Refrigeration System with an Oil Drain Conduit and Methods of Use

Refrigeration systems are used to regulate environmental conditions within an enclosed space. Refrigeration systems are used for a variety of applications, such as in supermarkets and warehouses, to cool stored items. For example, refrigeration systems may provide cooling operations for refrigerators and freezers.

The systems and methods in the present disclosure provide practical applications and technical advantages that overcome the current technical problems described herein. In certain instances, oil from various sources in refrigeration systems, such as compressors, may accumulate in the refrigerant and build up in heat exchanger coils and conduits surrounding the heat exchanger unit. The presence of oil in the heat exchanger coils reduces heat transfer efficiency and increases the total energy required to operate the system. Additionally, if enough oil accumulates at the outlet of the heat exchanger coils, a suction pressure applied by the compressor during start up conditions may pull the oil into the compressor. This may cause damage to the compressor. Although an oil separator may be included in the refrigeration system to reduce an amount of oil in the circulating refrigerant, oil separators do not operate at one-hundred percent efficiency, and therefore some residual oil remains in the refrigerant.

The provided systems and methods are integrated into the practical application of reducing an amount of oil contaminant in a heat exchanger unit to improve operating efficiency and reduce the total energy required to operate the system. During operation, working fluid that comprises refrigerant and an oil contaminant passes through a heat exchanger of the provided systems and methods and is transferred to a header. The oil contaminant may accumulate towards a bottom surface of the header due to the higher density of the oil relative to the refrigerant. The provided systems and methods may facilitate reducing the amount of oil contaminant in the heat exchanger unit using a check valve and an oil drain conduit. For example, the header may include a first outlet in fluid communication with the check valve and a second outlet in fluid communication with the oil drain conduit. The first outlet of the header is positioned at a height above the second outlet of the header. The oil drain conduit includes an outlet that discharges working fluid to a position located upstream of the check valve and downstream of a compressor. During operation, a differential pressure induced by the check valve and a suction pressure from the compressor positioned downstream of the check valve causes a portion of the working fluid to be suctioned from the header through the oil drain conduit. The suction of the working fluid through the oil drain conduit pulls the oil contaminant along with it and reduces an amount of oil contaminant in the heat exchanger unit, thereby improving operating efficiency and reducing the total energy required to operate the system.

In some embodiments, the present disclosure provides a refrigeration system. The refrigeration system includes a low side heat exchanger configured to receive a working fluid. The low side heat exchange includes one or more circuits of coils, where each of the one or more circuits of coils include a hollow interior configured to receive the working fluid. The one or more circuits of coils are configured to cool a space proximate the low side heat exchanger by transferring heat between airflow passing across an external surface of the one or more circuits of coils and the working fluid passing though the hollow interior of the one or more circuits of coils. The refrigeration system includes a header positioned downstream of the one or more circuits of coils. The header includes one or more inlets configured to receive the working fluid from the one or more circuits of coils. The one or more inlets place the hollow interior of the one or more circuits of coils in fluid communication with a hollow interior of the header. The header includes a first outlet in fluid communication with the hollow interior of the header, and a second outlet in fluid communication with the hollow interior of the header. The refrigeration system includes a check valve positioned downstream of the first outlet. The check valve is configured to allow the working fluid to flow through the check valve when a pressure difference across the check valve exceeds a threshold pressure. The refrigeration system includes a compressor positioned downstream of the check valve, where the compressor is configured to compress the working fluid received from the check valve. The refrigeration system includes an oil drain conduit comprising an inlet in fluid communication with the second outlet of the header. The oil drain conduit comprises an outlet configured to discharge at least a portion of the working fluid to a position downstream of the check valve and upstream of the compressor.

Certain embodiments of this disclosure may include some, all, or none of these advantages. These advantages and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

Embodiments of the present disclosure and its advantages are best understood by referring toof the drawings, like numerals being used for like and corresponding parts of the various drawings.

