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.

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. Kent
    Missouri
    January 24, 5:00 pm

    Jay,

    Do they make system that use both HVAC adn Radaint Heat?

    Kent

  2. karlez
    January 22, 4:01 pm

    My system is running like a champ and I haven’t had any problems

  3. Jay Egg
    January 20, 8:21 am

    Joe in DeWitt, IA,
    I’m pleased to hear that the geothermal system you installed ran so well last summer; that is typical of what I hear with regard to geothermal performance.
    The winter time performance relating to noise and continuous fan operation is likely a result of settings on the control board inside the geothermal heat pump (GHP) unit. In these settings, there are selections available to the installer to determine the CFM of the fan in different modes, as well as many other determinations, such as pump and DHW (domestic hot water) operation. I recommend that you call the installing contractor and ask them to adjust the settings accordingly.
    Please let me know if this helped you.

  4. Jay Egg
    January 20, 8:20 am

    Al in MA,
    Thank you for taking the time to review your service history.
    You have keyed in on some important factors; insulation of the home is the number one item that can help to reduce energy consumption in most cases. Second is the reduction of energy consumption, and with HVAC as the greatest consumer of energy in most homes, installation of a geothermal heat pump (GHP) system is the best choice. Even with the significant reduction in energy consumption by going GEO, most will still find the heating and cooling to be among the greatest of energy consumers in the home.
    I’m impressed that you have decreased your electric bill to below $100; I’m certain you are implementing a lot of good energy habits to make that happen. With your GHP and ground loop operating correctly, the electricity consumed will be less than the cost of fossil fuel equivalent to heat, so whatever you do, stay with the geothermal heating. You mentioned “hydro air”; I am thinking that you are speaking of radiant heating, which is fluid based, and a “water to water” GHP will be the best choice to make that happen. Please let me know if I understood that part correctly?

  5. Jay Egg
    January 20, 8:18 am

    Doug in Sullivan, IL,
    Thank you for your post. Geothermal (ground-sourced) heat pumps can be designed to work flawlessly for the entire winter, providing all of the heating needed for a building of any size. The key is in putting in the “right sized” and designed exchanger to extract the heat from the earth at the same rate as the earth is able to replenish the heat. A thermal conductivity test should be done to determine this rate of transfer, and then the linear feet of exchanger and borehole are designed accordingly. When a GHP heats a home adequately for a period of time, then loses its capability to heat adequately, that means that something with regard to the design of the ground heat exchanger is insufficient for the heating load. This could even be something as simple as one or more of your vertical wells not circulating water, an issue that can be checked and remedied in a variety of ways.
    My recommendation is to review this information with your contractor or designer and see what can be done to bring your system into alignment with the heating load of the home. Please feel free to email me directly or check with IGSHPA http://www.igshpa.okstate.edu/directory/directory.asp for other designers in your area that may be able to give a second opinion on the heating concern.

    Please let me know if this has helped you?

  6. Joe Paricka
    DeWitt, IA
    January 15, 12:56 pm

    I put in a Geo Thermal system this past summer. I ran the fan on continuous and it was whisper quiet during the summer months. However, during the winter the fan is significantly louder ever when the outdoor temps are in the 20’s and 30’s. Also, I switched the fan over to auto and it never goes off when the temp is reached.

  7. Al
    Massachusetts
    January 15, 9:57 am

    This is for a response from my posting of June 9, 2014, 10:12 am and you requested a follow up.

    I did contact Northeast Geo. Had a good conversation with them.
    They remembered the contractor who installed my system and not surprising that most of the staff didn’t consider him much of a professional. (He stubbornly refused all help and probably could have avoided all of the issues in the first place)

    So the situation boils down to lack of insulation n the attic. So I added more and not really sure it has made much of a different.

    I am thoroughly convinced after all of these years that Geo should only be installed in new modern houses that are properly insulated. And i don’t mean that old Pink Panther obsolete crap but the house should be foamed out.

    We have lowered our thermostat down to 64 (down from 70 last year). I also went through the entire house and removed any outdated bulbs and replaced with LED. Everything is shut off when not needed.

    This October I actually lowered my electric bill below $100 ($99) for the first time in 2 years.

    I purchased a TED (The Energy Detective) and added it to my electric panel so I can monitor my KWH to try and understand where the energy consumption is coming from. The GEO system is pulling in about 5K of KWH when running.

    So I believe this is the energy beast.

    National Grid, our electric supplier has increased supply costs by 37% starting in November. So regardless of how much we lower our electric consumption you can’t avoid the increase. Starting in the summer there will be an additional $50 per month added as well.

    So this makes running the GEO very costly in my opinion.

    When I installed the system costs per KWH was .07, now it’s .16. Doubled and of course it’s 37% per month more.

    I am looking to supplement the system with something that will heat the house ONLY (hydro air?) and then in the summer use the GEO for AC only.

    Remember that I have disconnected the backup heating system on the GEO (electric backup) so this doesn’t play a factor in the cost.

    Regards Al

  8. Doug Reeder
    Sullivan, Illinois
    January 14, 3:53 pm

    The GHP system was installed in late fall, but the plumber pulled off the job before he hooked up the backup (natural gas) to the system. When I speak of the backup, I mean the heating source that has to supplement the GHP when the outside temperature falls below a certain point where the GHP can not adequately heat the house. As construction on the house continued, we ran the GHP and it was able to heat the house adequately for several weeks. Then the outside temperature fell to 0 to 10 above zero for a week or 10 days. The GHP could no longer keep up with the heat load and was calling for emergency heat. We called the plumber (we had been trying for weeks to get him to complete the job) and he came out an hooked up the backup natural gas on a temporary basis. The system is now running exclusively on natural gas. My understanding is that the GHP depleted the heat in the 5 vertical wells, because the system was run exclusively on geothermal without any backup. We are now waiting on the heat from the earth in the 5 wells to replenish and the plumber to permanently hook up the natural gas back up to the GHP system.

  9. Greg
    Colorado
    January 13, 11:04 pm

    Jay,

    I’ll have a look at the book. I’ve found a couple of radiant cooling options (ceiling-mounted cooling panels) online. The problem is that to do heating and cooling will require not only the heat pump, but also the floor distribution system plus the ceiling system, thereby making the cost pretty high.

    Cheers,
    Greg