System-Specific Functions - Viessmann SCU224 User Manual

SCU224

System-specific functions

∆T control for backup heating by solid fuel boiler
DT3O:
Switch-on temperature diff.
Adjustment range: 2.0 ... 40.0°Ra
[1.0 ... 20.0 K]
in steps of 1 °Ra [0.5 K]
Factory setting: 12.0°Ra
[6.0 K]
DT3F:
Switch-off temperature diff.
Adjustment range: 1.0 ... 39.0°Ra
[0.5 ... 19.5 K]
in steps of 1 °Ra [0.5 K]
Factory setting: 8.0°Ra
[4.0 K]
Pump speed control
DT3S:
Nominal temperature difference
Adjustment range: 3.0 ... 60.0 °Ra
[1.5 ... 30.0 K]
in steps of 1 °Ra [0.5 K]
Factory setting: 20.0 °Ra
[10.0 K]
RIS3:
Rise
Adjustment range:
2 ... 40 °Ra [1 ... 20 K]
in steps of 2 °Ra [1 K]
Factory setting: 4 °Ra [2 K]
Minimum pump speed
n2MN:
Pump speed control
Adjustment range:
30 ... 100
in steps of 5 %
Factory setting: 30
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The following adjustments are used for the specific functions
in system layout 8.
Reference sensors for this function are S4 and S3.
In system layout 8, the controller is equipped with an ad-
ditional differential control for heat exchange from a solid
fuel boiler (e.g. woodstove). The basic differential function
is adjusted using the switch-on (DT3O) and switch-off
(DT3F) temperature differences.
When the switch-on difference is reached, relay 2 swit-
ches on. When the temperature difference falls below
the adjusted switch-off temperature difference, relay 2
switches off.
Note:
The switch-on temperature difference must be
at least 1 °Ra [0.5 K] higher than the switch-off
tempe rature difference.
Note:
For pump speed control of the solid fuel boiler
pump, the operation mode of relay 2 (MAN2)
must be set to Auto.
When the switch-on temperature difference is reached, the
pump is activated at full speed for 10 seconds. Then, the speed
is reduced to the minimum pump speed value (n2MN).
If the temperature difference reaches the adjusted nominal
temperature difference (DT3S), the pump speed increases by
one step (10 %). If the difference increases by the adjustable rise
value, the pump speed increases by 10 % respectively until the
maximum pump speed of 100 % is reached. The response of
the controller can be adapted via the parameter RIS3.
Note:
The nominal temperature difference must be
at least 1 °Ra [0.5 K] higher than the switch-on
tempe rature difference.
A relative minimum pump speed can be allocated to the
output R2 via the adjustment channel n2MN.
Note:
When loads which are not speed-controlled (e.g.
valves) are used, the value must be set to 100 % in
order to deactivate pump speed control.