The concept, characteristics and working principle of water source heat pump technology
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Summary of the concepts, characteristics and working principles of water source heat pump technology: This article first introduces the concept and working principle of water source heat pump technology, and compares it with boilers and air source heat pumps from the perspective of energy utilization. It is concluded that water source heat pump technology is a technology that utilizes renewable energy. Then, the characteristics of water source heat pumps were described in detail and the basic situation of ground source applications at home and abroad and the current prospects for the development and application of water source heat pumps in China were introduced. Finally, the technical characteristics of Tsinghua Tongfang water source heat pumps and some problems in the promotion and application of water source heat pumps in China were introduced in particular. 1. Concept and working principle of water source heat pump technology Water source heat pump technology is a technology that utilizes the solar energy and geothermal energy absorbed from shallow water sources on the earth's surface such as groundwater, rivers and lakes to form low-temperature and low-level thermal energy resources, and adopts the heat pump principle to realize the transfer of low-level thermal energy to high-level thermal energy through a small amount of high-level electrical energy input. Shallow water sources on the earth's surface, such as groundwater with a depth of less than 1,000 meters, surface rivers, lakes and oceans, absorb considerable radiation energy from the sun entering the earth, and the temperature of the water sources is generally very stable. The working principle of the water source heat pump unit is to transfer the heat in the building to the water source in the summer. Because the water source temperature is low, it can take away the heat efficiently. In the winter, the energy is extracted from the water source. The heat pump principle uses air or water as a refrigerant to raise the temperature and then send it to the building. Usually a water source heat pump consumes 1kW of energy, and users can get more than 4kW of heat or cooling. Water source heat pumps can be divided into closed systems and open systems according to the different ways of utilizing water sources. A closed system refers to a set of closed-circulation heat exchange casings on the water side. This set of casings is generally buried horizontally or vertically in the ground or in lake water and seawater, and achieves energy transfer by exchanging heat with soil or seawater. (The system buried in the soil is also called a soil source heat pump, and the system buried in seawater is also called a seawater source heat pump). An open system refers to a system that pumps water from underground or from the surface and discharges it directly through a heat exchanger. Compared with heating systems such as boilers (electricity, fuel) and air source heat pumps, water source heat pumps have obvious advantages. Boiler heating can only convert 90% to 98% of electric energy or 70 to 90% of fuel internal energy into heat for users to use. Therefore, ground source heat pumps save more than two-thirds of electric energy than electric boilers and more than one-half of energy than fuel boilers. ； Since the heat source temperature of water source heat pumps is relatively stable throughout the year, generally 10 to 25°C, its cooling and heating coefficients can reach 3.5 to 4.4, which is about 40% higher than traditional air source heat pumps. Its operating costs are 50 to 60% of ordinary central air conditioners. Therefore, in the past ten years, especially in the past five years, water source heat pump air conditioning systems have been widely used in North America such as the United States, Canada, and central and northern Europe such as Switzerland and Sweden. * * Having achieved rapid development, China's water source heat pump market is becoming increasingly active. It can be expected that this technology will become the most effective heating, cooling and air-conditioning technology in the 21st century. In China's traditional air conditioning system concept, due to * * Due to the influence of economic development conditions and policies, for a long period of time, coal-fired boilers were generally used in the north to solve the winter heating problem, and in the south, water-cooled units were used to solve the summer cooling problem. After the 1980s, the methods of refrigeration units began to diversify. At this time, lithium bromide units and air-cooled units appeared, and the capacity of the units also transitioned from the original large and medium-sized units to large, medium and small units. After the 1990s, new attempts and discussions began on heating methods. Especially with the improvement of sustainable development and public awareness of environmental protection, the structure of energy utilization in the world and China is changing, from the original coal and oil heating to clean energy such as natural gas and electricity. As one of the cities with the most serious air pollution, Beijing’s policies to control air pollution include the adjustment of the energy structure, from coal as the main source of energy to natural gas and electricity as alternative energy sources. However, although alternative energy can partially solve the problem of air pollution, natural gas and oil are non-renewable energy sources. From the perspective of sustainable development, it is necessary to improve energy efficiency or find renewable energy sources, and water source heat pump units are an ideal equipment.
