A method and system for managing compressor oil in a carbon dioxide based cooling system

Abstract

The present disclosure discloses a method (300) for regulating operation of a carbon dioxide (CO2) based cooling system (100). The method (300) includes regulating operation of a vapor control valve (18) connected between an intermediate pressure receiver (17) and a compressor unit (10) of the cooling system (100). The method (300) includes regulating operation of the vapor control valve (18) based on determination of oil level in an oil reservoir (13) fluidly coupled to the compressor unit (10). With such configuration, the method (300) recovers oil mixed with the refrigerant without reduction in efficiency / loading conditions of the cooling system (100) and may enhance heat exchanger (15) efficiency of the cooling system (100). Further, such method (300) may eliminate or reduce additional cost required to high capacity equipment required to compensate for mixing of lubricant oil and the refrigerant.

Description

[0001] “A METHOD AND SYSTEM FOR MANAGING COMPRESSOR OIL IN A CARBON DIOXIDE BASED COOLING SYSTEM”

[0002] TECHNICAL FIELD

[0003] Present disclosure, in general, relates to a field of refrigeration systems. Particularly, but not exclusively, the present disclosure relates to a carbon dioxide (CO2) based cooling system. Further, embodiments of the present disclosure relate to a method and system for managing compressor oil in a carbon dioxide based cooling system.

[0004] BACKGROUND OF THE DISCLOSURE

[0005] Cooling systems such as air conditioning systems, refrigeration systems, heat pumps and the like are often used to provide cooling to individual containers, rooms of a building, compartments of a vehicle, and / or to the whole building / vehicles. Vapor compression cooling systems are a type of cooling systems which provide such cooling by circulating a fluid refrigerant (e.g., a liquid and / or vapor) through a thermodynamic vapor compression cycle. In a vapor compression cycle, the refrigerant is typically compressed to a high temperature / pressure state by a compression unit, then cooled / condensed to a lower temperature state (e.g., in a gas cooler or condenser which absorbs heat from the refrigerant). Then the refrigerant is expanded to a lower pressure (e.g., through an expansion valve), and is evaporated to provide cooling by absorbing heat into the refrigerant.

[0006] Some cooling systems utilize a transcritical CO2 (TCO2) vapor compression cycle in marine air conditioning (AC) applications and the like, such cooling systems often employ CO2 as the refrigerant and the compressors utilize Polyol ester (POE) or Polyalkylene Glycol Oil (PAG) () oil as a lubricant. The refrigerant (CO2) is circulated in a closed-loop during which the refrigerant passes through compression and multiple stages of expansion. The process of evaporation takes place in the subcritical stage and heat rejection in the supercritical stage, defining it as a ‘transcritical’ cycle. During operation of such cooling systems, often, oil carryover occurs due to solubility of the lubricant oil in CO2. Such carryover is not desirable as whenever a leakage of the refrigerant occurs, the lubricant oil is also leaked to the surroundings, which is harmful to aquatic life, where the cooling systems are installed in water vehicles such as cruise ships, and the like. Furthermore, such mixture of lubricant and the refrigerant lead to decrease in heat exchanger efficiency, requiring higher capacity heat exchangers. Thus, leading to increase in overall cost of the cooling systems. Also, oil carryover leads to insufficient lubrication in compressor unit which is critical and in turn leads to breakdown of the compressor unit or shutdown of the cooling system.

[0007] With advancement in technology, capillary systems are utilized to recover lubricant oil from CO2. However, such systems reduce superheat at suction portion of the compressor units, where liquid refrigerant may enter the compressor unit. Further, due to reduced superheat, it is required to increase compressor discharge temperature to run the cooling system, which causes additional power consumption. Furthermore, such capillary systems require additional amount of lubricant oil as dead volume in intermediate pressure receivers.

[0008] The present disclosure is directed to overcome one or more limitations stated above or any other limitations associated with the conventional mechanisms.

