| Energy tower heat pump,as a device to extract heat from air for heating,has become a key research object in recent years due to its advantages of unrestricted heat source,anti-frosting and wide applicability to geographical areas,but its performance under low temperature working conditions decreases significantly has limited its further application and promotion.The use of cold water phase change energy coupled energy tower heat pump system is an effective way to solve this problem.In order to clarify the structural form and applicability of the coupled system at different temperature and water temperature conditions,the simulation study on the icing characteristics,performance,energy consumption and economy of the coupled system under different operating conditions was carried out,and the relevant studies and conclusions completed are as follows.The phase change energy coupled energy tower heat pump system was constructed,and the thermal performance and energy consumption model of the system was established based on its process principle and operation mode.A mathematical model of phase change heat transfer process is established,and the heat transfer process of single row heat exchanger tube row is simulated when the temperature of refrigerant water and cold water inlet changes.The influence of water temperature changes on heat exchanger,ice thickness and energy consumption of de-icing on both sides inside and outside the tube in the heat exchanger is analyzed in turn and the water temperature zoning diagram of icing condition is given.The analysis shows that:for the active and passive,passive and zero icing conditions of the water temperature partition point,where the refrigerant water inlet temperature is negatively related to the cold water side of the inlet temperature.For active icing conditions,with the change of water temperature,the maximum thickness of the ice layer in the range of 7.3mm～8.6mm,which requires the activation of de-icing devices to regularly de-ice;for passive icing conditions,with the change of water temperature,the maximum thickness of the ice layer is in the range of0.1mm～5.8mm.However,a spacing of 12mm should be reserved between the heat transfer tube to prevent ice blockage;for zero icing conditions,there is no ice generation,the conventional water-water heat exchanger could be used in this condition.The growth law of and the ice layer along the heat exchanger tube wall under the active icing condition and the influence of the change of the inlet water temperature,flow rate and cold water flow rate on the phase change heat process on the intermediate side are analyzed.The analysis shows that the change of inlet water temperature on the intermediary side has a greater impact on the heat transfer process of cold water phase change heat exchanger.Intermediary side of the inlet water temperature in the range of-6～-4.5℃for every 0.5℃,the average heat transfer coefficient increased by about 50W/(m~2·K);intermediary water flow rate changes on the cold water phase change heat exchanger heat transfer process is less than the intermediary side of the inlet water temperature,the intermediary water side of the maximum flow rate should not exceed0.5m/s;cold water flow rate changes on the cold water phase exchanger heat transfer process has a smaller impact.Cold water flow rate in the range of 0.06m/s to 0.12m/s every increase of 0.02m/s,the average heat transfer coefficient is only increased by20W/(m~2·K).The system performance and energy consumption under different temperature conditions were simulated and analyzed.By comparing the total annual energy consumption of the coupled system with other systems,the optimal applicable region of the system and the optimal heat source capacity ratio for different temperature conditions were obtained.Analysis shows that the daily minimum COP of the coupled system can be increased by 5.23%compared to a single energy tower heat pump system,and the daily total energy consumption can be reduced by up to 195.19 k W·h compared to the energy tower heat pump system.The optimal application area of the coupling system is mainly concentrated in the central region of China,with different heat source ratios in different climatic regions.The System economic evaluation criteria were established,and the coupled system was compared quantitatively with phase change energy heat pump system,energy tower heat pump system,direct combustion unit system,air source heat pump system,and municipal central heating and chiller for system initial investment cost and operation cost.The results show that the coupling system can save 20%to 40%of the initial investment cost and 10%to 50%of the annual operation cost compared with other heating and cooling systems.The heat source ratio varies in different climatic regions,with the energy saving rate of 48%,and the primary energy utilization rate of 0.98,which has high energy conservation and environmental protection.By constructing the chilled water phase change energy coupled energy tower heat pump system,the problem of low temperature performance degradation of energy tower heat pump is solved,the influence law of different temperature and water temperature conditions on system performance and energy consumption is simulated and analyzed,the applicability and structure form of the system under different operating conditions is explored,which provides theoretical and data reference for the system engineering design and equipment selection,and is of great significance for the promotion and application of this type of heat pump system. |
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