(Survey, Design and Research Institute of Zhongyuan Petroleum Exploration Bureau)
This paper introduces the concept and working principle of ground source heat pump, and then discusses the characteristics of ground source heat pump in detail, and the restrictive conditions of its development in China, and introduces its application and development prospect in China. Finally, it is clearly pointed out that ground source heat pump technology is the most friendly and effective heating and cooling technology for human beings.
1 Concept and working principle of ground source heat pump
Ground source heat pump is an efficient and energy-saving air conditioning system, which uses shallow underground geothermal resources (including groundwater, soil and surface water) to provide heating and cooling at the same time. Using inverse Carnot cycle, low-grade heat energy can be converted into high-grade heat energy by inputting a small amount of high-grade electric energy. Heat pump generally consists of evaporator, condenser, compressor and expansion valve.
The working principle of ground source heat pump is: in summer, the heat pump unit takes out heat from the building and transfers it to the stratum; In winter, heat is extracted from the stratum to provide heat for buildings. Generally, ground source heat pump consumes energy 1kW, and users can get heat or cooling capacity above 4kW.
2 characteristics of ground source heat pump
As we know, the ground temperature at a certain depth below the surface is relatively constant all year round, and the ground source heat pump uses shallow geothermal energy as a cold and heat source, thus eliminating the influence of environmental factors. Compared with other heating and cooling systems, it has the following remarkable characteristics.
2. 1 Use renewable energy.
Ground source heat pump absorbs the heat emitted by buildings in summer and stores it in shallow underground. Part of the heat is used for building heating in winter, and the other part is directly radiated into the air. As far as the whole year is concerned, the heating or cooling capacity of buildings using shallow geothermal energy is roughly the same. Therefore, the ground source heat pump uses renewable energy.
2.2 High efficiency and energy saving
Because the heat source temperature of ground source heat pump is generally 10 ~ 22℃ all year round, and the water temperature is higher than the ambient temperature when heating in winter, the evaporation temperature and energy efficiency ratio of heat pump cycle are improved. When cooling in summer, the water temperature is lower than the ambient temperature, which improves the cooling effect and unit efficiency. The refrigeration and heating coefficient of water source heat pump can reach above 4.0, which is about 40% higher than that of traditional air source heat pump. The operating cost is only 50% ~ 60% of that of ordinary central air conditioning, and it saves about 70% of electricity compared with electric boiler and electric heating film.
2.3 Significant environmental benefits
When the water source heat pump is running, it only needs the heat or cold of the source water, the water quality is unchanged, no pollution is produced, no water, smoke or dust is consumed, and only a small amount of electric energy is consumed.
In terms of power consumption, energy saving means environmental protection. The pollutant emission caused by using water source heat pump is 40% less than that of air source heat pump and 70% less than that of electric boiler. Although ground source heat pump also uses refrigerant, it reduces irrigation by 25% compared with conventional air conditioning. The ground source heat pump is completely sealed in the factory and will not leak easily when installed like split air conditioners.
2.4 One machine is multi-purpose
Ground source heat pump can provide heating, cooling and domestic hot water. That is, a set of equipment can replace the original boiler and air conditioning system, so the one-time investment is only 50% ~ 70% of the traditional heating and cooling. Especially when cooling in summer, the heat generated by heat pump can be used to provide domestic hot water for users free of charge. Therefore, ground source heat pump is especially suitable for buildings with both heating and cooling and domestic hot water supply.
2.5 Saving land resources
Water source heat pump has no other installation equipment except main engine and circulating water pump. Compared with boiler room, it saves water treatment room, fan room, chimney, coal yard and muck yard, and saves land resources.
2.6 Stable and reliable operation and long service life.
Because the water temperature of ground source heat pump is stable, compared with air source heat pump, it avoids the influence of frosting and defrosting. The heat pump has few moving parts, basically no maintenance, stable and reliable operation, and its service life can reach about 20 years.
2.7 High degree of automation
Generally, ground source heat pumps are fully computer-controlled, which can adjust the number of compressor workstations according to the change of external load, and are equipped with various protection measures such as compressor over-temperature protection and water cut-off protection, which can realize unattended operation.
Composition of ground source heat pump heating system
Ground source heat pump engineering generally consists of ground source water system, heat pump room and end fan coil cooling system. According to the form of ground source heat exchange system, it can be divided into open-loop system and closed-loop system.
Open-loop system is to pump water from wells (including lakes and rivers), send it to heat exchanger groups for heat exchange, and then inject the water after extracting heat energy or cold energy into the wells. In general, the water in the open-loop system is only treated simply, which will cause scaling on the surface of the heat exchanger. Open system is the main form of ground source heat pump application at present.
Closed-loop system is divided into vertical buried loop system and horizontal buried loop system. It exchanges heat with soil through buried polyethylene pipe loop. It is usually suitable for installation in buildings with large venues such as villas.
4 constraints of ground source heat pump
Ground source heat pump is called by experts as the friendliest and most effective form of heating and cooling available to mankind at present. In recent years, it has developed rapidly in research and application. However, due to the limitations of the following objective conditions, the application of this technology is not universal.
4. 1 Lack of publicity and understanding
Although the ground source heat pump technology is highly praised by heating experts, it needs the approval of leaders at all levels, especially those in charge of engineering, in order to be widely used in engineering. Because this technology is developed with the adjustment of China's energy strategy in recent years, even some heating technicians have insufficient understanding. Therefore, to gain social recognition, it is necessary to increase publicity.
