Abstract: Chiller systems can include a controller that is configured to determine whether to restart the chiller in a rapid restart mode or a soft loading restart mode, and methods can include determining the mode for restarting the chiller. The soft loading restart mode controls the chiller to provide a comparatively gradual loading, to avoid overshooting a target temperature. The rapid restart mode more aggressively loads the chiller to return more rapidly to a particular load level. The determination of the restarting mode can be based on characteristics of the interruption of power to the chiller system. In chiller systems, the controller can receive power from an uninterruptable power source to maintain continuity of power. The logic used by the controller can be based on whether or not the controller shares continuity of power with other components of the chiller system.

Abstract: Purge systems for heating, ventilation, air conditioning, and refrigeration (HVACR) circuits in chillers can use adsorbent and/or membranes to separate refrigerant from non-condensable gases, allowing the non-condensables to be exhausted while the working fluid can be recovered and returned to the HVACR circuit. The purge systems can include one or more separation chambers including either an adsorbent material or a selectively permeable membrane. The selectively permeable membrane can be solubility-based for its selectivity. Optionally, a pusher pump can be upstream of the separation chambers to pressurize the purge gas through the purge system, including in the separation chamber. The purge system can be controlled using a model correlating pressure differentials in the purge system with purge gas conditions such as non-condensable and working fluid concentrations.

Abstract: The unloading of multi-stage compressors may include the introduction of flow from a gas bypass from a condenser into a second-stage inlet duct to induce a swirl in the flow into second stage compression. This unloading may be performed on multi-stage compressors in heating, ventilation, air conditioning and refrigeration (HVACR) circuits that include a gas bypass from a condenser to the second-stage inlet housing of the compressor. The multi-stage compressor may include an impeller inlet duct including a flow straightener receiving fluid flow from the first stage discharge, and one or more channels to introduce gas from the gas bypass into the flow passing through the impeller inlet duct. The flow introduced by the channels may have a direction of flow including a component opposite to the direction of flow of the fluid flow from the first stage discharge via the flow straightener.

Abstract: The unloading of multi-stage compressors may include the introduction of flow from a gas bypass from a condenser into a second-stage inlet duct to induce a swirl in the flow into second stage compression. This unloading may be performed on multi-stage compressors in heating, ventilation, air conditioning and refrigeration (HVACR) circuits that include a gas bypass from a condenser to the second-stage inlet housing of the compressor. The multi-stage compressor may include an impeller inlet duct including a flow straightener receiving fluid flow from the first stage discharge, and one or more channels to introduce gas from the gas bypass into the flow passing through the impeller inlet duct. The flow introduced by the channels may have a direction of flow including a component opposite to the direction of flow of the fluid flow from the first stage discharge via the flow straightener.

Abstract: Methods and systems for controlling a chiller system to achieve control stability while maintaining optimum efficiency. Particularly, methods and systems for controlling a centrifugal compressor speed and an inlet guide vane position that establishes three distinct regions in the control path: (i) during initial unloading from full load, the inlet guide vane position is kept at a fully open position while the centrifugal compressor speed is changed to achieve the desired cooling capacity; (ii) between an inflection point and a transition point, keeping the centrifugal compressor speed constant while the inlet guide vane position is changed to achieve the desired cooling capacity; and (iii) between the transition point and zero cooling capacity, changing both the inlet guide vane position and the centrifugal compressor speed to achieve the desired cooling capacity.

Abstract: Embodiments of an accumulator for charge management are described. A fluid compression system, comprising an accumulator fluidly connected to an evaporator via a spillover port. The spillover port directs working fluid received from the evaporator to be collected and stored in the accumulator, where the stored working fluid is stored and released from the accumulator in response to an operating condition of the evaporator.

Abstract: Controls for chillers with variable speed and variable geometry compressors are disclosed. In exemplary embodiments, a centrifugal compressor equipped with a variable frequency drive and variable inlet guide vanes may be utilized. A controller is operable to determine a chiller capacity command, a speed command, and a vane position command. The speed command and vane position command may maintain system operation at or near a surge control boundary over one or more capacity ranges to enhance efficiency and deviate from the surge control boundary over certain capacity ranges to improve controllability or avoid control aberrations.

Abstract: Methods and systems to manage refrigerant levels in a chiller system are provided. An evaporator of the chiller system may be configured to have a spill over port allowing oil containing refrigerant to spill over through the spill over port. The spill over port may be positioned at a place that corresponds to a desired refrigerant level in the evaporator. The spill over refrigerant may be directed into a heat exchanger that is configured to substantially vaporize refrigerant of the spill over refrigerant to a slightly superheat temperature. A method of maintaining a proper refrigerant level in the evaporator may include regulating a refrigerant flow to the evaporator so that the vaporized refrigerant of the spill over refrigerant is maintained at the slightly superheat temperature.

Abstract: The embodiments disclosed herein are directed to systems and methods to control a HVAC system based on a state of an unloader of a compressor of the HVAC system.

Abstract: A spill over tank for an evaporator of a HVAC system may be configured to receive a refrigerant spilled over from the evaporator. The spill over tank may be configured to have an outlet that directs the refrigerant in the spill over tank out of the spill over tank. The refrigerant may flow through the outlet back to a compressor of the HVAC system. The spill over tank may be equipped with a refrigerant level sensor configured to measure a refrigerant level in the spill over tank. The measured refrigerant level in the spill over tank may be used to control and/or maintain a refrigerant level in the evaporator, and/or may be used to control a return refrigerant flow into the compressor of the HVAC system so as to manage an oil return to the compressor.

