Datasheet

5822 239
G
B
13
2.8 Standard values for water quality
2.8 Standard values for water quality
The service life of the heat generator and
the complete heating system is
influenced by the water conditions.
In any event, the cost of a water
treatment facility is less than the cost of
repairing defects on your heating system.
It is necessary to maintain the following
requirements to safeguard your warranty
rights.
The manufacturer’s warranty exc ludes
damage due to corrosion and scaling.
The following is a summary of essential
requirements for water quality.
For comprehensive references, see the
separate Technical Guide ”Standard
values for water quality”.
Heating systems with rated operating temperatures up to100 ºC (VDI 2035)
Long-term experience has shown that
scaling does not need to be completely
prevented in order to safeguard against
system defects. For this reason, the VDI
guideline 2035 permits, depending on the
respective total boiler rating of your
system, a certain amount of
calcium hydrogen carbonate to enter the
system along with the filling water (see
also the corresponding explanatory
remarks in the original text of the relevant
guideline).
The total filling volume comprises the
initial fill and the volume of replenishing
water plus any refill (an exception would
be, if the boiler is de-scaled).
Requirements to be satisfied by the heating water
Total boiler system output Calcium hydrogen carbonate concentration Max. volume of water for filling and
of the system [Q] [Ca(HCO
3
)
2
] of the fill and replenishing replenishing [V
max
]
water
Q≦310 0 kW no requirement
*1
no requirement
*1
100 kW < Q≦ 350 kW Ca (HCO
3
)
2
≦ 2.0 mol/m
3
V
max
[m
3
] = triple system volume
350 kW < Q≦1000 kW Ca (HCO
3
)
2
≦ 1.5 mol/m
3
(or calculation of V
max
as under
line: 1000 kW <Q
)
1000 kW < Q ––– V
max
[m
3
]=
*2
0.0313×
Q
.
[kW]
Ca(HCO
3
)
2
[mol∕m
3
]
*1
The requirements for systems with Q >100 kW apply to boiler changes in existing systems with an original value of Q > 100 kW
and system water volume
≧ 20 litres/kW.
*2
Apply this equation for heating systems <100 kW and with a specific system volume ≧ 20 litres/kW.
Prevention of damage due to corrosion of the primary side
The corrosion resistance of ferrous
materials on the primary side of heating
systems and boilers depends on the
absence of oxygen in the heating water.
The oxygen introduced into the heating
system with both the first fill and with
replenishing water reacts with the system
materials, without causing damage. The
characteristic blackening of the water
after some time in use indicates, that free
oxygen is no longer present. The
Technical Rules and in particular the VDI
guideline 2035-2 therefore recommend,
that heating systems are designed and
operate so that a constant ingress of
oxygen into the heating water is
prevented.
Oxygen can normally only enter during
operation via
H open expansion vessels with water flow
H system vacuum
H gas-permeable components
Correctly sized sealed systems operating
at the correct pressure – e.g. systems with
diaphragm expansion vessel – offer good
protection against the ingress of oxygen
from the air into the system. Every part of
the heating system, even the suction side
of the pump, should, under all operating
conditions, be higher than the ambient
atmospheric pressure. As a minimum
requirement, the inlet pressure of the
diaphragm expansion vessel should be
checked during the annual maintenance
procedure. Gas-permeable components,
e.g. plastic pipes in underfloor heating
systems, which are not impermeable,
should not be used. Provide system
separation if such components are used.
This should separate the water flowing
through the plastic pipes from other
heating circuits, e.g. from the heat
generator, by the provision of a corrosion
resistant heat exchanger.
Hot water heating s ystems which are
s ealed – from a c orros ion point of view –
and where the above points were taken
into consideration, require no additional
corrosion protection measures. However,
take additional precautions where there is
a danger of oxygen ingress, e.g. by adding
oxygen-binder sodium sulphite (5 – 10
mg/litre into the excess). The pH value of
the heating water should be between
8.2 - 9.5.
Different c onditions apply to s ys tem s
whic h inc lude alum inium c om ponents .
If chemicals are used to protect the system
agains t c orros ion, we would r ec om m end
that your chemical supplier c ertifies the
suitability of additives vis -à -vis the boiler
m aterials and the m aterials of other
heating s ys tem c om ponents .
We recommend you r efer to the r espective
s pec ialis t in ques tions of water quality/
treatment.
VDI guideline 2035 -2 contains further
details.
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