Research On Dynamic Characteristic And Control Strategy Of Solar Heating System With Seasonal Thermal Energy Storage

Due to the strong instability of solar radiation and building load,and the mismatch of solar energy and heating demand in time,solar space heating system with seasonal thermal energy storage is an efficient solar energy utilization technology to effectively improve the operation stability and solar fraction.For the solar heating system with seasonal thermal energy storage that has been put into operation,the main factors that affect the solar fraction and energy consumption are:the energy transfer relationship between the components of the system,the dynamic performance of the system,the performance of the collector subsystem and the optimization design of the control strategy.Focusing on the above issues,this paper carried out relevant research work with theoretical and experimental methods,aiming at comprehensively improving the utilization rate of solar energy and reducing the primary energy consumption.The work consisted of two aspects"efficient use of solar energy"and"energy conservation".The main research contents and conclusions are as follows:(1)Based on the 3000 m~2 solar space heating system with seasonal thermal storage of Fanshan Huangdicheng Town,the experimental research on the whole system along the whole year was carried out,including heliostat,receiver,seasonal thermal energy storage,heat supply and building load.Firstly,the energy transfer and conversion law of each component of the system was analyzed.Secondly,according to the operation mode and control strategies of the system,the influence of different operation modes on the dynamic performance of system components were analyzed,and the operation mode switching mechanism of the system under the linkage control of subsystems was discussed.Finally,the whole year experimental research on the system was carried out to analyze the overall operation performance of the system.The analysis results verified the feasibility of solar heating system with seasonal thermal energy storage applied in the northern heating.In the system,the efficiency of the heat collection system could reach more than 50.8%under the typical conditions;the storage efficiency of the seasonal thermal energy storage could reach 72.0%in the heat storage season,and the total storage efficiency in the first year was 49.4%.(2)As the core part of solar heating system with the seasonal thermal energy storage,the research on the performance of the solar receiver is carried out through the simulation.The model of solar collection system is established,including the heliostat field model and the one-dimensional unsteady simulation model of solar receiver under the non-uniform energy distribution.The model was verified by various working conditions,and the effect of the operation parameters on the heat efficiency and heat loss of the solar receiver is analyzed.The results showed that the inlet temperature has different influence on the heat performance of the solar receiver under different control modes.In the constant flow control mode,the thermal efficiency of solar receiver decreases with the increase of inlet temperature,while in the variable flow control mode,the inlet temperature has little influence on the performance of the solar receiver.The incident power has a great influence on the thermal performance of the solar receiver.Increasing the incident power can effectively improve the thermal efficiency of the solar receiver,and the higher the outlet temperature is,the greater the influence is.When the inlet temperature of the collector system is higher than 60℃,the thermal performance of tower collector system is better than that of flat plate collector and vacuum tube collector under different solar radiation conditions.The smaller the solar radiation,the more obvious the difference is.(3)The mathematical model of the whole system was established,which includes the main unit modules such as tower heat collection system,seasonal thermal energy storage,buffer tank,circulating pump and building load.The whole system model was established based on the energy flow transfer relationship of each component,combining with the control strategies of the system.The dynamic simulation platform of the whole system was built on the TRNSYS 17.0 software platform with the experimental system as the prototype,and the system level experimental verification was carried out.According to the temperature change characteristics of the seasonal thermal energy storage,a heating strategy combining quantity and quality regulation is proposed.This system has laid a foundation for the study of the dynamic performance and operation strategies of the solar heating system.(4)The dynamic operation performance of the system in different time dimensions were studied,and the influence mechanism of control strategies and related parameters on system performance was revealed.The results showed that:under the effect of"solar energy and heating load"and other unsteady boundary conditions,the system can efficiently and stably operation through coordinated regulation among the subsystems,and the annual solar fraction of the system can reach 85.9%.Good operation strategies of the collector side can effectively improve the operation performance of the system in the heat storage season.The exergy efficiency of the seasonal thermal energy storage under the variable flow constant temperature mode can be increased by 4.7%compared with the constant flow operation.At the end of the heat storage season,the monthly average thermal efficiency of the solar receiver under the variable flow mode can be increased by more than 4.8%compared with the temperature control mode.Compared with the constant temperature and constant flow heating strategy adopted in the experimental system,the solar fraction of the system can be increased by 17.5%and the pump consumption can be reduced by 44.6%under the combined operation strategy of quantity and quality regulation.The solar fraction of the system can reach 95.0%by adopting variable flow mode at the collector side and combining the quantity and quality control at the heating side with the fourth-generation lower temperature heating technology.