Geothermal

Soil temperature varies based on solar radiation, rainfall, air temperature, vegetation type, the type of soil, and the depth of the soil itself. The average soil temperature at 30-50 foot depth in Ohio is between 50°F - 55°F.18 With the use of geothermal heat pumps, also known as ground source heat pumps, Ohio residents can harness this constant temperature for heat transfer to and from a home’s outdoor heat pump unit. In short, heat pumps operate by transferring energy from outside of the house, and using that energy to condition a home’s interior space. This process can be more difficult for air-source heat pumps when the temperature of the air outside is very hot or very cold, leading to more inefficient operation, and increased operational costs. Geothermal systems solve this problem by having a constant ground temperature for the heat pump to always use, resulting in more efficient operation and reduced space conditioning costs.

U.S. Ground Temperatures

Geothermal heat pumps use 40%-70% less electricity compared to conventional heating and cooling systems. The EPA estimates that geothermal units reduce energy and carbon emissions up to 44% compared with air-source heat pumps and 72% compared to standard electric heating and cooling units.8

To learn more about the basics of geothermal heat pumps, visit the Department of Energy’s “Geothermal Heat Pumps” webpage. 

Geothermal System Types

In Ohio, typical ground source heat pumps utilize heat transfer between the ground and piping that is buried underground in a series of loops. These systems are referred to as closed loop systems. Alternatively, some systems pump ground water through a heat exchanger in the home and then discharge the water back into the ground to accomplish a similar effect as the previously described piping systems. These systems are referred to as open loop systems, which are not typically used in residential houses and are highly regulated.3

Closed loop systems use a heat transfer fluid that is pumped through a loop or multiple loops of piping placed in the ground, and eventually back into the heat pump heat exchanger in the home. Closed loop systems can be oriented vertically or horizontally depending on a home's available space, ground conditions, as well as your contractor's ability.7

  • Vertical loops are better for projects that aim to reduce the impact on the existing landscape, and are typically used with smaller properties. However, vertical loops tend to be more expensive to install, and can be more difficult to repair if damage occurs deep underground.
  • Horizontal loops require more land, but are cheaper to install since they do not require well drilling, and may be easier to maintain in the case of damage. Horizontal loops typically disturb the land more dramatically than vertical loops since they require a larger area, though the disturbed area should regrow in a couple of months following the proper installation.

Geothermal Closed Loop System

Open loop systems pump groundwater to the house for heat transfer and discharge the used water into a separate return well or surface water reservoir. If you are considering an open loop system, be sure to check with local and state codes, as many states do not allow such systems to be built.7

Geothermal Open Loop Systems

Geothermal Components

Geothermal heat pump units consist of four major components: a heat pump, geothermal loop piping and pump, ductwork, and desuperheaters.

Heat pump

provides compression and expansion of refrigerant in the heat pump loop. The heat pump transfers heat to and from the house to the geothermal system.2

Geothermal Piping and Pump

carries a heat transfer fluid (the working fluid) to the ground. High density plastics are often used for the piping material. In vertical systems, contractors typically put a material called grout around the pipes, which is more thermally conductive than soil and aids in heat transfer between the system and the ground.1

Ductwork

distributes the conditioned air from the heat pump to the home similar to conventional systems.

Desuperheater (optional)

heat exchanger that heats water for your home when extra heat is available in the geothermal system, to provide free hot water during the summer months. It does so by passing the heat through the water heater and compressor before expelling it to the ground.

By contacting a contractor, you can learn more about what system may be right for you.

Geothermal Flow Diagram

Geothermal Efficiency

The heating efficiency of the geothermal unit is based on the efficiency of the heat pump, which is typically evaluated using Coefficient of Performance (COP). A COP greater than 4.6 or 3.6 are considered energy efficient for open loop and closed loop geothermal heat pump systems, respectively. The cooling efficiency of a geothermal unit is based on the Energy Efficiency Ratio (EER), the ratio of heat removed to the electricity required to operate the heat pump. A EER greater than 20.0 or 16.0 are considered energy efficient for open loop and closed loop geothermal heat pump systems, respectively.2,9

Most high performance geothermal heat pumps voluntarily use the ENERGY STAR® label on their equipment to display their efficiency compared to other efficient systems. To earn this label, geothermal systems must adhere to EER and COP requirements for specific geothermal system types. Learn more about their rating system at Geothermal Heat Pumps Key Product Criteria by ENERGY STAR®.

