CAPACITY ALLOCATION STRATEGY FOR MULTI-MODULE OUTDOOR UNITS IN VARIABLE REFRIGERANT FLOW AIR CONDITIONING SYSTEM

摘要

Variable refrigerant flow (VRF) air conditioning system has developed into multi-module outdoor units with inverter compressor installed in each module, in which the compressor operating frequencies are undetermined. In this paper, the performance of VRF air conditioning system with two parallel outdoor units is studied, and the capacity allocation strategy for parallel outdoor units is proposed. Firstly, models including compressor, heat exchanger, expansion valve and VRF air conditioning system with multi-module outdoor units were described mathematically. Then, the VRF air conditioning system with two parallel outdoor units operating in a certain frequency range were simulated in nominal cooling condition, in the cases of two identical parallel outdoor units and two different parallel outdoor units. The results indicate that a highest efficiency can be achieved at the frequency ratio region of 0.9～1.0 in the case of identical parallel outdoor units, while the most efficient frequency ratio region is 1.1～1.3 in the case of different parallel outdoor units. Finally, a capacity allocation strategy of compressor speed synchronization for multi-module outdoor units is proposed from the aspect of highest efficiency of VRF air conditioning system.