Illustration of a geothermal heating and cooling system that handles multiple loads for a community. Illustration by Sarah Cheney.

Illustration of a geothermal heating and cooling system that handles multiple loads for a community. Illustration by Sarah Cheney.

Imagine a home in which the temperature is always comfortable, yet the heating and cooling system is out of sight. That system performs efficiently but doesn’t require extensive maintenance or knowledge on the part of the owners.

The air smells fresh; you can hear the birds chirping and the wind rustling lazily through the trees. The home shares energy with the earth similar to the way the roots of the trees exchange the essentials of life to their leaves and branches. Sounds comfortable, doesn’t it?

Geothermal heating and cooling makes that vision a reality. Geothermal HVAC (heating, ventilating, and air conditioning) brings a building in harmony with the earth beneath, taking advantage of subterranean temperatures to provide heating in the winter and cooling in the summer.

How Geothermal Heating and Cooling Works

Outdoor temperatures fluctuate with the changing seasons but underground temperatures don’t change as dramatically, thanks to the insulating properties of the earth. Four to six feet below ground, temperatures remain relatively constant year-round. A geothermal system, which typically consists of an indoor handling unit and a buried system of pipes, called an earth loop, and/or a pump to reinjection well, capitalizes on these constant temperatures to provide “free” energy.

(Note that geothermal HVAC should not be confused with “geothermal energy,” the process by which electricity is generated directly from the heat inside the earth. That takes place on the scale of utilities and uses different processes, normally by heating water to boiling.)

The pipes that make up an earth loop are usually made of polyethylene and can be buried under the ground horizontally or vertically, depending on the characteristics of the site. If an aquifer is available, engineers may prefer to design an “open loop” system, in which a well is drilled into the underground water. Water is pumped up, run past a heat exchanger, and then the water is returned to the same aquifer, through “reinjection.”

Diagram of how geothermal HVAC systems work

Diagram of how geothermal HVAC systems work. Illustration from Modern Geothermal HVAC

In winter, fluid circulating through the system’s earth loop or well absorbs stored heat from the ground and carries it indoors. The indoor unit compresses the heat to a higher temperature and distributes it throughout the building, as if it were an air conditioner running in reverse. In summer, the geothermal HVAC system pulls heat from the building and carries it through the earth loop/pump to reinjection well, where it deposits the heat into the cooler earth/aquifer.

Unlike ordinary heating and cooling systems, geothermal HVAC systems do not burn fossil fuel to generate heat; they simply transfer heat to and from the earth. Typically, electric power is used only to operate the unit’s fan, compressor, and pump.

A geothermal cooling and heating system has three main components: the heat-pump unit, the liquid heat-exchange medium (open or closed loop), and the air-delivery system (ductwork) and/or the radiant heating (in the floor or elsewhere).

Geothermal heat pumps, as well as all other types of heat pumps, have efficiencies rated according to their coefficient of performance, or COP. It’s a scientific way of determining how much energy the system moves versus how much it uses. Most geothermal heat pump systems have COPs of 3.0 to 5.0. This means for every unit of energy used to power the system, three to five units are supplied as heat.

Geothermal systems require little maintenance. When installed properly, which is critical, the buried loop can last for generations. The unit’s fan, compressor, and pump are housed indoors, protected from the harsh weather conditions, so they tend to last for many years, often decades. Usually, periodic checks and filter changes and annual coil cleaning are the only required maintenance.

Geothermal HVAC Spreads

Geothermal HVAC systems have been used for more than 60 years in the U.S. and beyond.

They work with nature, not against it, and they emit no greenhouse gases. (As mentioned earlier, they use a smaller amount of electricity to run, because they are coupled in with the earth’s average temperature.)

Geothermal HVAC systems are becoming common features of eco-friendly homes as part of the growing green building movement. Green projects accounted for 20 percent of all newly built homes in the U.S. last year. By 2016, a Wall Street Journal article predicted that green housing will grow from $36 billion a year to as much as $114 billion. That’s approaching 30 to 40 percent of the entire housing market.

But a lot of information out there on geothermal heating and cooling is based on outdated information, or outright myths. In our new book Modern Geothermal HVAC Engineering and Control Applications (Egg/Cunniff/Orio -McGraw-Hill 2013), co-authors Greg Cunniff, Carl Orio and I bust many of these myths.

Geothermal HVAC Myths Busted

1.     Geothermal HVAC systems are not considered a renewable technology because they use electricity.

Fact: Geothermal HVAC systems use only one unit of electricity to move up to five units of cooling or heating from the earth to a building.

2.     Photovoltaic and wind power are more favorable renewable technologies when compared to geothermal HVAC systems.

Fact: Geothermal HVAC systems remove four times more kilowatt-hours of consumption from the electrical grid per dollar spent than photovoltaic and wind power add to the electrical grid. Those other technologies can certainly play an important role, but geothermal HVAC is often the most cost effective way to reduce environmental impact of conditioning spaces.

