5.7 Fan humidity control (DhuCtl11y)
It is possible to use one extract air sensor (0…10V), and up to two room humidity
sensors QMX.P40, QMX.P70 and a POS8 with room humidity sensor. In this case,
the highest value of all valid sensors is used for humidity control. For Comfort,
Economy and Unoccupied operating modes, specific setpoint values can be given.
Air humidification is not possible.
Dehumidification tries to maintain the set humidity level by modulating the following
actuators:
1. Preheating coil brine, if existing and dehumidification enabled and possible
2. Increasing fan speed, if dehumidification is enabled
3. External dehumidifier
Preheating coil brine
Used as a first actuator, if the brine coil is configured for use with humidity control.
The brine coil is released for dehumidification, if the flow temperature is lower than
the room dewpoint (minus configurable offset) and the outside air temperature is
higher than the brine flow temperature. The brine pump is switched on with the
idea to condensate water in the outside air. A 2-point control with configurable
hysteresis is used.
Fan speed
Fan speed increase is used a second actuator.
If relative humidity exceeds the limit value, the speed for both fans is increased
(according to PI-control) up to Comfort fan speed. During active humidity control,
the speed of both fans will be increased and decreased linearly between the
maximum and minimum vales. If the r.H. value drops below the setpoint, humidity
control reduces the fan speed until the defined level for active operating mode is
reached.
Boost, kitchen hood and fireplace have priority, so that humidity control does not
influence the fan speed. Comfort operating mode already runs with maximum fan
speed for the system, so that humidity control does not have any influence.
Since increased ventilation alone cannot lower the humidity level in every situation,
the dew point temperature is used to define if outside air temperature is sufficient
for lowering the humidity level in the room. In case the outside air temperature is
low enough to assure dehumidification, the PI-control works continuously.
Otherwise, the PI works periodically with configurable on and off times for the
function.
The function is deactivated when the relative humidity drops below the current
setpoint.
Humidity control with fan speed is blocked if the configuration of the room
influence to fan speed is in mode 2, 3 or 4, for example in duct pressure mode,
see "Application use cases [➙ 55]".
External dehumidifier
An external dehumidifier can also be used. It can be installed in the room or in the
supply air duct. Depending on the design of the dehumidifier, it can have an
integrated controller with sensor or be controlled by the CU as part of humidity
control. In this case, a 2-point controller with configurable hsysteresis is used and
the humidifier is switched on if the brine coil and the fans are not able to maintain
the humidity setpoint or are not present.
When the external dehumidifier is installed in the room, it can run independently of
the air handling unit. In this case, only room sensors are used and extract sensors
are ignored.
Application functionalities
Fan humidity control (DhuCtl11y)
5
80 | 170
A6V10733786_en_c
