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. Alton Higgins
    Hiawasse, Georgia
    July 28, 2015, 8:56 pm

    MANY years ago, while living in Michigan, I sunk a 65 ft. deep well, and built my own open loop system, for a 1880s farm house with virtually NO insulation. When it was 20 below outside, I could make it 80 degrees inside!

    Now, (years later), at age 79, our air-to-air system just went belly up, and I wish I could convert to a ground water system. As an electical engineer, I designed all the control and safety features (sense water and air flow, monitor intake and exhaust water temps, etc.), it was the “ultimate” system.

  2. Bill Bryan
    Joliet Illinois
    July 25, 2015, 9:39 am

    Building lake house in spring. Looking for D.I.Y. information. I’m an Electrician with 36 years experience (20 as a contractor) . Hoping to do Trenching & piping myself! Comments & recommendations Apreciated.

  3. Jay Egg
    July 21, 2015, 2:36 pm

    Doug P in Watertown, CT,
    Thank you for taking the time to chronicle your experience for others to read. Experiences like yours are quite common, but when everything is going well, it’s oftentimes the last thing we’re thinking about.
    All the best to you…

  4. DougP
    Watertown, Connecticut
    July 14, 2015, 2:48 pm

    I designed my own home 23 years ago and I specified that we use Geothermal. Hired a great contractor (John Sima – Hydrodynamic Engineering in Southington, CT) to spec the system and install it. It is a closed loop system with two wells serving two separate heat pumps (larger one for downstairs and smaller one for upstairs) to heat and cool a 4,000 sq ft house (3,000 of it is heated and cooled). It has turned out to be an excellent choice.

    After 10 years, a water circulation pump started to leak and had to be replaced (total cost $400.00) and last year the compressor unit in our downstairs heat pump failed (total cost $1,300.00). Those two costs are the TOTAL amount of repairs over 23 years that we have had done with ZERO MAINTENANCE!

    The amount of money that we have saved over the past 23 years has been very significant and back then we did not even have any state or federal rebates or incentives to install it.

    Our units are FHP (Florida Heat Pump) with piston compressors. 3 ton for the downstairs unit and 2 ton for the upstairs unit.

    One thing that should be mentioned is these units work in the Winter and Summer so the units are being exercised year round. A conventional heating system (oil/gas) is used only in the cooler/colder months and sits unused during the summer. A conventional whole house air conditioning system sits idle during the cooler/colder months. Also, when it is 95 degrees outside and you want to cool your house to 75 degrees, you are pushing heat into heat with a conventional whole house air conditioning system. Not so with Geothermal. It uses the coolness of the ground (around 50 degrees) to dump the heat and let it disperse into the ground.

    Therefore, Geothermal uses much less electricity in the summertime to cool a house than a conventional whole house air conditioning unit. In the wintertime, the Geothermal has to “work harder” to heat a house to 70 degrees (20 degrees outside air temp, 50 degrees in the ground) but it is still very economical over a conventional gas/oil furnace.

    The last point is: NO CARBON MONOXIDE! Since Geothermal does not burn anything to generate heat in the wintertime, there is ZERO chance of these units generating ANY Carbon Monoxide inside the house. Read the newspapers in the Fall about houses starting their furnaces up for the season and people getting sick or dying from Carbon Monoxide due to a faulty furnace or flue/chimney.

  5. Jay Egg
    July 10, 2015, 4:15 pm

    John in Madison, WI,
    You are part of a forward thinking group of developers that are doing great things for consumers. Wisconsin has many incentives for going geothermal. This link http://goo.gl/K64Pu3 probably has enough information to keep you busy for quite a while. The website can be further “filtered-down” to include only geothermal heat pumps.
    The Whisper Valley neighborhood in Texas http://goo.gl/O8Mlq4 chose to go geothermal in a community-wide infrastructure, which would probably be the best scenario for your needs. With a community wide loop, the load is shared, and sizing by the home is not as important.
    Still, as with all geothermal projects, use a design firm that is qualified to ensure your project performs at its best.
    Did this answer your question?

  6. Jay Egg
    July 10, 2015, 4:13 pm

    DebiLyn in Baltimore,
    You can certainly heat and cool your home with just geothermal. I’m glad you took the time to write to me. You have a not-too-distant neighbor that I wrote about in this article http://goo.gl/YDn5AL that not only went all geothermal, but NetZero energy and CO2 also. He didn’t choose to go radiant, but wishes he had, because the feeling of warm floors is so pleasant under your feet, and overall.
    If you would like an introduction to the gentleman in the article, let me know and I’ll seek his permission to introduce you two.

  7. Jay Egg
    July 10, 2015, 4:12 pm

    Hilda in Portage La Prairie Manitoba,
    I’m pleased to hear that you have geothermal in your apartment. I’m reasonably certain that the controls may be upgraded if the geothermal system is still competent.
    How old is your system? Perhaps you would like to communicate some details to me and I’ll see if I can supply more specifics. You may email me at jayegg.geo@gmail.com

  8. Hilda Pentney
    Portage la prairie Manitoba
    July 8, 2015, 12:29 pm

    We have geothermal in our apartment and the controls are shot and the owner says he can’t replace them they are outdated. Can the heating registers be replaced

  9. DebiLyn
    Baltimore Md
    July 7, 2015, 2:43 pm

    Hi, I would like to remove my boiler and radiators as well as my traditional A/C and replace them with Geo-thermal heating and air. I own a 1920s row house. I plan on installing radiant floor heating on all three floors. For A/C I plan on mini-split ductless cooling. I have been told the radiant heating will not be enough to heat my home in the winter and I should consider augmenting with baseboard radiators. My goal is to be as “green” as possible. After reading your article, I’m thinking I can heat and cool my home just with the geothermal unit. Would this be safe to say? Thanks!

  10. John
    Madison, WI
    July 6, 2015, 5:49 pm

    P.S. I don’t build the homes but sell the lots to builders so I don’t know what will be built, but I can control through deed restrictions.