Cooling Tower Efficiency

Maximum cooling tower efficiency is limited by the wet-bulb temperature of the cooling air

Cooling towers use the evaporative cooling principle to cool the circulated water, and

  • they can achieve water temperatures below the dry bulb temperature - tdb - of the cooling air
  • they are in general smaller and cheaper for the same cooling loads than other cooling systems

cooling tower

Cooling towers are rated in terms of approach and range, where

  • the approach is the difference in temperature between the cooled water temperature and the entering air wet bulb - twb - temperature
  • the range is the temperature difference between the water inlet and exit

Since a cooling tower is based on evaporative cooling the maximum cooling tower efficiency is limited by the wet bulb temperature - twb - of the cooling air.

Cooling Tower Efficiency

Cooling tower efficiency can be expressed as

μ = (ti - to) 100 / (ti - twb)    (1)


μ = cooling tower efficiency (%) - common range between 70 - 75%

ti = inlet temperature of water to the tower (oC, oF)

to = outlet temperature of water from the tower (oC, oF)

twb = wet bulb temperature of air (oC, oF)

The temperature difference between inlet and outlet water (ti - to) is normally in the range 10 - 15 oF.

The water consumption - the make up water - of a cooling tower is about 0.2-0.3 liter per minute and ton of refrigeration. Compared with the use and waste of city water the water consumption can be reduced with about 90 - 95%.

There are two main types of cooling towers

  • forced draught (using fans)
  • natural draught

Both types are based on evaporative cooling.

  • Natural draught cooling towers are more dependent on temperature gradients between air and water and the wind forces than forced draught cooling towers
  • The efficiency of natural draught towers are more variable over time and in general lower

Note! Be aware that medium temperature systems like cooling towers are known sources of Legionella! Good cleaning and maintenance of the systems are important to minimize the potential damage.

Related Topics

  • Air Psychrometrics - The study of moist and humid air - psychrometric charts, Mollier diagrams, air-condition temperatures and absolute and relative humidity and moisture content

Related Documents

Tag Search

  • en: cooling tower efficiency wet bulb air water
  • es: refrigeración eficiencia torre de agua del aire de bulbo húmedo
  • de: Kühlturm Effizienz Feuchtluft Wasser

Need some Expert Advice?

JustAnswer can help you! Talk with a verified expert until your satisfied, 100% money- back guarantee.

Search the Engineering ToolBox

- "Search is the most efficient way to navigate the Engineering ToolBox!"

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your SketchUp model with the Engineering ToolBox - SketchUp Extension/Plugin - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Translate the Engineering ToolBox!
About the Engineering ToolBox!