5.5.2 Constant air flow regulation (VntCtl21y, FanSu21y, FanE-
h21y)
Fan speed control
Supply fan and exhaust fan setpoints have defined air flow settings for each
operating mode level. Setpoint used in the controller is m
3
/h.
These settings only define the flow used in various operating modes and they have
no effect on other functions like de-icing, AQ/r.H. control.
During active AQ/r.H. control, values set here are used as minimum level. During
active temperature control, the values are used as maximum levels. Depending on
deviations to setpoint, temperature, AQ, r.H. control can freely modulate the speed
of both fans simultaneously with symmetrical control signal which then keeps the
set supply / exhaust ratio in every situation.
By measuring either the dynamic pressure via pitot tube or the pressure drop over
a flow resistance (or a combination of both) air flow at these points can be
calculated by using a fan specific K-value. The following formulas are used and
only m³/h values can be set.
Range for setpoints depends on the ventilation unit’s capacity. K-value is a
constant and unique for each fan type.
If a pressure sensor becomes faulty and flow control can no longer be guaranteed,
the fan control of the fan with a faulty sensor is automatically switched to linear fan
speed control. Setpoints used for the linear fan speed control are then calculated
by using the unit’s nominal air flow value as 100 % and setting the actual flow
setpoint proportionally according to the maximum value.
Example: If the air flow nominal is 100 m
3
/h and the flow for the Away-setting is set
to 35 m
3
/h, a fan speed of 35 % (3.5 V) is used in the event of a fault.
Fan speed monitoring
The fan speed can be monitored to detect the actual speed of the fans or possible
device problems if fans with tacho signal output are used, or a separate analog
input for fan speed is available, or Modbus fans are used. The tacho input signal is
mapped to a 0…100 % value with each fan configurable to a minimum fan speed
and a minimum feedback signal assigned to the minimum fan speed value. A fan
speed feedback fault is detected if fan speed output is higher than the minimum fan
speed and the fan speed feedback drops below fan speed feedback fault limit for
longer than an allowed tolerance time.
The allowed tolerance time (limited to a maximum of 60 sec) is the time after
switch‑on that the fan has built up the correct air flow. The same conditions apply
for the startup procedure The startup configuration is also used for fan speed
monitoring.
Fan speed feedback fault is combined with the fan error signal to create a fan fault
alarm.
For Modbus fans, Modbus communication is also supervised.
The alarm category of all fan alarms for both fans can be configured as
●
A-Alarm (shutting down the plant) or
●
B-Alarm (only indication, no shutdown function) or
●
None (no fault supervision. Use only when no feedback signal exists and do
not use on Modbus fans).
Application functionalities
Fan speed control
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A6V10733786_en_c
