User Manual

27 / 66
Siemens RDF302 Basic documentation CE1P3079en
Smart Infrastructure 2020-12-01
3.6.2 2-pipe fan coil unit
On 2-pipe applications, the thermostat controls a valve in heating / cooling mode
with changeover (automatically or manually), heating only, or cooling only. Cooling
only is factory-set (P01 = 1).
ON/OFF control
The diagrams below show the control sequence for 2-position control.
Heating mode Cooling mode
½ SDH
1
0
½ SDH
w
Y
3
0
7
6
D
0
1
T[°C]
V1
Y
½ SDC
1
0
½ SDC
w
3
0
7
6
D
0
2
T[°C]
V1
T[°C] Room temperature SDH Switching differential “Heating” (P30)
w Room temperature setpoint SDC Switching differential “Cooling” (P31)
V1 Control command “Valve” or “Compressor”
Modulating control: 3-position
The diagrams below show the control sequence for modulating PI control.
Heating mode Cooling mode
XpH
100
0
w
Y [%]
3
0
7
6
D
0
3
T[°C]
V1
XpC
Y [%]
100
0
w
3
0
7
6
D
0
4
T[°C]
V1
T[°C] Room temperature XpH Proportional band “Heating” (P30)
w Room temperature setpoint XpC Proportional band “Cooling” (P31)
V1 Control command “Valve”
The diagrams only show the PI thermostat’s proportional part.
Setting the sequence and the control outputs
Refer to sections 3.4 "Applications", 3.6.1 "Sequences", and 3.7 "Outputs".
Control sequence
ON/OFF output
Control sequence
modulating output
Note: