Cooling Systems with Passive Sub-Coolers

This patent application claims priority to U.S. Provisional Patent Application No. 63/366,747 filed on Jun. 21, 2022, the entire disclosure of which is hereby incorporated herein by reference.

The present disclosure relates to cooling systems such as building air conditioning systems, refrigeration systems or other cooling systems.

In a conventional refrigeration system, a superheated refrigerant enters a condenser in gaseous state, where it is de-superheated and condensed by releasing heat to the outside air or other coolant fluid. Once the refrigerant is condensed, it can be further cooled (referred to as “subcooling”).

The inventor has determined a need for improved cooling systems with passive subcooling that can increase system capacity and efficiency.

One aspect of the present disclosure provides a cooling system comprising a primary refrigerant circuit wherein a primary refrigerant fluid is circulated through a heat exchanger and one or more of: an evaporator, a compressor, a metering device and a condenser; and a secondary refrigerant circuit wherein a secondary refrigerant fluid is circulated through the heat exchanger and a fluid cooler, wherein the secondary refrigerant circuit uses carbon dioxide as the secondary refrigerant fluid and does not include any compression components in order to provide passive subcooling to the primary refrigerant fluid.

In typical cooling systems, the subcooling capacity in the condenser occupies a small percentage of the heat exchanger and the refrigerant temperature at the outlet of the condenser or a regular subcooler is always higher than the temperature of the outside air or other coolant. This type of subcooling always has a high temperature difference (ΔT). Some prior art systems use subcoolers with mechanical compression to reduce the ΔT and increase the system capacity but not the system efficiency. Systems according to embodiments of the present disclosure provide passive subcooling to a primary refrigerant that increases system capacity without increasing power consumption. For example the following table sets out a comparison of various temperatures and other system parameters between an example prior art cooling system and an example system with a passive subcooler according to the present disclosure:

Increasing the subcooling in a refrigeration system increases the system efficiency and the refrigeration capacity.

Some embodiments of the present disclosure provide a passive sub-cooler in the form of a cascade refrigeration system installed at the outlet of a condenser to increase the system capacity and efficiency. The passive sub-cooler includes a heat exchanger that exchanges heat between the liquid refrigerant of the primary refrigeration system and a CO2 refrigerant in the passive sub-cooler. This process reduces energy in the liquid refrigerant and increases the primary circuit efficiency.

Some embodiments of the present disclosure provide a refrigeration system comprising a compressor in which a primary refrigerant is compressed, a heat rejection component in which heat from the primary refrigerant is rejected, a passive subcooling system in which the primary refrigerant is subcooled to a temperature below its saturation temperature, a metering device in which the refrigerant pressure is reduced to facilitate refrigerant evaporation and heat exchange, and a heat absorbent component in which the refrigerant evaporates to absorb heat from a space to be cooled.

Some embodiments of the present disclosure provide a cascade system as passive subcooling system which compromise a heat exchanger in which the primary refrigerant releases heat thru the heat exchanger to the secondary refrigerant (CO2) which absorbs heat and evaporates, a pipes configuration that allows the evaporated CO2 refrigerant to be directed from the heat exchanger to a refrigerant cooler by thermosyphon and vice versa to the heat exchanger, a refrigerant cooler in which the CO2 releases the heat to the outside air or cooling medium.

Some embodiments of the present disclosure provide a passive subcooler for cooling down the liquid refrigerant at the outlet of the condenser to a temperature lower than the condenser coolant temperature.

Some embodiments of the present disclosure provide a subcooler which uses the pressure differential of the CO2 refrigerant to eliminate the mechanical compression in the subcooler which will increase the system capacity without increasing the system power consumption.

Some embodiments of the present disclosure provide liquid refrigerant with lower enthalpy to the metering device in a primary refrigerant circuit. The lower enthalpy refrigerant will result in better refrigerant quality after the metering device, more liquid refrigerant than gaseous refrigerants which improves the system capacity. Further, in some embodiments, when the outside temperature is lower than a specific set point, the primary refrigerant will bypass the compressor and the condenser which will result by turning off the compressor and using the refrigeration system in free-cooling mode without any mechanical compression.

