| The solar assisted ground source heat pump(SAGSHP)system can compensate for the instability of solar energy as a single heat source on the basis of solar energy throughout the year,which is conducive to the sustainable use of resources and has been widely used in the field of HVAC.The underground pipes of traditional SAGSHP are connected in series or in parallel.For the parallel SAGSHP system,higher heat transfer efficiency can be obtained,but the overall heat transfer temperature difference is smaller.For the series SAGSHP system,larger heat transfer temperature difference can be obtained,but the heat transfer efficiency is lower.Therefore,in order to overcome the problem of small temperature difference in parallel connection and low efficiency in series connection in traditional SAGSHP system,and to obtain high temperature difference and efficiency in heat exchange,this study proposes a SAGSHP combined system with underground pipe group in series and in sections.Using trnsys-18,the physical model of sectional series and parallel SAGSHP is established,and the operating mode of the system,soil temperature,ground source heat pump inlet and outlet temperature,and short-term storage were simulated and analyzed under different serial-parallel partition areas and different heat storage conditions.The optimal partition and heat storage/heat extraction design principles of the partition seriesparallel SAGSHP combined system were obtained.Furthermore,the optimization model of the sectional series and parallel SAGSHP is established,and the matching relationship between the capacity and operation of the SAGSHP in different regions is studied to provide guidance for the rational utilization of the system.The main results and conclusions are as follows:(1)Through the simulation analysis of the system performance under different series parallel partition area and different heat storage ratio,and compared with the traditional system under the same scale,the results show that: It is not recommended to distribute the heat storage capacity of series area and parallel area according to the partition area.However,if the area of buried pipes is blindly reduced and the heat storage capacity is increased,the SAGSHP system can meet the conditions of direct heat supply in the early stage of heat supply,which can reduce the start-up time of heat pump,but the ground temperature drops too fast in the later stage,and the cop and system SCOP of heat pump are lower than those of traditional systems.When the area ratio of series area to parallel area is 1:4 and the heat storage capacity is 3:2,the system has the best comprehensive performance.At this time,the cop of heat pump can reach 4.5,the system SCOP can reach 5.2,the SCOP is 13.0% higher than the traditional parallel system,18.1% higher than the traditional series system,and the system operation condition is stable,which can meet the end heating demand.(2)With the minimum cost in the whole life cycle as the objective function,the capacity matching of the typical series of cities in the series and parallel SAGSHP combined system was performed.The results show that: In severe cold and cold regions rich in solar energy,the short-term heat storage of solar energy can meet the heating needs of users.Therefore,it is not recommended to use solar long-term heat storage as a building heating heat source in this climate area.For areas with severe cold-solar energy,it is recommended to use the lowest solar guarantee rate design system in the recommended range in such climate zones scale.For cold-solar-rich regions,it is recommended that such climate zones pass reasonable allocation of capacity to improve the overall performance of the system.(3)The single operation optimization results show: Recommended thermal storage temperature difference in each region is 5 ~ 8 ?.In severe cold regions,as the richness of solar energy resources decreases,the optimal heat storage temperature difference between cities gradually decreases,while in cold regions it shows the opposite trend.Except for Urumqi,which represents the general cold-solar resource area,if the temperature of the hot water storage tank is lower than the heating design water supply temperature,it is not recommended to increase the flow to obtain heat from the hot water storage tank.It is recommended to directly turn on the ground source heat pump to meet the users demand.(4)The comparison results of capacity matching and operation optimization of typical cities show that although the cop of the heat pump has little change on the whole after optimization,the system SCOP is significantly improved.After capacity matching,the system's SCOP can be increased by more than 20%,and after operation optimization,the rate of SCOP increase in cold area can be more than 4 times higher than that in severe cold area with the same solar energy resources.If there is no significant difference in the system economy,it is recommended to use capacity matching to optimize the operation in cold areas in areas with abundant solar energy resources and general areas.Through the above research,the optimal design principle of the subarea series parallel sagshp combined system is obtained,and the efficiency and stability of the system operation are proved.On this basis,the applicability and optimization of the system in different types of climate areas are studied,so that the system can save the cost of the whole life cycle,improve the system SCOP,and provide the design scheme and operation strategy for the efficient use of the system in various types of climate areas. |
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