Daikin RDT Installation And Maintenance Manual page 82

Optional Low Ambient Compressor Operation
Fixed Speed Scroll Compressors
Daikin's head pressure control operates in conjunction with
FanTrol by modulating the motor speed of the last condenser
fan of each refrigeration circuit in response to condenser
pressure. By varying the speed of the last condenser fan of
each refrigeration circuit, the VFD option allows mechanical
cooling operation in ambient temperatures down to 0°F (–18°
C). The VFD option senses refrigerant head pressure and
varies the fan speed accordingly. When the pressure rises, the
SpeedTrol increases the fan speed; when the pressure falls,
SpeedTrol decreases the fan speed.
The VFD throttling range is 250 to 400 psig, fixed. The VFD
fan motor is a three-phase motor, identical to the unit voltage
(208 V to 575 V) and is controlled by a variable frequency drive
(Figure 80). The variable frequency drive receives a signal
from a pressure transducer and varies the condenser fan
speed accordingly.
The pressure transducer is calibrated to provide a 1.0 to 5.0 V
(dc) signal with a 8 to 30 V (dc) input, starting at 1.0 V (dc) @
250 psig and up to 5.0 V (dc) @ 400 psig. In order to maintain
an acceptable condensing pressure, the VFD will modulate
the motor down to a minimum of 23 Hz, and will not allow
operation below this frequency level. At, or above 400 psig, the
VFD will operate the motor at 60 Hz. The control band between
the two frequencies (23 Hz and 60 Hz) is a linear relationship
with the condensing pressure as shown in
The VFDs and pressure transducers are located in the control
box mounted in the condensing section. Each refrigerant circuit
is independent and has its own respective VFD and pressure
transducer. The speedtrol option operates independently of the
main unit controller. It is required for variable speed inverter
compressors at 0°F ambient temperatures
IM 893-10 • ROOFPAK SINGLEZONE UNITS
Figure 80: R-410A Speedtrol
Figure 81: Speedtrol Operating Characteristics (for Fixed
Speed Compressor Unit)
(Figure 80).
82
AFD11
PB
F11A
L1 L1
Variable
L2 F11B
L2
Frequency
L3 F11C L3
Pressure
Transducer
60 Hz
23 Hz
250 psig
Condensing Pressure
u o
nIT PTIons
R11
P24 F Cndr Mtr #11
T1
T2
Mtr
Drive
T3
V1A OC
400 psig
(83°) (116°)
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