Viessmann VITOTRONIC 100 Installation And Service Instructions Manual page 46

Heating system designs
System version 15
Possible applications
The cascade and cylinder control
must be provided by a higher control
unit.
The Vitocrossal 300 (lead boiler) and
the next low temperature boiler
should be operated via a
weather−compensated control
system with modulating boiler water
temperature and load−dependent
sequential control
modulating burners are regulated.
46
(cont.)
two−stage or
Vitocrossal 300 is equipped with two
return connectors. The heating
circuits with the higher return
temperature are connected to the
upper return connector and those
with lower return temperatures to
the lower return connector. Note:
connect at least 15% of the rated
output to the lower return connector.
The return temperature raising
facility is available as an accessory
or must be provided on site.
Raise the return temperature
through a shunt−pump and by
closing the butterfly valve.
Temperature sensor T1 controls the
butterfly valve. Temperature sensor
T2 switches the shunt pump.