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REMKO WKF / WKF-compact
8
Corrosion protection
Oxygen always plays a role if metal materials in a heating system corrode. pH values and the salt content
also play a major role. The challenge: A licenced plumber who would like to be able to guarantee his cus-
tomers a hot water heating system not at risk of corrosion from oxygen - without the use of chemicals - must
pay attention to the following:
n
Correct system design by the heating contractor/planner and
n
subject to the installed materials: filling the heating system with demineralised softwater or fully deionised
water, checking the pH value after 8 to 12 weeks.
See the following table for the requirements in accordance with VDI 2035 Part 1 with regard to total hard-
ness.
Overall output in kW
to 50 kW
The following table provides the allowed oxygen content in connection with the salt content.
Reference values for the hot water in accordance with VDI 2035 Part 2
Electrical conductivity
at 25°C
Oxygen content
pH value at 25°C
*) For aluminium and aluminium alloys the pH value range is limited: the pH value at 25°C is 8.2-8.5 (max.
9.0 for aluminium alloys)
In low-salt water and the correct pH for a short time even to oxygen concentrations up 0.5 mg / l are
tolerated.
Water treatment with chemicals
Adding chemicals to treat water should only be
done as an exception. VDI 2035 Part 2 requires
explicitly under Point 8.4.1 that all water treatment
be explained and documented in the system log
book. This has reasons:
The improper use of chemicals often leads to
n
the failure of elastomer materials
n
To blockages and deposits because of sludge
formation
n
To defective floating seals in pumps
n
To the formation of biofilm which can cause
microbial influenced corrosion or significantly
impair heat transfer.
70
Total hardness [°dH] subject to the specific system volume
³20 l/kW and <50 l/kW
<20 l/kW
£16,8 °dH
μS/cm
mg/l
£11,2 °dH
low-salt
< 100
< 0,1
8,2 - 10,0 *)
³50 l/kW
£0,11 °dH
salline
100-1500
< 0,02
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