Water Quality In Heating Systems - Dimplex La 1118Cp Montage- Und Gebrauchsanweisungen

LA 1118CP
7.4 Water quality in heating
systems
7.4.1 Scale formation
Scale formation in heating systems cannot be avoided, but in
systems with flow temperatures below 60 °C the problem is so
small that it is negligible. With high-temperature heat pumps
and in particular with bivalent systems in the higher perfor-
mance range (heat pump + boiler combination), flow tempera-
tures of 60°C and more can be achieved. One preferred
method for preventing scale formation is softening because
this permanently removes alkaline earths (calcium and magne-
sium ions) from the heating system.
The following values for water quality in heating water and cold
water must be observed and checked during an on-site check:
 Degree of hardness
Conductivity

 pH value
Filterable materials

The following (limit) values must absolutely be observed:
Maximum degree of hardness of filling water and supple-

mentary water 3 dGH.
 The conductivity of demineralised water (DM water) (low-
salt) may not be greater than 100 μS/cm.
The conductivity of partially demineralised water (saline)

may not be greater than 1500 μS/cm.
The pH value must be between 7.5 and 9.

 The limit value for filterable materials in heating water is <
30 mg/l.
If necessary, for example in bivalent systems, the specifications
listed in the table below must also be observed, or the precise
guidelines for filling water and supplementary water and the
total hardness must be taken from the table in accordance with
VDI 2035 – Sheet 1.
NOTE
The specific volumes of a heating system must be determined
before filling the system.
The saturation index SI is used to determine whether water has
a tendency towards lime dissolution or lime separation. This
shows whether the pH value corresponds to a neutral pH point
or by how much it undershoots it due to excess acid or by how
much it exceeds it due to carbonic acid deficit. At a saturation
index below 0, the water is aggressive and will tend towards
corrosion. At a saturation index above 0, the water is calcare-
ous.
The saturation index SI should be between - 0.2 < 0 < 0.2
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Filling and supplementary water as well as heating water, depending on
heat output
Overall heat output in kW
Specific water content
heat generator > 0.3 k per kW
Specific water content
heat generator > 0.3 k per kW
(e.g. circulation water heaters)
and systems with electrical
heating elements
> 50 kW to 200 kW
> 200 kW to 600 kW
Heating water, depending on heating output
Operating mode
1. For the purpose of calculating the specific system volume, the smallest indi-
vidual heat output is to be used for systems with several heat generators.
2. In systems with several heat generators with different specific water con-
tents, the smallest specific water content is decisive.
3. Full softening is recommended for systems with aluminium alloys.
Fig. 7.6:Guideline values for filling and supplementary in accordance with
VDI 2035
CAUTION!
Non-compliance with the specified limit values for the
heating water can lead to damage.
 The minimum permitted pH value of 7.5 must be
observed.
 The specified limit values for water quality must be
ensured.
7.4.2 Corrosion
The VDI 2035 standard recommends the use of partially demin-
eralised water or demineralised water in systems with larger-
than-average 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.
452171.66.01-EN · FD 0212
Total alkaline earths in mol/m³
 20
Specific system volume in l/kW
50
none
2
50
2
 3.0 (16.8)
2.0 (11.2)
1.5 (8.4)
> 600 kW < 0.05 (0.3)
Electrical conductivity in µS/cm
3
Low-salt
Containing salt
clear, free from sedimentary substances
English
(total hardness in dGH)
20 to £ 50 50
1
Heat output
3.0 (16.8)
1.5 (8.4)
< 0.05 (0.3)
1.0 (5.6)
< 0.05 (0.3)
> 10 to  100
> 100 to  1500
Appearance
EN-17