[0009] SUMMARY OF THE DISCLOSURE

[0010] One or more shortcomings of the prior art are overcome by a method and a system as claimed and additional advantages are provided through the method and the system as claimed in the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

[0011] In one non-limiting embodiment of the present disclosure, a method for regulating operation of a carbon dioxide (CO2) based cooling system is disclosed. The method includes steps of receiving, by a control unit, at least one signal from one or more sensors disposable in an oil reservoir of the carbon dioxide (CO2) based cooling system and communicatively coupled to the control unit. The oil reservoir is configured to receive and store oil from a compressor unit. Further, the control unit is configured to determine the oil level in the oil reservoir based on the at least one signal received from the one or more sensors. The control unit then compares the determined oil level with a threshold oil level. Furthermore, the control unit transmits at least one actuation signal to a vapor control valve connected between an intermediate pressure receiver and the compressor unit based on comparison of the determined oil level with the threshold oil level. The intermediate pressure receiver is fluidly coupled to the compressor unit through the vapor control valve.

[0012] In an embodiment, the one or more sensors comprises at least one level sensor configured to transmit the at least one signal corresponding to the oil level in the oil reservoir and the compressor unit.

[0013] In an embodiment, the control unit is configured to transmit at least one actuation signal to close the vapor control valve upon determining the determined oil level is less than the threshold oil level.

[0014] In an embodiment, the control unit is configured to transmit at least one actuation signal to open a liquid control valve connected between the intermediate pressure receiver and an evaporator of the carbon dioxide (CO2) based cooling system upon determining the determined oil level is less than the threshold oil level.

[0015] In an embodiment, the intermediate pressure receiver is fluidly coupled to the compressor unit through the liquid control valve and an evaporator.

[0016] In an embodiment, the method comprises comparing the determined oil level with a second threshold oil level.

[0017] In an embodiment, the control unit is configured to transmit at least one actuation signal to open the vapor control valve upon determining the determined oil level is greater than the second threshold oil level.

[0018] In an embodiment, the threshold oil level is less than the second threshold oil level. In an embodiment, the method comprises indicating, by the control unit, the determined oil level through an indication device communicatively coupled to the control unit to regulate the vapor control valve.

[0019] In another non-limiting embodiment of the present disclosure, a system for regulating operation of a carbon dioxide (CO2) based cooling system is disclosed. The system comprises one or more sensors configured to transmit at least one signal from the one or more sensors disposable in an oil reservoir of the carbon dioxide (CO2) based cooling system. The system comprises a control unit communicatively coupled to the one or more sensors. The control unit is configured to receive the at least one signal from the one or more sensors. The control unit then determines an oil level in the oil reservoir based on the at least one signal received from the one or more sensors. The control unit compares the determined oil level with a threshold oil level. Furthermore, the control unit transmit at least one actuation signal to a vapor control valve connected between an intermediate pressure receiver and a compressor unit based on comparison of the determined oil level with the threshold oil level.

[0020] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

[0021] BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0022] The novel features and characteristic of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which: Figure la is a schematic layout of a carbon dioxide (CO2) based cooling system, in accordance with an embodiment of the present disclosure.

[0023] Figure lb is a schematic layout of the carbon dioxide (CO2) based cooling system depicting reduced level of oil in an oil reservoir, in accordance with an embodiment of the present disclosure.

[0024] Figure 2 is a block diagram of a system for regulating operation of the carbon dioxide (CO2) based cooling system, in accordance with an embodiment of the present disclosure.

[0025] Figure 3 is a flow diagram of illustrating a method for regulating operation of the carbon dioxide (CO2) based cooling system, in accordance with an embodiment of the present disclosure.

[0026] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the system and method illustrated herein may be employed without departing from the principles of the disclosure described herein.

[0027] DETAILED DESCRIPTION

[0028] While the embodiments in the disclosure are subject to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0029] The terms “comprises”, “comprising”, or any other variations thereof used in the disclosure, are intended to cover a non-exclusive inclusion, such that a system, method that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system, or assembly, or device. In other words, one or more elements in a system proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or method.

