Acfm —
The actual volumetric flow rate of air-vapor mixture.
Unit: cu ft per min.
Aerosol - A
suspension in gaseous medium of solid particles, liquid
particle or solid and liquid particles having negligible
falling velocity
Air
Horsepower — The power output developed by a fan in
moving a given air rate against a given resistance.
Unit: hp. Symbol: ahp.
Air
Inlet — Opening in a cooling tower through which air
enters. Sometimes referred to as the louvered face on
induced draft towers.
Air
Rate — Mass flow of dry air per square foot of
cross-sectional area in the tower's heat transfer region
per hour. Unit: Ib per sq ft per hr. Symbol: G'. (See
Total Air Rate).
Air
Travel — Distance which air travels in its passage
through the fill. Measured vertically on counter flow
towers and horizontally on cross flow towers. Unit: ft.
Air
Velocity — Velocity of air-vapor mixture through a
specific region of the tower (i.e. the fan). Unit: ft
per min. Symbol: V.
Algae
— Small, usually aquatic plants which require light
to grow
Ambient Wet-Bulb Temperature — The wet-bulb
temperature of the air encompassing a 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. Unit: °F. Symbol: AWB.
Approach — Difference between the cold water
temperature and either the ambient or entering wet-bulb
temperature. Unit: °F.
Atmospheric — Refers to the movement of air through
a cooling tower purely by natural means, or by the
aspirating effect of water flow.
Automatic Variable-Pitch Fan — A propeller type fan
whose hub incorporates a mechanism which enables the fan
blades to be re-pitched simultaneously and
automatically. They are used on cooling towers and
air-cooled heat exchangers to trim capacity and/or
conserve energy.
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B
Basin
— See "Collection Basin" and "Distribution Basin".
Basin
Curb — Top level of the cold water basin retaining
wall; usually the datum from which pumping head and
various elevations of the tower are measured.
Bay —
The area between adjacent transverse and longitudinal
framing bents.
Bent —
A transverse or longitudinal line of structural
framework composed of columns, girts, ties, and diagonal
bracing members.
Biocide — A chemical capable of killing living
microorganisms.
Biofilm — A secretion of microorganisms clinging to
pipe surfaces
Bleed
— Water deliberately removed from a cooling system
to control the concentration factor of dissolved solids
Bleed-Off — See "Slowdown".
Blowdown — Water removed from a cooling tower to
prevent excessive buildup of impurities within the
system. Impurities increase in concentration as water
evaporates during the cooling cycle.
Blower
— A squirrel-cage (centrifugal) type fan; usually
applied for operation at higher-than-normal static
pressures.
Blowout — See "Windage".
Brake
Horsepower — The actual power output of a motor,
turbine, or engine. Unit: hp. Symbol: bhp.
Bromine — An element found in liquid form at room
temperature added to water to kill microorganisms.
Corrosive to human tissue and toxic to inhale in vapor
form. The element is broken down by sunlight.
Btu
(British Thermal Unit) — The amount of heat gain (or
loss) required to raise (or lower) the temperature of
one pound of water 1°F.
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C
Capacity — The amount of water (gpm) that a cooling
tower will cool through a specified range, at a
specified approach and wet-bulb temperature. Unit: gpm
Casing
— Exterior enclosing wall of a tower, exclusive of
the louvers.
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.
Chiller — A machine that removes heat from a liquid
via a vapor-compression or absorption refrigeration
cycle. Usually water is passed through a chiller, but
this water may also contain ~20% glycol and corrosion
inhibitors; other fluids such as thin oils can be
chilled as well. A typical chiller for air conditioning
applications is rated between 15 to 1500 tons (180,000
to 18,000,000 BTU/h or 53 to 5,300 kW) in cooling
capacity
Chimney — See "Shell".
Circulating Water Rate — Quantity of hot
water entering the cooling tower. Unit: gpm.
Cold
Water Temperature — Temperature of the water leaving
the collection basin, exclusive of any temperature
effects incurred by the addition of make-up and/or the
removal of blowdown. Unit: °F. Symbol: CW.
Collection Basin — Vessel below and integral with
the tower where water is transiently collected and
directed to the sump or pump suction line.
Conductivity — conductivity is the ability of a
material to carry electrical current. In water, it is
generally used as a measure of the mineral or other
ionic concentration. Conductivity is a measure of the
purity of water or the concentration of ionized
chemicals in water. However, conductivity is only a
quantitative measurement: it responds to all ionic
content and cannot distinguish particular conductive
materials in the presence of others. Only ionizable
materials will contribute to conductivity; materials
such as sugars or oils are not conductive.
