1. Early development stage
With the research and development of heat pump technology, the research and development of shallow geothermal energy is on the rise. As early as 186 years ago (1824), French physicist Carnot laid the theoretical foundation of heat pump. Later, the British physicist Joule proved the principle of temperature change caused by changing gas pressure. Professor Thomson, Lord of England, first put forward the idea that "heat multiplier" can provide heat. In Zurich 19 12, Switzerland, a set of heat pump equipment using river water as low-grade heat source was successfully installed, and a patent was applied. This is an early water source heat pump system, and it is also the first water source heat pump system in the world.
In the following decades, ground source heat pump was basically in the experimental research stage, and surface water source heat pump, underground water source heat pump and ground source heat pump system came out and developed successively. Surface water source heat pump system came out in 1930s, and it is one of the earliest heat pump systems for ground source heat pump. The first large-scale heat pump device in Europe was put into operation in Zurich, Switzerland from 1938 to 1939. It uses river water as heat source, and the heating capacity is 175 kW. In the 1940s and 1950s, the underground water source heat pump system used in Switzerland and Britain was not only used for building heating, but also used for swimming pool heating, rayon factory process heating and shoe factory air conditioning. Subsequently, some other European countries began to install surface water source heat pump systems, and the heat supply of the heat pump system increased continuously, and the performance coefficient was greatly improved.
Underground water source heat pump was also born in 1930s. By 1940, the United States had installed 15 large commercial heat pumps, most of which used well water as heat source. 1937, Japan installed two 194k W compressors and heat storage tanks in a large office building, with a performance coefficient of 4.4. From 1940s to 1950s, ground source heat pumps were mainly used in the United States.
194 1 after the outbreak of world war ii, the research and development of heat pump technology for air conditioning and heating was affected and interrupted. After World War II, the research and application of heat pump technology gradually resumed. By 1950, more than 20 manufacturers and 10 university research institutes in the United States had been engaged in heat pump development and research. Of the 600 heat pumps owned at that time, 50% were used for residential heating. Ground source heat pump technology was first developed in the United States and Britain. 1950 or so, the two countries began to use underground pipelines to absorb geothermal energy as a heat source to heat domestic houses. 1000 heat pumps were shipped in the United States in 1952, and about 2000 heat pumps were shipped in 1954. Due to the maturity of ground source heat pump, the wide application of shallow geothermal energy has been effectively promoted.
1957 A large number of houses in the US military base used heat pump heating instead of gas heating, and the output of heat pump reached 20,000 sets, which increased to 76,000 sets in 1963. By the early 1960s, nearly 80,000 heat pump units had been installed in the United States. However, at that time, the compressor quality was not up to standard, and the high equipment cost affected the popularization of heat pump heating technology and began to stagnate.
By 1964, the reliability of heat pump has become a very serious problem. The continuous decline of electricity price in 1960s led to more and more applications of electric heaters, which limited the development of heat pumps.
2. Rapid development stage
In the 1970s, the emergence of the world oil crisis aroused people's concern and interest in underground water source heat pumps, which were widely installed and used, and the heat pump industry entered a golden age. During this period, countries all over the world attach great importance to the research work of heat pump. For example, both the International Energy Agency and the European Community have made large-scale heat pump development plans, and new heat pump technologies are emerging one after another, and the uses of heat pumps are constantly being explored, and they are widely used in air conditioning and industrial fields, playing an important role in energy conservation and environmental protection.
The real commercial application of heat pump has only a history of nearly 20 years. Since 1990s, with the further improvement of environmental protection requirements, the application of underground water source heat pump system in the United States has been on the rise. According to a survey conducted by the US Department of Energy and Information, the output of underground water source heat pumps in the United States increased from 5,924 in 1994 to 9,724 in 1997. Another example is the United States. By the end of 1985, there were 14000 platform source heat pumps in China, while 1997 installed 45000. Up to now, 400,000 units have been installed, with an annual growth rate of 10%. 1998 ground source heat pump systems in commercial buildings in the United States have accounted for 19% of the total air conditioning, of which 30% are in new buildings. At present, about 50 thousand ground source heat pumps are installed every year, of which open systems account for 5%. The American Heat Pump Industry established the American Ground Source Heat Pump Association, which is composed of the US Department of Energy, Environmental Protection Agency, Addison Electric Power Research Institute and many ground source heat pump manufacturers. In recent years, the association will invest 654.38 billion dollars in development, research and promotion.
