Geothermal heat pumps (GHPs), also known as ground-source heat pumps, are similar to ordinary heat pumps, but use the thermally stable mass of the earth below the ground instead of outside air to provide heating, air conditioning and, in most cases hot water as well. Because these systems use the earth’s natural reservoir of stable temperatures, they are among the most efficient and comfortable heating and cooling technologies around. GHPs can save substantial amounts of energy and significantly reduce peak demand in buildings that incorporate them.

Geothermal Heat Pumps Can Save Lots of Energy

ENERGY STAR qualified geothermal heat pumps use about 30% to 40% less energy than a standard heat pump and are also quieter than conventional systems. Approximately 70% of the energy used in a geothermal heat pump system is renewable energy from the ground. The earth’s constant temperature is what provides this renewable “source” of energy. Below a relatively thin layer of ground the temperature of the earth remains very stable changing very little even when air temperatures swing between freezing winter cold and blistering summer heat. This stability is exploited by GHPs using only a relatively small amount of energy to pump a heat exchange fluid, which may be water but is often a heavy brine, through the earth source loop and then through the building heat exchange. Ground sourced heat pumps draw in heat during the winter and “coolnes” in the summer. They are one of the most efficient, comfortable, and quiet heating and cooling technologies available today.

When GHPs are equipped with a device called a desuperheater they can also be used to heat household water, which is circulated back into the regular water heater tank. Systems that are equipped with a desuperheater can provide for all of the household hot water needs during the summer months and about half of the hot water heating needs during the winter months.

According to a recent DOE report on geothermal heat pumps Geothermal (Ground-Source) Heat Pumps: Market Status, Barriers to Adoption, and Actions to Overcome Barriers, produced by the Oak Ridge National Laboratory for the Department of Energy and published in December 2008, GHP’s have the potential to help our nation address our future energy security challenges through saving vast amounts of energy and avoiding the need for massive quantities of new capacity.

“If the federal government set a goal for the U.S. buildings sector to use no more nonrenewable primary energy in 2030 than it did in 2008, based on previous analyses (updated and summarized in this report), it is estimated that 35 to 40 percent of this goal, or a savings of 3.4 to 3.9 quads annually, could be achieved through aggressive deployment of GHPs.”

“GHPs could also avoid the need to build 91 to 105 GW of electricity generation capacity, or 42 to 48 percent of the 218 GW of net new capacity additions projected to be needed nationwide by 2030. In addition, $33 to 38 billion annually in reduced utility bills (at 2006 rates) could be achieved through aggressive deployment of GHPs.”

Think about this last figure… 91 to 105 GW of new power plant capacity can be avoided by aggressively pursuing earth sourced heat pumps. That is staggering figures… imagine 100 large thermal electric power plants each delivering enough electricity to power a medium sized city. Translating the energy savings figure from quads into a more graphic equivalent will stagger the mind… That is like saving somewhere around 30 billion… yes billion… gallons of gasoline per year; or to look at it another way 120 to 140 million tons of coal per year.

These massive energy savings are made possible because GHPs exploit the fact that the ground is always cooler during the summer and always warmer during the winter. According to the American Physical Society’s report How America can look within to achieve energy security and reduce global warming, “Today’s GHPs move 3 – 5 times as much energy between the building and the ground than they consume while doing so. If there were sufficient motivation, the GHP industry could integrate the most advanced commercially available components into their heat pumps and increase this multiplier effect to 6 – 8, and theoretically the multiplier could be as high as 14.”

The US Has Fallen Behind Other Nations, but May Be Positioning Itself for Rapid Growth in this Sector

The US used to lead the world in this technology, but as in so many areas of renewable technology we have fallen behind other nations in Europe and Asia that have pursued this eminently practical energy saving technology more effectively than has our own country. America still leads the world in terms of its total installed base of geothermal units, but has been losing ground in terms of annual number of new units installed.

Tax credits for home and business owners investing in GHP systems were enacted in October 2008 through 2016. The government is offering a 30% tax credit with no upper limit to promote various renewable energy and energy efficiency property improvements on new or used construction. This very generous tax credit extends to geothermal heat pumps. For more information on these tax credits see the Energy Star information page: Federal Tax Credits for Energy Efficiency In addition to this federal program a growing number of states are also offering their own incentives to install geothermal heat pumps into existing and new construction.

