External Heat Exchanger With Scu 224/345; Parallel Relay With Scu 345; Multiple Tank Operation With Scu 224 And 345; Tank Priority Control With Scu 224 And 345 - Viessmann VITOSOL 200-FM SV2F Design Manual

Solar System Design Guide
External Heat Exchanger with SCU 224 and 345

Parallel Relay with SCU 345

Multiple Tank Operation with SCU 224 and 345

Tank Priority Control with SCU 224 and 345

Option #1: The DHW tank is heated via the heat
exchanger. The primary pump P1 operates
based on the temperature differential between
S1 and S2. Secondary pump P2 starts in
parallel with solar circuit pump P1. This is
done by using the field supplied external relay
connected to the glycol pump output of the
control R1.
Option #2: The DHW tank is heated via the heat
exchanger. The primary pump P1 operates
based on the temperature differential between
S1 and S2. The secondary pump P2 operates
based on another temperature differential
between sensors S3 and S2.
With this function, a further relay will be switched
(subject to the system control layout) in addition to the
relay (R1) which switches the circulation pump, e.g. to
control a diverting valve or a second pump.
In systems with several storage tanks or thermal loads.
With this function, storage tanks or thermal loads can be
excluded from solar heating.
Note: Only with the SCU 345 can the end-user
deactivate a tank or load from the control layout.
For the SCU 224, the system commissioning
agent, must properly select the control layout
which reflects the true hydraulic layout.
In systems with several storage tanks or thermal loads. It
is possible to determine the order in which the heating of
the storage tanks or thermal loads will occur.
If the storage tank or thermal load cannot be heated with
priority, the next storage tank or thermal load in line will
be heated for an adjustable cycle time. After this time has
expired, the solar control unit will stop the pump(s) and
monitor the rise of the collector temperature during the
adjustable cyclical pause. As soon as the start conditions
for the storage tank or thermal load with priority have
been met, that storage tank or thermal load will be heated
again. Otherwise, the next-in-line storage tank or thermal
load will continue to be heated.
Solar Control
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