pH
s
is calculated from:
pH
s
= (9.3 + A + B) - (C + D),
in which
• A : depends on the total solids concentration
• B : depends on the water temperature at the outlet of the heat exchanger
• C : depends on the calcium hardness (CaCO
3
)
•
D : depends on the HCO
3
-
concentration or M-alkalinity
The values of A, B, C and D can be found in below table:
Total
dissolved
solids
(mg/l)
A Temperature
(°C)
B Ca hardness
(ppm CaCO
3
)
C M-
Alkalinity
(ppm
CaCO
3
)
D
< 30 0.1 0 - 1 2.3 9 - 11 0.6 10 - 11 1.0
30 - 320 0.2 2 - 6 2.2 12 - 14 0.7 12 - 14 1.1
> 320 0.3 7 - 11 2.1 15 - 17 0.8 15 - 17 1.2
12 - 16 2.0 18 - 22 0.9 18 - 22 1.3
17 - 22 1.9 23 - 28 1.0 23 - 28 1.4
23 - 27 1.8 29 - 35 1.1 29 - 35 1.5
28 - 32 1.7 36 - 44 1.2 36 - 44 1.6
33 - 38 1.6 45 - 56 1.3 45 - 56 1.7
39 - 43 1.5 57 - 70 1.4 57 - 70 1.8
44 - 49 1.4 71 - 89 1.5 71 - 89 1.9
50 - 55 1.3 90 - 112 1.6 90 - 112 2.0
56 - 61 1.2 113 - 141 1.7 113 - 141 2.1
62 - 67 1.1 142 - 177 1.8 142 - 177 2.2
68 - 73 1.0 178 - 223 1.9 178 - 223 2.3
74 - 79 0.9 224 - 281 2.0 224 - 281 2.4
80 - 85 0.8 282 - 355 2.1 282 - 355 2.5
86 - 91 0.7 356 - 446 2.2 356 - 446 2.6
92 - 95 0.6 447 - 563 2.3 447 - 563 2.7
564 - 707 2.4 564 - 707 2.8
708 - 892 2.5 708 - 892 2.9
893 - 1000 2.6 893 - 1000 3.0
Interpretation of the values obtained:
• RSI < 6: boiler scale formation
• 6 < RSI < 7: neutral water
• RSI > 7: corrosive water
As a general rule, the RSI index should be between 5.6 and 7.5. If that is not the case,
contact a specialist.
5. Free chlorine (Cl
2
)
Disinfecting with chlorine is not done in closed systems, neither in energy recovery
systems.
Instruction book
2920 7110 05 73
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