Corrosion Inhibitors — Chemicals designed to prevent
or slow down the waterside corrosion of metals
Counterflow — Air flow direction through the fill is
countercurrent to that of the falling water.
Crossflow — Air flow direction through the fill is
essentially perpendicular to that of the falling water.
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D
Deadleg — A length of pipe, normally closed at one
end, or ending at a fitting
Disinfection -— Reduction of population of
micro-organisms using chemical or physical means.
Dispersant — A chemical usually added with other
treatment chemicals to loosen organic material adhering
to surfaces and prevent accumulation of sludge.
Distribution Basin — Shallow pan-type elevated basin
used to distribute hot water over the tower fill by
means of orifices in the basin floor. Application is
normally limited to crossflow towers.
Distribution System — Those parts of a tower,
beginning with the inlet connection, which distribute
the hot circulating water within the tower to the points
where it contacts the air for effective cooling. May
include headers, laterals, branch arms, nozzles,
distribution basins, and flow-regulating devices.
Double-Flow — A crossflow cooling tower where two
opposed fill banks are served by a common air plenum.
Drift
— Circulating water lost from the tower as liquid
droplets entrained in the exhaust air stream. Units: %
of circulating water rate or gpm. (For more precise
work, an UG parameter is used, and drift becomes pounds
of water per million pounds of exhaust air. Unit: ppm.)
Drift
Eliminators — An assembly of baffles or labyrinth
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.
Driver
— Primary drive for the fan drive assembly. Although
electric motors predominate, it may also be a gas
engine, steam turbine, hydraulic motor or other power
source.
Dry-Bulb Temperature — The temperature of the
entering or ambient air adjacent to the cooling tower as
measured with a dry-bulb thermometer. Unit: °F. Symbol:
DB.
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E
Entering Wet-Bulb Temperature — The wet-bulb
temperature of the air actually entering the tower,
in-eluding any effects of recirculation. In testing, the
average of multiple readings taken at the air inlets to
establish a true entering wet-bulb temperature. Unit °F.
Symbol: EWB.
Entrainment — Water in the air being brought into
the cooling plumes as the liquid wastes are discharged
Exhaust Air — The air removed from the cooling tower
during the cooling process. Exhaust air also contains
water vapor that has evaporated during the cooling
process.
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".
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F
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
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
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.
Filtration — the process of separating solids from a
liquid by means of a filter media through which
only the liquid passes.
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.
Fouling — Organic growth or other deposits on heat
transfer surfaces causing loss of efficiency.
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H
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.
Head
Pressure — "Head"
may be simply defined as any resistance to the flow of a
pump. When pump manufacturers list the head pressure,
they are referring to the vertical discharge pressure
head. Described in very simple terms, a pump's vertical
discharge "pressure-head" is the vertical lift in height
(usually measured in feet of water) at which a pump can
no longer exert enough pressure to move water.
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 measured 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 system. Unit:
°F. Symbol: HW.
Hydrogen Ion Concentration — See "pH".
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I
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.)
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L
Leaving Wet-Bulb Temperature — Wet-bulb temperature
of the air discharged from a cooling tower. Unit: °F.
Symbol: LWB.
Legionella — A genus of bacterium which is
ubiquitous in aqueous environments and found in water
systems in the built environment, including cooling
systems that are not properly maintained. It comprises
numerous species.
Length
— For crossflow towers, length is always
perpendicular to the direction of air flow through the
fill (air travel), or from casing to casing. For counter
flow 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 occurrences 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.
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M
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.
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N
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
structural 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 deliver
water in a spray pattern either by pressure or by
gravity flow.
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P
Packing — See "Fill".
Partition — An interior wall subdividing the tower
into cells or into separate fan plenum chambers.
Partitions may also be selectively installed to reduce
windage water loss.
Performance — See "Capacity".
pH —
A scale for expressing acidity or alkalinity of the
circulating or make-up water. A pH below 7.0 indicates
acidity and above 7.0 indicates alkalinity. A pH of 7.0
indicates neutral water. Stands for "potential
Hydrogen".
Pitot
Tube — An instrument that operates on the principle
of differential pressures. Its primary use on a cooling
tower is in the measurement of circulating water flow.
Plenum
Chamber — The enclosed space between the drift
eliminators and the fan in induced draft towers, or the
enclosed space between the fan and the fill in forced
draft towers.
Plume
— The effluent mixture of heated air and water vapor
(usually visible) discharged from a cooling tower.
Psychrometer — An instrument incorporating both a
dry-bulb and a wet-bulb thermometer, by which
simultaneous dry-bulb and wet-bulb temperature readings
can be taken.
