The existence of faults in heating, ventilating, air-conditioning, and refrigerating (HVAC&R) systems plays a significant role in the degradation of comfort levels for building occupants. In this paper, a mechanical model for fault detection and diagnosis (FDD) in a chiller subsystem is developed. With the model, the characteristic quantities (CQs) that are most appropriate for identifying faults are found. A detailed mechanistic model originally developed by Braun (Braun et al. 1988) and used to analyze a 5500-ton centrifugal chiller at Dallas/Fort Worth (D/FW) Airport is used as a base for the fault detection development. The model is calibrated using data from an operating site. The use of the model in identifying operating faults is discussed.

Units: I-P