Abstract: A control system for a heat transfer circuit, an HVAC unit containing a heat transfer circuit, and a method of retrofitting an HVAC unit are described. The control system includes a thermostat having a first cooling stage signal output terminal and a second cooling stage signal output terminal; a controller electrically connected to the thermostat; a sensor electrically connected to the controller; and a switch electrically connected to the controller, and that receives a first cooling stage signal output from the thermostat. The switch is in a first state when a sensor value from the sensor is less than a threshold, and a second state when the sensor value from the sensor is greater than or equal to the threshold.

Abstract: Apparatuses, systems and methods are directed to heat exchangers that are made of microchannel tubes and that have offset fins of various geometries and density. The heat exchanger coils can be implemented in various refrigeration and/or heating, ventilation, and air conditioning (HVAC) units or systems thereof.

Abstract: Embodiments of a heat exchanger, e.g. a micro-channel heat exchanger are disclosed. The heat exchanger may include a plurality of rows of micro-channel tubes, each of which can be configured to direct a working fluid in a specific direction. The heat exchanger may include one or more distributors in a distribution header of the heat exchanger, each of which can be connected to a different application circuit (e.g. a refrigeration circuit) so that a capacity of the heat exchanger may be regulated. The heat exchanger as disclosed herein can be used as an evaporator and/or a condenser in a refrigeration system.

Abstract: Apparatuses, systems and methods are directed to heat exchangers that are made of microchannel tubes and that have offset fins of various geometries and density. The heat exchanger coils can be implemented in various refrigeration and/or heating, ventilation, and air conditioning (HVAC) units or systems thereof.

Abstract: A control system for a heat transfer circuit, an HVAC unit containing a heat transfer circuit, and a method of retrofitting an HVAC unit are described. The control system includes a thermostat having a first cooling stage signal output terminal and a second cooling stage signal output terminal; a controller electrically connected to the thermostat; a sensor electrically connected to the controller; and a switch electrically connected to the controller, and that receives a first cooling stage signal output from the thermostat. The switch is in a first state when a sensor value from the sensor is less than a threshold, and a second state when the sensor value from the sensor is greater than or equal to the threshold.

Abstract: Embodiments of a heat exchanger, e.g. a micro-channel heat exchanger are disclosed. The heat exchanger may include a plurality of rows of micro-channel tubes, each of which can be configured to direct a working fluid in a specific direction. The heat exchanger may include one or more distributors in a distribution header of the heat exchanger, each of which can be connected to a different application circuit (e.g. a refrigeration circuit) so that a capacity of the heat exchanger may be regulated. The heat exchanger as disclosed herein can be used as an evaporator and/or a condenser in a refrigeration system.

Abstract: A refrigerant system includes a compressor with a discharge valve that temporarily restricts the compressor's outflow at startup so that the discharge pressure can quickly rise to force lubricant back to the compressor. The discharge valve also helps prevent an axial face of a rotor of a screw compressor from rubbing against a bearing housing axial face of the compressor's housing. When the system turns off under certain low ambient air temperature conditions, the valve closes to help prevent the system's evaporator from freezing up. The discharge valve includes a novel arrangement of a piston, a valve stem extending from the piston, and a valve plug pivotally attached to the valve stem. The pivotal connection ensures a positive seal between the valve plug and a valve seat. A somewhat restricted fluid passageway between the valve's discharge chamber and piston chamber helps prevent the valve from chattering as the valve opens.

Abstract: A refrigerant system includes a compressor with a discharge valve that temporarily restricts the compressor's outflow at startup so that the discharge pressure can quickly rise to force lubricant back to the compressor. The discharge valve also helps prevent an axial face of a rotor of a screw compressor from rubbing against a bearing housing axial face of the compressor's housing. When the system turns off under certain low ambient air temperature conditions, the valve closes to help prevent the system's evaporator from freezing up. The discharge valve includes a novel arrangement of a piston, a valve stem extending from the piston, and a valve plug pivotally attached to the valve stem. The pivotal connection ensures a positive seal between the valve plug and a valve seat. A somewhat restricted fluid passageway between the valve's discharge chamber and piston chamber helps prevent the valve from chattering as the valve opens.

