2 Ground Source Heat Pump Development in Foreign Countries The concept of "ground source heat pump" first appeared in a patent report of Switzerland in 1912. The proposal of this technology began in Britain and the United States. In 1946, the first ground-source heat pump system in the United States was successfully installed in the downtown area of ​​Portland, Oregon. However, influenced by the industrial age at that time, the way of energy utilization did not attract the attention of all sectors of society at that time, and there was not much development both in technology and theory. In the early 1970s, due to the emergence of the oil crisis and the deterioration of the environment, which led to the development and utilization of new energy sources, ground-source heat pumps started to pay attention to their energy-saving features. At this time, scientists and technologists from the Nordic countries started the practical application research and development of ground-source heat pumps and received strong support from the national government. Since 1974, demonstration projects funded by the governments of Switzerland, the Netherlands and Sweden have been gradually established, and the technology of geothermal heat pump production has been gradually improved. In terms of system technology, most of the underground heat conduction systems in this issue use direct groundwater, require a certain water temperature, and the technology is relatively rough, or even no injection well. In the late 1970s, Swedish scientists began to study underground open-loop heat recovery systems. 80s of last century is the rapid development of ground-source heat pump technology. During this period, the ground source heat pump manufacturer in the United States was very active. The Federation of Ground Source Heat Pump Manufacturers of China was established and the network of installation projects was gradually improved. European countries, such as Switzerland, Sweden and Austria, represented the major efforts to promote ground-source heat pump heating and cooling technology. The government of the country has taken corresponding subsidy and protection policies to make the production and use of ground-source heat pumps rapidly expand. In the late 1980s, ground-source heat pump technology has matured. More and more scientists are devoted to the study of underground systems, striving to improve the heat absorption and heat transfer efficiency, while paying more and more attention to the impact of the environment. Ground-source heat pump production showed a rising trend year by year, Switzerland and Sweden, the annual increase rate of more than 10%. During this period, the production and promotion of ground-source heat pumps in the United States were rapid with rapid technological development, making it the number-one powerhouse in the world for the production and use of ground-source heat pumps. Since the 1990s, the scientists and technicians in Europe and the United States have been in closer contact with each other and have conducted extensive and in-depth studies on the environmental issues related to ground source heat pumps. At the 1995 International Conference on Geothermal Science, British scholar Curtis delivered a survey report on the application of ground-source heat pump systems on behalf of the International Geothermal Organization. The conclusions were summarized as follows: 1) Ground-source heat pump system is a mature technology in the world energy market One of them has the advantages of good stability, high reliability and less expense compared to the existing electric heating / cooling technology, 2) the ground source heat pump system is economically comparable to the fuel and gas boilers, and 3) if Taking into account environmental benefits, energy security and long-term use, the ground-source heat pump system is the best and most technologically advanced alternative. According to the international statistics of 1995-1999, the development of ground-source heat pump products in developed countries is very impressive. The use of ground source heat pumps in the United States, Europe, Japan and other countries is as follows: 1) The United States: Ground source heat pump systems have been installed with over 200,000 sets, an annual increase of about 20%. It is estimated that by 2000, 50,000 to 600,000 sets can be installed Ground source heat pump system, of which 40,000 sets of ground source heat pump system. In the United States, one million new homes (villas) are built each year, of which one quarter are heated by floor heating. This is an overground thermal system that directly matches the ground source heat pump and is also a potential market for ground source heat pump systems. On the other hand, the U.S. government is very much concerned about the development and market promotion of ground source heat pump technology. The DOE and the university research institutes strongly promote the participation of relevant enterprises and civil science and technology forces. Once the local heat pump was listed as a national utility plan, Conducted many years of research. The U.S. government has funded more than a dozen major ground-source heat pump pilot demonstration projects and encouraged municipalities and public schools and hospitals to take the lead in installing ground-source heat pump heating and cooling systems in more than 20 states. An optimistic study suggests that by the year 2000, the number of ground-source heat pump installations in the United States will increase by 35% annually. 2) Canada: Ground source heat pump technology developed slightly later, of which the closed loop ground source heat pump system has just begun in Canada. By 1994, only 7,000-8,000 closed loop ground source heat pump systems were put into operation, together with the total number of open system geothermal pumps Not more than ten thousand. 3) Sweden: In the early days of GSHP applications, the Swedish government adopted a certain subsidy policy. Since 1990, government subsidies have been canceled, but ground-source heat pump installations are still increasing at a rate of 1,000 units / year. Sweden has installed 230,000 ground-source heat pumps nationwide, of which about 50,000 are ground-source heat pump systems. 