[0030] Embodiments of the present disclosure discloses a method for regulating operation of a carbon dioxide (CO2) based cooling system. The method includes steps of receiving, by a control unit, at least one signal from one or more sensors disposable in an oil reservoir of the carbon dioxide (CO2) based cooling system and communicatively coupled to the control unit. The oil reservoir is configured to receive and store a mixture of an oil and CO2 from a compressor unit. Further, the control unit is configured to determine an oil level in the oil reservoir based on the at least one signal received from the one or more sensors. The control unit then compares the determined oil level with a threshold oil level. Furthermore, the control unit transmits at least one actuation signal to a vapor control valve connected between an intermediate pressure receiver and the compressor unit based on comparison of the determined oil level with the threshold oil level. The intermediate pressure receiver is fluidly coupled to the compressor unit through the vapor control valve. With such operation, the method recovers oil mixed with the refrigerant without reduction in efficiency / loading conditions of the cooling system and may enhance heat exchanger efficiency of the cooling system. Further, such method may eliminate or reduce additional cost required to high capacity equipment required to compensate for mixing of lubricant oil and the refrigerant.

[0031] The disclosure is described in the following paragraphs with reference to Figures la to 3. In the figures, the same element or elements which have same functions are indicated by the same reference signs. One skilled in the art would appreciate that the system and the method as disclosed in the present disclosure may be used in any systems including but not liming to cooling systems, refrigeration systems in water vehicles and the like. The system and the method of the present disclosure may also be implemented in cooling systems having a lubricant oil miscible with refrigerant of the cooling system and / or refrigerant system without deviating from the principles of the present disclosure. Figures la and lb refer to an exemplary embodiment of the present disclosure which illustrates a carbon dioxide (CO2) based cooling system (100). The cooling system (100) comprises a compressor unit (10) configured to compress a refrigerant. In an embodiment, the refrigerant is liquid carbon dioxide (CO2). The compressor unit (10) includes at least one compressor configured to receive and compress the refrigerant. In an embodiment, the compressor unit (10) may include three compressors such as a first compressor (10a), a second compressor (10b), and a third compressor (10c) as shown in Figures la and lb, where the second compressor (10b) and the third compressor (10c) may be continuously running, while the first compressor (10a) may act as a back-up compressor. The configuration and number of compressors may be varied based on design requirements of the cooling system (100) and the same shall not be construed as a limitation. The compressor unit (10) is fluidly coupled to an oil reservoir (13) of an oil separator. In an embodiment, the oil reservoir (13) may include an oil separator cum oil reservoir where the oil separator and the oil reservoir are structured as a single component or may include a separate oil reservoir and a separate oil separator fluidly connected to each other by one or more conduits for flow of oil. For the sake of simplicity, the oil reservoir (13) is depicted as a single components. The oil separator is configured to receive the compressed refrigerant from the compressor unit (10) and separate the lubricant oil from the compressed refrigerant. For sake of explanation, the carbon dioxide (CO2) based cooling system (100) is depicted with an oil separator and the same shall not be construed as a limitation. In an embodiment, the lubricant oil is deposited in an oil sump of the compressor unit (10), where the carbon dioxide (CO2) based cooling system (100) may not necessarily comprise an oil separator. In an embodiment, the oil sump may be considered as the oil reservoir of the compressor unit (10), where the oil sump may include at least one level sensor configured to detect oil level in the oil sump.

[0032] Further, the oil reservoir (13) is configured to receive and store the separated lubricant oil received from the oil separator. The oil reservoir (13) is configured to supply the oil to the compressor unit (10) whenever oil level in the compressor unit (10) is low. The oil separator is fluidly coupled to a gas cooler (14) configured to receive and cool the compressed gas from the oil separator. The gas cooler (14) is configured to cool the compressed gas by exchanging heat with a first coolant such as cooled water or other conventional coolants as can be seen in Figure la. In an embodiment, the gas cooler (14) may be thermally coupled to a heat exchanger (15) to cool the compressed refrigerant from the oil reservoir (13) by cooling the first coolant by allowing heat exchange between the first coolant and a second coolant as can be seen in Figure la. In an embodiment, the cooling system (100) may include a pump (11) and a pneumatic expansion tank (12) configured to pump the first coolant for cooling the compressed refrigerant in the gas cooler (14). In the illustrative embodiment, the oil separator is inefficient in separation of the lubricant oil from the compressed refrigerant. In an embodiment, the oil separator may separate the lubricant oil up to an efficiency of 95 to 99 percent, where the separated compressed refrigerant includes a portion of the lubricant oil.

