Controls Interface)
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
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
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
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
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.
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