Sizing a Used Cooling Tower: Crossflow vs Counterflow

A cooling tower is the most forgiving major piece of a water-cooled plant to buy used, because there is no compressor or sealed refrigerant circuit to fail. But two buyers looking at the same nominal tonnage can end up with very different machines, because tower capacity depends on your design conditions, and airflow geometry changes how the tower lives on your site. Here is how to size a used tower correctly and how to choose between crossflow and counterflow.

Nominal tons are a starting point, not an answer

A tower rated at 500 nominal tons is not guaranteed to reject your 500 tons of heat. Nominal ratings assume a standard set of conditions: a specific flow rate, a specific range, and a specific wet-bulb temperature. Florida breaks the standard assumption on the last one, because our design wet-bulb runs higher than most of the country. A tower selected for a cooler climate loses real capacity in a Central Florida July.

To size honestly, you need three numbers from your plant:

• Flow rate in gallons per minute the tower must handle, set by your chiller's condenser.
• Range, the difference between the hot water coming in and the cold water leaving, usually around 10 degrees on comfort cooling.
• Approach, how close the cold water gets to the ambient wet-bulb. A tighter approach needs a bigger tower.

Match those to Florida's design wet-bulb, not the tower's rating-plate assumption, and you get a tower that actually keeps up when it is hot and humid and the plant is running flat out.

Crossflow towers

In a crossflow tower, air moves horizontally across the fill while water falls vertically through it. The hot water sits in an open distribution basin on top and gravity-feeds down, which means the water distribution runs at very low pressure.

The practical upsides: crossflow towers use gravity distribution, so pump head is lower and you spend less on pumping energy over the life of the plant. The open hot-water basins are easy to see into and clean, and the fill is generally accessible for inspection and replacement. Marley and SPX built enormous numbers of induced-draft crossflow towers, so parts and rebuild kits are everywhere on the used market.

The tradeoffs: crossflow units tend to have a larger footprint for the same capacity, and the open distribution basins are exposed to sunlight, which encourages algae in the Florida climate unless you keep up with treatment.

Counterflow towers

In a counterflow tower, air moves straight up against the water falling down. Water is distributed through a closed, pressurized spray system rather than an open gravity basin.

The upsides: counterflow towers are more compact for a given capacity, which matters on a tight roof or pad, and the closed pressurized distribution is less exposed to sunlight, so algae growth is easier to control. Thermal performance per square foot of footprint is strong.

The tradeoffs: the pressurized spray system needs more pump head, so pumping energy over the plant's life runs higher. The spray nozzles can clog and are harder to inspect than an open crossflow basin, so water treatment discipline matters more.

Which one to buy used

For most Florida buyers, footprint and pumping cost drive the decision. If you have roof or pad space and want the lowest long-term pumping bill and the easiest cleaning, a used crossflow tower is the practical pick, and the supply is deep. If space is tight or you want the most capacity in the smallest package and you will keep up with nozzle maintenance, a counterflow unit earns its place. Either way, favor corrosion-resistant construction for coastal service, and stick to BAC, Marley or SPX, or Evapco so fill, drift eliminators, and mechanical parts stay easy to source.

Inspect before you commit

Whichever geometry you choose, the inspection is the same discipline: check the basin and cold-water pan for rust-through, check the fill for scale and sagging, confirm the drift eliminators are present, and megger the fan motor while checking the gearbox or belt drive. A rotted basin is a full replacement, not a repair, and on a large tower a fresh fill pack runs into the thousands, so price those in.

Bottom line

Size the tower to your real flow, range, and approach against Florida's design wet-bulb, not the nameplate's standard assumptions. Choose crossflow for lower pumping cost and easy cleaning when you have the footprint, counterflow when space is tight and you will keep the nozzles clean. Then inspect the basin, fill, and fan drive hard before you buy.

We recover and test towers off decommissioned plants across Florida from our Auburndale yard and ship statewide. Tell us your flow and tonnage and we will match a unit. Browse used cooling towers for sale, see what we buy and recover, or call (689) 323-4676. To balance the whole loop, read our guide on matching a used cooling tower to a chiller.