When a plant needs to shed large amounts of heat, blowing air over a radiator only goes so far. Evaporating a little water is far more effective, and that is what a cooling tower does. This guide explains what a cooling tower is, how evaporative heat rejection works, the difference between open and closed circuit towers, why drift, blowdown, and water treatment matter, and where cooling towers fit in oil and gas facilities.
Cooling Tower in one line: A cooling tower is a heat-rejection device that cools warm water by evaporating a small fraction of it into an upward stream of air. Warm water from a plant's condensers or process is distributed over a fill that spreads it into a thin film or droplets; air moving through the fill evaporates part of the water, and the heat that evaporation carries away cools the rest. The cooled water collects in a basin and returns to the plant, and this evaporative cooling rejects far more heat per unit of airflow than dry cooling.
The physics is evaporative cooling: turning liquid water to vapor absorbs a large amount of latent heat, and that heat comes from the surrounding water, cooling it. In the tower, warm water is sprayed or distributed over a fill (packing) that greatly increases the water surface area exposed to air. Fans move air through the fill - drawn in the top (induced draft) or blown in the bottom (forced draft) - so the passing air carries away moisture and heat. Because it uses evaporation, a cooling tower can cool water below the surrounding air's dry-bulb temperature, toward the wet-bulb temperature.
The cooled water drops into a collection basin and is pumped back to the loads. Cooling towers are the heat-rejection stage for water-cooled chillers and for many process cooling duties - the condenser-water loop carries heat from the chillers or process to the tower, where it is finally dumped to atmosphere.
In an open-circuit tower, the process or condenser water is exposed directly to the air as it cascades over the fill. This is simple and efficient but means the circulating water picks up airborne dust and is subject to evaporation. In a closed-circuit (fluid cooler) tower, the process fluid stays inside a coil while spray water and air cool the coil from outside - keeping the process water clean and sealed, at the cost of some efficiency and higher price.
Because water constantly evaporates, a tower loses pure water and concentrates dissolved minerals in what remains. Operators add makeup water and periodically bleed off concentrated water (blowdown) to keep mineral concentration in check, and dose treatment chemicals to control scale, corrosion, and biological growth - notably Legionella. A small amount of water also escapes as fine droplets (drift), which drift eliminators minimize. Managing makeup, blowdown, and water chemistry is a core part of running a tower.
Gas plants, refineries, terminals, and processing facilities use cooling towers to reject heat from process cooling loops and from water-cooled chiller plants that serve building and control-room cooling. The tower is often a shared utility that many systems depend on, so its performance - the temperature it can deliver and its reliability - affects both process and facility cooling.
A cooling tower's instruments report basin and supply water temperature, fan status, water level, makeup and blowdown flow, and conductivity used to trigger blowdown, typically through the plant controls or a building automation system. A cloud SCADA such as Merobix can read those points over protocols such as Modbus or BACnet, so operators can watch tower performance, water chemistry indicators, and fan or level alarms from anywhere rather than only at the tower.
It relies on evaporative cooling. Warm water is spread over a fill to expose a large surface to moving air, and evaporating a small fraction of the water absorbs a large amount of latent heat from the rest, cooling it. Because it uses evaporation rather than just blowing air over a dry surface, a cooling tower can cool water below the air's dry-bulb temperature, toward the wet-bulb temperature.
In an open-circuit tower the circulating water is exposed directly to the air as it flows over the fill - simple and efficient, but the water picks up dust and evaporates. In a closed-circuit (fluid cooler) tower the process fluid stays sealed inside a coil while external spray water and air cool the coil, keeping the process water clean at the cost of some efficiency and higher cost.
Makeup is fresh water added to replace what the tower loses. Evaporation removes pure water and concentrates dissolved minerals, so operators periodically bleed off concentrated water - blowdown - to keep mineral levels in check. Drift is the small amount of water that escapes as fine droplets in the exhaust air; drift eliminators reduce it. Managing makeup, blowdown, and water chemistry keeps the tower efficient and controls scale, corrosion, and biological growth.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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