Study On Operation Strategy And Optimization For Solar Hot Water System With Dual Heat Storage Devices

At present,there are two ways of sensible heat storage and latent heat storage in the thermal storage device,but both of them has their shortcomings.Sensible heat storage system has the advantages of simple structure,always regard water as heat storage medium,heating up fast,easy to obtain,etc.but there are some shortcomings that low in energy storage density and large heat loss;latent heat storage has the advantages of a large storage density,charge / discharge thermal process temperature fluctuations small,but the phase change storage heat is indirect heat exchange,cannot fast charge and discharge.Therefore,we propose a new kind of solar hot water system-solar hot water system with dual heat storage devices in this paper,integration of two kinds of heat storage technology,mutually compensate for each other's shortcomings,in order to improve the system of storage energy density,collector efficiency and thermal heat.Firstly this paper made the corresponding presentation about system structure and the operation mode of solar hot water system with dual heat storage devices,according to the characteristics of the system structure the operation mode is divided into four operating modes,respectively is water-PCM series connection mode,and PCM–water series connection mode,parallel operation mode,and combination operating mode.Due to the integration of two kinds of storage technologies,the design of solar hot water system with dual heat storage devices has different from the design of traditional hot water system,referencing the design of traditional hot water system to design solar hot water system with dual heat storage devices.Secondly,this paper establish a mathematical models of solar collectors,water tank heat storage,phase change heat storage,hot water load and auxiliary electric heating.The simulation model of system is established based on TRNSYS software.Finally,this paper mainly uses TRNSYS software to analyze and contrast the pros and cons of the solar hot water system with dual heat storage devices with the traditional hot water system,the results show that solar hot water system with dual heat storage devices is more efficient than the traditional hot water system in the heat storage capacity,the heat storage density and the collector efficiency;and the solar hot water system with dual heat storage devices structure parameters and operating parameters were analyzed and optimized,consider collector efficiency and solar fraction,volume ratio of thermal storage devices is 3:1,solar collector area is 24m2,split ratio belong 0.3~0.5,solar collector flow is 0.02kg/(m2·s);The effect of different operation modes on the efficiency of the solar collector and solar guarantee rate was studied under different illumination,and the composition of the hot water load under different operating modes was analyzed.The control strategy of the system under different illumination levels and different operation modes is presented with household hot water demand.