop and the environment.
AKA Closed loop.
A traditional heatpump is an air-air heatpump, a geothermal heatpump is a water-air heatpump.
Basically, the advantage of the geo heatpump is that the liquid comes back out of the loop and into the heatpump at about 7 degrees C all year.
It is much easier for a heatpump to heat your inside air to 22C by extracting heat from a 7C liquid than from -30C outside air.
Similarly, cooling your inside air by dumping heat into a 7C liquid is easier than by dumping it into +30C outside air.
The heatpump itself is installed inside where the old furnace was, which means it’s also more protected than a traditional heatpump that’s installed outside, hopefully increasing its lifetime.
Don’t get me wrong, traditional heatpumps are also great and might a great fit on lots of places.
Having (some) pretty cold days up here, we went with the geothermal and it is more than sufficient year round. The only times the aux heat kicks in is when I test it manually.