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. Jay Egg
    January 28, 2:46 pm

    Deborah in Southwest Michigan
    It’s an easy choice to go with this home, because the geothermal heat pump is likely only coming up on the halfway point of it’s life expectancy. When it does come time to replace it in the next 15 to 20 years, you will find the job simple because the ground loop will remain intact, making the replacement affordable.
    See if you can get copies of the installation drawings, and history on the energy bills. This will be a good indicator of the performance of the system. There are several different kinds of geothermal loops that may be installed, and depending on the geology at the location, one type may be better performing than another. If you have questions about what you see, email me; I’d love to help evaluate them!

  2. Jay Egg
    January 28, 2:45 pm

    Brain in Denmark,
    Thank you for the evaluation. I can see that you are educated in these items. I think it would be fair to say that the heat pump uses 1 unit of electricity to pump 4 or 5 units of heat into the building, wouldn’t you? I look forward to getting your take on that explanation.

  3. Deborah HallKayler
    Southwest Michigan
    January 18, 7:21 pm

    My husband and I are looking to move to this area full time, from Chicago. When I’m looking at various homes, one in particular is already Geothermal. What sort of questions should I be asking about the system? I believe it was installed no more than 12 Years ago.

  4. Brian Seger
    Denmark
    January 16, 3:15 pm

    Jay,

    You greatly oversimplified #1. The efficiency (electricity/temperature) is a function of what temperature you want your house to be at.

    In #2 Solar and Wind produce electricity which is a much higher value of exergy than heat. Simply put electricity can go 100% to heat (or even higher efficiencies with a heat pump) but heat can not go 100% to electricity because of Carnot efficiency issues. Comparing solar/wind to geothermal heating is like comparing apples to bread. You need both, but comparing them has a greater chance to confuse the general public rather than inform them (in my opinion)

  5. Jay Egg
    January 14, 2:17 pm

    Jared in Alabama,
    Please review the list of accredited installers at this link to the International Ground Source Heat Pump Association (IGSHPA): http://www.igshpa.okstate.edu/directory/dresult.asp . These entities/persons have all completed proficiency training in geothermal installation. As always, you should get at least 3 prices, and check references.
    Please let me know how your search progresses. I’m here to help whenever you need me.

  6. Jared Vaughn
    United States
    January 10, 10:00 pm

    I am in Alabama and I do not believe that there is one single business installing these.

  7. Jay Egg
    December 22, 2015, 11:31 am

    Jason Townsend in Upstate NY,
    I’m so pleased that you are enjoying your new GHP system! Radiant heat is the best, isn’t it?
    I’ve noted that you said there was an immediate jump in electrical consumption. Were you using combustion/gas heat before going to geothermal? If so, what were those charges?
    Since a geothermal heat pump (GHP) is electrically powered, it is typical that you would see an increase in electrical consumption (but a reduction or elimination of fossil fuel consumption). The GHP uses electricity to pump 4 units of heat out of the earth for every unit it consumes.
    I look forward to hearing back, and thank you for writing!

  8. Jason Townsend
    United States
    December 17, 2015, 2:24 pm

    Hi Jay:

    Thanks for the information. We recently installed a 4-ton heat pump (Water Furnace) and installed radiant floor (Roth panels, above floor) in a 2000 sq. foot log cabin.

    We like the heat, and feel so far, but electricity consumption immediately jumped 40-50 kwh per day…this seems high to us. We are in upstate NY, experience a harsh winter most years, but so far avg. temp has been only 41 F.

    Can you advise as to what to expect in terms of electricity consumption with this system?

    Thanks!

  9. Jay Egg
    November 30, 2015, 5:14 pm

    Deborah in Maryland,
    I am so glad that you stumbled on this blog! There are many good geothermal contractors in the Maryland/DC area. If you are in need of further assistance in your pursuit, check out the industry website at http://www.igshpa.okstate.edu/directory/directory.asp for a design professional near you. You may feel free to email me at jayegg.geo@gmail.com anytime for further guidance.
    I will be near you later this week as I provide industry updates to the DOE in Washington DC on December 3rd. I always love visiting our Nation’s Capital!