As described above, in certain instances, oil from various sources in refrigeration systems, such as compressors, may accumulate in the refrigerant and build up in heat exchanger coils and conduits surrounding the heat exchanger unit. The presence of oil in the heat exchanger coils reduces heat transfer efficiency and increases the total energy required to operate the system. Additionally, if enough oil accumulates at the outlet of the heat exchanger coils, a suction pressure applied by the compressor during start up conditions may pull the oil into the compressor. This may cause damage to the compressor.

The provided systems and methods may facilitate reducing the amount of oil contaminant in the heat exchanger unit using a check valve and an oil drain conduit. For example, the header may include a first outlet in fluid communication with the check valve and a second outlet in fluid communication with the oil drain conduit. The first outlet of the header is positioned at a height above the second outlet of the header. The oil drain conduit includes an outlet that discharges working fluid to a position located upstream of the check valve and downstream of a compressor. During operation, a differential pressure induced by the check valve and a suction pressure from the compressor positioned downstream of the check valve causes a portion of the working fluid to be suctioned from the header through the oil drain conduit. The suction of the working fluid through the oil drain conduit pulls the oil contaminant along with it and reduces an amount of oil contaminant in the heat exchanger unit, thereby improving operating efficiency and reducing the total energy required to operate the system.

illustrates an example refrigeration systemaccording to various embodiments of the present disclosure. In general, the refrigeration systemincludes a refrigerant conduit subsystem, a first compressor unit, an oil separator, a first high side heat exchanger, a valve, a flash tank, a flash gas valve, a first low side heat exchanger unit, a second low side heat exchanger(), and a second compressor unit, and a controller. In some embodiments, the refrigeration systemis a transcritical refrigeration system that circulates a working fluid, such as a transcritical refrigerant (e.g., CO).

Refrigerant conduit subsystemfacilitates the movement of a working fluid (e.g., refrigerant) through a refrigeration cycle such that the working fluid flows as illustrated by arrows in. The refrigerant conduit subsystemincludes any conduit, tubing and the like that is illustrated influidly connecting components of the refrigeration system.

The first compressor unitis fluidly coupled to the refrigerant conduit subsystem. The first compressor unitincludes one or more compressors that is configured to compress (i.e., increase the pressure) of the refrigerant. In some embodiments, the first compressor unitis positioned downstream of the first low side heat exchanger unitand the second compressor unit. The one or more compressors of the first compressor unitis in signal communication with the controllerusing wired and/or wireless connection. The controllerprovides commands and/or signals to control operation of the one or more compressors of the first compressor unit. For example, the controllermay provide signals to instruct the one or more compressor(s) to operate at a predetermined compressor speed. The one or more compressor(s) of the first compressor unitmay vary by design and/or capacity. For example, some compressor designs may be more energy efficient than other compressor designs, and the one or more compressor(s) of the first compressor unitmay have modular capacity (e.g., a capability to vary capacity).

The oil separatoris fluidly coupled to the refrigerant conduit subsystemand may be located downstream of the first compressor unitand the second compressor unit. The oil separatoris operable to separate an oil contaminant (e.g., compressor oil) from the refrigerant. The refrigerant exiting the oil separatoris provided to the first high side heat exchanger, while the oil may be collected and returned to the first compressor unitand the second compressor unit, as appropriate.

The first high side heat exchangeris fluidly coupled to the refrigerant conduit subsystem. The first high side heat exchangeris positioned downstream from oil separator, the first compressor unitand the second compressor unit. The first high side heat exchangeris configured to receive refrigerant from the first compressor unitand the second compressor unit. The first high side heat exchangeris configured to apply a cooling stage to the received refrigerant. In some embodiments, the first high side heat exchangeris a gas cooler or a condenser. The first high side heat exchangermay comprise cooling coils configured to circulate the received refrigerant, where air is forced across an external surface of the cooling coils. In certain configurations, heat is removed from the refrigerant and transferred to the air surrounding the cooling coils. The first high side heat exchangermay be positioned on a rooftop so that heat removed from the refrigerant may be discharged into the air. In some embodiments, the first high side heat exchangercomprises a fan that transports the air across the outer surface of the coils. The fan may be in communication with the controller(e.g., via wired and/or wireless communication) to receive control signals for turning the fan on, off, and for controlling the speed of the fan to regulate the flow of air across the coils.

