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Embedded Application Contro...
Ramp
6
6
Illustration 6.17 Start-up Sequence
When switching to and from Defrost mode, the start speed
hold time is disabled. The compressor then ramps up
continuously to the compressor speed setpoint and skips
the start speed hold time. This allows for a more efficient
defrosting.
6.3.5.2 Restart Timer
To increase compressor lifetime, there is a minimum time
between compressor starts. This restart time (at least 1
minute) is defined by
Restart time register: THERMO_SETUP_RESTART_TIME_SEC
When switching to and from Defrost mode, the restart
timer is disabled. This results in a quick switch in system
mode and allows for a more efficient defrosting of the
outdoor coil.
If the system mode is changed, or compressor is stopped
and started too frequently, the drive will stop and raise an
alarm. Only 6 compressor restarts within 600 s are allowed,
there after the system will stop and raise an alarm.
6.3.5.3 Compressor Safety Envelope
Given the allowed ranges of suction pressure and
condensing pressure, the compressor safety envelope
defines the speed range (min and max RPM) that the
compressor is allowed to run at, however limited by the
over all compressor speed range 900-4200 RPM, see
Illustration 6.18.
40
®
VLT
Inverter Scroll CDS 801 Operating Instructions
Start Speed
Time
Start speed
hold time
MG10V402 - VLT
Performer VSD Operating Envelope
160
150
140
130
120
110
100
90
80
70
60
50
40
30
900-4200 RPM
20
10
-30
-20
-10
Saturated evaporating temp. (° F)
Illustration 6.18 Compressor Safety Envelope
The compressor safety envelope takes precedence over
any requested compressor capacity and external speed
request. Crossing from one envelope to another will not
stop the drive if it is running at a low compressor speed.
Instead, the compressor speeds up to the minimum speed
of the newly entered envelope.
When operating in Defrost mode, the envelope limits are
extended to allow for a lower saturated condensing
temperature (> 20 °F), which can be necessary when
defrosting the outdoor coil. Because the envelope has an
extension for defrosting, there is also a maximum duration
of defrost allowed. The system can only operate for 1800 s
in Defrost mode. If the OEM controller does not terminate
the defrosting before the timer has elapsed, the system
stops and raises an alarm.
6.3.5.4 Oil Return
The scroll compressor needs oil to be protected against
wear. When running, oil leaves the compressor together
with the refrigerant. The rate of oil loss is estimated as a
function of compressor speed.
The oil return is executed if the speed stays below the oil
return speed for a time defined by
THERMO_SETUP_OIL_LOSS_TRIG_TIME_SEC. The oil return
sequence is defined by the oil return speed
THERMO_SETUP_OIL_RETURN_SPEED_HZ and the oil return
hold time THERMO_SETUP_OIL_RETURN_HOLD_TIME_SEC.
6.3.5.5 Derating
The purpose of the derating functions is to keep the
compressor and drive within the specified operating
conditions, while still providing cooling/heating.
®
is a registered Danfoss trademark
1300-4200 RPM
1100-4200 RPM
900-4200 RPM
900-4200 RPM
(defrost)
0
10
20
30
40
50
60
70
80
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