211
FORM 160.54-M1
ISSUE DATE: 10/25/2019
JOHNSON CONTROLS
JCI COMPANY CONFIDENTIAL
23
SECTION 23 - HOT GAS BYPASS
With the optional hot gas bypass feature, the control
center modulates a valve located in the hot gas bypass
connection between the condenser and the evaporator
to control the flow of gas to the evaporator. The valve
is modulated in response to load and surging condi-
tions.
A hot gas bypass Screen, accessed from the COM-
PRESSOR Screen displays all the applicable param-
eters and allows a Service technician to program the
applicable s and manually control the Hot gas valve. If
the chiller is equipped with the optional Hot gas bypass
Control, it must be enabled from the OPERATIONS
Screen using a procedure in
CALIBRATION, SERVICE SETPOINTS, AND RESET
of this manual. If disabled, the valve is
driven to the fully closed position.
The microboard controls the hot gas valve by sending
a positioning command over the COM3 RS-485 serial
communications link to the optional I/O Board that is
mounted inside the Control Center. This board converts
the command into the appropriate signal to control the
valve as explained later in this section. The valve posi-
tion is displayed on the Hot gas bypass Screen as 0%
(closed) to 100% (fully open).
A potentiometer mounted on the Pre-rotation Vanes
provides PRV position for this feature, as explained
later in this section). It is displayed on the hot gas by-
pass screen as 0% (closed) to 100% (fully open).
The evaporator and condenser pressure transducers
provide these pressure values to the microboard. The
microboard uses these values to calculate the Delta P/P
parameter as follows:
Condenser Pressure - Evaporator Pressure
Evaporator Pressure
Although this parameter is not used in the Hot gas Con-
trol, it represents compressor “Head” and is displayed
on the Hot gas bypass Screen for reference only. These
pressures are also used to detect when a surge occurs.
The hot gas valve is modulated in response to certain
load conditions and surge events as described below
under Operations. The load conditions are represent-
ed by the value “Temperature Differential (Leaving
Chilled Liquid Temperature minus setpoint)” on the
hot gas screen. The surge events it reacts to are de-
tected by the surge protection feature (See
). For reference, surge de-
tect indicators and the total surge count are displayed
on the Hot gas Screen as follows.
Each time a surge is detected, the Surge Avoidance
Surge Detected indicator illuminates momentarily (if
equipped with a VSD or MV VSD, this feature only
detects surges while the drive is running at maxi-
mum frequency) (If equipped with software version
C.OPT.01.18.307 or earlier, the indicator is labeled
Surge Detected and it illuminates whenever a surge
is detected, regardless of VSD operating frequency.
If equipped with a VSD (in Modbus Protocol config-
uration) or a MV VSD, the ACC Surge Detected in-
dicator illuminates momentarily when a surge is de-
tected by the ACC function in the microboard, while
the drive is running at less than maximum frequency.
Software version C.OPT.01.18.307 or earlier does not
have this indicator. The Surge Avoidance Surge Count
(displayed as “Total Surge Count” in software version
C.OPT.01.18.307 (and earlier)) is the total number
of surges detected by the Surge Protection feature (if
equipped with a VSD or MV VSD, this feature only
detects surges while the drive is running at maximum
frequency).
SETPOINTS
Hot gas bypass setpoints are as follows:
•
Surge Sensitivity
(0.3 to 1.3; default 0.3) – Deter-
mines the surge detection sensitivity. The smaller
the number, the greater the sensitivity. Program-
mable in 0.1 increments. This setpoint is pro-
grammed on the SURGE PROTECTION Screen
and is common to the Surge Protection feature.
•
Hold Period
(30 to 120 minutes; default 30) –
This is the period of time after no more surges are
detected that the Hot gas valve closing will begin.
It will be driven toward the closed position in in-
crements equal to the Close Percentage setpoint
at 10 minute intervals until fully closed. Program-
mable in 1 minute increments.
•
Close Percentage
(5 to 15%; default 5%) – This
is the incremental amount that the Hot gas valve
will be closed at 10 minute intervals after the Hold
Period has elapsed. See
Hold Period
above.
