fisair HEF7 Series, Installation And Maintenance Manual

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HEF7 series manual 27
14. Setting the valve regulating the bleed-off flow
Water evaporation is caused by a higher water vapour pressure in the evaporative panel than in the air moving
across it. Because only the water evaporates, dissolved mineral salts remain in solution, and gradually increase in
concentration, despite new water being added to compensate for the evaporation.
To prevent the formation of mineral deposits on the surfaces of the evaporative panel (this would lead to a
progressive decrease in air pressure and in operating performance) it is essential to discharge some of the
recirculated water to the drainage network in tandem with the evaporation.
Analytical parameters of the drinking water network.
Water hardness: (CaCO3): 50-170 ppm
Chlorine: (Cl): <55
ppm pH: 6-8
Silica: (SiO): <30 ppm
Iron (Fe): <0.2 ppm
Oils and grease: <2 ppm
Total dissolved solids: <550ppm
Total alkalinity: (CaCo3): 50-170 ppm
Suspended solids: <5 ppm
Bleed-off based on the cycle of concentration COC.
Bleed-off=Evaporation/(COC-1)
Cycle of concentration COC based
on conductivity (100-
1000 μS/cm)
Observation: Always using the
parameters of the drinking water
network.
100
μS/cm = 9 COC
550
μS/cm = 6 COC
1000 μS/cm = 2 COC
Calculation example:
Based on parameters of the drinking water network
Water evaporation=3.23 l/min
Water
conductivity=550
μS/cm COC=6
Bleed-off= 3.23/(6-1)= 0.65 l/min
The flow of the bleed-off valve can be set approximately
to begin with as 10% of total irrigation flow. By regularly
observing the state of the panels (on the air input side);
after 1 to 2 weeks working, if there are no signs of
mineral deposits whitening the surface, the bleed-off
flow can
be reduced or left the same, or, if on the other
hand, lime deposits are noticeable, it can be
increased