Signs Your Cooling Tower Needs Service

A cooling tower is easy to ignore. It sits on the roof or behind the building, it is loud and wet, and as long as the chillers are making cold water, nobody goes up to look at it. But the cooling tower is where a lot of chiller plant problems start. In South Florida, towers run nearly year round, pull in salt, dust and pollen, and stay warm enough to grow biology all twelve months.

Here are the signs that a commercial cooling tower needs service, and what they usually mean.

The chiller is working harder

The first sign is often not at the tower at all. It shows up at the chiller. Condenser water coming back from the tower is warmer than it should be, condenser pressure goes up, and the chiller draws more power to make the same amount of cooling.

Watch the tower approach, which is the difference between the cold water leaving the tower and the outdoor wet bulb temperature. If the approach is creeping up over weeks or months, the tower is losing capacity. Common causes are fouled or damaged fill, clogged distribution nozzles, poor airflow, or problems with the fan.

On the chiller side, a rising condenser approach temperature usually points to fouled condenser tubes, which is often a water treatment problem that started at the tower.

Scale on the fill or the basin

White or tan crusty deposits on the fill, the basin or the distribution deck are scale. Scale forms when minerals in the water concentrate as water evaporates. It insulates heat transfer surfaces and blocks the fill, which reduces cooling.

Scale usually means the water treatment is off. Either the chemistry is wrong, the bleed off is not working, or the cycles of concentration are too high. If you see scale at the tower, there is a good chance it is building up in the condenser tubes too.

Slime, algae or biofilm

Green algae on the deck, slimy surfaces, or brown or black biofilm in the basin are signs of biological growth. In our climate, sunlight and warm water make cooling towers ideal for it.

This is more than an efficiency problem. Biofilm can harbor Legionella bacteria, which cause Legionnaires' disease, and cooling towers have been linked to outbreaks. ASHRAE Standard 188 calls for building owners to have a water management program for systems like cooling towers, and the CDC publishes a toolkit to help develop one. If you see biological growth, call your water treatment vendor and your mechanical contractor promptly.

Excessive drift or water loss

Cooling towers lose water through evaporation, which is how they work, and through bleed off, which controls mineral buildup. They should not be throwing a lot of water out as mist or spray. If you see wet surfaces downwind of the tower, puddles on the roof, or a makeup water meter reading higher than usual, the drift eliminators may be damaged or out of place. Leaking basins, failed float valves or a stuck bleed valve can also waste a lot of water.

Drift matters for health reasons as well as water bills, because drift can carry bacteria off site.

Noise and vibration

Cooling tower fans and drives should run smoothly. New noises, such as grinding, squealing, knocking or rattling, often point to bearing problems, a failing gearbox, loose belts, or a fan blade out of balance. Vibration can loosen connections and crack structural members.

Most towers have a vibration switch that shuts down the fan if vibration gets too high. If yours is tripping, find out why. Do not just reset it.

Oil leaks at the gearbox

Gear driven towers have gearboxes that need correct oil level and quality. Oil on the deck or around the gearbox, or milky looking oil, means a seal is leaking or water is getting in. Gearboxes are expensive. Oil changes are not.

Corrosion and structural damage

Look at the casing, the basin, the structural supports and the hardware. Rust, white powdery corrosion on galvanized steel, cracked fiberglass and loose panels are warning signs. Salt air near the coast speeds up corrosion. Wind is the other threat. Broward and Miami Dade are in the High Velocity Hurricane Zone under the Florida Building Code, and a tower with weakened anchors or casing is a risk in a storm. After any hurricane, inspect the tower before restarting.

Uneven water distribution

Look down at the fill while the tower is running. Water should be spread evenly. Dry spots or channels mean the distribution nozzles or spray system is clogged or broken. Debris from trees and construction often ends up here.

Dirty basin and strainers

Sediment in the basin, leaves and trash, and clogged strainers reduce flow and feed biological growth. In South Florida, many towers need basin cleaning at least once or twice a year, and more often near construction or heavy vegetation.

Controls not working

Fan cycling, variable speed drives, basin heaters if you have them, and bleed controllers should all be working as designed. A fan stuck at full speed wastes energy. A fan that is not running wastes chiller capacity. A bleed controller that is not working leads straight to scale.

What regular service looks like

A sound program usually includes frequent checks of the water chemistry by the water treatment provider, regular inspection of the fan, drive and structure, cleaning of the basin and strainers, fill inspection, and annual or semiannual cleaning and disinfection as called for by the water management program. Record what you find. A cooling tower with a maintenance log is much easier to keep healthy than one that only gets attention when the chiller alarms.

When to call

If you are seeing any of these signs, especially rising approach temperatures or biological growth, do not wait for the chiller to trip. We service cooling towers and chiller plants across Broward, Miami Dade and Palm Beach. Read more about our chiller and cooling tower work, call 954.577.7923, or request service.