Fault Detection and Diagnostics for Rooftop Air Conditioners

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point sensor placement is generally used, many measurements often are biased and
noisy. The FDD should be able to handle these practical difficulties.
3. Multiple-simultaneous faults are common for packaged air conditioners, so the
FDD technique should be capable of handling them.
1.3.2 Methodology
There are two aspects to the general approach proposed for achieving the
objectives: 1) actively create favorable conditions for application of the FDD techniques
and 2) provide improved FDD methodologies to handle multiple-simultaneous faults and
reduced model training requirements.
Because of economic constraints, some practical difficulties are impossible to
overcome passively. For example, it is not possible for a single-point sensor to measure
the mixing box temperature accurately under varying damper position. To reduce
measurement uncertainty and bias and dimensionality, favorable conditions for FDD can
be created proactively as follows:
1. Schedule application of the FDD methods at special times (e.g. night time) instead
of around the clock to eliminate the unfavorable impact of weather conditions, such
as solar radiation, and occupant intervention.
2. Override routine controls to fix the speed of the condenser fan and evaporator
blower and damper position. Constant condenser fan and evaporator blower speed
is equivalent to constant air mass flow rate under normal operation condition. Fixed
damper position eliminates the mixing problem with single-point sensor.
From a methodology point of view,
1. Existing FDD methods were examined to identify their advantages and drawbacks.
The statistical rule-based (SRB) FDD method proposed by Rossi & Braun only
uses low cost sensor and has good performance under laboratory test, so it
provided a start for further improvement.
2. The FDD problem was analyzed from a control and mathematical point of view.
From the control point of view, decoupling is an efficient way to handle