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. Because the device is efficient, clean, safe, and convenient, it adapts to the climate condition, energy situation and environment request in China. But there are some shortage of ordinary single-stage heat pump in low-temperature environment, such as high compression ratio, devoid heating power and low efficiency.
Two-stage compress...