The effects of capacity coupling and wet air return on the energy performance of chiller-cooling tower systems

This study uses a novel concept of capacity coupling of chiller-cooling tower system to investigate the system energy performance. System performance factor (SPF) of the chiller-cooling tower system is used in the analysis. A regression function is obtained for hourly reset of condensing water temperature so to achieve maximum SPF. The regression function includes parameters such as ambient wet bulb temperature, chiller load ratio, tower capacity ratio, and a dimensionless relative efficiency of chiller and cooling tower. The regression function has an R ² close to 1 compared to the computed results. It is found that for capacity coupling ratio of 1.1 ∼ 1.6, SPF would increase by about 3 ∼ 6% compared with a typical base control. The effect of wet air return is presented as an equivalent wet bulb temperature. It has been found that SPF would decrease significantly when higher equivalent wet bulb temperature occurs at the tower inlet.