The emergence of increasingly affordable variable speed drive technology has changed the approach for how chilled water systems equipped with variable speed drives should be controlled. The purpose of this research was to estimate the potential energy savings that can be achieved through optimization of a single chiller system equipped with Variable Frequency Drives (VFDs) on all pieces of equipment in the condenser water system. Data for a case study was collected from a local museum’s chilled water system. To accomplish the objective, physical component models of the centrifugal chiller, cooling tower and condenser water pump were established with the goal of incorporating the system’s condenser water flow rate and cooling tower fan speeds as optimization variables. Furthermore, a cooling load prediction algorithm was developed using a multiple non-linear regression model to approximate the buildings cooling load subject to a range of environmental conditions. The inputs and outputs of the individual component models were linked to estimate how adjusting the cooling tower fan and condenser water pump speed would influence the system’s overall performance. The overall system model was then optimized using a generalized reduced gradient optimization algorithm to determine the potential energy savings through speed control with VFDs and ascertain a simple control logic strategy for the building automation system to operate the system. The saving potential of the optimized system was found to be 12-15%.
Keywords chilled water system, variable speed drive, condenser water system, cooling tower, HVAC optimization