TWO-STAGE COMPRESSION IN A MEDIUM-TEMPERATURE CO2 CDU APPLICATION

Abstract

A refrigeration system includes a switching valve configured to pass heated refrigerant from an evaporator that cools a load to the first compressor when in the first position and to pass the heated refrigerant to the second compressor when in a second position. The second compressor is configured to receive either refrigerant from the first compressor or the evaporator, depending on the position of the switching valve. The second compressor compresses the received refrigerant to produce compressed refrigerant, which is then used by the refrigeration system after cooling it with a gas cooler by the evaporator. The controller determines an ambient temperature using the ambient temperature sensor and causes the switching valve to be in the first position when the ambient temperature is greater than a predetermined threshold and causes the switching valve to be in the second position when the ambient temperature is less than the predetermined threshold.

Description

TECHNICAL FIELD

This disclosure relates generally to refrigeration systems and specifically to carbon dioxide (CO₂) condenser units (CDUs). In particular, the disclosure relates to a two-stage compression in a medium-temperature CO₂ CDU application.

BACKGROUND

Refrigeration systems regulate environmental conditions within an enclosed space. They are used for a variety of applications, such as in supermarkets, warehouses, and other applications to cool stored items. Refrigeration systems such as CDUs are also used for cooling data centers and a variety of other applications.

SUMMARY OF THE DISCLOSURE

Refrigeration systems use a compressor to pull refrigeration through the refrigeration system and provide compression to the refrigerant. In many refrigeration systems, a single compressor may be able to handle the load. However, as refrigeration systems are sized up, a single compressor may no longer be sufficient to provide the needed increase in compression. Previously, this has been addressed by using two or more compressors working together in tandem.

Operating two compressors in tandem, however, is not always desirable. When two compressors are operated in tandem, oil management problems often occur. This may require additional components to be added to the refrigeration system to manage oil, causing an increase in cost and complexity. Further, providing and operating two compressors in tandem requires increased power, even when changes in the load or environmental factors are such that the refrigeration system does not currently need the additional compression provided by using the two compressors in tandem.

This disclosure provides technical solutions to the problems of previous technology, including those described above. In one or more embodiments, a refrigeration system is provided, which includes a switching valve that is configured to pass heated refrigerant from an evaporator to a first compressor when in the first position and to pass the heated refrigerant to a second compressor when in a second position. The second compressor is configured to receive either refrigerant from the first compressor or the evaporator, depending on the position of the switching valve. The second compressor compresses the received refrigerant to produce compressed refrigerant, which is then used by the refrigeration system, after cooling with a gas cooler, by the evaporator. The controller determines an ambient temperature using the ambient temperature sensor and causes the switching valve to be in the first position when the ambient temperature is greater than a predetermined threshold and causes the switching valve to be in the second position when the ambient temperature is less than the predetermined threshold.

The system and method provide additional compression using a first and second compressor when the refrigeration system needs additional compression, such as when ambient temperatures are high, reducing the ability of a gas cooler to cool the compressed refrigerant. When the additional compression is no longer needed, one of the compressors may be bypassed, with only the second compressor providing compression. This reduces the amount of power required to operate the compressors when the additional compression is not needed, such as when ambient temperatures are below a threshold. Further, since the compressors are not operated in tandem, many of the oil management problems may be avoided, reducing the resulting refrigeration system's cost and/or complexity.

In an embodiment, a refrigeration system is provided, which includes an evaporator, a switching valve, a first compressor, a second compressor, and a gas cooler. The evaporator is configured to receive cooled refrigerant and cause the cooled refrigerant to absorb heat from a load to produce heated refrigerant. The switching valve is configured to receive the heated refrigerant from the evaporator and pass the heated refrigerant to the first compressor when in a first position and the second compressor when in a second position. The first compressor is configured to receive the heated refrigerant from the switching valve when the switching valve is in the first position and compress the heated refrigerant to produce a first compressed refrigerant. When the switching valve is in the first position, the second compressor is configured to receive the first compressed refrigerant, provide additional compression, and produce a second compressed refrigerant. When the switching valve is in the second position, the second compressor is configured to receive the heated refrigerant from the switching valve, compress the heated refrigerant, and produce a second compressed refrigerant.

The refrigeration system further includes a gas cooler, an ambient temperature sensor, and a controller. The gas cooler is configured to receive the second compressed refrigerant from the second compressor and cool the second compressed refrigerant with ambient air to make the cooled refrigerant and pass the cooled refrigerant to the evaporator. The ambient temperature sensor is associated with the gas cooler and is configured to determine the ambient temperature of the gas cooler's environment. The controller is communicatively coupled to at least the switching valve. The controller is configured to determine the ambient temperature using the ambient temperature sensor and cause the switching valve to be in the first position when the ambient temperature is greater than a predetermined threshold and a second position when the ambient temperature is less than a predetermined threshold. The controller also may cause the first compressor to deactivate, providing increased operational efficiency when the ambient temperature is less than the predetermined threshold.

In one or more embodiments, the refrigeration system may also include a flash tank. The flash tank receives the cooled refrigerant from the gas cooler and flashes the cooled refrigerant to produce a vapor refrigerant from a portion of the cooled refrigerant. The vapor refrigerant is passed to the second compressor, which compresses the vapor refrigerant with the first compressed refrigerant to produce the second compressed refrigerant. The remaining portion of the cooled refrigerant is passed to the evaporator. A variable valve may be provided to adjust the amount of vapor refrigerant from the flash tank passed to the second compressor. The controller controls the variable valve based on the ambient temperature, increasing the amount of vapor refrigerant passed to the second compressor when the ambient temperature increases and decreasing the amount when the ambient temperature decreases. In one or more embodiments, when the ambient temperature exceeds a second threshold, the controller controls the variable valve to completely open, allowing the vapor refrigerant to pass to the second compressor unimpeded.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a diagram of an example refrigeration system of this disclosure configured to operate both compressors to compress refrigerant;

FIG. 2 is a diagram of the example refrigeration system of FIG. 1 configured to use only one of the compressors to compress refrigerant; and

FIG. 3 is a flowchart of an example method of operating the refrigeration system of FIGS. 1 and 2 to provide two-stage compression.

