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Siemens RDF302 Basic documentation CE1P3079en
Smart Infrastructure 2022-06-17
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 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
• 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.B does not have inputs X1 and X2.
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