4.2 the policy is not strong enough
In China's Energy Conservation Law, cogeneration and central heating technology are encouraged and developed, but there is no clear stipulation to encourage the development of ground source heat pump technology with double comprehensive energy utilization rate.
4.3 restrictions on water conditions
Whether the open-loop ground source heat pump system has sufficient water and whether the local geological soil conditions can ensure the smooth implementation of tail water recharge is the premise of the application of ground source heat pump. Generally speaking, when used for district heating, the building floor area ratio should be ≤ 1. For the closed system, it is limited by environmental conditions such as whether the local geological conditions are suitable for burying pipes and whether there is enough ground for burying pipes.
4.4 The heat transfer calculation theory of buried pipe system is immature.
At present, the technology of ground source heat pump unit and terminal fan coil cooling system is quite mature. For the open system, the local water conservancy department is also quite familiar with the water source situation; For the buried pipe system, the theory of heat transfer calculation of soil buried pipe is not mature at present, the design lags behind the engineering application, and the engineering quality is difficult to guarantee, which limits the wide application of this technology.
4.5 Limited by the policies of local water conservancy departments
South China is rich in water resources, but most areas in the north are short of water resources. In order to protect the limited water resources, every local government has formulated local water resources utilization regulations. Although the ground source heat pump system does not consume water and pollute groundwater, it needs a lot of water as a heat carrier. Some local departments charge double fees for water intake and recharge, which makes the energy-saving effect of ground source heat pump not fully reflected and limits the development of this technology in these areas.
Application of Ground Source Heat Pump
5. 1 foreign application
Ground source heat pumps are widely used in Japan, South Korea, the United States, Central Europe and Northern Europe. According to 1999 statistics, the proportion of ground source heat pump in residential heating devices is 96% in Switzerland, 38% in Austria and 27% in Denmark. The ground source heat pump system in the United States accounts for 30% of the new buildings in 1998, and it is growing steadily at the rate of 10%. The most famous ground source heat pump project is the waterfront office building in Louisville, Kentucky, with a service area of 15.8× 104 m2, saving 25,000 USD per month. With the application and development of this technology, the research on its organization has also developed rapidly. According to relevant data, the high-temperature water-ground source heat pump developed in Japan has an outlet water temperature of 80 ~ 150℃ and a heating coefficient of COP as high as 8.0.
5.2 Domestic application
Professor Lv Canren from the Institute of Thermal Energy of Tianjin University started the earliest heat pump research in China in 1954, and successfully developed the first water-cooled heat pump unit in China in 1965. At present, many universities and research institutions are studying water source heat pumps.
Tsinghua Tongfang Artificial Environment Equipment Co., Ltd. and Shandong Haiyang Fulda are the earlier water source heat pump manufacturers in China, and their products have been serialized. At present, the outlet water temperature of heat pump unit has reached 65℃, and the refrigeration coefficient COP can reach 6.7. At present, the typical domestic user is Shenyang Northeast Electric Power Residential Area, with a service area of 8×104m2; ; The service area of Beijing Friendship Hospital is 7. 1× 104m2, which saves about 9 yuan /m2 in heating and cooling operation cost every year.
The water source heat pump demonstration project of the office building of Zhongyuan Oilfield Drilling Company No.3 is the first ground source heat pump system in our bureau. Two ZYRB240 heat pump units jointly developed and produced by General Drilling Office and Tsinghua University are selected, with a service area of 6000m2. The successful implementation of this project will definitely promote the popularization and application of ground source heat pump in Zhongyuan Oilfield.
6 development prospect of ground source heat pump
6. 1 meets the requirements of relevant government departments.
Ground source heat pump is efficient and energy-saving, with good environmental benefits, in line with China's energy policy and environmental protection policy. The comprehensive energy utilization rate of heat pump technology is about 120% ~ 180%. Therefore, the country encourages the development of cogeneration technology as a general energy-saving technology and promotes the development of ground source heat pump technology.
6.2 in line with the interests of the owner
Because the ground source heat pump can supply heat and cool at the same time. One system can replace the original two systems with less investment. Ground source heat pump occupies less land, has low operating cost and convenient management, which is in line with the fundamental interests of the owners.
6.3 in line with the interests of users
The heating cost of ground source heat pump is half of that of coal-fired centralized boiler room, and the cooling cost in summer is about 60% of that of water chillers, which reduces the expenditure of heating and cooling costs for users and conforms to their vital interests.
6.4 Wide scope of application
Water chillers can only be used for cooling in summer, air-cooled units are only suitable for heating and cooling in the Yangtze River basin, and ground source heat pumps are suitable for most areas except a few areas where groundwater cannot be used and pipes cannot be buried.
6.5 The scope of application is constantly expanding.
Ground source heat pump not only develops rapidly in building heating and refrigeration, but also is widely used in chemical industry, food, paper making, agriculture, metallurgy, wood drying, pharmacy and other industries. It is predicted that more than 1200 ground source heat pumps will be used in these industries in 2000, and the development momentum is strong.
To sum up, ground source heat pump technology has developed rapidly in China in recent years with its unique advantages. With the adjustment of China's energy structure policy, China's traditional coal-fired boiler heating and air source heat pump cooling will be replaced by more efficient ground source heat pump. With the research and development of ground source heat pump technology, it will become the most common and effective heating and cooling technology in 2 1 century.
refer to
Liu. Introduction of water source heat pump system.2001
[2] Wu. Ground source heat pump air conditioning system.2001
Note: This paper is quoted from Proceedings of the National Conference on Geothermal Development and Utilization in Oil-producing Towns, Metallurgical Industry Press, 2003.