Further aspects of the present disclosure and details of example embodiments are set forth below.

The following describes example cooling systems that can be utilized for various types of cooling and refrigeration needs. Some embodiments provide hybrid refrigeration systems that can provide low, medium, or high temperature refrigeration for cold rooms, supermarkets and ice rinks or any type of refrigeration application. Cooling systems according to embodiment of the present disclosure can also serve as an air-conditioning system for buildings and data centers.

As discussed in more detail below, cooling systems according to some embodiments of the present disclosure comprise a primary refrigeration circuit that includes a compressor and an evaporator and uses a primary refrigerant to remove heat from a space to be cooled, and a secondary refrigeration circuit without any compression components that uses carbon dioxide (CO2) to further cool the primary refrigerant. In some embodiments the primary refrigeration circuit is designed to operate in substantially the same way as a regular refrigeration system, and is configured to use all types of synthetic or natural refrigerants as the primary refrigerant. The secondary refrigeration system uses CO2 refrigerant without any compression components to provide passive subcooling for the primary refrigerant. The CO2 refrigerant in the secondary refrigeration circuit circulates in thermosyphon mode and cools down the primary refrigerant via a heat exchanger.

For simplicity and clarity of illustration, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. Numerous details are set forth to provide an understanding of the examples described herein. The examples may be practiced without these details. In other instances, well-known methods, procedures, and components are not described in detail to avoid obscuring the examples described. The description is not to be considered as limited to the scope of the examples described herein.

shows an example cooling systemaccording to one embodiment of the present disclosure. The cooling systemcomprises a primary refrigeration circuit wherein a primary refrigerant (in gaseous form) is compressed by a compressorand forced through an output lineto a condenser. At the condenser, a cooling medium (e.g. air) is moved across the condenser (e.g. by a fan), and the gaseous primary refrigerant is de-superheated, condensed and lightly sub-cooled.

The condenser output linecan hold the primary refrigerant in both liquid and gaseous states, and the liquid refrigerant is directed to a heat exchanger. The primary refrigerant flows into a primary inputand out of a primary outputof the heat exchanger, wherein the primary refrigerant is further cooled at low temperature by transferring heat to a secondary CO2 refrigerant, which flows into a secondary inputand out of a secondary outputand circulated in a secondary refrigeration circuit as described further below. The subcooled primary refrigerant leaving the heat exchangeris directed through a primary heat exchanger output lineto a primary refrigerant reservoirand then through a liquid lineto a metering device.

In the illustrated examples, the heat exchangeris installed after the condenser, but in other embodiments the order of the heat exchangerand reservoircould be reversed, with the condenser output lineconnected directly to the reservoir, and an output line from the reservoirconnected to the primary inputof the heat exchanger.

The primary refrigerant exits the metering devicein a mixed gas/liquid state (mainly liquid) and enters an evaporatorwhere it evaporates and absorbs heat from the surrounding area, thus cooling the medium around the evaporator(e.g. air in the case of an air conditioning system, or water or another liquid in the case of a chiller system). The lineis used to direct the primary refrigerant (now in a gaseous state) to a suction accumulator. The suction accumulatorprotects the compressorfrom any liquid entrained with the gaseous primary refrigerant. Gaseous primary refrigerant is provided to the compressorfrom the suction accumulatorthrough a compressor input line.

schematically illustrates a system with a single compressor, condenserand evaporator, but it is to be understood that any or all of these elements could comprise multiple units connected in parallel. Also, although not shown in the drawings, systemmay also include pressure sensors for measuring the pressures in the various portions of the primary and secondary refrigerant circuits, as well as temperature sensors for measuring temperatures at the various components of the system. The systemmay also include other refrigeration accessories.

In the secondary circuit, liquid CO2 refrigerant is provided from a CO2 reservoirthrough a lineand metering deviceto the secondary inputof the heat exchanger, and the CO2 refrigerant exits the secondary outputof heat exchangerin a gaseous state and is directed to a fluid coolerthrough a secondary heat exchanger output lineby thermosyphon and natural convection. In the example illustrated in, the fluid cooleris cooled by the same fanthat is used to cool the condenserof the primary refrigerant circuit. In other embodiments, the fluid coolermay be in a different location than condenser, as described below. As one skilled in the art will appreciate, location of the elements of systemcan vary depending on the physical characteristics of the space to be cooled, so long as the evaporatoris located either within or adjacent to the space to be cooled.