DETAILED DESCRIPTION

Embodiments of the present disclosure and its advantages are best understood by referring to FIGS. 1 and 2 of the drawings, like numerals being used for like and corresponding parts of the various drawings.

As described above, conventional refrigeration systems suffer from certain inefficiencies and drawbacks when refrigeration systems increase in size and/or require additional compression. This disclosure's refrigeration system improves upon prior methods for compensating for the increased size and need for additional compression. In one or more embodiments, the refrigeration system of this disclosure uses a switching valve that is configured to pass heated refrigerant from an evaporator that cools a load to a first compressor when in the first position and to pass the heated refrigerant to the second compressor when in a second position. The second compressor is configured to receive either refrigerant from the first compressor or the evaporator, depending on the position of the switching valve. The second compressor compresses the received refrigerant to produce compressed refrigerant, which is then used by the evaporator after cooling it with at least a gas cooler. The controller determines an ambient temperature using the ambient temperature sensor and causes the switching valve to be in the first position when the ambient temperature is greater than a predetermined threshold and causes the switching valve to be in the second position when the ambient temperature is less than the predetermined threshold.

In one or more embodiments, the load may be a refrigerated case, an electronic device enclosure, or any other structure that needs refrigeration. The one or more embodiments are not limited to a refrigeration system and may be any type of system that utilizes refrigerant to cool an environment. In one or more embodiments, the refrigeration system of this disclosure may be a CO₂ refrigeration system. CO₂ refrigeration systems may differ from conventional refrigeration systems in that these systems circulate refrigerant that may become a supercritical fluid (i.e., where distinct liquid and gas phases are not present) above the critical point. For example, the critical point for carbon dioxide (CO₂) is 31° C. and 73.8 MPa, and above this point, CO₂ becomes a homogenous mixture of vapor and liquid called a supercritical fluid. This unique characteristic of transcritical refrigerants is associated with certain operational differences between transcritical and conventional refrigeration systems. For example, transcritical refrigerants are typically associated with discharge temperatures that are higher than their critical temperatures and discharge pressures that are higher than their critical pressures. When a transcritical refrigerant is at or above its critical temperature and/or pressure, the refrigerant may become a “supercritical fluid”—a homogenous mixture of gas and liquid. Supercritical fluid does not undergo a phase change process (vapor to liquid) in a gas cooler as occurs in a compressor of a conventional refrigeration system circulating traditional refrigerant. Rather, supercritical fluid cools down to a lower temperature in the gas cooler. Stated differently, the gas cooler in a CO₂ transcritical refrigeration system may receive and cool supercritical fluid, and the transcritical refrigerant undergoes a partial state change from gas to liquid as it is discharged from an expansion valve.

While in one or more embodiments, the refrigeration system of this disclosure is described as a CO₂ refrigerant system, the disclosure is not limited to a CO₂ refrigeration system. The refrigeration system may use other fluids with similar properties to CO₂. Alternatively, the refrigeration system of this disclosure may use any refrigerant or system that, combined with the switching valve, first compressor, and second compressor, provides two-stage compression in a medium-temperature application.

Refrigeration System

FIGS. 1 and 2 illustrate examples of refrigeration systems 100 and 200 configured for providing refrigeration to a load (not explicitly shown). The refrigeration system 100 includes an evaporator 106, a first compressor 104, a second compressor 110, a flash tank 120, a desuperheater 132, a condenser/gas cooler 108, a switching valve 112, a variable valve 114, and a controller 150 for controlling at least the switching valve 112. The refrigeration system 100, as shown in FIG. 1, is configured to use the switching valve 112 to pass the heated refrigerant from the evaporator 106 to the first compressor 104. The refrigeration system 200, as shown in FIG. 2, is configured to use the switching valve 112 to pass the heated refrigerant to the second compressor 110. Controller 150 controls the switching valve 112 based on measured ambient temperature by an ambient temperature sensor 136 mounted on or near the condenser/gas cooler 108. While the systems of FIGS. 1 and 2 include a single evaporator, e.g., 106; two compressors, e.g., 104 and 110; a single desuperheater, e.g., 132; a single flash tank, e.g., 120; and a single condenser/gas cooler, e.g., 108; the systems 100 and 200 may comprise more or fewer components without departing from the disclosure.

In one or more embodiments, refrigeration system 100 may include a first compressor 104 and a second compressor 110. Each of the compressors, e.g., 104, may be a single compressor or may comprise a plurality of compressors. The compressors, e.g., 104, may be any type and have any capacity. Each of the compressors, e.g., 104, may be configured as a low-temperature compressor or a medium-temperature compressor. In one or more embodiments, the first compressor 104 and the second compressor 110 may be the same type and/or have the same capacity and capabilities. Alternatively, in one or more embodiments, the first compressor 104 may have a smaller capacity than the second compressor 110, with the first compressor 104 being configured to boost the pressure of the refrigerant received from the evaporator 106 prior to it entering the second compressor 110. The controller 150 communicates with the first compressor 104 and the second compressor 110 and controls their operation.

As shown in FIG. 1, when the switching valve 112 is in the first position, heated refrigerant from the evaporator 106 is directed through conduit 124 to the first compressor 104. The first compressor 104, is configured to provide initial compression, lift, or boost to the heated refrigerant. The resulting first compressed refrigerant is then lifted and/or provided to the second compressor through conduit 126 and optional desuperheater 132. The first compressor 104 in one or more embodiments may be smaller, in terms of capacity or in terms of compression, than the second compressor 110 as it may be provided to simply reduce the amount of work the second compressor 110 has to perform when the ambient temperature is above a first threshold resulting in higher pressure and temperature in the heated refrigerant. However, the first compressor 104 may be of any size, capacity, and capability, including being the same as the second compressor 110 without departing from the disclosure. In one or more embodiments, the first compressor 104 may be able to provide variable compression, which may be adjusted by the controller 150 based on the ambient temperature measured by the ambient temperature sensor 136 or based on any other factors such as the temperature or pressure of the refrigerant exiting the evaporator 106.