[0033] Further, the gas cooler (14) is fluidly coupled to an intermediate pressure receiver (17) configured to receive the separated compressed refrigerant from the gas cooler (14). The intermediate pressure receiver (17) is configured to receive the separated compressed refrigerant. Such separated compressed refrigerant comprises liquid phase and vapor phase upon being cooled at the gas cooler (14). In an embodiment, the gas cooler (14) is connected to the intermediate pressure receiver (17) by a gas control valve (16) configured to selectively allow flow of the separated compressed refrigerant. In an embodiment, the gas control valve (16) is an expansion valve configured to expand the refrigerant (CO2) received from the gas cooler (14) which in turn converts the gaseous refrigerant into liquid vapour mixture. The liquid vapour mixture enters the intermediate pressure receiver (17). The liquid refrigerant settles at bottom of the intermediate pressure receiver (17), while the vapor phase refrigerant is directed back to compressor suction. The oil mixed with the refrigerant, due to its higher density compared to liquid refrigerant, settles at the bottom most portion of the intermediate pressure receiver (17). The intermediate pressure receiver (17) is fluidly coupled to an evaporator (20) by a liquid control valve (19). The liquid control valve (19) is connected to a portion of the intermediate pressure receiver (17) containing liquid phase of the refrigerant and the lubricant oil. For the sake of explanation, the liquid control valve (19) is connected to a conduit extending from a bottom portion of the intermediate pressure receiver (17) as can be seen in Figures la and lb. The evaporator (20) is fluidly coupled to the compressor unit (10) to allow heat absorption by the liquid phase for conversion to vapor and is configured to supply the vapor to the compressor unit (10). In an embodiment, the intermediate pressure receiver (17) is fluidly coupled to the compressor unit (10) by a vapor control valve (18) to selectively supply vapor to the compressor unit (10). The vapor control valve (18) is connected to a conduit extending from a portion of the intermediate pressure receiver (17) containing vapor phase of the refrigerant. For the sake of explanation, the vapor control valve (18) is depicted to be connected to a top portion of the intermediate pressure receiver (17). In the illustrative embodiment, the evaporator (20) is configured with a distributor (21), where during distribution of the refrigerant, a portion of the lubricant oil mixed with the refrigerant is deposited in the distributor (21) and also at the bottom most portion of intermediate pressure receiver (17).

[0034] Referring again to Figures la and lb, the cooling system (100) is configured to circulate the refrigerant between the evaporator (20), the compressor unit (10), the gas cooler and the intermediate pressure receiver (17) sequentially. During such operation, as the lubricant oil may mix with the refrigerant. In the illustrative embodiment, the refrigerant is liquid CO2 and the lubricant oil is either polyol ester (POE) or Poly alkylene Glycol Oil (PAG), where the lubricant oil is miscible with the refrigerant. In an embodiment, after a certain duration of operation of the cooling system (100), the oil level in the oil reservoir (13) may reduce as can be seen in Figure lb as the lubricant oil is being mixed with the refrigerant and is flowing along with the refrigerant. In an embodiment, when the cooling system (100) is turned off, the lubricant oil may be deposited in the intermediate pressure receiver (17) at a bottom portion as can be seen in Figure lb. In an embodiment, the oil may be deposited in the intermediate pressure receiver (17) during operation of the cooling system (100).

[0035] Referring now to figure 2, which is an exemplary block diagram illustrating a system (200) for regulating operation of the carbon dioxide based cooling system (100). The system (200) includes one or more sensors (1) disposable in the oil reservoir (13) and the compressor unit (10). The one or more sensors (1) may include at least one level sensor configured to detect oil level in one of the oil reservoir (13) and the compressor unit (10). The sensors (1) are configured to transmit the at least one signal corresponding to the oil level in the oil reservoir (13). In an embodiment, the at least one level sensor may include but not limited to a capacitive level sensor, a resistance based level sensor, optoelectronic sensor and the like. In an embodiment, the oil reservoir (13) may include a first sensor disposed at a top portion and a second sensor disposed at a bottom portion of the oil reservoir (13) and the compressor unit. The number of sensors (1) and configuration of the one or more sensors (1) may be varied based on requirements of the cooling system (100) and the same shall not be construed as a limitation. In an embodiment, the one or more sensors (1) may transmit at least one signal in real-time or at regular intervals based on requirement. In an embodiment, the one or more sensors (1) may include at least one sensor disposed in the intermediate pressure receiver (17) configured to detect and transmit at least one signal corresponding to oil level of the lubricant oil accumulated in the intermediate pressure receiver (17).

