4-pipe fan coil unit - Basic Documentation - RDF302 - RDF302.B - RDF302/VB

Semi-flush mount room thermostats with RS485 Modbus communications RDF302, RDF302.B, RDF302/VB
Product Family
Product Group
Thermostats (temperature controller with sensor)
Content Language
English
Content Type
Technical Documentation > Basic Documentation
Product Version
Status
Valid
Date
2022-06-17
Document No
CE1P3079en
Download ID
A6V10350339
Stock No.
S55770-T238
S55770-T416
S55770-T428
Product No.
RDF302
RDF302.B
RDF302/VB
Access level
Internet
File Type
html

Heating and cooling

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.

4-pipe application with manual changeover

The heating or cooling output can be released via operating mode button if parameter P01 is set to Manual (P01 = 2).

"Main and secondary" application (4-pipe with changeover)

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

Note:

This example shows ON/OFF control;
for modulating con­trol, connect the appropri­ate output terminals

Notes:

  • 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.

ON/OFF control

The diagrams below show the control sequence for 2-position control.

Heating mode with manual selection (P01=2) or

for P09 >= P10 in heating sequence *)

Cooling mode with manual selection (P01=2) or

for P09 >= P10 in cooling sequence *)
Diagram, schematic Description automatically generated
Heating and cooling mode (P01 = 04)

T[°C] Room temperature

w Room temperature setpoint

V1 Control command “Valve” or “Comp.” (H)

V2 Control command “Valve” or “Comp.” (C)

SDH Switching differential “Heating” (P30)

SDC Switching differential “Cooling” (P31)

Xdz Dead zone (P33)

Note:

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".