2. Characteristics of water source heat pumps Since water source heat pump technology uses surface water as the source of cooling and heating for air conditioning units, it has the following advantages:: 1. It is a renewable energy utilization technology. Water source heat pump is a heating and air conditioning system that uses the solar energy resources stored in the earth's water bodies as a cold and heat source to convert energy. Water bodies that can be utilized include groundwater or rivers, surface rivers and lakes, and oceans. The surface soil and water bodies are not only a huge solar collector, collecting 47% of the solar radiation energy, which is more than 500 times the energy used by humans every year (the underground water body indirectly receives solar radiation energy through the soil), but also a huge dynamic energy balance system. The surface soil and water bodies naturally maintain a relative balance of energy reception and dispersion. This makes it possible to harness the nearly unlimited amount of solar or geothermal energy stored within it. Therefore, water source heat pumps use clean renewable energy technology. 2. The water temperature that can be utilized by the high-efficiency and energy-saving water source heat pump unit is 12 to 22°C in winter. The water temperature is higher than the ambient air temperature, so the evaporation temperature of the heat pump cycle increases and the energy efficiency ratio also increases. In summer, the water temperature is 18-35°C, and the water temperature is lower than the ambient air temperature, so the condensation temperature of refrigeration is reduced, making the cooling effect better than air-cooling and cooling tower types, and the unit efficiency is improved. According to estimates by the U.S. Environmental Protection Agency, a well-designed and installed water source heat pump can save users 30 to 40% of the operating costs of heating, cooling and air conditioning on average. 3. Stable and reliable operation The temperature of the water body is relatively stable throughout the year, and its fluctuation range is much smaller than the fluctuation of the air. It is a good heat source for heat pumps and cold sources for air conditioners. The relatively constant temperature of the water body makes the operation of the heat pump unit more reliable and stable, and also ensures the efficiency and economy of the system. There are no difficult problems such as defrosting in winter with air source heat pumps. 4. Significant environmental benefits Water source heat pumps use electric energy, which is a clean energy source. However, when generating electricity, it consumes primary energy and results in the emission of pollutants and carbon dioxide greenhouse gases. Therefore, energy-saving equipment itself causes less pollution. The power consumption of a well-designed water source heat pump unit is equivalent to a reduction of more than 30% compared with an air source heat pump, and is equivalent to a reduction of more than 70% compared with electric heating. The refrigerant used in water source heat pump technology can be alternative common materials such as R22 or R134A, R407C and R410A. The operation of water source heat pump units does not cause any pollution and can be built in residential areas. There is no combustion, no smoke exhaust, and no waste. There is no need for a place to store fuel waste, and there is no need to transport heat over long distances. 5. One machine has multiple uses and has a wide range of applications. The water source heat pump system can be used for heating, air conditioning, and domestic hot water. One machine has multiple uses. One system can replace the original two devices or systems of boiler and air conditioning. Especially for buildings with both heating and cooling requirements, water source heat pumps have obvious advantages. Not only does it save a lot of energy, but one set of equipment can meet the heating and cooling requirements at the same time, reducing the initial investment in equipment. Water source heat pumps can be used in hotels, shopping malls, office buildings, schools and other buildings. Small water source heat pumps are more suitable for heating and air conditioning in villas. 6. Due to the stable working conditions of the automatic water source heat pump unit, a simple system can be designed with fewer components, the unit operation is simple and reliable, and the maintenance cost is low. ； It has a high degree of automatic control and a long service life of more than 15 years. Of course, like anything, water source heat pumps are not perfect, and their applications will be restricted. ⑴, Available water source conditions limit Water source heat pumps can theoretically utilize all water resources. In fact, in actual projects, the cost difference of different water resource utilization is quite large. Therefore, whether there are suitable water sources in different areas has become a key to the application of water source heat pumps. Among the current water source heat pump utilization methods, closed systems generally have higher costs. In an open system, the ability to find a suitable water source becomes a restriction for the use of water source heat pumps. For split systems, the water source requirements must meet certain temperature, water volume and cleanliness. ⑵2. Restrictions on the geographical structure of the water layer. For the use of pumping water from underground for recharge, the geological structure of the place of use must be taken into consideration to ensure that a suitable water source can be found by drilling a well under economic conditions. At the same time, the local geology and soil conditions should also be considered to ensure that the recharge of tail water after use can be achieved. ⑶, the economics of investment are affected by different regions, different users and * * The impact of energy policies, fuel prices, and differences in basic conditions of water sources ； One-time investment and operating costs will vary from user to user. Although generally speaking, water source heat pumps have higher operating efficiency and lower costs. However, compared with traditional air conditioning, cooling and heating methods, the investment economics of water source heat pumps will be different under the conditions of different needs in different regions. 3. Development and characteristics of water source heat pumps at home and abroad
