Detection and Diagnosis of HVAC Faults via Electrical Load Monitoring

Detection and diagnosis of faults (FDD) in HVAC equipment have typically relied on measurements of variables available to a control system, including temperatures, flows, pressures, and actuator control signals. Electrical power at the level of a fan, pump, or chiller has been generally ignored because power meters are rarely installed at individual loads. This paper presents two techniques for using electrical power data for detecting and diagnosing a number of faults in air-handling units. The results from the two techniques are compared and the situation for which each is applicable is assessed. One technique relies on gray-box correlations of electrical power with such exogenous variables as airflow or motor speed. This technique has been implemented with short-term average electrical power measured by dedicated submeters. With somewhat reduced resolution, it has also been implemented with a high-speed, centralized power meter that provides component-specific power information via analysis of the step changes in power that occur when a given device turns on or off. This technique was developed to detect and diagnose a limited number of air handler faults and is shown to work well with data taken from a test building. A detailed evaluation of the method is presented in the companion paper, which documents the results of a series of semiblind tests. The second technique relies on physical models of the electromechanical dynamics that occur immediately after a motor is turned on. This technique has been demonstrated with submetered data for a pump and for a fan. Tests showed that several faults could be successfully detected from motor startup data alone. While the method relies solely on generally stable and accurate voltage and current sensors, thereby avoiding problems with flow and temperature sensors used in other fault detection methods, it requires electrical data taken directly at the motor, downstream of variable-speed drives, where current sensors would not be installed for control or load-monitoring purposes.

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