[0036] Further, the system (200) includes a control unit (2) communicatively coupled to the one or more sensors (1), the gas control valve (16), the liquid control valve (19) and the vapor control valve (18) to regulate operation of the cooling system (100). In an embodiment, the control unit (2) may also be communicatively coupled to the compressor unit (10), the intermediate pressure receiver (17), the evaporator (20) and the gas cooler (14). The control unit (2) is configured to receive the at least one signal from the one or more sensors (1) corresponding to oil level in the oil reservoir (13). In an embodiment, the control unit (2) may receive a plurality of signals from the one or more sensors (1) disposed in the oil reservoir (13), and the intermediate pressure receiver (17). The control unit (2) then determines an oil level in the oil reservoir (13) based on the at least one signal received from the one or more sensors

[0037] (1). In an embodiment, the control unit (2) may determine the oil level in the oil reservoir (13) based on the plurality of signals received from the one or more sensors (1) disposed in the oil reservoir (13), the intermediate pressure receiver (17). For example, the control unit (2) may determine the oil level in the oil reservoir (13) based on at least one signal of the plurality of signals or may determine the oil level based on the plurality of signals collectively.

[0038] In an embodiment, the control unit (2) may determine the oil level based on at least one signal received from the sensors (1) disposed in the oil reservoir (13) as a first iteration and may again determine the oil level based on at least one signal received from the sensors (1) disposed in the intermediate pressure receiver (17) as a second iteration. In an embodiment, the control unit (2) may then determine the oil level by correlating the oil levels obtained determined in the first iteration and the second iteration. The control unit (2) then compares the determined oil level with a threshold oil level. In an embodiment, the threshold oil level may be an oil level which corresponds to indicate an oil level where a decline in performance and / or efficiency of the cooling system (100) may begin due to mixing of the lubricant oil and the refrigerant. In an embodiment, the threshold oil level may be an oil level which corresponds to indicate an oil level where the oil level in compressor is insufficient for lubrication which may cause damage. In an embodiment, the threshold oil level may be an oil level which corresponds to indicate an oil level where the decline in performance and / or efficiency of the cooling system (100) may have already declined in a range of 10 to 15 % due to mixing of the lubricant and the refrigerant.

[0039] Referring again to Figure 2, the control unit (2) is configured to transmit at least one actuation signal to the vapor control valve (18) based on comparison of the determined oil level with the threshold oil level. In an embodiment, the control unit

[0040] (2) is configured to transmit an actuation signal to close the vapor control valve (18) when the determined oil level is less than the threshold oil level indicating that the oil level is less than required amount in the oil reservoir (13). Upon closing of the vapor control valve (18) as vapor from the intermediate pressure receiver (17) is not discharged to the compressor unit (10), pressure within the intermediate pressure receiver (17) increases. The liquid control valve (19) is open to allow flow of the liquid phase to the compressor unit (10). In an embodiment, the control unit (2) transmits at least one actuation signal to open the liquid control valve (19) upon determining the determined oil level is less than the threshold oil level. Such operation of the vapor control valve (18) and the liquid control valve (19) result in pressurized flow of the liquid in the intermediate pressure receiver (17) with high velocity and high pressure. The flow of the liquid with high pressure and high velocity causes the refrigerant and the lubricant oil in the intermediate pressure receiver (17) and the distributor (21) to flow to the compressor unit (10) and subsequently to the oil reservoir (13) through the oil separator. Such method (300) of operating the vapor control valve (18) and the liquid control valve (19) substantially reduces the amount of lubricant oil deposited in the intermediate pressure receiver (17) and the distributor (21) as can be seen in Figure la. In an embodiment, the proposed method (300) may reduce the lubricant oil level up to 80 to 90% in the intermediate pressure receiver (17) and the distributor (21).

