How Does a Geothermal Heat Pump Work?

Geothermal heat pumps employ a series of underground loops to transfer heat energy from one location to another by utilizing the constant ground temperatures and stored heat energy properties of the earth. Geothermal systems transfer heat from your home to the earth in the cooling mode, or from the earth to your home in the heating mode. In contrast, a traditional air-source heat pump draws on outside air temperature to either extract or expell heat and because of temperature fluctuations and gradients, are less efficient and demand more energy.

Geothermal heat pumps consist of four
main parts:
       1. The heat pump unit. (located indoors)
       2. Ground loop system
       3. Loop circulator pump
       4. Air delivery system (the ductwork)

How Geothermal Heat Pumps
Transfer Heat

In the heating mode, geothermal heat pumps work by transferring the Earth's natural heat through a network of loops installed below the surface of the ground or submersed in a pond or lake. Fluid circulates through the loop and carries heat extracted from the ground to its source. There, an electrically driven compressor and a heat exchanger concentrate the Earth's energy and transfer the heat energy inside the home or building at a higher temperature. In contrast an air-source heat pump in the heating mode draws heat from colder outside air and thus requires more energy (remember 54°F vs potentially 35°F).

How Geothermal Heat Pumps Act as an Air Conditioner

In the cooling mode, the process is reversed. The geothermal heat pump extracts heat from the house or building, transfers the heat to underground loops which is absorbed by the Earth. The heat is expelled to the relatively cooler ground rather than delivering it to the hot outside air as a traditional heat pump (remember 54°F vs a possible 90°F). As a result the heat is transferred over a greater temperature difference leading to higher efficiency and lower energy use. The system cools your home in the same way that a refrigerator keeps your food cool - by drawing heat from the interior, not by blowing in cold air.

How Geothermal Heat Pumps Act as a Water Heater

Many geothermal systems installed today are equipped with or have the add-on option of a desuperheater, to provide domestic hot water. The desuperheater is a small auxiliary heat recovery system that provides, on average, 60% of all domestic hot water. The system transfers excess heat from the heat pump’s refrigeration cycle to a water line that circulates water to the house’s hot water tank. In summer, when the air conditioning runs frequently, the desuperheater may provide all the hot water needed by a household (up to 8 gallons per each ton of cooling, per hour of operation). This system provides less hot water during heating season, mostly supplemental, and provides no hot water while the heat pump is not operating.

There are 2 Types of Systems: Open-Loop and Closed-Loop

Closed-loop systems: Uses a continuous loop that acts as a heat exchanger with the earth either transferring heat from the ground to the source or from the source back to the ground. The loop system is connected to the indoor heat pump to form a sealed, underground connection through where a environmentally friendly water/anti-freeze solution is circulated. The following are the two most common closed-loop applications.

Horizontal closed-loop systems: A horizontal loop installation may be preferred depending on the available lot. This type of installation involves burying pipe in trenches over an area determined by the size of the system. On average, trenches are 5 ft. – 6 ft. deep, and 3 ft. wide. In some cases, the excavation involved with a horizontal loop is more cost effective than a vertical loop. Drainage and grading issues may be addressed during the excavation and installation process.

Vertical closed-loop systems: A vertical loop installation is accomplished by drilling a well straight down to a depth determined by the size of the system. On average, a single well ranges from 100 ft. – 400 ft. deep. Vertical loops are less invasive to the surrounding landscape, and may be preferred. Depending on the landscape or system size, multiple wells may need to be drilled.

Open-loop systems: Uses groundwater from a conventional well, pond or lake as a heat source in winter, and a heat sink in summer. The groundwater is pumped through the heat pump where heat is extracted (in winter) or expelled (in summer) while the return water is disposed back to its original source or through a drilled groundwater well.