One of the main impediments for growth in the number of GHP installations according to the report on GHP by the Oak Ridge National Laboratory is in their words, “The primary GHP market failure is the expectation that building owners finance the ―GHP infrastructure, or outside-the-building portion of the GHP system, such as the ground heat exchanger. GHP infrastructure will outlive the building and many generations of heat pumps, and is akin to utility infrastructure (poles and wires, underground natural gas piping). This begs the question ─ why do we expect building owners to finance GHP infrastructure, but not other utility infrastructure? The outside portion of the GHP system can be half or more of the overall GHP system cost, and if this cost is excluded, GHP systems have about the same price as competitive alternatives and could cost less in volume production.”

How Much Do Geothermal Heat Pumps Cost Up Front and How Long Before They Pay for Themselves

As a general rule of thumb GHP units cost around twice what conventional heating and cooling cost. The cost of drilling the ground source loop needs to be added to this total amount. The cost of installing the ground source loop depends on whether the ground source loop is a vertically oriented one drilled deep underground or will be installed in a horizontal manner a short distance below ground, but over a wide area. By far the largest upfront cost of GHP systems is in fact the cost of drilling or conversely the cost of digging up a relatively large area of ground to bury the loop if it is in a horizontal orientation. The drilling cost can run anywhere from $10,000 to $30,000, or more depending on the terrain and other local factors.

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An efficient geothermal system saves enough on utility bills that the initial investment can be recouped in five to ten years. The underground piping used in the system is often guaranteed to last 25 to 50 years and is virtually worry-free.

Geothermal Heat Pumps Are the Low Hanging Fruit of Renewable Energy

Buildings are built on the ground below; the only exception I can think of is over the water structures such as on piers or floating structures such as house boats. Furthermore in almost all cases the ground is cooler than outdoor air in summer and warmer in winter. Geothermal heat pumps exploit this energy gradient, which is the thermal stability of the earth, to provide the only renewable energy resource that is available at every building’s point of use.

GHP sourced heating and cooling energy is always available on-demand unlike other renewable energy sources such as solar or wind that are subject to weather and may not always be available. It is a renewable energy source that cannot be depleted, assuming the GHP system is properly designed and is one that is potentially affordable across the nation.

GHPs may be among the most affordable and widely deployable renewable energy resources available, especially if the investments in electrical transmission, storage etc. that will be necessary to deliver many of the best wind, solar, and geothermal power generation resources to market are factored in to the costing equations.

Correction: In the original article I stated that air is pumped through the GHP outer earth buried loop. Strictly speaking this is not the case for GHPs, which use a liquid heat exchange fluid that may be water, but often is a heavy brine. Earth tubes, which operate on the exact same principles as GHPs, however do draw air through a buried outer loop network of tubes and there is an understandable confusion between GHPs and Earth tubes because they both exploit the same phenomena and operate in much the same manner. Thanks Gary for bringing this to my attention [see comments section] Corrected on 12/1/09.

© 2009, Chris de Morsella. All rights reserved. Do not republish.

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Author: Chris de Morsella (146 Articles)

After a decade performing as a lead guitarist for rock bands, Chris de Morsella decided to return to the career his uncle mentored him in as a youth....Software Engineering. Since that time he has thrown himself into his work. He has designed a compound document publishing architecture for regulatory submissions capable of handling very large multi-document FDA regulatory drug approval submissions, for Liquent, a division of Thompson Publishing. At the Associated Press, Chris worked with senior editors at facilities around the world, to develop a solution for replacing existing editorial systems with an integrated international content management solution. He lead the design effort at Microsoft for a help system for mobile devices designed to provide contextual help for users. Chris also helped to develop the web assisted installer for LifeCam2.0, the software for Microsoft’s web cam and developed late breaking features for the product He also served with the Rhapsody client team to redesign and build a major new release of Real Networks Rhapsody client product. His most recent assignment has been Working with the Outlook Mobile Time Management team for the next release of Outlook Mobile for the SmartPhone. Chris' interests are in green building and architecture, smart grid, the cloud, geo-thermal energy, solar energy, smart growth, organic farming and permaculture. Follow Chris on Twitter.

