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.