When considering your home's heating and cooling options, you can draw electricity from the local utility company for powering air conditioners or air-source heat pumps, or heat with oil, natural gas, or propane. All these options put carbon dioxide into the atmosphere and contribute to climate change to varying degrees. Instead, opting for renewable energy sources like solar, wind, or geothermal energy ( which we’ll be discussing here) is a more eco-friendly and sustainable choice.

Geothermal energy (and specifically ground source heat pumps) stands out as one of the most versatile renewable energy options for homes. Unlike solar or wind power, geothermal does not require a year-round sunny climate or specific geographical features. All you need is a small area adjacent to your home for the installation of underground pipes that supply your heating and cooling system. Let’s take a look at how it all works.

Geothermal versus Ground-Source Heat Pumps

Geothermal energy refers to the heat emanating from the Earth's core, which can manifest in many ways, such as volcanoes, geysers, hot springs, or boiling mud. While some of these sources can be harnessed for electricity generation, they are limited to specific locations like Japan, Iceland, and certain areas in the Western USA. If you don't live close to such sites, direct access to this form of geothermal energy is not possible. That electricity might still be part of the energy mix that reaches your home, though. Through large-scale energy systems that harness and transmit this energy over long distances, geothermal heat can be converted into electricity and delivered to regions far away from the actual sources.

When people talk about geothermal systems for their homes, they usually are thinking of systems that derive energy from the temperature difference between the outside air and the ground a few feet below. While technically not "geothermal" in the strict sense, these systems are known as ground source heat pumps, essentially serving the same purpose.

How does a ground-source heat pump work?

Once you get several feet below the surface, the ground temperature stays a consistent temperature throughout the year, usually around 50 to 55 degrees Fahrenheit. As the outside air temperature fluctuates between hot in summer and cold in winter, a ground-source system can exploit that difference.

In summer, the ground-source heat pump system uses refrigerant to cool the home. The refrigerant absorbs heat from the indoor air, cools down in the condenser, and circulates the cooled air back inside. The compressed refrigerant then releases heat into the ground, where the consistent temperature cools it, and the process repeats.

In winter, the system works in reverse, using the indoor coil as a condenser to heat the outside air. The warmed refrigerant, under pressure, turns into a gas and releases heat into the home. The refrigerant then passes through an expansion valve, cooling it down rapidly, and the cycle continues.

History of Geothermal Energy

People have been using geothermal energy for thousands of years, with American Indians relying on hot springs for heat and cleaning as long ago as 10,000 years. In the early 1900s, people started harnessing geothermal energy for electricity generation.

As for utilizing the temperature difference between the air and the ground, early ideas surfaced in the mid-1800s and early 1900s, but it was not practically implemented until the end of World War II. Doctor Carl Nielsen of Ohio State University in 1948 was the first to successfully install a residential system.

Today, over one million geothermal heat pumps are operating globally, with an annual increase rate of 10 percent, largely driven by the USA and Japan. As climate change becomes more apparent and energy costs rise, many expect to see increased demand for this clean energy source.

Advantages of Ground-Source Heat Pumps

Ground-source energy, particularly when used in heat pumps for homes, offers several advantages that make it an appealing choice:

Ground-source heat pumps operate silently, unlike traditional air conditioners and heaters.

With fewer moving parts, these systems are more reliable and often include backup systems or computer-based controls.

• Clean: Ground-source heat pumps do not emit greenhouse gasses by burning fuel to heat homes (though they do require electricity to run), contributing to a cleaner environment.
• Renewable: Geothermal energy is essentially renewable, requiring only a small amount of electricity from the grid to operate the system.
• Less Resource-Intensive: Geothermal heat pumps have a smaller impact on the energy grid compared to solar or wind power systems because they’re just transferring existing heat from the earth, not creating it
• Long-Lasting: Ground-source heat pump systems have a long lifespan since most components are housed indoors or in the ground.

In addition to these advantages, homeowners can save 30 to 60 percent on heating costs and 20 to 50 percent on cooling costs compared to traditional heating and cooling systems. Additionally, federal tax credits are available for homeowners who install certified geothermal heat pumps, making the system more cost-effective.

Disadvantages of Ground-Source Heat Pumps

The biggest disadvantage to ground-source heat pumps is the up-front cost. Systems can range in cost from $18,000 to $30,000. Most homeowners should qualify for the 30% Inflation Reduction Act tax credit, bringing that initial outlay down, but they’re still more expensive than other options.

Ground-source energy systems offer several engineering designs for residential heat pumps, tailored to the layout and available space on your property. The main types of geothermal installations include:

• Horizontal: This installation is less expensive and suitable for properties with ample space. Cooling loops are placed in trenches at least four feet underground.
• Vertical: Vertical installations are more expensive but necessary for properties with limited space. Cooling loops extend down vertical holes in the ground.
• Pond or Lake: Cooling loops can also be run through nearby ponds or lakes, which can be a cost-effective alternative if available.

Ground-source heat pumps are a sustainable solution for heating and cooling your home and can be quite cost-effective over the long term. With reliable performance, low noise levels, and minimal greenhouse gas emissions, geothermal energy can significantly reduce your energy costs while contributing to a cleaner environment.

Even as demand for ground-source installations grows, it’s important to talk with a qualified installer to understand the options for your home. Understanding how much space you have for the equipment and other site-specific concerns is the first step in considering a geothermal system. The International Ground Source Heat Pump Association is recommended by the Department of Energy as a great source for dependable, reputable contractors.