Global warming is an unprecedented threat. I congratulate Wednesday Journal for publishing articles and letters that raise awareness about saving energy. Excellent recent examples of such articles are: “A recipe for greening our village,” April 18, by Gary Cuneen; “OP should take steps toward a green village,” April 25, by Doug Burke; and “Let’s have an electricity reduction contest,” April 25, by Joyce Gradel.
This letter is a response to a much earlier article, “A more detailed look at geothermal conversion,” March 7, by Cheryl Pomeroy.
It is clear that Ms. Pomeroy is an advocate for adding insulation and reducing air leaks in buildings. I applaud her advocacy. Those are important first steps in saving energy. However, additional means of saving energy are equally important.
In a 1993 landmark study analyzing the efficiency and cost-effectiveness of competing heating and cooling technologies, the U.S. Environmental Protection Agency (EPA) concluded that “Geothermal systems are the most energy-efficient and environmentally clean space-conditioning systems available.” (Space Conditioning: The Next Frontier – The Potential fo Advanced Residential Space Conditioning Technologies for Reducing Pollution and Saving Consumers Money, EPA, Apr. 1993).
To date, there are over a million geothermal installations in the U.S. The average payback time for the majority of recent installations has been 5-8 years. The estimate of 43 years given in Ms. Pomeroy’s article is not based on all of the facts. The geothermal industry and organizations such as the Geothermal Heat Pump Consortium (www.geoexchange.org) have published many case studies of real geothermal installations. The U.S. General Accounting Office (GAO) in a 1994 report (Outlook for Geothermal Energy) said, “Key to greater acceptance of this technology is more knowledgeable and better-informed consumers, building developers, and utilities.”
Some writers on the subject feel that slow acceptance of geothermal is due primarily to two reasons: 1) The name is confusing; 2) Consumers feel that payback time is much more important than saving energy.
The systems we are talking about are based on a heat pump technology (similar to that in a refrigerator), so it is more precise to use the term geothermal heat pump. Because a geothermal heat pump system provides heating and cooling by removing heat from the ground in winter and adding heat to the ground in summer, the most common name used by the industry is ground source heat pump (GHP).
The demand for short payback time is a real concern. Future generations will curse us for not having taken advantage of proven energy-saving technologies (geothermal as well as solar and wind) that could have slowed the pace of global warming because we decided that the payback time was too long. Our “survival” may require that we change our thinking about payback. Regardless of the payback time, ground source heat pump systems save energy and money.
Next, Ms. Pomeroy’s statements about COP (coefficient of performance), energy efficiency, and source efficiency deserve a short response. She implied that a 4.2 COP ground source heat pump is not four times more efficient than a high efficiency gas furnace. COP is defined as the usable heat energy you get out of a system divided by the energy you put into it. COP is usually used only for heat pump systems, but if we applied the definition to a very high efficiency gas furnace, it would have a COP of maybe 0.95. That means the energy efficiency of a geothermal system, which has a COP of 4.2, is by definition more than four times more efficient than a high-efficiency gas furnace. Such a geothermal heat pump system would use about one fourth (25 percent) of the equivalent energy used by a gas furnace. That is, it will use about 75 percent less equivalent energy than a gas furnace.
However, if we include the efficiency of the energy “source,” the net efficiencies of both a gas furnace and a ground-source heat pump are different from the point-of-use efficiencies.
Ms. Pomeroy correctly points out that an electric generating station uses about three units of energy to deliver one unit of energy to the point of use. Similarly, a natural gas supplier uses about 1.1 units of energy to deliver one unit of energy to the point of use. This is because electric power generation and transmission losses can be as high as 75 percent compared to natural gas transmission losses of about 10 percent. Even with these losses, a 4.0 COP ground source heat pump converts the one unit of energy it receives into 4 units of heat energy (3 units are extracted from the ground). By contrast, the gas furnace converts the one unit it receives into about 0.95 units of heat energy. This means that to provide the same amount of heat, a ground-source heat pump requires about 30 percent less energy from the “source” than a gas furnace.
I appreciate Ms. Pomeroy’s article because it expands the discussion. People who use energy-saving technologies do us all a favor because they create less greenhouse gases and other pollutants.
