Optimal Design Of Heat Storage Water Tank Capacity For Distributed Solar Central Heating System

The traditional solar heating system is mainly divided into two kinds from the scale:the single building solar heating system and the centralized solar heating system.The former system is a system of one build,and the heat between users cannot be used mutually.So each user needs heat storage equipment and auxiliary heat source to ensure the stability of its heating.The latter system in order to improve the overall solar guarantee rate of the system,They require a large area of collectors and a large centralized heat storage tank,so it is not suitable for the town without open space.The distributed solar central heating system combines the characteristics of the two systems,which will be scattered on the roofs of all buildings in cities or towns with solar collectors.When some of the buildings still generate heat surplus after satisfing their own heat demand,the heat surplus will be transferred to the network to supply other users in the system.Therefore,the characteristic of the system is to make full use of the roof heat collection while reducing the demand for heat collection land,so that heat energy is used mutually among users,as far as possible to improve the system solar energy guarantee rate.Because users of distributed solar central heating system is both heat source and heat consumers,its thermal equilibrium state is two-way exchange with network,which is different from the users from the network one-way hot equilibrium state of the traditional system.And its users collector area design is no longer according to user load,but considering the user on the basis of mutual help from the collector area of design,so the original design according to the collector area of heat storage tank volume method is applied to the distributed system is not reasonable.For the heat storage system of distributed solar central heating,it is necessary to set up the user heat accumulator to regulate the user’s own heat gain and loss,and set up the centralized heat accumulator to regulate the total heat surplus of the network.Therefore,for the efficient operation of the system,this study proposes a new matching design method for the capacity of two types of heat storage tank in the distributed system.The specific research contents of this paper are as follows:First of all,introduces the basic principle of distributed solar central heating system,and the mathematical model of the system is established by analyzing the thermodynamic process of the system.Then on the basis of the foregoing theory,further elaborated in TRNSYS software build system simulation model adopted by the module,and to set up between the various modules and system operation strategy is introduced in detail.It lays a theoretical foundation for the subsequent research on the optimization of heat storage capacity configuration of distributed system.Secondly,the influence of the user’s heat storage tank volume and the central heat storage tank volume in the distributed solar central heating system on the thermal performance and economy of the system is analyzed to prepare for the subsequent establishment of the optimization model of the configuration of the heat storage system.Then,according to the above-mentioned impact analysis results,economy was taken as the follow-up optimization objective.On this basis,the heat storage volume of each part of the heat storage system was taken as the optimization variable.Hooke-Jeeves optimization algorithm was used to establish the optimization model of the heat storage system,and a residential area in Xining City was taken as a case to optimize the heat storage system.Finally,the distributed system of distributed solar central heating system is simulated under three different heat storage modes: user-only heat storage mode,centralized heat storage mode,user and centralized combined heat storage mode,and the comparison and analysis are made according to the optimization results of each mode.The conclusions are as follows:1)The influence of the change of the volume of the the user’s heat storage tank on the distributed system network and users themselves was studied.The volume of the heat storage tank at the user increases,which reduces the fluctuation of the temperature of the user’s water supply.With the increase of the volume of the user’s heat storage tank,the fluctuation of thermal gain and loss of heat release from the user to the pipe network decreasesand the time of heat release is delayed,which is the lower the instantaneous thermal shock to the network.2)The influence of the centralized heat storage tank volume on the energy saving and economy of the distributed system was studied.When the heat storage volume at the user is determined,with the central heat storage tank volume is larger,the heat supply of the auxiliary heat source is smaller and the energy saving performance is better.However,the initial investment of the system is larger and the economy will be lower.In the case of the same initial investment in the heat storage system,the ratio of the user to the central heat storage affects the amount of heat supply from the auxiliary heat source of the system,and further affects the operation investment of the system.3)The optimization model for calculating the volume of heat storage water tank in distributed solar central heating system is studied and established.The results show that the optimal volume of each heat storage tank in the distributed system calculated by the above optimization model is reduced by more than 40% compared with the calculation results of the traditional solar system.The optimal ratio of the user’s total heat storage capacity to the centralized heat storage capacity is 3:2.The maximum heat storage capacity of residential building users is about 20%,and that of office building is about30%.4)Comparing the three heat storage modes of the distributed system,it is found that the combined user and centralized heat storage mode has the best energy saving performance and the smallest heat gain and loss fluctuation.The mode with the lowest energy consumption is concentrated heat storage mode,but this mode cannot meet the heat demand of the system.The economical optimum is the combination of user and centralized heat storage mode.In this paper,an optimal design method for the storage water tank capacity of distributed solar central heating system is proposed,which provides a theoretical basis for the design of the storage system of distributed solar central heating system.