To measure the energy use and economic benefits of variable primary flow chilled-water systems, ARTI conducted a study that compared variable primary flow chilled-water system energy use with that of other common system types, including constant flow/primary-only chilled-water systems, constant primary flow/variable secondary flow chilled-water systems, and primary/secondary chilled-water systems with a check valve installed in the decoupler.

According to the ARTI study results, primary-only chilled-water systems reduced the total annual plant energy by 3 percent to 8 percent, first cost by 4 percent to 8 percent, and life-cycle cost by 3 percent to 5 percent relative to conventional constant primary flow/variable secondary flow chilled-water systems. The study also revealed that several factors significantly influenced energy savings and economic benefits of the variable primary flow system relative to other system alternatives. These included the number of chillers, climate, and chilled-water temperature differential.