Abstract: Disclosed are modeling and process control techniques for manufacturing products. More specifically, computer-aided modeling techniques are described that allow the manufacturer to predict a profile for a multivariate output that is necessary to achieve a target performance property for a manufactured product.

Abstract: A chiller system includes at least two refrigerant circuits. In a low ambient temperature condition, only one refrigerant circuit is activated, but its condenser fan is de-energized. To provide some airflow across the condenser of the activated circuit, a condenser fan of the inactive circuit is energized. A small air duct allows the condenser fan of the inactive circuit to draw a low volume of air across the condenser of the active circuit.

Abstract: An evaporator for a refrigeration chiller includes a tube bundle in which at least a portion of the tubes of the tube bundle are immersed in a pool which include both liquid refrigerant and is lubricant. Liquid refrigerant and lubricant are deposited into the pool at a first pool location. Because of the vaporization of refrigerant that occurs within the pool, a pattern of flow is established and managed that causes the lubricant in the pool to migrate from the location of its deposit into the pool to a second pool location. An outlet is provided at the second pool location from which lubricant is drawn out of the evaporator.

Abstract: An evaporator for a refrigeration chiller includes a tube bundle in which at least a portion of the tubes of the tube bundle are immersed in a pool which include both liquid refrigerant and is lubricant. Liquid refrigerant and lubricant are deposited into the pool at a first pool location. Because of the vaporization of refrigerant that occurs within the pool, a pattern of flow is established and managed that causes the lubricant in the pool to migrate from the location of its deposit into the pool to a second pool location. An outlet is provided at the second pool location from which lubricant is drawn out of the evaporator.

Abstract: A heat exchanger comprising: a plurality of longitudinally extending tubes grouped into at least first, second and third passes; the tubes in the first pass being serially connected with tubes in the second pass; the tubes in the second pass being serially connected with tubes in the third pass; and wherein the number of tubes in the first pass is greater than the number of tubes in the third pass.

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: An assured supply of lubricant to the compressor in a refrigeration chiller is provided by a reservoir that is connected in parallel with the main line by which lubricant is supplied to the compressor. The reservoir is connected to the main lubricant supply line in a manner such that if the lubricant supply line is blown dry, as can occur as a result of an unusual or abnormal chiller shutdown condition, a critical portion of the supply line will be refilled by the reservoir relatively very quickly which assures the immediate availability of lubricant to the compressor from that portion of the lubricant supply line when it next starts up.

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 protection system for a compressor. The system comprises a compressor having a discharge and including at least one rotor and at least one bearing; a lubrication system including at least one oil recovery device for recovering oil from the compressor, and further including bearing conduit connecting the oil recovery device to the compressor bearing and including rotor conduit for connecting the oil recovery device to the compressor rotors; and an oil protection system. The oil protection system includes a compressor discharge temperature sensor located in the discharge for sensing the temperature of a lubricant/refrigerant mixture discharged by the compressor, a differential pressure sensor located in the bearing conduit for measuring a differential pressure in the bearing conduit, and an oil detector located in the rotor conduit for detecting the presence of oil in the rotor conduit.

Abstract: A refrigeration system employing a screw compressor and a falling film evaporator makes use of high-side pressure to drive lubricant, which escapes the compressor and collects as a lubricant-rich mixture of lubricant and refrigerant in the system evaporator, back to the compressor. The mixture is cyclically exposed to high-side pressure for a period of time which (i) varies in accordance with the difference between a sensed condenser-related pressure and a sensed evaporator-related pressure and (ii) is calculated to maintain a predetermined oil concentration in the lubricant-rich mixture in the evaporator so as to minimize the parasitic losses to system efficiency associated with the oil return process.