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NXW REVERSIBLE CHILLER INSTALLATION MANUAL
Anti Short Cycle
High Pressure Protection
Low Pressure Protection
Advanced Freeze Detection Setpoint
Random Start
Display for diagnostics
Reset Lockout at disconnect
Intelligent reset for field installed flow switches
1 Accessory output
Optional DDC control add-on
Compressor Lead/Lag
Compressor Current Switches
Field Selectable Options
Freeze Detection Sensing Select (DI-4 and DI-5)
The freeze detection temperature sensing selection inputs
allow the user to adjust the setpoints. The source sensors
are wired to inputs AI-3 and AI-4 while the load sensors are
wired to inputs AI-5 and AI-6. The setpoints for both, the
load and source, are factory set for 30°F. In order to change
the setpoint to 15°F on the source, remove the jumper wire
from DI-4 (wire #56). The load setpoint can be changed by
removing the jumper wire from DI-5 (wire #55).
Accessory Output (DO-4)
The accessory Output will be energized 90 seconds prior
to the lead compressor output being energized. When the
lead compressor output is turned off the accessory output
will be deactivated immediately. The output is selectable
for normally open or normally closed operation through the
unit mounted user interface or from a building automation
system.
Control and Safety Features
Emergency Shutdown
The emergency shutdown mode can be activated by a
command from a facility management system or a closed
contact on DI-2. The default state for the emergency
shutdown data point is off. When the emergency shutdown
mode is activated, all outputs will be turned off immediately
and will remain off until the emergency shutdown mode is
de-activated. The first time the compressor starts after the
emergency shutdown mode has been de-activated, there
will be a random start delay present.
Lockout Mode
Lockout mode can be activated by any of the following
fault signals: refrigerant system high pressure, refrigerant
system low pressure, heating freeze detection, cooling
freeze detection, and compressor current sensor. When any
valid fault signal remains continuously active for the length
of its recognition delay, the controller will go into fault
retry mode, which will turn off the compressor. After the
Compressor short cycle delay, the compressor will attempt
to operate once again. If three consecutive faults are
recognized during a single heating or cooling demand, the
unit will go into lockout mode, turning off the compressor
Control Features
and enabling the alarm output until the controller is reset.
The fault count will automatically reset when the heating or
cooling command becomes satisfied. If a fault occurs on a
dual compressor unit, the other compressor will continue
to operate based on the heating or cooling demand. The
lockout condition can be reset by powering down the
controller, by a command from the facility management
system, or by holding both the enter and escape keys on
the optional user interface.
Reversible Chiller Advanced Freeze
Detection System
The reversible chiller source and load heat exchangers are
protected by a multi-sourced temperature logic strategy. The
temperature logic is based upon the refrigerant temperature
sensed as the refrigerant is about to enter the heat
exchanger; while entering and leaving water temperatures
are being used as correlating factors. The detection scheme
is shown as basic and advanced algorithms.
Basic Freeze Detection Operation: “Comp1 or
Comp2 Freeze” Alarm
This alarm can be triggered by one of two detection schemes.
Hard Limit Freeze Detection
If the refrigerant temperature drops below the freeze
detection setpoint by 1.8°F, the associated compressor
is locked out immediately regardless of any other
factors and requires a manual reset.
NOTE: This Lockout
produces a “Comp 1 or Comp 2 Freeze” error on the
MUI display.
Freeze Detection
The refrigerant temperature is compared to the freeze
detection setpoint (15°F [antifreeze] or 33°F [water]
field selectable), and if the temperature falls below the
setpoint for 30 continuous seconds, the associated
compressor will be halted. This function becomes
enabled after the first two minutes of compressor
operation. Three such events in 60 minutes will trigger a
compressor lockout that requires a manual reset.
NOTE:
This Lockout produces a “Comp 1 or Comp 2 Freeze”
error on the MUI display.
In addition to the above:
Entering Water Temperature Influence
If the entering water temperature of the evaporative
heat exchanger is within 10°F of the freeze setpoint,
the previously mentioned two minute delay will be
eliminated. This allows the freeze detection to operate
immediately when the compressor starts based on
entering water temperature.
Leaving Water Temperature Influence
If the leaving water temperature of the evaporative
heat exchanger is within 10°F of the freeze setpoint, the
previously mentioned 30 second delay will begin to be
proportionately reduced, ending at a 1 second delay
