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SECTION 31 - HEAT PUMP DUTY
FORM 160.54-M1
ISSUE DATE: 10/25/2019
JOHNSON CONTROLS
JCI COMPANY CONFIDENTIAL
31
Heating LCHLT (Leaving Chilled Liquid Tempera-
ture) Shutdown threshold, a cycling shutdown is per-
formed and “Leaving Chilled Liquid – Low Tempera-
ture” is displayed. The Heat Pump will restart when
the Leaving Chilled Liquid Temperature exceeds this
shutdown temperature by 5°F. In most applications,
the 50% (default) setting of the Heating Sensitivity
setpoint will properly control the Leaving Condenser
Liquid Temperature to the Leaving Condenser Liquid
Temperature setpoint. If greater Pre-rotation Vanes
response is needed, use the NORMAL setting. If less
PRV response is needed, due to setpoint overshoot, the
Heating Sensitivity setpoint can be incrementally re-
duced (50%, 30%, 10%) until the overshoot is reduced
or eliminated.
In Cooling Mode, the chiller controls the leaving
Chilled Liquid Temperature to the Leaving Chilled
Liquid Temperature setpoints as displayed on the
EVAPORATOR Screen. While running, “System run
– Cooling Mode” on the System Status Line and “Heat
Pump – Leaving Chilled Liquid Control” is displayed
on the System Details line while running. In this mode,
all functions of the chiller are the same as in a standard
YK chiller without Heat Pump ability.
HOT GAS BYPASS CONTROL
In Cooling Mode, the hot gas operates as it does in a
standard YK chiller without Heat Pump ability.
In heating mode, hot gas operation is the same as Cool-
ing mode except for the operation during low load
conditions, which is as follows: When the Leaving
Condenser Liquid Temperature exceeds the Minimum
Load setpoint (1 to 4°F above the Leaving Condens-
er Liquid Temperature Setpoint) the Hot gas valve is
opened to the position allowed per the Maximum Open
setpoint (25 to 100%). For example, if the Minimum
Load setpoint equals 4°F, Maximum Open setpoint
equals 100%, Heating setpoint equals 105°F, and leav-
ing Condenser Liquid Temperature greater than 109°F,
the Hot gas valve would be opened to the 100% posi-
tion. When the leaving Condenser Liquid Temperature
falls to 107°F, the valve closes to 50% and finally to
0% when this temperature falls back to 105°F. All other
aspects of Hot gas control remain unchanged in Heat-
ing Mode. See
in
this manual for details of the hot gas bypass operation.
HEAT RECOVERY AND HEAD PRESSURE
CONTROL
When Heat Pump Duty is enabled, Heat Recovery and
Head Pressure Control are automatically disabled and
locked.
QUICK START
The Quick Start feature is only available when Heat
Pump operation is set to Cooling Mode and is auto-
matically disabled when Heating Mode is selected.
VARIABLE SPEED DRIVE
If the chiller is equipped with a VSD, it will operate at
full speed (50Hz or 60Hz) at all times when Heat Pump
operation is set Heating Mode. In Cooling Mode, it op-
erates normally.
CONDENSER TEMPERATURE RANGE
The Condenser Temperature Range setpoint is auto-
matically set to Extended.
CONDENSER HIGH PRESSURE WARNING
The Condenser High Pressure Warning Setpoint thresh-
old is automatically set to 193 psig.
GPIC OBJECTS
Read objects:
• Active Leaving Condenser Liquid Temperature
setpoint: Object Type AV, Object Slot 34
• Local Leaving Condenser Liquid Temperature
setpoint: Object Type AV, Object Slot 35
The only write object is Remote Leaving Condenser
Liquid Temperature setpoint with an Object type of AV,
Object Slot 3.
