Verification of the universal thermodynamic model for cooling systems on two water chillers in the field
Date
2012-07-04
Authors
Leong, Ryan Patrick
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Abstract
An analysis and verification study was conducted into the Universal Thermodynamic Model for
cooling systems, which claims to accurately assess the performance of all refrigerating machines
from only a few, non-intrusive measurements. The model and its derivation were studied to
confirm its applicability to vapour-compression water chillers and its accuracy was practically
investigated via tests on two such chillers serving the air-conditioning system of an office
building. The two chillers used employ reciprocating and centrifugal compressors, respectively.
The experimental method entailed recording a number of measurements under normal, or faultfree,
conditions and, for each set of data, calculating the COP obtained directly from
measurement and that predicted by the model. Comparisons between the two values for each
data set were used as an indication of accuracy. The predicted COP for the reciprocating
machine was shown to be very accurate with a 2.97% maximum difference between COP values,
while that for the centrifugal chiller was even more precise, yielding a maximum difference of
1.14%.
An additional test was conducted on the centrifugal chiller that simulated an operational fault –
excessive fouling in its condenser – and the model showed the presence, though not the nature,
of this simulated fault. Comparisons between key constants and graphs obtained under normal
and throttled conditions allowed for some fault diagnosis. The predicted and measured COP
values under the faulty conditions were also calculated and shown to correspond within 2.45%.
The Universal Thermodynamic Model proved to be an accurate and reliable performance
assessment tool for the two chillers. In every case the difference between predicted and
measured COP was less than the experimental uncertainty of the latter. It was also shown that
the model could be used for limited fault diagnosis through simulation of a practical operation
defect and analysing certain parameters. Practical recommendations for similar future work are
provided based on experimental shortcomings of this study.