Energy Savings and Payback Period

According to homeadvisor.com, a geothermal heating and cooling system typically ranges from $3,474 - $12,655, depending on the complexity of the design. This leads to a payback of 2-10 years depending on the type, size, and efficiency of the system, your location, and incentives available. To get a rough estimate for your potential system, you should check out the the following links in the resource section. 13,14,15

Additionally, some mortgages provide special "energy-efficiency mortgages," which will further reduce the costs of retrofit projects. Contact your bank or mortgage company for more information.

Contact a Contractor

Geothermal heat pump systems are complex, and are certainly not a do-it-yourself project. You will need to contact a contractor to assess your site. Contractors will design a geothermal system based on your heating and cooling loads, soil type, hydrology, land availability, and other factors.

You can find geothermal heat pump contractors by contacting your utility company, the International Ground Source Heat Pump Association, the Ohio Geothermal Directory, or the Geothermal Heat Pump Consortium.

 

Resources

 

  1. "Geothermal Heat Pump Loop Fields" by geothermalgenius.org - Geothermal background information related to piping and system types.
  2. "Choosing and Installing Geothermal Heat Pumps" by the Department of Energy - Dicussion of efficiency, economics, site evaluation, installation, and benefits of geothermal heat pump systems. 
  3. "Geothermal Heat Pumps" by the Department of Energy - Introduction to geothermal system types. 
  4. "Geothermal Energy" by alternative-energy-tutorials.com - Introduction to various geothermal energy sources including a discussion of advantages and disadvantages of the technology. 
  5. "Geothermal Directory" by geothermal-directory.com - List of contact information for geothermal companies located in Ohio. 
  6. "Geothermal Heat Pumps Key Product Criteria" by Energystar.gov - Energy efficiency requirements for ENERGY STAR® rated getoehrmal heat pumps. 
  7. "Recommendations for Geothermal Heating and Cooling Systems" by Ohio Water Resources Council - Information about geothermal heating and cooling system best practices, siting, construction, and decommissioning for open loop and closed loop systems. 
  8. "Geothermal Heating and Cooling Technologies" by the United States Environmental Protection Agency - Introduction material for geothermal heating and cooling, including project resources. 
  9. “Geothermal Heat Pump Systems” by Curtis J. Klaassen P.E. - PowerPoint introduction into geothermal heat pump technology, discussing pros and cons, applications, and economics of implementing geothermal systems. 
  10. "Small Scale Geothermal" by Casey, Nicholas, University of Iowa - Introduction to small scale geothermal applications, with a discussion of economics and advantages & disadvantages of small scale systems. 
  11. "Database of State Incentives for Renewables & Efficiency®" by NC Clean Energy Technology Center - Policy and incentives for renewables for all states. 
  12. "Ten Myths About Geothermal Heating and Cooling" by Jay Egg, energyblog.nationalgeographic.com - Discussion of geothermal technology myths. 
  13. "Geothermal Calculator" by geothermalgenius.org - Site specific geothermal heat pump cost analysis tool.
  14. "By the Numbers - Real Results of a Home Geothermal Installation" by geothermalgenius.org - Cost analysis of a case study in Pennsylvania. 
  15. "How Much Does it Cost to Install a Geothermal Heating or Cooling System" by homeadvisor.com - Reported low, average, and high costs based on cost data for geothermal heating and cooling systems.
  16. "Geothermal Directory" by International Ground Source Heat Pump Association - Global geothermal directory. 
  17. "Geothermal Directory" by geoexchange.org 
  18. "Ground Temperatures as a Function of Location, Season, and Depth" by builditsolar.com - Discussion of soil temperature. 

Image sources

  1. http://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm 
  2. epa.ohio.gov/portals/28/documents/sccgw/GHCS.pdf 
  3. epa.ohio.gov/portals/28/documents/sccgw/GHCS.pdf
  4. https://wiki.uiowa.edu/display/greenergy/Small+Scale+Geothermal