4-Pipe Fan Coil Unit - Siemens RDF302 Documentation

Heating and cooling
4-pipe application with
manual changeover
"Main and secondary"
application (4-pipe with
changeover)
V2
T
B2
V1
Notes:
Siemens
Building Technologies
3.6.4

4-pipe fan coil unit

On 4-pipe applications, the thermostat controls 2 valves in heating and cooling
mode, heating / cooling mode by manual selection, or heating and cooling mode
with changeover. Heating and cooling mode (P01 = 4) is factory-set.
The heating or cooling output can be released via operating mode button if
parameter P01 is set to Manual (P01 = 2).
If parameter P01 is set to changeover (P01 = 3), the heating and cooling output is
swapped according to the input state of the changeover sensor / switch / Modbus
input (see automatic heating and cooling changeover sensor in section 3.5). This
mode is used for the so-called "Main and secondary" application. This is a 4-pipe
fan coil unit system with different capacities of the 2 coils. The water circuit is
changed to optimize the energy exchange depending on the season (summer /
winter):
– Winter: Large coil (V1) for heating, small coil (V2) for cooling
– Summer: Large coil (V1) for cooling, small coil (V2) for heating
Y
1
0
M1
T
B1
 The parameter for the heating and cooling changeover sensor (B2 in the above
diagram) must be set to 2 (X1 or X2, P38 or P40)
 The thermostat assumes winter operation when B2 > P37 (factory setting 28 °C)
 The thermostat assumes summer operation when B2 < P36 (factory setting 16 °C)
RDF302 Basic documentation
Changeover
YH
YC
w
w
YH V1
YC
V2
T[°C] Note:
This example shows
ON/OFF control;
for modulating con-
trol, connect the
appropriate output
Changeover
terminals
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CE1P3079en
07 Dec 2011