| DDC Chiller Sequencer
The DDC Chiller Sequencer is a sequencing panel that provides start/stop
control of two chillers and associated pumps, setpoint
control, lead/lag, soft loading, failure recovery, chilled water reset, and ice
making mode.
Software Capabilities
- System enable - A contact closure input to the panel selects either
enable or disable mode. This input is typically
connected to a time clock for time of day scheduling, but can be wired to a
MANUAL/OFF/AUTO switch and thermostat to provide an
ambient interface.
- Chiller/pump control. The DDC Chiller Sequencer provides binary
outputs to control two chillers and two pumps.
- Lead/lag control. The operator can select manual or automatic chiller
rotation through the panel keypad. Automatic rotation
forces daily rotation at midnight. In the manual rotation mode, a separate manual
2-position switch is used to determine the lead
chiller.
- Soft loading prevents unnecessary operation of the lag chiller on
initial system startup.
- Failure recovery.
In the event of a chiller failure, the lag chiller
starts (through a normal Add program) when the system supply water
temperature exceeds setpoint. The sequencer turns on its alarm output if:
- the system setpoint is exceeded
for an extended period of time,
- a sensor fails,
- the DDC Chiller Sequencer loses
power,
- or the DDC Chiller Sequencer has a power failure,
- Setpoint control (optional).
The operator can enter the system
setpoint through the sequencing panel keypad. The sequencing software sends a
setpoint to each chiller. No manual setpoint
coordination is required. .
- Common leaving water control for one-pump systems.
The individual chiller setpoint is automatically
adjusted to maintain the common leaving water temperature at setpoint in 1-pump
systems with one chiller enabled (constant flow through
both chillers)
- Chilled water reset resets the system setpoint based on either return
water temperature or a separate reset sensor input as
determined in system setup.
Hardware Description
The DDC Chiller Sequencer package consists of a Trane 20-point PCM with
LCD and keypad, a matched pair of thermistor sensors, and the sequencer
software. |
