Develops a methodology for fault detection in HVAC systems based on optimal control The control strategy is determined using information that could come from an energy management and control system. This information is also used to detect faults in system operation. Deviations from optimal performance are detected by comparing the measured system power with the power predicted with the optimal strategy. Describes various statistical approaches to using the difference between actual and optimal power. Both individual measurements and sequences of data are used to determine the existence and location of faults. Discusses the trade-off between the level at which faults can be detected and the speed of detecting faults. Describes the testing of the methodology using simulations of a HVAC system operated both with and without faults.KEYWORDS: Controls, statistics, calculating, optimum, heating, ventilation, failure, monitoring, air conditioning.