The second compressor 110, as shown in FIG. 1, when the switching valve 112 is in the first position, receives the first compressed refrigerant from the first compressor 104 and provides additional compression to produce a resulting second compressed refrigerant, which it passes through conduit 128 to a gas cooler 108. The second compressor may also receive vapor refrigerant from a flash tank 120 through conduit 140. The second compressor compresses the first compressed refrigerant and the vapor refrigerant to obtain the desired operating pressure for the refrigeration system 100, which may be determined based on the type and capabilities of the gas cooler 108, the type and configuration of at least conduit 128, and other components of the system 100. The second compressor 110 may take any form, including multiple compressors, without departing from the disclosure.

As shown in FIG. 2, when the switching valve 112 is in the second position, the heated refrigerant is directed directly to the second compressor 110. This occurs when the ambient temperature at or around the gas cooler 108 is below a predetermined threshold. When this happens, the pressure and temperature of the heated refrigerant are such that the first compressor 104 may no longer be needed to provide the additional compression. In one or more embodiments, the first compressor 104, along with the optional desuperheater 132, is deactivated or idled, reducing the power requirements of the refrigeration system 200. As shown in FIG. 2, the heated refrigerant from the evaporator 106 is directed by the switching valve 112 through conduit 134 to the second compressor 110. The second compressor compresses this heated refrigerant along with any vapor refrigerant received from the flash tank 120 through conduit 140 to produce the second compressed refrigerant, which is supplied to the gas cooler 108 through conduit 128.

As described above with regards to system 100 of FIG. 1, in one or more embodiments, an optional desuperheater 132 is provided to receive the first compressed refrigerant from the first compressor 104 through conduit 124 when the switching valve 112 is in the first position. Because the heated refrigerant received by the first compressor 104 from the evaporator 106 may initially be at a higher temperature due to the increased ambient temperature of the gas cooler 108 and/or added cooling needs of the load (not explicitly shown) by the evaporator 106, the resultant first compressed refrigerant that is passed from the first compressor 104 may be at a higher temperature than what is ideal or safe for the second compressor 110 to use. The desuperheater 132 is provided to reduce the temperature of the first compressed refrigerant so that the second compressor 110, may operate more efficiently. The desuperheater 132 may comprise a heat exchanger (not explicitly shown) that exchanges heat from the first compressed refrigerant received from the first compressor 104 with a different refrigerant, such as, but not limited to, water. The different refrigerant may then carry away the excess heat to use it for other purposes or discharge it into an external environment. By reducing the temperature of the first compressed refrigerant, the second compressor 110 receiving the first compressed refrigerant may work at a lower temperature and/or with more efficiency.

Once the second compressed refrigerant leaves the second compressor 110 and passes through conduit 128, it enters the condenser/gas cooler 108. Gas cooler 108 is configured to receive the second compressed refrigerant from the second compressor 110 and cool it before providing it to flash tank 120 through conduit 130. The gas cooler 108 is generally operable to apply cooling to the received second compressed refrigerant to produce cooled refrigerant. In one or more embodiments, gas cooler 108 is a heat exchanger comprising cooler tubes or coils configured to circulate the received second compressed refrigerant. Ambient air is forced through the tubes or coils to cool the second compressed refrigerant. Since the gas cooler 108 relies on ambient air to cool the second compressed refrigerant, the amount of cooling that the second compressed refrigerant and its resulting temperature and pressure depend on the ambient temperature. For example, when the ambient air is below freezing, the second compressed refrigerant undergoes much more cooling than when the ambient air is at room temperature or higher.

An ambient temperature sensor 136 is associated with the gas cooler 108 in one or more embodiments. The ambient temperature sensor 136 may be mounted on the gas cooler 108, as shown in FIGS. 1 and 2, or may be provided in another location that is near (e.g., adjacent) to the gas cooler 108 and exposed to the same ambient environment as the gas cooler 108. The ambient temperature sensor 136 is configured to determine the ambient temperature of an environment at the gas cooler. For example, if the gas cooler 108 is mounted outside the facility using the refrigeration system, e.g., 100, the ambient temperature sensor would be configured to determine the ambient temperature at or near where the gas cooler 108 is positioned. The ambient temperature sensor 136 may be a thermocouple sensor, a thermistor sensor, a resistance temperature detector, an infrared (IR) temperature sensor, a semiconductor-based sensor, or any other type of temperature measurement device. The ambient temperature sensor 136 may be a combination of temperature sensor types, and the disclosure is not limited to a particular type or configuration of the ambient temperature sensor 136.

While only one ambient temperature sensor 136 is shown, a plurality of ambient temperature sensors, e.g., 136 may be provided, and they may be positioned at a variety of locations that may provide accurate ambient temperature measurements using statistical methods or other methods of determining the ambient temperature from a plurality of ambient temperature sensors, e.g., 136. The results of the ambient temperature measurements are used by controller 150 to determine how to adjust at least the switching valve 112 and operate the first compressor 104. The number, configuration, and location of the ambient temperature sensor 136 as shown in FIGS. 1 and 2 are simply examples, and the ambient temperature sensor 136 may take any form and be located at any appropriate location without departing from the disclosure. Additionally, while the disclosure described the use of an ambient temperature sensor 136, in one or more embodiments, the sensor may take the form of a pressure sensor that detects the pressure in conduit 130 or any other conduit and is used by the controller 150 to determine when the switching valve 112 should be in the first position or the second position.