Some European countries have adopted active promotion policies (including financial subsidies, tax cuts, preferential electricity prices and advertisements), and the heat pump market has developed rapidly. 1997, the European Development Foundation put forward the heat pump development plan again. By 2000, the total number of heat pumps used for heating and hot water supply in Europe was about 467,000, of which underground water source heat pumps accounted for about 1 1.75%. Different from the development of heat pumps in the United States, Sweden, Switzerland, Austria, Germany and other central and northern European countries mainly use shallow geothermal resources and ground source heat pumps with buried soil for indoor floor radiant heating and domestic hot water supply. According to 1999 statistics, the proportion of ground source heat pump in domestic heating devices is 96% in Switzerland, 38% in Austria and 27% in Denmark.
3. Development trend
In recent years, the scale and speed of shallow geothermal energy development and utilization in various countries are increasing rapidly. Some universities and research institutions in the United States and Canada have conducted in-depth experimental research on ground source heat pumps and obtained some important data. The U.S. Department of Energy, the U.S. Environmental Protection Agency, Edison Electric Power Research Institute (EEI), the National Agricultural Electric Power Cooperation Corporation and other consortia formed an international industrial facility group with government participation to promote heat pump heating system. At present, from the development trend of foreign countries, the development and utilization of shallow geothermal energy will be the mainstream and direction of geothermal resources development and utilization.
Shallow geothermal energy is a valuable new energy. Compared with natural resources that are not controlled by human power, such as wind energy and solar energy, shallow geothermal energy is a kind of renewable energy that can be used artificially during the exploitation and utilization time. It is a clean, cheap and widely used new energy which integrates heat, mineral and water. The exploitation and utilization of shallow geothermal energy can reduce conventional energy consumption, reduce environmental pollution, especially air pollution, and play a certain role in developing some related industrial economies and improving people's quality of life, which has remarkable commercial value. Therefore, its development and utilization have attracted the attention of all countries. Especially since the 1973 world energy crisis, the exploration, development and utilization of shallow geothermal energy are developing rapidly in depth and breadth.
4. Research progress of numerical simulation of groundwater heat transfer
After the operation of the groundwater source heat pump, the cold and hot energy injected into the aquifer by the recharge well moves to the pumping well under the action of convection and heat conduction, which has an impact on the groundwater temperature field. Therefore, it is necessary to study the heat transfer process of groundwater in depth. Numerical simulation method has gradually become an effective tool to study this problem because of its high efficiency, convenience and flexibility. In view of this, this section summarizes the research progress of numerical simulation of groundwater heat transfer at home and abroad, which provides the basis and reference for the follow-up research of this topic.
Since the end of 1970s, many mathematical models describing the heat transfer in aquifers have been put forward abroad. Mercer et al. (1985), Crawford et al. (1982), Mirza et al. discussed some simulation technologies of aquifer energy storage. 1985.P.Heijde and Y.Bachmat counted 2 1 mathematical models of heat migration at that time. These models only consider convection and heat conduction, ignoring the influence of natural convection on heat transfer. Except the two models are three-dimensional water flow coupling models, the others are one-dimensional and two-dimensional. Tsang et al. (198 1) and Sykes et al. (1982) used the finite difference numerical simulation method to simulate the water and heat transfer law in the field test of underground aquifer energy storage in Auburn University, and the simulation results were basically consistent with the experimental observation results. Buscheck et al. (1983) made a two-dimensional numerical simulation using the data of the first two cycles of the energy storage test in Auburn University, and considered the influence of natural convection in the simulation process. Rouve et al. (1988) used the finite element simulation method to conduct a two-dimensional numerical simulation of the artificial aquifer seasonal energy storage test in Stuttgart University, Germany, and optimized the permeability spatial combination of each filling sub-layer in the aquifer. Molson et al. (1992) used the experimental data of phreatic aquifer energy storage in Ontario, Canada, and made a three-dimensional finite element simulation of the test process, in which the influence of natural convection and the change of density with temperature were considered. The model is relatively complete, but the test conditions are simple and the continuity equation is not perfect. Forkeli et al. (1995) used two-dimensional axisymmetric model and three-dimensional finite element model to simulate the energy storage effect of artificial aquifer energy storage system, and determined the best artificial energy storage system through comparative simulation. Travi et al. (1996) established a two-dimensional unsteady flow model, and gave the temperature change on the aquifer profile through numerical calculation. Chevalier et al. (1999) simulated the energy storage of porous media aquifer by stochastic dissociation method, and found that the flow of regional groundwater can accelerate the diffusion of stored thermal energy to the downstream aquifer, thus reducing the recovery rate of stored thermal energy. Nagano(2002) obtained through laboratory test and finite difference numerical simulation that if the temperature of reinjection water is high during thermal storage (&; gt； 50℃), natural convection is likely to occur in the aquifer, which will greatly affect the heat recovery rate of aquifer energy storage. Chounet et al. (1999) used mixed finite element method to simulate water flow and heat transfer in soil, which improved the simulation accuracy, but the model adopted was a two-dimensional model with cross section.
