Danfoss VLT Inverter Scroll CDS 801 Operating Instructions Manual page 39

Embedded Application Contro...
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Illustration 6.7 AC Mode
Delta T Control
In Delta T mode, the fan speed control attempts to maintain a temperature difference of Delta T to ambient temperature,
see Illustration 6.8.
In AC mode, the fan speed control attempts to maintain condensing temperature Delta T above ambient temperature.
To run Delta T mode:
Set THERMO_IN_FAN_MODE = 1
The temperature difference Delta T is set through the register THERMO_SETUP_DELTA_TEMP.
Tamb + Delta T
Illustration 6.8 Delta T Control
Open Loop/External Speed Control
In external speed control, the fan speed is set externally
from the OEM controller through the Modbus. The speed
can be overruled by the fan protection functions like min
and max condensing pressure derating, see Illustration 6.9.
To set the fan speed control in to external speed control:
Set THERMO_IN_FAN_MODE = 2
The external speed % is set in the
THERMO_IN_FAN_EXTERNAL_SPEED_PCT register.
Fan
External
FanMotor
speed setpoint
Protection
Illustration 6.9 Open Loop/External Speed Control
Bypass fan speed control
In Bypass speed control, the fan speed is set externally
from the OEM controller through the Modbus. In the
bypass mode the external speed is bypassing the fan
®
VLT Inverter Scroll CDS 801 Operating Instructions
P 2 T Tc set
Σ
Tc
Σ PI
Tc
Condensing
c
P
Unit
®
MG10V402 - VLT is a registered Danfoss trademark
FanMotor
PI
P 2 T
FanMotor
P 2 T
protection functions, and will never be overruled by
functions like min and max condensing pressure derating,
see Illustration 6.10. To set the fan speed control in to
bypass:
Set THERMO_IN_FAN_MODE = 3
The external speed % is set in the
THERMO_IN_FAN_EXTERNAL_SPEED_PCT register.
External
FanMotor
speed command
Illustration 6.10 Bypass Fan Speed Control
Condensing
Unit
Pc
Condensing
Unit
Pc
Condensing
Pc
Unit
37
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