The Application Research Of Phase Change Thermal Storage For Heat Pump Air-conditioning System

With the rapid development of economy and the progress of our society, the problemof energy and environment has become more and more serious, for which, newenergy-saving technologies of increasing energy utilization and decreasing the use offormal energy sources should be used to achieve sustainable development. The techniqueof phase change thermal storage is equipped with characteristics of high heat storagedensity, easy to control, easy to match, and having a good application to solve the problemof different steps of energy supply and consumption in time and spaces. As an effectivemethod to improve energy utilization, it has been widely studied in recent years. Nowadays,technology of heat pump has found wide use in many fields because of its energy savingand environmental protection features. And it is earning more eyes in the field ofpreparing domestic hot water. While the heat pump water heater in the present haveweaknesses in its big size and unsmooth working. To solve the weak points above, phasechange thermal storage heat pump heater is studied to improve the system performance andimprove energy utilization at the same time.The heat pump condensing heat recovery system of phase change thermal storage wasbe studied as this paper’s object. Combined with phase change thermal heat storagetechnology, the performance of traditional air source heat pump system was experimentedand simulated. All study of condensing heat recovery for system performance was carriedout with the partial condensing heat recovery mode in this paper, and characteristics of heattransfer for the system was deeply studied by experiments testing and numerical calculationthese methods. The main research work for this paper were as follows：1. The thermal characteristics of phase change heat transfer was analyzed, andobtained the feature of phase change thermal storage technology, the calculation mode ofheat transfer coefficient for phase change heat storage tank. The Differential ScanningCalorimetry（DSC）was used for measuring physical property parameters of phase changematerial, results indicated the melting point was59℃, the freezing point was54.3℃, andthe latent heat of phase change was187kJ/kg, so theoretical basis was provided for latercalculation of system performance.2. The characteristics of heat pump air-conditioning system by phase change heatstorage was studied through experiments. Used the method of simulating indoor andoutdoor environment condition to test condensing heat recovery. Results indicated theaverage system integrated coefficient of property was3.1, and the ratio of heat recoverywas20percent. Compared with no condensing heat recovery system of refrigeration mode,average COPt was increased23percent from the former2.4. From the system performance, combined the phase change heat storage technology with traditional heat pumpair-conditioning system could improve the COPt. In addition, the results of phase changematerial melting condition indicated that partial paraffin in the heat storage tank was stillsolid when system worked10h.4. An experimental test on heat release process of paraffin in the phase change thermalstorage box is done, studying the heat release process of paraffin in the phase changethermal storage box with changing cold water temperature at the entrance of heat storagebox and cold water flow. It is showed that hot water heating time can be cut down withincreasing water flow or raising cold water temperature at the entrance of heat storage box.Time of hot water output could be decreased about1.6h, if there is a just increase in flowrate. Moreover the time could be cut down3.3h approximately. It is also shown that there isa small change of hot water temperature in1h, about2～3℃, which can be concluded thatthe efficiency of heat exchanging is at a low level.5. A physical and mathematical model of heat transfer process in the phase changethermal storage tank was created to simulate temperature changes of paraffin when thermalstorage on process. Results indicated agreement between simulation and experiment, theerror is controlled in0.3%~0.7%, so the simulation was proved be effective. In the processof thermal storage, great temperature stratification appeared in the tank and the maximumtemperature difference comes to32℃. The effectiveness of phase change thermal storagetank was not well with former results, so the system’s performance really needed to makean advancement.