YORK YK — Leaving chilled liquid - Low temperature

The OptiView Touchscreen Control Center shows Leaving chilled liquid - Low temperature. The manual prints the message in this single form, and it is reached through the Cycling faults messages list under Display messages.

This is a cycling shutdown: the chiller has stopped because the leaving chilled liquid temperature decreased to the programmed shutdown temperature setpoint. The stop is gradual — if the chiller is running when it occurs, the PRVs are driven fully closed before shutting down the chiller — and the manual lists this message among the events that initiate a soft shutdown, in which a system coastdown is performed. When the chiller is operating in heat pump heating mode, with heat pump duty enabled and the heat pump operational mode setpoint set to heating, additional logic causes the same shutdown when the LCHLT decreases below the programmed heating LCHLT shutdown temperature setpoint.

• The leaving chilled liquid temperature has decreased to the programmed shutdown temperature setpoint.
• In heat pump heating mode, additional logic causes this shutdown when the LCHLT decreases below the programmed heating LCHLT shutdown temperature setpoint.

1. Read the Cooling Shutdown Temperature on the control center — it displays the leaving chilled liquid temperature at which the chiller shuts down on this message.
2. Read the offset in use, displayed as Effective Offset. Although the offset setpoint is changed manually, the offset being used can change automatically so the leaving chilled liquid temperature never goes below the minimum allowed value: 34°F (water) or 6°F (brine).
3. If the unit is in heat pump heating mode, look up the programmed heating LCHLT shutdown temperature setpoint on the Heat Pump Screen; the manual refers there for details of this setpoint.

• Cooling Shutdown Offset (Enhanced): defines the shutdown point as an offset below the leaving chilled liquid temperature setpoint. It is programmable over a range of 1°F to 70°F below the setpoint (default 4°F), to a minimum cutout of 34°F for water or 6°F for brine.
• If the leaving chilled liquid temperature setpoint is increased, the shutdown threshold is ramped up from the present setpoint to the new one at a rate of 0.1°F/s (adjustable) to prevent a nuisance shutdown.
• Cooling Restart Offset (Enhanced): defines the restart point as an offset above the leaving chilled liquid temperature setpoint, programmable over a range of 0°F to 51°F above the setpoint, to a maximum restart value of 96°F. It can be used to reduce chiller cycling by delaying the restart until the cooling load has increased.
• The Effective Cooling Shutdown Offset display shows the calculated value: Active Cooling setpoint - Cooling shutdown Temperature. The Cooling Restart Temperature display shows the restart temperature, with its OFFSET value adjacent.
• Heating mode: the low limit of the heating LCHLT shutdown temperature setpoint is the higher of the selected heating setpoint minus 71°F (21.7°C) or the cooling mode leaving chilled liquid temperature shutdown temperature; its high limit is the selected heating setpoint. The default is the selected heating setpoint minus 60°F (15.6°C).

No manual reset action is described — recovery is automatic. The chiller comes back once the liquid temperature rises to the programmed restart temperature setpoint: The chiller automatically restarts when the temperature increases to the programmed restart temperature setpoint. In heat pump heating mode, the heat pump restarts when the leaving chilled liquid temperature exceeds this shutdown temperature by 5°F.