The valveis configured to receive refrigerant from the first high side heat exchangerand is fluidly coupled to the refrigerant conduit subsystem. The valvemay be an expansion valve, a flow control valve (e.g., a thermostatic expansion valve), or any suitable valve that is configured to reduce the pressure of the refrigerant in the refrigerant conduit subsystem. The valvemay be in communication with controller(e.g., via wired or wireless communication) to receive control signals for opening, closing, and/or to provide flow measurement signals corresponding to flow rate of refrigerant through the valve.

The flash tankis fluidly coupled to the refrigerant conduit subsystemand is positioned downstream of the first high side heat exchanger. The flash tankis configured to separate the refrigerant into a vapor refrigerant and a liquid refrigerant. Typically, the vapor refrigerant collects near the top of the flash tankand the liquid refrigerant is collected at the bottom of the flash tank. In some embodiments, the liquid refrigerant flows from flash tankand provides cooling to the first low side heat exchanger unitand the second low side heat exchanger unit(). The flash gas valvemay be positioned in the refrigerant conduit subsystemand located in a portion of the refrigerant conduit subsystemthat connects the flash tankto the first compressor unit. The flash gas valveis configured to open and close to permit or restrict the flow of flash gas discharged from flash tank. The controlleris in communication with the flash gas valveand controls its operation.

The first low side heat exchanger unitis fluidly coupled to the refrigerant conduit subsystemand is located downstream of the flash tank. The first low side heat exchanger unitis configured to receive liquid refrigerant from the flash tankthrough the refrigerant conduit subsystem. The first low side heat exchanger unitis configured to use the refrigerant to provide cooling to a first space proximate to the first low side heat exchanger unit. As an example, the first low side heat exchanger unitmay be part of a refrigerated case and/or cooler for storing items that should be kept at particular temperatures. The refrigeration systemmay include any appropriate number of first low side heat exchanger unitswith the same or a similar configuration to that shown for the example the first low side heat exchanger unitin.

In some embodiments, the first low side heat exchanger unitcomprises a first expansion valvepositioned upstream of a first low side heat exchanger. The first expansion valveis fluidly coupled to the refrigerant conduit subsystemand configured to reduce the pressure of the refrigerant. The first expansion valvemay be a flow control valve (e.g., a thermostatic expansion valve valve) or any other suitable valve for reducing pressure from the working fluid while, optionally, providing control of the rate of flow of the refrigerant. The first expansion valvemay be in communication with the controller(e.g., via wired and/or wireless communication) to receive control signals for opening and/or closing associated valves and/or provide flow measurement signals corresponding to the rate of refrigerant through the refrigerant conduit subsystem.

The first low side heat exchangeris fluidly coupled to the refrigerant conduit subsystemand configured to receive refrigerant from the first expansion valve. The first low side heat exchangeris generally any heat exchanger configured to provide heat transfer between the refrigerant flowing through the refrigerant conduit subsystemand airflow passing across an external surface of the first low side heat exchanger. The first low side heat exchangermay include one or more circuits of coilsconfigured to circulate the refrigerant received through the first low side heat exchanger.

Referring to, the one or more circuits of coilsinclude a hollow interiorconfigured to receive the refrigerant from the first expansion valve. The first low side heat exchangermay act as an evaporator to transfer heat between the airflow passing across an external surfaceof the one or more circuits of coilsand the refrigerant to produce conditioned airflow. The conditioned airflow may then be transferred to the first space proximate the first low side heat exchanger unitto cool the first space. The first low side heat exchanger unitmay include a fan to transport airflow across the external surfaceof the one or more circuits of coils. The fan may be in communication with the controller(e.g., via wired and/or wireless communication) to receive control signals for turning the fan on, off and for controlling the speed of the fan to regulate the flow of air across the coils. In some embodiments, the first expansion valveis configured to achieve a refrigerant temperature into the first low side heat exchangerat a predefined temperature for a given application (e.g., about −6° C.).

