On-line optimization control method based on extreme value analysis for parallel variable-frequency hydraulic pumps in central air-conditioning systems

This paper proposes a class of theoretical models based on parallel hydraulic pump characteristics and on-line control optimization methods for variable-flow hydraulic pumps in central air-conditioning systems, which includes the optimized allocation of parallel variable-frequency hydraulic pump speed ratios and the optimized number of operating units. It is suitable for use in fast load variations and for on-line control of variable-flow central air-conditioning systems that use a variable differential pressure setpoint control strategy. This study first establishes a model of parallel variable-frequency hydraulic pump characteristics and uses the extreme value analysis method to investigate the optimal combination of speed ratios of multiple parallel variable-frequency hydraulic pumps. We then explore the optimal number of operating units of parallel variable-frequency hydraulic pumps that utilize the same hydraulic operating point. Using these two methods and monitoring parameters such as the total flow rate and total head of parallel hydraulic ptumps, this study proposes an optimization control method that can perform on-line decision-making for the optimal number of operating hydraulic pumps based on automatically calculated operational zones. The proposed method was applied to a plant with a primary pump variable-flow air-conditioning system that uses a variable differential pressure setpoint control strategy. The actual application shows that this method obtained electricity savings of 15.8% and 4% compared with single-pump operation scheme and dual-pump operation scheme, respectively, for the hydraulic pumps. The method is universal and simple for on-line implementation, which is suitable for control optimization of chilled-water pumps in a variable-flow air-conditioning system.