4) Switzerland: In Switzerland, the countries with the highest per capita GDP share of ground source heat pump applications have a higher proportion of ground source heat pump systems. By 1998, ground source heat pump systems now account for more than 70% of the ground source heat pump installation market (Rybach, 1999), bringing the total to more than 200,000 units, claiming the highest density of ground-source heat pump systems in the world. The increase in the total installed geothermal heat pump capacity in Switzerland has been on the upward trend since the late 1970s. 5) Austria: Austria is an independent source of ground source heat pump technology in the country, ground source heat pump production technology and installation technology system. Austria has a land area of ​​83,850 km2 and a population of about 7.5 million. According to 1995 statistics, ground source heat pump systems account for more than 65% of ground source heat pump installations. In addition, the Austrian government adopted the most stringent certification system for the installation of ground source heat pumps and their environmental assessment. 6) Japan: Japan's heat pump manufacturing technology is quite good, the number of water-water heating heat pump is also the world's highest, annual production reached 4 million units. However, due to the abundant hot water resources in Japan and the relatively high cost of land use in Japan, ground-source heat pump applications for residential heating / cooling are still rare, and are mainly supplied to ice thermal storage / heating systems and tank-type heating / cooling system. Some municipal construction projects and non-profit buildings (such as hospitals, nursing homes, roads, etc.) have used geothermal pumps for heating, cooling, hot water supply and road snow melting and other comprehensive services. From the ground source heat pump applications [10], the Nordic countries mainly focus on winter heating, while the United States is focusing on winter and summer supply. Because the weather conditions in the United States are very similar to those in China, it is of great significance to study the application of ground source heat pumps in the United States to the development of ground source heat pumps in China. 3 Ground Source Heat Pump Development Status and Prospects in China At present, groundwater heat pump systems have begun to be widely used in China, while ground source heat pump systems are still in the research and engineering exploration and research phase. From the survey, groundwater heat pump project is not much success [11]. The reason is that it is not easy to achieve 100% recharge and recharge to the same aquifer without contaminating the groundwater and allowing long-term stable operation. At the same time, a large number of heat pump projects that do not carry out recharge have also appeared. What is more, there has been a direct use of groundwater to access the fan coil for air conditioning. In doing so, one pollutes the water and the second one is wasting water resources. The development of ground-source heat pump mainly from the beginning of 1998. Several domestic universities have set up soil source heat pump experimental bench, and most of them conducted long-term joint operation of underground heat exchangers and ground heat pump equipment. In 1998, Chongqing University of Construction built a heat pump system including shallow buried vertical pipe heat exchanger and horizontal buried pipe heat exchanger. In 1998, Qingdao Polytechnic University built a polyethylene vertical ground source heat pump system. In 1998, Hunan University The construction of a horizontal buried soil source heat pump system; 1999 Tongji University built a vertical ground source heat pump system. These systems have laid the foundation for China to promote ground-source heat pumps. Since 2000, a series of demonstration projects of ground-source heat pump systems have been established in Changchun, Jinan, Wenzhou, Chongqing and Miquan in China. More and more ground source heat pump systems are used by real estate developers. In view of the domestic conditions and the characteristics of GSHP systems, we analyze their respective prospects. With the improvement and standardization of groundwater heat pump engineering technology, there is still a huge potential market due to its outstanding energy conservation and protection of the atmospheric environment [11]. Although the ground-based heat pump with horizontal buried pipe covers a large area, it can naturally return to ground temperature by surface heat exchange and has advantages in the application of annual heat and imbalance in heat absorption [12]. The vertical buried soil source heat pump, with the installation of professional installation team, the improvement of drilling equipment, is bound to make a substantial cost reduction, will undoubtedly become the most competitive air conditioning in the future [7]. 4 Comparison between ground-source heat pump and ordinary central air-conditioning system As the main direction of development of ground-source heat pump, ground-source heat pump is compared with common central air-conditioning system in the following five aspects [11,13,14]. 1) Host Setting For the ordinary central air conditioning system, if the air-cooled heat pump unit is set for hot and cold air conditioning, the setting of the air-cooled heat pump main unit must be well ventilated with the outside world, either on the roof or on the ground, The limit is more serious, for public buildings, heat pump host will be limited to the roof set. Therefore, the ordinary central air-conditioning heat pump host settings have been greatly limited. The ground source heat pump host set up very flexible, can be set in any position of the building, regardless of the location set restrictions. If you set the chiller + boiler for hot and cold air conditioning, the cooling tower and the boiler location is even more limited. Therefore, in terms of host setting, ground source heat pump system
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