Ground source heat pump characteristics and development prospects (a)

Abstract: This paper introduces the categories and characteristics of ground-source heat pumps in an all-round way, and analyzes the development status and development prospects of ground-source heat pumps both in foreign countries and domestically. Keywords: Ground Source Heat Pump Energy Saving Ground Source Heat Pump In recent years, with the development of our society and economy and people's living standards continue to improve, to improve the thermal comfort of the building has become a more prominent requirement. As the current air conditioning to improve the thermal comfort of the building tools, has quietly entered our lives. According to a survey conducted by relevant authorities, the air-conditioned family ownership rate in Shanghai has reached an average of more than one. However, with the increasing popularity of air-conditioning equipment, building energy consumption is bound to increase rapidly, the pollution of the atmosphere will also become increasingly serious. How to reduce the building energy consumption and reduce the pollution to the atmospheric environment under the condition that the building thermal comfort conditions are improved has become the primary problem to be solved by the HVAC industry. At this stage, we should adopt various effective technical and management measures to ensure that the use of functions will not be reduced. We will significantly reduce the energy consumption of new building construction and carry out planned energy conservation retrofits of the existing buildings , Achieve the purpose of saving energy, protecting the environment and improving the quality of people's life [1]. As a kind of environment-friendly, energy-saving and economically viable building heating and cooling technology, ground source heat pump is attracting more and more attention. It is the use of underground relatively stable soil temperature, through the media to get the soil cold (heat) energy of the new device, the building can easily adjust the temperature throughout the year. Since the cooling and heating method does not exist in the form of energy conversion, almost a kind of energy "handling" process, so its high energy conversion efficiency, low operating costs [2-4]. At the same time, ground source heat pump system also provides a good solution to the worldwide problem of improving building thermal conditions in hot summer and cold winter area [5]. In summer hot and cold winter, its July temperature is about 2 ℃ higher than other parts of the same latitude, which is the hottest area except the arid and arid areas in this latitude range. In addition, the water network in this area is very humid , Humidity is often maintained at about 80%, due to difficult to volatile human sweat, generally feel hot and uncomfortable. While the temperature in January is 8-10 ℃ lower than other parts of the same latitude, and the humidity is high, reaching 73% -83% [6]. In this period, the sunshine is relatively small and wet moisture absorbs heat from the human body and therefore Cold cold. However, because the middle and lower reaches of the Yangtze River is a traditional non-heating area, residential buildings lack of energy-saving design standards, thermal insulation performance of building envelope structure is much worse than the heating area; summer is usually air-cooled air-conditioning to cool the winter people Often with the help of high-energy electric heating. Therefore, the energy efficiency of the area is quite low. Considering that the number of cooling days in summer in this area is comparable to the number of days in winter, the ground source heat pump system can give full play to the characteristics of underground energy storage and carry out energy season migration to obtain the maximum benefit with minimum energy consumption. 1 Ground source heat pump classification and their respective characteristics Ground source heat pump in the country is also known as ground heat pump. According to the different types and ways of using geothermal resources, they can be divided into the following three categories [7, 8]: ground source heat pump or soil coupled heat pump (GCHP), groundwater heat pump (GWHP), surface water heat pump (SWHP). 1.1 Ground-source heat pump Ground-source heat pump to the ground as a heat source and heat sink, heat pump heat exchanger buried in the ground, with the ground for hot and cold exchange. Ground source heat pump system host usually water - water or heat pump unit or water - air heat pump unit. According to the layout of underground heat exchangers, mainly divided into vertical buried pipe, horizontal buried pipe and snake buried pipe three categories. Vertical pipe heat exchanger is usually U-shaped way, according to the depth of the buried pipe can be divided into shallow (100m) three. Buried deep, underground rock temperature is relatively stable, drilling covers an area of ​​?? less, but the corresponding will bring drilling, drilling equipment and high cost of buried pipe cost increases. In general, the advantages of vertical borehole heat exchanger heat pump systems lie in: (1) small footprint, (2) small changes in soil temperature and thermal properties, (3) minimal need for tubing and low pump energy consumption, ( 4) high energy efficiency. The disadvantage is mainly due to: due to the lack of appropriate construction equipment and construction workers, high cost. Horizontal buried heat exchanger has a single tube and multi-tube two forms. Including single-tube horizontal heat exchanger covers an area of ​​?? the largest, although the multi-tube horizontal borehole heat exchanger covers an area reduced, but the tube length should be increased to compensate for thermal interference between adjacent tubes. Horizontal borehole heat exchanger heat pump system due to the extensive use of construction equipment and easy to find for construction workers, plus many families have large enough construction site, so the cost can be reduced. In addition to the need for larger sites, the disadvantage of a horizontal borehole heat exchanger system is that the operating performance is not stable (due to changes in temperature and thermal characteristics of the shallow ground with season, rainfall and depth) High; system efficiency is reduced. Snake tube heat exchanger is more suitable for limited and more economical venue. Although the amount of digging only single pipe horizontal buried heat exchanger 20% to 30%, but the use of pipe capacity will be significantly increased. The advantages and disadvantages of this method is similar to the horizontal borehole heat exchanger, so some literature classified it as a horizontal borehole heat exchanger. 1.2 Groundwater heat pump system In the ground source heat pump has been developed before, Europe and the United States the most commonly used ground source heat pump system is groundwater heat pump system. Currently in civilian use has been rarely used, mainly used in commercial buildings. The most common form of system is the use of water - water plate heat exchanger, one side to groundwater, heat pump cooling water on one side. Early groundwater systems used a single-well system, where groundwater was discharged directly through a plate heat exchanger. In doing so, one will waste groundwater resources and the other will easily cause subsidence of the ground and cause geological disasters. As a result, a double well system was created, one well pumped and one well recharged. Groundwater heat pump system has the advantage of cost is lower than the ground source heat pump system, the other well is very compact, does not occupy any site, technology is relatively mature, well contractors are also easy to find. The disadvantage is that: 1. Some local regulations prohibit the extraction or recharge of groundwater; 2. Available groundwater is limited; 3. If the water quality is not good or well failed to pay attention to water treatment; 4. If the pump is too large, the control Poor or wells and buildings remote, pump energy will be too large. 1.3 Surface Water Heat Pump System Surface water heat pump systems are mainly open and closed system. In cold regions, open systems are not suitable and can only be closed systems. In general, surface water heat pump systems have the advantages of relatively low cost, low pump energy consumption, low maintenance and low running costs. However, in public rivers, other equipment in pipelines or water is easily damaged. In addition, if the lake is too small or too shallow, the temperature of the lake changes significantly with the outdoor climate, which can lead to reduced efficiency and reduced cooling or heating capacity. Figure 1 ground source heat pump classification

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