The Simulation Of Variable Refrigerant Flow Air Conditioning System For Control Analysis

Variable Refrigerant Flow (VRF) air conditioning systems have beenapplied widely, because its excellent performance in energy efficiency andimproving indoor environment comfort. Compared to ordinary frequencyair conditioning system, VRF system usually has one outdoor unit andseveral indoor units, and the operations of indoor units have influences oneach other, thus it is a critical problem that how to ensure precise control ofthe whole system.For the study on the control of VRF system, simulation study is acommon method. However, due to strong coupling characteristic of VRFsystem, most studies focus on the system with less three indoor units aswell as the performance of complex systems previously, and the controlanalysis of system is less involved. Besides, the simulation modelsestablished have significant limitations, and they are not suitable to thesimulation of control analysis on the system with more than three indoor units.The VRF system of a commercial building in Shanghai is thesimulation object in this paper, and the simulation platform is establishedwith TRNSYS based on the system design parameters and equipmentperformance parameters, for the simulation of control analysis. Thesimulation platform aims at executing control analysis and developingoptimal control strategies, thus there are several new requirements for themathematical models and algorithm, not only ensuring the exact results,but also ensuring a reasonable computation time. Based on theserequirements and previous studies, the models suitable for control analysishave been established, including components, refrigerant properties and airproperties; in addition, three system simulation algorithms of triple loopiteration have been designed, by comparing their computation time andcalculated results to determine the best simulation algorithm as the corepart of the system simulation platform.In order to control the indoor temperature and superheated degree,two basic systematic control strategies have been put forward in this paper,and the control stability of two strategies has been compared to determinebetter control strategy as the strategy in the simulation of systemperformance. To further validate the reasonability and versatility, the simulation of system performance is executed under typical days insummer and transition season. The simulation results show that thechanges of system performance are consistent with the trend of the actualsystem operation.