1. History of the development of ground source heat pumps

The research on heat pump technology in my country began in the 1950s. The Thermal Energy Research Institute of Tianjin University carried out the earliest research on heat pumps in my country. Professor Lu Canren's 1956 article "Heat Pumps and the Prospects of their Application in my country" is the earliest existing document on heat pump research in my country.

In the 1960s, my country began to apply and develop heat pumps in HVAC and achieved a large number of results. In 1960, Professor Wu Chenyuan of Tongji University published "Introduction to Heat Pump Heating and Suggestions for Trial of Heat Pump Heating in Jinan City"; in 1963, the former East China Architectural Design Institute and Shanghai Air Conditioner Factory began to develop heat pump air conditioners; in 1965, Shanghai Refrigerator Factory successfully developed my country's first CKT-3A heat pump window air conditioner with a heating capacity of 3720W; in 1965, Tianjin University and Tianjin Air Conditioner Factory developed the first domestic groundwater heat pump air conditioning unit; in 1966, it cooperated with the Sifang Rolling Stock Research Institute of the Ministry of Railways* In 1965, a scientific research group led by Professor Xu Bangyu and Professor Wu Yuanwei of the former Harbin Institute of Architectural Engineering proposed for the first time the application of an auxiliary condenser as a constant temperature and humidity air conditioning unit based on the heat pump theory. The new process of secondary heater is the world's first new process; in 1966, together with Harbin Air Conditioning Factory, we began to develop a new vertical cabinet-type constant temperature humid heat pump air conditioner that uses the condensation waste heat of the refrigeration system as secondary heating of the air conditioner. .

From 1978 to 1988, the application and development of heat pumps in my country entered a stage of comprehensive recovery. During this period, in order to fully understand the current status and progress of foreign heat pump development, a large number of relevant works were published. Domestic publications actively published translations of heat pumps, 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, the American Carrier Company was one of the first foreign companies to invest in China and took the lead in establishing a joint venture in Shanghai in 1987.

During the period from 1989 to 1999, heat pumps in my country ushered in a new development milestone. The forms of heat pumps used in our country have begun to diversify, including air/air heat pumps, air/water heat pumps, water/air heat pumps and water/water heat pumps. During this period, there were no less than 300 household air conditioner manufacturers in China, including state-owned, private, wholly-owned, and Taiwan-funded, gradually forming a complete industrial system for heat pump air conditioners in my country. Water loop heat pump air conditioning systems are widely used in our country. According to statistics, by 1999, there were about 100 projects and 20,000 groundwater heat pump units in operation across the country. Mass production of air source heat pump hot and cold water units began in the early 1990s, well groundwater heat pump cold and hot water units were developed in the mid-1990s, and sewage groundwater heat pump systems began to appear in the late 1990s. Research on soil-coupled heat pumps has become a hot research topic in the domestic HVAC industry. Domestic research directions and contents mainly focus on underground pipe heat exchangers, with innovations based on foreign technologies.

After entering the 21st century, due to my country's rapid urbanization and the growth of per capita GDP, it has promoted the development of China's air-conditioning market and promoted the wider application of heat pumps in our country. The development of heat pumps is very rapid. Heat pumps Technology research continues to innovate. From 2000 to 2003, the application and research of heat pumps were unprecedentedly active and fruitful.

In the four years from 2000 to 2003, the total number of patents was 287, with an annual average of 71.75, which was 4.9 times the average number of patents from 1989 to 1999. From 2000 to 2003, there were 119 invention patents, with an annual average of 29.75, which is 4.25 times the average number of invention patents from 1989 to 1999.

The number of heat pump literature increased dramatically from 2000 to 2003. For example, the number of literature in 2003 was five times that of 1999. There are 105 graduate students studying heat pump technology in universities across the country, with an average of 26.25 per year, more than seven times the average in the 1990s.

There are engineering examples of applying heat pump technology in almost all provinces and cities across the country. Research on heat pump technology has become more active, with numerous innovative results. In just a few years, three innovative achievements have come out: the same well recirculation heat pump system, the soil cold storage and soil coupling heat pump integrated system, and the single- and double-stage coupled heat pump systems for cold areas.

2. Research on the application foundation and practice of ground source heat pumps

The research on ground source heat pumps in my country started in the 1980s. First, some universities and scientific research institutions related to ground source heat pumps. A special study was conducted on technology. Some research projects are listed in Table 3-1.

Table 3-1 Some research topics on ground source heat pumps in universities

Research work mainly focuses on the following aspects: heat transfer model and heat transfer research of underground buried tube heat exchangers; Research on numerical simulation of transient operating conditions in summer; theoretical and practical research on simulation models of heat pump devices and components;

Research on refrigeration working fluid substitution in ground source heat pump air conditioning systems; other energy sources such as solar energy, water energy, etc. Research on the joint application of geothermal sources; design and construction of geothermal heat pump systems; research on the economic performance and operating characteristics of geothermal heat pump systems; underground groundwater heat pump recharge technology and practice; experimental research on soil thermal physical properties and soil thermal conductivity.

Numerical simulation and experimental research on groundwater migration in the same well recharged underground groundwater heat pump; basic research on the application of soil cold storage and soil source heat pump integrated systems, etc.