Specifications

79
To avoid unnecessary surge prevention, add about 10 psid
(70 kPad) to P2 from these conditions:
T4 = 10º F (5.5º C)
P4 = 93 psid (642 kPad)
Hand Calculate Minimum Load
— To calculate the mini-
mum load conditions, estimate the temperature difference the
cooler will have at 10% load, then estimate what the suction
and condensing temperatures will be at this point. Use the
proper saturated pressure and temperature for the particular re-
frigerant used.
Suction Temperature:
43 F (6.1 C) = 38 psig (262 kPa) saturated
refrigerant pressure (HFC-134a)
Condensing Temperature:
70 F (21.1 C) = 71 psig (490 kPa) saturated
refrigerant pressure (HFC-134a)
Minimum Load T1 (at 20% Load): 2 F (1.1 C)
Minimum Load P1:
71 – 38 = 33 psid (490 – 262 = 228 kPad)
Again, to avoid unnecessary surge prevention, add 20 psid
(140 kPad) at P1 from these conditions:
T1 = 2 F (–16.7 C)
P1 = 53 psid (365.3 kPad)
The Options screen can be configured with up to four dis-
tinct pairs of HGBP/Surge Prevention points to represent the
surge line of the compressor. The version of Chiller Builder
used to select the chiller and the ICVC software version at the
time the chiller was manufactured will determine if either two
pairs of points or four pairs of points were generated. Either
two pairs of four pairs of points will also be displayed on a la-
bel on the inside of the control panel.
If software requires four points of HGBP surge prevention
and only 2 points of data are available — Enter the MIN
LOAD POINT (T1/P1) and the FULL LOAD POINT (T2/P2)
from the Chiller Builder Selection in the spaces provided in the
MIN LOAD POINT (T1/P1) and FULL LOAD POINT (T4/
P4) section of the OPTIONS screen. Also, enter the FULL
LOAD POINT (T2/P2) data from ChillerBuilder in the LOW
LOAD POINT (T2/P2) section and the MID LOAD POINT
(T3/P3) section of the OPTIONS screen.
If surge prevention occurs too soon or too late:
If software requires four points of HGBP surge prevention
and 4 points of data are available — Enter the MIN LOAD
POINT(T1/P1), LOW LOAD POINT (T2/P2), MID LOAD
POINT (T3/P3) and the FULL LOAD POINT (T4/P4) from
the Chiller Builder Selection in the spaces provided in the OP-
TIONS screen.
If surge prevention occurs too soon or too late:
If surge prevention occurs too soon or too late at a load that
falls between two SURGE/HGBP DELTA T points it is accept-
able to change the two adjacent SURGE/HGBP DELTA P
points simultaneously to keep the slope of the modified surge
prevention curve nearer to the original curve.
This is illustrated in Fig. 36. If the adjustment is needed be-
tween (∆T1, ∆P1) and (∆T2, ∆P2) adjust both P1 and P2 by the
same amount. Do the same between any two points.
HAND CALCULATE VARIABLE PRIMARY FLOW
(VPF) SURGE PREVENTION CONFIGURATIONS
(Machines with S/N 1410Qxxxxx and Larger and Machines
with Version 9 Software or Higher) — The configurations en-
tered determine the Surge Prevention line that the controls use
to raise the speed of the VFD if the compressor operating point
nears this line.
Calculate ΔP maximum and ΔP minimum using 2 point
method in the preceding section. If the original selection con-
figuration points are available, use ΔP1 and ΔP4 from that se-
lection as ΔP maximum and ΔP minimum. If the original selec-
tion configuration was for a 2 point surge line, use ΔP1 and
ΔP2.
Use the default values for the following configurations:
• Surge / HGBP IGV min. = 5.0
• Surge / HGBP IGV max = 100.0
• Surge Line Shape Factor = -0.040
• Surge Line Speed Factor = 1.85
• Surge Line High Offset = 1.0
• Surge/ HGBP Deadband = 1
Calculate Surge/ HGBP Delta Tsmin
— Convert design suc-
tion temp to pressure using an R-134a pressure/temperature
chart.
Min. Cond. Pressure = (suction pressure) + (ΔP minimum)
Convert Min. Cond. Pressure to Min. Cond. Temperature
using a saturation pressure/temperature chart for R-134a.
Surge / HGBP Tsmin = (Min. Cond. Temp.) – (design suc-
tion temperature)
Calculate Surge/ HGBP Delta Tsmax
Max. Cond. Pressure = (suction pressure) + (ΔP maximum)
Convert Max. Cond. Pressure to Max. Cond. Temperature
using a saturation pressure/temperature chart for R-134a.
Surge / HGBP Tsmax = (Max. Cond. Temp) – (design suc-
tion temperature)
VPF Surge Prevention Configurations are defined as fol-
lows:
• Surge/HGBP Delta Tsmin is the minimum difference
between cooler and condenser saturation temperatures.
(See Fig. 37.)
• Surge/HGBP IGVmin is the lowest position of the guide
vanes that affects Surge prevention. This is not likely to
require adjustment at the jobsite other than to ensure that
it matches the value supplied with the machine selection.
These values produce the minimum load point of the Surge
Prevention line:
• Surge/HGBP Delta Tsmax is the maximum difference
between cooler and condenser saturation temperatures.
(See Fig. 38.)
• Surge/HGBP IGVmax is the highest position of the
guide vanes that affects Surge prevention. This is not
likely to require adjustment at the jobsite other than to
ensure that it matches the value supplied with the
machine selection.
NOTE: The preceding two values produce the full load point
of the surge prevention line.
• Surge Line Shape Factor determines the curvature of the
line mainly in the low load zone. (See Fig. 39.)
LOAD
SURGE PREVENTION
OCCURS TOO SOON
SURGE PREVENTION
OCCURS TOO LATE
At Low Loads (<50%)
Increase SURGE/HGBP
DELTA P1 by 2 PSID
(14 kPaD)
Decrease SURGE/
HGBP DELTA P1 by
2 PSID (14 kPaD)
At High Loads (>50%)
Increase SURGE/HGBP
DELTA P2, SURGE/
HGBP DELTA P3 and
SURGE/HGBP DELTA
P4 by 2 PSID (14 kPaD)
Decrease SURGE/
HGBP DELTA P2,
SURGE/HGBP DELTA
P3 and SURGE/HGBP
DELTA P4 by 2 PSID
(14 kPaD)
LOAD
SURGE PREVENTION
OCCURS TOO SOON
SURGE PREVENTION
OCCURS TOO LATE
Near Min Load Delta T1
Increase SURGE/HGBP
DELTA P1 by 2 PSID
(14 kPaD)
Decrease SURGE/
HGBP DELTA P1 by
2 PSID (14 kPaD)
Near Low Load Delta T2
Increase SURGE/HGBP
DELTA P2 by 2 PSID
(14 kPaD)
Decrease SURGE/
HGBP DELTA P2 by
2 PSID (14 kPaD)
Near Mid Load Delta T3
Increase SURGE/HGBP
DELTA P3 by 2 PSID
(14 kPaD)
Decrease SURGE/
HGBP DELTA P3 by
2 PSID (14 kPaD)
Near Full Load Delta T4
Increase SURGE/HGBP
DELTA P4 by 2 PSID
(14 kPaD)
Decrease SURGE/
HGBP DELTA P4 by
2 PSID (14 kPaD)