Specifications

80
• Surge Line Speed Factor determines how much the surge
line moves to accommodate lower compressor speed. As
compressor speed drops the ΔT values on the surge pre-
vention line decrease. Increasing the Speed Factor causes
Surge Prevention to activate sooner as the compressor
speed drops. (See Fig. 40.)
• Surge Line High Offset determines the ΔT increase
beyond the surge prevention line where the high stage of
Surge Prevention takes effect. The high stage produces
larger RPM increase steps. This is not likely to require
adjustment at the jobsite other than to ensure that it
matches the value supplied with the machine selection
• Surge/HGBP Deadband controls the amount the ACTIVE
DELTA TSAT must drop below the Surge Prevention to
de-activate Surge Prevention.
Fine Tuning VPF Surge Prevention
— Figures 37-40 show
how the parameters defined below will affect the configured
surge line.
NOTE: Before tuning surge prevention check for VFD speed
limitation or capacity overrides. If the source of low capacity is
found in one of these places, do not proceed with an attempt to
tune the Surge Prevention configurations.
If capacity is not reached
and
1. ACTUAL GUIDE VANE POSITION < GUIDE VANE
TRAVEL RANGE
and
2. SURGE PREVENTION ACTIVE = YES
and
3. PERCENT LINE CURRENT < 100%
then the surge line is probably too conservative.
Note the following parameters from ICVC when maximum
AVERAGE LINE CURRENT achieved:
• EVAPORATOR REFRIGERANT TEMP
• EVAPORATOR PRESSURE
• CONDENSER REFRIG TEMP
• CONDENSER PRESSURE
• ACTUAL GUIDE VANE POSITION
• AVERAGE LINE CURRENT
The ACTIVE DELTA Tsat and the SURGE LINE DELTA
TSAT can be monitored on the VPF_STAT screen. When
DELTA TSAT exceeds SURGE LINE DELTA TSAT surge
prevention will occur.
If ACTUAL GUIDE VANE POSITION is less than 30%,
then increase SURGE/HGBP DELTA TSMIN in steps of 2º F
until one of the three conditions listed above no longer applies.
Do not change SURGE/HGBP DELTA TSMAX.
If ACTUAL GUIDE VANE POSITION is greater than
60%, then increase SURGE/HGBP DELTA TSMAX in steps
of 2º F until cooling capacity is reached or one of conditions
listed above no longer applies. Do not change SURGE/HGBP
DELTA TSMIN.
If ACTUAL GUIDE VANE POSITION is more than 30%
AND less than 60%, then:
1. Increase SURGE/HGBP DELTA TSMIN in steps of 2º F.
2. Increase SURGE/HGBP DELTA TSMAX in steps of
2º F.
3. Repeat Steps 1 and 2 until one of the conditions listed
above no longer applies.
NOTE: DELTA TSMIN should seldom need to be increased
more than 10 degrees above the selection program value. Like-
wise, DELTA TSMAX rarely requires more than a 2 degree
increase.
If surge is encountered then the surge line is probably too
optimistic or high. Note following parameters from ICVC at
surge:
• EVAPORATOR REFRIGERANT TEMP
• EVAPORATOR PRESSURE
• CONDENSER REFRIG TEMP
• CONDENSER PRESSURE
• ACTUAL GUIDE VANE POSITION
• AVERAGE LINE CURRENT
If ACTUAL GUIDE VANE POSITION is less than 30%,
go to Step 1. If ACTUAL GUIDE VANE POSITION is greater
than 60%, then go to Step 3.
1. Do not change SURGE LINE SHAPE FACTOR from
the value selected by Chiller Builder (ECAT). Decrease
SURGE/HGBP DELTA TSMIN in 1° F steps up to 5
times. Monitor chiller for surge.
0
5
10
15
20
25
30
35
40
0 102030405060708090100110
Tsmin=30
Tsmin=40
Tsmin=50
GV_POS
Delta Tsat
Fig. 37 — Effect of SURGE/HGBP DELTA TSMIN
on Surge Prevention
a19-1959
0
5
10
15
20
25
30
35
40
45
0 102030405060708090100110
Tsmax=60
Tsmax=70
Tsmax=80
GV_POS
Delta Tsat
Fig. 38 — Effect of SURGE/HGBP DELTA TSMAX
on Surge Prevention
a19-1960