Cooling Tower Capacity Calculation

I am invariably finding many hits on cooling tower capacity & performance calculation and related queries. Therefore, I have decided to include the detailed calculation procedure in order to enable many students & process engineers who are interested in improving cooling towers performance by following these simple steps.

If you have any query, kindly post them in the comments section. I’ll try my level best to answer those queries as soon as possible.

First you should collect all the data as given below. Be sure that the data collected for these temperatures is most accurate because of lower absolute level of generally ~40°C average temperatures, an error of 0.5°C due to manual data collection & judgment will cause more than 1.2% error in the result at one calculation. Repeating such errors may result in cumulative errors of more than 10% in totality giving you totally absurd results.

So the basic point is that collect the data on regular basis, keep a watch to have a feel of real values & then proceed.

Actual Data

Cooling water flow rate - 4134 M3/hr

Cooling water inlet Temp - 44.0 °C

Cooling water exit Temp - 35.0 °C

Inlet air-wet bulb - 30.0 °C

Inlet air-dry bulb - 38.8 °C

Exit air-wet bulb - 40.7 °C

Exit air-dry bulb - 42.0 °C

Now follow step by step procedure for the calculation.

Step-1

Calculate waterside actual heat load, which is as below

Qw = 4134 x 1000 x (44 – 35) / 1000000

= 37.21 Gcal/Hr

Step-2

Calculate absolute humidity at wet bulb of inlet air, which is at 30°C in this case. This is a function of wet bulb temperature only.

The equation for the same is

1.4478310678E-10*(Tw^7)-2.6920*10e-8*(Tw^6)+1.99053*10e-6*(Tw^5)-6.65614*10e-5* (Tw^4)+0.00131879344*(Tw^3)+0.00125483272*(Tw^2)+0.291649083*Tw+3.802441

Where Tw is wet bulb temperature in °C. So,

H1 = 27.29 Kg/ ‘000Kg of dry air

Step-3

Calculate absolute humidity at dry bulb of inlet air, which is at 38.8°C in this case. It will give you saturation...