Research On Collaborative Optimization Of Seawater-Soil Dual Source Heat Pump System Based On Source-Load Coupling

With the acceleration of energy transformation process in various countries,how to efficiently use clean energy has become a hot spot of concern.The seawater-soil dual source heat pump system embedded in seabed sand with front-end capillary box heat exchanger can effectively use seawater heat to meet the demand for space heating and cooling and relieve the energy pressure in coastal areas.At the same time,the unique arrangement of capillary box heat exchanger at the front of this heat pump system,the heat generated by the temperature difference between surface seawater and bottom seawater and seabed sand is fully utilized,avoiding the freezing of the heat exchanger in severe cold weather.In practice,the seawater-soil dual source heat pump system contains several subsystems that are coupled to each other,with complex boundary conditions and numerous interference factors.A full understanding of the system and the use of synergistic cooperation between equipment can help improve its performance coefficient and reduce economic costs under partial load conditions.In this paper,a multi-platform co-simulation approach is applied to the seawater-soil dual source heat pump system to carry out research on system operation characteristics,economy,environmental protection,influencing factors and operation optimization.The main conclusions of this study are as follows:(1)As the physical model,a demonstration project of a seawater-soil dual-source heat pump system is presented,the numerical model is established by using collaborative simulation method through reasonable assumptions.De ST,MATLAB and Fluent are responsible for dynamic load calculation,dynamic system control and unsteady heat transfer simulation of heat exchanger respectively.To ensure the correctness of the heat transfer model,the temperature of the inlet and outlet water of the demonstration project’s heat exchanger was evaluated.(2)An analysis of the energy consumption of a seawater-soil dual source heat pump system annually was conducted,with the operating characteristics of the system being evaluated across various time frames.The results showed that the heat pump system had good performance and no hot(cold)accumulation in intermittent operation.Finally,the economy and environmental protection of this heat pump system are discussed.(3)The effects of the space between pieces,backfill sand,burial depth and physical properties of heat transfer fluid on the system were compared and analyzed.For different backfilled sand,the greater the Peclet number,the better the heat transfer the smaller the heat capacity.At the same time,the smaller the heat capacity of backfilled sand,the shorter the time required to respond to the demand side.The sheet spacing and burial depth should meet the user’s needs while minimizing economic costs.When the cold index is less than or equal to 100W/m~2,the recommended piece spacing is 10cm-20cm.When the cold index is between125 and 150 W/m~2,the recommended sheet spacing is 20cm-25cm.The recommended buried depth of capillary mat heat exchangers is 0.75m-1m.The greater the thermal conductivity of the heat transfer fluid and the smaller the kinematic viscosity,the better the performance of the system.When the heat transfer fluid is water,COP_s is 3.14 and EER_s is 4.7.(4)Based on the matching of supply and demand,a functional relationship is established to achieve the minimum power consumption of the system,indicating that the flow rate on the source side is the key factor to improve the coefficient of system performance.Select a day of the heating season as the optimization object.Through simulation,it is found that the system applying the variable flow temperature difference(real-time flow rate in the heat exchanger tube changes with load)operation strategy has the best energy saving,which verifies the advantages of system collaborative operation.