  • http://energystimulus.net Nolan

    I think it is fantastic how the stimulus funds are making a difference. They are being taken advantage of all the time with the installation of geothermal heat pumps to replace high energy heating and cooling systems.

    • http://www.cn-skysea.com Jason

      Support GHP system.

  • David White

    I was very enthusiastic about geothermal systems for a long time, until I saw a few very bad numbers for performance and high costs (about four times as much as a standard gas boiler). I looked around more, and was disappointed to find almost no real studies of actual performance of geothermal systems in the US, but did find one good summary of several field studies totaling over 100 installations in Germany (Feldtest Elektro – Wärmepumpen: Nicht jede Wärmepumpe trägt zum Klimaschutz bei Erfassung der Leistungsfähigkeit von Elektro – Wärmepumpen unter realistischen . Betriebsbedingungen am Oberrhein) The study found an average COP of 3.5. In Germany engineers can be sued for oversizing systems, and I suspect that US geothermal systems do not fare as well as the German systems. But assuming a COP of 3.5, if a geothermal system uses conventional electricity, it is only performing about 15% better than the best condensing gas boiler technology.

    The only advantage I see is that geothermal can be powered with renewable electricity. But so can mini-split air source heat pumps, which are mass produced and therefore far more predictable and reliable in their performance. They may not perform quite as well as geothermal, but a single-point ductless split, which can heat an entire superinsulated single family home, costs $4000.00 installed.

    • http://greeneconomypost.com Chris de Morsella

      David you raise a valid concern about geothermal heat pump systems, especially for regions that have rather mild climates. For climates with moderate heating and cooling needs, heat pumps offer an energy-efficient alternative to furnaces and air conditioners and the extra cost associated with the ground source loop is not warranted. The coefficient of performance (COP) of the most efficient air-source heat pumps is typically about 3.3, which as you point out is close to the slightly higher 3.5 efficiency achieved by current ground sourced heat pumps.

      COP is an acronym for coefficient of performance for those who may not be familiar wwith the term. The COP of a heat pump is determined by dividing the power output of the heat pump by the electrical power needed to run the heat pump, with both powers measured using the same units, e.g. watts. The higher the COP, the more efficient the heat pump.

      From what I understand the efficiency of air sourced heat pumps goes down as temperatures drop. I experienced this first hand while living in an apartment in Philadelphia that was heated by a heat pump. It worked fine as long as the outside air temperature was above 40 degrees (F), but if the outside air temperature got any colder (and being Philly it did) the heat pump labored away (consuming electricity) bu produced little heat.

      Essentially, the COP of air sourced heat pumps decreases with temperature because it is more difficult to extract heat from cooler air. The efficiency of most air-source heat pumps as a heat source drops dramatically at low temperatures, generally making them unsuitable for cold climates. Ground sourced heat pumps avoid this rapid drop in energy efficiency, because their heat source is very stable and close in temperature range to the what needs to be achieved. As soon as the outside air temperature drops much below 40 degrees (F) this difference in energy efficiency becomes pronounced.

      I would be interested in hearing your thoughts on this and want to thank you for emphasizing what is a valid concern about geothermal heat pump systems… that at least in relatively mild climates the extra cost of the external ground loop necessary for these systems may not be warranted and efficient air sourced systems can achieve comparable efficiencies at a much lower up front capital cost.

      • http://www.cn-skysea.com Jason

        100% agree on your comment. Application of heat pumps is depending on the annual ambient temperature. When the annual ambient temperature varies too much from 38 degC hot to -10 degC cold, GHP is no doubt the best selection under the condition that you do consider renewable energy is of the first priority compared to conventional heating and cooling method since the outside loops constuction is quite expensive to the GHP system iteslf. However, if the annual ambient temperature is mild all year round, a high efficiently air source heat pump will be enough and can reach the same effect.

    • http://www.virstar.com/ Gary L Maedl

      To David White:

      Your statements put forth many misconceptions regarding Geo (Ground Source Heat Pumps) that I would like to set straight.

      1. You wrote: I was very enthusiastic about geothermal systems for a long time, until I saw a few very bad numbers for performance and high costs (about four times as much as a standard gas boiler).

      The installation of a properly designed and priced Geo system should cost about 2 times as much as a high efficiency (>95%) gas fired boiler. The cost for Geo is reduced by 30% with the Federal Tax Credits.

