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Heating and cooling
4-pipe application with
manual changeover
"Main and secondary"
application (4-pipe with
changeover)
V2
T
B2
V1
Note:
Siemens.........................RDF301, RDF301.50..., RDF600KN, RDF600KN/VB, RDF600KN/S
Smart Infrastructure
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.
Y
YH
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).
Changeover
YC
w
T[°C]
w
YH
V1
YC
V2
Note:
This example shows
ON/OFF control;
for modulating con-
trol, connect the
appropriate output
Changeover
terminals
Basic Documentation
41 / 92
CE1P3171en
2020-02-21
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