Simulation and optimization of water-based hybrid VRF systems with bifurcating bare-tube heat exchangers

摘要

Hybrid VRF (hVRF) systems enjoy reduced refrigerant charge and wider selection of refrigerantscompared to traditional VRF systems. However, due to relatively low heat transfer rate in the indoorcoil, hVRF system COP was reported to be 10% lower than a traditional VRF system COP. To solvethe COP degradation problem of hVRF system, a bi-objective optimization method was proposed fora water-based hVRF system that uses bifurcating bare-tube heat exchangers (bBTHX) as the indoorcoils. The two objectives are minimizing bBTHX envelop volume and maximizing system COP. Theoptimization problem is separated into two steps. First, refrigerant loop parametric analysis wasperformed to determine the optimal water loop operating conditions. Next, bBTHX optimization wasconducted subjected to the constraints of capacity requirements from step one and dimensionlimitations. Then we simulated the entire hVRF system with the optimal bBTHX designs and obtainedthe Pareto front between system COP and bBTHX volume. The results show that comparing withVRF direct expansion system, hVRF system suffered 10% COP degradation with tube-fin indoorunit, and 4% COP degradation with the bBTHX.