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Operating & installation instructions bravour
Subject to technical changes.
V 2.1.5
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21
Water analysis and water treatment
Planners and installers must check on the system if the available feed water is appropriate to fill the heating system with
regard to the total hardness according to VDI 2035 sheet 1. The result of this test must be transmitted in writing to the
builder / operator. The decisive factors are the heating performance and the specific system volume:
Regarding this treatment the VDI 2035 gives three options:
Softening / demineralisation
Hardness stabilisation
Hardness precipitation
At this, the
softening
represents the preferred procedure to avoid stone formation, at which the alkaline earths (mag-
nesium and calcium ions) are permanently removed from the system. However, hereby sodium hydrogen carbonate
(NaHCO
3
) is formed in the system, which converts to alkalinized sodium carbonate (Na
2
CO
3
) by heating up the heating
water. Since the generated CO
2
escapes from the system at the same time, the pH value demanded in the VDI 2035
sheet 2 between 8.2 and 9.5 (when using aluminium maximum 8.5) may considerably be exceeded. However, if the ph
value is exceeded, there is a risk of corrosion damages, so that it is necessary to counteract such damages in a second
step.
In the
hardness stabilisation
additives are added to the heating water by which the lime deposits in the system are influ-
enced in a way that formation of stone is being avoided. Contrary to the softening the stone formers are not removed
from the system. Regarding the selection, dosing, monitoring and disposal of the additives and of the conditioned heat-
ing water it is necessary to take additional measures. It is necessary to make sure that the additives themselves as well
as combined with other products which need to be used do not cause any corrosion damages. Furthermore, no prod-
ucts containing phosphates should be used for hardness stabilisation since they precipitate as calcium phosphate mud
together with lime.
In the frame of the
hardness precipitation
substances are added to the heating water, which let the dissolved alkaline
earths precipitate as mud. This mud must be removed from the heating system by system technical and operational
measures (desludging).
Total heat output
Total hardness
Total hardness
Total hardness
In kW
In °dH at <20l/kW least
boiler screen surface
In °dH at >20l/kW<50l/kW
least boiler screen surface
In °dH >50l/kW least
boiler screen surface
<50kW
No requirements or
11.2°dH
0.11°dH
<16.8°dH
>50kW<200kW
11.2°dH
8.4°dH
0.11°dH
