WaterSense at Work: Best Management Practices for Commercial and Institutional Facilities
Single-pass or once-through cooling systems use water to remove heat and cool
equipment components. After water is passed once through a coil within or casing
around a piece of equipment, the water is discharged to the sewer. Types of equip-
ment that use single-pass cooling include:
Point-of-use chillers or other refrigeration systems
Vacuum pumps, X-ray equipment, ice machines, and wok stoves use water for pro-
cesses in addition to the water used for single-pass cooling. Such equipment and its
associated water use, apart from single-pass cooling, are discussed in other sections
WaterSense at Work
Eliminating single-pass cooling offers a significant opportunity for water savings.
Single-pass systems use approximately 40 times more water to remove the same
heat load than a cooling tower operating at five cycles of concentration.
of equipment cooled with single-pass water can be replaced with air-cooled systems.
For equipment that requires cooling with water, installing an air-cooled, point-of-
use chiller or converting to a recirculating water system that makes use of a process
water chiller and/or a cooling tower will eliminate single-pass cooling.
The International Association of Plumbing and Mechanical Officials
Plumbing & Mechanical Code Supplement
which establishes requirements for green
building and water efficiency applicable to plumbing, prohibits the use of single-
pass cooling. The American Society of Heating, Refrigerating, and Air Conditioning
Standard for the Design of High-Performance, Green Buildings
Except Low-Rise Residential Buildings
ASHRAE Standard 189.1) also prohibits the use
of single-pass cooling.
U.S. Environmental Protection Agency and U.S. Energy Department, Energy Efficiency & Renewable Energy, Federal Energy Management Program. May 2005.
Laboratories for the 21st Century: Best Practices, Water Efficiency Guide for Laboratories