Cooling Tower Terminology
Approach – difference between cold water temperature and the measured wet-bulb temperature.
Bleed Off – is the circulating water in the tower which is discharged to waste to help keep the dissolved solids concentration of the water below a maximum allowable limit. As a result of evaporation, dissolved solids concentration will continually increase unless reduced by bleed off.
Blowdown – water intentionally discharged from the cooling system to control concentrations of salts and other impurities in the circulating water
British Thermal Unit (BTU) – the heat energy required to raise the temperature of one pound of water one degree Fahrenheit in the range from 32° F to 212° F
Cell – smallest tower subdivision which can function independently
Cold water temperature – temperature of the circulating water leaving the cooling tower
Counterflow tower – design in which air flows upward through the fill section and interfaces counter currently with the down coming hot water.
Crossflow tower – design in which air flows horizontally across the fill section and interfaces perpendicularly with the falling hot water
CTI – Cooling Tower Institute. Organization for testing and certification of cooling towers
Cycles of Concentration – compares dissolved solids in makeup with solids in the circulating water
Drift – water lost from the tower as liquid droplets entrained in the exhaust air stream
Drift eliminators – baffling to control the drift loss in towers
Heat load – heat removed from the circulating water within the tower
Makeup – water added to the circulating water to replace water lost from the system by evaporation, drift, blowdown and leakage
Mechanical draft tower – tower in which a fan moves the air through the fill
Natural draft tower – hyperbolic design in which air moves through the fill because of pressure difference between top and bottom of tower, creating a chimney effect
pH – number between 0 and 14 indicating degree of acidity (below 7) and alkalinity (above 7)
Pumping head – minimum pressure required to lift water from basin level to tower top and force it into the water distribution system
Recirculation air – portion of the exhaust air which reenters the tower measured on the basis of the increase in entering wet-bulb temperature compared to the ambient
TDS – total dissolved solids contained in solution in cooling system water
Ton – an evaporative cooling ton is 15,000 Btu / hr
Water loading – circulating water flow expressed in gal / min per square foot of effective horizontal wetted area of the tower
Wet-bulb temperature – temperature indicated by a psychrometer