²
K glycol
= 1.8 MW
Result:
When using 40 % of the antifreeze named above in the heating network, the boiler output is reduced by 10 %.
The specific heat capacity is subject to the mixing ratio and temperature, therefore each system must be designed individually.
Prevention of damage through corrosion on the water side
The corrosion resistance of ferrous materials on the heating water side
of heating systems and boilers depends on the absence of oxygen in
the heating water.
The oxygen introduced into the heating system with the first fill and the
top-up water reacts with the system materials without causing dam-
age.
The characteristic blackening of the water after some time in use indi-
cates that free oxygen is no longer present.
The technical rules and in particular VDI Directive 2035-2 therefore
recommend that heating systems are designed and operated so that
a constant ingress of oxygen into the heating water is prevented.
Opportunities for oxygen ingress during the operation:
■ Through overflowing open expansion vessels
■ Through negative pressure in the system
■ Through gas-permeable components
Sealed unvented systems, e.g. with a diaphragm expansion vessel,
offer good protection against the ingress of airborne oxygen into the
system, if correctly sized and operating at the correct pressure.
At every part of the heating system, even at the suction side of the
pump and under all operating conditions, the system pressure should
be above ambient atmospheric pressure.
The pre-charge pressure of the diaphragm expansion vessel should
be checked at least during the annual service.
The use of permeable components, e.g. plastic pipes that are perme-
able to gas in underfloor heating systems, should be avoided. Provide
system separation if such components are nevertheless used. This
must separate the water flowing through the plastic pipes from other
heating circuits, e.g. from the heat source, by the provision of a heat
exchanger made of corrosion-resistant material.
No further anti-corrosion measures are required for sealed hot water
heating systems subject to the above points being observed.
However, take additional precautions where there is a risk of oxygen
ingress, for example by adding oxygen binder sodium sulphite (5 - 10
mg/litre into the excess). The heating water should have a pH value
between 9.0 and 10.5.
Different conditions apply to systems that contain aluminium compo-
nents.
Where chemicals are used as part of the corrosion protection, we rec-
ommend that the manufacturer of the chemicals issues a certificate of
suitability of the additives with regard to the boiler materials and the
materials of the other heating equipment components.
We recommend you refer questions of water treatment to Viessmann
industrial services or an appropriate specialist.
Further details can be found in VDI Directive 2035-2 and EN 14868.
10.10 Vitotrans 300 flue gas/water heat exchanger
Downstream installation of a Vitotrans 300 flue gas/water heat exchanger for raising the efficiency
The installation of a Vitotrans 300 flue gas/water heat exchanger
downstream of a boiler significantly raises the efficiency. By condens-
ing the flue gases inside the heat exchanger, the boiler turns into a
condensing boiler, as required by the Efficiency Directive 92/42/
EEC.
■ In the case of gas boilers, efficiency is increased by up to 12 %.
■ When using fuel oil EL, efficiency is raised by up to 6 % due to the
lower water content and, compared to gas, the lower dew point.
The Vitotrans 300 flue gas/water heat exchangers are designed to
enable retrofitting in existing heating systems.
Vitotrans 300 for oil operation
The Vitotrans 300 flue gas/water heat exchangers are available with
surfaces, which are in contact with flue gas, made from high-grade
stainless steel 1.4539 to enable constant or prolonged operation with
fuel oil EL.
Specification
See the datasheet for the relevant boiler.
Energy savings from using a Vitotrans 300 flue gas/water heat exchanger in conjunction with Vitoplex and
Vitorond boilers
The increase in efficiency and therefore the energy savings compared
to systems without flue gas/water heat exchangers are significantly
influenced by the return temperature of the return water flowing
through the heat exchanger.
The return temperatures are influenced by the system size and reduce
with increasing outside temperature. For heating systems with design
temperatures of 75/60 ºC and 40/30 ºC, the development of the return
temperature in relation to the outside temperature is illustrated in the
diagram on page 48.
The increased efficiency achievable through the downstream flue gas/
water heat exchanger when operating with gas and at various heating
system temperatures, is shown in the following table. The feasible
increases in efficiency are based on the modulating development of
the return temperature, and are subject to outside temperature. The
various increases in efficiency result from the different flue gas tem-
peratures produced by the upstream boiler.
Heating system design temperature Increase in efficiency
through the Vitotrans 300 with a Vitoplex 300
Increase in efficiency
through the Vitotrans 300 with a Vitoplex 200 and
Vitorond 200
90/70 ºC 6.0 % 7.0 %
75/60 ºC 9.0 % 10.0 %
60/50 ºC 10.0 % 11.0 %
40/30 ºC 11.5 % 12.5 %
Design information
(cont.)
OIL/GAS BOILERS
VIESMANN
47
5822 426 GB
10
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