Domestic research on geothermal numerical simulation began in the late 1980s. Zhang Juming et al. (1982) used the finite element method to simulate the two-dimensional geothermal migration problem, and gave the finite element program. , Wang, etc. Sources and conditions of hot water supply in Pingdingshan No.8 Mine. Investigation report of Xi branch of Coal Science Research Institute.
Two-dimensional and three-dimensional mathematical models of Pingdingshan geothermal field are established and solved by finite element method, but the model is only a stable model, and the changing law of water flow field is not studied. Xue Yuqun et al. (1987) established a three-dimensional mathematical model of Shanghai energy storage test, considering thermal dispersion. The water flow model is a stable model, and a simple analytical expression is used instead of the water flow model, without considering the changes of water density and hydrodynamic viscosity coefficient with temperature. Zhang Juming (1994) established a three-dimensional mathematical model of geothermal field and proposed a finite element solution, but did not consider the water flow equation. Hu Baigeng Hu Baigeng. 1995. Study on heat and mass transfer in geothermal field. Beijing: Tsinghua University's doctoral thesis.
The heat and mass transfer process of geothermal field is simulated by two-dimensional dual porous medium model, and the heat and mass transfer laws of Naqu geothermal field in Tibet and yangbajain geothermal field are simulated respectively. Ren Li et al. (1998) used alternating direction finite difference method to study the law of two-dimensional soil water and heat transport. He Manchao et al. (2002) first studied the variation law of permeability coefficient in the process of underground hot water recharge, and then established the mathematical model of geothermal recharge seepage field according to the dynamic change of seepage field in the process of single well and double well recharge, and deduced the theoretical formulas of single well and double well recharge under the condition of constant and variable permeability coefficient.
Experts at home and abroad have also done some simulation research on groundwater heat transfer specifically for water source heat pump. Gringarten et al. (1975) theoretically studied the thermal energy collection of aquifer under the condition of uniform groundwater flow. By simplifying boundary conditions and appropriate assumptions, a mathematical model of heat transfer to well system is established, and the thermal breakthrough events under different given conditions are quantitatively evaluated by this model, which provides effective guidance for the rational layout design of French well energy recovery system. In order to quantitatively evaluate the thermal migration characteristics of the target aquifer system and guide the design of energy recovery system, Wiberg used finite element method to compare and simulate the geothermal field distribution characteristics of the ideal aquifer system under two different assumptions of pure heat conduction and conduction convection coexistence. Andrews( 1978) quantitatively evaluates and predicts the influence of water source heat pump utilization on underground temperature field by using two-dimensional finite element model according to the requirements of cooling and heating load in Wisconsin, USA. The simulation results show that when the regional groundwater flows at a certain speed, the temperature drop around the winter irrigation well is relatively small, but the influence radius increases, and the temperature disturbance area moves along the water flow direction. Rahman( 1984) established a simulation model of well recharge system by assuming aquifer conditions, and made a quantitative simulation study on the influencing conditions such as different recharge volume, aquifer thickness, initial reservoir temperature and well spacing. The results show that the aquifer thickness has a significant influence on the thermal breakthrough time, except the recharge and the spacing between wells. However, the influence of water storage rate and permeability coefficient of aquifer on thermal breakthrough events is not significant. In order to determine the reasonable layout between production wells and recharge wells, Paksoy(2000) used CONFLOW program to quantitatively simulate the migration characteristics of thermal front in the process of aquifer energy recovery. By limiting the water levels of production wells and recharge wells and ensuring that thermal breakthrough does not occur, the minimum distance between production wells and recharge wells under the above constraints is finally determined. Tianma established an ideal well pattern model, and quantitatively compared and simulated different mining and recharging speeds, the length and position of well filter tubes and the operation cycle by using FEHM software. The results show that the first two factors are the main factors controlling the temperature variation range of the model. In China, Xin et al. (2002) used the HST3D program compiled by the US Geological Survey to simulate the annual velocity field and temperature field of a typical double-well confined aquifer. Due to the limitation of the program, the method of constant flow and constant temperature throughout the year is adopted in the simulation. Zhou Jianwei et al. (2008) simulated an underground water source heat pump system in Wuhan by using the Flowheat program based on HST3D, and analyzed the rationality of the combination of well layout and pumping and irrigation. Zhang et al. (1998) simulated the operation of water source heat pump in large diameter wells in winter, and the results showed that the well water flow in large diameter wells decreased uniformly.
