Estimating the Size of Incipient Faults in HVAC Equipment

It may be necessary to estimate the size of a fault if the fault develops slowly and the associated loss of performance could go unnoticed for a long period of time. This paper describes an observer-based method of estimating the magnitudes of slowly evolving faults in HVAC equipment. The sizes of two types of incipient faults in a cooling coil subsystem are estimated using a fault identification scheme based on a fuzzy relational proportional-integral observer. Because it would take a long time for a fault to develop in a real system, a detailed computer simulation is used to assess the performance of the scheme. The main causes of inaccuracy in the fault estimates are examined and long-term simulation results are presented, which demonstrate that an adaptive version of the scheme can generate satisfactory estimates of the sizes of the faults.