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 to condition 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. While in an air-conditioning mode, warmth from the home is rejected into the ground or ground water.
What makes these systems such a good choice for residential heating and cooling is that they do not depend on outside air temperatures. They will keep your home comfortable 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 and a well-designed system will use 25-50% less energy than conventional heating and cooling systems (Source: US DOE).
Water-to-Water Geothermal Heat Pumps
These types of systems are generally used for heating only. They are installed instead of a traditional gas or oil furnace to keep your home warm and provide domestic hot water.
It is important to know that heat pumps work most efficiently when the temperature difference between the warm source (ground) and the heat sink 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 water temperatures of 180 degF. Floor heat and low-temperature radiators require water temperatures in the range of 95 to 140 degF.
Some newer models are now equipped with so-called desuperheaters that can transfer excess rejected energy from the compressor to heat domestic 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 ground „water“ is the heat sink, where you reject the heat from the house while in air conditioning mode. While in heating mode, energy is extracted from the ground water and „pumped“ into the „air“ through the compressor. The „air“ is distributed through your home via duct work.
Otherwise, they 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.
These highly efficient and reliable systems are best designed and installed by professionals. It is not recommended to make this a DIY project. 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.