Geothermal Energy for Heating and Cooling


How is Geothermal Energy Used for Heating and Cooling the Home?

Geothermal Energy is potentially the largest source of energy in the United States and the world today. Geothermal Energy comes from deep within the planet itself; and, if properly developed, could match all of the energy available from coal, oil and gas combined.

Cross Section of the Earth

There are two ways that heat is naturally generated from inside the earth – convective heat transfer and conductive heat. Convective heat transfer is the movement of molecules within fluids or gas. Conductive heat transfer is the transfer of thermal energy between neighboring molecules in a substance due to a temperature gradient. It always takes place from a region of higher temperature to a region of lower temperature, and acts to equalize temperature differences. Additionally, the earth’s crust has its own independent source of heat – which is the heat created in the decaying process of naturally occurring radioactive elements present in the earth’s crust and the absorption of heat from the sun.

How does it work?

Solar Absorption

Solar Absorption

Heat Extraction

Heat is extracted from the ground through the use of geothermal heat pumps; also known as ground source heat pumps. The use of geothermal heat pumps provides a highly economical way to sharply reduce the cost of heating and cooling buildings. They make use of common drilling technologies, such as the drilling of water wells, making geothermal technology feasible for both new construction and retrofit scenarios. The operation of the heat pumps is even more efficient because of the added advantage of the relatively constant temperature of the earth. In fact, the earth’s temperature averages 50 °F anywhere from a few dozen to a few hundred below the surface. To be more exact, the earth’s temperature is equivalent to the year-round average air temperature at the surface of each drilling site.

 

Example – Average Temperatures for Boston, MA

AIR TEMPERATURE EARTH TEMPERATURE
Average High (°F) Average Low (°F) Average Year-Round (°F)
January 36° 22° Approximately 50°
July 82° 65° Approximately 50°

 

The relatively constant earth temperatures make geothermal technology naturally efficient for both heating and cooling. It is much easier to raise temperatures from an average 50 °F than to start with outdoor temperatures in the winter months. And, it is likewise easier to cool air temperature if you have a source of fluid (in the ground) at a standard 50 °F.

The Geothermal Process

No matter which design option is used, the process is virtually the same. Although some designs will use water as the transfer liquid, TJ’s recommends the use of a Glycol solution in a closed loop system. The geothermal process for both heating and cooling is illustrated below.

Winter Months

In the winter months, circulator transfer a Glycol solution through the earth loop heat exchanger and the heat pump heat exchanger. As this transfer occurs, it removes the cold temperatures produced by the high-efficiency compressor as it is producing heat for the building.

Conceptual drawing by TJ's Geothermal Technology (A division of TJ's Plumbing and Heating, Inc.)

Summer Months

In the summer months, it is the same process, but in reverse. The circulator transfer a Glycol solution through the earth loop heat exchanger and the heat pump exchanger. As this transfer occurs, it removes the hot temperatures produced by the high-efficiency compressor as it is producing cooling for the building.

Conceptual drawing by TJ's Geothermal Technology (A division of TJ's Plumbing and Heating, Inc.)

 


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Efficiency of Geothermal Technology

The Department of Energy (DOE) and the Environmental Protection Agency (EPA) have both endorsed ground source heat pump systems as among the most energy-efficient and environmentally friendly heating, cooling, and water heating systems available. In a 1993 report, the EPA concluded that geothermal technologies represent a major opportunity for reducing national energy use and pollution, while delivering comfort, reliability and savings to homeowners.

Geothermal systems take one unit of electricity and three units of free energy from the earth, producing four units of heating or cooling, at a fraction of the cost of fossil fuels. In fact, heating efficiencies are 50 to 70% higher than other heating systems and cooling efficiencies are 20 to 40% higher than available air conditioners.

Energy Transfer

 

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Cost Effectiveness of Geothermal Systems

Geothermal systems can be installed in a residential structure of any size, anywhere, whether it is single-family or multi-family. Ground source heat pumps can be installed on almost any size lot: under lawns, landscaped areas, driveways, or the house itself. An existing house can be retrofitted with a ground source heat pump using the ductwork that is already there. Waste heat can be used to heat domestic hot water. And because geothermal systems take advantage of existing technology (e.g. well drilling), it is a cost-effective, feasible alternative to fossil fuels for everyone.

What’s The Next Step?

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