Cooling Tower Make-up Water Flow Calculation

To calculate the make-up water flow rate, determine the evaporation rate using one of the following:

1. The evaporation rate is approximately 2 GPM per 1 million BTU/Hr of heat rejection.

2. The evaporation rate is approximately 3 GPM per 100 tons of refrigeration.

3. Evaporation Rate (GPM) = Water Flow Rate (GPM) x Range (°F) x 0.001.

Multiply the evaporation rate by the appropriate correction factor in the table below to calculate the make-up water flow rate, in GPM.

Cycles of
Concentration

Correction
Factor

2

2.00

3

1.50

4

1.33

5

1.25

6

1.20

7

1.17

8

1.14

9

1.13

10

1.11