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35
30
25
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15
10
5
0
0
10
20
30
40
50
GV_POS
Fig. 32 — Effect of SURGE LINE SPEED FACTOR
on Surge Prevention
Note the following parameters from HMI when maximum AC-
TUAL LINE CURRENT is achieved:
•
EVAPORATOR REFRIGERANT TEMP
•
EVAPORATOR PRESSURE
•
CONDENSER REFRIG TEMP
•
CONDENSER PRESSURE
•
ACTUAL GUIDE VANE POSITION
•
ACTUAL LINE CURRENT
The ACTIVE DELTA TSAT and the CALC REF DELTA TSAT
can be monitored on the MAINTENANCE MENU
CORRECTION screen. When ACTUAL DELTA TSAT exceeds
CALC REF DELTA TSAT + ENVELOPE LINE OFFSET surge
prevention will occur.
If ACTUAL GUIDE VANE POSITION is less than 30%, then in-
crease SURGE DELTA TSMIN in steps of 2ºF (1.2ºC) until one
of the three conditions listed above no longer applies. Do not
change SURGE DELTA TSMAX.
If ACTUAL GUIDE VANE POSITION is greater than 60%, then
increase SURGE DELTA TSMAX in steps of 2ºF (1.2ºC) 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 DELTA TSMIN in steps of 2ºF (1.2ºC).
Alternatively if Pressure Ratio Method is used for surge
protection increase PR at Minimum Opening.
2.
Increase SURGE DELTA TSMAX in steps of 2ºF (1.2ºC).
Alternatively if Pressure Ratio Method is used for surge
protection increase PR at Full Load Opening.
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. Likewise,
DELTA TSMAX rarely requires more than a 2ºF (1.2ºC) increase.
Speed Factor
=1.60
Speed Factor
=1.85
Speed Factor
=2.00
a19-1962
60
70
80
90
100
110
SURGE
If surge is encountered then the controls surge prevention algo-
rithm surge line is probably too optimistic or high. Note following
parameters from HMI 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 DELTA TSMIN or PR at Minimum Opening.
Monitor chiller for surge.
2.
If ACTUAL GUIDE VANE POSITION is still less than
30% and Step 1 failed, increase the value of SURGE LINE
SHAPE FACTOR in steps of 0.01 up to 2 times. For
example, if surge is encountered when shape factor is –
0.06, increase the SURGE LINE SHAPE FACTOR to –
0.05. If this does not solve the problem, go to Step 5, even
if ACTUAL GUIDE VANE POSITION is less than 30%.
3.
Do not change SURGE LINE SHAPE FACTOR from the
value selected by Chiller Builder (ECAT). Decrease
SURGE DELTA TSMAX or PR at Full Load Opening.
Monitor chiller for surge.
4.
If ACTUAL GUIDE VANE POSITION is greater than
60% and Step 3 failed to eliminate surge, then set SURGE
DELTA TSMAX or PR at Full Load Opening to below the
value specified by Chiller Builder (ECAT). Increase the
value of the SURGE LINE SHAPE FACTOR in steps of
0.01 up to 2 times. For example, if surge is encountered
when the SURGE LINE SHAPE FACTOR is –0.06,
increase the SURGE LINE SHAPE FACTOR to –0.05. If
this does not solve the problem, go to Step 5, even if
ACTUAL GUIDE VANE POSITION is greater than 60%.
5.
If ACTUAL GUIDE VANE POSITION is greater than 30%
but less than 60% or if Step 2 failed (with ACTUAL GUIDE
VANE POSITION less than 30) or if Step 4 failed (with
ACTUAL GUIDE VANE POSITION greater than 60), then
perform this step. Do not change SURGE LINE SHAPE
FACTOR from the value specified by Chiller Builder
(ECAT). Reset SURGE DELTA TSMIN or PR at Minimum
Opening and SURGE DELTA TSMAX, or PR at Full Load
Opening to the value specified by Chiller Builder (ECAT).
Decrease both SURGE DELTA TSMIN / PR at Minimum
Opening and SURGE DELTA TSMAX / PR at Full Load
Opening with equal steps. Monitor chiller for surge.
If the chiller is equipped with a VFD and the drive does not slow
down adequately at part load, then the machine is likely operat-
ing at a point above the configured "software" surge line and the
machine is in surge prevention mode. Check for a surge protec-
tion message on the HMI. If the unit is not in a surge protection
state, then the ENVELOPE SPEED FACTOR may need to be
increased (more aggressive surge line protection) in combination
with a decrease (less negative) in the SURGE LINE SHAPE
FACTOR. Units configured with Surge Line Configuration
0=PR (Pressure Ratio) can be similarly adjusted. In lieu of
changing Tsmax/Tsmin values, pressure ratios at Full/Minimum
Load are to be adjusted to obtain the same results.
NOTE: A good starting point if adjustments are needed with a
two stage compressor is a shape factor of 2.10 and a speed factor
of –0.045.
33
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