Constant Duct Pressure (Vntctl22Y, Fansu22Y, Faneh22Y) - Siemens Climatix S300 HRV Application Manual

5.5.3 Constant duct pressure (VntCtl22y, FanSu22y, FanEh22y)

A6V10733786_en_c
Fan speed control
Supply fan and exhaust fan have defined duct pressure setpoints for each
operating mode, Pascal value is used. By using PSu and PEx pressure sensors,
the function controls fan speed to maintain duct pressure at a constant level.
These settings only define the pressure used in various operating modes and they
have no effect on other functions, like de-icing or AQ/r.H. control.
If AQ/r.H. control is active, the values set here are used as the minimum level. With
active temperature control, the values are used as maximum values. Depending on
deviations from setpoint, temperature, the AQ/r.H. control can freely increase or
decrease the speed of both fans simultaneously with a symmetrical control signal,
which then maintains the setpoint ratio in any situation.
Special operation with only one pressure sensor
In some situations, it might be sufficient to select the use of only one pressure
sensor in a duct. In this case, the pressure control is made with that fan which is in
the same duct as the pressure sensor. The other fan always follows the "master"
fan according to the following formula:
If the pressure sensor becomes faulty and control can no longer be guaranteed,
fan control of the duct with faulty sensor is automatically switched to linear fan
speed control. Setpoints used for the linear fan speed control are then calculated
by using the maximum unit pressure value as 100% and setting the actual
pressure setpoint proportionally according to the maximum value.
Example: When maximum unit pressure is 100 Pa and AWAY pressure is set to 35
Pa then fan speed of 35 % is used in case 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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