These photos came off our preventive maintenance rounds this summer — two different cooling towers serving commercial buildings in south Louisiana. Each pair below shows a basin the way we found it, and the same basin a few hours later, after a clean-out. Nothing exotic happened in between: isolate, drain, muck out, scrape, disinfect, rinse, service the strainer, verify the float, refill. This is what cooling tower maintenance actually looks like — and it is the single most neglected line item on the commercial HVAC equipment list.
BEFORE
AFTERWhere all that sludge comes from
A cooling tower is an air scrubber whether you want it to be or not. It pulls thousands of cubic feet of outside air per minute through falling water, and everything riding in that air — dust, pollen, leaves, insects, construction grit, exhaust soot — gets washed out and settles in the basin. Add Louisiana sun, ninety-degree water, and a long cooling season, and algae grows on every wet surface the light touches. The result is the first photo: a biological mud layer coating the basin floor, the suction strainer, and the makeup float.
Water treatment slows this down. It does not stop it, and it removes nothing that has already settled. Chemical treatment without periodic physical cleaning is how towers end up looking like our before photos while the treatment invoices keep getting paid.
What it costs to run a tower like this
Chiller efficiency. Fouling insulates. A dirty tower cannot reject heat at design conditions, so condenser water returns to the chiller warmer than it should. As a rule of thumb, every degree of unnecessary condenser water temperature costs roughly one to two percent in chiller energy — on a large chiller running a Louisiana cooling season, that is real money every month.
Starved pumps and clogged strainers. The sludge that does not stay put migrates to the suction strainer, and a choked strainer cavitates the condenser water pump. That is a mechanical failure caused by a housekeeping problem.
Makeup water control. Look at the float valve in the photos. A float buried in sludge sticks. Stuck low, the valve runs constantly and dumps treated water down the overflow. Stuck high, the basin runs shallow and the pump pulls air. Either way, your water and chemical bills climb and your tower level control stops meaning anything.
Bacteria — including Legionella. A warm, stagnant nutrient bed is exactly the environment Legionella and other bacteria want. Basin hygiene is a core element of any water management program built to ASHRAE Standard 188, and it is the part that no chemical feed can substitute for.
Corrosion under the deposits. Sludge holds moisture and depleted chemistry against the metal, and under-deposit corrosion quietly eats basins, sumps, and hardware years ahead of schedule.
BEFORE
AFTERWhy keeping towers clean matters
Everything in the section above runs in reverse, too. A tower that gets regular physical cleaning gives you:
- Full-rated heat rejection. Condenser water comes back at design temperature, so the chiller runs at its rated efficiency instead of fighting a fouled tower through every Louisiana afternoon.
- Capacity when you need it most. A clean tower is often the difference between riding out a 98-degree week and losing a chiller to a high head pressure trip at 2 PM in August.
- Longer equipment life. Clean basins do not corrode under deposits, clean strainers do not cavitate pumps, and a free-moving float does not flood or starve the basin.
- Lower water and chemical spend. Treatment chemistry works the way it was dosed to work, and the makeup valve is not quietly sending treated water down the overflow.
- A defensible water management program. Basin hygiene is a core control in any Legionella risk plan built to ASHRAE Standard 188 — and it is the first thing an auditor, health department, or insurer asks about after an incident.
None of that requires anything sophisticated. It requires the basin actually being cleaned, on a schedule, by someone who looks at the whole system while they are in there.
What a real clean-out includes
- Isolate and drain the tower, with lockout on the fan and pumps before anyone reaches into the basin.
- Physically remove the sludge — vacuum and scrape, not just a rinse. If it settled, it gets lifted out.
- Disinfect and rinse all wetted basin surfaces.
- Pull and clean the suction strainer, and inspect fill media and drift eliminators for scale, algae, and collapse.
- Free, stroke, and verify the makeup float valve, then confirm shutoff and basin operating level.
- Refill and rebalance with the water treatment program — biocide and inhibitor levels restored before the tower returns to service.
How often this should happen
ASHRAE Standard 180 — the standard practice for commercial HVAC inspection and maintenance — puts cooling tower inspection on a regular calendar, and in the Gulf South the practical answer is a full clean-out at least twice a year, typically at the start and end of the cooling season, with visual checks monthly while the tower is running hard. Towers near construction, agriculture, or heavy tree cover need more. If nobody can remember the last time your basin was drained, the photos above are a fair preview of what is in it.
Where your controls fit in
This is the part most maintenance plans miss: your building automation system can see a fouling tower long before anyone climbs up to look. Condenser water supply temperature trending away from setpoint on the same weather, basin level alarms, conductivity creeping outside the blowdown band, fan runtime climbing — each one is an early warning that heat rejection is degrading. We configure those points and alarms as part of tower service, so the BAS tells you when the tower needs attention instead of the chiller telling you with a high-head trip in August.
Cooling tower service is part of our preventive maintenance contracts — scheduled clean-outs, strainer and float service, fill inspection, and the BAS-side monitoring to catch problems between visits. One contractor, both sides of the system.