In some embodiments, a headeris positioned downstream of the one or more circuits of coils. As shown in, the headerincludes one or more inletsconfigured to receive the refrigerant from the one or more circuits of coils. The one or more inletsplaces the hollow interiorof the one or more circuits of coilsin fluid communication with a hollow interiorof the header. The headerincludes a first outletin fluid communication with the hollow interiorof the headerand a second outletin fluid communication with the hollow interiorof the header. In some embodiments, the second outletis positioned below the first outlet. For example, the headermay extend between a top surfaceand a bottom surface. The first outletmay be positioned at a height (H) above the bottom surfaceof the header. A volume between the first outletand the bottom surfacemay define an oil collection space. The second outletmay be positioned in the oil collection space. In some embodiments, the second outletis positioned on the bottom surfaceof the header. During operation, oil contaminant that is present in the refrigerant may accumulate within the oil collection spaceof the header.

In some embodiments, a check valveis positioned downstream of the first outletof the header. The check valveis configured to allow the refrigerant to flow through the check valvewhen a pressure difference across the check valveexceeds a threshold pressure. For example, if the pressure difference across the check valvedoes not exceed the threshold pressure, the check valvewill remain in a closed position. If the pressure difference across the check valveexceeds the threshold pressure, the check valvewill open and allow the refrigerant to flow through the check valve. In some embodiments, the threshold pressure of the check valvemay be 0.5 psi to 5 psi.

In some embodiments, an oil drain conduitis positioned downstream of the second outletof the header. The oil drain conduitincludes an inletthat is in fluid communication with the second outletof the header. The oil drain conduitincludes an outletthat is configured to discharge at least a portion of the refrigerant to a position in the refrigerant conduit subsystemthat is downstream of the check valveand upstream of the first compressor unit. In some embodiments, the oil drain conduithas a cross-sectional area that is less than a cross-sectional area of the header. For example, the cross-sectional area of the headermay be at least four times greater than the cross-sectional area of the oil drain conduit, or at least five times greater, at least six times greater, to at least seven times greater, or less than nine times greater, or less than ten times greater than the cross-sectional area of the oil drain conduit. In one non-limiting example, the diameter of the oil drain conduitis a quarter of an inch.

In some embodiments, the oil drain conduitis sized such that during operation a differential pressure induced by the check valveand a suction pressure from the first compressor unitcauses at least a portion of the oil contaminant in the refrigerant to pass from the inletto the outletof the oil drain conduit. The suction of the refrigerant through the oil drain conduitpulls oil contaminant along with it and reduces an amount of the oil contaminant in the headerand the first low side heat exchanger, thereby improving operating efficiency and reducing the total energy required to operate the refrigeration system. The oil drain conduitmay have any suitable geometry, e.g., a U-shape, square, or rectangular geometry.

A valvemay be positioned downstream of the check valveand upstream of the first compressor unit. The valvemay be configured to regulate the flow rate of the refrigerant directed to the first compressor unit. In some embodiments, the oil drain conduitis configured to discharge at least a portion of the refrigerant to a position in the refrigerant conduit subsystemthat is downstream of the check valveand upstream of the valve.

The valvemay be in communication with the controller(e.g., via wired and/or wireless communication) to receive control signals for opening and/or closing the valveand/or provide flow measurement signals corresponding to the rate of refrigerant through the refrigerant conduit subsystem.

The second low side heat exchanger unit() is generally similar to the first low side heat exchanger unitbut configured to operate at lower temperatures (e.g., for deep freezing applications near about −30° C. or the like). The second low side heat exchanger unit() is fluidly coupled to the refrigerant conduit subsystemand is located downstream of the flash tank. The second low side heat exchanger unit() is configured to receive liquid refrigerant from the flash tankthrough the refrigerant conduit subsystem. The second low side heat exchanger unit() is configured to use the refrigerant to provide cooling to a second space proximate to the second low side heat exchanger unit(). As an example the second low side heat exchanger unit() may be part of a refrigerated case and/or cooler for storing items that should be kept at particular temperatures. The refrigeration systemmay include any appropriate number of second low side heat exchanger units() with the same or a similar configuration to that shown for the example the second low side heat exchanger unit() in.

