Performance Study On The Harvest-type Dynamic Ice Thermal Storage System

With the rapid development of economic, urban power load is increasing dramatically. Ice thermal storage technology attracts extensive attention because of having the function of chipping peak off and filling valley up, and has been more and more applied in practical engineering. There are two main ice-making methods for ice-storage air conditioning, one is static type and the other is dynamic type. Research and apply on static ice-making technology is earlier, and this technology is more mature at present. But it’s evaporating temperature is lower so that the system’s COP is lower. There are fewer researches on the dynamic ice-making technology, but it gains rapidly development in recent years with the advantages of higher unit efficiency, quick melting and stable discharge performance.The harvest-type ice thermal storage system, as a representative type of dynamic ice thermal storage system, stores ice with the direct evaporation mode. And ice will shed when its thickness achieves the required value, which depresses the thermal resistance significantly. So the evaporating temperature of refrigeration units was increased, and the efficiency was improved. This paper focuses on the harvest-type ice thermal storage system and proposes the analysis of it mainly from the aspects of ice-making performance, exergy efficiency and the impact on the system caused by ice shedding. The economic contrast analysis between harvest-type ice thermal storage system and conventional air conditioning system is performed, and the static payout period of investment is got.Firstly, this paper shows the operating principle of the harvest-type dynamic ice thermal storage system, and analyses its characteristics of freezing and melting and main performance features, which is then compared to that of static ice thermal storage system. Its ice-making process has been simulated with the method of numerical analysis to find out the ice thickness variation with inlet temperature and evaporating temperature. The variations of ice thickness, ice storage volume and ice-making cycle over time have also been obtained. Moreover, the ice thickness under different inlet temperature has been tested and the simulation results are compared with the experimental results.Secondly, the refrigerant circulation processes of dynamic and static ice storage systems have been studied, and then the exergy efficiency and distribution of exergy lose in each unit are calculated with the exergy analysis method. The calculated results of two systems are contrasted in detail to analyze the primary cause of the difference of exergy efficiency between these two systems, and the measures to reduce exergy loss are put forward. Besides, the exergy loss computing model for practical refrigeration cycle including the ice-shedding process of the harvest-type ice thermal storage system has been established, and the exergy loss on a given variable is calculated by this model. By comparing the exergy loss of refrigeration cycle with ice-shedding process or not, the influence of ice-shedding by hot refrigerant vapor on harvest-type ice thermal storage system has been discussed.Lastly, this paper makes the economic analysis of harvest-type ice thermal storage system in electronic trading market 5 of China South city in Shenzhen city. The energy efficiency ratio under corresponding operation strategy of different load rate has been evaluated. Then compares the harvest-type ice thermal storage system to the conventional air conditioning system from the aspects of initial investment, electricity consumption and operating cost in cooling season. Finally, the payback period of harvest-type ice thermal storage system has been computed by the static economic evaluation method.