Basic Documentation

30 / 68

Siemens RDU341 Basic Documentation CE1P3172en

Building Technologies 2017-02-17

3.6.5 Single-duct with electric heater

General rule: In case of insufficient air flow, the thermostat cannot protect the

electric heater against overtemperature. Therefore the electric heater MUST

feature a separate safety device (thermal cutout).

On single-duct applications with electric heater, the thermostat controls a valve plus

an auxiliary electric heater. Parameter P01 is not available.

The output signal for the air flow can be limited to a minimum and maximum value

if required using parameters P63 and P64. With application " Single-duct with

electric heater", the min. value of P63 is overridden, so that the air flow never drops

below 10 % while the electric heater is ON.

The air flow starts to rise depending on the acquired room temperature, the current

supply air temperature (if available) and the setpoint.

The electric heater receives an ON command when the acquired room temperature

drops below setpoint (= setpoint for electric heater).

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 3.8.

The electric heater can also be enabled / disabled via bus.

If “Enable electric heater” input is used via bus, then the function must not be

assigned to a local input X1 or X2.

On start-up of the controller and if the primary controller sends the information that

the primary fan is off, the thermostat disables the electric heater, see section

3.10.9.

To avoid overheating of an electric heater when switched off, the air flow signal of

Vmin must be maintained for a preset "fan overrun time" (P54, factory setting

60sec).

In conjunction with a Synco primary controller it will be assured that the primary fan

keeps running during the fan overrun time.