[0041] Further, the control unit (2) may compare the determined oil level with a second threshold oil level. In an embodiment, the second threshold oil level may be greater than the threshold oil level. In the illustrative embodiment, the second threshold oil level corresponds to an oil level corresponding to sufficient lubricant oil level required for efficient performance of the cooling system (100) to regulate the operation of the vapor control valve (18). The control unit (2) may transmit at least one actuation signal to open the vapor control valve (18) to allow vapor to flow through the vapor control valve (18) to the compressor unit (10) when the control unit (2) determines the determined oil level is greater than the second threshold oil level. In an embodiment, the control unit (2) may transmit at least one actuation signal to open the vapor control valve (18) to allow vapor to flow through the vapor control valve (18) to the compressor unit (10) when the control unit (2) determines the determined oil level is equal than the second threshold oil level. Thus the control unit (2) is configured to keep the vapor control valve (18) closed until the oil level in the oil reservoir (13) reaches required level for efficient performance of the cooling system (100). Such method (300) of operation of the cooling system (100) separates / recovers the lubricant oil from the refrigerant without any drop in efficiency and / or loading conditions. Further, such method (300) of operation does not require any additional flow path for recovering / separating the lubricant oil from the refrigerant. In an embodiment, the control unit (2) is configured to indicate the determined oil level through an indication device [not shown explicitly in Figures] communicatively coupled to the control unit (2) to regulate the vapor control valve (18). the indication device may include, but not limited to, a wireless display, an LED screen mounted on the cooling system (100), and the like to display the determined oil level to an operator for manually regulating operation of the vapor control valve (18). In an embodiment, the control unit (2) may indicate an indication corresponding to close the vapor control valve (18) through the indication device.

[0042] The control unit (2) may be comprised of a processing unit. The processing unit may comprise at least one data processor for executing program components for executing user- or system (200) -generated requests. The processing unit may be a specialized processing unit such as integrated system (bus) controllers, memory management control units, floating point units, graphics processing units, digital signal processing units, etc. The processing unit may include a microprocessor, such as AMD Athlon, Duron or Opteron, ARM’s application, embedded or secure processors, IBM PowerPC, Intel’s Core, Itanium, Xeon, Celeron or other line of processors, etc. The processing unit may be implemented using a mainframe, distributed processor, multi-core, parallel, grid, or other architectures. Some embodiments may utilize embedded technologies like application- specific integrated circuits (ASICs), digital signal processors (DSPs), Field Programmable Gate Arrays (FPGAs), etc.

[0043] The control unit (2) may be disposed in communication with one or more memory devices (e.g., RAM, ROM etc.) via a storage interface. The storage interface may connect to memory devices including, without limitation, memory drives, removable disc drives, etc., employing connection protocols such as serial advanced technology attachment (SATA), integrated drive electronics (IDE), IEEE-1394, universal serial bus (USB), fiber channel, small computing system interface (SCSI), etc. The memory drives may further include a drum, magnetic disc drive, magnetooptical drive, optical drive, redundant array of independent discs (RAID), solid- state memory devices, solid-state drives, etc.

[0044] Referring now to Figure 3 which is an exemplary embodiment of the present disclosure illustrating a method (300) of regulating operation of a carbon dioxide (CO2) based cooling system (100).

[0045] The method (300) may describe in the general context of processor executable instructions in the control unit (2). Generally, the executable instructions may include routines, programs, objects, components, data structures, procedures, modules, and functions, which perform particular functions or implement particular abstract data types.

[0046] The order in which the method (300) is described is not intended to be construed as a limitation, and any number of the described method (300) blocks may be combined in any order to implement the method (300). Additionally, individual blocks may be deleted from the methods without departing from the scope of the subject matter described herein. Furthermore, the method (300) can be implemented in any suitable hardware, software, firmware, or combination thereof.

[0047] At block 301, the control unit (2) is configured to receive the at least one signal from the one or more sensors (1) corresponding to oil level in the oil reservoir (13). In an embodiment, the control unit (2) may receive a plurality of signals from the one or more sensors (1) disposed in the oil reservoir (13), and the intermediate pressure receiver (17).

