Integrated Control and Fault Detection of Air-Handling Units

Abstract

A new method for integrated control and fault detection of air-handling units (AHUs) is described in this paper. The method uses sensors commonly installed in AHUs and collects much of the key diagnostic information at times when steady-state conditions are imposed on the AHU by the sequencing logic, thereby eliminating the need for a steady-state detector. A model-based fault detection method processes these data and generates residual values that can be further processed to detect faults. For faulty operation, one or more of the residuals is expected to have a value that is significantly different from 0, the expected value for normal operation. In parallel to model-based residual generation, an algorithm calculates state-based performance indices of control loops for the processes used for sequential control of the AHU. The method was assessed through simulations of 16 faults, which consisted of temperature sensor offset faults, stuck and leaking damper faults, and stuck and leaking valve faults. With the exception of the return air temperature sensor offset faults, each fault impacted numerous residuals. In addition, two faults (stuck-closed recirculation air damper and heating coil valve stuck 10% open) caused control performance indices to saturate, which should not happen for a properly designed and operating system. The complementary aspect of the model-based residuals and state-based performance indices is described and illustrated with these faults.