GSHP heating might help U.K. meet renewable target
Despite lack of 3-phase electricity, report upbeat about ground-source pumps
BY THOMAS GOUNLEY FOR GREENING OF OIL
A December report by the U.K.’s Environment Agency found that ground-source heat pumps could produce a third of the United Kingdom’s renewable heat requirements by 2020, providing a significant boost in helping it meet its goal of increasing its overall use of renewable energy to 15 percent.
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The pumps use energy stored in the ground to heat and sometimes to cool buildings. They can also provide hot water. Electricity is used to power the pumps and, according to the Environment Agency, they will typically generate three to four times the amount of energy used to drive them.
There are two principal types of ground-source heat pumps, or GSHP: open loop, which extracts water from an underground well, pumps it through a heat exchanger and back underground through a second well, and closed loop, which consist of a closed piping system buried in the ground and filled with water and antifreeze. When the liquid travels around the pipe loops it absorbs heat from the ground.
U.K. target 15 percent by 2020
As part of a 2008 initiative to increase its share of renewable energy sources to 20 percent of total energy use by 2020, the European Union set a target of 15 percent for the United Kingdom.
As of June 2008, the amount of renewable energy being used in the United Kingdom was less than 2 percent, according to the U.K.’s Renewables Advisory Board.
In a December press release Tony Grayling, head of Climate Change and Sustainable Development at the Environment Agency, said, “Ground-source heating is a rapidly growing technology that has the potential to produce at least 30 percent of the country’s renewable heat needs, but it needs financial support in order to grow.”
The report the agency released, “Ground-source heating and cooling pumps—state of play and future trends,” addressed the total ground-source energy market, including both heating and cooling systems, although it was most concerned with heating systems.
Growth and high-growth scenarios predicted
The report estimated there were 8,000 ground-source heat pump units in the United Kingdom at the start of 2009, half of which had been installed in 2008. It estimated that they accounted for 8.7 percent of the United Kingdom’s current total renewable heat generated, so a growth to one-third by 2020 would be quite substantial.
The Environment Agency’s report included both growth and high-growth scenarios in predicting future market trends. The growth scenario predicts there will be 320,000 ground-source heat pumps installed by 2020, with an annual installation rate of 40,000 by 2019.
The high-growth scenario predicts an annual installation rate of 400,000 in 2019, with a total of 1.2 million installed systems. The report described the growth scenario as “eminently achievable” and “at the low end of other stakeholder predictions.” It described the high-growth scenario as “at the high end of what is physically achievable, but not impossible.”
Pumps take advantage of constant temperature below ground
The U.S. Environmental Protection Agency defines ground-source heat pumps as “electrically powered systems that tap the stored energy of the earth.”
They can be used to provide heating, cooling and hot water to both commercial and residential settings.
According to the U.S. Department of Energy’s Web site, ground-source heat pumps work because the ground a few feet below the earth’s surface, where the pumps are placed, remains at a relatively constant temperature all year, even as the temperature above ground can fluctuate between subzero temperatures and scorching heat.
Generally, the constant temperature is somewhere between 45 and 75 degrees Fahrenheit, depending on location.
Not without environmental impacts
Closed loop systems do not require a permit from the U.K.’s Environment Agency. However, open loop schemes, which have a larger thermal output than closed loop systems, “usually require a licence to investigate groundwater, an abstraction licence and a discharge consent.”
“There are a number of potential environmental and other impacts associated with GSHPs that we must manage and avoid in the permitting process,” the agency said. “These principally relate to the fact that open loop pumps will affect the temperature of the groundwater,” which “can have implications for the structure and ecology of the aquifer and any dependent surface waters.”
This impact is due to the fact that open loop systems take water directly from the groundwater supply for use as the fluid in the heat pump. This water is then either re-injected directly back into the groundwater or diverted to a nearby waterway. Open loop systems have the potential to deplete an area’s aquifer, as well as cause a build-up of salts and minerals in the topsoil, according to the Sierra Club.
Closed loop systems use refrigerants, which are toxic
The impacts are less with closed loop systems, in which the same liquid and antifreeze mix is continuously circulated in a closed system.
