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: 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: 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 generator for an absorption chiller boils an absorption solution with steam heat by conveying the steam through a tube bundle with the steam flowing counter to the flow of solution. The tube bundle runs downhill in the direction of steam flow, while in some embodiments of the invention a bottom surface of the generator runs uphill in the direction of solution flow. The amount of solution in the generator is kept to an appropriately low level by submerging the tube bundle deeper at one end of the generator than the other.

Abstract: A method of controlling chiller capacity in a chiller system. The method comprises the steps of: measuring entering the fluid temperature of a fluid entering a heat exchanger; measuring the fluid temperature of the fluid leaving the heat exchanger; determining a desired leaving fluid temperature; establishing chiller capacity as a function of the difference between leaving fluid temperature and the desired leaving fluid temperature; and adjusting the determined chiller capacity as a function of the difference between entering fluid temperature and the desired leaving fluid temperature.

Abstract: A method of controlling an expansion valve including the steps of: measuring a primary system condition; determining an error in the primary system condition; measuring a secondary system condition; determining an error in the secondary system condition; and modulating the expansion valve based upon the larger of the first or second error.

Abstract: A method of controlling chiller capacity in a chiller system. The method comprises the steps of: measuring entering the fluid temperature of a fluid entering a heat exchanger; measuring the fluid temperature of the fluid leaving the heat exchanger; determining a desired leaving fluid temperature; establishing chiller capacity as a function of the difference between leaving fluid temperature and the desired leaving fluid temperature; and adjusting the determined chiller capacity as a function of the difference between entering fluid temperature and the desired leaving fluid temperature.

Abstract: A method of controlling an expansion valve including the steps of: measuring a primary system condition; determining an error in the primary system condition; measuring a secondary system condition; determining an error in the secondary system condition; and modulating the expansion valve based upon the larger of the first or second error.

Abstract: A method of controlling compressor minimum capacity. The method comprises the steps of: measuring a first condition; comparing the first condition to a first setpoint to determine a first conditioned error; modulating compressor capacity relative to the first condition error; measuring a second condition; comparing the second condition to a second setpoint to determine a second condition error; and modulating compressor capacity relative to the second condition error if the magnitude of the second conditioned error is greater than the magnitude of the first conditioned error.

Abstract: A method of controlling an expansion valve in a refrigeration system. The method comprises the steps of controlling the modulation of the expansion valve based upon a first feedback control criteria; and controlling the modulation of the expansion valve based upon a second feed forward control criteria.

Abstract: A method of controlling an expansion valve in a refrigeration system. The method comprises the steps of controlling the modulation of the expansion valve based upon a first feedback control criteria; and controlling the modulation of the expansion valve based upon a second feed forward control criteria.

Abstract: A process for controlling an absorbent-refrigerant solution concentration in an absorption cooling system to prevent crystallization of the solution in which the crystallization temperature of the absorbent-refrigerant solution is calculated and the temperature of an absorbent-enriched solution, or strong solution, from the absorption unit heat exchanger is measured. Based upon the crystallization temperature and the measured absorbent-enriched solution temperature, the concentration of the absorbent is calculated using an iteration algorithm. Based upon the calculated concentration of absorbent in the absorbent-enriched solution, the concentration of the absorbent-enriched solution is adjusted by adjusting the heat input to the absorption system generator to prevent crystallization of the absorbent.

Abstract: A method of controlling the capacity of a chiller system, the chiller system including a circularly linked compressor, condenser, expansion device, and evaporator. The method comprises the steps of: measuring a first chiller system parameter; determining a first parameter error as a function of the difference between the first parameter and a first setpoint; measuring a second chiller system parameter; determining a second parameter error as a function of the difference between the second parameter and a second setpoint; providing a first mode of capacity control where the compressor is modulated in response to the first parameter error and the expansion valve is modulated in response to the second parameter error; and providing a second mode of capacity control where the compressor is maintained at a minimum capacity and the expansion valve is modulated in response to the first parameter error.