3.     Geothermal HVAC needs lots of yard or real estate in which to place the polyethylene piping earth loops.

Fact: Depending on the characteristics of the site, the earth loop may be buried vertically, meaning little above-ground surface is needed. Or, if there is an available aquifer that can be tapped into, only a few square feet of real estate are needed. Remember, the water is returned to the aquifer whence it came after passing over a heat exchanger, so it is not “used” or otherwise negatively impacted.

4.     Geothermal HVAC heat pumps are noisy.

Fact: The systems run very quiet and there is no equipment outside to bother neighbors.

A technician inspects a geothermal HVAC air handler

A technician inspects a geothermal HVAC air handler. Photo courtesy of Jay Egg

5.     Geothermal systems eventually “wear out.”

Fact: Earth loops can last for generations. The heat-exchange equipment typically lasts decades, since it is protected indoors. When it does need to be replaced, the expense is much less than putting in an entire new geothermal system, since the loop or well is the most pricey to install. New technical guidelines eliminate the issue of thermal retention in the ground, so heat can be exchanged with it indefinitely. In the past, some improperly sized systems did overheat or overcool the ground over time, to the point that the system no longer had enough of a temperature gradient to function.

6.     Geothermal HVAC systems only work in heating mode.

Fact: They work just as effectively in cooling and can be engineered to require no additional backup heat source if desired, although some customers decide that it is more cost effective to have a small backup system for just the coldest days if it means their loop can be smaller.

7.     Geothermal HVAC systems cannot heat water, a pool, and a home at the same time. Fact: Systems can be designed to handle multiple loads simultaneously.

8.     Geothermal HVAC systems put refrigerant lines into the ground.

Fact: Most systems use only water in the loops or lines.

9.     Geothermal HVAC systems use lots of water.

Fact: Geothermal systems actually consume no water. If an aquifer is used to exchange heat with the earth, all the water is returned to that same aquifer. In the past, there were some “pump and dump” operations that wasted the water after passing over the heat exchanger, but those are exceedingly rare now. When applied commercially, geothermal HVAC systems actually eliminate millions of gallons of water that would otherwise have been evaporated in cooling towers in traditional systems.

10.  Geothermal HVAC technology is not financially feasible without federal and local tax incentives.

Fact: Federal and local incentives typically amount to between 30 and 60 percent of total geothermal system cost, which can often make the initial price of a system competitive with conventional equipment. Standard air-source HVAC systems cost around $3,000 per ton of heating or cooling capacity, during new construction (homes usually use between one and five tons). Geothermal HVAC systems start at about $5,000 per ton, and can go as high as $8,000 or $9,000 per ton. However, new installation practices are reducing costs, to the point where the price is getting closer to conventional systems under the right conditions.

Factors that help reduce cost include economies of scale for community, commercial, or even large residential applications and increasing competition for geothermal equipment (especially from major brands like Bosch, Carrier, and Trane). Open loops, using a pump and reinjection well, are cheaper to install than closed loops.

Thanks for the thousands of likes and hundreds of comments!  National Geographic has closed comments for this blog.  Please continue the conversation and get the answers you need for geothermal heating and cooling on Jay Egg’s blog, “Geothermal Heating and cooling Questions and Answers

Jay Egg is the co-author of the new book Modern Geothermal HVAC Engineering and Control Applications (McGraw-Hill 2013), with Greg Cunniff and Carl Orio. He co-wrote the book Geothermal HVAC, Green Heating and Cooling in 2010 with National Geographic’s Brian Clark Howard. Jay consults with the geothermal HVAC industry. He previously served as an installer of the technology through his company EggGeothermal.

Comments

  1. Joey
    Jackson, MI
    January 28, 2014, 1:24 pm

    Jay,

    i am considering purchasing a home that has a geothermal system that was installed in 1982. What is the life expectancy of a geothermal unit that is this old?

    Joey

  2. Jay Egg
    January 28, 2014, 5:39 am

    Betty in Ontario,

    Geothermal heating and cooling systems designs should be set up in a such a way that you always have the heat you need. In the coldest of seasons, if the ground loop is engineered to handle the heating load for less than 100% of circumstances to which you may be subjected (this is done to save up front costs), then a backup heat source should engage, such as electric or gas heat. Since this is more expensive to operate (speaking of the backup heat), customers are sometimes encouraged to limit the difference between set-point and actual temperature in such a manner as you have been advised. Intelligent recovery thermostats can do this through programming, and will alleviate that inconvenience. Energystar.gov has guidelines that I referenced in earlier comments stating basically that, “Adaptive recovery units (thermostats) are constantly calculating the amount of time required to heat or cool the house, so that it reaches that temperature when the homeowner programmed it (without engaging 2nd or 3rd stages such as backup heat). By “examining” the performance of the past few days the thermostat can keep track of the seasons. In this way, your house is always at the comfort levels when occupied, but saving the most energy when unoccupied.” Please let me know if this helped-

