Study On Operation Characteristic And Parameters Optimization Of Novel Energy-Efficient Refrigerator

Household refrigerators are largely produced in China; over80million of household refrigerators are produced every year. Energy consumption of household refrigerator is huge in China. Energy consumption of household refrigerator makes up40%～50%of the residential electricity consumption. Therefore, studying energy-saving technology of the refrigerators improves the quality of refrigerators and capacity of independent innovation for refrigerator enterprises in China. Energy saving of refrigerator has also important significance for alleviating energy scarce and reducing greenhouse gas emission for China.A novel energy storage energy-efficient household refrigerator with heat storage condensers is studied. When the refrigerator is in "on-time" state, one part of condensation heat is too late to release to ambient and stored in the energy storage materials; when the refrigerator is in "off-time" state, the heat of condensation stored within the energy storage materials can be released to ambient. Thus the intermittent heat dissipation of the hot-wall condenser is replaced by the continuous heat dissipation of heat storage condensers during a complete cycle, which improves the overall heat transfer performance of condensers and energy saving of the refrigerator. Systematic research of the novel energy storage energy-efficient household refrigerator is studied by the analysis of experimental test and dynamic simulation. A novel multi-objective global optimization method based on Genetic algorithm NSGA-Ⅱ is proposed for increasing overall performance of household refrigerator. Parameters optimization of refrigerators is analyzed. The influence of cool storage evaporator on operation of refrigerators is primarily studied at last. The experimental basis and theoretical basis is provided by the research result of this paper for performance improvement and popularization of the novel energy-efficient household refrigerator.The novel refrigerators with heat storage condensers are constructed on the base of different kinds of household refrigerators. The contrast experiments of different kinds of the novel and ordinary refrigerators were done for study of operating characteristic of refrigerators under the stable operating condition. For any kind of refrigerator, the starting power of the novel refrigerator is smaller than that of the ordinary refrigerator. The novel refrigerator needs shorter time to achieve stable status. Because of heat storage of energy storage materials, on-time, off-time and complete cycle time of the novel refrigerator are respectively lower than those of the ordinary refrigerator, the ratio of on-time to off-time of the novel refrigerator is reduced. Due to continuous heat dissipation, the overall heat transfer performance of the heat storage condenser is increased, condenser temperature of the novel refrigerator is reduced and subcooling degree at outlet of condenser is increased during on-time. In this way, energy consumption of the novel refrigerator is reduced greatly. For any kind of refrigerator, energy saving of the novel refrigerator is about10%. According to related experiments, the heat storage condenser can improve performance of any kind of refrigerator. The universality of the heat storage condenser for energy saving of refrigerator is proved by the experimental results of different kinds of refrigerators.Mathematical model of heat storage condensers and the refrigerator dynamic model are established for further study of the influence of heat storage condensers on the novel refrigerator. Dynamic simulations of the novel refrigerator and ordinary refrigerator are both carried out. The numerical results of the novel refrigerator and ordinary refrigerator both agree well with the experiment results; the correctness and accuracy of refrigerator dynamic model are validated. According to the result of simulation, coefficient of performance (COP) of the novel refrigerator is increased by about20%; however the energy storage materials reduces the heat preservation effect of insulation and increases the average heat leakage, which offsets a part of energy saving effect and actual energy saving of the novel refrigerator is about10%. Some key parameters such as ambient temperature, freezer temperature and peak of phase change temperature of energy storage materials are studied to further discuss the influence of these key parameters on energy saving effect of the novel refrigerator. After simulation, it is concluded that the increasing of ambient temperature and decreasing of freezer temperature can both increase the energy saving of the novel refrigerator; the best peak of phase change temperature of energy storage materials are found. Theoretical basis is provided by dynamic simulation for further analysis of the energy-saving mechanism and performance improvement of the novel refrigerator.A novel multi-objective global optimization method combining refrigerator dynamic model and Genetic algorithm NSGA-Ⅱ is proposed for increasing overall performance of household refrigerator. The novel refrigerator with heat-storage condensers and ordinary refrigerator with hot-wall condensers are optimized by the method for multi-objectives of minimizing total cost and energy consumption per24h. Optimized curves on multi-objectives of the novel refrigerator and ordinary refrigerator are obtained and compared with each other. In the optimized curve, for one value of energy consumption per24h, a corresponding minimum total cost is acquired; otherwise, for one value of total cost, a corresponding minimum of energy consumption per24h is acquired. For whether total cost or energy consumption, the performance of the novel refrigerator is improved greatly, which indicates that the energy saving of the novel refrigerator with heat storage condensers is not optimal on the base of the original design parameters. The design parameters of refrigerators need optimization. Optimization results of the novel refrigerator and the ordinary refrigerator are compared with each othe. Under the condition of same total cost, energy saving of optimized novel refrigerator compared with optimized ordinary refrigerator is20%-26%. Under the condition of same energy consumption per24h, cost saving of optimized novel refrigerator compared with optimized ordinary refrigerator is￥11～￥21.The influence of cool storage evaporator on the refrigerator operation is analyzed for further improving energy saving of the refrigerator. Energy storage materials in which the phase change temperature is lower than the design temperature of refrigerator compartment is selected as cool storage material to construct the cool storage evaporator. When the refrigerator is during on-time, a part of cooling capacity is stored in cool storage material; when the refrigerator is during off-time, cooling capacity within cool storage material is released to frozen-food compartment. Therefore the continuous heat transfer between evaporator and frozen-food compartment is realized in a complete cycle. Mathematical model of cool storage evaporator is established and combined with refrigerator dynamic model to simulate the refrigerator with cool storage evaporator. Because of cool storage materials, the power decreasing of the refrigerator with cool storage evaporator becomes slower; on-time, off-time and ratio of off-time to on-time of the refrigerator are all increased. Because the overall heat transfer performance of the cool storage evaporator is better than that of the conventional evaporator, energy saving effect of the refrigerator is further improved by cool storage evaporator. Simulation results show that energy consumption of the refrigerator is decreased by about20%by cool storage evaporator, which provides the new thinking for energy-saving technology of the refrigerators.