Cooling Tower Glossary: Essential Terms and Definitions

A–C

Ambient Wet Bulb Temperature (AWB)

The wet bulb temperature of the air encompassing cooling tower not including any temperature contribution by the tower itself. Generally measured upwind of a tower in a number of locations sufficient to account for all extraneous sources of heat.

Approach

The temperature difference between the cold water temperature and either the ambient or entering wet bulb temperature (LWT-WBT = Approach)

Blowdown or Bleed

Water discharged from the system to control concentrations of salts or other impurities in the circulating water.

BTU (British Thermal Unit)

The amount of heat gain (or loss) required to raise (or lower) the temperature of one pound of water one degree Fahrenheit.

Capacity

The amount of water (GPM) that a cooling tower will cool through a specified range, at a specified approach and wet bulb temperature.

Cell

Smallest tower subdivision which can function as an independent unit with regard to air and water flow; it is bounded by either exterior walls or partition walls.

Cold Water Temperature (CWT)

Temperature of the water leaving the collection basin, exclusive of any temperature effects incurred by addition to make up and/or the removal of blowdown.

Counterflow

Air flow direction through the fill is counter current to that of the falling water.

Crossflow

Air flow direction through the fill is essentially perpendicular to that of the falling water.

D–F

Delta T

Difference between the hot water temperature and the cold water temperature (HWT-CWT = Range).

Drift

Circulating water lost from the tower as liquid droplets entrained in the exhaust stream.

Drift Eliminators

An assembly of baffles or labyrinth passages through which the air passes prior to exit, removing entrained water droplets.

Evaporation Loss

Water evaporated from the circulating water into the air stream in the cooling process.

Fan Deck

Surface enclosing the middle structure of an induced draft cooling tower.

Fan Pitch

The angle which the blades of a propeller fan make with the plane of rotation.

Fan Stack

An extended fan cylinder whose primary purpose is to elevate the discharge plume.

Fill

The portion of the cooling tower which constitutes its primary heat transfer surface.

Float Valve

A valve mechanically actuated by a float to control make-up water supply.

Forced Draft

Movement of air under pressure through a cooling tower.

G–L

Heat Load

Total heat to be removed from the circulating water per unit time.

Hot Water Temperature (HWT)

Temperature of circulating water entering the cooling tower distribution system.

Induced Draft

Movement of air through a cooling tower by means of an induced partial vacuum.

Louvers

Blade or passage type assemblies installed at the air inlet face to control splash-out and airflow.

M–P

Make-Up

Water added to replace water lost by evaporation, drift, windage, blowdown, and leakage.

Plume

The visible mixture of heated air and water vapor discharged from a cooling tower.

T–W

Tower Pumping Head (TDH)

The static lift plus total pressure needed for proper water distribution.

Wet Bulb Temperature

The temperature of the entering or ambient air measured with a wet bulb thermometer.

Wind Load

The load imposed upon a structure by wind blowing against it.