Once heat is released from the CO2 refrigerant in the fluid cooler, a partial condensation occurs, and liquid CO2 refrigerant returns by gravity to the CO2 liquid reservoirvia a fluid cooler output line. Liquid CO2 from reservoiris provided through lineto a metering deviceto the secondary inputof the heat exchanger. The metering devicecontrols the flow of CO2 to the heat exchangerbased on the pressure differential between the CO2 reservoirand the secondary inputof the heat exchanger. In some embodiments, the metering devicemay, for example, comprise an electrostatic valve that can be controlled to be fully open when the pressure differential is below a certain threshold. Alternately, the metering devicemay, for example, comprise a thermostatic expansion valve (TXV), electric expansion valve (EEV), or other element configured to allow CO2 to passed based on the pressure differential, and a meter bypass line (not shown) may be provided to bypass the metering device when the pressure differential is below a certain threshold.

The primary condenserand the fluid coolercan be installed in cascade, as shown in, or in two different places. For example,shows an example cooling systemA that is substantially the same as systemofexcept that in systemA of, the fluid coolerof the secondary refrigerant circuit is located separately from the condenserof the primary refrigerant circuit, and systemA comprises a secondary fanA for cooling the fluid cooler.

In the illustrated examples, the condenserand fluid coolerare cooled by a fan(or fansandA in the examples where the condenserand fluid coolerare installed in different location) that uses air as a coolant. In other embodiments other cooling media, such as water or any other type of coolant can be used for cooling the condenserand fluid cooler.

is a schematic diagram of a cascade refrigeration cooling systemaccording to another embodiment of the present disclosure, wherein the system is configured to be operable in a free cooling mode. Systems such as cooling systemmay, for example and without limitation, be utilized for cooling spaces such as computer rooms and packaged units. The example cooling systemofis similar to systemofand has a number of components in common with systemof, except that in systemof, a three-way valveis provided in the primary refrigerant circuit for bypassing the compressor. The three-way valveis connected to the evaporator output line, and in normal mode the three-way valveconnects the evaporator output lineto a lineconnected to the suction accumulator. Systemremains in normal mode as long as the outside air temperature at the inlet of condenseris at least as high as the temperature of the return air for the evaporator. When the outside air temperature is lower than the temperature of the return air for the evaporator, the systemis controlled to operate in “free cooling” mode. In free cooling mode, the three-way valveis operated to connect the evaporator output lineto a bypass lineconnected to the input of the condenser, thereby directing the primary refrigerant to bypass the suction accumulatorand the compressor. A check valveis provided in the compressor output lineof the systemto prevent the primary refrigerant from reaching the compressorwhen the three-way valveis in the free cooling position. In free cooling mode, the gaseous primary refrigerant from evaporatoris directed via evaporator output line, the three-way valveand the bypass lineto the condenserby thermosyphon. The gaseous primary refrigerant condenses in the coil(s) of condenserand liquid primary refrigerant is directed by gravity through lineto the heat exchanger, where the CO2 refrigerant absorbs heat from the primary refrigerant and evaporates. The primary refrigerant is subcooled in the heat exchangerand then directed to the primary reservoirvia the heat exchanger primary output line. The liquid primary refrigerant exits the reservoirand is be directed to the metering devicethat will be opened or by-passed based on the pressure and air temperature and then to the evaporator. The CO2 refrigerant evaporates in the heat exchangerand gaseous CO2 is directed via the lineto the fluid cooler. Once the heat is released from the CO2 refrigerant, a partial condensation occurs, and liquid CO2 refrigerant returns by gravity to the CO2 liquid reservoirvia the line. The liquid CO2 refrigerant is directed from the CO2 reservoirto the heat exchangervia the lineand the metering device.

shows an example cooling systemA that is substantially the same as systemofexcept that in systemA of, the fluid coolerof the secondary refrigerant circuit is located separately from the condenserof the primary refrigerant circuit, and systemA comprises a secondary fanA for cooling the fluid cooler.

