Analysis of the operating characteristics of hybrid heat sources: heat pump water heater under variable conditions

To analyze the operating characteristics of hybrid heat sources, heat pump water heater, under variable condition, the apparatus of the direct-expansion solar-air source water heat pump was established using a variable capacity compressor and an electronic expansion valve. The mathematical model of this system was developed and verified. The simulated results were in good agreement with the experimental results. The validated mathematical model was used to further analyze the effect of ambient temperature, solar radiation intensity and compressor frequency on the system performance. The frequency conversion control strategy of the compressor was developed, and the recommended frequency and heating time under different working conditions were obtained, which can provide guidance to operations under variable conditions. Based on the meteorological parameters of typical meteorological years in Nanjing, the annual operating characteristics of the system in different modes were simulated and compared. The results showed that, compared with the constant capacity mode, the COP of the system in the variable capacity mode annual increased by an average of 49.27%, while the power consumption decreased by 29.73%, and the energy saving was quite remarkable. © 2017, Chemical Industry Press. All right reserved.