One strange misconception about geothermal is that a geothermal system can either Heat OR Cool your home. This is not true. Geothermal heat pumps are not like the air conditioners that are common in homes in the fact that they are true heat pumps, which means they can do both. This article will focus on how geothermal heating works.
The Short Answer
The best way to describe how geothermal heating works is that heat is taken from the ground, and a heat pump circulates that heat throughout your home or workplace. Water goes through pipes that are buried in the ground, and the ground temperature heats the water. The warm water is pumped to the heat pump, the heat is taken from the water and the heat pump uses this heat to heat refrigerant, which heats the air you feel coming out of your vents. The process is controlled by a regular thermostat. The process is energy efficient and has a lower lifetime cost.
The Engineering Answer
Geothermal heating works by using the heat in the ground to heat your home. This is done using a series of heat transfer mechanisms with several different sources. First, water is circulated through pipes buried in the earth. The water can be warm or cool depending on the cycle of the heat pump, but the goal is to have it reach the undisturbed earth temperature. The water is then pumped to the heat pump. The water will go to the supply side of the geothermal heat pump and through the water side heat exchanger. It will heat the refrigerant in the heat pump, causing it to evaporate. The compressor then compresses this vapor so that it is high pressure, superheated vapor. In geothermal heating cycle, this vapor is directed in a reverse cycle due to the reversing valve. It is this reversing valve that makes heat pumps different than air conditioners. The refrigerant flows to the airside heat exchanger. Air from the heat pump fan is blown across this finned heat exchanger. This air becomes hot and is blown through the house, which is what you feel in the heating cycle. The mechanical process does not end there though. After the superheated refrigerant contacts the heat pump air, it is cooled and condenses. It then does through an expansion device, which lowers its temperature and pressure. It now will go through the heat pump condenser, which is the water side heat exchanger. It contacts the geothermal supply water, from which it absorbs heat. The refrigeration process has made a complete cycle. The water from the condenser has now been cooled by the heat pump, and must now be pumped back to the pipes in the ground to warm to the earth temperature. That is one complete cycle of geothermal heating.
Isn’t This Like Any Other Heat Pump?
It is. Geothermal heat pumps use the same refrigeration circuit that any other heat pump uses. The difference is the water cooled condenser. With an air cooled condenser (e.g. your current split system heat pump) the outdoor unit is what does the cooling or heating of the refrigerant. The refrigerant must either gain heat or reject heat to the air based on what cycle it is on. The same goes for geothermal heating, except you are using water that is at a much more moderate temperature.
There are some instances where geothermal heating will not be enough. In these instances, the traditional heat pump itself will not suffice. Different configurations of heat pump exist and there are some hybrid ways to supplement heat if necessary. But the normal heating cycle is a routine process that all heat pumps are equipped for, and add to the versatility of a geothermal system.