Flash tank 120 is configured to receive mixed-state cooled refrigerant from the gas cooler 108 and separate the received cooled refrigerant into a first portion comprising flash gas or vapor and a second portion comprising liquid refrigerant. This further reduces the temperature of the cooled refrigerant sent to the evaporator 106 and provides the refrigerant in a purely liquid form to the evaporator 106. Flash tank 120 may include one or more tanks operable to hold refrigerant at least temporarily. Typically, the flash gas or vapor collects near the top of the flash tank 120, and the cooled refrigerant in the form of a liquid is collected at the bottom of the flash tank 120. The portion of the cooled refrigerant that forms as flash gas is directed through conduit 140 to the second compressor 110, and the remaining portion in the form of liquid refrigerant is directed through conduit 140 to the evaporator 106. A valve 116 may be disposed at or near an inlet of the flash tank 120 in conduit 130 to reduce the pressure of the cooled refrigerant received by the flash tank 120.

In one or more embodiments, at least a portion of the flash gas or vapor from the flash tank 120 is sent through an outlet through conduit 140 to the second compressor 110. A variable valve 114 may be provided in conduit 140 to allow the controller 150 to control the amount of vapor from the flash tank 120 sent to the second compressor 110. Any appropriate motorized or electronically controllable valve, such as a motorized ball valve, solenoid valve, and/or the like. The controller 150, which communicates with variable valve 114 through the input-output (I/O) interface 156, controls the variable valve's 114 operations. By controlling the variable valve 114 to increase or decrease the amount of vapor sent to the second compressor 110, the controller may control the pressure in the flash tank as well as the pressure of the cooled refrigerant received by evaporator 106.

In one or more embodiments, the variable valve 114 may be controlled to decrease the amount of vapor refrigerant sent to the second compressor 110 when the ambient temperature decreases and increase the amount of vapor refrigerant sent to the second compressor 110 when the ambient temperature increases. In one or more embodiments, the variable valve 114 may be caused to completely open when the ambient temperature is greater than a second threshold or to completely close when the ambient temperature is less than a third threshold. The second and third thresholds may be any temperature and may be chosen based on the specific type and operating parameters of the second compressor 110. Alternatively, the variable valve 114 may be opened, adjusted, or closed based on measuring the pressure in conduit 140 or in or at the flash tank 120.

In one or more embodiments, the variable valve 114 may be controlled to ensure that the pressure in the flash tank 120 and/or conduit 140 is not too high. For example, in a non-limiting example, on a hot summer day, the ambient temperature may be such that the gas cooler 108 is unable to remove sufficient heat from the refrigerant received by the flash tank 120; this results in less liquid refrigerant forming in the flash tank, 120 by diverting more of the vapor to the second compressor, the pressure in the flash tank 120 may be reduced and more cooled liquid refrigerant may form that may be passed to the evaporator.

Once liquid refrigerant has been condensed in the flash tank 120, the refrigerant flows in conduit 140 to the evaporator 106. The evaporator 106 receives the cooled liquid refrigerant from conduit 140 and uses the cooled refrigerant to provide cooling to a load (not explicitly shown) by having the refrigerant absorb heat from the load. For example, the evaporator 106 may provide cooling to a load that may take the form of a refrigerator, a refrigerated case, or one or more computational devices in a data center. The specific type of load is not limited to those just described and may be any load that needs and is able to be cooled by the refrigeration systems 100 and 200. The refrigeration systems 100 and 200 may include any appropriate number of evaporators, e.g., 106 with the same or a similar configuration to that shown in FIG. 1. The evaporator 106 may be a medium-temperature evaporator or a low-temperature evaporator depending on the type of load and configuration of the refrigeration system, e.g., 100. For example, in a non-limiting example, the evaporator 106 may be a medium-temperature evaporator that maintains a predefined temperature for a given load (e.g., about −6° C.).

The evaporator 106 may include one or more expansion valves, e.g., 118, configured to receive the cooled refrigerant from flash tank 120 through conduit 140 and further reduce the pressure and/or temperature of the received cooled refrigerant. In some embodiments, this reduction in pressure causes some of the refrigerant to vaporize. The expansion valve(s) 118 may be configured to cause cooled refrigerant to pass into the evaporator 106 at a predefined temperature for a given application (e.g., about −6° C.), for example. The expansion valve 118 may be adjusted based on temperature readings by one or more sensors (not explicitly shown) provided in or adjacent to the conduit 140 and/or the evaporator 106. The evaporator 106 may be operated at any temperature, and the disclosure is not limited to operating at a particular temperature. The operation temperature is determined by the application as well as, or instead, the preferences of the operator of the refrigeration systems 100 and/or 200.

Refrigerant from the evaporator 106, once used to cool a load (e.g., a region, a structure, or an environment that is adjacent to and/or in thermal communication with evaporator 106), is then provided to either the first compressor 104 through conduit 124 (as shown in FIG. 1) or to the second compressor 110 through conduit 134 (as shown in FIG. 2) as described above and below with respect to FIG. 3, depending on whether switching valve 112 is in a first position or a second position. In one or more embodiments, the switching valve 112 is configured to switch between a passing refrigerant to conduit 124 when in a first position and passing refrigerant to conduit 134 when in a second position. The switching valve 112 may have more positions than those described herein, with additional positions being needed for other applications, compressors, or other purposes without departing from the disclosure.

Similar to the variable valve 114, the switching valve 112 may be any appropriate motorized or electronically controllable valve, such as a motorized ball valve, solenoid valve, and/or the like. The controller 150, which communicates with switching valve 112 through the input-output (I/O) interface 156, controls the switching valve's 112 operations. By controlling the switching valve 112, the controller 150 may control whether the heated refrigerant from the evaporator 106 is directed to the first compressor 104 or the second compressor 110. The switching valve 112 may be disposed in conduit after the evaporator 106 and before the first compressor 104.

As shown in FIG. 1, when the switching valve 112 is in the first position, the heated refrigerant from evaporator 106 is directed through conduit 124 to the first compressor 104. When the refrigerant is directed through conduit 124 to the first compressor 104, conduit 134 does not receive any refrigerant and may be largely empty. An optional check valve 170 may be provided in conduit 134 to ensure that the suction pressure of the second compressor 110 does not damage conduit 134 and/or the switching valve 112 when the switching valve 112 is in a first position. While described as a check valve, check valve 170 may be any type of valve without departing from the disclosure.

