The following terms are commonly used in cooling tower science, many of which are unique to the
cooling tower industry:

Evaluation — A determination of the total cost of owning a cooling tower for a specific period of time. Includes first cost of tower and attendant devices, cost of operation, cost of maintenance and/or repair, cost of land use, cost of financing, etc., all normalized to a specific point in time.
Evaporation Loss — Water evaporated from the circulating water into the air stream in the cooling process. Units: % of circulating water rate or gpm.
Exhaust (Exit) Wet-Bulb Temperature — See "Leaving Wet-Bulb Temperature".
Fan Cylinder — Cylindrical or venturi-shaped structure in which a propeller fan operates. Sometimes referred to as a fan "stack" on larger towers.
Fan Deck — Surface enclosing the top structure of an induced draft cooling tower, exclusive of the distri-bution 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 Scroll — Convolute housing in which a centrifugal (blower) fan operates.
Fill — That portion of a cooling tower which constitutes its primary heat transfer surface. Sometimes referred to as "packing".
Fill Cube — (1) Counterflow: The amount of fill required in a volume one bay long by one bay wide by an air travel high. Unit: cu ft.
(2) Crossflow: The amount of fill required in a volume one bay long by an air travel wide by one story high. Unit: cu ft.
Fill Deck — One of a succession of horizontal layers of splash bars utilized in a splash-filled cooling tower. The number of fill decks constituting overall fill height, as well as the number of splash bars incorporated within each fill deck, establishes the effective primary heat transfer surface.
Fill Sheet — One of a succession of vertically-arranged, closely-spaced panels over which flowing water spreads to offer maximum surface exposure to the air in a film-filled cooling tower. Sheets may be flat, requiring spacers for consistent separation; or they may be formed into corrugated, chevron, and other patterns whose protrusions provide proper spacing, and whose convolutions provide increased heat-transfer capability.
Film-Filled — Descriptive of a cooling tower in which film-type fill is utilized for the primary heat-transfer surface.
Float Valve — A valve which is mechanically actuated by a float. Utilized on many cooling towers to control make-up water supply.
Flow-Control Valves — Manually controlled valves which are used to balance flow of incoming water to all sections of the tower.
Flume — A trough which may be either totally enclosed, or open at the top. Flumes are sometimes used in cooling towers for primary supply of water to various sections of the distribution system.
Fogging — A reference to the visibility and path of the effluent air stream after having exited the cooling tower. If visible and close to the ground, it is referred to as "fog". If elevated, it is normally called the "plume".

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.
Geareducer® — See "Speed Reducer".
Heat Load — Total heat to be removed from the circulating water by the cooling tower per unit time. Units: Btu per min. or Btu per hr.
Height — On cooling towers erected over a concrete basin, height is measured from the elevation of the basin curb. "Nominal" heights are usually measured to the fan deck elevation, not including the height of the fan cylinder. Heights for towers on which a wood, steel, or plastic basin is included within the manufacturer's scope of supply are generally mea-sured from the lowermost point of the basin, and are usually overall of the tower. Unit: ft.
Hot Water Temperature — Temperature of circulating water entering the cooling tower's distribution sys-tem. Unit: °F. Symbol: HW.
Hydrogen Ion Concentration — See "pH".
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.
Inlet Wet-Bulb Temperature — See "Entering Wet-Bulb Temperature".
Interference — The thermal contamination of a tower's inlet air by an external heat source, (i.e. the discharge plume of another cooling tower.)
Leaving Wet-Bulb Temperature — Wet-bulb temperature of the air discharged from a cooling tower. Unit: °F. Symbol: LWB.
Length — For crossflow towers, length is always per-pendicular to the direction of air flow through the fill (air travel), or from casing to casing. For counterflow towers, length is always parallel to the long dimension of a multi-cell tower, and parallel to the intended direction of cellular extension on single-cell towers. Unit: ft.
Liquid-to-Gas Ratio — A ratio of the total mass flows of water and dry air in a cooling tower. (See Total Air Rate & Total Water Rate) Unit: Ib per Ib. Symbol: L/G.
Longitudinal — Pertaining to occurrances in the direction of tower length.
Louvers — Blade or passage type assemblies installed at the air inlet face of a cooling tower to control water splashout and/or promote uniform air flow through the fill. In the case of film-type crossflow fill, they may be integrally molded to the fill sheets.
Make-Up — Water added to the circulating water system to replace water lost by evaporation, drift, windage, blowdown, and leakage. Units: % of circulating water rate or gpm.
Mechanical Draft — Refers to the movement of air through a cooling tower by means of a fan or other mechanical device.
Module — A preassembled portion or section of a cooling tower cell. On larger factory-assembled towers, two or more shipped modules may require joining to make a cell.
Natural Draft — Refers to the movement of air through a cooling tower purely by natural means. Typically, by the driving force of a density differential.
Net Effective Volume — That portion of the total struc-tural volume within which the circulating water is in intimate contact with the flowing air. Unit: cu ft.
Nozzle — A device used for controlled distribution of water in a cooling tower. Nozzles are designed to de-liver water in a spray pattern either by pressure or by gravity flow.

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