Second, the domestic research status and development trend
1. Early application and initial stage of heat pump (1949 ~ 1966)
Compared with the development of heat pump in the world, the research work of heat pump in China is about 20 ~ 30 years later. In 1950s, Professor Lu Canren from the Institute of Thermal Energy of Tianjin University started the earliest heat pump research in China. The article "Heat Pump and Its Application in China" written by Professor Lu in 1956 is the earliest existing research document on heat pump in China. In 1960s, China began to apply and develop heat pumps in the field of HVAC, and achieved a lot. 1960 Professor Wu Shenyi of Tongji University published "Introduction to Heat Pump Heating and Suggestions for Jinan to Try Heat Pump Heating"; 1963 The former East China Architectural Design Institute and Shanghai Air Conditioning Factory began to develop heat pump air conditioners. 1965 Shanghai refrigerator factory has successfully developed the first CKT-3A heat pump window air conditioner with a heating capacity of 3720W in China. 1965 Tianjin University and Tianjin Air Conditioning Factory have successfully developed the first underground water source heat pump air conditioning unit in China; 65438-0966 Tianjin University cooperated with Sifang Vehicle Research Institute of the Ministry of Railways to carry out the air/air heat pump test of trunk passenger cars. 1965 according to the heat pump theory, the research team led by Professor Xu Bangyu and Professor Wu of Harbin Institute of Architecture and Engineering put forward a new technology of using auxiliary condenser as the secondary heater of constant temperature and humidity air conditioning unit for the first time, which is the first time in the world. Chongqing jianzhu university, Tianjin Business School and other units have also conducted research on underground coil ground source heat pump for many years. Guangzhou Energy Research Institute of Chinese Academy of Sciences and other units have also held many national seminars on the development and application of heat pump technology. Tsinghua University and Tianjin University respectively formed Industry-University-Research consortium with related enterprises to develop ground source heat pump systems with China brand, and several demonstration projects have been completed. More and more users in China have become familiar with heat pumps and become interested in their applications.
The early heat pump in China has experienced a development course of 17 years and a long initial development stage. Its characteristics can be summarized as follows: ① For new China, it started early and started high, and some researches reached the advanced level in the world; ② The application and development of heat pump air conditioning in China was always slow because of the weak industrial base and the particularity of energy structure and price; (3) Take the road of innovation on the basis of learning from foreign countries, and point out the direction for the future development of heat pump research in China.
2. Stagnation of heat pump application (1966 ~ 1977)
This period is in a "ten-year turmoil" period, during which the application and development of heat pumps are basically at a standstill. During this period, no academic papers about heat pump were published, and no translation and works about heat pump were officially published. China has never had a heat pump academic seminar, nor has it sent anyone to any international heat pump academic conference, so it has been isolated from the world for more than 10 years. Only the research team led by Xu Bangyu and Wu of Harbin Institute of Architecture and Engineering completed the final work of developing LHR20 heat pump unit from 1966 to 1969, and passed the technical appraisal at 1969, which was the only heat pump research work in China during the Cultural Revolution. Then, Harbin Air Conditioning Machinery Factory started small batch production, and the first unit was installed in the finishing workshop of Anda Machine Repair Factory in Heilongjiang Province. The actual operation results in the field completely meet the requirements of constant temperature and humidity of (20 1)℃ and (60 10)%. This is the first constant temperature and humidity project realized by heat pump unit in China.