In some embodiments, the second low side heat exchanger unit() includes a second expansion valve() that is positioned upstream of a second low side heat exchanger(). In some embodiments, the second expansion valve() is configured to achieve a refrigerant temperature into the second low side heat exchanger() at a predefined temperature for a given application (e.g., about −30° C.). The second expansion valve() is fluidly coupled to the refrigerant conduit subsystemand configured to reduce the pressure of the refrigerant. The second expansion valve() may be a flow control valve (e.g., a thermostatic expansion valve valve) or any other suitable valve for reducing pressure from the working fluid while, optionally, providing control of the rate of flow of the refrigerant. The second expansion valve() may be in communication with the controller(e.g., via wired and/or wireless communication) to receive control signals for opening and/or closing associated valves and/or provide flow measurement signals corresponding to the rate of refrigerant through the refrigerant conduit subsystem.

The second low side heat exchanger() is fluidly coupled to the refrigerant conduit subsystemand configured to receive refrigerant from the second expansion valve(). The second low side heat exchanger() is generally any heat exchanger configured to provide heat transfer between the refrigerant flowing through the refrigerant conduit subsystemand airflow passing across an external surface of the second low side heat exchanger(). The second low side heat exchanger() may include one or more circuits of coils() configured to circulate the refrigerant received through the second low side heat exchanger. The second low side heat exchanger() and the one or more circuits of coils() may have the same or similar configuration to the first low side heat exchangeras described in. The second low side heat exchanger unit() may include a fan to transport airflow across the one or more circuits of coils(). The fan may be in communication with the controller(e.g., via wired and/or wireless communication) to receive control signals for turning the fan on, off and for controlling the speed of the fan to regulate the flow of air across the coils.

In some embodiments, a second header() is positioned downstream of the one or more circuits of coils(). The second header() has the same or similar configuration to the headerdescribed in. As shown in, the second header() includes one or more inlets() configured to receive the refrigerant from the one or more circuits of coils(). The one or more inlets() places the hollow interior() of the one or more circuits of coils() in fluid communication with a hollow interiorof the second header(). The second header() includes a first outlet() in fluid communication with the hollow interior() of the second header() and a second outlet() in fluid communication with the hollow interior() of the second header(). In some embodiments, the second outlet() is positioned below the first outlet(). For example, the second header() may extend between a top surface() and a bottom surface(). The first outlet() may be positioned at a height (H) above the bottom surface() of the second header(). A volume between the first outlet() and the bottom surface() may define the oil collection spaceof the second header(). The second outlet() may be positioned in the oil collection space. In some embodiments, the second outlet() is positioned on the bottom surface() of the second header(). During operation, oil contaminant that is present in the refrigerant may accumulate within the oil collection spaceof the second header().

In some embodiments, a second check valve() is positioned downstream of the first outletof the second header(). The second check valve() is configured to allow the refrigerant to flow through the second check valve() when a pressure difference across the second check valve() exceeds a threshold pressure. For example, if the pressure difference across the second check valve() does not exceed the threshold pressure, the second check valve() will remain in a closed position. If the pressure difference across the second check valve() exceeds the threshold pressure, the second check valve() will open and allow the refrigerant to flow through the second check valve(). In some embodiments, the threshold pressure of the second check valve() may be 0.5 psi to 5 psi.

In some embodiments, a second oil drain conduit() is positioned downstream of the second outlet() of the second header(). The second oil drain conduit() includes an inlet() that is in fluid communication with the second outlet() of the second header(). The second oil drain conduit() includes an outlet() that is configured to discharge at least a portion of the refrigerant to a position in the refrigerant conduit subsystemthat is downstream of the second check valve() and upstream of the second compressor unit. In some embodiments, the second oil drain conduit() has a cross-sectional area that is less than a cross-sectional area of the second header(). For example, the cross-sectional area of the second header() may be at least four times greater than the cross-sectional area of the second oil drain conduit(), or at least five times greater, at least six times greater, to at least seven times greater, or less than nine times greater, or less than ten times greater than the cross-sectional area of the second oil drain conduit(). In one non-limiting example, the diameter of the second oil drain conduit() is a quarter of an inch.

