Study On Unsteady Condition Of Low Temperature Phase Change Heat Source For Water Source Heat Pump

With the continuous improvement of people’s requirements on indoor environment,the heat consumption of building heating in winter is increasing day by day.In order to adhere to the strategy of human sustainable development,the development and utilization of new energy for indoor environmental heating has become an important research direction.The traditional water source heat pump ignores the latent heat energy of the water source,and mainly uses the sensible heat energy of the water source as the heat source.The latent heat energy of the water source is huge.If it is utilized,it can increase the practicability of the heating system and save a lot of resources.In this paper,a low temperature phase change heat source heating system of water source heat pump is proposed,and the characteristics of phase change and heat transfer of heat source water at the evaporator side are analyzed under different water flows by controlling the water flow at the inlet and outlet of the heat source during heat exchange in the evaporator.The research method is a combination of experimental research and numerical simulation,and the specific contents are as follows:Firstly,an experimental platform was designed and built to study the heat dissipation of the heating system,the heat exchange in the evaporator and the icing situation in the evaporator under different inlet and outlet water flow conditions.The experimental results show that with the increase of the inlet flow of the evaporator,the temperature at the outlet of the water source gradually decreases,and the amount of ice in the evaporator decreases,but the freezing trend of different water flows is the same.During the operation of the heat pump unit,the water temperature in the evaporator is basically unchanged,and the heat pump unit can continue to provide heating stably.In terms of heat dissipation,in the same time,the working condition of 500 L/h loses the most heat and consumes less power.When the water does not flow,that is,the water flow is 0 L/h,the water temperature decreases with the growth of the operating time of the heat pump unit,and the heat energy provided for the unit is gradually reduced,unable to meet the needs of heating for a long time.Secondly,based on the established experimental platform,the three-dimensional unsteady water source heat pump low temperature phase change heat source numerical model was established,and the solidification/melting equation was used to solve the problem of phase change icing in the evaporator.The experimental data and simulation results were compared to verify the correctness of the established model.Based on the numerical model,the liquid rate distribution and temperature distribution in the evaporator with different flow rates were studied,and the results showed that the phase change icing was carried out at the interface between the evaporator and water,and the direction was spread from the bottom to the evaporator upward,and from the edge to the center.With the increase of the flow rate,the heat transfer effect is enhanced,and the freezing rate is consistent with the melting rate,so as to ensure that the ice thickness is basically unchanged,the heat transfer reaches a balance,and the water temperature at the exit of the evaporator remains constant.The stability of the heat exchange condition guarantees the stable and long-time operation of the unit.Based on the experimental and numerical simulation results,an actual WSHP heating system was upgraded and refit,and a low-temperature phase-change WSHP was added as an auxiliary heat source to extend the heating time of the original system and ensure its heating demand.Then,the technical and economical comparison with the conventional auxiliary heat source setting system is made.Finally,the feasibility and maneuverability of the system reconstruction are illustrated.