The defining characteristics and basic principles of water source heat pump technology

Abstract: 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 in terms of energy utilization, and concludes that water source heat pump technology is a technology that uses renewable energy. Subsequently, the characteristics of water source heat pumps are described in detail and the basic situation of ground source applications at home and abroad and the prospects of current water source heat pump development and application in China are introduced. Finally, the technical characteristics of Tsinghua Tongfang water source heat pumps and the promotion and application of water source heat pumps in China are introduced. Some problems in.
1. The concept and working principle of water source heat pump technology
Water source heat pump technology is a low-temperature low-level thermal energy resource formed by using solar energy and geothermal energy absorbed from shallow water sources on the earth’s surface, such as groundwater, rivers and lakes, and adopts the principle of heat pump to realize the transfer of low-level thermal energy to high-level thermal energy through a small amount of high-level electrical energy input. Of a technology.
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 radiant 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 from the building to the water source in summer. Due to the low temperature of the water source, the heat can be taken away efficiently. In winter, energy is extracted from the water source. The heat pump principle uses air or water as the carrier. The refrigerant raises the temperature and sends it to the building. Usually 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 two types: closed system and open system according to different ways of using water sources. Closed system refers to a set of closed-loop heat exchange sleeves on the water side. The set of sleeves are generally buried horizontally or vertically in the ground or in lake water and seawater to achieve energy transfer by exchanging heat with soil or seawater. (The system buried in the soil is also called the ground source heat pump, and the system buried in the sea water is also called the seawater source heat pump). An open system refers to a system in which water is pumped from the ground or the surface is directly discharged through a heat exchanger.
Compared with the heating system of boiler (electricity, fuel) and air source heat pump, water source heat pump has obvious advantages. Boiler heating can only convert 90%-98% of electric energy or 70-90% of fuel internal energy into heat for users to use. Therefore, ground source heat pumps can save more than two-thirds of the electric energy compared to electric boiler heating, which is more than fuel. The boiler saves more than one-half of the energy; because the heat source temperature of the water source heat pump is relatively stable throughout the year, generally 10～25℃, its cooling and heating coefficient can reach 3.5～4.4. Compared with the traditional air source heat pump, it needs It is about 40% higher, and its operating cost is 50-60% of that of ordinary central air-conditioning. Therefore, in the past ten years, especially in the past five years, water source heat pump air conditioning systems have achieved rapid development in North America such as the United States, Canada, and Central and Northern Europe such as Switzerland, Sweden and other countries. China’s water source heat pump market has also become increasingly active. It is expected that this technology will become the most effective heating and cooling air-conditioning technology in the 21st century.
In China’s traditional air-conditioning system concept, due to the country’s economic development and policies, for a long period of time, coal-fired boilers are generally used to solve the winter heating problem in the North, and water-cooled units are used to solve the summer cooling problem in the South. After the 1980s, the methods of refrigeration units began to diversify. At this time, lithium-ion units and air-cooled units appeared. After the 1990s, there have been new attempts and discussions on heating methods. Especially with the increase in sustainable development and public awareness of environmental protection, the structure of energy utilization in the world and China is changing from the original coal, Oil heating has transitioned to clean energy such as natural gas and electricity. As one of the cities with the most serious air pollution, Beijing’s air pollution control policies include the adjustment of energy structure, from coal-based to natural gas and electricity as alternative energy sources. However, although alternative energy sources can partially solve the problem of air pollution, natural gas and oil are non-renewable energy sources. From the perspective of sustainable development, energy efficiency must be improved or renewable energy sources must be found. Water source heat pump units are An ideal device.
Second, the 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. Belonging to renewable energy utilization technology
Water-source heat pump is a heating and air-conditioning system that uses solar energy stored in the earth’s water bodies as a source of cold and heat for energy conversion. The water bodies that can be used include groundwater or rivers, rivers and lakes on the surface, and the ocean. The surface soil and water body is not only a huge solar collector, collecting 47% of solar radiation energy, which is more than 500 times the energy used by humans every year (the underground water body receives solar radiation energy indirectly through the soil), but also A huge dynamic energy balance system, the soil and water on the surface naturally maintain a relative balance of energy reception and emission. This makes it possible to use the nearly unlimited solar or ground energy stored in it. Therefore, the water source heat pump uses a technology of clean renewable energy.
