Let’s look at how efficient these systems are and how that efficiency is measured.First, it’s important to know that a kilowatt of electricity is equal to 3,413 Btus.So, for every kilowatt of electricity used to run the compressor, blower, and pumps, a geothermal system can extract 4 to 5 kilowatts (13,652 to 17,065 Btus) from the ground.This translates into efficiencies in the neighborhood of 400 to 600%. The term coefficient of performance (COP) is used to explain how efficient the system is in heating mode, and the term energy efficiency ratio (EER) is used to determine the cooling efficiency.
COP is the ratio of heat output to the amount of energy input of a heat pump. It’s a little like real life in that what you get out depends on how much you put into it. Except that with geothermal you get a lot more out than you put in. If a heat pump delivers 5 units of heat for every unit of energy input, the COP is 5.
Geothermal heat pumps can operate in the neighborhood of 5 COP in heating mode. So if a property owner is using 1kW and getting 5 kW in return, that is 400% efficiency. Compare that to a fossil fuel furnace’s 96% efficiency, and it becomes clear why geothermal just makes sense.
On the other hand, EER is a measure of the cooling efficiency. If a geothermal heat pump in cooling mode draws 1 kW to produce 10,000 BTUs per hour cooling, the efficiency is calculated as 10 EER. Geothermal heat pumps have EER ratings in excess of 20 on average, so that 1KW is actually producing 20,000 BTUs of cooling.
Most people are familiar with air-source heat pumps, where heat is extracted from the ambient air or rejected into the outdoors.With a geothermal heat pump, heat is extracted or rejected to a loop field.We all have a heat pump in our homes now, because a refrigerator is really a heat pump. It extracts heat from the interior contents like fruits and vegetables, or fluids like milk or beer, and rejects it to the interior of the home.