Verifying site performance of water chilling machines by refrigerant-circuit measurements

The well-known overall energy balance method is widely used to verify the apparent performance of water chilling machines on site. In harsh environments where the water circuits are liable to contamination, though, the uncertain accuracy of water flow meters renders this method unreliable. Apparent performance should then be verified by confirming measurements in the refrigerant circuit, because this is closed and less liable to contamination. A rigorous method of doing this, accounting for the complexities of large machines, is described. A graphical acceptability plot lucidly depicts the degree of accuracy of the apparent performance. This method has two advantages over merely computing the heat imbalance. It indicates whether a small such imbalance is concealing large but similar errors in the apparent constituents of the heat balance. It also identifies the erroneous such constituents responsible for a large or small heat imbalance. A case study illustrates the method.