| 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 compression refrigeration cycle was put forward to use in air-source heat pump to solve the low temperature adaptability of ASHP in this paper. By comparing four different cycles, two-stage throttle with superheated suction gas was proposed for ASHP in low temperature environment. Combining the single-stage heat pump, two-stage compression air-source heat pump water heater was designed. This system could switch the two cycles to adapt to bigger field of applicationTwo-stage compression air-source heat pump water heater was theoretically analyzed. By designing and calculating, the experimental instrument of prototype has been built up for experimental study. Some conclusions are obtained through actual test. Compared with single-stage compression cycle, the two-stage cycle's compression ratio is much less, and the heating power is higher all along. The COP of two-stage system surpasses the single-stage cycle when the temperature of the environment fall to 5 degree, and it could keep to about 1.5 when 20 degree below 0.According to the performance of the two-stage compression air-source heat pump water heater, the system could be set two switching modes to adapt to changeful practical situation. One mode is principle of COP, and the other is principle of heating rate. The system, which follows the mode of principle of COP, was economically analyzed under the climate of a north city. All-year operating cost decreases by 60% compared to electric water heater, 15% compared to gas water heater. |
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