Heat pumps are being in use for several decades in refrigerators and air conditioning units. It is a well insulated unit that move heat from one "space A" to " space B. When heat is removed from space 'A' and space ' A' becomes cool and 'B' becomes hot. Based on the need and space 'A' can be made cool or hot. This concept is in use since 1850 when James Harrison made the first refrigerator. The ground source heat pump works on the same principle. The ground source heat pumps (GSHP) are also known under several names: Ground Heat Pumps-GHP, Ground Coupled Heat Pump-GCHP, Groundwater Heat Pump-GWHP.The basic principle on which the GHP works is "refrigeration cycle". The refrigerant carries the heat from one "space" to another. The heat pump's process can be reversed. The earth is the main source and sink of heat. In winters it provides heat and summers it takes the heat.
The heat pumps are very common in USA, Europe, E. Europe and China. The heat pumps can be adopted to any kind of building at any place. In the United States of America, over 400 000 GHPs are working in schools, hospitals, commercial complexes and government buildings. GHPs have low carbon dioxide emissions, low energy consumption (~ 40-60 % lower than the conventional systems), low operating cost and competitive life cycle cost compared to the conventional HVACs.
The common two types of GHPs in use are 1) earth-couple (closed loop) system that uses sealed pipes/tubes-placed vertically or horizontally, through water or a mixer of water and antifreeze circulates transferring heat to and from the earth and 2) water source (open loop) system where water from the underground aquifer pumps water to the heat exchanger. Between the two, earth coupled GHPs are very popular because they are very adoptable.
The technology is very matured and systems can be installed adopting the local temperature variations. According to the reports published in the World Geothermal Congress 2010, up to the year 2010 (ending December 2009) the installed capacity of GSHP in the world is 50583 MWt and the energy generated was 438071 TJ/year (121696 GWh/y: CF of 0.27). The country that has the highest installed capacity of GSHP is USA (12611 MWt) followed by China ( 8898 MWt). In China the amount of utilizable geothermal energy (for space cooling and heating) at shallow depths, according to a news published in "Renewable Energy World.com" in 2011, is equivalent to about 350 million tons of standard coal, which is equivalent to 2.8 million GWh of electricity. If this energy source is tapped, then this will reduce emission of 500 million tons of CO2 by avoiding to mine 250 million tons of coal. The extractable geothermal energy in China's 12 major geothermal provinces is equivalent to about 853 billion tons of standard coal that could generate seven billion GWh of electric power!!
China is using its GSHP technology to adjust/ modify its energy structure to reduce CO2 and other GHG emissions. Today in China research on GSHP technology is given top priority with full government support. Thus academic institutions, industries and companies are enjoying a boom with regard to this technology and it is paying rich dividends to the country today. According a paper published in the Proceedings of the World Geothermal Congress 2010, China has proved its supremacy in GSHP technology by providing 26% of energy to the Olympic Games in 2008 from geothermal sources. Excellent examples where such GSHP technology in the Olympic games is seen from the Olympic tennis courts, the National Olympic Stadium ( Bird's nest), National Swimming Centre and Olympic Gymnastics Hall and Badminton Hall. Besides this, the hostels for the athletes were also temperature controlled through GSHPs. For the tennis courts, 35 holes were drilled within a 7 x7m layout. This GHP unit has 138.2 kW heating capacity ( in put power 37.5 kW) and cooling capacity of 139.6 kW (in put power 32 kW). The Olympic National Stadium (Bird's Nest) drilled 140 holes with depth of 80-100 m. With such a strong GSHP technology in hand, it is not surprising to read about China's determination to reduce CO2 emissions and phase out HCFC by 2015 by adopting clean technology for space heating and cooling.
The performance of a heat pump is a measure of its COP ( Coefficient of performance). Commercially available HVAC systems have COP of 3 to 4 while GHPs have greater than 6. The COP also depends on the temperature difference. When the temperature difference is small then the COP will be large. Similarly the cooling performance, measured as energy efficiency ratio (EER). The GHPs EER, depending on the seasonal temperature variation is about 80% and above.
In the case of HVAC systems, the heat is transferred between the inside and out side air to cool or heat the space. The COP of such systems vary drastically since air temperature variation is diurnal and as well as seasonal. This problem does not arise in the case of GHP system. The heat transfer takes place in the ground/soil that maintains more or less constant temperature. This is a very great advantage where GHPs score its COP. The GHPs can be installed vertically/horizontally, before the construction of the building or after the construction of the building. It is cost effective if the design of the system goes along with the building plan. The builder and the architect should work in collaboration in the installation of GHPs for cooling and heating. Besides heating and cooling the space, GHPs can also provide hot water to the house hold at no cost.
The GHP technology is very well matured and can be bought off-the-shelf. Countries in Europe have installed GHPs at district level and residential spaces, office buildings and commercial establishments have been put under GHP technology. This is why Europe is able to save carbon emissions and are able trade it to countries like India. Buying carbon credits is not good to any country, especially those that are on the development path. China is ahead among all the non-OECD countries in controlling carbon dioxide emissions without compromising the industrial and commercial growth. India, with its large geographical spread and with a large temperature variation, GHP technology will bring a sea change to Indian economy, GDP growth and provide carbon free environment to the future generations.
For an excellent world review of GHPs go to:
http://geoheat.oit.edu/bulletin/bull25-3/art1.pdf
GSHP are more economical than the conventional HAVC. The following table will give cost comparison from a case study.
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