Fault Detection and Diagnostics for Rooftop Air Conditioners

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1 INTRODUCTION
1.1 Background on FDD
FDD is an acronym for fault detection and diagnosis. Fault detection involves
identifying whether the supervised system deviates from normal operation and fault
diagnosis is diagnosing or isolating the detected fault(s) from other possible faults. Some
literature uses the acronym FDI to refer to fault detection and isolation.
FDD has been successfully applied to critical systems such as space exploration
and nuclear power plants, in which early identification of small malfunctions would
prevent loss of life and damage of equipment. In these applications, FDD sensitivity is a
vital feature. However, false alarm rate is also an important index because of economic
concerns. A high false alarm rate could result in unnecessary economic loss due to
stoppage of equipment operation. In order to increase FDD sensitivity and decrease false
alarm rate, FDD techniques generally use multiple hardware such as sensors and
computation sources for the same purpose. The high cost of hardware redundancy has
limited the application of FDD to non-critical systems such as HVAC&R systems.
However, with the growing realization of the benefits brought by FDD and the decreasing
cost of hardware especially for computation, more and more applications of FDD have
been attempted for non-critical equipment such as HVAC&R systems.
HVAC systems often do not function as well as expected due to faults introduced
during initial installation or developed in routine operation. Rooftop and other packaged
air conditioners are used extensively throughout small commercial and institutional
buildings, but compared to larger systems, they tend to be not well maintained. As a
result, widespread application of automated FDD will significantly reduce energy use and
peak electrical demand, down time and maintenance costs. Unlike critical systems, FDD
for HVAC systems, especially for small packaged air conditioners, is subject to economic