In foreign countries, research on water source heat pumps falls into two types of heat pump systems: One is a ground source heat pump and the other is a seawater heat pump. Among them, the real commercial application of ground source heat pumps only has a history of more than ten years, but it is developing quite rapidly. For example, in the United States, as of 1985, there were 14,000 ground source heat pumps in the country, and 45,000 units were installed in 1997. So far, 400,000 units have been installed, with a steady growth of 10% every year. In 1998, ground source heat pump systems accounted for 19% of the total air conditioner holdings in commercial buildings in the United States, including 30% in new buildings. The U.S. ground source heat pump industry has been established by the Energy & Environmental Research Center, the National Ground Water Association, the Edison Electric Institute and many ground source heat pump manufacturing, design and sales companies. * * The American Geothermal Heat Pump Association, composed of 146 members including institutions and builders, will invest US$100 million in development, research and promotion in recent years. The United States plans to reach the goal of installing 400,000 ground-source heat pumps per year by 2001, of which water-source heat pumps account for 15%. By then, it will reduce greenhouse gas emissions by 1 million tons, which is equivalent to reducing pollutant emissions from 500,000 cars or planting 1 million acres of trees. The annual energy cost savings will reach 420 million US dollars. After that, the annual energy cost savings will increase by another 170 million US dollars. American water source heat pump manufacturers include well-known companies such as Addison Products Company, Advanced Geothermal Technology, Carrier Corporation, Climate Master Inc., Econar Energy Systems Corporation, FHP Manufacturing, Mammoth Inc., The Trane Company, Water Furnace International and other companies. The research and application of water source heat pumps in the United States is more focused on small-scale residential and commercial systems (below 20RT), mostly using water-air systems, such as products launched by the well-known TRANE. In terms of large buildings, the United States promotes WLHP systems, which are water loop heat pump systems. Different from the development of ground source heat pumps in the United States, central and northern Europe such as Sweden, Switzerland, Austria, Germany, etc. * * It mainly uses shallow geothermal resources and coils buried in the underground soil (buried depth
Tsinghua Tongfang's water source adopts the technical route when designing its products:: R22 was selected as the refrigerant, mature heat pump technology was adopted, China's actual national conditions were considered, the focus was on the realization of high water temperature and wide operating temperature, the compressor operating point and operating range were selected and determined, and a segmented water heat exchanger with a large temperature difference was designed based on the idea of saving water and energy. The design of the fluorine system adopts a complete sub-system * * Based on the modular idea, the system components are small in number and of high quality. The control system fully considers the coordinated and unified control of multiple systems and sets up a variety of safety protections. It also considers the pump control and remote operation of the water system. In addition to having all the characteristics of traditional water source heat pumps, Tsinghua Tongfang's water source heat pump unit is a system designed according to China's national conditions. Its noteworthy features include:: 1. The heating outlet water temperature is high. Under standard working conditions, the water source heat pump we provide can ensure that the outlet water temperature is stable at 52°C. In testing and actual use by users, we have conducted operating experiments at 56°C. Providing high outlet water temperature can improve efficiency, reduce the selection capacity of indoor equipment, and ensure indoor thermal comfort. 2. The temperature difference between the inlet and outlet water on the water source side is large, saving water resources. When the unit is working, the temperature difference between the inlet and outlet water on the water source side in winter is 7℃, while the temperature difference between the inlet and outlet water in summer is 10℃. Different from the traditional 5℃ temperature difference design, it can save 20%-50% of water and correspondingly reduce the cost of water intake (such as well digging and water pump operation). This idea was demonstrated by Mr. Yan Qisen in the 1997 "Technological Development Status and Prospects of my country's Refrigeration and Air Conditioning Industry". 