Specifications
60
Confirm that the following parameters in the VFD_CONF
screen match the values on the Machine Electrical Data Name-
plate (see Fig. 37):
• Motor Nameplate Voltage — Voltage required to run at
motor rating.
• Compressor 100% Speed — Compressor speed required to
run at chiller design point.
• Rated Line Voltage — Nominal line voltage selected for the
job site.
• Rated Line Amps — Line current required for the chiller to
run at the design point.
• Rated Line Kilowatts — Line power required for the chiller
to run at the design point.
• Motor Rated Load kW — Power consumed by the motor
when running at the chiller design point.
• Motor Rated Load Amps — Motor current required for the
chiller to run at the design point.
• Motor Nameplate Amps — Motor nameplate full load
amps.
• Motor Nameplate RPM — Rated speed of the motor
when running at motor nameplate rated frequency, rated
current, and rated voltage.
• Motor Nameplate kW — Motor nameplate rated power.
• Inverter PWM Frequency — Sets the carrier frequency
for the pulse width modulation output.
NOTE: Other parameters on these screens are normally left at
the default settings; however, they may be changed by the
operator as required. The voltage and current imbalance level
and imbalance persistence time on the VFD_CONF table can
be adjusted to increase or decrease the sensitivity of these fault
conditions. Increasing time or persistence decreases sensitivity.
Decreasing time or persistence increases sensitivity to the fault
condition.
Modify Minimum and Maximum Load Points (HGBP
DELTA T1/ HGBP DELTA P1, HGBP DELTA T2/ HGBP
DELTA P2) If Necessary — The default settings of the stall
prevention parameters in the OPTIONS screen are set so the
optional HGBP will not be energized during normal operating
conditions. In addition to stall prevention, hot gas bypass may
be useful for preventing excessive recycle restarts and main-
taining temperature control in response to rapid load changes at
low compressor speed. The chiller needs only to close the
optional hot gas bypass valve to increase capacity when the
chiller is running at low load with hot gas bypass active. It
takes a few minutes for the chiller to start if it has shut down in
recycle restart mode.
When HGBP option is set to 1, hot gas bypass operation can
be adjusted for minimum chiller load and lift control. The
HGBP DELTA T1/HGBP DELTA P1, HGBP DELTA T2/
HGBP DELTA P2 parameters in the OPTIONS screen deter-
mine when the optional hot gas bypass valve will open and
close. These points should be set based on individual chiller
operating conditions.
An example of such a configuration is shown below.
Refrigerant: HFC-134a
Estimated Minimum Load Conditions:
44 F (6.7 C) LCL
45.5 F (7.5 C) ECL
43 F (6.1 C) Suction Temperature
70 F (21.1 C) Condensing Temperature
Estimated Maximum Load Conditions:
44 F (6.7 C) LCL
54 F (12.2 C) ECL
42 F (5.6 C) Suction Temperature
98 F (36.7 C) Condensing Temperature
Calculate Maximum Load
— To calculate the minimum load
points, use data from the sales requisition or estimate the
chilled liquid delta T based on a percentage of full load where
the HGBP should be energized. The minimum condensing
pressure can be based on the entering condenser liquid temper-
ature available at minimum load. Use the proper saturated pres-
sure and temperature for R-134a.
Suction Temperature:
43 F (6.1 C) = 38 psig (262 kPa) saturated
refrigerant pressure (R-134a)
Condensing Temperature:
70 F (21.1 C) = 71 psig (490 kPa) saturated
refrigerant pressure (R-134a)
Minimum Load HGBP DELTA T1 (at 15% load):
0.15 X (54-44) = 1.5º F (0.15 X (12.2 – 6.7) = 0.8º C
Minimum Load HGBP DELTA P1:
71 – 38 = 33 psid (490 – 262 = 228 kPad)
Determine HGBP DELTA T2/HGBP DELTA P1:
Set HGBP DELTA T2 equal to 0.1º F larger than HGBP
DELTA T1:
HGBP DELTA T2 = HGBP DELTA T1 + 0.1 = 1.6º F
(0.8 + 0.06 = 0.9º C)
Set HGBP DELTA P2 to a large value to create a steep slope
(see Fig. 22 and 23) HGBP DELTA P2 = 200 psid (1379 kPa).
If the hot gas bypass is energized too soon or too late:
If variable evaporator flow is applied, changes to
DELTA T1 proportional to the reduction in evaporator liquid
flow rate are required.
The differential pressure (P) and temperature (T) can be
monitored during chiller operation by viewing ACTIVE
DELTA P and ACTIVE DELTA T (HEAT_EX screen). Com-
paring HGBP DELTA T to ACTIVE DELTA T will determine
when the HGBP valve will open. The smaller the difference
between the HGBP DELTA T and the ACTIVE DELTA T
values, the closer to stall prevention or the point at which the
HGBP will open.
If the ACTIVE DELTA T is less than the HGBP DELTA T,
the HGBP valve will be activated. The HGBP will be deacti-
vated once the ACTIVE DELTA T is greater than the HGBP
DELTA T plus the HGBP DEADBAND if the ACTIVE DELTA
P is less than HGBP DELTA P1.
When the HGBP option is set to 2, HGBP ON DELTA T
should be based on the estimated minimum load conditions as
was HGBP DELTA T1 in the example above. HGBP OFF
DELTA T functions similar to a deadband above the tempera-
ture entered in HGBP ON DELTA T as shown in Fig. 23.
MODIFY EQUIPMENT CONFIGURATION IF NECES-
SARY — The EQUIPMENT SERVICE table has screens to
select, view, or modify parameters. Carrier’s certified drawings
have the configuration values required for the jobsite. Modify
these values only if requested.
SERVICE Screen Modifications
— Change the values on
these screens according to specific job data. See the certified
drawings for the correct values. Modifications can include:
• Chilled liquid reset
• Entering chilled liquid control (Enable/Disable)
• 4 to 20 mA demand limit
• Auto restart option (Enable/Disable)
• Remote contact option (Enable/Disable)
Owner-Modified CCN Tables
— The following EQUIP-
MENT CONFIGURATION screens are described for reference
only.
HGBP ENERGIZED
TOO SOON
HGBP ENERGIZED
TOO LATE
Decrease HGBP DELTA T1
and HGBP DELTA T2 by
0.5° F (0.3° C)
Increase HGBP DETLA T1
and HGBP DELTA T2 by
0.5° F (0.3° C)