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Siemens
RDF300… / RDF340... / RDF400… / RDF600… Basic Documentation
CE1P3076.en
Smart Infrastructure
2020-02-21
4.6.2
2-pipe fan coil unit with electrical heater
In 2-pipe applications with electrical heater, the controller controls a valve in
heating/cooling mode with changeover, heating only mode, or cooling only mode
plus auxiliary electrical heater. Cooling only is factory set (P01=1) with enabled
electrical heater (P13).
In cooling mode, the valve receives an
OPEN
command if the acquired
temperature is above the setpoint. The electrical heater receives an
ON
command
if the acquired room temperature drops below “setpoint” – “dead zone” (=“setpoint
for electrical heater”) while the electrical heater is enabled (parameter P13).
Note: “Setpoint for electrical heater” is limited by parameter “Maximum heating
setpoint” (P10).
In heating mode, the valve receives an
OPEN
command if the acquired
temperature is below the setpoint. The electrical heater is used as additional
heating source when the heating energy controlled by the valve is insufficient. The
electrical heater receives an
ON
command, if the temperature is below “setpoint” –
“setpoint differential” (=setpoint for electrical heater).
The electrical heater is active in heating mode only and the control output for the
valve is permanently disabled when manual changeover is selected (P01=2).
Remote enabling/disabling of the electrical heater is possible via digital input X1/X2
for tariff regulations, energy saving etc.
Input X1 or X2 must be commissioned accordingly. See section 4.9 “Multifunctional
input”.
The diagram below shows the control sequence for on/off (2-position) control.
Heating mode
(automatic changeover=heating or heating only)
Cooling mode
(man. /auto. changeover=cooling or cooling only)
Heating mode with manual changeover
(P01=2)
(manual changeover=heating)
T[°C] Room temperature
W
Room temperature setpoint
V1
Control command “Valve” or “Compressor”
E1
Control command “electrical heater”
SDH Switching differential “Heating”
SDC Switching differential “Cooling”
X
dz
Dead zone
w
D
Setpoint differential
Heating or cooling with
electrical heater
Electrical heating,
active in cooling mode
Electrical heating in
heating mode
Electrical heating, and
manual changeover
Digital input “Enable
electrical heater”
Control sequence
on/off output
