SA-12-016 -- Secondary Control Strategies for Cycling of Air Conditioning and Refrigeration Systems

A large percentage of air conditioning and refrigerationsystems rely on compressor cycling strategies to meet coolingloads. This paper examines the impact of expansion valve andheat exchanger fan control strategies on system efficiency,assuming an on-off cycle of the compressor. The first step is thedevelopment of a start-up/shut-down dynamic simulationmodel that is used as a tool to understand the effect that valve/fan cycling has on the systems cyclic efficiency. Refrigerantmigration due to valve strategies and fan delay at shutdown aredetermined as crucial issues that have an effect on systemscyclic efficiency. Optimization approaches are then used tosearch for the optimal cycle strategies. The simulation studiesare followed by extensive experimental tests conducted on a 3-ton residential air conditioner, confirming the major conclusionsof the simulation study, namely that the valve and fancontrol strategies during compressor shutdown can result insignificant variations in cyclic COP.