6 Installation
Boiler draining
Fig. 2-39: Draining on the back of the heat exchanger
1 Boiler draining, G 1/ 2“ OT
Install thermal overload protection
7.3 Make-up water requirements
Recommendation: Low salt driving - filling with
demineralised water
, see VDI 2035 sheet 2.
Water-side corrosion
Corrosion is usually triggered by the available oxygen
in the water. This value can be brought into a safe
range with proper planning, design, installation and
maintenance of the heating system. A constant input
of oxygen should be avoided
Important in this regard:
Check pressure mainte-
nance at regular intervals
(operating pressure of the
heating system, pressure in the expansion tank).
Formation of scaling
Scaling is the formation of firmly adhering deposits on
water-contacting walls of hot water heating systems.
The cause of scaling is the presence of limestone in
the water.
Parameters that play a role in the formation of scaling:
–
System volume (the bigger it is, the less total hard-
ness is permissible, e.g. buffer tank fitted).
–
Total heat output (the bigger it is, the less total hard-
ness is permissible).
To determine the total allowable hardness, the
specific
water content
must be determined.
Example:
The fill and make-up water should meet the following
guideline values according to VDI 2035 Part 1.
Total heat
output
Specific system volume (VDI 2035)
<20
l/kW
≥20 <50
l/kW
≥50
l/kW
< 50 kW
≤ 16.8°dH
≤ 11.2°dH
< 0.1°dH
50 - 200 kW
≤ 11.2°dH
≤ 8.4°dH
< 0.1°dH
20 - 600 kW
≤ 8.4°dH
< 0.1°dH
< 0.1°dH
> 600 kW
< 0.1°dH
< 0.1°dH
< 0.1°dH
In the event of exceeding the above values, the filling
water is to be treated (e.g., ion exchanger resin).
pH value
In the normal case (mixed installation) no measures
are required to influence the pH
(control: value
should be in the range of 8.2 to 9.5).
For the resistance of the materials steel and copper in
heating systems a pH in the alkaline range is favou-
rable.
Exception: If aluminium materials are used in the hea-
ting system, a pH from 8.2 to 8.5 must be maintained
(heavy corrosion of aluminium from pH > 8.5).
If the value is significantly less than < 8.2 after filling,
then perform a check again after 8-12 weeks.
If no increase in pH could be achieved then add 10
g/m³ trisodium phosphate (Na
3
PO
4
) or 5g/m³ sodium
hydroxide (NaOH).
Allow 2 to 4 weeks of operation before further cor-
rections.
Electrical conductivity
The probability of corrosion usually decreases with
decreasing electrical conductivity of the heating water.
Recommendation: Low salt driving - filling with
demineralised water
, see VDI 2035 sheet 2.
Low salt
Electrical conductivity at 25°C
< 100 µS/cm
Operation manual
maximus
25