However, according to the Energy Saving Trust, a London-based organization focused on promoting action that leads to the reduction of carbon dioxide emissions, there is an environmental risk stemming from the use of refrigerants in GSHPs. The toxic chemicals could conceivably contaminate the groundwater if they leak from the pipes.
The trust does note that new types and blends of refrigerants are being developed which would minimize these negative aspects. A properly fitted system also greatly decreases leakage potential.
U.K. grid does not support three-phase electricity to homes
The Environment Agency’s report found eight barriers to growth in the U.K.’s ground-source power market. Of the eight, three of them were likely to continue past 2020.
The first barrier is the U.K. Electricity Distribution Network. The heat pumps are driven by an electric motor that requires three-phase electricity, but, unlike several other European countries where ground-source heat pumps are more common, the U.K. grid is designed only to offer single-phase domestic electricity.
The report said conversion to three-phase electricity for homes would require significant grid reinforcement, a prohibitively high investment. The second barrier is competition from natural gas.
Seventy-two percent of U.K. housing is served by a gas distribution grid, which the report describes as a “permanent barrier,” as natural gas is typically the U.K.’s cheapest heating fuel, and the cleanest of the fossil fuels.
However, the Environment Agency also notes that, for the 28 percent of housing not connected to the grid, “GSHPs are particularly attractive due to the limited and expensive alternatives.”
The report predicts that electrically driven heating systems such as ground-source heat pumps will become more attractive if natural gas reserves diminish and prices increase.
Final major barrier is thermal efficiency
The final barrier likely to continue past 2020 is the thermal efficiency of the majority of the United Kingdom’s housing, which the Environment Agency said is built with “very low levels of insulation in comparison to other European countries. Buildings with poor thermal performance are less suitable for GSHP systems, which work best with a steady and low heat demand.”
Another barrier is capital and maintenance costs, the agency said, pointing out that the government’s “Renewable Heat Incentive,” which will be introduced in 2012, will pay homeowners and businesses a guaranteed price for generating renewable heat, “the most important factor in determining how much the GSHP industry grows.”
The U.S. Department of Energy estimates that GSHPs cost about $2,500 per ton of capacity. A typical home would use a three-ton unit, which would cost roughly $7,500. This figure does not include the cost of drilling to place the unit below the ground. Drilling costs can vary widely, but horizontally placed systems generally require less drilling than vertically placed systems. In comparison, other traditional heating systems cost about $4,000.
Other barriers include the possibility of an insufficient GSHP installer-technician network if demand increases, a lack of awareness among consumers and the disruptive and expensive nature of accessing the existing GSHP market.
“The disturbance associated with retrofitting a system, which includes ground excavation for the loop and fitting the distribution system, for example, may well put off even the most ardent GSHP advocate when compared to the relative ease of installing a gas boiler,” the report noted. “A GSHP system requires either under floor heating, which is not usually economic for retrofitting, or oversized radiators, which cause significant disturbance and add to the project costs.”
Other European nations leading the way
Ground-source heat pumps are used widely in some other European countries. In particular, Austria and Sweden are cited in the report.
“Both of these countries have mature GSHP markets,” the report noted.
The agency attributed this primarily to the fact that they have addressed or avoided some of the barriers facing the United Kingdom.
In terms of gas distribution competition, the report found that in Austria less than 30 percent of housing is served by the gas network, compared to 72 percent in the United Kingdom, and in Sweden gas accounts for just 1.5 percent of the nation’s primary energy use.
In addressing thermal efficiency, the report said, “For example, the levels of insulation expected in the U.K. are much the same as those required in Sweden thirty-five years ago.”
Finally, the other countries also benefit from their requirement that domestic electricity supplies be three-phase, which supports increased numbers of GSHP installations.
Links of Interest
U.K.’s Environment Agency report
U.K.’s Renewables Advisory Board
20 20 by 2020: Europe's climate change opportunity
U.S. Department of Energy on Geothermal Heat Pumps
And on Cost of Geothermal Heat Pumps
Environment Agency press release: Underground technology could produce a third of UK’s renewable heat needs
Energy Savings Trust: Ground-source Heat Pumps Fact Sheet
Sierra Club on Geothermal Heat Pumps
May 2009 report from Department of Energy’s Energy Information Administration
Contact Thomas Gounley: tai36@cisunix.unh.edu