| When air source heat pump (ASHP) unit is in heating mode, frost may formon its outdoor coil surface due to the low ambient temperature and high humidity.Accumulated frost affected its performance and energy efficiency adversely.Therefore, defrosting process is undertook periodically. At present, reverse-cycledefrosting (RCD) method is widely used for defrosting of ASHP. As4-way valvereverses during the defrosting process, outdoor unit serves as condenser whileindoor unit becomes evaporator. In order to ensure the comfortability of indoorenvironment, indoor fan is closed generally, which will cause the lack of energysource, time lag of defrosting and low defrosting efficiency.Experimental setup with normal defrosting system and energy storagedefrosting system was established. It analyzes defrosting energy consumption,dynamic characteristics and the influence of defrosting process on indoorenvironment of energy storage defrosting system under different defrosting mode.Comparative experiments with normal defrosting system are also carried out.By using the dissipated heat of compressor, a defrosting system for ASHP isdeveloped. Defrosting energy consumption and heat storage of phase change heataccumulator are calculated the oretically. And then it preselects the phase changematerial (PCM) and design the phase change heat accumulator, besides,thermostability of preselected PCM are studied.Experimental setup is established for the thermostability testing of PCM. Themixture composed of65%capric acid and35%lauric acid has been tested4000times, which indicates that binary organic PCM has good thermo stability.The characteristics of normal defrosting and energy storage defrosting havebeen studied respectively. The results demonstrate that the performance ofenergy storage defrosting is much better than that of normal defrosting. Throughthe comparisons among different defrosting mode of energy storage defrostingsystem, it can be concluded that phase change thermal storage defrosting modewith indoor continuous heating has good effect in indoor heating and outdoordefrosting, meanwhile, energy consumption is the lowest. Control strategy of defrosting system has been developed. When it reachesthe defrosting condition, based on the temperature measurements under outerring of phase change heat accumulator, as the temperature is below finaltemperature of PCM22.0?, it carries out defrosting mode without indoorheating, whereas it carries out defrosting mode with indoor heating.The main achievement of this study is to provide theoretical support andtechnological reserve for the promotion of phase change energy storage and theimprovement of performance of ASHP in winter, advancing the career ofbuilding energy efficiency. |
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