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Condenser water supply temperature (CWST) resets are control strategies that reduce chiller plant energy consumption. Optimizing the CWST based on parameters such as outside wet bulb temperature, chiller load, and chilled water supply temperature (CHWST) setpoints can minimize total power across chiller plant components. An algorithm was developed for finding the optimal CWST for a given chiller plant. The algorithm generates lookup tables that show the optimal CWST and minimal power for a set of operating conditions. The results of the algorithm suggest three beneficial sequences of operation: resetting the CWST setpoint based on weather and cooling demand, running multiple cooling towers, and distributing chiller loads evenly. [ABSTRACT FROM AUTHOR]

A chilled water plant optimization program has been implemented on central plants at Texas A&M University, College Station, Texas. Due to the conflict conclusions drawn by other researchers, there was a debate on the advantage of applying variable condenser water flow control sequence. A calibrated component-based model is used to evaluate the energy savings potential with variable condenser water flow control sequence. The simulation result indicates that maximum achievable energy savings at the load profile of case study plant is only 1.03%. If counting the requirement of cooling tower minimum water flow, the energy saving will be negative which means the annual power consumption may increase by 3.4%. Considering the increased complex of control sequence, it is not recommended to implement variable condenser water flow control sequence for case study project. [ABSTRACT FROM AUTHOR]

This study investigates the optimization of the cooling tower condenser-water leaving temperature using a component-based model. This model consists of a chiller, a condenser-water pump, and two cooling towers. The chiller is modeled with a Gordon-Ng model for vapor-compression chillers with variable-condenser flow. The cooling tower is simulated with an effectiveness-NTU model. The pump power is calculated from the pump flow rate, pump head, and efficiency. This optimization problem is formulated as that of minimizing the total power of the chiller, pump, and fans by selecting an optimal cooling tower condenser-water leaving temperature at given weather conditions, chiller load, chilled-water leaving temperature, and condense-water flow rate. The model is applied in an example chiller CW system, and a generalized reduced gradient solver is used to search the optimal cooling tower approach setpoint. Simulation results show that the optimal cooling tower approach reset schedule can be approximated with two straight lines. Significant energy savings could be achieved if compared with the scenario with a constant cooling tower condenser-water leaving temperature. Further simulations show that the chilled-water leaving temperature, chiller part-load ratio, and the climate zones the plant locates in have a minor effect on the optimal approach reset schedule. A higher condenser-water flow rate per cooling ton leads to a higher optimal cooling tower approach, but this effect can be neglected for a system with a constant CW flow rate. The approach setpoint reset schedule that yields optimal control depends on the performance characteristics of the chiller and the cooling tower. [ABSTRACT FROM AUTHOR]