      2. You wrote: …was disappointed to find almost no real studies of actual performance of geothermal systems in the US….

      The US Department of Energy (doe.gov) has many documents published on Geo (Ground Source). Most electric utility companies also have extensive data for homes heated/cooled with Geo in their area. Public Service of New Hampshire, for example, has data for hundreds of Geo homes for many years.

      3. You wrote: …I suspect that US geothermal systems do not fare as well as the German systems…

      I specify Hydron Module (made in South Dakota) GSHP equipment for all of the projects that I design. Both Water Furnace and Climatemaster manufacture fine GSHP equipment and both are made in the USA. All three of these manufacturers offer GSHP units that have COP’s ranging from 4.1 to 5.1 with 32°F closed horizontal loop source water, and much higher COP’s if using vertical loop source water (42-52°F). In addition, I just replaced a Hydron Module unit for a customer that has run his unit non-stop for over 25 years without problems. The unit was still running, but he wanted to have the higher efficiencies of today’s equipment.

      4. You wrote: …assuming a COP of 3.5, if a geothermal system uses conventional electricity, it is only performing about 15% better than the best condensing gas boiler technology…

      It is misinformed comments like this that cause so many people in the world to be confused instead of working together to reverse the buildup of CO2 in our atmosphere.

      The BEST condensing gas boiler technology has between 92-97% efficiency. Even if they had 100% efficiency, they would not compare to Geo systems.

      COP is the ratio of the Heat Energy produced and the Energy is takes to create that heat energy. For a 97% efficient condensing gas boiler, which produces a max of 97,000 BTUs for every Therm (100,000 BTUs) of gas it consumes, its COP is equal to 97,000 / 100,000 = 0.97 COP. Straight resistance electric heat, the most expensive heat you can have, has a COP = 1.0.

      A Hydron Module H050 (2008 model) water-to-air GSHP has a COP = 4.17 with a 50°F, 9.6 GPM source loop (including pumping penalties). This is 5.96 TIMES as efficient (4.17 / .97) as the best gas condensing boiler, or 330% More Efficient ( [4.17 – 0.97] / 0.97 ).

      As for cost comparisons, the average 2008 USA price for natural gas was $1.33 / therm, and $3.33 / therm for electricity. So, to produce 1 Therm (100,000 BTU) of heat for your home (or about 2 hours of heat for a 2,000 sq.ft. well insulated home on a 0°F day), it would cost you $1.37 in gas (COP = 0.97) and it would cost you $0.798 in electricity (COP = 4.17). Therefore, with these average pricings, the Geo system costs 41.7% less to produce the same amount of heat.

      Most importantly, assuming that the electricity is produced 100% with fossil fuel power plants (which it is not), the Geo system has only 23.2% of the carbon footprint as does the gas fired boiler. And as more and more renewable energy sources (wind, solar, nuclear, etc.) generating electricity come on line, this percentage will only drop in the future.

  • Gary L Maedl

    To Chris de Morsella:

    You wrote: This stability is exploited by GHPs using only a relatively small amount of energy to pump air through the earth source loop and then through the building heat exchange.

    GHP or GSHP systems pump WATER through the earth source loop, not air. Otherwise, the article is excellent.

    • http://greeneconomypost.com Chris de Morsella

      Gary ~ Thanks for clarifying this. The term Geothermal Heat Pump does refer to ground coupled heat exchange systems that employ a liquid heat exchange (often a brine liquid, i.e. heavily salted water). At first I was going to rebut this, because I know that many dual loop heat exchange systems exist and are in wide use that DO in fact use air, but as I researched the matter you are correct and I will update the article to reflect this.

      However, it is also true that many GHP-like ground-coupled heat exchanger systems exist that DO in fact use air — pumped through a buried outer loop of piping. These systems, commonly called Earth Tubes and widely used around the world exploit the same stable median temperature thermal mass of GHPs and in principle operate in the same way. My approach to this eminently sensible sustainable building architecture/engineering and building technology occurred many years ago when I first became excited by earth tubes. Earth tubes are very closely related to Geothermal Heat Pumps and I would argue that they are in fact a type of GHP, in that they operate on precisely the same principles.

