How to calculate fresh water consumption and pump capacity
In the water distribution system, there are five different water flows, which are defined in the illustration below

E= Evaporation B= Bleed-off
F= Fresh Water D= Distribution
P= Pump capacity

1 Calculate the Bleed-off rate B
To calculate the bleed-off rate N, you need an analysis of your fresh water, depending on the water quality, a so called bleed-off constant CB can be found in the water quality graph below.

Example
Assume that our water analysis shows:
pH value of fresh water 7.1
Bicarbonate concentration Hco3 100mg / It
Calcium concentration Ca2+ 20 mg / It

Using the water quality graph, the bleed-off constant cB=0.2
Then the bleed-off rate B is calculated as :
B= CB x E It/min
B= 0.2 x 99 =20 It/min

2 Calculate the fresh water consumption F
The fresh water consumption F is calculated as

F= E+B It/min

Our example gives:
F=99 + 20 = 119 It/min

3 Calculate the Distribution flow rate D
To get sufficient wetting and optimal performance, a minimum specific water flow per m2 top surface of the pad is needed. The specific water flow CB for different models are:

Pad type Specific Water flow, CB
Per m2 top surface

7060-15 60 It/min
7090-15 60 It/min
5090-15 90 It/min

The distribution flow rate D to the total length of the pads is calculated as follows:
D=CD x L x D It/min

Our example with 7090-15 pad
L=100 m and D=0.1m gives:

D=60 x 100 x 0.1 =600 It/min

4 Calculate the pump capacity P
The pump capacity P is calculated as :
P = D + B It/min

Our example gives:
P = 600 + 20 =620 It/min

Why bleed off click on the image for enlarged                    view