There is a simple formula to measure the tonnage (capacity) of a chiller. One ton is equivalent to 12,000 btu/h, and a btu/h (water) = 500 x (T in - T out) x flow (gpm).
We can measure the temperature in and out of the chiller and the flow rate through it so we can calculate the tonnage. If this is recorded over time and adjusted for outdoor conditions, the values can be plotted to give the chiller operator/engineer a profile of the load and estimated efficiency.
At the same time if we measure the energy going into the compressor we can
produce a curve "in the field" of the efficiency of the chilled water
system at varying loads.