2. High efficiency and energy saving
The usable water temperature of the water source heat pump unit is 12-22°C in winter, and the water temperature is higher than the ambient air temperature. Therefore, the evaporation temperature of the heat pump cycle increases and the energy efficiency ratio increases. In summer, the water body is 18～35℃, and the temperature of the water body is lower than the ambient air temperature, so the condensing temperature of refrigeration is lowered, making the cooling effect better than air-cooled and cooling towers, and the efficiency of the unit is improved. According to EPA estimates, a well-designed and installed water source heat pump can save users 30-40% 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 that of the air. It is a good heat pump heat source and air-conditioning cold source. The water temperature is relatively constant, which makes the heat pump unit run more reliable and stable, and also ensures the efficiency and economy of the system. There are no difficult problems such as winter defrosting of air source heat pumps.
4. Significant environmental benefits
Water source heat pumps use electric energy. Electricity itself is a clean energy source, but when generating electricity, it consumes primary energy and causes the emission of pollutants and carbon dioxide greenhouse gases. Therefore, the pollution of energy-saving equipment itself is small. 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 a reduction of more than 70% compared with electric heating. The refrigerant used in water source heat pump technology can be R22 or 4A, R407C and R410A. The water source heat pump unit operates without any pollution and can be built in residential areas without burning, exhaust smoke, and no waste. There is no need to store fuel waste, and there is no need to transport heat over long distances.
5. One machine with multiple functions, with a wide range of applications
The water-source heat pump system can be used for heating, air conditioning, and domestic hot water. One machine can be used for multiple purposes. One system can replace the two original boiler and air-conditioning devices or systems. Especially for buildings that have both heating and cooling requirements, water source heat pumps have obvious advantages. It not only saves a lot of energy, but also can meet the requirements of heating and cooling at the same time with a set of equipment, reducing the initial investment of 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. Automatic operation
Due to the stable working conditions of the water source heat pump unit, it is possible to design a simple system with fewer components, simple and reliable operation, and low maintenance costs; the automatic control degree is high, and the service life can reach more than 15 years. Of course, like anything, the water source heat pump is not perfect, and its application will also be restricted.
⑴, available water source conditions restrictions
Water source heat pumps can theoretically use all water resources, but in actual projects, the cost difference of different water resources 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, the closed system generally has a higher cost. In the open system, whether a suitable water source can be found has become a limiting condition for the use of water source heat pumps. For the split system, the water source requirements must meet a certain temperature, water volume and cleanliness.
⑵ Restrictions on the geographical structure of the water layer
For the use of pumping water from the ground for recharging, the geological structure of the place of use must be considered to ensure that a suitable water source can be found under economic conditions. At the same time, the local geology and soil conditions should be considered to ensure the tail water after use. Recharge can be achieved.
⑶, the economics of investment
Due to the impact of different regions, different users, national energy policies, and fuel prices, the basic conditions of water sources are different; one-time investment and operating costs will vary from user to user. Although in general, water source heat pumps have higher operating efficiency and lower costs. However, compared with traditional air-conditioning, cooling and heating methods, the investment economy 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 ground source heat pump and the other is seawater heat pump. Among them, the true commercial application of ground source heat pumps has only a history of nearly ten years, but it has developed quite rapidly. For example, in the United States, as of 1985, there were 14,000 ground source heat pumps in the country, but 45,000 were installed in 1997, 400,000 have been installed so far, and the annual growth rate is 10%. In 1998, ground-source heat pump systems in commercial buildings in the United States accounted for 19% of the total air-conditioning inventory, and new buildings accounted for 30%. The U.S. ground source heat pump industry has been established by the U.S. Energy & Environmental Research Center (Energy&Environmental Research Center), the National Ground Water Association (National Ground Water Association), the Edison Electric Institute (Edison Electric Institute), and many ground source heat pump manufacturing, design and sales companies, as well as government agencies and builders. The American Ground Source Heat Pump Association, composed of 146 members, will invest 100 million U.S. dollars 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 vehicles or planting trees1 One million acres, annual energy savings of 420 million U.S. dollars, since then, annual energy savings of an additional 170 million U.S. dollars.
American water source heat pump manufacturers include well-known companies such as Addison Products Company, Advanced Geothermal Technology, Carrier Corporation, ClimateMaster Inc., Econar Energy Systems Corporation, FHP Manufacturing, Mammoth Inc., The Trane Company, WaterFurnace International and other companies. The research and application of water source heat pumps in the United States are more focused on residential and commercial small-scale systems (below 20RT), mostly using water-air systems, such as the well-known TRANE products. In terms of large-scale buildings, the United States has implemented the WLHP system, that is, the water loop heat pump system.
The development of ground source heat pumps in the United States is different. Central and Northern Europe such as Sweden, Switzerland, Austria, Germany and other countries