period one
Types of Water Chillers
notes
Part-Load Efficiency Rating
▲Integrated Part-Load Value (IPLV)
◆Weighted-average load curves
◆Based on an “average” single-chiller installation
◆Standard operating conditions
▲Non-Standard Part-Load Value (NPLV)
◆Weighted-average load curves
◆Based on an “average” single-chiller installation
◆Non-standard operating conditions
Figure 22
The IPLV predicts chiller efficiency at the ARI standard rating conditions, using weighted-average load curves that represent a broad range of geographic locations, building types, and operating-hour scenarios, both with and without an airside economizer. The NPLV uses the same methods to predict chiller efficiency at non-standard rating conditions. Although these weighted-average load curves 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 systems. Chillers in these systems exhibit different unloading characteristics than the IPLV weighted formula indicates. Appendix D of Standard 550/590–1998 explains this further:
The IPLV equations and procedure are intended to provide a single- number, part-load performance number for water-chilling products. The 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 the 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.
Here is the important part:
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.
