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Siemens RDF302 Basic documentation CE1P3079en
Smart Infrastructure 2022-06-17
3.6.3 2-pipe fan coil unit with electric heater
On 2-pipe applications with electric heater, the thermostat controls a valve in
heating / cooling mode with changeover, heating only, or cooling only plus an
electric heater.
Cooling only is factory-set (P01 = 1) with enabled electric heater (P13).
In cooling mode, the valve receives an OPEN command if the acquired tempera-
ture is above the setpoint.
The electric heater receives an ON command if the acquired room temperature
drops below “setpoint” minus “dead zone” (= setpoint for electric heater) while the
electric heater is enabled (parameter P13 = ON).
Note: “Setpoint for electric heater” is limited by parameter “Maximum setpoint for
Comfort mode” (P10).
In heating mode, the valve receives an OPEN command if the acquired tempera-
ture is below the setpoint. The electric heater is used as an additional heating
source when the heating energy controlled by the valve is insufficient.
The electric heater receives an ON command, if the temperature is below “setpoint”
minus “setpoint differential” (= setpoint for electric heater).
The electric 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 electric heater is possible via input X1 or X2 for
tariff regulations, energy savings, etc.
Input X1 or X2 must be commissioned accordingly (parameters P38, P40). See
section 3.9 “Multifunctional input”.
The electric heater can also be enabled / disabled via Modbus.
If “Enable electric heater” input is used via Modbus, then the function must not be
assigned to a local input X1 or X2.
An electric heater must always be protected by a safety limit thermostat!
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