4754 - Dynamic Model of a Centrifugal Chiller System - Model Development, Numerical Study, and Validation PDF

Dynamic models of heat pumps are useful in developing feedback controllers and fault-detection-diagnostic (FDD) studies. Several system models have been documented in the literature, but few are for centrifugal chillers. Existing publications focus on model development and validation, providing minimal detail on the numerical aspects of the solution. The solution of the PDEs that are obtained to model the heat exchangers is critical in terms of accuracy and execution speed. This paper presents the development of a centrifugal chiller system model, using the finite-volume (FV) approach for shell-and-tube heat exchangers and aspects such as mesh dependence, integration order, and step size. Sufficient and necessary mesh sizes for accurate steady-state prediction are determined for the heat exchangers. Execution speeds with integration algorithms of the first, second, and fourth order are compared for equivalent accuracy. The model is based on first principles, allowing it to be used over a wide range of operating conditions and transients. The model is validated using data from a 90-ton R-134a centrifugal chiller.

Units: SI