Cooling Tower Efficiency Calculations:
Cooling Tower plays a major role in the Chemical Process Industry. They reject process heat from the cooling water to the atmosphere and keep the water cool. The performance of the cooling tower depends on various parameters like Range & Approach. We shall see those terminologies in Detail.
Cooling Tower Approach:
The difference between the Cold Water Temperature (Cooling Tower Outlet) And ambient Wet Bulb Temperature is called a Cooling Tower Approach.
Approach = Cold Water Temperature – Wet Bulb Temperature
Cooling Tower approach is the better indicator of the performance.
Cooling Tower Range
The difference between the Hot Water Temperature (Cooling Tower Inlet) Temperature and Coldwater (Cooling Tower Outlet) temperature is called Cooling Tower Range.
Range = Hot Water Temperature – Cold Water Temperature
Cooling Tower Efficiency Calculation
The calculation of cooling tower efficiency involves the Range and approach of the cooling Tower. Cooling tower efficiency is limited by the ambient wet-bulb temperature. In the ideal case, the cold water temperature will be equal to the wet-bulb temperature. This is practically not possible to achieve. This requires a very large tower and results in huge evaporation and Windage or drift loss resulting in a practically not viable solution. In practice, the cooling tower efficiency will be between 70 to 75%.
Cooling Tower Efficiency = (Hot Water Temperature – Coldwater Temperature) x 100/
(Hot Water Temperature – Wet bulb temperature)
Cooling Tower Efficiency = Range/ (Range + Approach) x 100
In summer the ambient air wet-bulb temperature raises when compared to winter thus limiting the cooling tower efficiency.
Other Cooling Tower Calculations
This includes determination of cycle of concentration, Evaporation loss, Drift or Windage Loss, Blowdown water requirement makeup water requirement.
Cycle of Concentration
The cycle of concentration is a dimensionless number. It is a ratio between parameter in Cooling Water to the parameter in Makeup water. It can be calculated from any of the following formulae.
COC= Silica in Cooling Water / Silica in Makeup Water