A drill rig sits outside a home during the installation of a geothermal heat pump system in White Plains, N.Y. Monday, May 8, 2023. The loop runs several hundred feet deep in the yard and either carries heat away or into the house, depending on the season. In the future, industry experts expect the technology to be more popular. Some homeowners looking to outsource their heating and cooling systems are turning to home geothermal heat pumps, or ground source heat pumps, AP photo Julia Nikhinson said. It's a technology that relies on a simple fact: If you dig several feet below the earth's surface in the coldest winter or the hottest summer, the temperature will be around 55 degrees.
Geothermal benefits from that constant temperature by pushing water with some antifreeze through a loop of flexible pipe that runs deep underground. A heat pump system, usually located in the basement, circulates the water.
When the house needs cooling - says on an 85-degree July day - a refrigerant, a special fluid, absorbs unwanted heat indoors and transfers it to water in the long piping, circulating it underground, providing it time to cool to the constant mid-50 s below. Air blows across the cool fluid from the cooling system. After dumped its heat, it can absorb more for transfer to the outdoors.
The building works much the same, in reverse. On a sub-freezing January day, the system circulates the water underground, resulting in a temperature of about 55 degrees. The water in the loop now heats the refrigerant, making it want to expand. The temperature rises as the electric pump compresses it. The system then pushes air over the hot refrigerant and into the house until the air temperature in the house reaches the thermostat temperature.
In apartment buildings, schools or other commercial buildings, the underground loop may be just a few feet deep and extend horizontally over a wide area. For smaller residential lots, the solution is to drill deep - or at least 300 feet or more - to find a loop that is long enough for water to be in contact with the ground and adjust with its constant temperature.
The cost of geothermal systems is higher than typical furnaces, sometimes thousands of dollars. Supporters say lower operating expenses eventually make that worthwhile, because the superpower of ground source heat pumps is that they use very little electricity to move heat around. They're designed to last for more than 50 years for the underground parts, with the above-ground components expected to last 25 years or more. On average, gas furnaces last for 15 to 30 years.
The rule is that geothermal or ground-source heat pumps are still the exception rather than the rule. Air-source heat pumps are often utilized to cool and heat the environment by extracting energy from outdoor air.
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