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35CG-PRC007-EN
Head Pressure Control — Condenser
head pressure control is provided in the
UCM by staging condenser fans on or
off to maintain the saturated condensing
temperature. This function will allow
cooling operation down to 30°F as
standard. Minimum on and off timing is
built into the algorithm to prevent rapid
cycling.
Pump down — This feature can be
enabled or disabled through the Human
Interface. When it is enabled, pump
down will be initiated prior to shutting
down the last capacity stage on each
circuit by de-energizing a liquid line
solenoid valve. Pump down is
terminated by the opening of the low
pressure switch, or 30 seconds after the
cycle is initiated. On units equipped with
hot gas bypass, pump down will be
initiated upon termination of the hot gas
bypass cycle.
Chiller Solution Pump Control — The
UCM has two operating modes for the
chiller solution pump control, Auto and
On. The UCM additionally has a relay
output that will energize/de-energize the
chiller’s solution pump control circuit.
The relay is de-energized, stopping the
pump, when emergency stop is
activated. The solution pump relay is
energized to run the pump in the
following modes: freeze protection,
normal cooling control, low ambient
freeze protection, ice building and loop
stabilization, and service mode. Modes
that will request the pump to stop are ice
building complete, ice building delay,
unit stop and external auto/stop.
Low Ambient Start Control — Tw o
functions are integrated into the control
to allow operation in extreme conditions
and still protect the overall system. Low
ambient start control will allow
compressor operation below 65°F. In
order to avoid nuisance tripping, the low
pressure control will be bypassed for a
period of time. If the low pressure
control is still open at the end of the
period, the compressor is shut down and
the solenoid valve is opened. The loss of
refrigerant flow protection is active in
this sequence to additionally protect the
chiller.
Hot Start Control — A high ambient start
sequence will permit only one
compressor to operate when the leaving
solution temperature is in the user
adjustable range of 60-80°F. When the
leaving solution temperature falls below
this high limit, the second compressor
will be active.
Low Ambient Compressor Lockout —
This function will lock out the
compressor if the outdoor air
temperature is below the low ambient
compressor lock out temperature set
point. This set point is adjustable at the
Human Interface Panel (HI) between 0-
60°F. Compressors will be locked out
when outdoor air temperatures fall
below that selected temperature and will
be allowed to start again when the
temperature rises 5° F above the set
point.
Compressor Lead/Lag — Compressor
lead/lag is a user-selectable feature
through the Human Interface Panel
available on all units. When enabled, the
algorithm in the UCM will start
compressors based upon the least
number of starts and/or run time. This
feature is not available with the hot gas
bypass option.
Emergency Stop Input — A binary input
is provided on the Unit Control Module
(UCM) for installation of field provided
switch or contacts for immediate
shutdown of all unit functions.
External Auto/Stop — A set of contacts
or switches can be field installed that will
start and stop the chiller.
Demand Limit — The UCM will accept an
input from a field installed device which
will prevent one or more compressors
from operating. The user can select the
number of compressors to be turned off.
Leaving Solution Reset — This flexible
option allows active leaving solution
reset based on customer selectable
inputs from the zone, entering solution
temperature or outside air temperature.
When the application is sensitive to one
of these parameters, subcooling of
critical zones is prevented.
Optional Control Features
Compressor Current Sensing — This
option will measure and average the
amp draw of 2 phases of each
compressor.
Superheat/Subcooling Option — This
option will include the necessary
temperature and pressure sensors to
measure and calculate the chiller’s
superheat and subcooling numbers for
each circuit. These temperatures and
pressures, along with calculated values
of superheat/subcool, will be displayed
in the status menu of the Human
Interface. No external refrigerant gauges
need to be installed on the chiller for the
system operator to check out these
conditions.
External Leaving Solution Set point —
Remote set point potentiometer can be
ordered to allow adjustment of the
leaving solution set point remotely.
(20–60 Ton
Interface)Controls