Experiment and simulation of two-stage compression air-source heat pump water heater

Air-source heat pump (ASHP) water heater is a device for hot water in which heat is absorbed from air by heat pump through consuming a little electric. While there are some disadvantages of ordinary single-stage heat pump used in low-temperature environment condition, such as high compression ratio, scarce heating ability and low efficiency. Two-stage compression refrigeration cycle was put forward to use in the air-source heat pump to improve the low temperature adaptability of ASHP in this paper. Combining the single-stage heat pump, a two-stage compression air-source heat pump water heater was designed, and the experimental instrument of prototype had been built up for experimental study. The results of actual tests showed that, compared with single-stage compression cycle, the compression ratio of two-stage cycle's was much less, and the heating ability was generally higher. The COP of the two-stage system could keep to about 1.5 while the environment temperature dropped to -20 degrees C. The lumped parameters steady model was built for the two-stage compression air-source heat pump water heater, and the simulated results were good agreement with the measured data.