ARTI Announces Final Report on the Benefits of Variable Primary Flow Chilled Water Systems

ARLINGTON, Va -- The Air-Conditioning and Refrigeration Technology Institute (ARTI) has released a final report on a research project entitled "Variable Primary Flow Chilled Water Systems: Potential Benefits and Application Issues." The final report can be downloaded from the ARTI Web site at

To measure the energy use and economic benefits of variable primary flow chilled water systems, ARTI conducted an extensive 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 to 8 percent, first cost by 4 to 8 percent, and life cycle cost by 3 to 5 percent relative to conventional constant primary flow/variable secondary flow chilled water systems. 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.

“In view of both the state-of-the-art review and parametric study results obtained in this project, it can be concluded that variable primary flow is a feasible and potentially beneficial approach to chilled water pumping system design,” according to the study. “However, the magnitude of energy and economic benefits varies considerably with the application and is obtained at the cost of more complex and possibly less stable system control. The literature on effective application of variable primary flow is growing and should promote its appropriate and effective use in the future.”

To download a copy of the final report, visit the ARTI Web site at or contact Steve Szymurski, ARI’s director of Research, at [email protected].

The ARTI 21st Century Research (21CR) program is a not-for-profit research consortium of the HVACR industry. Management support and co-funding of the program is provided by Air-Conditioning and Refrigeration Institute. Other associations providing industry co-funding include the Copper Development Association; the Heating, Refrigeration and Air-Conditioning Institute of Canada; and the Refrigeration Service Engineers Society. The New York Energy Research and Development Authority and the California Energy Commission have provided state funding and the U.S. Department of Energy’s Office of Building Technology is providing federal funding through cooperative agreement number DE-FC05-99OR22674.

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