In some embodiments, the second oil drain conduit() is sized such that during operation a differential pressure induced by the second check valve() and a suction pressure from the second compressor unitcauses at least a portion of the oil contaminant in the refrigerant to pass from the inlet() to the outlet() of the second oil drain conduit(). The suction of the refrigerant through the second oil drain conduitpulls oil contaminant along with it and reduces an amount of the oil contaminant in the second header() and the second heat exchanger(), thereby improving operating efficiency and reducing the total energy required to operate the refrigeration system. The second oil drain conduit() may have any suitable geometry, e.g., a U-shaped, square, or rectangular geometry.

A second valve() may be positioned downstream of the second check valveand upstream of the second compressor unit. The second valve() may be configured to regulate the flow rate of the refrigerant directed to the first compressor unit. In some embodiments, the second oil drain conduit() is configured to discharge at least a portion of the refrigerant to a position in the refrigerant conduit subsystemthat is downstream of the second check valve() and upstream of the second valve(). The second valve() may be in communication with the controller(e.g., via wired and/or wireless communication) to receive control signals for opening and/or closing the second valve() and/or provide flow measurement signals corresponding to the rate of refrigerant through the refrigerant conduit subsystem.

The second compressor unitis fluidly coupled to the refrigerant conduit subsystem. The second compressor unitincludes one or more compressors that is configured to compress (i.e., increase the pressure) of the refrigerant. In some embodiments, the second compressor unitis positioned downstream of the second low side heat exchanger unit(). The one or more compressors of the second compressor unitis in signal communication with the controllerusing wired and/or wireless connection. The controllerprovides commands and/or signals to control operation of the one or more compressors of the second compressor unit. For example, the controllermay provide signals to instruct the one or more compressor(s) to operate at a predetermined compressor speed. The one or more compressor(s) of the second compressor unitmay vary by design and/or capacity. For example, some compressor designs may be more energy efficient than other compressor designs, and the one or more compressor(s) of the second compressor unitmay have modular capacity (e.g., a capability to vary capacity).

The controlleris in communication with various components in the system including but not limited to: valves,,,(),,(); compressors of the first compressor unitand the second compressor unit; fans and/or blowers of the first high side heat exchanger, the first low side heat exchanger unit, and the second low side heat exchanger unit(). The controllerincludes a processor, a network interface circuit, and a memory. The processorincludes one or more processors operably coupled to the memory. The processoris any electronic circuitry including, but not limited to, state machines, one or more central processing unit (CPU) chips, logic units, cores (e.g., a multi-core processor), field-programmable gate array (FPGAs), application specific integrated circuits (ASICs), or digital signal processors (DSPs) that communicatively couples to memoryand controls the operation of refrigeration system. The processormay be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processoris communicatively coupled to and in signal communication with the memory. The one or more processors are configured to process data and may be implemented in hardware or software. For example, the processormay be 8-bit, 16-bit, 32-bit, 64-bit or of any other suitable architecture. The processormay include an arithmetic logic unit (ALU) for performing arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memoryand executes them by directing the coordinated operations of the ALU, registers, and other components. The processormay include other hardware and software that operates to process information, control the refrigeration system, and perform any of the functions described herein (e.g., with respect to). The processoris not limited to a single processing device and may encompass multiple processing devices. Similarly, the controlleris not limited to a single controller but may encompass multiple controllers.

