Simulation and optimum control of a two-stage compression air source heat pump system: A comparison of two kinds of variable volume approaches
Applied Thermal Engineering
Two-stage vapor compression technology can effectively improve the performance of an air source heat pump, and a staged compression system with two separate compressors has a highly flexible modulation capacity. However, the effect of different volume modulation approaches on the heating COP requires further analysis. In this study, a Modelica-based dynamic simulation model of a two-stage air-source heat pump was developed and verified with experimental data. A numerical optimization method was used to obtain the optimum frequencies and low- or high-stage cylinder volumes of the compressors that maximize the COP. The results show that the three optimization approaches have different effects. At lower ambient temperatures, varying the high-stage compressor cylinder volume can yield the maximum COP among the three optimization methods, followed by varying the low-stage compressor cylinder volume and compressor frequencies. At higher ambient temperatures, varying low-stage cylinder volume can yield the maximum COP, followed by varying the compressor frequencies and high-stage cylinder volume. The further the working condition deviates from the design point, the greater the improvement in the COP. The maximum improvements in the COP achieved with optimization in this study were 8.23%, 6.39% and 5.39% by varying the high-stage cylinder volume, low-stage cylinder volume, and frequencies, respectively.
Open Access Status
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Natural Science Foundation of Liaoning Province