5.6 Cooling water requirements
General
Cooling water needs to fulfill certain requirements in order to avoid problems of scaling,
fouling, corrosion or bacterial growth.
In open circuit cooling towers, protective measures must be taken to avoid the growth of
harmful bacteria such as legionella pneumophila when there is a risk of inhalation of the
water droplets.
No general recommendation can encompass the effects of all combinations of the various compounds,
solids and gases typically found in cooling water in interaction with different materials. Therefore the
recommendations formulated in our Cooling Water Specifications are a general guide line for acceptable
coolant quality. However, where strict limits apply, a statement is made in the specification.
The water requirements refer to untreated water. When water is treated, some parameters will change.
Water treatments should be carried out by a specialized water treatment company, taking the responsibility
for the performance of the treated cooling water and the compatibility with the materials in the cooling
circuit. This includes not only the selection of the appropriate additives, but also the correct application,
monitoring of concentrations and properties, prevention of sludge formation and maintenance of the
system. This applies also to treatment with antifreeze products. They must be provided with suitable
stabilizers and inhibitors. Specifications are also depending on the type of cooling circuit (open, once
through / recirculating with tower / closed) and on the application (Standard – max 65 °C cooling water
temperature at the outlet) or Energy Recovery (water temperature up to 95 °C).
In case water is not in line with recommended values or if any doubt, consult the manufacturer.
Cooling water parameters
1. pH
The effect of pH is already included in the Ryznar Stability Index (RSI - see item 4 below), but also
the pH itself is subject to limitations:
pH
Type of cooling system Materials Standard Energy recovery
Single pass Containing copper 6.8 - 9.3 6.8 - 9.3
Stainless steel with carbon
steel and / or cast iron
6.8 - 9.3 6.8 - 9.3
Stainless steel only 6 - 9.3 6 - 9.3
Recirculating (with tower) Containing copper 6.8 - 9.3 not applicable
Stainless steel with carbon
steel and / or cast iron
6.8 - 9.3
Stainless steel only 6 - 9.3
Closed loop Containing copper 7.5 - 9.3 7.5 - 9.3
Stainless steel with carbon
steel and / or cast iron
7.5 - 9.3 7.5 - 9.3
Stainless steel only 6 - 9.3 6 - 9.3
The values in bold are rejection limits.
When the system contains Zn or Al, the pH must be < 8.5.
Instruction book
126 2920 7180 30
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