As shown in FIG. 2, when the switching valve 112 is in the second position, the heated refrigerant from the evaporator 106 is directed through conduit 134 to the second compressor 110, bypassing the first compressor 104 and option desuperheater 132. When the refrigerant is directed through conduit 134 to second compressor 110, conduits 126 and 124 do not receive any refrigerant and may be largely empty. An optional check valve 172 may be provided in conduit 126 to ensure that the suction pressure of the second compressor 110 does not damage conduits 126, 124, desuperheater 132, first compressor 104, and/or the switching valve 112 when the switching valve 112 is in the second position. While described as a check valve, check valve 172 may be any type of valve without departing from the disclosure.

The various conduits 124, 126, 128, 130, 134, and 140 may form a refrigerant conduit subsystem that facilitates the movement of refrigerant (e.g., CO₂) through refrigeration cycles, both when the switching valve 112 is in a first position and when the switching valve 112 is in a second position. The refrigerant moves through the conduits, e.g., 126, as illustrated by the arrows in FIGS. 1 and 2. The refrigerant conduit subsystem includes conduit, tubing, piping, and the like that facilitate refrigerant movement between components of the refrigeration systems 100 and 200. The conduits 124, 126, 128, 130, 134, and 140 may be copper conduits or other types of appropriate conduit, tubing, or piping. Different sections of the conduit, e.g., 124, may be made of different materials, be designed to handle different amounts of pressure, or take different forms without departing from the disclosure.

The components of the refrigeration system, 100 and 200, may be controlled by the controller 150. The controller 150 includes a processor 152, memory 154, and input/output (I/O) interface 156. The processor 152 includes one or more processors operably coupled to the memory 154. The processor 152 is 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 memory 154 and controls the operation of the refrigeration systems 100 and 200.

The processor 152 may be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processor 152 is communicatively coupled to and in signal communication with the memory 154. The one or more processors 152 are configured to process data and may be implemented in hardware or software. For example, the processor 152 may be 8-bit, 16-bit, 32-bit, 64-bit, or of any other suitable architecture. The processor 152 may 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 memory 154 and executes them by directing the coordinated operations of the ALU, registers, and other components. The processor 152 may include other hardware and software that operates to process information, control the refrigeration systems 100 and 200, and perform any of the functions described herein (e.g., with respect to FIGS. 1-3). The processor 152 is not limited to a single processing device and may encompass multiple processing devices. Similarly, the controller 150 is not limited to a single controller but may encompass multiple controllers.

The I/O interface 156 is configured to communicate data and signals with other devices. For example, the I/O interface 156 may be configured to communicate electrical signals with the refrigeration system 100, including, but not limited to, the switching valve 112 and the variable valve 114. The I/O interface 156 may be configured to communicate with other devices and systems and is not limited to those just described or those present in FIGS. 1 and 2. The I/O interface 156 may 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 system 100 and 200 and send electrical signals to the components of the refrigeration system 100 and 200. The I/O interface 156 may include ports or terminals for establishing signal communications between the controller 150 and other devices. The I/O interface 156 may be configured to enable wired and/or wireless communications.

The memory 154 includes one or more disks, tape drives, or solid-state drives. It may be used as an over-flow data storage device to store programs when such programs are selected for execution and to store instructions 158 and data read during program execution. The memory 154 may 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 memory 154 is operable (or configured) to store information used by the controller 150 and/or any other logic and/or instructions for performing the function described in this disclosure.

The controller 150 may provide instructions 158 for controlling at least the switching valve 112, the variable valve 114, first compressor 104, and second compressor 110. The instructions 158 may cause the switching valve 112 to be in the first position when the ambient temperature measured by the ambient temperature sensor 136 is greater than a predetermined threshold and may cause the switching valve 112 to be in the second position when the ambient temperature is below the predetermined threshold. Similarly, the instructions may cause the variable valve 114 to open, close, increase, and/or decrease the amount of vapor refrigerant that flows from the flash tank 120 to the second compressor 110.

The valves may be controlled using the valve settings 160 stored in the memory. These settings may include an indication of a first predetermined threshold temperature, a second predetermined threshold temperature, and a third predetermined threshold temperature, as well as settings specific to variable valve 114 to control the amount of vapor refrigerant to provide to the second compressor 110, depending on the ambient temperature or another pertinent measurement. The first, second, and third predetermined thresholds may be determined by a user, manufacturer, installer, or other individual based on the specific design of the system, e.g., 100 and/or the characteristics of the first compressor 104, second compressor 110, flash tank 120, evaporator 106, gas cooler 108 and/or any other component of the system, e.g., 100.

As described above, the first threshold is a temperature at which the first compressor 104, is no longer needed to provide boosted or first compressed refrigerant to the second compressor, 110. When the ambient temperature is less than the first threshold, the switching valve 112 may be switched to the second position, allowing the heated refrigerant to bypass the first compressor 104 and allowing the first compressor 104 to be deactivated or idled.

The second and third thresholds are temperatures where the variable valve 114 may either be completely opened (second threshold) or completely closed (third threshold). By completely opening the variable valve 114, vapor refrigerant from the flash tank 120 may be provided to the second compressor 110 unimpeded, decreasing the pressure in the flash tank 120. By completely closing the variable valve 114, pressure may be significantly increased in the flash tank 120 when the ambient temperature is such that refrigerant entering the flash tank 120 is colder than what is ideal.

These valve settings 160 may be stored in memory 154 in the form of a table or may take any other form. The valve settings 160 and/or instructions 158 may also provide other conditions and/or measurements used for determining the settings for the switching valve 112 and/or the variable valve 114, and the disclosure is not limited to those described herein. The specific valve setting 160, including the first predetermined temperature threshold, second predetermined temperature threshold, and third predetermined temperature threshold, may be any value, and the disclosure is not limited to any specific values. These values may be determined during testing of the system, e.g., 100, based on the specific components in the system, e.g., 100, based on simulations, and/or modified during the operation of the system, e.g., 100 after deployment.

