Viessmann VITOTRONIC 100 Installation And Service Instructions Manual page 52

Heating system designs
System version 17
Possible applications
For heating circuits with temperature
differentials y 20 K.
The cascade and cylinder control
must be provided by a higher control
unit.
The Vitocrossal 300 (lead boiler) and
the next low temperature boilers
should be operated via a
weather−compensated control
system with modulating boiler water
temperature and load−dependent
sequential control
modulating burners are regulated.
52
(cont.)
two−stage or
Vitocrossal 300 are 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.
Temperature sensor T1 records the
return temperature.
The boiler control unit regulates the
three−way mixing valve to ensure
that the system never falls below the
minimum return temperature.