How Ground-Source Geothermal Heat-Pump Systems Work
Geothermal heating and cooling is referred to by many names such as Geothermal heat pumps, water source heat pumps, earth-coupled heat pumps and ground source heat pumps. These systems have been used for over 70 years now. The first residential geothermal heat pump systems were installed in the 1940s.
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So how do geothermal heat pumps work? To understand this lets first look at how an air conditioner works. An air conditioner removes heat from the home. This is done by moving the hot damp air across the evaporator coil, which then absorbs this heat and transfers it to the unit outside of the home. If you walk by an air conditioner running in the summer the air coming out of the top is hot. The most important thing to understand is that the air conditioner is technically not blowing out cold air, it is removing the hot air, reducing the temperature of the air coming out of the register causing it to feel colder. The challenge with conventional air conditioning is that the air outside where it is dispersing the heat from the home is generally hot and the hotter it gets outside the less heat transfer that is taking place.
Now that we understand how an air conditioner works lets graduate to the next level and learn how a heat pump works. A conventional heat pump operates in the summer as an air conditioner. In the winter time it simply reverses the flow of refrigerant and absorbs heat from the outside then dispersing that heat into the home. Most people would say how is it absorbing heat from outside in the middle of winter? We must turn to science to understand that. Even when it feels bitter cold outside there is still heat in the air. Certainly not as much in the winter time but there is still heat. In fact there is heat in the air all the way down to -460 Fahrenheit (“Absolute Zero”). This is the temperature when everything stops moving including atoms and molecules. Most heat pump technology has the ability to extract heat from the air down to -5 degrees F. The colder it gets outside the less heat there is for the heat pump to obtain. The lower the temperature the less efficient an air to air heat pump becomes and at -5 degrees F the air to air heat pump will not extract heat from the air and will simply spin its wheels. This is why in many northern states there must be a form of back up heat, or supplemental heat.
Now that we have a basic understanding of how air conditioners work and heat pumps work, it will be much easier to understand how a geothermal heat pump works. The main geothermal equipment resides inside of the home and is connected to a set of “loops” or “wells” that are buried under the ground or in a pond or lake. The reason for this is that the ground temperature is on average a consistent 55 degrees F. The ground becomes the source of energy and is transferred from the earth to the fluid that is being circulated inside of the pipes (wells or loops) and then transferred into the home. The main geothermal unit is what pushes and pulls that fluid in and out of the home. The geothermal heat pump is using basic air conditioner and heat pump technology to remove the energy or heat from the fluid in earth loop.
The key to the success of these systems is that they are using minimal energy to extract the heat from the earth in the winter time and transfer that heat into the home. In the summertime the reverse happens and the system extracts the heat form the home and disperses that heat into the consistent temperature of the earth. In other words, unlike ordinary heat pumps whose efficiency depends on the inconsistent outside air temperature and therefore varies greatly, the geothermal system relies on the consistent temperature deep underground, delivering high efficiency no matter what the weather is.