The controller 150 may control other components of the refrigeration systems 100 and 200 and is not limited to just controlling switching valve 112 and variable valve 114. Although this disclosure describes and depicts refrigeration systems 100 and 200, including specific components, it recognizes that refrigeration systems 100 and 200 may include any suitable components. For example, refrigeration systems 100 and 200 may include one or more additional sensors configured to detect temperature and/or pressure information.

In an example operation of the refrigeration system 100 of FIG. 1, when the controller 150 determines the ambient temperature, measured by the ambient temperature sensor 136, is greater than the first threshold, the controller causes the switching valve 112 to be in the first position. Cooled refrigerant is received by the evaporator 106, which uses the cooled refrigerant to extract heat from a load (not explicitly shown), warming the cool refrigerant by causing the cool refrigerant to absorb heat from the load, which results in cooling of the load and/or its surrounding environment (not explicitly shown). The resulting heated refrigerant then passes to the switching valve 112, which provides the heated refrigerant through conduit 124 to the first compressor 104. The first compressor compresses the heated refrigerant to produce the first compressed refrigerant. It passes the heated refrigerant to the desuperheater 132, which extracts heat from the first compressed refrigerant, and the first compressed refrigerant is passed through conduit 126 to the second compressor 110. The second compressor 110 then further compresses the first compressed refrigerant received from the first compressor 104 and any vapor refrigerant received from the flash tank through conduit 140 to produce the second compressed refrigerant. The second compressor then passes the second compressed refrigerant through conduit 128 to a gas cooler 108 and then to the flash tank 120, which cools the second compressed refrigerant to produce the cooled refrigerant used by the evaporator 106 to cool the load.

In an example operation of the refrigeration system 200 of FIG. 2, when the controller 150 determines the ambient temperature measured by the ambient temperature sensor 136 is less than the first threshold, the controller causes the switching valve 112 to switch to the second position. When the switching valve 112 is in the second position, the heated refrigerant from the evaporator passes through conduit 134 to the second compressor 110, bypassing the first compressor 104. The controller may also deactivate the first compressor 104 and/or desuperheater 132 to increase the efficiency of the system 200. The second compressor 110 then compresses the uncompressed first heated refrigerant and any vapor refrigerant received from the flash tank through conduit 140 to produce the second compressed refrigerant. The second compressor then passes the second compressed refrigerant through conduit 128 to a gas cooler 108 and then to the flash tank 120, which cools the second compressed refrigerant to produce the cooled refrigerant used by the evaporator 106 to cool the load (not explicitly shown).

Example Method of Operation

FIG. 3 illustrates an example method 300 of operating refrigeration systems 100 and 200 based on a measured ambient temperature. Method 300 may be implemented using the processor 152, memory 154, and I/O interface 156 of the controller 150 of FIG. 1. While described with the switching valve 112 being in a first position when the ambient temperature is greater than a predetermined temperature and in the second position when the ambient temperature is less than the predetermined temperature, method 300 may be used for any measured condition besides ambient temperature for determining if the system 100 should be operated with a first compressor 104 providing compression to the refrigerant from the evaporator 106 before providing the compressed refrigerant to the second compressor 110 or with only the second compressor 110 providing compression to the refrigerant without departing from the disclosure.

The method 300 may begin at operation 305. In operation 305, the controller 150 detects the ambient temperature using the ambient temperature sensor 136. The ambient temperature sensor 136 determines the temperature of the environment where the gas cooler 108 operates. For example, if the gas cooler 108 is positioned outside a facility where the evaporator 106 cools a load, the ambient temperature sensor 136 determines the temperature of the air outside the facility. If the gas cooler 108 is inside, then the ambient temperature sensor 136 may be at that location. The ambient temperature sensor 136 may be located at any location and is not limited to outside a facility. The ambient temperature sensor 136 is not limited to determining the ambient temperature of the environment of the gas cooler 108. It may determine the ambient temperature of the environment where the flash tank 120 is located, a first compressor 104 or a second compressor 110. The specific environment measured by the ambient temperature sensor 136 and/or the location of the ambient temperature sensor 136 is not limited to those just described and may be an environment and/or location without departing from the disclosure.

Once the ambient temperature is determined in operation 305 by the ambient temperature sensor 136 and provided to controller 150, the controller 150 in operation 310 determines if the ambient temperature is greater than a predetermined temperature. The predetermined temperature is determined based on the operation capabilities of the second compressor 110 and other components of systems 100 and 200. The predetermined temperature may be determined by a user of the refrigeration system, e.g., 100, or the manufacturer. The predetermined temperature may be adjusted as the system, e.g., 100, continues to operate over time or may be a set temperature based on laboratory measurements and/or simulations for the refrigeration systems, e.g., 100 specific configuration and components.

If controller 150 in operation 310 determines that the ambient temperature is greater than the predetermined temperature, then controller 150 in operation 315 places the switching valve 112 in the first position, as shown, for example, in FIG. 1. This allows the refrigerant from evaporator 106 to flow through conduit 124 to the first compressor 104. In operation 320, the controller causes the first compressor 104 to activate. The first compressor 104 compresses the refrigerant and provides the first compressed refrigerant to the second compressor 110 to produce the second compressed refrigerant that is then used by the gas cooler 108 and flash tank 120 to provide cooled refrigerant to the evaporator 106 to cool the load.

If controller 150 in operation 310 determines that the ambient temperature is not greater than the predetermined temperature, the controller 150 places the switching valve 112 in a second position in operation 325, as shown, for example, in FIG. 2. In the second position, the refrigerant from the evaporator 106 is directed through conduit 134 directly to the second compressor 110. In one or more embodiments, the controller 150 deactivates the first compressor 104 in operation 330, reducing the amount of power the refrigeration system needs, e.g., 100. Once the first compressor is deactivated in operation 330, the refrigeration system, e.g., 100, may provide cooling to the load using just the second compressor 110, in combination with other components of the refrigeration system, e.g., 100.