Pump
Head — See "Tower Pumping Head".
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R
Range
— Difference between the hot water temperature and
the cold water temperature (HW - CW) Unit: °F.
Recirculation — Describes a condition in which a
portion of the tower's discharge air re-enters the air
inlets along with the fresh air. Its effect is an
elevation of the average entering wet-bulb temperature
compared to the ambient.
Riser
— Piping which connects the circulating water supply
line, from the level of the base of the tower or the
supply header, to the tower's distribution system.
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S
Scale
Inhibitor — Chemical added to inhibit formation of
scale
Shell
— The chimney-like structure, usually hyperbolic in
cross-section, utilized to induce air flow through a
natural draft tower. Sometimes referred to as a "stack"
or "veil".
Slowdown — Water discharged from the system to
control concentrations of salts or other impurities in
the circulating water. Units % of circulating water rate
or gpm.
Sludge
— A general term for soft mud-like deposits on heat
transfer surfaces or other important sections of a
cooling system
Slug
Dose — addition in one portion or shot over a
relatively short period of time by metered delivery,
rather than over an extended period of time.
Speed
Reducer — A mechanical device, incorporated between
the driver and the fan of a mechanical draft tower,
designed to reduce the speed of the driver to an optimum
speed for the fan. The use of geared reduction units
predominates in the cooling tower industry, although
smaller towers will utilize differential pulleys and
V-belts for the transmission of relatively low power.
Splash
Bar — One of a succession of equally spaced
horizontal bars comprising the splash surface of a fill
deck in a splash-filled cooling tower. Splash bars may
be flat, or may be formed into a shaped cross-section
for improved structural rigidity and/or improved heat
transfer capability. When flat, they are sometimes
referred to as "slats" or "lath".
Splash-Filled — Descriptive of a cooling tower in
which splash-type fill is used for the primary heat
transfer surface.
Spray-Filled — Descriptive of a cooling tower which
has no fill, with water-to-air contact depending
entirely upon the water break-up and pattern afforded by
pressure spray nozzles.
Stack
— An extended fan cylinder whose primary purpose is
to achieve elevation of the discharge plume. Also see
"Fan Cylinder" and "Shell".
Stack
Effect — Descriptive of the capability of a tower
shell or extended fan cylinder to induce air (or aid
in its induction) through a cooling tower.
Standard Air — Air having a density of 0.075 Ib per
cu ft. Essentially equivalent to 70°F dry air at 29.92
in Hg barometric pressure.
Story
— The vertical dimension between successive levels
of horizontal framework ties, girts, joists, or beams.
Story dimensions vary depending upon the size and
strength characteristics of the framework material used.
Unit: ft.
Sump —
A depressed chamber either below or alongside (but
contiguous to) the collection basin, into which the
water flows to facilitate pump suction. Sumps may also
be designed as collection points for silt and sludge to
aid in cleaning.
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T
Thermal Capacity — Cooling Tower Capacity
representing the amount of liquid, measured in gallons
per minute, that a cooling tower can process.
Total
Air Rate — Total mass flow of dry air per hour
through the tower. Unit: Ib per hr. Symbol: G.
Total
Water Rate — Total mass flow of water per hour
through the tower. Unit: Ib per hr. Symbol: L
Tower
Pumping Head — The static lift from the elevation of
the basin curb to the centerline 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.
Transverse — Pertaining to occurrences in the
direction of tower width.
Turbidity — measurement of light through water.
Suspended particles in water affect the turbidity
measurement. In general, turbidity is a good initial
measurement of water clarity and quality.
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V
Velocity Recovery Fan Cylinder — A fan cylinder on
which the discharge portion is extended in height and
outwardly flared. Its effect is to decrease the total
head differential across the fan, resulting in either an
increase in air rate at constant horsepower, or a
decrease in horsepower at constant air rate.
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W
Water
Loading — Circulating water rate per horizontal
square foot of fill plan area of the cooling tower.
Unit: gpm per sq ft.
Water
Rate — Mass flow of water per square foot of fill
plan area of the cooling tower per hour. Unit: Ib per sq
ft per hr. Symbol: L'.
Wet-Bulb Temperature — The temperature of the
entering or ambient air adjacent to the cooling tower as
measured with a wet-bulb thermometer. Unit: °F. Symbol:
WB.
Wet-Bulb Thermometer — A thermometer whose bulb is
encased within a wetted wick.
Windage — Water lost from the tower because of the
effects of wind. Sometimes called "blowout".
Wind
Load — The load imposed upon a structure by a wind
blowing against its surface. Unit: lb per sq ft.
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