Fault Detection and Diagnostics for Rooftop Air Conditioners

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APPENDIX 2 RTD TEMPERATURE SENSOR MEASURING ISSUE
The experiment data collected by Breuker (1997), Chen (2000) and Harms (2002)
were measured using thermocouples, so the compressor energy analysis is balanced very
well. However, the field data energy analysis shows that there are over 50% heat losses
from the compressor, which is impossible from the heat transfer point of view. It was
found that the misleading result is caused by inaccurate discharge-line temperature
readings measured using RTDs. Figure A2-1 illustrates the RTD measuring scheme.
T
of
α
o
T
ow
α
i
δ
w
= d 2
− d 1 λ
T
if
T
iw
Figure A2-1 RTD measuring scheme
It is described in the literature that: “If the sensor is not insulated, the sensor’s
reading would be a weighted average of the tube wall and ambient air temperature”. In
addition, the temperature of the sensor is not geometrically distributed uniformly even if
the sensor is insulated properly, which is difficult to evaluate. Ideally, assume the
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