P2-3. Air Handling Unit and VAV Box Diagnostics > Outcomes

Technical Outcomes:

• In laboratory testing, the APAR and VPACC tools were both found to be successful at finding a wide variety of faults. Faults correctly detected included stuck or leaking dampers and control valves, sensor drift, and improper control sequencing. It was also found that some faults could not be detected under certain operating conditions because the control system was able to mask the problem or because sensor data needed to detect the fault is not commonly available in commercial systems.
  
  
• In field-testing, APAR and VPACC successfully detected faults using data from several different sources. Data sources included an office building, a restaurant, and community college and university campuses, featuring constant- and variable-air-volume systems. Any evaluation using field data must contend with some inherent difficulties: reliance on sensor data to discern the true state of the system, the inability to report a "false negative" (an undetected fault), and ambiguity regarding what constitutes a fault. However, in this case consistent results across diverse testing environments give a high level of confidence that the FDD tools will perform in an even greater variety of applications. Faults have been successfully detected and confirmed by building operations staff. Every site has been found to have at least one fault. Even though the sample size is small, these results appear to confirm the hypothesis that faults of the type that can be detected by these tools are common.
  
  
• The APAR and VPACC rule sets were successfully embedded in controllers from three manufacturers using their respective native programming languages.

Market Outcomes:

• The results will produce better indoor environments in California buildings. Usually equipment malfunctions are only detected when someone complains about a lack of cooling, heating, fresh air, or other comfort issues. Other problems simply continue unreported. Automatic FDD for AHUs and VAV boxes will call attention to problems before they lead to discomfort or health problems in a building's occupants.
  
• FDD can lead to more effective utilization of technician's labor. Having diagnostic results available before arriving at the site would allow technician's to plan their work time and have the right parts on the truck. Multiple trips to the site to work on the same problem could be avoided.
  
• FDD will prevent premature equipment failure. Compressor failure is the most expense repair on packaged rooftop units, and FDD technology can detect the faults that cause it as well as other problems.
  
• FDD technology will reduce unplanned outages. Using FDD to track repair histories as well as fault occurrences can assist building owners and mechanical contractors to make better "repair or replace" decisions.
  
• The results will provide energy benefits. Using FDD may improve AHU and VAV box performance, providing better indoor conditions for less energy input. FDD may also allow a technician to rule out problems with a unit and look for problems elsewhere in the building. For example low flow across the cooling coil may be due to clogging of the coil caused by filter bypass, but it may also result from blockages or closed dampers.

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