Once the controller 150, either activates the first compressor 104 in operation 320 or deactivates the first compressor 104 in operation 330, the controller 150 determines if the ambient temperature is greater than a second predetermined threshold in operation 335. The second predetermined threshold is an ambient temperature that causes the temperature and/or pressure of the refrigerant at the flash tank 120 to be such that it is desirable to pass the vapor refrigerant from the flash tank 120 unimpeded to the second compressor 110. If the controller 150 determines that the ambient temperature is greater than the second predetermined threshold in operation 335, the controller 150 in operation 340 causes the variable valve 114 to completely open, allowing the vapor from the flash tank 120 to flow to the second compressor 110 unimpeded. This may allow the second compressor 110 to operate more efficiently when the ambient temperature is high, as well as reduce the pressure in the flash tank 120, so the flash tank 120 may provide sufficient cooling to the refrigerant passed to the evaporator 106.

If the controller 150 in operation 335 determines the ambient temperature is not greater than the second predetermined threshold in operation 335, The controller 150 determines in operation 345 if the ambient temperature is less than a third predetermined threshold. The third predetermined threshold is an ambient temperature where the refrigerant is cooled by the gas cooler 108 such that the pressure in the flash tank is not sufficient for the efficient operation of the system, e.g., 200. If the controller determines in operation 345 that the ambient temperature is less than the third predetermined threshold, then controller 150 causes the variable valve to completely close in operation 350, increasing the pressure in the flash tank 120, allowing the system, e.g., 200, to operate efficiently.

If, instead, the ambient temperature is determined to be less than the second predetermined threshold in operation 335 and greater than the third predetermined threshold in operation 345, the controller 150 variably operates the variable valve 114 in operation 355. In operation 355, the controller 150 may adjust variable valve 114 to control the amount of vapor from the flash tank 120 provided to the second compressor 110 through conduit 140. The controller 150 causes the variable valve 114 to increase the amount of vapor supplied to the second compressor 110 when the ambient temperature increases and decrease the amount of vapor provided to the second compressor 110 when the ambient temperature decreases.

Once controller 150 adjusts the variable valve 114 in one of operations 340, 355, or 350, the controller 150 then begins operating the refrigeration system, e.g., 100 in operation 360. In operation 360, refrigerant is circulated through the refrigeration system, e.g., 100 by at least the second compressor 110, causing the cooled refrigerant to be received by the evaporator 106. The cooled refrigerant absorbs heat from the load, and the resulting warm refrigerant is then circulated by at least the second compressor 110 in a continuous cycle. Once the controller 150 begins operating the refrigeration system, e.g., 100 in operation 360, the method 300 may end. In one or more embodiments, method 300 may be continuously performed, and operations 305-360 may be repeated continuously as long as systems 100 and 200 continue to be used/operated.

Method 300 may include more, fewer, or other operations. For example, operations may be performed in parallel or in any suitable order. Modifications, additions, or omissions may be made to method 300, depicted in FIG. 3. While at times discussed as controller 150, refrigeration systems 100 and 200, or components thereof performing the operations, any suitable refrigeration system, e.g., 100, or components of the refrigeration system, e.g., 100, may perform one or more operations of method 300.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated into another system, or certain features may be omitted or not implemented.

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.

Claims

1. A refrigeration system, comprising:

an evaporator configured to receive cooled refrigerant and facilitate the cooled refrigerant to absorb heat from a load to produce heated refrigerant;

a switching valve configured to receive the heated refrigerant from the evaporator and pass the heated refrigerant to a first compressor when in a first position and to pass the heated refrigerant to a second compressor when in a second position;

the first compressor configured to receive the heated refrigerant from the switching valve when the switching valve is in the first position and compress the heated refrigerant to produce a first compressed refrigerant;

the second compressor is configured to produce a second compressed refrigerant, wherein: the second compressor is configured to receive the first compressed refrigerant from the first compressor when the switching valve is in the first position and provide additional compression to the first compressed refrigerant to produce the second compressed refrigerant, and the second compressor is configured to receive the heated refrigerant from the switching valve when the switching valve is in the second position and compress the heated refrigerant to produce the second compressed refrigerant;

a gas cooler configured to receive the second compressed refrigerant from the second compressor and cool the second compressed refrigerant with ambient air to produce the cooled refrigerant and pass the cooled refrigerant to the evaporator;

an ambient temperature sensor associated with the gas cooler, wherein the ambient temperature sensor is configured to determine an ambient temperature of an environment at the gas cooler; and

a controller communicatively coupled to the switching valve, wherein the controller is configured to: determine the ambient temperature using the ambient temperature sensor; cause the switching valve to be in the first position when the ambient temperature is greater than a predetermined threshold; and cause the switching valve to be in the second position when the ambient temperature is less than the predetermined threshold.

2. The refrigeration system of claim 1, wherein the controller causes the first compressor to deactivate when the ambient temperature is less than a predetermined threshold.

3. The refrigeration system of claim 1, further comprising a flash tank configured to:

receive the cooled refrigerant from the gas cooler;

flash the cooled refrigerant to produce a vapor refrigerant from a portion of the cooled refrigerant;

pass the vapor refrigerant to the second compressor, which is configured to compress the vapor refrigerant with the first compressed refrigerant to produce the second compressed refrigerant; and

pass a remaining portion of the cooled refrigerant to the evaporator.

4. The refrigeration system of claim 3, further comprising a variable valve configured to adjust an amount of vapor refrigerant from the flash tank that is passed to the second compressor.

5. The refrigeration system of claim 4, wherein the variable valve is controlled by the controller, and wherein the controller causes the variable valve to adjust the amount of vapor refrigerant from the flash tank that is passed to the second compressor based on the ambient temperature, wherein the amount of vapor refrigerant is increased when the ambient temperature increases and the amount of vapor is decreased when the ambient temperature decreases.

6. The refrigeration system of claim 5, wherein the controller adjusts the amount of vapor refrigerant from the flash tank that is passed to the second compressor by partially opening the variable valve when the ambient temperature is less than a second predetermined threshold and causes the variable valve to completely open when the ambient temperature is greater than a second predetermined threshold.

