Technical data

www.dimplex.de 01.2012 | Project planning manual for heat pumps for heating and domestic hot water preparation | 109
Integration of the heat pump in the heating system 8.9
8.9 Scale formation in domestic hot water heating systems
Scale formation in domestic hot water heating systems cannot be
avoided, but in systems with flow temperatures below 65 °C, the
problem can be disregarded. With medium or high-temperature
heat pumps and in particular with bivalent systems in the higher
output range (heat pump + boiler combination), flow tempera-
tures of 60 °C and more can be achieved. The following standard
values should therefore be adhered to regard the filling and
make-up water according to VDI 2035, sheet 1: These values
can be found in the table.
Table 8.7: Guideline values for filling and make-up water in accordance with
VDI 2035
Irrespective of the legal requirements, the following limit values
for the heating water used for different materials must not be un-
dercut or exceeded to guarantee safe heat pump operation. A
water analysis must be carried out before commissioning the
system. If the water analysis shows a "-" for a maximum of one
indicator or a "o" for a maximum of two indicators, the analysis
must be classed as negative.
Table 8.8: Limit values for the quality of heating water
Resistance of copper-soldered or welded stainless-steel plate
heat exchangers to substances contained in the water
Notes
"+" = Normally good resistance
"o" = corrosion problems can arise,
particularly if several factors receive a evaluation of "o".
"-" = should not be used
The water quality should be checked again after 4 - 6 weeks, as
the quality could change during the first few weeks of operation
due to chemical reactions.
Total heat
output in
[kW]
Specific system volume (VDI 2035)
< 20 l/kW
≥ 20 < 50 l/kW ≥ 50 l/kW
< 50kW
≤ 16.8 °dH ≤ 11.2 °dH
< 0.11 °dH
1
50 - 200 kW
≤ 11.2 °dH ≤ 8.4 °dH
< 0.11 °dH
1
20 - 600 kW
≤ 8.4 °dH
≤ 0.11 °dH
1
< 0.11 °dH
1
> 600
< 0.11 °dH
1
1. This value lies outside the permissible value for heat exchangers in heat
pumps (see Fig. 8.8 on page 109).
< 0.11 °dH
1
< 0.11 °dH
1
Evaluation
characteristic
Concentration
range
(mg/l or ppm)
Stainless
steel
Copper
HCO
3
-
<70 + o
70-300 + +
>300 + o/+
Sulfate (SO
4
2-
)
<70 + +
70-300 + o/-
>300 o -
HCO
3
-
/ SO
4
-
<1.0 + +
>1.0 + o/-
Electrical
conductivity
< 10
µS/cm
+o
10-500 µS/cm
+ +
> 500
µS/cm
+o
pH-value
< 6.0 o o
6.0-7.5 o/+ o
7.5-9.0 + +
> 9.0 + o
NH
4
+
< 2 + +
2-20 + o
> 20 + -
Cl
-
<300 + +
>300 o o/+
Cl
2
<1 + +
1-5 + o
> 5 o/+ o/-
Hydrogen sulphide
(H
2
S)
< 0.05 + +
> 0.05 + o/-
CO
2
< 5 + +
5-20 + o
>20 + -
Water hardness
(°dH)
4.0-8.5 + +
Nitrate (NO
3
)
<100 + +
>100 + o
Iron (Fe)
< 0.2 + +
> 0.2 + o
Aluminium (Al)
< 0.2 + +
> 0.2 + o
Manganese (Mn)
< 0.1 + +
> 0.1 + o