Geo-Thermal Heat Pumps

Topics: Heat pump, Geothermal heat pump, Central heating Pages: 13 (4967 words) Published: April 28, 2013
maqlGeothermal Heat Pumps
The heat pump was described by Lord Kelvin in 1853 and developed by Peter Ritter von Rittinger in 1855. After experimenting with a freezer, Robert C. Webber built the first direct exchange ground-source heat pump in the late 1940s. The first successful commercial project was installed in the Commonwealth Building (Portland, Oregon) in 1946, and has been designated a National Historic Mechanical Engineering Landmark by ASME. The technology became popular in Sweden in the 1970s, and has been growing slowly in worldwide acceptance since then. Open loop systems dominated the market until the development of polybutylene pipe in 1979 made closed loop systems economically viable. As of 2004, there are over a million units installed worldwide providing 12 GW of thermal capacity. Each year, about 80,000 units are installed in the US (geothermal energy is used in all 50 US states today, with great potential for near-term market growth and savings) and 27,000 in Sweden.

The rising cost of energy gives homeowners an opportunity to explore alternative heating and cooling systems. Geothermal heat pumps are one available option. Even though geothermal heat pumps are expensive, their efficiency and reliability will provide a value capable of recovering the high installation cost. The tremendous benefits this system provides will overcome the additional cost. Geothermal heat pumps can reduce energy consumption— and corresponding air pollution emissions—up to 44% compared to air source heat pumps and up to 72% compared to electric resistance heating with standard air-conditioning equipment. Geothermal heat pumps are different from other heat pumps in that they use ground heat instead of extracting heat out of the air. This provides greater efficiency especially as the air temperature becomes very cold. “While many parts of the country experience seasonal temperature extremes – from scorching heat in the summer to sub-zero cold in the winter – a few feet below the earth’s surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45°F (7°C) to 75°F (21°C). Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. This allows the system to reach fairly high efficiency. Some confusion exists with regard to the terminology of heat pumps and the use of the term "geothermal". "Geothermal" derives from the Greek and means "heat from the Earth" - geologists understand it as describing hot rocks, volcanic activity or heat derived from deep in the earth. Confusion arises when the term "geothermal" is also used to apply to temperatures within the first 100 meters of the surface which closely match the mean annual air temperature at the surface where the sun is the predominant influence on temperature. Below 100 meters, geothermal heat, as understood by geologists, begins to become significant as the Geothermal gradient increases by 2°C with each 100 meters of depth. Heat pumps provide winter heating by extracting heat from a source and transferring it into a building. Heat can be extracted from any source, no matter how cold, but a warmer source allows higher efficiency. A ground source heat pump uses the top layer of the earth's crust as a source of heat, thus taking advantage of its seasonally moderated temperature. In the summer, the process can be reversed so the heat pump extracts heat from the building and transfers it to the ground. Transferring heat to a cooler space takes less energy, so the cooling efficiency of the heat pump gains benefits from the lower ground temperature. Ground source heat pumps employ a heat exchanger in contact with the ground or groundwater to extract or dissipate heat. This component accounts for a fifth, up to half of the total system cost, and would be the most cumbersome part to repair or replace. Currently they are often designed to have minimal installation...
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