Performance Optimization Analysis And Experimental Study On Small Air-source Heat Pump Water Heater

In recent years, the air-source heat pump water heater (ASHPWH) for domesticuse is developing very rapidly. It has many advantages, such as safety, environmentalprotection and energy-conservation. So it is very consistent with the state increasinglystringent energy requirements. With people’s living standard is improving and thedemand for hot water is constantly increasing, ASHPWH has broad prospects fordevelopment.In this thesis, household ASHPWH system is optimized by means of exergyanalysis and experiment research. The main work is as follows:The theoretical calculation of Exergy loss of the system has found that thecompressor and heat exchanger are the most serious part of the exergy loss, thereforethe system optimization should be focused on this two parts.Based on the experiments, the influence of ambient temperature on theperformance of the unit was analyzed. The results showed that: as the ambienttemperature rises, the suction and discharge pressure, suction and discharge temperature,heating capacity, power and the coefficient of performance are increased. When theambient rises from16℃to30℃, the COP is increased from2.71to3.37.Through effective combination of experiments and simulations, the effect of theevaporator air velocity on the unit performance was analyzed. The results showed that:there exists an optimal value of evaporator air velocity to increase COP, and theoptimum air velocity reduces as the ambient temperature increases. For example, whenthe ambient temperature is20℃,25℃,30℃, the optimum air flow rate is6m/s,5m/s, 4m/s.Through experiments with the different ambient temperatures, the influence of theevaporation area on the unit performance was analyzed. When the ambient temperatureis low, increasing evaporation area can reduce the compressor discharge temperature,shorten the heating time and improve the unit performance. At higher ambienttemperatures, increasing evaporation area can cause the compressor power to becometoo large even result in overload phenomenon, the system heating coefficient is declined.When the evaporation area is doubled, the unit COP would be increased from2.46to2.71with the ambient temperature at15℃, improved by10.2%, but the compressorworks close to the maximum power, the unit COP fell by2.4%with the ambienttemperature at30℃.Through comparison on the latest evaluation indicator of ASHPWH energyefficiency, the deficiencies are analyzed and the basic calculation formulas of annualperformance factor (APF) are modified. The theoretical APF values of an ASHPWHproduct in some typical climate regions prove its valuable on evaluating ASHPWHenergy efficiency.This thesis focuses on small household ASHPWH system, aiming to understand itsoperation characteristics in different conditions, and to provide the theoretical methodson product design, optimization, even to accelerate the products application.