Sub-optimal on-off switching control strategies for chilled water cooling systems with storage

A dynamic model of vapour compression refrigeration system is developed. The overall model consists of the following basic components: a compressor, a condenser, an expansion valve, an evaporator, an evaporative cooler and a cool storage. The integrated system is referred to as chilled water cooling system with storage (CWCS). The mathematical modelling of the CWC system undertaken in this study predicts the change in state of refrigerant in the system with respect to lime. A computer program is developed to solve the dynamic equations along with empirical correlations describing refrigerant properties. Open-loop tests are carried out to study the performance characteristics of the system under varied cooling load and compressor speed. The model is intended to serve as an analytical design tool and to provide a basis for control analysis. Based on a heuristic method,'sub-optimal on-off control' strategies for the chilled water cool storage system are developed using a reduced order model. The methodology of generating such control profiles is illustrated and the tests for optimality show that the control profiles are near optimal. The on-off control scheme is simulated on the full order CWC system. The operating performance of the system is described under several simulated cases. The results show that the control scheme is capable of maintaining the chilled water temperature in the chosen range. (C) 1998 Elsevier Science Ltd.