4.7.8 4-pipe fan coil unit with electric heater
In 4-pipe applications with electric heater, the thermostat controls 2 valves in
heating and cooling mode by manual selection, heating only, or cooling only plus
an auxiliary electric heater. Heating and cooling is factory-set (P001 = 4).
The electric heater is used as an additional heat 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 "1/2 "dead zone" minus "setpoint differential" (= setpoint for electric heater).
Remote enabling/disabling of the electric heater is possible via input X1, X2, or U1
(RDG2..KN)/X3 (RDG2..T) for tariff regulations, energy saving, etc.
Input X1, X2, or U1/X3 must be commissioned accordingly (P150, P153 and
P155). See Multifunctional input, digital input [➙ 115].
The electric heater can also be enabled/disabled via bus. (RDG2..KN)
Do not assign the function to a local input X1, X2 or U1 if the bus input is used.
CAUTION! The electric heater must always be protected by a safety limit
thermostat!
The heating or cooling output can be released via operating mode button if P001 is
set to Manual (P001 = 3).
The diagrams below show the control sequence for On/Off control.
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