Filter
Top Products
TRG-TRC010-EN 47
period five
Application Considerations
notes
given system—they simply define a common rating point to aid comparisons.
Trends toward improved humidity control and energy efficiency have changed
some of the actual conditions selected for specific applications.
Impurities in the chilled- and condenser-water systems eventually deposit on
evaporator and condenser tube surfaces, impeding heat transfer. Catalogued
performance data includes a fouling factor that accounts for this effect to more
closely predict actual chiller performance.
ARI’s part-load efficiency rating system establishes a single, blended estimate
of stand-alone chiller performance. The Integrated Part Load Value (IPLV)
predicts chiller efficiency at the ARI standard rating conditions using weighted
averages representing a broad range of geographic locations, building types,
and operating-hour scenarios, both with and without an air-side economizer.
While the weighted averages place greater emphasis on the part-load operation
of an average, single-chiller installation, they will not—by definition—represent
any particular installation.
Additionally, ARI notes that more than 80 percent of all chillers are installed in
multiple-chiller plants. Chillers in these plants exhibit different unloading
characteristics than the IPLV weighted formula indicates. Appendix D of the
Standard explains this further:
...The [IPLV] equation was derived to provide a representation of the
average part-load efficiency for a single chiller only. However, it is best
to use a comprehensive analysis that reflects actual weather data,
building load characteristics, operational hours, economizer
capabilities, and energy drawn by auxiliaries such as pumps and
cooling towers, when calculating the chiller and system efficiency. This
becomes increasingly important with multiple chiller systems because
individual chillers operating within multiple chiller systems are more
heavily loaded than single chillers within single chiller systems.
Remember that the ARI rating is a standardized representation. Many chillers
do not run at standard rating conditions and few are applied in single-chiller
installations. Performing a comprehensive energy analysis is the best method
of comparing the system operating cost difference between 2 chillers.
trgtrc010_book.book Page 47 Wednesday, September 1, 1999 10:42 AM