Technical data

3.6.5 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 / bus 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.
T
B1
V2
V1
M1
3181D112
T
B2
Y
1
0
w
w
3181D117
T[°C]
YC
YH
Changeover
YH
YC
V1
V2
Changeover
Note:
This example shows
ON/OFF control;
for modulating con-
trol, connect the
appropriate output
terminals
• 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).
Heating and cooling
4
-pipe application with
manual changeover
"
Main and secondary"
application (4
-pipe with
changeover)
Note:
38 / 92
Siemens RDF301, RDF301.50..., RDF600KN Basic documentation CE1P3171en
Building Technologies Functions 2014-05-23