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Siemens
RXB (KNX) application library
FNC Description of functions for FC-10, FC-11, FC-12 CM110385en_05
Building Technologies
Fan control
28 Feb 2009
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.
TR [°C]
Q
SpH
H
10385D19
C
Q14
Y
100%
SpC
Valve sequence
Fan
TR [°C]
SpH SpC
10385D20
Q14
Q24
(B)
(A)
100%
Y
Q
H
a
C
a
Relays switch alternately
Example:
(A)
Speed 1 relay OFF
(B)
Speed 2 relay ON
after delay of 1 s
TR [°C]
Q
H
10285D21
C
Q14
Q24
Q34
SpH
SpC
a
a
Y
100%
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
Room unit
Automatic mode
Single-speed (relay Q14)
2-speed (relays Q14, Q24)
Three-speed (relays
Q14, Q24 and Q34)
