Technical data

24
Heating system designs
System version 7 (continued)
Possible applications
The Vitocrossal 300, CT3 (lead boiler) and the Vitorond 200, VD2 (lag boiler) are operated via a Viessmann control system
with outoor reset logic, modulating boiler water temperature, and load-dependent sequential control – two-stage or
modulating burners are controlled.
Vitocrossal 300, CT3 is equipped with two return connections. The heating circuits with the higher return temperature are
connected to the upper return connection, and those with lower return temperatures to the lower return connection. Please
note: Connect at least 15% of the rated output to the lower return connection. The return temperature control is available
as accessory or must be provided on site.
Return temperature control for Vitorond can be achieved using the shunt pump and by closing the isolation valve.
Temperature sensor T1 controls the isolation valve. Temperature sensor T2 switches the shunt pump.
Due to the LON-BUS communication between controls, a boiler supply temperature is automatically set.
This temperature is based on the highest required mixing valve circuit temperature plus adjustable differential.
The connection diagram is only a
recommendation and needs to be
verified for completeness and
functionality at the installation site.
Single-phase and three-phase pumps
must be connected with field supplied
motor contactors and/or motor
starters.
5351 340 v1.4
IMPORTANT