3. The system is optimized and simple, and the components are excellent and reliable. Through the optimized design of the system and * * Through the combination of modules, the final unit system is quite simple and reliable, but the refrigeration components are all selected from high-quality brands in the industry to ensure reliable operation of the unit. 4. The unit has large capacity and a wide range of applications. The minimum capacity of a single unit designed for the unit is 150KW of heat. It can be an open system or a closed system. Groundwater can be utilized by drilling wells for recharge, or an intermediate heat exchanger can be added to utilize river water, lake water or even sea water. You can even use geothermal tailwater. 5. Simple and quiet operation. Due to the intelligent automatic control, the operation of the unit is quite simple. Due to the use of efficient protection and noise reduction measures, the operating noise of the unit is no longer unacceptable. 5. Problems existing in the current promotion and application of water source heat pumps in China As a new cooling and heating method, water source heat pumps should be quite mature and problem-free from a technical point of view, especially from the point of view of heat pump units. However, considering China's national conditions and the promotion and application of water source heat pump cooling and heating as a whole system, there are still some problems.: 1. Water source use policy In order to protect limited water resources, my country has formulated the "Water Law of the People's Republic of China", and each city has also formulated its own "Urban Water Management Regulations". These policies all emphasize water use approval and water use charging. There are no requirements for similar water source heat pump technologies in the approval standards, so water source heat pumps are easily restricted by water use indicators. Even if the water use approval is passed, because some places charge twice for the extraction and discharge of water sources, and the charging standards are not uniform across the country, the result may be that the water fee is high, making the energy-saving cost of operating the water source heat pump insufficient to increase the water fee, and the economics of the water source heat pump will change. Therefore, the promotion of water source heat pumps needs * * From the perspective of sustainable development, considering all aspects of energy, environmental protection and resources, the policy of adjusting the water source of water source heat pumps needs to be re-determined how to manage and charge water sources in order to promote its large-scale development. 2. Water source detection and extraction technology and cost In China, the current detection and extraction technology of water sources, especially urban water sources, should be improved. One of the prerequisites for the application of water source heat pumps is to understand the situation of local water sources. In the early stage of the use of water source heat pumps, the status of the water sources must be investigated on the spot to see whether there is water in the groundwater, whether the water volume will be sufficient, and whether the site is suitable for well drilling and recharge. The improvement of detection and mining technology and the reduction of costs will promote the better application of water source heat pump units.
3. Groundwater recharge technology. If the water source heat pump uses groundwater, the recharge of the water source must be considered. For the recharge technology, the recharge technology must be considered based on the local geological conditions. We still don’t know much about the geological structures in different regions, which also restricts the promotion and use of water source heat pump units. 4. Design of the overall system. As a system, the energy saving of a water source heat pump system must be considered from all aspects. If the water source heat pump unit can provide more energy with a smaller water flow, improper selection or control of energy-consuming equipment such as water pumps in the system design will also reduce the energy saving effect of the system. Similarly, if the unit provides a high water temperature, but the end of the air-conditioning system is designed without corresponding consideration, it may also make the effect of the entire system worse, or increase the initial investment of the entire system. Therefore, the promotion and application of water source heat pumps requires the joint efforts of more people from various professions and fields, including government policies, host design and manufacturing, system design and operation management, and other aspects.
It is not as good as expected. Maintenance of the pumping system, maintenance of the compressor system, water filtration, and many other issues are not that easy. Groundwater is not available to any company or unit, and when it is recharged, it cannot be recharged just anywhere. There is also an air source heat pump, which cannot be used when the temperature is below zero in winter. In summer, the temperature is too high and the compressor is a problem. This is also the reason why it has not been widely popular even after it was invented for decades.
Nowadays, gray water source heat pumps in sewage treatment plants are more commonly used. The source of heat is relatively easy, but there is a problem. It can only be used at short distances. When the distance is long, there is a problem of pipeline transportation and heat dissipation. Our group has now used many gray water source heat pumps, and the results are quite good. It feels similar to central air conditioning. In any space in the building, the temperature is more suitable.
The most difficult part of heat pump technology is underground. It is relatively easy to do it above. However, there is a lack of data on underground factors.