IM 893-10 • ROOFPAK SINGLEZONE UNITS 94 www.DaikinApplied.com
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nIT
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PTIons
VFD Compressor Operation
When a RTU is equipped with the VFD compressor option
there are two refrigeration circuits, one VFD controlled
compressor with up to 3 fixed speed compressors depending
on unit model. The VFD compressor must always be the “lead”
circuit or first one on and last one off.
VFD compressor modulation is controlled by an analog signal
(0 – 10 Vdc) from the unit controller. Refer to
. The
minimum VFD compressor speed is 25 rps (1500 rpm) and
the maximum VFD compressor speed is 100 rps (6000 rpm),
but the minimum and maximum limits may vary depending on
operating conditions and unit model size.
The VFD compressor is a 4 pole motor design that operates off
a frequency signal from the VFD between 50Hz and 200Hz.
At Start-up the VFD compressor will automatically ramp up to
50 rps for first 10 seconds for lubrication requirements.
Refer to
on condenser fan/head pressure regulation
with VFD compressors.
Crankcase heating for VFD Compressor models VZH-088
& VZH-117 is performed by the VFD via DC-holding current
through the motor windings. The VZH-170 compressor
requires the use of an external banded heater.
VFD compressor modulation is additionally monitored and
adjusted in order to maintain operation within the approved
compressor operating envelope.
If the VFD compressor were to become inoperative, the unit
can to continue to operate on the remaining fixed speed
compressors until the unit can be serviced.
When the VFD compressor is at its maximum speed and more
capacity is required, the available fixed compressor with the
fewest run hour total is started while the VFD compressor
is reduced to minimum speed at which point it resumes
modulating to maintain the discharge temperature. When the
VFD compressor is at its minimum speed and less capacity is
required the fixed compressor with the highest run hour total is
stopped while the VFD compressor is increased to maximum
speed at which point it resumes modulating to maintain
discharge temperature.
Table 20: VFD Compressor Modulation Ranges
RPS/RDT / Unit
Model
VFD Modulation Range
LoOilBoostRps/
LoOilBoostV*
HiOilBoostRps/
HiOilBoostV*
VFD Min Rps/
VFD Min V
VFD Max rps
VFD and Fixed Comp(s) On
VFD Comp Only
VFDMaxRps/
VFDMaxV
1 Fixed On
2 Fixed On
3 Fixed On
VFD1MaxRps/
VFD1MaxV
VFD2MaxRps/
VFD2MaxV
VFD3MaxRps/
VFD3MaxV
016
25 rps / 0 Vdc
55 rps / 4.0 V
NA
—
100 rps / 10.0 V
70 rps / 6.0 V
100 rps / 10.0 V
021
25 rps / 0 Vdc
70 rps / 6.0 V
NA
NA
100 rps / 10.0 V
70 rps / 6.0 V
100 rps / 10.0 V
026
25 rps / 0 Vdc
85 rps / 8.0 V
NA
NA
100 rps / 10.0 V
70 rps / 6.0 V
100 rps / 10.0 V
031
25 rps / 0 Vdc
70 rps / 6.0 V
NA
NA
100 rps / 10.0 V
70 rps / 6.0 V
100 rps / 10.0 V
042
25 rps / 0 Vdc
100 rps / 10.0 V
95 rps / 9.33 V
NA
100 rps / 10.0 V
70 rps / 6.0 V
100 rps / 10.0 V
045
25 rps / 0 Vdc
75 rps / 6.7 V
75 rps / 6.7 V
NA
75 rps / 6.7 V
70 rps / 6.0 V
75 rps / 6.7 V
051
25 rps / 0 Vdc
85 rps / 8.0 V
85 rps / 8.0 V
NA
85 rps / 8.0 V
70 rps / 6.0 V
85 rps / 8.0 V
063
25 rps / 0 Vdc
95 rps / 9.33 V
95 rps / 9.33 V
NA
95 rps / 9.33 V
70 rps / 6.0 V
95 rps / 9.33 V
074
25 rps / 0 Vdc
70 rps / 6.0 V
50 rps / 3.3 V
100 rps / 10.0 V
100 rps / 10.0 V
70 rps / 6.0 V
100 rps / 10.0 V
* High and Low Oil Boost are explained on
Figure 101: VFD Compressor Modulation Signal
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0
1
2
3
4
5
6
7
8
9
10
C
om
pr
ess
or
S
pe
ed
(rp
s)
Voltage (Vdc)
VFD Compressor Analog Modulation Signal
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