| Controls 20 - 60 Tons
Interface UCM’s response to
changing cooling requirements.
This value can be set through the HI to allow
flexibility in maintaining precise control conditions.
Chiller Freeze Protection
The microprocessor will prevent the evaporator
fluid from freezing by reducing chiller capacity,
ultimately shutting down all compressors and sending a manually resettable diagnostic.
The inputs for freeze protection are the low leaving
solution temperature cutout and the leaving solution temperature.
Evaporator Solution Flow Interlock
The IntelliPak controls offer both an
internal loss of flow protection, as well as an external evaporator flow switch interlock. Internally, the control algorithm
will sense and compare the entering solution
temperature and the leaving solution temperature to
detect loss of flow during or after start-up. This input to the UCM shall have priority
over all other commands and will stop the chiller and a
manually resettable diagnostic will result. Additionally, an external field installed flow switch can be wired into the unit terminal
strip; this feature can be enabled or disabled. When an
open condition is detected for 6 seconds or longer, the chiller will shut down and send a manually resettable diagnostic alarm.
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 deenergized, 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
Two 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 setpoint. This setpoint 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 setpoint.
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.
Optional Control Features
Phase/Voltage Monitoring
This option will detect high and low
incoming line voltage. There are three options that the operator can select in response to high or low voltage; no action,
information only diagnostic, and auto reset diagnostic
which disables all unit functions. The actual voltage will be displayed on the HI. The option will check for phase loss and phase
reversal on the main power terminal. If these
conditions are detected, the user can select whether
to provide an information only diagnostic, or a "shut down the unit" command, displaying a manual diagnostic.
Current Monitoring
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. |
