Carel k.Air, User Manual, Page: 78 / 192

78
Functions
k.air +030220981 rel. 1.2 - 01.12.2020
9.18.1 F an speed control based on pressure/fl ow-rate
The fan speed is automatically modulated based on the diff erential pressure/air fl ow-rate set points. The PI control parameters
are the same for both. The diff erential pressure sensor is used in both pressure and fl ow-rate mode; the conversion between the
values depends on the coeffi
cient K.
30220980_038_R01
∆p
V = k √∆p
·
·
V = portata/flow rate
∆p = pressione/pressure
Fig. 9.ah
R if D escription D ev Min Max UoM D ir Modbus BAC net
FANS
Ba24 Fan K factor for air fl ow calculations 100.0 0.0 99999.0 - R/W HR1506 AV3007
Tab. 9.ak
The example below shows PID control
30220980_205_R01
100%
0%
Min_req
St
RegPrb
Fan Speed
request (%)
diff
Key
St Set point
Diff Diff erential (100/kp)
Min_req
Minimum request
RegPrb Air fl ow-rate or static pressure
Fig. 9.ai
Note:
a post- ventilation time can be set to extend operation of the fans after the unit shutdown command. The function is
useful and sometimes necessary when electric heaters are used, to avoid overheating after switching off .
R if D escription D ev Min Max UoM D ir Modbus BAC net
FANS
Bb06 Supply fan: Minimum regulation value 0.0 0.0 100.0 % R/W HR1896 AV3376
Supply fan: Maximum regulation value 100.0 0.0 100.0 % R/W HR1897 AV3377
Bc06 Return fan: Minimum regulation value 0.0 0.0 100.0 % R/W HR1898 AV3378
Return fan: Maximum regulation value 100.0 0.0 100.0 % R/W HR1899 AV3379
Tab. 9.al
9.18.2 F low and thermal overload alarm
On k.air the following digital contacts can be enabled to check correct functioning of the fans
• Supply fan thermal protector, total unit shutdown
• Return fan thermal protector, fans stopped
• Fan thermal protector, total unit shutdown. The thermal protectors for the two fans must be connected in series
• Supply fan fl ow, total unit shutdown with semi-automatic alarm
• Return fan fl ow, exhaust fan shutdown with semi-automatic alarm
• Fan fl ow, total unit shutdown. The fl ow switches for the two fans must be connected in series, semi- automatic alarm
In addition to the digital inputs for fl ow control, the diff erential pressure probes can be used to determine correct operation of
the fans. In this case, the pressure threshold must be confi gured on screen Ba09. See chapter “Check fl ow switch” for a complete
description of the fl ow control function.