JOHNSON CONTROLS
212
FORM 201.23-NM2
ISSUE DATE: 3/9/2015
SECTION 7 - OPERATION
MINIMUM VSD COMPRESSOR START / RUN
FREQUENCY
Minimum VSD Start Frequency
The Minimum VSD Compressor Start Frequency is
based on ambient temperature and determines the
frequency (speed) the compressor(s) is ramped to at
start. At higher ambients, higher speeds are needed
to provide adequate motor cooling. At low ambients,
higher motor speeds are needed to develop oil pressure
differential at start. The temperature ranges and the as-
sociated start frequency follows the guidelines below:
•
If the ambient temperature is 25°F or less, the
Minimum VSD Start Frequency will be 70 Hz.
•
If the ambient temperature is between 26 and 40
°F (-3 and 4°C), the Minimum VSD Start Fre-
quency is 60 HZ.
•
If the ambient temperature is between 41 and 110
°F (5 and 43°C), the Minimum VSD Start Fre-
quency will be 50 Hz.
•
If the ambient is between 110 and 125 °F (43 and
52°C), the Minimum VSD Start Frequency is
scaled according to the following formula:
(3 x Ambient Temperature) - 280°F.
The formula is also represented by the graph in
.
NOTE: The graph above also illustrates the scaled frequency:
FIGURE 51 -
MINIMUM VSD START FREQUENCY
LD10627
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
Ambient Temperature (°F)
Mi
ni
mu
m
VSD
F
re
que
ncy
(H
z)
•
Above 125°F, the minimum VSD Start Frequency
is 95 Hz.
Minimum VSD Run Frequency
The Minimum VSD Compressor Run Frequency is
based on ambient temperature and determines the
minimum frequency (speed) the compressor(s) is per-
mitted to run as the system unloads. At high ambients,
higher motor speeds are needed to cool the compressor
motor. The temperature ranges and the associated start
frequency follows the guidelines below:
•
If the ambient temperature is less than110°F, the
Minimum VSD Run Frequency will be 50 Hz.
NUMBER OF COMPS
TO START LOGIC
NUMBER OF COMPS TO
START
REDUCTION TABLE
4 COMPS -> 3 COMPS
3 COMPS -> 2 COMPS
2 COMPS -> 1 COMP
1 COMP -> 1 COMP
SET NUM COMPS
TO START = NUM
COMPS IN UNIT
LAST RUN TIME
< 5 MIN ?
YES
REDUCE NUM COMPS
TO START PER
REDUCTION TABLE
OFF TIME
< 5 MIN ?
YES
REDUCE NUM COMPS
TO START PER
REDUCTION TABLE
NO
CONTINUE
LCHLT RATE
< 3 °F/MIN AND
LCHLT < CR+5°F?
NO
YES
REDUCE NUM COMPS
TO START PER
REDUCTION TABLE
NO
FIGURE 50 -
NUMBER OF COMPRESSORS TO START
LD10626
Summary of Contents for YCIV0157
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