Cooling Tower Glossary
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Cooling Tower Glossary

Cooling Tower Glossary
Common Terms Associated with Cooling Towers


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. Each cell may have one or more fans and one or more distribution systems

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

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 baggles or labyrinths passages through which the air passes prior to its exit from the tower, for the purpose of removing entrained water droplets from the exhaust air

Evaporation Loss:Water evaporated from the circulating water into the air stream in the cooling process. Units: % of circulating water rate or GPM

Fan Deck: Surface enclosing the middle structure of an induced draft cooling tower, exclusive of the distribution basins on a crossflow tower

Fan Pitch: The angle which the blades of a propeller fan make with the plane of rotation, measured at a prescribed point on each blade. Unit: Degrees 

Fan Stack: An extended fan cylinder whose primary purpose is to achieve elevation of the discharge plume.

Fill: The portion of the cooling tower which constitutes its primary heat transfer surface. Sometimes referred to as "packing".

Float Valve: A valve which is mechanically actuated by a float.  Utilized on many cooling towers to control make-up water suppy.

Forced Draft: Refers to the movement of air under pressure through a cooling tower. Fans of forced draft towers are located at the air inlets to "force" air through the tower 

Heat Load- Total heat to be removed from the circulating water by cooling tower per unit time. Units: BTU/min or BTU/hr

Hot Water Temperature (HWT):Temperature of circulating water entering the cooling towers distribution system. Unit: F Symbol: HW

Induced Draft: Refers to the movement of air through a cooling tower by means of an induced partial vacuum. Fans of induced draft towers are located at the air discharges to "draw" air through the tower

Louvers: Blade or passage type assemblies installed at the air inlet face of a cooling tower to control water splash out  and/or promote uniform air flow through the fill.  

Make-Up: Water added to the circulating water system to replace water lost by evaporation, drift, windage, blowdown, and leakage. Unit: % of circulating water rate or GPM 

Plume: The effluent mixture of heated air and water vapor (usually visible) discharged from a cooling tower. 

Tower Pumping Head (TDH): The static lift from the elevation of the basin curb to the center line elevation of the distribution system inlet plus the total pressure (converted to ft of water) necessary at that point to effect proper distribution of the water to its point of contact with the air. Unit: Ft of water

Wet Bulb Temperature: The temperature of the entering or ambient air adjacent to the cooling tower as measured with a wet bulb thermometer. 

Wind Load: The load imposed upon a structure by a wind blowing against surface.