Fault Detection and Diagnostics for Rooftop Air Conditioners

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2. Existing techniques for online FDD mainly have three drawbacks. First, they are
expensive to apply practically because of requirements for model training and large
computational demand. Second, they have only been tested in the laboratory and
have not considered factors that occur in the field. Third, they can not handle
multiple-simultaneous faults.
3. No one has performed economic assessments of FDD. It is a complicated problem
that requires field evaluations.
So, a general objective of this research was to develop a practical automated FDD
technique, whose cost is low enough to be affordable for packaged air conditioners and
heat pumps, and whose performance is robust and capable of handling multiplesimultaneous
faults. Another objective was to perform an initial economic assessment of
FDD applied to vapor compression equipment in California.
The biggest technical difficulties associated with development of a practical FDD
method are associated with the economic constraints. To realize the general objective,
some sub-objectives should be achieved.
1. Only inexpensive hardware can be used, which means that redundant analyses
should be conducted using limited computation and memory resources. This is a
particular problem in fault diagnosis since some faults may have similar symptoms
and more sensors can help in distinguishing them. On the one hand, features as
sensitive as possible should be extracted from limited inexpensive measurements,
and on the other hand, the diagnosis method should be as sensitive as possible to
isolate several faults with similar symptoms and insensitive features. Computation
should be small enough to be implementable within a microprocessor.
2. Packaged air conditioners are used in diverse weather and climates, so their
behavior will vary drastically. Unmeasured ambient weather conditions, such as
solar radiation, rain, and strong wind on the condenser can impact performance.
Since the mixing chamber is small, outdoor air and return air are not mixed well
and varying damper positions even exaggerate this impact. In addition, since single-