Figure 1 compares the efficiency of three (3) different chiller plant operating strategies at various loads, and illustrate the curve for an ideal variable speed plant. Note that the Hartman Loop Plant is more than twice as efficient as an Optimized Constant Speed Chiller Plant arrangement, at 50% of design capacity.
Figure 2 shows typical operating profiles for chiller plants in six (6) different climates. Most plants operate a majority of their time below 60% capacity.
These numbers come from meteorological data and building analysis. As an example, Los Angeles has hot summers and warm winters, but a typical chiller plant operates below 20% capacity 50% of the year. A plant designed to operate most efficiently at full load will be at peak efficiency less than 1% of the year!
The tall bars at the right simply demonstrate the annual chiller plant operation in each region. Honolulu, Taipei and LA operate year round, while Seoul and New York take time off throughout their cold winters.
Tropical climates will shift the plot such that a chiller plant operates around 60% chiller capacity 40% of the year. Temperate climates may show 80% to 100 % capacity is only reached 1% of the time. The key is this: while warmer climates have larger chiller loads than cooler climates, plants everywhere rarely operate at high capacity.