    Jay Egg

  3. chris
    el campo tx
    January 25, 2014, 12:12 am

    Ive been in the hvac business for about 10 years.. I know these systems work great.. ive installed countless numbers of them.. my only complaint… coming from the installers side is the fact that they are so heavy. .. other than that they’re great

  4. Betty
    ontario canada
    January 24, 2014, 5:43 pm

    had our geo furnace turned down while we went on vacation.
    what do you set it at? live at sarnia Ontario canada
    Really cold here around the Great Lakes
    then are u suppose to only put it up 2 degrees at a time until
    u get it up to your desired temp
    not real happy with our unit / our house is never hot enough
    any suggestions?

  5. Jay Egg
    New York
    January 17, 2014, 2:56 pm

    Mary in Sacramento,

    On-demand hot water systems interface well with a properly designed geothermal heat pump system. The secret is to tie the geothermal heat pump’s integrated domestic hot water generator into a buffer or holding tank. This buffer tank need not have (and in my opinion, should not have) a heat source. The tank is there to simply store the heated water provided by the geothermal heat pump’s hot water generator. This facilitates the incoming water that goes through the on-demand hot water system already being heated up mostly, or all of the way to the desired domestic hot water temperature.

    Geothermal systems interface well with solar photovoltaic, especially because they reduce the power needed for heating and cooling a structure, which translates into fewer solar collectors and the associated cost savings.

    We will be discussing this in an open forum next week along with other geothermal questions at the AHR Expo in New York City: http://www.phcnews.com/geo.php .Or view it @ https://www.youtube.com/user/tmbpublishing?feature=watch

  6. Mary
    Sacramento, CA
    January 16, 2014, 5:33 pm

    Can a geothermal system interface with an on-demand hot water system, or is the use of a conventional water heater required? I assume such a system could interface with a solar system to supply the electricity needed to run it, correct?

  7. Jay Egg
    Florida
    January 13, 2014, 3:52 pm

    Lonnie in Alberta,
    Perfect! This industry can use young contractors who are ready to enter the geothermal HVAC field, because demand is growing tremendously. I am directing you to the International Ground Source Heat Pump Association (IGSHPA) where you can receive information on the course work that you will need to complete to become a certified Geo Exchange installer/contractor http://www.igshpa.okstate.edu/training/ . Remember, that there are other local mechanical certifications that may be required in your jurisdiction to enter into geothermal HVAC design and installation. IGSHPA in Stillwater, Oklahoma is where I received my training back in 1990. Back then, Dr. Jim Bose (retired now) was teaching much of the class. Now, they have classes held in multiple locations by certified trainers.
    There are a couple of books mentioned in this article that can help as a ready reference: Geothermal HVAC, Green Heating and Cooling and; Modern Geothermal HVAC Engineering and Control Applications. You can find links to those in the body of this article (just scroll up). Good luck!
    Jay Egg

  8. Lonny
    Alberta
    January 13, 2014, 7:55 am

    I am only 30 but have had a fasincation with geo Hvac. I am interested in learning the various methods for installing these systems for the pupose of starting a buisness. Do you know of anywhere a person can become educated as such?

  9. Jay Egg
    Florida
    January 8, 2014, 3:58 pm

    Jeff P in Denver,
    You bet you can e-mail me; anyone can shoot an e-mail to jayegg.geo@gmail.com .
    Properly installed, geothermal heat pumps make fiscal sense in every situation with which I’ve been involved. The payback times vary, and the energy savings are greater than any other heating and cooling technology available. Usually, first cost is the only deciding factor that would ever exclude a Geo. In new construction, the 30% federal tax credit almost offsets the cost of the geothermal loop. And once you have a geothermal system installed in your home, you eliminate outdoor equipment, increase the longevity of your HVAC system, reduce maintenance costs, and will no longer have to be concern about outside noise and equipment issues.
    As far as handling the cold winters, it might be interesting to note that according to the Canadian Geo-Exchange Organization; almost 40% of retrofits in Canada are geothermal heat pumps: and those guys really know cold weather! Here’s that report: http://www.geo-exchange.ca/en/UserAttachments/article81_Final%20Stats%20Report%202011%20-%20February%206,%202012_E.pdf Look at bullet point #6 on page 2.
    Jay Egg

  10. Mike
    Stow,ma
    January 7, 2014, 10:22 pm

    Id love to speak with mjm from stow , we’re thinking about a geothermal HVAC system and being in town any advice/ info would be greatly appreciated.

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