Laboratory Assessment of Retrofit Fault Detection and Diagnostics Tools on a Commercial HVAC Packaged Rooftop Unit

Fault Detection and Diagnostics (FDD) and Heating, Ventilating, and Air Conditioning (HVAC) maintenance show ample opportunity to achieve and maintain significant energy and demand savings in support of strategic initiatives, goals and policies across California. The goal of this project (ET13SCE7040) is to explore the outputs of three commercially available FDD technologies on a 5-ton commercial packaged rooftop unit (RTU) air conditioner, across different plausible fault test scenarios. Two in-field FDD technologies and one onboard FDD technology were laboratory-tested. FDD performance was explored through laboratory testing at an external private lab, and at SCE’s Technology Test Centers (TTC), using the test method developed under project ET13SCE7030. The FDD technologies were tested under 47 scenarios; these scenarios comprise of different single and multiple fault scenarios, test chamber conditions common to climate zones in SCE territory, and varying fault intensities. The scope of faults included low/high refrigerant charge, liquid line restrictions, non-condensables, evaporator airflow reduction, and condenser airflow reduction (also two non-steady-state-performance-style economizer fault scenarios were also explored). The three technologies bring different unique value, and the FDD analysis mechanisms used here need further refinement to better capture this value and make it more transparent. Furthermore, the FDD analysis method still needs acceptance across the HVAC FDD industry. The findings presented here illustrate the challenging nature of troubleshooting HVAC systems. The output rate for correct responses is a quick and intuitive metric to gauge FDD performance and differentiate across the test units; a correct response is one where the HVAC operating condition, whether faulted or unfaulted, is correctly identified. For the purposes of this study, the fault threshold chosen (when the RTU can be considered faulted) is when EER degradation (air-side or refrigerant-side) is greater than 10%. Additionally, overcharge greater than 5% is considered a fault due to system reliability concerns and lesser-pronounced steady-state efficiency impacts. Across all tests, FDD technologies A, B, and C had correct output rates of 0.55, 0.54, and 0.29, respectively. Across the single-fault tests only, FDD technologies A, B, and C had correct output rates of 0.57, 0.61, and 0.4, respectively. Across the multiple-fault tests only, FDD technologies A, B, and C had correct output rates of 0.33, 0.30, and 0.33, respectively. All test units were not able to identify all multiple simultaneous faults as they occurred in the lab setup; test units were able to identify at least one of the multiple simultaneous faults. When three FDD technologies (all employing unique methods) were investigated in a controlled laboratory environment, results fall short of achieving idealized output rates of 100% correct response, 0% no response, 0% false alarm, 0% misdiagnosis, 0% missed detection. This should come as no surprise, as such expectations are unrealistic and arbitrary. The appropriate expectations for response rates has yet to be properly established. It is unknown, what technician response rates would be without the use of FDD technologies. The method for quantifying the value of FDD is still very much at the early stages of discussion. Based on these lab test results, it is reasonable to suggest that the consistency brought by implementing FDD technologies, likely minimizes the variability and adds value to troubleshooting HVAC systems. FDD technologies also add metrics and accountability to the value of HVAC troubleshooting. This project successfully applied a preliminary analysis mechanism for laboratory evaluation of FDD technologies, but is not intended to be the final and universal solution to fully understand FDD and HVAC maintenance. The FDD test units were not subjected to scenarios that capture transient impacts of faults, and cannot inform of the actual severity, incidence, and prevalence of faults experienced by equipment in the field. The overwhelming permutations of fault severities, fault combinations, indoor/outdoor conditions, and HVAC equipment characteristics make laboratory testing a potentially large and complex burden for directly exploring FDD technologies via lab testing alone. Industry acceptance of an FDD laboratory test method should continue to be a priority for key stakeholders in the HVAC maintenance/FDD industry (utilities, HVAC manufacturers, HVAC service contractors, FDD developers, etc.), with a clear understanding of how it fits into a combination of other diverse efforts. California utilities should continue their efforts to lead and support these activities. Ideally, field efforts, lab efforts, and simulation efforts across all stakeholders will be cohesively orchestrated and leveraged to best understand and enhance FDD and HVAC maintenance. In this scheme, a larger variety of scenarios can be explored, in an informed, effective manner.