| Solar energy and air energy have been widely used in the field of HVAC due to their advantages of wide distribution and low utilization cost.The development of solar energy and air energy utilization technology,and further improvement of the renewable energy utilization rate,are significant to reduce building energy consumption,delay the trend of global warming,and achieve the national strategic goal of "Emission Peak and Carbon Neutrality".The heat-source tower heat pump system uses air energy as the heat source,which can realize the functions of refrigeration in summer and heating in winter,and the system is not easy to frost when heating in winter.At present,the research on heat-source towers mainly focuses on heating performance,heat and mass transfer theory,and solution regeneration technology of heat-source towers.Although the heat-source tower can absorb low-temperature air heat energy as the heat source of the heat pump,its energy efficiency also decreases with air temperature decreases.Combining the solar hot water system and heat tower heat pump can improve the renewable energy utilization rate and solve the problem of poor performance of heat-source tower heat pump at low temperatures.However,there is little research on the combined heating technology of solar energy and heat source tower heat pump in a composite system.So there are some research gap that need to be solved: a.Improving the system utilization rate of one single energy;b.enhancing the coupling effect between various energy sources;c.improving the matching between the energy supply system and energy consumption system;d.improving the efficiency and stability of the heating system.In this study,the composite system consisting of solar collectors and heat-source tower was analyzed by using the theory of heat and mass transfer,and the heat and mass transfer analysis model was established.The closed heat-source tower of air energy utilization performance and collector of solar energy utilization performance are simulated and experimental study,the heat-source tower heat exchanger outlet air temperature relative error less than 8.50%,the heat source tray tube outlet temperature of the heat transfer fluid relative error less than 7.32%,the heat-source tower thermal mass transfer analysis of simulation results can better actual reaction.On this basis,the relation between thermal performance of composite system components and its heating was analyzed,with the intensity of solar radiation,collector area size,collector for/heat loss,heat-source tower air flow rate,inlet air temperature of tower,heat transfer fluid temperature,inlet air temperature of heat exchanger in heat source tower,and input power of the composite system as independent variables.The analysis and evaluation models of heating capacity,COP,and the renewable energy utilization rate of the composite system were established.Solar radiation intensity and collector area size are significant parameters affecting the thermal performance of the composite system.With the increase of solar radiation intensity,the heating capacity and COP of the composite system increase.When the solar radiation intensity is lower than 330W/m2,the solar energy absorbed by the collector is less than its heat dissipation loss,and the collector is in a state of heat loss.Increasing the collector area size can improve the heating capacity and COP of the composite system.The renewable energy utilization rate of the composite system is related to the solar energy utilization rate of the collector.When the solar energy utilization rate is greater than the air energy utilization rate of the heat-source tower,the increase of the collector area will improve the renewable energy utilization rate of the system;otherwise,the rate will be reduced.Taking the composite heating system including the heat-source tower,heat pump host,solar collector,heat storage tank,and other equipment as the research object,several kinds of composite heating methods are proposed,such as solar collector in parallel with heat pump condenser,solar collector in series with heat pump condenser,solar collector preheating heat pump evaporator.Using the TRNSYS simulation computing platform,the heating performance calculation models of parallel,series,and preheating composite systems are established.The influences of solar radiation intensity and ambient temperature on the thermal performance parameters of the composite system with different connection modes were analyzed,such as the temperature of the heat-carrying fluid,heat transferred in the heat-source tower,heat transferred from the collector to the fluid,input power of the heat pump,system heat production and COP.The parameter values of the parallel composite system are proportional to the ambient temperature.In series composite systems,with low ambient temperature and low solar radiation,the solar collector prioritized system will have better heating and COP values.The preheating system provides heat from the solar collector and the heat-sources tower to heat pump of the evaporator simultaneously,then the connection mode of the solar collector and heat-source tower,a variety of preheating composite system types can be formed.Among the connection modes,the COP of the preheating system with priority series of the heat-source tower is higher than the other two preheating composite systems.To further analyze and compare the heating performance of the parallel,series,and preheating composite systems,the optimal operating condition range of the composite system based on the heat pump capacity and solar collector capacity of the heat-source tower was drawn with solar radiation intensity as ordinate and ambient air temperature as ordinate.The simulation results show that the preheating system has the best performance when the ambient temperature and solar radiation intensity are low.When the solar radiation intensity and ambient temperature are high,the COP of the series system is greater than that of the other two systems.The series system has the best performance between the preheating system and the series system.Taking Changsha area as an example,the differences have been analyzed based on the Changsha district heating season months the greatest efficiency of the system.Specifically,the parallel connection systems in December and March show the best performance coefficient,the preheating systems in January show the best performance coefficient,and the series systems in February show the best performance coefficient.If one single connection mode is used,the seasonal performance coefficients of single heat-source tower heat pump,preheating type,series type,and parallel type are 2.80,2.99,3.15,and 3.25 respectively,and the parallel type system has better heating performance.According to the monthly solar radiation intensity and ambient air temperature,the combined operation mode with the best energy efficiency connection mode in the optimal operating condition diagram can be 21.07%,13.38%,7.62%,and4.31% higher than the single heat-source tower heat pump system,preheating system,series system,and parallel system.The compound operation mode has good heating performance. |
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