      But again I want to than you for clarifying this because it thinking about it there are a few other key differences. With earth tubes the air mass that is drawn through the buried tubes — gaining or losing heat in the process, depending on whether it is colder or warmer in the outside ambient air — is typically circulated through the inner environment; while in a GHP only heat is exchanged.

      Earth tubes — or the idea of using the stable thermal mass that exists below the topmost layer of earth to cool and heat a structure by drawing air through buried tubes — has been around for thousands of years, with examples dating back to the Persian empire. Properly designed earth tubes can even be passive in many cases, especially when coupled with solar chimneys that heat exhaust air creating a vacuum that draws cool air in through the buried network of earth tubes.

      An important design consideration with earth tubes is to use a large diameter piping and to keep the earth area that is being used as the thermal sink and in which the tubes are buried as dry as possible. Tubes should also avoid 90 degree angles as this lowers the efficiency of the airflow through them.

      GHPs and Earth Tubes are very closely related and operate on the same principle, but they do have some important differences.

      • http://www.virstar.com/ Gary L Maedl

        Hi Chris,

        I am familiar with Earth Tubes. I typically use them on commercial projects to pretreat the fresh air that I am pulling into the building. With the latest LEED and ASHRAE fresh air per person numbers being so high, it is vitally important to pretreat fresh air intakes (in combination with HRVs and ERVs) to minimize the energy costs for HVAC systems.

        The only reason that I commented on your Geo description using air is that this might only confuse people who are just starting to learn about Ground (water) Source Heat Pumps. And more confusion is the LAST thing that we need.

        • http://greeneconomypost.com Chris de Morsella

          Gary — you are right the last thing this sector needs is more confusion . I would love to hear more on your practical field experience using these technologies. What kinds of problems have you run into? How have you “sold” clients on the benefits that GHP & Earth Tube systems offer? Is it getting easier to justify these systems to the suits as more developers and building owners become aware of the philosophy and benefits of sustainable building?

          Getting adequate fresh air flow into the inside environment of buildings is one of those unavoidable trade-offs faced by those designing and constructing sustainable buildings and — as I am sure you are aware of — has been a stubborn problem with many early attempts at energy efficient buildings that essentially sealed the structures up and overly limited fresh air flow with deleterious consequences for indoor air quality in these buildings. It is certainly challenging to provide adequate airflow without losing too much heat energy (or gaining heat during the summer). Earth tubes seem like a natural design element that can pretreat fresh ambient air before it is flowed into the building space. Do you also use heat exchangers on the exhausted air that is being vented out of the structure to recover some of its thermal energy/coolness in order to maximize overall energy efficiency?

  • Gary L Maedl

    Chris- The main problem has always been “first cost”. I installed my first Geo system in 1978, and the cost was over two times as expensive as a conventional HVAC system, just as it is today.

    The only way to “sell” Geo systems, super insulation, HRV/ERV units, and earth tube fresh air feeds is to do the math for the building owner. If the owner is someone who is interested in the long term cost of ownership, then the cost savings speak for themselves.

    As you stated above, when the buildings are made tighter to save energy, the air quality quickly goes downhill. This is where the earth tube fresh air feeds used in combination with HRVs or ERVs deliver a cost effective solution. As you well know, it is impossible to deliver the right amount of fresh air without tempering the air on the way in and recapturing its energy on the way out.

    • http://greeneconomypost.com Chris de Morsella

      “First cost” or the upfront capital outlay is a major obstacle for many other green technologies from other renewable energy systems such as wind and solar to building retrofits to increase energy efficiency and so on. Geothermal heat pumps also are faced with this upfront capital sticker shock barrier that is difficult in many cases to overcome. I think you give good advice about the need to educate the owners on the long term payoff and other benefits of installing these systems.

      I am following several innovative financing programs — the city of Berkeley, CA for example is financing rooftop solar power and recapturing the capital plus a low interest over time. This type of capital financing makes a lot of sense for GHP systems as well and is one of the ways in which GHP and other capital intensive building improvement systems could be financed. The building owner would not bear the entire cost up front, something that is quite often difficult for someone or a small business to do. The capital could be recouped by the financing entity — ether in the form of a higher property tax rate (until the capital investment is payed back), a monthly item on the utility bill or through some other payment means.