[0048] At block 302, the control unit (2) then determines an oil level in the oil reservoir (13) based on the at least one signal received from the one or more sensors (1). In an embodiment, the control unit (2) may determine the oil level in the oil reservoir (13) based on the plurality of signals received from the one or more sensors (1) disposed in the oil reservoir (13), the intermediate pressure receiver (17). For example, the control unit (2) may determine the oil level in the oil reservoir (13) based on at least one signal of the plurality of signals or may determine the oil level based on the plurality of signals collectively.

[0049] In an embodiment, the control unit (2) may determine the oil level based on at least one signal received from the sensors (1) disposed in the oil reservoir (13) as a first iteration and may again determine the oil level based on at least one signal received from the sensors (1) disposed in the intermediate pressure receiver (17) as a second iteration. In an embodiment, the control unit (2) may then determine the oil level by correlating the oil levels obtained determined in the first iteration and the second iteration.

[0050] At block 303, the control unit (2) then compares the determined oil level with a threshold oil level. In an embodiment, the threshold oil level may be an oil level which corresponds to indicate an oil level where a decline in performance and / or efficiency of the cooling system (100) may begin due to mixing of the lubricant oil and the refrigerant. In an embodiment, the threshold oil level may be an oil level which corresponds to indicate an oil level where the decline in performance and / or efficiency of the cooling system (100) may has already declined in a range of 10 to 15 % due to mixing of the lubricant and the refrigerant.

[0051] At block 304, the control unit (2) is configured to transmit at least one actuation signal to the vapor control valve (18) based on comparison of the determined oil level with the threshold oil level. In an embodiment, the control unit (2) is configured to transmit an actuation signal to close the vapor control valve (18) when the determined oil level is less than the threshold oil level indicating that the oil level is less than required amount in the oil reservoir (13). Upon closing of the vapor control valve (18) as vapor from the intermediate pressure receiver (17) is not discharged to the compressor unit (10), pressure within the intermediate pressure receiver (17) increases. The liquid control valve (19) is open to allow flow of the liquid phase to the compressor unit (10). In an embodiment, the control unit (2) transmits at least one actuation signal to open the liquid control valve (19) upon determining the determined oil level is less than the threshold oil level. Such operation of the vapor control valve (18) and the liquid control valve (19) result in pressurized flow of the liquid in the intermediate pressure receiver (17) with high velocity and high pressure. The flow of the liquid with high pressure and high velocity causes the refrigerant and the lubricant oil in the intermediate pressure receiver (17) and the distributor (21) to flow to the compressor unit (10) and subsequently to the oil reservoir (13) through the oil separator. Such method (300) of operating the vapor control valve (18) and the liquid control valve (19) substantially reduces the amount of lubricant oil deposited in the intermediate pressure receiver (17) and the distributor (21) as can be seen in Figure la. In an embodiment, the proposed method (300) may reduce the lubricant oil level up to 80 to 90% in the intermediate pressure receiver (17) and the distributor (21).

[0052] Further, the control unit (2) may compare the determined oil level with a second threshold oil level. In an embodiment, the second threshold oil level may be greater than the threshold oil level. In the illustrative embodiment, the second threshold oil level corresponds to an oil level corresponding to sufficient lubricant oil level required for efficient performance of the cooling system (100) to regulate the operation of the vapor control valve (18). The control unit (2) may transmit at least one actuation signal to open the vapor control valve (18) to allow vapor to flow through the vapor control valve (18) to the compressor unit (10) when the control unit (2) determines the determined oil level is greater than the second threshold oil level. In an embodiment, the control unit (2) may transmit at least one actuation signal to open the vapor control valve (18) to allow vapor to flow through the vapor control valve (18) to the compressor unit (10) when the control unit (2) determines the determined oil level is equal than the second threshold oil level. Thus the control unit (2) is configured to keep the vapor control valve (18) closed until the oil level in the oil reservoir (13) reaches required level for efficient performance of the cooling system (100). Such method (300) of operation of the cooling system (100) separates / recovers the lubricant oil from the refrigerant without any drop in efficiency and / or loading conditions. Further, such method (300) of operation does not require any additional flow path for recovering / separating the lubricant oil from the refrigerant.

[0053] In an embodiment, the method (300) and system (200) of the present disclosure avoid reduction in performance of heat exchangers of the carbon dioxide base cooling system (100). Thus, eliminating need for higher capacity heat exchangers and in turn reducing inherent expenses.