The network interface circuitis configured to communicate data and signals with other devices. For example, the network interface circuitmay be configured to communicate electrical signals with the components of the refrigeration system. The network interface circuitmay be configured to communicate with other devices and systems. The network interface circuitmay provide and/or receive, for example, compressor speed signals, compressor on/off signals, valve open/close signals, temperature signals, pressure signals, temperature setpoints, environmental conditions, and an operating mode status for the refrigeration systemand send electrical signals to the components of the refrigeration system. The network interface circuitmay include ports or terminals for establishing signal communications between the controllerand other devices. The network interface circuitmay be configured to enable wired and/or wireless communications. Suitable network interface circuitsinclude a WIFI interface, a local area network (LAN) interface, a wide area network (WAN) interface, a modem, a switch, or a router. The network interface circuitmay be configured to use any suitable type of communication protocol as would be appreciated by one of ordinary skill in the art.

The memoryincludes one or more disks, tape drives, or solid-state drives, and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store valve instructions, compressor instructions, and fan and/or blower operating instructionsand data that are read during program execution. The memorymay be volatile or non-volatile and may include ROM, RAM, ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM). The memoryis operable (or configured) to store information used by the controllerand/or any other logic and/or instructions for performing the function described in this disclosure.

illustrates an example operational flowfor operating the refrigeration system of. The operational flowcan logically be described in two parts. The first part includes operations-, which generally includes cooling a working fluid using a first high side heat exchanger, reducing the pressure of the working fluid exiting the first high side heat exchangerusing a valve, flashing the working fluid exiting the expansion valve in a flash tankto generate a liquid refrigerant and a vapor refrigerant, cooling a first space using a portion of the liquid refrigerant exiting the flash tankin a first low side heat exchanger unit, and compressing the working fluid exiting the first low side heat exchanger unitin a first compressor unit. The second part includes operations-, which generally includes determining whether a cooling demand exists for a second low side heat exchanger unit(). If a cooling demand exists, the second part includes cooling a second space using a portion of the liquid refrigerant exiting the flash tank in a second low side heat exchanger unit, and compressing the refrigerant exiting the second low side heat exchanger unit in a second compressor unit.

In operation, the operational flowmay begin at operation, which includes cooling a working fluid using a first high side heat exchanger. For example, the first high side heat exchanger may receive the working fluid from the first compressor unit, where the oil separatormay optionally reduce an amount of oil contaminant in the working fluid before the first high side heat exchangerreceives the working fluid. The first high side heat exchangeris configured to apply a cooling stage to the working fluid received. In some embodiments, the first high side heat exchangeris a gas cooler or a condenser that is configured to transfer heat from the working fluid within the first high side heat exchangerto air that is forced across the first high side heat exchanger.

In operation, the operational flowincludes reducing the pressure of the working fluid exiting the first high side heat exchangerin valve. In some embodiments, the valvemay be an expansion valve or a flow control valve that is configured to reduce the pressure of the working fluid in the refrigerant conduit subsystem.

In operation, the operational flowincludes flashing the refrigerant exiting the valvein a flash tank. The flash tankis configured to separate the refrigerant into a vapor refrigerant and a liquid refrigerant. Typically, the vapor refrigerant collects near the top of the flash tankand the liquid refrigerant is collected at the bottom of the flash tank. The flash gas valvemay regulate the flow rate of vapor refrigerant exiting the flash tank, which is in fluid communication with the first compressor unit. In some embodiments, the liquid refrigerant flows from flash tankand provides cooling to the first low side heat exchanger unitand the second low side heat exchanger unit().

In operation, the operational flowincludes cooling a first space proximate the first low side heat exchanger unit. For example, operationmay include cooling the first space with the liquid refrigerant exiting the flash tankusing the first low side heat exchanger unit. To cool the first space, operationmay include reducing the pressure of the liquid refrigerant exiting the flash tankin a first expansion valveand cooling the first space by passing the refrigerant through the first low side heat exchanger. The first low side heat exchangermay act as an evaporator to transfer heat between the airflow passing across an external surfaceof the one or more circuits of coilsand the refrigerant to produce conditioned airflow. The conditioned airflow may then be transferred to the first space proximate the first low side heat exchanger unitto cool the first space.

