Abstract: A chiller system includes a compressor, a condenser and an evaporator in fluid communication. A motor drives the compressor. A variable speed drive powers the motor. An oil heater and pump system circulate heated lubricating oil in the compressor. A control panel is arranged to determine whether an input parameter is greater than or equal to a threshold parameter; deactivate the VSD in response to sensing that the input parameter is less than the threshold parameter; determine at least one chiller capacity control parameter at a point when the VSD is deactivated, and maintain the at least one chiller capacity control parameter while the VSD is deactivated; determine that the input parameter has been restored; determine a motor rotation and motor rotational speed; and in response to determining that the input parameter is restored and the motor is rotating in a forward direction, reactivate the VSD.

Abstract: A control system controls the output capacity of a compressor to avoid surge conditions in the compressor. The control system determines a capacity control output for the compressor and then modifies the capacity control output in view of any output limiters or overrides as determined by system operating parameters and to maintain a minimum frequency of operation for the compressor.

Abstract: A control system is provided that can identify the occurrence of a single surge cycle in centrifugal compressor using various methods and devices. Once the occurrence of a single surge cycle is identified, the control system can take remedial action to respond to the surge cycle, such as by adjusting the position of a variable geometry diffuser, and restore the centrifugal compressor to stable operation.

Abstract: A method of controlling the frequency of a compressor in a chiller system is disclosed. The method includes determining a nominal minimum frequency of a compressor, and providing a control algorithm for controlling the period of time and the deviation of the actual operating frequency below the nominal minimal frequency that the compressor may operate without shutting down the chiller system. The time period of operation below nominal minimum frequency may be predetermined as a fixed time period of operation below nominal minimum frequency, or as a variable time period based on the amount by which the frequency deviates below nominal minimum frequency. Also, an absolute minimum operating frequency is provided that results in the control algorithm shutting down the chiller system and the compressor.

Abstract: A control algorithm for controlling an economizer circuit in a chiller system is provided. The control algorithm opens and closes a port valve in the economizer circuit in response to predetermined criteria to engage and disengage the economizer circuit. The predetermined criteria can include an operating parameter of a compressor and a level of liquid refrigerant in a flash tank.

Abstract: A pull-down control process for a chiller system is provided. The pull-down control process can override the capacity control process for the chiller system to pull-down the leaving chilled liquid temperature faster than the capacity control process. The pull-down control process can maintain pre-rotation vanes in a fully open position to pull-down the leaving chilled liquid temperature as quickly as possible to a predetermined setpoint.

Abstract: A noise control method is provided for a cooling system having at least one refrigerant circuit. The refrigerant circuit includes a compressor, a condenser, at least one condenser fan, and an evaporator. Noise control is only performed periodically in response to requirements for reduced operation at predetermined times. The request for reduced noise triggers the commencement of the noise control method. The noise control method involves reducing the operating speed of the compressor, as well as reducing the operating speed of at least one condenser fan, to within a predetermined range of allowable reduced operating speeds. The noise control method temporarily overrides the ability of the cooling system to fully respond to increased cooling or heating demands.

Abstract: A pull-down control process for a chiller system is provided. The pull-down control process can override the capacity control process for the chiller system to pull-down the leaving chilled liquid temperature faster than the capacity control process. The pull-down control process can maintain pre-rotation vanes in a fully open position to pull-down the leaving chilled liquid temperature as quickly as possible to a predetermined setpoint.

Abstract: A control algorithm for controlling an economizer circuit in a chiller system is provided. The control algorithm opens and closes a port valve in the economizer circuit in response to predetermined criteria to engage and disengage the economizer circuit. The predetermined criteria can include an operating parameter of a compressor and a level of liquid refrigerant in a flash tank.

Abstract: A control algorithm for controlling an economizer circuit in a chiller system is provided. The control algorithm opens and closes a port valve in the economizer circuit in response to predetermined criteria to engage and disengage the economizer circuit. The predetermined criteria can include an operating parameter of a compressor and a level of liquid refrigerant in a flash tank.

Abstract: A method of controlling the frequency of a compressor in a chiller system is disclosed. The method includes determining a nominal minimum frequency of a compressor, and providing a control algorithm for controlling the period of time and the deviation of the actual operating frequency below the nominal minimal frequency that the compressor may operate without shutting down the chiller system. The time period of operation below nominal minimum frequency may be predetermined as a fixed time period of operation below nominal minimum frequency, or as a variable time period based on the amount by which the frequency deviates below nominal minimum frequency. Also, an absolute minimum operating frequency is provided that results in the control algorithm shutting down the chiller system and the compressor.

Abstract: A startup control algorithm for a multiple compressor liquid chiller system is provided wherein the maximum number of compressors to be started to satisfy system load conditions is provided. The control algorithm designates all of the compressors of the multiple compressor system for starting and reduces the number to be started in response to the satisfaction of several predetermined criteria. The predetermined criteria are related to the leaving chilled liquid temperature, the shutdown time for the chiller system and the last operating time period for the chiller system.

Abstract: A capacity control algorithm for a multiple compressor liquid chiller system is provided wherein the speed and number of compressors in operation are controlled in order to obtain a leaving liquid temperature setpoint. In response to an increase in the load in the chiller system, the algorithm determines if a compressor should be started and adjusts the operating speed of all operating compressors when an additional compressor is started. In response to a decrease in the load in the chiller system with multiple compressors operating, the algorithm determines if a compressor should be de-energized and adjusts the operating speed of all remaining operating compressors when a compressor is de-energized.

Abstract: A motor disconnect arrangement is provided for a variable speed drive having a plurality of inverters electrically connected in parallel to a DC link to power a plurality of motors. The disconnect arrangement includes a contactor or other disconnect device connected in series between each inverter output of the variable speed drive and its corresponding motor. The contactor operates to disconnect, isolate or remove the motor from the variable speed drive in the event of a failure of the motor. By removing a failed motor from the variable speed drive, the other motors connected to the variable speed drive can continue to operate normally.

Abstract: A flash tank configuration for an economizer is provided that is inexpensive and simple to construct, reliable to operate, and efficient for use in an economizer compression refrigeration system. The configuration includes an upper baffle and a lower baffle configured and arranged within the flash tank so as to separate the liquid and gas phases of intermediate pressure refrigerant, and to convey each phase to other components in the refrigeration systems. The flash tank has a generally cylindrical shape, and is dimensioned so as to provide adequate internal volume for expansion of refrigerant to a desired pressure, separation of the resulting refrigerant gas and refrigerant liquid phases, and temporary storage of the refrigerant phases before conveying the liquid phase to the main refrigerant line between the condenser and the evaporator, and returning the gas phase to the compressor. Additionally, methods are provided for using the flash tank to separate refrigerant phases.