is a schematic diagram of a cascade refrigeration cooling systemaccording to another embodiment of the present disclosure, wherein the system is configured to be operable in a free cooling mode wherein both the compressor and the condenser can be bypassed. Systems such as cooling systemmay, for example and without limitation, be utilized for cooling spaces where the evaporatoris installed within a building and the other elements of systemare installed on the roof of the building, and may be suitable for applications where the distance between the roof and the evaporatoris large such that piping is used instead of ducting. The example cooling systemofis similar to systemofand has a number of components in common with systemof, except that in systemof, two three-way valvesandare provided in the primary refrigerant circuit for bypassing the compressorand the condenserin free cooling mode. In normal mode, three-way valveconnects the condenser output lineto a linewhich is connected to the primary input of heat exchanger, and three-way valveconnects the evaporator output lineto a lineconnected to the suction accumulator. As with system, systemremains in normal mode as long as the outside air temperature at the inlet of condenseris at least as high as the temperature of the return air for the evaporator. When the outside air temperature is lower than the temperature of the return air for the evaporator, the systemis controlled to operate in free cooling mode, wherein the three-way valveis operated to connect the evaporator output lineto a linebetween valvesand, and three-way valveis operated to connect that lineto the lineconnected to the primary input of heat exchanger, such that after evaporating in the evaporatorthe gaseous primary refrigerant is directed via line, three-way valve, line, three-way valveand lineto the heat exchanger. In the heat exchangerthe primary refrigerant in gaseous state will condense and will be subcooled by releasing heat and then directed to the primary reservoirvia the heat exchanger primary output line. The remainder of the primary refrigeration circuit, and the secondary refrigeration circuit functions in the same was as described above with reference to.

shows an example cooling systemA that is substantially the same as systemofexcept that in systemA of, the fluid coolerof the secondary refrigerant circuit is located separately from the condenserof the primary refrigerant circuit, and systemA comprises a secondary fanA for cooling the fluid cooler.

is a schematic diagram of a cascade refrigeration cooling systemaccording to another embodiment of the present disclosure, wherein the system is configured to be operable in a free cooling mode wherein both the compressor and the condenser can be bypassed. The example cooling systemofis similar to systemofand has a number of components in common with systemof, except that in systemof, a four-way valveis provided in the primary refrigerant circuit for bypassing the compressorand the condenserin free cooling mode. In normal mode, the four-way valveconnects the condenser output lineto a linewhich is connected to the primary input of heat exchanger, and connects the evaporator output lineto a lineconnected to the suction accumulator. As with systemsand, systemremains in normal mode as long as the condenser inlet temperature is at least as high as the temperature of the return air for the evaporator. When the outside air temperature is lower than the temperature of the return air for the evaporator, the systemis controlled to operate in free cooling mode, wherein the four-way valveconnects the evaporator output lineto the lineconnected to the primary input of heat exchanger, such that after evaporating in the evaporatorthe gaseous primary refrigerant is directed via line, valveand lineto the heat exchanger. In the heat exchangerthe primary refrigerant in gaseous state will condense and will be subcooled by releasing heat and then directed to the primary reservoirvia the heat exchanger primary output line. The remainder of the primary refrigeration circuit, and the secondary refrigeration circuit functions in the same was as described above with reference to.

shows an example cooling systemA that is substantially the same as systemofexcept that in systemA of, the fluid coolerof the secondary refrigerant circuit is located separately from the condenserof the primary refrigerant circuit, and systemA comprises a secondary fanA for cooling the fluid cooler.

is a flowchart illustrating steps in an example methodof controlling a cascade refrigeration system with passive subcooling according to one embodiment of the present disclosure. Methodmay, for example, be carried out by one or more processors connected to control a cooling system configured to operate in free cooling mode such as any of systems,A,,A,orA described above. At block, the cooling system is operated to passively subcool primary refrigerant in the primary circuit with CO2 refrigerant in the secondary circuit. At blockthe outside air temperature (T_outside) and the temperature of the return air at the evaporator (T_return) are determined, and at blockthese temperatures are compared. If the outside air is not at a lower temperature than the evaporator return air (blockNO output), the valve(s) are operated to be in a “normal” position so that the compressor remains a part of the primary refrigerant circuit, and the compressor is activated at block. If the outside air is at a lower temperature than the evaporator return air (blockYES output), the valve(s) are operated to be in a “free cooling” position so that the compressor is cut out of primary refrigerant circuit, and the compressor is deactivated at block.

