366
FORM 160.54-M1
ISSUE DATE: 10/25/2019
SECTION 36 - SOFTWARE ENHANCEMENTS
JCI COMPANY CONFIDENTIAL
JOHNSON CONTROLS
Head Pressure Control
YK chillers are capable of operation within a wide
range of condenser water temperatures. However, a
minimum condenser water temperature, as specified in
the engineering guide, is required to maintain sufficient
pressure differential (head) between the condenser and
evaporator for proper oil and refrigerant management
in the chiller.
Should colder condenser water temperatures be antici-
pated at the cooling source, a field mounted facility
control means may be provided to ensure adequate head
pressure exists. The preferred means would be a cool-
ing tower bypass circuit that maintains a constant flow
rate through the condenser, since this would maintain
adequate tube velocity in the condenser, while regulat-
ing the return cooling water to the condenser. However,
a two-way condenser water throttling valve, a variable
speed cooling tower pump, or tower fan control circuit
might also be employed.
The head pressure control function provides an ana-
log output control signal from the OptiView Control
Center that responds to the programmed head pres-
sure (condenser pressure minus evaporator pressure)
setpoint. The output is direct acting (as the head pres-
sure increases above the setpoint, the valve is driven
more open to provide less tower bypass or more flow
through the condenser).
If the chiller is equipped with HEAD PRESSURE
CONTROL, the feature must be enabled on the SETUP
screen using the head pressure control setpoint. Oth-
erwise it must be disabled. Once enabled, the HEAD
PRESSURE CONTROL screen is available from the
CONDENSER screen. All of the head pressure control
parameters are displayed on this screen. If heat recov-
ery is also enabled, the head pressure parameters ap-
pear on the HEAT RECOVERY screen (No separate
HEAD PRESSURE CONTROL screen is in this con-
figuration).
A complete explanation of this feature is contained in
Service Manual (Form 160.54-M1)
.
Quick Start Mode
The quick start feature is useful in data center and pro-
cess control applications where it is desirable to re-es-
tablish cooling as fast as possible after a shutdown or
power failure. This feature, when enabled, allows quick-
er starts and restarts than normal control, which is done
by reducing the time cycle for chiller restart and once
running, loading the chiller as fast as possible. After the
chiller is running, and has met a specified setpoint or a
specified period of time has elapsed, control returns to
normal.
To use this feature, the chiller must be equipped with
a VSD (in Modbus Protocol configuration) or a MV
VSD. The low inrush current of a VSD allows more
starts per hour and allows the chiller to start with a
more open vane position.
Although not required, the hot gas bypass option is rec-
ommended, as it will allow the chiller to startup more
smoothly with less chance of surging.
Quick Start has two different start modes:
•
Quick Restart –
When a chiller shuts down, if
certain conditions are met at the completion of
coastdown (and within 30 seconds thereafter), the
VSD is started immediately with no pre-lube. The
vanes are given a constant open pulse and after the
VSD achieves its start frequency, the speed ramp
rate is faster than with normal control.
•
Quick Normal Start –
If the conditions for a
quick restart are not met, the next time the chiller
is started, it has a pre-lube period just like a nor-
mal start, however the vanes will begin to open at
the beginning of pre-lube, instead of waiting un-
til system run. At the completion of pre-lube, the
VSD is started and after the VSD achieves its start
frequency, the speed ramp rate is faster than with
normal control.
To take full advantage of the quick start feature after a
power failure, the OptiView Control Center and VSD
control power (except for the trigger board) must be
on a UPS, which prevents a reboot of both on a power
failure and keeps communications between them ac-
tive throughout the utility power failure. This provides
the fastest possible ability to start or restart after gen-
erator or utility power is restored.
SI0212 - SOFTWARE ENHANCEMENTS (VER 21) EFFECTIVE JUNE 2009 (CONT'D)