Tracer™ Chiller Controller
The chiller controller uses proportional- integral-derivative (PID) control for all limits—there is no dead band. This removes oscillation above and below setpoints and extends the capabilities of the chiller.
Some of the standard protection features of the chiller controller are described in this section. There are additional protection features not listed here.
High Condenser-Pressure Protection The chiller controller’s condenser limit keeps the condenser pressure under a specified maximum pressure. The chiller runs all the way up to 100 percent of the setpoint before reducing capacity using its adaptive control mode.
Starter-Contactor Failure Protection The chiller will protect itself from a starter failure that prevents the compressor motor from disconnecting from the line to the limits of its capabilities.
The controller starts and stops the chiller through the starter. If the starter malfunctions and does not disconnect the compressor motor from the line when requested, the controller will recognize the fault and attempt to protect the chiller by operating the evaporator-and condenser-water pumps and attempting to unload the compressor.
Loss of Water-Flow Protection
The chiller controller has an input that will accept a contact closure from a proof-of-flow device such as a flow switch or pressure switch. Customer wiring diagrams also suggest that the flow switch be wired in series with the cooling-water (condenser-water) pump starter’s auxiliary contacts. When this input does not prove flow within a fixed time during the transition from Stop to Auto modes of the chiller, or if the flow is lost while the chiller is in the Auto mode of operation, the chiller will be inhibited from running by a nonlatching diagnostic.
Evaporator Limit Protection Evaporator Limit is a control algorithm that prevents the chiller tripping on its low refrigerant-temperature cutout. The machine may run up to the limit but not trip. Under these conditions the intended chilled-water setpoint may not be met, but the chiller will do as much as it can. The chiller will deliver as much cold water as possible even under adverse conditions.
Low Evaporator-Water Temperature Low evaporator-water temperature protection, also known as Freeze Stat protection, avoids water freezing in the evaporator by immediately shutting down the chiller and attempting to operate the chilled-water pump. This protection is somewhat redundant with the Evaporator Limit protection, and prevents freezing in the event of extreme errors in the evaporator- refrigerant temperature sensor.
The cutout setting should be based on the percentage of antifreeze used in the customer’s water loop.The chiller’s operation and maintenance documentation provides the necessary information for percent antifreeze and suggests leaving-water temperature- cutout settings for a given chilled-water temperature setpoint.
Oil-Temperature Protection
Low oil temperature when the oil pump and/or compressor are running may be an indication of refrigerant diluting the oil. If the oil temperature is at or below the low oil-temperature setpoint, the compressor is shut down on a latching diagnostic and cannot be started. The diagnostic is reported at the user interface. The oil heaters are energized in an attempt to raise the oil temperature above the low oil- temperature setpoint.
High oil-temperature protection is used to avoid overheating the oil and the bearings.
Low Differential Oil-Pressure
Protection
Oil pressure is indicative of oil flow and active oil-pump operation. A significant drop in oil pressure indicates a failure of the oil pump, oil leakage, or other blockage in the oil-circuit.
The differential pressure during oil pump, compressor prelube mode should not fall below 12 psid. A failure on this parameter generates a shutdown diagnostic. When the compressor is running, a diagnostic is issued when the differential pressure is lost.
Phase-Unbalance Protection Phase-unbalance protection is based on an average of the three phase- current inputs. The ultimate phase-unbalance trip point is 30 percent. In addition, the RLA of the motor is derated by resetting the active current-limit setpoint based on the current unbalance. The RLA derate protection can be disabled in the field- startup menu.
The following derates apply when the phase-unbalance limit is enabled:
10% unbalance = 100% RLA derate
15% unbalance = 90% RLA derate
20% unbalance = 85% RLA derate
25% unbalance = 80% RLA derate
30% unbalance = Shutdown
Phase-Loss Protection
The controller will shut down the chiller if any of the three phase currents feeding the motor drop below 10 percent RLA. The shutdown will result in a latching phase-loss diagnostic. The time to trip is 1 second at minimum, 3 seconds maximum.
Phase Reversal/Rotation Protection The controller detects reverse phase rotation and provides a latching diagnostic when it is detected. The time to trip is 0.7 seconds. Phase-rotation protection can be disabled inTechView.