The embodiments of the systems and methods described herein may be implemented in a combination of both hardware and software. These embodiments may be implemented on programmable controller, each controller including at least one processor, a data storage system (including volatile memory or non-volatile memory or other data storage elements or a combination thereof), and at least one communication interface. For example, the programmable controller may be a server, network appliance, connected or autonomous vehicle, set-top box, embedded device, computer expansion module, personal computer, laptop, personal data assistant, cloud computing system or mobile device. A cloud computing system is operable to deliver computing service through shared resources, software and data over a network. Program code is applied to input data to perform the functions described herein and to generate output information. The output information is applied to one or more output devices to generate a discernible effect. In some embodiments, the communication interface may be a network communication interface. In embodiments in which elements are combined, the communication interface may be a software communication interface, such as those for inter-process communication. In still other embodiments, there may be a combination of communication interfaces.

Program code is applied to input data to perform the functions described herein and to generate output information. The output information is applied to one or more output devices. In some embodiments, the communication interface may be a network communication interface. In embodiments in which elements may be combined, the communication interface may be a software communication interface, such as those for inter-process communication. In still other embodiments, there may be a combination of communication interfaces implemented as hardware, software, and combination thereof.

Each program may be implemented in a high level procedural or object oriented programming or scripting language, or both, to communicate with a computer system. However, alternatively the programs may be implemented in assembly or machine language, if desired. In any case, the language may be a compiled or interpreted language. Each such computer program may be stored on a storage media or a device (e.g. ROM or magnetic diskette), readable by a general or special purpose programmable computer, for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the system may also be considered to be implemented as a non-transitory computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner to perform the functions described herein.

Furthermore, the system, processes and methods of the described embodiments are capable of being distributed in a computer program product including a physical non-transitory computer readable medium that bears computer usable instructions for one or more processors. The medium may be provided in various forms, including one or more diskettes, compact disks, tapes, chips, magnetic and electronic storage media, and the like. The computer useable instructions may also be in various forms, including compiled and non-compiled code.

Embodiments described herein may relate to various types of computing applications, such as image processing and generation applications, computing resource related applications, speech recognition applications, video processing applications, semiconductor fabrication, and so on. By way of illustrative example embodiments may be described herein in relation to image-related applications.

Throughout the foregoing discussion, numerous references may be made regarding servers, services, interfaces, portals, platforms, or other systems formed from computing devices. It should be appreciated that the use of such terms is deemed to represent one or more computing devices having at least one processor configured to execute software instructions stored on a computer readable tangible, non-transitory medium. For example, a server can include one or more computers operating as a web server, database server, or other type of computer server in a manner to fulfill described roles, responsibilities, or functions.

The technical solution of embodiments of the present disclosure may be in the form of a software product. The software product may be stored in a non-volatile or non-transitory storage medium, which can be a compact disk read-only memory (CD-ROM), a USB flash disk, or a removable hard disk. The software product includes a number of instructions that enable a computer device (controller, programmable logic controller (PLC), personal computer, server, or network device) to execute the methods provided by the embodiments.

The embodiments described herein are implemented by physical computer hardware, including computing devices, servers, receivers, transmitters, processors, memory, displays, and networks. The embodiments described herein provide useful physical machines and particularly configured computer hardware arrangements.

It will be appreciated that numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. Furthermore, this description is not to be considered as limiting the scope of the embodiments described herein in any way, but rather as merely describing implementation of the various example embodiments described herein.

The description provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.

As will be apparent to those skilled in the art in light of the foregoing disclosure, many alterations and modifications are possible to the methods and systems described herein. While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as may reasonably be inferred by one skilled in the art. The scope of the claims should not be limited by the embodiments set forth in the examples, but should be given the broadest interpretation consistent with the foregoing disclosure.

The present disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive.