Adjustment Channels - Viessmann SCU 123 Manual

SCU 123
5.2

Adjustment channels

∆T -regulation
DT1O / DT2O :
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]
DTF:
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]
TMN:
Minimum runtime
Adjustment range:
1 ... 10 min
in steps of 1 min
Factory setting: 2 min
Pump speed control
TAR
Target temp.
Adjustment range:
70 ... 210 °F [20 ... 99 °C]
in steps of 2 °F [1 K]
Factory setting:140 °F [60 °C]
Minimum pump speed
n1MN, n2MN:
Adjustment range:
30 ... 100
in steps of 5 %
Factory setting: 30
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The controller works as a standard differential controller. It
calculates the temperature difference between the collec-
tor sensor S1 and the upper DHW store sensor S3. If this
temperature difference reaches the switch-on temperature
difference DT1O, the primary loop pump is switched on. If
the temperature difference falls below the switch-off diffe-
rence DTF, the pump is switched off.
If the switch-on temperature difference between the upper
heat exchanger sensor S4 and the upper DHW store sensor
S3 is reached (DT2O), the secondary loop pump will be
switched-on.
Solar loading will be carried out for the adjustable minimum
runtime TMN during which the switch-off condition will be
ignored in order to stabilize the system.
If the temperature difference between the upper heat ex-
changer sensor S4 and the lower heat exchanger sensor S2
falls below the switch-off temperature difference DTF both
loops will be switched off.
Note:
The switch-on temperature difference must be
at least 1 °Ra [0.5 K] higher than the switch-off
tempe rature difference.
The pump speed is controlled dependant on the target
temperature (see above).
The primary and the secondary loop pumps will run at mini-
mum speed until the target temperature at S4 is reached. If
the target temperature is exceeded by 5 K, the speed of the
primary loop pump will increase by one step. This state will
be hold for 2 min even if the target temperature decreases.
If, during this time, the target temperature (S4) increases by
more than 5 K, the pump speed of the secondary pump will
as well increase by 1 step (10 %).
This state will be hold for 2 min each time the target tempe-
rature increases unless the temperature increases by 5 K. If
the temperature decreases, first the secondary pump speed
and then the primary pump speed will decrease by 1 step.
A relative minimum pump speed can be allocated to the
outputs R1 and R2 via the adjustment channels n1MN and
n2MN