Abstract: Embodiments of an accumulator for charge management are described. A fluid compression system, comprising an accumulator fluidly connected to an evaporator via a spillover port. The spillover port directs working fluid received from the evaporator to be collected and stored in the accumulator, where the stored working fluid is stored and released from the accumulator in response to an operating condition of the evaporator.

Abstract: Methods and systems for controlling a chiller system to achieve control stability while maintaining optimum efficiency. Particularly, methods and systems for controlling a centrifugal compressor speed and an inlet guide vane position that establishes three distinct regions in the control path: (i) during initial unloading from full load, the inlet guide vane position is kept at a fully open position while the centrifugal compressor speed is changed to achieve the desired cooling capacity; (ii) between an inflection point and a transition point, keeping the centrifugal compressor speed constant while the inlet guide vane position is changed to achieve the desired cooling capacity; and (iii) between the transition point and zero cooling capacity, changing both the inlet guide vane position and the centrifugal compressor speed to achieve the desired cooling capacity.

Abstract: Methods and systems for detecting and recovering from control instability caused by impeller stall in a chiller system are provided. In one embodiment, an impeller stall detection and recovery component of a chiller control unit calculates a control error signal frequency spectrum for an evaporator leaving water temperature, determines whether a high frequency signal content of the control error signal frequency spectrum exceeds acceptable limits, and adjusts a surge boundary control curve downward by a predetermined incremental value in order to resolve instability caused by impeller stall.

Abstract: Methods and systems to manage refrigerant levels in a chiller system are provided. An evaporator of the chiller system may be configured to have a spill over port allowing oil containing refrigerant to spill over through the spill over port. The spill over port may be positioned at a place that corresponds to a desired refrigerant level in the evaporator. The spill over refrigerant may be directed into a heat exchanger that is configured to substantially vaporize refrigerant of the spill over refrigerant to a slightly superheat temperature. A method of maintaining a proper refrigerant level in the evaporator may include regulating a refrigerant flow to the evaporator so that the vaporized refrigerant of the spill over refrigerant is maintained at the slightly superheat temperature.

Abstract: Methods and systems for controlling a chiller system to achieve control stability while maintaining optimum efficiency. Particularly, methods and systems for controlling a centrifugal compressor speed and an inlet guide vane position that establishes three distinct regions in the control path: (i) during initial unloading from full load, the inlet guide vane position is kept at a fully open position while the centrifugal compressor speed is changed to achieve the desired cooling capacity; (ii) between an inflection point and a transition point, keeping the centrifugal compressor speed constant while the inlet guide vane position is changed to achieve the desired cooling capacity; and (iii) between the transition point and zero cooling capacity, changing both the inlet guide vane position and the centrifugal compressor speed to achieve the desired cooling capacity.

Abstract: Methods and systems to manage refrigerant levels in a chiller system are provided. An evaporator of the chiller system may be configured to have a spill over port allowing oil containing refrigerant to spill over through the spill over port. The spill over port may be positioned at a place that corresponds to a desired refrigerant level in the evaporator. The spill over refrigerant may be directed into a heat exchanger that is configured to substantially vaporize refrigerant of the spill over refrigerant to a slightly superheat temperature. A method of maintaining a proper refrigerant level in the evaporator may include regulating a refrigerant flow to the evaporator so that the vaporized refrigerant of the spill over refrigerant is maintained at the slightly superheat temperature.

Abstract: Embodiments of a spill over tank for an evaporator of a HVAC system are described. The spill over tank may be configured to receive a refrigerant directed out of the evaporator. The spill over tank may be configured to have an outlet directing refrigerant in the spill over tank out of the spill over tank and flowing back to a compressor of the HVAC system. The spill over tank may be equipped with a refrigerant level sensor configured to measure a refrigerant level in the spill over tank. The measured refrigerant level in the spill over tank may be used to control and/or maintain a refrigerant level in the evaporator, and/or may be used to control a return refrigerant flow into the compressor of the HVAC system so as to manage an oil return to the compressor.

Abstract: A system for managing fluid level in an HVAC system includes a spill over tank for an evaporator of the HVAC system. The spill over tank may be configured to receive a refrigerant directed out of the evaporator. The spill over tank may be configured to include an outlet directing refrigerant into the spill over tank, out of the spill over tank and flowing back to a compressor of the HVAC system. The spill over tank may be equipped with a refrigerant level sensor measuring a refrigerant level in the spill over tank. The measured refrigerant level in the spill over tank may be used to control and/or maintain a refrigerant level in the evaporator, and/or to control a return refrigerant flow into the compressor of the HVAC system so as to manage an oil return to the compressor.

Abstract: Methods and systems for controlling a chiller system to achieve control stability while maintaining optimum efficiency. Particularly, methods and systems for controlling a centrifugal compressor speed and an inlet guide vane position that establishes three distinct regions in the control path: (i) during initial unloading from full load, the inlet guide vane position is kept at a fully open position while the centrifugal compressor speed is changed to achieve the desired cooling capacity; (ii) between an inflection point and a transition point, keeping the centrifugal compressor speed constant while the inlet guide vane position is changed to achieve the desired cooling capacity; and (iii) between the transition point and zero cooling capacity, changing both the inlet guide vane position and the centrifugal compressor speed to achieve the desired cooling capacity.

Abstract: Methods and systems for detecting and recovering from control instability caused by impeller stall in a chiller system are provided. In one embodiment, an impeller stall detection and recovery component of a chiller control unit calculates a control error signal frequency spectrum for an evaporator leaving water temperature, determines whether a high frequency signal content of the control error signal frequency spectrum exceeds acceptable limits, and adjusts a surge boundary control curve downward by a predetermined incremental value in order to resolve instability caused by impeller stall.