Cascaded superheat control with a multiple evaporator refrigeration system

Variable refrigerant flow (VRF) systems are increasingly being used in commercial buildings in preference to chilled water or ducted air systems. The closely coupled dynamics of VRF systems, however, create a need for effective control strategies to ensure safe and effective operation. Of particular interest is the regulation of evaporator superheat. In this paper a cascaded architecture for controlling superheat is applied to a multiple evaporator system, and compared to traditional PID-controlled evaporators. The effects of the architecture on dynamic coupling are explored, and efficacy is demonstrated with experimental results.