[0054] In an embodiment, the method (300) of operation may reduce or eliminate need for external equipment and / or procedures for separation of the lubricant oil from the refrigerant in the cooling system (100).

[0055] In an embodiment, the method (300) and system (200) of the present disclosure avoid harm to environment and marine life by eliminating leakage of the lubricant oil along with the refrigerant in cooling systems equipped in water vehicles and the like.

[0056] In an embodiment, the method (300) and the system (200) regulate the cooling system (100) to separate the lubricant oil from the refrigerant without reducing the performance and load conditions of the cooling system (100).

[0057] EQUIVALENTS

[0058] With respect to the use of substantially any plural and / or singular terms herein, those having skill in the art can translate from the plural to the singular and / or from the singular to the plural as is appropriate to the context and / or application. The various singular / plural permutations may be expressly set forth herein for sake of clarity.

[0059] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and / or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the. recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and / or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

[0060] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0061] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

[0062] Referral Numeral:

Claims

We claim:

1. A method (300) for regulating operation of a carbon dioxide (CO2) based cooling system (100), the method (300) comprising: receiving, by a control unit (2), at least one signal from one or more sensors (1) disposable in an oil reservoir (13) of the carbon dioxide (CO2) based cooling system (100) and communicatively coupled to the control unit (2), wherein the oil reservoir (13) is configured to receive and store an oil from a compressor unit (10); determining, by the control unit (2), an oil level in the oil reservoir (13) based on the at least one signal received from the one or more sensors (1); comparing, by the control unit (2), the determined oil level with a threshold oil level; transmitting, by the control unit (2), at least one actuation signal to a vapor control valve (18) connected between an intermediate pressure receiver (17) and the compressor unit (10) based on comparison of the determined oil level with the threshold oil level, and wherein the intermediate pressure receiver (17) is fluidly coupled to the compressor unit (10) through the vapor control valve (18).

2. The method (300) as claimed in claim 1, wherein the one or more sensors (1) comprises at least one level sensor configured to transmit the at least one signal corresponding to the oil level in the oil reservoir (13).

3. The method (300) as claimed in claim 1, wherein the control unit (2) is configured to transmit at least one actuation signal to close the vapor control valve (18) upon determining the determined oil level is less than the threshold oil level.

4. The method (300) as claimed in claim 1, wherein the control unit (2) is configured to transmit at least one actuation signal to open a liquid control valve (19) connected between the intermediate pressure receiver (17) andan evaporator (20) of the carbon dioxide (CO2) based cooling system (100) upon determining the determined oil level is less than the threshold oil level.

5. The method (300) as claimed in claim 4, wherein the intermediate pressure receiver (17) is fluidly coupled to the compressor unit (10) through the liquid control valve (19) and an evaporator (20).

6. The method (300) as claimed in claim 1, comprises comparing the determined oil level with a second threshold oil level.

7. The method (300) as claimed in claim 6, wherein the control unit (2) is configured to transmit at least one actuation signal to open the vapor control valve (18) upon determining the determined oil level is greater than the second threshold oil level.

8. The method (300) as claimed in claim 7, wherein the threshold oil level is less than the second threshold oil level.

9. The method (300) as claimed in claim 1, comprises indicating, by the control unit (2), the determined oil level through an indication device communicatively coupled to the control unit (2) to regulate the vapor control valve (18).

10. A system (200) for regulating operation of a carbon dioxide (CO2) based cooling system (100), the system (200) comprising: one or more sensors (1) configured to transmit at least one signal from the one or more sensors (1) disposable in an oil reservoir (13) of the carbon dioxide (CO2) based cooling system (100); and a control unit (2) communicatively coupled to the one or more sensors (1), the control unit (2) is configured to: receive the at least one signal from the one or more sensors (1); determine an oil level in the oil reservoir (13) based on the at least one signal received from the one or more sensors (1);compare the determined oil level with a threshold oil level, and transmit at least one actuation signal to a vapor control valve (18) connected between an intermediate pressure receiver (17) and a compressor unit (10) based on comparison of the determined oil level with the threshold oil level.

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