Specifications
41
ACTIVE DELTA T (actual temperature difference between the
LEAVING CHILLED LIQUID and ENTERING CHILLED
LIQUID) is on the left side of the line plotted in Fig. 22A and
22B, the algorithm will energize the hot gas bypass valve to
falsely load the chiller. If the ACTIVE DELTA T falls to the
right side of the line plotted in Fig 22A and 22B by more than
the HGBP DEADBAND, the hot gas bypass valve is de-
energized. The HGBP valve is also deenergized if the ACTIVE
DELTA P (actual difference between CONDENSER PRES-
SURE and EVAPORATOR PRESSURE) falls to below HGBP
DELTA P1. Instructions to configure the MIN LOAD
POINT(T1/P1) and FULL LOAD POINT(T2/P2) are on
page 60.
When the HGBP OPTION = 2, the option energizes the Hot
Gas Bypass relay solely based on the ACTIVE DELTA T
(actual temperature difference between the LEAVING
CHILLED LIQUID and ENTERING CHILLED LIQUID).
Evaluation of the ACTIVE DELTA T begins at the completion
of ramp loading. The hot gas bypass valve is energized if the
ACTIVE DELTA T is less than the HGBP ON DELTA T. The
hot gas bypass relay will be turned off when the ACTIVE
DELTA T is greater than or equal to the sum of HGBP ON
DELTA T plus HGBP OFF DELTA T. See Fig. 23.
Head Pressure Output Reference (See
Fig. 24) —
The PIC III control outputs a 4 to 20 mA signal
for the configurable Delta P (CONDENSER PRESSURE –
EVAPORATOR PRESSURE) reference curve shown in
Fig. 24. The DELTA P AT 100% (default at 50 psi). DELTA P
AT 0% (default at 25 psi) and MINIMUM OUTPUT are
configurable in the EQUIPMENT SERVICE-OPTIONS table.
When configuring this output, ensure that minimum require-
ments for proper condenser FLASC orifice performance
are maintained. The 4 to 20 mA output from VFD TB1
terminals 17 and 18 can be used as a reference to control a
tower bypass valve, tower speed control, or condenser pump
speed control. The head pressure output is designed for use
with non-grounded controllers with a maximum input
impedence of 500 ohms.
NOTE: It is up to the site design engineering agent to integrate
this analog output with any external system device(s) to pro-
duce the desired effect. Carrier does not make any claim that
this output is directly usable to control any specific piece of
equipment (that is, without further control elements or signal
conditioning), although it may be.
The head pressure reference output will be on whenever the
condenser pump is operating. It may also be manually operated
in CONTROLS TEST. When the head pressure differential is
less than the value entered for DELTA P AT 0%, the output will
be maintained at 4 mA. The output is 2 mA when the chiller is
not running.
LEGEND
P—Condenser Pressure-
Cooler Pressure
T—ECL-LCL
ECL — Entering Chilled
Liquid Temperature
LCL — Leaving Chilled
Liquid Temperature
HGBP — Hot Gas Bypass
Fig. 22A — 23XRV Hot Gas Bypass
Option 1 (English)
DEFAULT VALUES:
POINT HFC-134a
T
1
1.5
P
1
150
T
2
4
P
2
200
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Fig. 22B — 23XRV Hot Gas Bypass Option 1 (SI)
LEGEND
P—Condenser Pressure-
Cooler Pressure
T—ECL-LCL
ECL — Entering Chilled
Liquid Temperature
LCL — Leaving Chilled
Liquid Temperature
HGBP — Hot Gas Bypass
DEFAULT VALUES:
POINT HFC-134a
T
1
0.8
P
1
1034
T
2
2.2
P
2
1379
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HGBP ON
DELTA T
HGBP OFF
DELTA T
HGBP
Off
HGBP
On
HGBP Off As ACTIVE
DELTA T Decreases
HGBP On As ACTIVE
DELTA T Increases
ΔT
ΔP
Fig. 23 — Hot Gas Bypass Option 2
LEGEND
P—Condenser Pressure –
Evaporator Pressure
T—Entering Chilled Liquid –
Leaving Chilled Liquid
HGBP — Hot Gas Bypass
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NON-ZERO
EXAMPLE
OF
MINIMUM HEAD
PRESSURE REFERENCE
OUTPUT
DELTA P
AT 100%
DELTA P
AT 0%
DELTA P
0 mA 2 mA
4 mA
(0%)
20 mA
(100%)
4 T0 20 mA OUTPUT
Fig. 24 — Head Pressure Output
Reference Control
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