Modern buildings are being designed with increasingly sophisticated energy management and control systems (EMCS) that have seemingly limitless capabilities for monitoring and controlling the conditions in buildings. Nonetheless, building heating, ventilating and air-conditioning (HVAC) equipment routinely fails to satisfy performance expectations envisioned at design. Furthermore, such failures often go unnoticed for extended periods of time. How does this happen? There are a number of explanations. First, HVAC equipment is typically instrumented with the minimum number of sensors sufficient to implement basic local-loop and supervisory control strategies. Lack of sensor information is a significant barrier to assessing the operation of the equipment. A second explanation is that the data that is collected overwhelms building operators because there is little effort to consolidate the information into a clear and coherent picture of equipment status. Trend data from today's EMCS are useful, but only when analyzed by a human, and this is not a cost-effective way to continuously monitor system operation. A third explanation is that building operators may overlook symptoms of a failure because they may not fully understand the control strategies implemented. A related explanation is that lack of understanding of sophisticated control strategies leads to manual overrides that may temporarily alleviate a problem, but may lead to unintended and undetected operating problems in the future. Undoubtedly other explanations exist; however, there is little argument that there is vast room for improvement in the way buildings are monitored.

• maintenance, inspection, and diagnose