Fan Control; Description - Siemens Desigo RXB Technical Manual

Room unit
Automatic mode
Single-speed (relay Q14)
2-speed (relays Q14, Q24)
Three-speed (relays
Q14, Q24 and Q34)
Siemens
Building Technologies
9

Fan control

9.1

Description

All fan coil applications incorporate single-speed, two-speed or three-speed automatic
fan control. The fan speeds are enabled and disabled via volt-free relay contacts. The
controllers operate with an algorithm optimized for thermal or motorized valve actuators
for each fan speed.
Certain room units allow the user to select the fan speeds MANUALLY (in Comfort
mode only).
There are two types of automatic mode:
• "AUTO" applies to automatic operation at Comfort temperature setpoints.
• The symbol " " does not mean "Fan Off ", but "automatic operation at reduced
setpoints", e.g. Precomfort mode.
In the reduced room operating modes, the fan speeds CANNOT be selected
manually.
In automatic mode, the fan speeds are controlled in accordance with the response of a
PI controller to the control deviation.
The relays are operated in alternation. Example: When the controller switches from
Speed 1 to Speed 2, first the relay for Speed 1 switches off (A), and then, after a delay
of 1 s, the relay for Speed 2 switches on (B). The same applies in reverse when
switching down.
Y Q
100%
H
Q14
SpH
Y Q
H
a
100%
Q24
Q14
SpH
Y Q
H
a
100%
Q34
Q24
Q14
SpH
RXB (KNX) application library
Fan control
10385D19
C
TR [°C]
SpC
10385D20
C
a
(B)
(A)
TR [°C]
SpC
10285D21
C
a
TR [°C]
SpC
FNC Description of functions for FC-10, FC-11, FC-12
Valve sequence
Fan
Relays switch alternately
Example:
(A) Speed 1 relay OFF
(B) Speed 2 relay ON
after delay of 1 s
Y Output signal
TR Room temperature
SpH Effective heating setpoint
SpC Effective cooling setpoint
H Heating sequence
C Cooling sequence
Q14 1. Fan speed 3
Q24 2. Fan speed 3
Q34 3. Fan speed 3
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