Steady-state simulation of screw liquid chillers

In order to predict the performance of screw liquid chillers in a wide range of configuration parameters and operating conditions, a steady-state simulation model is presented, which is suitable for non-economized and economized chillers. The model includes sub-models for key components, such as non-economized compressor, economized compressor, shell-and-tube condenser, expansion valve, and flooded evaporator. Sequential modular method and successive substitution methods are combined together to carry out the simulation of the chillers. The convergence properties of this simulation technique are also analyzed. The present model can predict the performance within +/-10% for large scale of cooling capacity including four specifications of non-economized chillers and three specifications of economized chillers. With the validated model, a sensitivity analysis on the economizer system is made. It is found that the cooling capacity of screw liquid chiller can be increased apparently by adding the economizer, but only when the volumetric ratio of the first stage internal compression is greater than a certain value, the economized screw liquid chiller can gain a higher COP than that of the non-economized one at the same time. (C) 2002 Elsevier Science Ltd. All rights reserved.