Parameterization study on the operating efficiency of air-cooled chillers

The chiller plants for providing cooling in buildings in a dense urban environment, as is Hong Kong, often require heat rejection by air-cooled condensers.]Improved efficiency of air-cooled reciprocating chillers requires knowledge of the behaviours of the operating parameters. A parameterization study aiming at exploring such behaviours was carried out with the hybrid use of the operating data from an installed chiller in an existing building and the predicted data by a validated chiller model. The chiller efficiency generally increases with the chiller part load ratio. A close relationship between the evaporator performance and the chiller part load ratio was observed, but varying the chilled water flowrate and the evaporating temperature shows a diverse effect on the evaporator performance. Multiple steps of capacity control would result in fluctuating compressor power input. Evaluation of the condenser performance indicates that the performance cannot be simply represented by any one of the control parameters: part load ratio, refrigerant mass flow, heat rejection airflow and condensing temperature. The opportunity of reducing the condensing temperature at below-design outdoor conditions for better efficiency and energy saving was exploited through the evaluation of the boundary and the means to achieve the lowest possible working condensing temperature.