During operation, the working fluid exiting the first low side heat exchangeris placed in fluid communication with the header. The headerincludes one or more inletsconfigured to receive the refrigerant from the one or more circuits of coilsin the first low side heat exchanger. The one or more inletsplaces the hollow interiorof the one or more circuits of coilsin fluid communication with a hollow interiorof the header. The headerincludes a first outletand a second outlet.

The check valveis positioned downstream of the first outletof the header, and the oil drain conduitis positioned downstream of the second outletof the header. The oil drain conduitincludes an inlet that is in communication with the second outletand an outlet that is configured to discharge at least a portion of the refrigerant and oil contaminant to a position in the refrigerant conduit subsystemthat is downstream of the check valveand upstream of the first compressor unit. During operation, an oil contaminant that is present in the refrigerant may accumulate towards a bottom surfaceof the headerdue to the higher density of the oil contaminant relative to the refrigerant. In some embodiments, the oil drain conduitis sized such that during operation a differential pressure induced by the check valveand a suction pressure from the first compressor unitcauses at least a portion of the oil contaminant in the refrigerant to pass from the inletto the outletof the oil drain conduit. The suction of the refrigerant through the oil drain conduitpulls oil contaminant along with it and reduces an amount of the oil contaminant in the headerand the first heat exchanger, thereby improving operating efficiency and reducing the total energy required to operate the refrigeration system. The operational flowcontinues to operation, which includes compressing the refrigerant exiting the first low side heat exchanger unitusing the first compressor unit.

At decision block, the operational flowincludes determining whether a cooling demand exists for the second low side heat exchanger unit(). If a cooling demand exists, the operational flowproceeds to operation, which includes cooling a second space proximate the second low side heat exchanger unit(). For example, operationmay include cooling the second space with the liquid refrigerant exiting the flash tankusing the second low side heat exchanger unit(). To cool the second space, operationmay include reducing the pressure of the liquid refrigerant exiting the flash tankin a second expansion valve() and cooling the second space by passing the refrigerant through the second low side heat exchanger(). The second low side heat exchangermay act as an evaporator to transfer heat between the airflow passing across an external surface() of the one or more circuits of coils() and the refrigerant to produce conditioned airflow. The conditioned airflow may then be transferred to the second space proximate the second low side heat exchanger unit() to cool the second space.

During operation, the working fluid exiting the second low side heat exchanger() is placed in fluid communication with the second header(). The second header() includes one or more inlets() configured to receive the refrigerant from the one or more circuits of coils() in the second low side heat exchanger(). The one or more inlets() places the hollow interior() of the one or more circuits of coils() in fluid communication with a hollow interior() of the second header(). The second header() includes a first outlet() and a second outlet().

The second check valve() is positioned downstream of the first outlet() of the second header(), and the second oil drain conduit() is positioned downstream of the second outlet() of the second header(). The second oil drain conduit() includes an inlet that is in communication with the second outlet() and an outlet that is configured to discharge at least a portion of the refrigerant and oil contaminant to a position in the refrigerant conduit subsystemthat is downstream of the second check valve() and upstream of the second compressor unit. During operation, an oil contaminant that is present in the refrigerant may accumulate towards a bottom surface() of the second header() due to the higher density of the oil contaminant relative to the refrigerant. In some embodiments, the second oil drain conduit() is sized such that during operation a differential pressure induced by the second check valve() and a suction pressure from the second compressor unitcauses at least a portion of the oil contaminant in the refrigerant to pass from the inlet() to the outlet() of the second oil drain conduit(). The suction of the refrigerant through the second oil drain conduit() pulls oil contaminant along with it and reduces an amount of the oil contaminant in the second header() and the second low side heat exchanger(), thereby improving operating efficiency and reducing the total energy required to operate the refrigeration system. The operational flowcontinues to operation, which includes compressing the refrigerant exiting the second low side heat exchanger unit() using the second compressor unit. Once operationis complete, the operational flowmay end or may be repeated by re-starting operation.

In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants note that they do not intend any of the appended claims to invoke 35 U.S.C. § 112 (f) as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.