Condensing temperature control to enhance the efficiency of air-cooled chillers

This paper describes an operating strategy of condensing temperature control (CTC), which means regulating the set point of condensing temperature based on the outdoor temperature, to enhance the efficiency of air-cooled chillers used in air-conditioned buildings. A mathematical model of an air-cooled chiller is developed for simulation and is validated by using the operating data of an existing chiller and of an experimental chiller. Compared to head pressure control (HPC) with a fixed set point of condensing temperature, CTC brings a moderate rise in the condensing temperature above the outdoor temperature, and hence enables the compressors to operate at a lower condensing pressure through staging more condenser fans. While more condenser fan power is consumed, compressor power can drop considerablely, reducing the annual chiller power consumption by 18.4%. It is suggested that the condensing temperature can be coupled with the outdoor temperature and the part load ratio of chillers to gauge the achievable part load efficiency.