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Intern Research – Geothermal Heat Pumps

Sean O'Sullivan - Mechanical Engineering Intern

By Sean O’Sullivan

October 12, 2022
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On average, 35 percent of energy use for commercial buildings in the United States is for the purpose of heating and cooling spaces (Department of Energy). A large percentage of this energy comes from non-renewable resources such as natural gas, petroleum, and coal (Penn State). While renewable energy is becoming more prevalent, total dependence on these resources is still years away. Currently, a simple way to heat and cool your building is by installing a geothermal heat pump.

 

A geothermal heat pump takes advantage of the constant temperature underground throughout the entire year. For example, in Fort Wayne this temperature is 47 degrees Fahrenheit. The geothermal heat pump moves fluid, typically water or a refrigerant, throughout the ground in an underground loop system, absorbing or dispelling heat. This system can save up to 50 percent of electricity compared to traditional HVAC systems.

Image Source: PennState College of Earth and Mineral Sciences – Energy Production and Consumption in the United States
Geothermal Heat
Geothermal Heat
Underground Heating

Open Loop System

The simplest form of a geothermal heat pump system is an open loop system. This is reliant on a source of water to pull from. Once the water runs through the heat pump, it is discharged into the ground again. While this system is typically cheaper than other versions, it is dependent on whether there is a sufficient source of water nearby. There can also be issues with clogs due to the natural elements of water.

Horizontal Loop System

The most cost-efficient system to install for residential purposes is a horizontal loop. Instead of relying on a continuous source of water, the same fluid is pumped throughout the piping. Some disadvantages of this system include its need for more square footage. Another disadvantage is that because of its shallow depth, 4-6 feet, it requires more piping to obtain its heating/cooling needs.

Vertical Loop System

Another common system is the vertical loop. This requires drilling boreholes directly into the ground. These boreholes can as deep as 300-500 feet, depending on the area. Because the pipes go straight down into the ground, less square footage is required to install these systems, as well as less piping. This is because once the depth passes 20 feet, the temperature is much more stable than it is closer to the surface.

Image Source: The Tennessee Magazine – Is a Geothermal Heat Pump Right for You?
Underground Heating

Geothermal Heat Pump Costs

In terms of cost for geothermal heat pumps, this is usually communicated with a payback period. This can range from anywhere between two to fifteen yars. This payback period is calculated using the cost for installation which includes drilling, piping, and the heat pump itself. Once the savings from switching to geothermal surpass the cost for installation, the system is “paid off” and remaining savings can be used for new projects.

According to a sales representative for geothermal heat pumps, the average cost of drilling is $8.80 per foot for a vertical loop. Currently, there is also a tax credit for installing these systems. If installed in 2022, 26 percent of the cost for installation will be covered. This tax credit may increase to 30 percent due to legislation currently moving through congress, the Inflation Reduction Act of 2022.
Geothermal Costs
Geothermal Costs
Verticle Loop Heat Pump

Environmental Effects

Geothermal heat pumps are also fantastic for the environment. These systems emit less greenhouse gases due to there being no burning of fossil fuels. The building’s air quality also improves by using these systems. For example, a 3-ton unit will emit a pound less per hour of carbon monoxide when compared to traditional HVAC systems. Installing 100,000 of these units would be equivalent to planting 120,000 acres of trees (Energy Environmental Corporation). In terms of replacement and requiring maintenance, geothermal heat pump systems have a much longer lifespan. Traditional HVAC equipment has a lifespan around 15 years. For a geothermal system, the indoor components can last as long as 25 years, and the underground loops can last up to 75 years. When factoring in a shorter payback period of five years, the savings are evident.

Image Source: West Michigan Geothermal – Installation Techniques-Commercial
Verticle Loop Heat Pump

These systems are a clear and simple way to reduce emissions and save energy. When looking at the rising costs of electricity and natural gas, the economic benefits become obvious as well. Numerous efforts are underway in academia to make these heat pumps more efficient and cost-effective. As time goes on, these systems will only improve. The time is now to install a geothermal heat pump.

Resources

“Efficiency and Environmental Benefits.” Geothermal Heat Pumps: Environmental Benefits and Efficiency, Energy Environmental Corporation.

An Assessment of Energy Technologies and Research Opportunities. Department of Energy, Sept. 2015.

“Energy Production and Consumption in the United States.” Energy Production and Consumption in the United States | EBF 301: Global Finance for the Earth, Energy, and Materials Industries, Penn State.

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