Sizing & Selection
Cooling Tower Side-Stream Filtration: When It Makes Sense and How to Size It
Learn how side-stream filtration removes suspended solids from cooling tower water, reduces fouling, and supports more reliable cooling system operation.
Cooling tower side-stream filtration continuously filters a portion of the recirculating water instead of treating the full condenser-water flow at once. That smaller side stream removes suspended solids over time, helping reduce sediment buildup, fouling, and maintenance without requiring a full-flow filter sized for the entire recirculation rate.[1][2]
Cooling towers are unusually exposed pieces of equipment. They pull large volumes of air through water, which means dust, organic material, airborne debris, corrosion products, scale particles, and biological solids can all become part of the circulating water. Filtration does not replace chemical treatment or a water management program, but it can reduce the suspended solids that make fouling and maintenance worse.[3][4]
When Side-Stream Filtration Is a Good Fit
- The tower basin accumulates sediment between scheduled cleanings
- Heat exchangers or strainers show recurring fouling from suspended solids
- The system runs continuously and cannot be interrupted often for manual cleaning
- Water-quality swings create periodic solids loading from wind, dust, construction, or seasonal conditions
- The owner wants to reduce basin cleaning frequency, cartridge use, or unplanned maintenance
Sizing should start with the actual cooling system problem. A side-stream filter for basin sediment control may not need the same flow fraction or micron rating as a filter intended to protect tight heat exchanger passages. Particle size distribution and total suspended solids testing are useful because they replace guesswork with a clearer picture of what the filter must remove.[5][6]
- Decision point
- Side-stream flow rate
- Engineering note
- Higher side-stream flow turns over the basin faster but increases filter size and flush demand
- Decision point
- Filter type
- Engineering note
- Automatic screen, media, disc, and separator technologies solve different solids problems
- Decision point
- Micron rating
- Engineering note
- Fine filtration is not always better if it causes frequent cleaning or pressure loss
- Decision point
- Maintenance access
- Engineering note
- Cooling towers need filters that can be inspected and serviced without disrupting operations
| Decision point | Engineering note |
|---|---|
| Side-stream flow rate | Higher side-stream flow turns over the basin faster but increases filter size and flush demand |
| Filter type | Automatic screen, media, disc, and separator technologies solve different solids problems |
| Micron rating | Fine filtration is not always better if it causes frequent cleaning or pressure loss |
| Maintenance access | Cooling towers need filters that can be inspected and serviced without disrupting operations |
References
- DOE FEMP, Side Stream Filtration for Cooling Towers: https://www.energy.gov/cmei/femp/water-efficient-technology-opportunity-side-stream-filtration-cooling-towers
- GSA, AWT for Cooling Towers Guidance: https://origin-www.gsa.gov/governmentwide-initiatives/federal-highperformance-buildings/highperformance-building-clearinghouse/emerging-technology-evaluations/water/awt-for-cooling-towers-guidance
- CDC, Controlling Legionella in Cooling Towers: https://www.cdc.gov/control-legionella/php/toolkit/cooling-towers-module.html
- ASHRAE Handbook, Cooling Towers: https://handbook.ashrae.org/Handbooks/S20/IP/s20_ch40/s20_ch40_ip.aspx
- U.S. EPA, Total Solids: https://archive.epa.gov/water/archive/web/html/vms58.html
- U.S. Geological Survey, Turbidity and Water: https://www.usgs.gov/water-science-school/science/turbidity-and-water