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Abstract: This paper summarizes the development and current situation of water source heat pump, analyzes the problems existing in application of water source heat pump unit and puts forward an energy-saving structure of water source heat pump unit, which plays an important role in the application and development of water source heat pump in our country. Keywords: water source heat pump energy-saving double-Evaporator series parallel ABSTRACT: The development and current state of water source heat pump is briefly introduced in this paper. Problems existed in the application of water source heat pump are also discussed. A new configuration of heat pump , Which the consumption of less water and improves COP value is presented. Therefore, the application and development of water source heat pump will be promoted. KEY WORDS: water source heat pump, energy saving, two evaporators in series and parallel Energy consumption and environmental pollution are two major problems plaguing human society and have drawn great attention from all countries in the world. According to statistics from the IEA Heat Pump Center and the European Heat Pump Association (EHPA), at present, there are 4.5 million heat pumps in Europe for residential use, 1.5 million heat pumps for the tertiary industry, and 2.5 to 30,000 heat pumps For industry. EHPA's goal is to have at least 15 million heat pumps in Europe by 2010 for residential use, equivalent to saving 100 TWh of energy annually and reducing 40 million tons of CO2 emissions. By 2002, the heat pump in Switzerland accounted for more than one-third of new houses and Japan's buildings had a heat pump share of 20%. However, the application of heat pumps in our country only enjoyed rapid development after 1990, reaching 11.4 million units in 1997 , But also the momentum of rapid development. With China's accession to the WTO and the successful bidding for the 2008 Olympic Games, the city center of our country is gradually banning the use of coal-fired boilers. At the same time, the use of oil-fired boilers is also being limited to some extent, thus providing heat pump units with applications A huge space for development. The heat pump unit is mainly divided into air source heat pump and water source (ground source) heat pump. Because air source heat pump is greatly affected by environment and climate, its application has been greatly restricted, while the groundwater temperature has little change in winter and summer. Therefore, Cold and heat source water source heat pump system so that this issue has been effectively resolved. It has been widely welcomed by all walks of life due to many advantages such as less energy consumption, utilization of renewable energy sources, non-consumption of water resources, non-pollution of the environment and compliance with the requirements of sustainable development. Second, the status of water source heat pump: water source heat pump application of the biggest problem is to combine the actual situation, to provide a stable source of water, to solve the problem of recharge of groundwater and winter how to maximize the use of water contained in the energy. At present, the application of such projects generally takes natural recharge. Since natural recharge is only gravity, and water is power, it is necessary to maintain the balance of the water system and ensure that the water taken out is fully recharged. The proportion of wells to recharge wells is normal Take 1: 2 or 2: 3. This not only increases the investment but also the utilization of the recharge well at part load. Therefore, whether it can solve the problem of reducing investment and saving operating costs while ensuring 100% recharge will directly affect the application and development of water source heat pumps. Therefore, the research and development of a water-saving and energy-efficient water source heat pump unit is helpful for the application and promotion of water source heat pump, and will have a good market prospect. Third, energy-saving water source heat pump units: In order to overcome the heat pump temperature increase in heat transfer caused by many technical problems, we have conducted a study on the unit structure and exploration. Its structure is the unit uses two small evaporators, each evaporator and one or more compressors and condensers, expansion valves and Other components of the independent refrigeration cycle. Between the two evaporator inlet and outlet pipes through the valve control to achieve two evaporator water system in series or in parallel. The valve between the two evaporator pipes opens in the summer cooling condition, and the backwater of the end system of the air conditioner enters two evaporators at the same time in two paths at the same time, enters the end of the air conditioner after the outlet of the evaporator joins, that is, the cold water flows in parallel Two evaporators. The cooling capacity of the system is realized by two evaporators. The inlet and outlet water temperature of each evaporator is 12/7 ° C (Δt = 5 ° C). In winter heat pump operation, Between the closure of the valve, as a heat source of groundwater flow through the two evaporators, which means that the two evaporators water in series, as the source of groundwater through two evaporators to achieve Δt = 10 ℃ temperature drop. Compared with the parallel flow of water through the evaporator, the flow area of ​​the water through the evaporator decreases in tandem to make up for the effect of reduced flow on the flow rate, so that the flow of water through each evaporator, the flow rate, and the summer operating conditions When the same, the heat transfer performance of the smaller, both to achieve the purpose of saving groundwater, without affecting the heat transfer performance. Fourth, the project application examples: The following is a unit of office buildings using the new energy-saving water source heat pump unit as a cold source design examples: 1, office building area: 4600m2, indoor end of the embedded wind plate, calculated by the required cooling load Q0 = 460kW, required heat load Qh = 506kW. 2, water conditions: single well water volume 50 ~ 60m3 / h, water temperature: summer 16 ℃, winter 15 ℃. 3, choose four 40HP semi-sealed piston compressor, two compressors and an evaporator, a Condenser composed of two independent systems. 4, the design conditions: the cooling conditions: evaporator 1,2 water system in parallel, the fluorine system is independent, the inlet and outlet temperature 12/7 ℃, evaporation temperature 2 ℃; condenser 1,2 water system in parallel, fluorine system independent, Its inlet and outlet temperature 16/26 ℃, condensing temperature 31 ℃. Heating conditions: evaporator 1, 2 water system in series, independent fluorine system, evaporator inlet and outlet water temperature 15 / 9.5 ℃, the evaporation temperature 5.5 ℃; evaporator 2 inlet and outlet water temperature 9.5 / 5 ℃, evaporation temperature 1 ℃; Condenser 1,2 water system in parallel, the fluorine system is independent, the inlet and outlet temperature 40/45 ℃, condensing temperature 50 ℃. 5, the calculation results are as follows: ①cooling conditions: total system cooling capacity: Q0 = 466kW, the total system power: Pi = 89.5kW system cooling factor: Cop = 5.2 well water (water system parallel) Water: 47.2m3 ② heat pump Total system heat capacity: Qk = 511kW, Total system power: Pi = 121.7kW System heating coefficient: Cop = 4.2 Well water (water system in series) Water withdrawal: 34m3 After a winter and summer operation results show that in the local Under the condition of water source, the two wells can realize the safe and reliable operation of the unit, and the cooling and heating effects fully meet the requirements of users. Reduce the initial investment and operating costs, received a very good economic efficiency V. Conclusion: The use of this structure so that the evaporator inlet and outlet water both in the cooling of the 5 ℃ temperature difference, or in the heating 10 ℃ temperature difference, evaporation The heat exchanger performance is basically the same, that is, the evaporator heat transfer area in winter and summer under two conditions has been fully utilized. At the same time, heat pump operating conditions, the water decreased by 20%, the system's heating capacity increased by about 10%, Cop increased by about 7%. In summary, by improving the structure of the heat pump unit, changing the series and parallel of the evaporator water system, not only to achieve the saving of groundwater intake, reduce the number of wells and recharge wells, and rational use of the evaporator heat transfer Area, while increasing the system of heating and energy efficiency ratio. This will not only reduce the initial investment, but also reduce operating costs, with significant economic and social benefits, the application of water source heat pump in our country and development will play a catalytic role. Author: The author in the writing process has been Tsinghua University Professor Zhao Rongyi, Professor Chen Yutian great help, and made a lot of valuable comments, would like to thank you. References: 1, "Heat Pumps - 7th International Energy Agency Conference on Heat Pumping Technologies" ........................ China Building Industry Press 2, "refrigeration principle and equipment" ........................ .................. Wu Yezheng editor