The term geothermal literally means Earth/Ground (Geo) Heat (thermal). Geothermal, or ground source heat pumps, take advantage of the constant ground or groundwater temperatures. These heat pumps use geothermal energy to heat and/or cool your home.
A refrigerant loop with a compressor extracts heat from one side (the ground) and pumps it to the heating loop in your home. It is essentially the same process that happens in your refrigerator: heat is extracted via a compressor and refrigerant loop from the inside of your refrigerator/freezer and rejected into your house.
In the summer the geothermal heat pump reverses its cycle, if you have an air-conditioning system, and heat from the home is rejected into the ground or ground water.
What makes geothermal heat pumps such a good choice for residential heating and cooling is that they do not depend on outside air temperatures. These heat pumps will heat your home as efficiently on a windy, zero-degree winter day as on a 40-degree day. Provided of course, that your house is well insulated and tight.
Geothermal heat pumps are also a very efficient way for heating and cooling your home. They use 25-50% less energy than conventional heating and cooling systems (Source: US DOE).
Residential applications of geothermal energy systems use water-to-water or water-to-air heat pumps.
Water-to-Water Geothermal Heat Pumps
Water-to-water geothermal heat pumps are generally used for heating only. They replace the gas or oil furnace that you might currently have to heat your home and water with.
It is important to know that heat pumps work most effectively when the temperature difference between the heat source (ground) and heat sink (floor heat or radiators) is small.
Ground temperatures range anywhere from 50 to 75 degF, depending on where you live. This means that geothermal heat pumps are generally not suitable for standard hot water baseboard applications, which are designed for heating water temperatures of 180 degF. Floor heat and low-temperature radiators require water temperatures in the range of 95 to 140 degF.
Some newer heat pump models are now equipped with so-called desuperheaters that can transfer excess heat from the geothermal heat pump compressor to the domestic water heater. Your geothermal heat pump can also effectively and quickly heat water for your bathtub, shower and sinks.
Water-To-Air Geothermal Heat Pumps
These types of ground source heat pumps are generally used when you need air conditioning. The Water is the heat sink, where you reject the heat from the house. The Air is the air that is distributed through your home via ductwork.
Otherwise, these heat pumps function the same way as water-to-water heat pumps. And again, the efficiency of a geothermal heating and cooling system is far better than that of a traditional system.
Important To Know
The first step towards making a geothermal heat pump system be a reliable and efficient heating (and cooling) system for your home is to minimize the heating and cooling requirements with a well-insulated building envelope and strategically placed windows for passive solar gain.
Not only is your first cost reduced, because your system will be smaller. You will also tremendously increase the comfort of your home.
Geothermal heat pump systems are best designed and installed by professionals. It is not recommended to DIY. These systems must meet specific requirements. Especially the piping laid out in the ground, or down to the ground water table, must be designed and installed correctly to ensure that your geothermal heat pump system works as intended.