Requirements Through Heat Load - Viessmann VITOCROSSAL 200 Type CM2 Technical Manual

Design information

Requirements through heat load

The requirements of EN 12831 relating to the heat load calculation are
met by the weather-compensated control units. To reduce the heat-up
load, the night setback is reduced in the case of low outside temper-
atures. The flow temperature will be raised for a limited time to reduce
the heat-up time after a setback phase.
Selection of rated heating output
Select boilers according to the required heat load. The efficiency of low
temperature and condensing boilers is stable in a wide range of boiler
loads. Therefore, the heating output for low temperature boilers, con-
densing boilers and multi boiler systems may be higher than the cal-
culated heat load of the building.
The output of condensing boilers is substantially influenced by the
return temperature and the condensation gain which depends on that
temperature. Lower condensation can be caused particularly in winter,
when a high heating output is required, and therefore higher return
temperatures result. We therefore recommend that the rated heating
output is selected in line with the heating output data at T
T 80/60 °C.
R
Selection of rated heating output
Temperature flow/re- Rated heating output in kW
turn (T /T )
F R
40/30 °C –
50/30 °C 87
80/60 °C 80
8.3 Water connection
Heating connections
Existing systems
Flush the heating system thoroughly to remove dirt and sludge depos-
its before connecting a condensing boiler to an existing heating sys-
tem.
Otherwise, this dirt and sludge will be deposited inside the boiler and
can lead to local overheating, noise and corrosion. Boiler damage
caused by such deposits are excluded from our warranty. Where nec-
essary, install dirt traps.
Boiler circuit pumps
These boilers do not require boiler circuit pumps, due to their design,
their large water content and the low internal pressure drop on the
heating water side.
Heating return
Route the return water from all consumers or heating circuits via the
return connectors into the condensing boiler. The Vitocrossal 300 is
equipped with two return connectors. If only one heating circuit is
installed, connect this to connector "KR 1".
Connection for the utilisation of condensing technology
■ Only install suitable 3-way mixing devices in heating circuits,
because the utilisation of condensing technology demands low
return temperatures. Avoid 4-way mixers.
The high efficiency of the Vitocrossal condensing boilers or condens-
ing units with the Vitotrans 300 can be further enhanced by the fol-
lowing measures:
■ Design the heating circuits for the lowest possible temperatures,
preferably 40/30 °C or 50/40 °C.
■ If several heating circuits with different temperature levels are inten-
ded to be used, connect the heating circuits with the lowest temper-
atures to connector "KR 1" of the Vitocrossal 300.
Gas condensing boilers
(cont.)
/
F
– – 187 248
115 142 186 246
105 130 170 225
The following table compares the rated heating outputs at various flow
and return temperatures.
314 408 508 635
311 400 500 620
285 370 460 575
If several heating circuits are installed, connect the heating circuits with
the lowest temperature level (e.g. underfloor heating system) to con-
nector "KR 1". Connect at least 15 % of the rated heating output to
connector "KR 1". This achieves optimum boiler efficiency. If several
heating circuits with identical temperature levels are installed, connect
these to connector "KR 1".
Heating circuits
For heating systems with plastic pipes, we recommend the use of
impermeable pipes to prevent the diffusion of oxygen through the pipe
walls.
Provide system separation in heating systems with plastic pipes (DIN
4726) that are permeable to oxygen. We supply a separate heat
exchanger for this purpose.
■ Reduce the water flow in the heating circuits with variable speed
pumps, or pumps whose speed is regulated subject to the flow and
return temperatures.
■ Measures taken to limit the return temperature may lead to increases
in efficiency.
■ Never install overflow valves between the heating flow and return.
– – – –
787 978 1100 1400
720 895 1006 1280
VIESMANN
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