7. The refrigeration system of claim 1, further comprising a desuperheater configured to receive the first compressed refrigerant, reduce the first compressed refrigerant's temperature, and pass the first compressed refrigerant to the second compressor.

8. The refrigeration system of claim 1, wherein the first compressor and the second compressor have a same capacity.

9. The refrigeration system of claim 1, wherein the first compressor has a smaller capacity than the second compressor.

10. A method of operating a refrigeration system, the method comprising:

operating an evaporator to absorb heat from a load to produce heated refrigerant from received cooled refrigerant;

determining an ambient temperature using an ambient temperature sensor associated with a gas cooler, wherein the ambient temperature sensor is configured to determine an ambient temperature of an environment at the gas cooler;

causing a switching valve to be in a first position when the ambient temperature is greater than a predetermined threshold and to be in a second position when the ambient temperature is less than the predetermined threshold, wherein the switching valve is configured to receive the heated refrigerant from the evaporator and pass the heated refrigerant to a first compressor when in a first position and to pass the heated refrigerant to a second compressor when in a second position;

operating the first compressor to compress the heated refrigerant to produce a first compressed refrigerant, wherein the first compressor is configured to receive the heated refrigerant from the switching valve when the switching valve is in the first position and compress the heated refrigerant to produce the first compressed refrigerant;

operating a second compressor to produce a second compressed refrigerant wherein: the second compressor is configured to receive the first compressed refrigerant from the first compressor when the switching valve is in the first position and provide additional compression to the first compressed refrigerant to produce the second compressed refrigerant, and the second compressor is configured to receive the heated refrigerant from the switching valve when the switching valve is in the second position and compress the heated refrigerant to produce the second compressed refrigerant; and

operating the gas cooler to cool the second compressed refrigerant with ambient air to produce the cooled refrigerant and pass the cooled refrigerant to the evaporator.

11. The method of claim 10, further comprises deactivating the first compressor when the switching valve is in the second position.

12. The method of claim 10, further comprises:

receiving by a flash tank positioned between the gas cooler and the evaporator, the cooled refrigerant from the gas cooler;

flashing the cooled refrigerant to produce a vapor refrigerant from a portion of the cooled refrigerant;

passing the vapor refrigerant to the second compressor, which is configured to compress the vapor refrigerant with the first compressed refrigerant to produce the second compressed refrigerant; and

passing a remaining portion of the cooled refrigerant to the evaporator.

13. The method of claim 12, further comprises adjusting, using a variable valve, an amount of vapor refrigerant from the flash tank that is passed to the second compressor based on the ambient temperature, wherein the amount of vapor refrigerant is increased when the ambient temperature increases, and the amount of vapor is decreased when the ambient temperature decreases.

14. The method of claim 13, wherein the variable valve controls the amount of vapor refrigerant from the flash tank that is passed to the second compressor by partially opening when the ambient temperature is less than a second predetermined threshold and completely open when the ambient temperature is greater than a second predetermined threshold.

15. A controller of a refrigeration system, the controller comprising:

an input/output interface communicatively coupled to: an evaporator configured to receive cooled refrigerant and facilitate the cooled refrigerant to absorb heat from a load to produce heated refrigerant; a switching valve configured to receive the heated refrigerant from the evaporator and pass the heated refrigerant to a first compressor when in a first position and to pass the heated refrigerant to a second compressor when in a second position; the first compressor configured to receive the heated refrigerant from the switching valve when the switching valve is in the first position and compress the heated refrigerant to produce a first compressed refrigerant; the second compressor is configured to produce a second compressed refrigerant, wherein: the second compressor is configured to receive the first compressed refrigerant from the first compressor when the switching valve is in the first position and provide additional compression to the first compressed refrigerant to produce the second compressed refrigerant, and the second compressor is configured to receive the heated refrigerant from the switching valve when the switching valve is in the second position and compress the heated refrigerant to produce the second compressed refrigerant; a gas cooler configured to receive the second compressed refrigerant from the second compressor and cool the second compressed refrigerant with ambient air to produce the cooled refrigerant and pass the cooled refrigerant to the evaporator; and an ambient temperature sensor associated with the gas cooler, wherein the ambient temperature sensor is configured to determine an ambient temperature of an environment at the gas cooler; and

a processor configured to: determine the ambient temperature using the ambient temperature sensor; cause the switching valve to be in the first position when the ambient temperature is greater than a predetermined threshold; and cause the switching valve to be in the second position when the ambient temperature is less than the predetermined threshold.

16. The controller of claim 15, wherein:

the second compressor is further configured to receive vapor refrigerant from a flash tank and to compress the vapor refrigerant with the first compressed refrigerant to produce the second compressed refrigerant when the switching valve is in the first position; and

the flash tank is positioned between the gas cooler and the evaporator and is configured to: receive the cooled refrigerant from the gas cooler; flash the cooled refrigerant to produce the vapor refrigerant from a portion of the cooled refrigerant; pass the vapor refrigerant to the second compressor; and pass a remaining portion of the cooled refrigerant to the evaporator.

17. The controller of claim 16, wherein the processor is further configured to adjust an amount of vapor refrigerant from the flash tank that is passed to the second compressor using a variable valve.

18. The controller of claim 17, wherein the processor causes the variable valve to adjust the amount of vapor refrigerant from the flash tank that is passed to the second compressor based on the ambient temperature, wherein the amount of vapor refrigerant is increased when the ambient temperature increases, and the amount of vapor is decreased when the ambient temperature decreases.

19. The controller of claim 18, wherein the controller adjusts the amount of vapor refrigerant from the flash tank that is passed to the second compressor by partially opening the variable valve when the ambient temperature is less than a second predetermined threshold and causes the variable valve to completely open when the ambient temperature is greater than a second predetermined threshold.

20. The controller of claim 15, wherein the controller causes the first compressor to deactivate when the ambient temperature is less than a predetermined threshold.