3. Recovery and prosperity period of heat pump application development (1978 ~ 1999)
From 1978 to 1988, the application and development of heat pumps in China have entered a comprehensive recovery stage. During this period, in order to fully understand the current situation and progress of heat pump development abroad, a large number of related works have been published, domestic publications have actively published heat pump translations, tested and analyzed foreign heat pump products, and actively participated in international academic exchanges. At the same time, some well-known foreign heat pump manufacturers began to invest and build factories in China. For example, American Carrier Company was one of the first foreign companies to invest in China, and took the lead in establishing a joint venture company in Shanghai on 1987.
During the period from1989 to1999, heat pumps in China ushered in a new development course. The forms of heat pumps used in China are diversified, including air-to-air heat pump, air-to-water heat pump, water-to-air heat pump and water-to-water heat pump. During this period, there were no fewer than 300 state-owned, private, sole proprietorship, joint venture and other air-conditioning enterprises in China, gradually forming a complete heat pump air-conditioning industrial system in China, and water source heat pump air-conditioning systems were widely used in China. According to statistics, by 1999, there were about 100 projects in China and 20,000 underground water source heat pumps were in operation. In the early 1990s, a large number of air source heat pump cold and hot water units were produced. In the mid-1990s, the underground water heat pump cold and hot water unit was developed. In the late 1990s, sewage source heat pump system began to appear. The research of soil coupled heat pump has become a hot spot in the field of HVAC in China. The domestic research direction and content mainly focus on the underground heat exchanger, which is an innovation based on foreign technology.
1978- 1999 The Second Professional Committee of China Refrigeration Society hosted the 9th National Academic Conference on Waste Heat Refrigeration and Heat Pump Technology. 1988 Guangzhou institute of energy, Chinese academy of sciences hosted an expert seminar on the application and development of heat pumps in China. Since the 1990s, the HVAC Committee of China Architecture Society and China Refrigeration Society has specially added "heat pump" to the annual meeting of HVAC in China.
1988, China Building Industry Press published the textbook Heat Pump written by Professor Xu Bangyu. The principle and application of heat pump edited by Professor Yu was published by Mechanical Industry Press 1993, the technology and application of heat pump for air conditioning edited by Professor Jiang Nengzhao 1997, and the application of heat pump technology in air conditioning edited by Dr. Zheng Zuyi 1998. 1994 Huazhong university of science and technology press published Zheng zuyi's design and innovation of heat pump air conditioning system. From 1989 to 1999, a total of 270 papers related to heat pumps were officially published, including 16 1 and 77 invention patents. The publication of these textbooks, works, translations and papers and the application of patented technology have promoted the popularization and popularization of heat pump technology in China.
4. The rapid development period of heat pump technology
After entering the 2 1 century, due to the acceleration of urbanization and the growth of per capita GDP, the development of China's air-conditioning market has been promoted, and the application scope of heat pumps in China has become more and more extensive. The development of heat pump is very rapid, and the research of heat pump technology is also constantly innovating. The application and research of heat pump are unprecedentedly active and fruitful. From 2000 to 2003, the total number of patents was 287, which was 4.9 times that of 1989 to 1999. From 2000 to 2003, there were 1 19 invention patents, which was 4.25 times of the average 1989 ~ 1999 invention patents. From 2000 to 2003, the number of heat pump literature increased sharply, for example, the number of literature in 2003 was five times that of 1999. Almost all provinces and cities in China have engineering examples of applying heat pump technology. The research of heat pump technology is more active, and innovative achievements emerge one after another. In just a few years, there are three world-leading innovations, including: the same well recharge heat pump system, the integrated system of soil cold storage and soil coupled heat pump, and the two-stage coupled heat pump system for cold regions.
