Switchover Control Strategies for Improving Performance of Refrigeration Systems under Off-Design Conditions

Abstract

A typical 3-ton vapor compression refrigeration system using R-22 as the refrigerant is addressed. Two models are developed: a design model and a hierarchical control model. The design model is operated to observe the response of a typical system under various off-design operating conditions. In lieu of laboratory experiments, the normalized responses from the design model (normalized with respect to the design conditions) are compared to the normalized values based on the experimental data reported in the literature. This is done to validate the design model to the extent possible, limited by the reported experimental data in the literature. From this design model a hierarchical control model is developed, in which different control techniques for system capacity regulation and for operation over a range of ambient temperature are employed. By varying corresponding control parameters in each technique, information is developed regarding the refrigerant conditions within the system and system performance under different operating conditions. From the results of these simulations, hierarchical or switchover control strategy for an integrated refrigeration system is postulated to achieve the specific operational requirements with the highest feasible system efficiency over a wide range of off-design operating conditions. A similar approach can be used to postulate different hierarchical control based on other performance measures and considerations.