Understanding how geothermal heat pumps work is an important first step to understanding how these products can lower your heating and cooling bills. The science behind this technology is actually very old, but surprisingly not well known. Below we’ve included everything you need to know about the science behind geothermal heat pumps, or you can watch this YouTube video for a quick explanation:
Let’s get started by explaining how geothermal heat pumps make use of the warm earth to heat and cool your home:
Energy Supply Source
A geothermal heat pump harvests free energy from the warm earth and transfers that heat into your home to provide space heating. This is done using what is known as a ground loop, or energy supply source. There are three difference types of energy supply sources:
An open loop harvests heat for your home from ground water. This is done by drilling a water well on your property. The incoming water temperature will be at least 40°F (4.4°C) and may be warmer depending on your location. The water is circulated through the geothermal heat pump, and the heat exchanger picks up heat from the water.
The heat pump will remove about 6°F (3°C) of heat from the water. The slightly cooler water is then deposited into a second water well where it is recirculated with the ground water and reheated. The heat pump only removes heat from the water, and does not treat it with any chemicals.
If you can’t drill a water well on your property or you don’t have enough flow to accommodate a geothermal heat pump, you can instead choose a closed loop. A closed loop uses a closed system to harvest the heat. There are two types of closed geothermal loop: horizontal and vertical.
Horizontal Closed Loop
A horizontal closed loop consists of plastic piping buried in six-foot deep trenchs on your property. The system is completely sealed and will not interact with the ground water. A typical horizontal ground loop consists of several trenches about 250 feet long. Once the piping is installed the trenches are backfilled, and you can install landscaping or even a driveway on top. The piping made of is high-density polyethylene plastic and is fused together. The plastic has a long life and should last fifty years or more.
Inside the piping is a fluid that circulates through the ground loop, absorbing heat. The heated fluid is sent to the heat pump, which picks up the heat via a heat exchanger. The fluid is then sent back out to the ground loop to take more heat, and the process continues.
A horizontal ground loop is the most space intensive option for a ground loop and will take up to half an acre. If you don’t have this much space, you can opt for a vertical closed loop instead.
Vertical Closed Loop
A vertical closed loop operates on the same principle as the horizontal closed loop above, except this time the loops are installed vertically by drilling boreholes into the ground. Each borehole is between 150 and 300 feet deep. Most homes need between two and six boreholes to supply enough heat to the heat pump.
A vertical closed loop will take up much less space than a horizontal closed loop and is ideal for a city lot.
How Does Geothermal Work in Your Home?
Once the outdoor loop fluid picks up the heat, the fluid is circulated to the heat pump. The large volume of low-temperature heat is transferred to a refrigerant inside the heat pump. The refrigerant cycles through a compressor, which compresses the refrigerant and subsequently raises the heat level. Finally, the refrigerant transfers its heat via another heat exchanger to your heat distribution system. The refrigerant is part of a closed system and operates on the same heat exchange principle as your refrigerator.
Energy Distribution System
So far the ground loop has harvested the heat, the compressor has boosted its temperature, and now the energy distribution system will distribute it to your home. There are three main types of energy distribution systems:
This is the most common way to heat and cool your home with a geothermal heat pump. With this system, the heat from the refrigerant is transferred to air and is blown into your home via ductwork. Ductwork will run to each room in your home and ensure that your whole house stays warm in winter.
Another way to distribute heat to your home is via in-floor heating. With this method, heat is transferred from the refrigerant to a buffer tank that feeds your radiant in-floor system. Radiant in-floor heating is usually plastic piping installed underneath your floorboards or encased in cement.
Some homes may use a combination of both in-floor heating and ductwork. In this case, your installer would select a geothermal heat pump that can switch between air and water heating.
How Geothermal Heat Pumps Save You Money on Heating Bills
A geothermal heat pump is so efficient because it doesn’t burn fuel for heat. Instead, it is harvesting the freely available heat in the ground. Because it is harvesting heat that already exists (as opposed to burning fossil fuels to create heat), geothermal heat pumps are an extremely efficient way to heat your home. The only cost is for the electricity to run the pump.For every watt of electricity you use to run the heat pump, you’ll get three watts of heat energy for free from the ground, for a total of four watts of heat energy. In comparison, electric baseboards only yield one watt of heat for every watt of electricity used.
To put things in perspective: For every watt of electricity you use to run the heat pump, you’ll get three watts of heat energy for free from the ground, for a total of four watts of heat energy. In comparison, electric baseboards only yield one watt of heat for every watt of electricity used.
You can learn all about geothermal heat pump efficiency on our economic benefits page.
How Geothermal Heat Pumps Save You Money on Domestic Hot Water Costs
Geothermal heat pumps also allow you to save money on your domestic hot water heating. You can learn more about how that works in this blog post: How Geothermal Heat Pumps can Help You Save On Domestic Hot Water Costs.