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Controls Interface
NOTICE
Equipment Damage!
Failure to remove moisture from system could cause
corrosion within the chiller/heater components, and
degrade performance.
Perform vacuum evacuation of system to remove
moisture.
Low Pressure Bypass
A control that uses a time delay that temporarily bypasses
the low-pressure switch for cold weather start up. Once the
delay opens (times out) the normal controls are put back on
line within the control circuit.
Low Pressure Pump Down (LPPD) Controls
Allows the system to start in low ambient conditions and
prevents flood-back to the compressor by pumping the
liquid refrigerant out of the brazed plate heat exchanger.
The LPPD control consists of a pressure switch that is set
at "cut in" and "cut out" pressures that depend on the type
42
of refrigerant in the system and is based on pressure at
which the refrigerant reaches the freezing point of the load
heat exchanger water/glycol mixture.
The set points are typically just below the freezing point.
For R410A refrigerant and using water, the pressure is set
at a 90 psi "cut out" (corresponding to 50 °F (10 °C)) and a
105 psi "cut in" (corresponding to 40 °F (4.4 °C)) cut in. For
any other water/glycol mixture, contact Trane technical
support for proper set points.
High and Low Ambient Controls
Some heat pump modules must be required to operate in
low ambient temperatures to prevent refrigerant migration
to the air coil. Without good head pressure control,
insufficient refrigerant is fed to the brazed plate heat
exchanger and will cause low suction pressure, heat
exchanger freezing and will ultimately shut down the heat
pump.
Thermal Capacity
The thermal capacity of the heat pump modules is
dependent on the leaving temperature of the fluid
maintaining a minimum fluid flow rate through the brazed
plate heat exchanger and keeping debris out of the aircoil.
In applications where it is desired to operate with a lower
flow rate or higher temperature change, consult technical
support for recommendations.
ARTC-SVX006A-EN
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