BMP #9 - Single-Pass Cooling Equipment

Background

Single-pass or once through cooling systems provide an opportunity for significant water savings. In these systems, water is circulated once through a piece of equipment and then is disposed down the drain. The types of equipment that typically use single-pass cooling include: CAT scanners, degreasers, hydraulic equipment, condensers, air compressors, welding machines, vacuum pumps, ice machines, x-ray equipment, and air conditioners. To remove the same heat load, single-pass systems use 40 times more water than a cooling tower operated at 5 cycles of concentration. To maximize water savings, single-pass cooling equipment should be either modified to recirculate water or if possible, should be eliminated altogether.

For more information on this and other FEMP Water Efficiency Best Management Practices, please see the resources section.

Operation and Maintenance Options

Provide proper insulation on piping, chiller, or storage tank.
Inventory cooling equipment and identify all single-pass cooling systems.
Check entering and leaving water temperatures and flow rates to ensure that they are within the manufacturer's recommendations. For maximum water savings, water flow rates should be near the minimum allowed by the manufacturer.
Keep coil loops clean to maximize heat exchange with the refrigerated enclosure.
Check operation of water control valve. Water control valves adjust the flow rate of water based on demand. Regular valve maintenance will ensure that water is used as efficiently as possible.

Retrofit Options

To maximize water savings, eliminate single pass cooling by modifying equipment to operate on a closed loop that recirculates the water instead of discharging it.
If modification of equipment to a closed loop system is not feasible, add an automatic control to shut off the entire system during unoccupied night or weekend hours. This option should only be considered where shutdown would have no adverse impact on indoor air quality.
Installation of a chiller or cooling tower is also an economical alternative. Excess cooling capacity may already exist within the building that can be utilized.
Find another use for the single-pass effluent, in boiler make-up supply or landscape irrigation, and implement. Note some equipment effluent may be contaminated such as degreasers and hydraulic equipment. This effluent must not be used in boilers.

Replacement Options

Replace water-cooled equipment with air-cooled equipment or best available energy/water-efficient technology.
Replace the once through cooling systems with a multi-pass cooling tower or closed loop system.
For specifics on this technology, consult with experts in the field. Your first resource should be your local or higher headquarters engineers, but do not overlook or rule out the benefits of input from experienced contractors or other Governmental agencies (DOE, FEMP, etc.).