21
RW SERIES REVERSIBLE CHILLER INSTALLATION MANUAL
Control Features
enabled, and if the logic determines that a freeze condition is
likely to happen based on current conditions, the compressor of
the involved refrigerant circuit is immediately stopped. Three (3)
such events in 60 minutes will trigger a compressor lockout that
requires a manual reset. In the absence of such a condition,
the compressor is allowed to operate so that the refrigerant
temperature may eventually be at the threshold of the freeze
detection setpoint. NOTE: This Lockout produces a “Pre
Freeze” detection error on the MUI display.
Capacity Limiting
If the leaving water temperature drops to 1.8°F above the freeze
detection setpoint, the lead compressor is halted. When the leaving
water temperature rises to 3.6°F above the freeze detection setpoint,
it will be allowed to resume operation. This limiting is allowed to
repeat indefinitely. This causes “COMP1 Low Limit” to be displayed
on the MUI.
If the leaving water temperature drops to the freeze detection
setpoint, the lag compressor is halted. When the leaving water
temperature rises to 1.8°F above the freeze detection setpoint,
it will be allowed to resume operation. This limiting is allowed to
repeat indefinitely. This causes “COMP2 Low Limit” to be displayed
on the MUI.
Compressor Current Switch (AI-3 EXP and AI-4 EXP)
The compressor current switch is designed to insure that the
compressor is on when the compressor output is energized. This
switch is normally open and closes when current is flowing to the
compressor. If the compressor fails to start the switch will open.
The switch must be open for a continuous 15 seconds for a fault to
occur. After 3 faults in 60 minutes the control will put the unit into an
alarm state.
Flow Proving Switch (DI-1 and DI-10)
The load and source flow-proving switches are optional and can be
field installed. These switches shall be normally open flow switches
that will close when the water flow through the heat exchangers
reach an acceptable level. The flow-proving switches must be
closed 15 seconds prior to enabling either compressor output (DO-1
and DO-2). If the load flow-proving switch opens at any time both
compressor outputs (DO-1 and DO-2) must be disabled immediately.
High Pressure (DI-11 and DI-12)
The high-pressure switches shall be a normally closed (NC)
switch that monitors the systems compressor discharge refrigerant
pressures. There shall be an individual high pressure switch for each
circuit. If the input senses the high-pressure switch is open during
the period that the compressor output is enabled, it must shut down
the compressor immediately and count the fault. The compressor
minimum on time does not apply if the high-pressure switch trips.
The compressor will not restart until the short cycle time delay has
been satisfied. If the high-pressure fault occurs in one circuit the
other compressor will continue to operate based on the heating or
cooling demand.
Advanced Freeze Detection System
The 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 when the leaving water
temperature is 1.5°F above the freeze setpoint.
Dual Circuited Heat Exchanger Protection
A low temperature condition on either refrigerant circuit will
prevent the start of both compressors. If the low temperature
condition exists for 5 minutes when both compressors are
off, a lockout is triggered for both compressors. However,
if –for instance-both compressors are operating and circuit
1 experiences a refrigerant temperature below the freeze
detection setpoint such that compressor 1 is halted, compressor
2 will not be halted as a result.
Advanced Freeze Detection Operation:
“Pre Freeze” Alarm
Predictive freeze condition detection:
If the refrigerant temperature is within 7.2°F of the freeze
detection setpoint, the predictive freeze detection algorithm is
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