5. Application and research of ground source heat pump
The research on ground source heat pump in China began in 1980s. At first, some universities and scientific research institutions made special research on the related technologies of ground source heat pump. For example, Beijing University of Technology has studied deep geothermal water, and designed several ground source heat pump test systems with vertical and horizontal buried pipes. Basic research and evaluation on the application of water-loop heat pump air conditioning system in Harbin Institute of Technology, numerical simulation and experimental research on the integrated system of soil cold storage and soil coupled heat pump, and research on the coupling theory and key technologies of heat and seepage in ground source heat pump system; Hunan University has built a horizontal ground source heat pump system. In addition, Qingdao Institute of Civil Engineering and Architecture, Shandong Institute of Civil Engineering and Architecture, Shanghai Tongji University, Tianjin Business School, chongqing jianzhu university and other universities have also conducted research in this field. In recent years, several universities in China have carried out experimental research on ground source heat pump system and water source heat pump system, and achieved some important results.
At present, the research on the development and utilization of shallow geothermal energy in China is developing rapidly. After nearly 20 years of research and development, heat pump technology has made great progress in China, especially the ground source heat pump technology has developed rapidly. The construction technology and technical requirements, well group design and calculation methods, water quality evaluation and treatment methods and environmental evaluation methods of various underground water source heat pump systems are initially established.
By the end of 2008 10, the application area of shallow geothermal energy in China exceeded 1× 108 m2 (published by ground source heat pump in May 2009). All over Beijing, Shanghai, Tianjin, Hebei, Henan, Shanxi, Liaoning, Sichuan, Hunan, Tibet, Xinjiang and other places. The types of buildings used are hotels, houses, shopping malls, office buildings, schools, stadiums (gymnasiums), hospitals, exhibition halls, military camps, villas and factories. And has a broad application prospect.
6. Development and utilization of shallow geothermal energy and its development trend
The development and utilization of shallow geothermal energy involves urban energy structure, environmental protection and improving people's quality of life. In particular, the renewable energy collection system of shallow underground water source heat pump and ground source heat pump is the key to solve the above main problems, and its energy collection is basically unaffected by the use area and the four seasons climate. Shallow geothermal energy, as the initial collection of building cold and heat sources, has more popularization value.
The development and utilization of shallow geothermal energy is not only concerned by academic and business circles, but also paid more and more attention by the government. The Renewable Energy Law of People's Republic of China (PRC) clearly points out that the state lists the scientific and technological research and industrialization development of renewable energy as the priority areas of scientific and technological development and high-tech development. The state finance supports the investigation and evaluation of renewable energy resources and the construction of related information systems. The implementation of this law provides a strong basis and guarantee for the investigation, evaluation and development of shallow geothermal energy. The Ministry of Land and Resources, China Geological Survey and other departments have held many experience exchanges and technical seminars on shallow geothermal energy exploration and development, and compiled and promulgated the shallow geothermal energy exploration and evaluation norms, so that shallow geothermal energy exploration and development has standards to follow. In recent years, with the country building a "resource-saving, environment-friendly" society and achieving the goal of energy conservation and emission reduction, the state has arranged special funds from the central government to support the demonstration and promotion of renewable energy building applications, and the Ministry of Finance and the Ministry of Construction have approved three batches of demonstration and promotion projects of renewable energy building applications, including shallow geothermal energy utilization. Various localities have also introduced projects to support the development and utilization of shallow geothermal energy. For example, on May 3, 20061,the Beijing Municipal Development and Reform Commission, together with the Municipal Water Conservancy Bureau and the Land and Resources Bureau, issued a document to subsidize the heating and cooling projects using the ground source heat pump system according to the standard of 35 yuan per square meter, and the heating and cooling projects using the ground source heat pump system according to the standard of 50 yuan per square meter; In the "Implementation Opinions on the Construction and Application of Ground Source Heat Pump System" issued by Shenyang, it is required to plan and study buildings that meet the application of groundwater heat pump technology in the core area of 455km2 within the Third Ring Road of Shenyang in principle.
In the 2 1 century, with the rapid development of China's economy, people's requirements for quality of life and comfort have been continuously improved, and the urban energy structure has changed. The huge construction market has created unprecedented opportunities for the popularization of shallow geothermal energy development and utilization technology. China has made gratifying achievements in theoretical research, experimental research, product development and engineering project application.
At present, China has established a relatively complete engineering technology, mechanical equipment and monitoring system for the development and utilization of shallow geothermal energy, but the water quality control and evaluation of the impact of recharge on reservoirs and water pipes, the treatment technology of blocked wells, the simulation calculation method of temperature field, chemical field and pressure field of well group mining and irrigation system, and the method of obtaining parameters are still under study.