I have known about heat pumps and also knew that geothermal was an alternative to solar and wind although, at first, I thought that such a source of energy was available only where natural geothermal activity was close to the surface, e.g., “hot springs”. Even when I learned that geothermal applications would work in most temperate, geologically stable areas, I nevertheless considered it a more expensive technology than solar or wind, and potentially more disruptive to the environment.
I had avoided much further investigation until recently when my curiosity revived after learning from a Sustainable Home article about the mechanical system that architect Michael McDonough employed in the eHouse.
An in-ground cistern (under a summer kitchen and terrace) acts as a ground-coupled thermal reservoir, collecting rainwater and storing warm or cool water rejected by building systems during normal operation. A WaterFurnace water-to-water geo-exchange heat pump allows this energy to be employed for domestic hot water preheat — this using Amtrol’s StorageMate — in conjunction with its new BoilerMate EZ Series and Extrol Expansion Tanks.
Then I saw that World Changing had posted an article about this source of sustainable energy, followed by Australia's own Big Gav mention of the World Changing story in a post about whether getting oil from Canadian oil shale is worthwhile?
Geothermal Heat Pump Description
A geothermal heat pump is a heat pump that draws heat from or removes heat to the ground or ground water, instead of air. In the winter, a geothermal heat pump transfers heat from the ground or ground water to provide space heating. In the summer, the heat transfer process is reversed; the ground or groundwater absorbs heat from the living or working space and cools the air. A geothermal heat pump benefits from nearly constant ground and ground water temperatures over most of the “temperate” climate zone found in the continental United States, regardless of outside air temperatures. These temperatures are higher on average than winter air temperatures and lower on average than summer temperatures. The heat pump does not have to work as hard to extract heat from or move heat to the ground or groundwater at a moderate temperature as from the cold air in winter or to the hot air in summer. The energy efficiency of a geothermal system is thus higher than that of a conventional heat pump. Many geothermal systems are also more efficient than fossil-fuel furnaces. As with any heat pump, the actual pump used in a geothermal system is powered by electricity. — Source: Geothermal Heat Pump Consortium.
A geothermal heat pump also can provide hot water at greatly reduced costs using a device called a “desuperheater” that transfers excess heat from the heat pump's compressor to a hot water tank. In the summer, hot water is provided free; in the winter, water heating costs are cut approximately in half. Depending on the location, geothermal heat pumps can reduce energy consumption and, correspondingly, emissions by more than 20 percent compared to high-efficiency outside air heat pumps. Although residential geothermal heat pumps are generally more expensive to install than outside air heat pumps, they can reduce energy consumption, lower energy bills and emissions of carbon and other air pollutants, and operate without need of a backup heat source over a very wide range of climates. For commercial buildings, geothermal heat pump systems are very competitive with boilers, chillers, and cooling towers. “Geothermal Heat Pump Analysis“
The Geothermal Heat Pump Consortium has information about state initiatives, to include one in New York begun in 1999 with funding from NYSERDA (New York State Energy and Research Development Authority). Phase One of this initiative was to increase “customer awareness of geothermal heat pumps by building knowledge, expertise and acceptance among architects and engineers”. The GeoExchange web site lists a number of projects in New York State.
Local GeoExchange Installation
The information that elicited my “Cool” exclamation was CS-066: the Kopernick Space Education Center, which is right across the river and up a steep, rocky hill in Vestal, NY. The features of this particular GeoExchange System features include:
- Vertical closed-loop
- 16 x 250-foot boreholes
- Two 1½-hp pumps
- Two-speed heat pumps
- Heat pump control system permits remote control and monitoring
- Total heat exchanger length: 8,000 feet
- Total installed GeoExchange capacity: 24 tons (five heat pumps)
The local geothermal installation was somewhat atypical in that it lacked two components usually part of a “conventional” geothermal system: rooftop air conditioning and electric baseboard radiators.
The GeoExchange CS-066 report (PDF) describes the basis of the system:
16 boreholes makes up the ground heat exchanger. The subsurface temperature of the bedrock remains relatively constant year-round, and heat from the surround granite warms the fluid in the tubes. The heat is carried into the building, where it is transferred to the internal water loop system that heats and cools the facility. Valves in the system permit the borefield to be bypassed when conditions warrant, or for individual run-outs to be shut off. The heat pump system runs about 15 to 24 hours per day during the summer, and about five to ten hours per day during the winter when there are fewer visitors and the Center is used less.
The claims are that geothermal is the most energy-efficient, environmentally clean, and cost-effective space conditioning system available way of cooling or heating homes. So, I wonder why so few home and business owners across the United States are enjoying a high level of comfort if they can reduce significantly their energy use with geothermal ground source heating and cooling systems?
A few ergs later… (Well, actually more than a few, as it is a balmy, one degree Fahrenheit outside at present.)
Enviropundit has some links to residential ground source heat pumps.
8 Comments
First, and most importantly, it is probably because of first cost. Geothermal is typically about twice as expensive as a normal heat pump. The good thing is that the additional cost can be recouped in less than 5 years typically. First cost has historically been the measure by which HVAC systems in homes are chosen, unfortunately.
Second, there is the general misconception of geothermal heat pumps as needing a higher earth temperature than normal, as you and I have described. Unfortunately, there’s just not alot of awareness of the product, from either consumers or contractors or designers.
Third, there can potentially be a problem with changing ground temperatures if one mode, either heating or cooling, is more prevelant than the other. This can cause loss of efficiency but can and should be considered when doing controls for it.
Fourth, installing one can be extremely expensive or even impossible if adding it as a retrofit.
Good post though!
Oregon Tech, the only completely geothermally heated university campus in America, is home to the Geo-Heat Center, a national resource for geothermal development, and the Oregon Renewable Energy Center (OREC), which conducts applied research on photovoltaic power systems, ground-source heating systems, fuel-cell systems, wind, biomass and integrated systems.
Cool! Thanks for that link!
Previously, in Sustainable Energy Blog, Hans De Keulenaer had noted:
I forgot to give you this link: Cold Climate Heat Pumps. In areas where it is too difficult to install ground-source HP and it is too cold for air-source HP (anything north of Baltimore), these will work.
“… The bottom line depends on many variables, but the CCHP can generate savings of 40% or more. In addition, local utility companies may provide further rebates and incentives.
In warmer months, the Cold Climate Heat Pump can reduce cooling costs by 25%. The pump’s SEER (Seasonal Energy Efficiency Ratio) is an exceptionally high 16.”
Interesting. Thanks.
Building Green lists it as one of the top ten, “green” building products for 2004. “While more expensive than standard air-source heat pumps, the installed cost is less than that of most ground-source heat pumps.”
November 2005 EERE Consumer Info states:
The EERE Consumer Page also contains info about geothermal heat pumps:
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[...] Often such homes use more than one renewable energy technology. The three, principle, renewable energy sources used to achieve “net zero” are 1) solar, and 2) geothermal, with some people using 3) wind. [...]
[...] BTW: The eHouse is an excellent example of such combinations. [...]
[...] This is a generalization that can be proved wrong with specific examples, e.g., heat pumps, and there well could be other ways to gain efficiencies for less investment. Furthermore, while there is good evidence of sufficient effectiveness in agriculture, industry, and congregate housing, there seems to be a lack of studies as to whether co-generation is economical at the scale of home combined heat and power. [...]