Development of an Automated Fault Detection and Diagnostic Tool for Unitary HVAC Systems at Industrial Energy Audits

Industrial energy audits generally focus on optimization of manufacturing process systems but fail to focus on the non-process industrial HVAC systems. This is in spite of the well-documented widespread prevalence of efficiency degrading faults occurring in the HVAC systems used in these facilities. Since these unitary air conditioners are not the primary energy consumers in the facility, energy auditors of IAC can find it difficult and time-consuming to identify air conditioning faults and justify their repair with a monetary value without the use of a quick tool. Existing methods and tools require system specific models or manufacturer?s map models that are not easily available to energy auditors.

The proposed automated fault detection and diagnostic device for unitary air conditioners overcomes these challenges. It uses 7 surface temperature and 2 pressure sensors, with easily obtainable information to detect refrigerant undercharge, refrigerant overcharge, liquid line restriction, condenser fouling and evaporator fouling faults, and also predict the related energy and cost saving for each fault. It generates ?features? from the sensor inputs that are sensitive to the fault, but less sensitive to operating conditions. The fault detection rules are based on whether a set of features are High, Low or Normal in comparison to the thresholds. Multiple fault detection is achieved by first checking for charge related faults and then checking for fouling faults in presence or absence of the charge related faults.

The developed device was tested for individual and multiple faults with systems using thermal expansion valve and fixed orifice valve. Results showed that the sensitivity of the device was good for refrigerant line faults but not as good for the fouling faults. Results of the multiple fault tests showed that the device could detect at least one of the two faults, generally the refrigerant line fault, over 60% of the time. Overall, the device gave conservative estimates of energy and cost savings, which is usually preferred by IAC energy auditors.

Finally, the device was also prepared for field tests, to verify that it was quick, low cost and easy to use. It took about 20 minutes to install the device that cost less than $2,500.