On-line monitoring and fault detection

Modern energy management and control systems have alarm and trend features that allow building operators to monitor and troubleshoot building systems. The alarm feature can provide nearly immediate feedback when, for instance, a sensor value is outside specified limits. Using the trend feature, building operators can view graphs of sensor and controller output versus time. In the case of an alarm, information obtained using the trend feature can assist the operator in isolating the cause of the alarm. However, it can be difficult to select the alarm limits. If the limits are too narrow, the building control system likely will issue a number of false alarms and building operators eventually will ignore them. If the limits are too wide, faulty conditions will tend to go unnoticed because alarms are not issued.