Improving the process of certified and witnessed factory testing for chiller procurement

Currently, consulting engineers and/or design/build engineers involved in the process of performance-based chiller procurement perform four activities: (1) determine bid specifications, (2) identify a few different vendors and sales representatives of chiller manufacturers and request them to submit bids along with chiller performance maps in the form of tabular data, (3) select a particular chiller (or mix of chillers) from these bids, and (4) perform a certified and witnessed factory test on the performance of the selected chiller, which provides an insurance policy and a last chance to reject the equipment if the engineer deems that the chiller is not consistent with manufacturer's published performance data. Usually, the factory tests are performed based on ARI Standard 550/590 or on operating conditions that better reflect the actual load profile. This paper suggests a methodology to select the optimal set of test conditions that provide the most useful chiller performance data. It is shown that using the Gordon-Ng (GN) chiller model allows the engineer to accurately predict the complete chiller performance map with only four well-chosen operating points. This paper justifies both the choice of the GN model and the experimental design proposed using monitored data from two actual chiller data sets (one from a laboratory chiller, and the other from a field-operated chiller using about five months of data). The methodology suggested in this paper should be of great benefit to chiller professionals, and enhance the quality assurance process of the entire chiller procurement process.