Dimplex LIA 0608BWCF M - Page 17

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LIA 0608BWCF M - LIA 1316BWCF M English
6.4.2 Corrosion
The VDI 2035 recommends the use of partially demineralised
water or demineralised water in systems with larger-than-aver-
age specific system volumes of 50 l/kW.
These measures (e.g. pH stabilizers) are implemented to set the
pH value of the heating water to minimise the risk of corrosion
in the heat pump and in the heating system.
Irrespective of the legal requirements, the following limit values
in the heating water used for various substances must not be
undershot or exceeded. This is to ensure safe operation of the
heat pump. A water analysis must be carried out before com-
missioning the system. If the water analysis produces a "-" for a
maximum of one indicator or a "o" for a maximum of two indica-
tors, the analysis must be classed as negative.
Fig. 6.2:Limit values for the quality of heating water
Resistance of copper-soldered or welded stainless-steel plate
heat exchangers to the substances present in water:
Notes
 "+" = Normally good resistance
 "o" = Corrosion problems may arise,particularly if several
factors receive an evaluation of "o"
 "-" = Should not be used
NOTE
º
ºººº
The water quality should be checked again after 4 to 6 weeks,
as the quality could change during the first few weeks of
operation due to chemical reactions.
NOTE
º
ºººº
It is mandatory to use hydraulically closed systems. It is not
permissible to use any open hydraulic systems!
Evaluation characteristic
Concentration
range
(mg/l or ppm)
Stain-
less steel
Copper
Bicarbonate (HCO
3
-
)
< 70 + o
70 - 300 + +
> 300 + o
Sulphate (SO
4
2-
)
< 70 + +
70 - 300 o o/-
> 300 - -
Hydrogencarbonate/sulphate
HCO
3
-
/SO
4
2-
> 1.0 + +
< 1.0 o -
Electrical conductivity
1
< 10 µS/cm o o
10 - 500 µS/cm + +
> 500 µS/cm o o
pH value
2
< 6.0 - -
6.0 - 8.2 o o
8.2 - 9.0 + +
> 9.0 o o
Ammonium (NH
4
+
)
< 2 + +
2 - 20 o o
> 20 - -
Chloride ions (Cl
-
)
< 50 + +
50 - 150 o o
> 150 - -
Free chlorine (Cl
2
)
< 0.5 + +
0.5 - 5 - o
> 5 - -
Hydrogen sulphide (H
2
S)
< 0.05 + +
> 0.05 + o/-
Carbon dioxide (CO
2
)
< 5 + +
5 - 10 + o
> 10 o -
Nitrate (NO
3
-
)
< 100 + +
> 100 o o
Iron (Fe)
< 0.2 + +
> 0.2 o o
Aluminium (Al)
< 0.2 + +
> 0.2 + o
Manganese (Mn)
< 0.05 + +
> 0.05 o o
Saturation Index
< -0.2 o o
-0.2 - 0.1 + +
0.1 - 0.2 + o
> 0.2 o o
Filterable materials
< 30 + +
> 30 - -
Total hardness
< 6 °dGH o/+ o/+
6 - 11 °dGH + +
> 11 °dGH - -
Oxygen (O
2
)
< 0.02 + +
< 0.1 +/o +/o
> 0.1 - -
Nitrite (NO
2
-
)
< 0.1 + +
> 0.1 - -
Sulphide (S
2-
)
< 1.0 + +
> 1.0 - -
1. If the limit values in the VDI 2035 are more restrictive, these apply accord-
ingly.
2. When using demineralised water, ensure that the minimum permissible pH
value of 8.2 is not undershot. Failure to comply with this value can result in
the heat pump being destroyed.