Understanding Geothermal Heat Pumps

Geothermal heating… Geo=ground… thermal=heat. Someone told me the other day that it was really hot under the ground and that’s how they worked. Well I hate to ruin this simple view, but that’s not how they work. It’s a little more complicated than that. This post gives the simple explanation, and then the physics explanation.

Simple explanation

Geothermal heat pumps use a pumping mechanism to absorb heat energy from under the ground and “pump” it into your house. The clever part is that due to a clever trick, they only use about one unit of electricity to “pump” about 4 units of heating into your house. Electric heaters use one unit of electricity to generate one unit of heating, so Geothermal Heat Pumps are 4 times more efficient. The downside is that they only work on lower temperature systems, meaning you really need to have underfloor heating to make use of them effectively.

Physics explanation

First you must realise that there is energy in everything. Once it’s not at absolute zero, it’s got energy in it, thermal energy. Next you need to have a vague understanding of pressure. In a fluid the molecules are all flying around, vibrating, that sort of thing. If you heat them up, they vibrate more, and so the fluid expands. What’s really interesting here though is that it also works in reverse. If you compress a fluid, it tries to give out heat. Similarly if you let a fluid decompress, it will try to suck in heat from its surroundings. Basically what I’m saying is that by changing pressure, you can actually make a fluid give out, or suck in, thermal energy.

That’s the key to Heat pumps. They use a loop of fluid, which is allowed to expand in one place (under your lawn or somewhere like that). It then absorbs thermal energy from the surroundings. The fluid is then pumped into your house, where it is compressed, and so needs to give out that energy. The heat pump then transfers that heat to the heating system in your house and boom!

Thanks to daviddarling.info for the pic


13 Responses to Understanding Geothermal Heat Pumps

  1. Kelly B. says:

    Could you explain further what you mean by “they only work on lower temperature systems”. We just installed a geothermal system retrofitted to our forced air ductwork and the system is working great. We got rid of the oil furnace and saved about $140 in our first month running the geothermal. I do understand that you cannot retrofit it to radiators, is that what you mean?

  2. greennav says:

    Hi Kelly,

    Thats right. Some systems work on water at 55C, like radiators. Others work on lower temperatures, like underfloor heating. The problem with underfloor heating is that it is very difficult to retrofit


  3. Nolan says:

    That is a great explanation of geothermal heating. Here is a simpler version.

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  5. Patty says:

    EcoMech Green Company of Georgia I enjoyed reading your blog ! Thanks for the info!

  6. GeothermalHeatPump is much more energy-efficient because underground temperatures are more stable than air temperatures through the year. Seasonal variations drop off with depth and disappear below seven meters due to thermal inertia.

  7. lHeatPumps says:

    Heat pumps are always more efficient at heating than pure electric heaters, even when extracting heat from cold winter air. But unlike an air-source heat pump, which transfers heat to or from the outside air, a ground source heat pump exchanges heat with the ground.

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