A direct expansion liquid carbon dioxide circulation system

Abstract

This invention discloses a direct expansion liquid carbon dioxide circulation system, comprising a variable frequency carbon dioxide compressor matrix, a liquid refrigeration condenser, a high-pressure liquid carbon dioxide receiving tank, a primary expansion valve, a low-pressure carbon dioxide liquid tank, a secondary expansion valve, and a cold storage tank, all connected sequentially via pipelines. A liquid carbon dioxide pump is installed between the low-pressure carbon dioxide liquid tank and the secondary expansion valve. The outlet of the cold storage tank is connected to the return port of the low-pressure carbon dioxide liquid tank, and an intelligent pressure regulating valve is installed between the return port and the inlet of the compressor matrix. This system uses environmentally friendly carbon dioxide as the working fluid, significantly improving energy efficiency and reducing throttling losses through a direct expansion phase change refrigeration cycle. The integrated intelligent control of the compressor matrix and multi-stage heat exchange process achieves dynamic matching of heating and cooling energy and efficient recovery of condensation heat, enabling a single system to collaboratively meet diverse heating and cooling needs and significantly improve overall energy utilization efficiency.

Description

Technical Field

[0001] This invention relates to the field of refrigeration and heat pump technology, and more specifically, to a direct expansion liquid carbon dioxide circulation system. Background Technology

[0002] In the field of refrigeration and heat pump technology, traditional refrigeration systems commonly use refrigerants such as Freon or ammonia. However, Freon refrigerants are ozone-depleting and have high global warming potential, while ammonia refrigerants are toxic and flammable, both posing significant environmental and safety hazards. With increasingly stringent global environmental policies, finding green and safe alternative refrigerants has become an urgent industry need.

[0003] Carbon dioxide, as a natural working fluid, has advantages such as being environmentally friendly, non-toxic, and non-flammable, making it an ideal alternative. However, existing carbon dioxide refrigeration systems mostly employ transcritical cycles, which suffer from problems such as high compressor discharge temperatures, large throttling losses, and low system operating efficiency. The energy efficiency degradation is particularly significant under low-temperature refrigeration conditions, limiting its widespread application.

[0004] Furthermore, existing refrigeration systems often fail to fully utilize the heat generated during the condensation process, which is frequently released directly into the environment, resulting in energy waste. For applications requiring simultaneous cooling and heating, two separate systems are often necessary, leading to high equipment investment, large footprint, and poor system synergy. Therefore, a new type of circulating system that balances environmental friendliness, high efficiency, and comprehensive energy utilization is urgently needed. Summary of the Invention

[0005] In view of the above-mentioned technical problems in related technologies, the present invention proposes a direct expansion liquid carbon dioxide circulation system, which can overcome the above-mentioned shortcomings of the prior art.

[0006] To achieve the above-mentioned technical objectives, the technical solution of the present invention is implemented as follows:

[0007] A direct expansion liquid carbon dioxide circulation system;

[0008] The direct expansion liquid carbon dioxide circulation system includes a variable frequency carbon dioxide compressor matrix; the outlet of the variable frequency carbon dioxide compressor matrix is ​​connected to the inlet of the first flow channel of a liquid refrigeration condenser; a high-pressure liquid carbon dioxide receiving tank is connected to the outlet of the first flow channel of the liquid refrigeration condenser; the outlet of the high-pressure liquid carbon dioxide receiving tank is connected to the inlet of a primary expansion valve; the outlet of the primary expansion valve is connected to the inlet of a primary evaporator; the liquid inlet of the low-pressure carbon dioxide liquid tank is connected to the outlet of a secondary expansion valve; a cold storage tank is connected to the inlet of the low-pressure carbon dioxide liquid tank; and a liquid carbon dioxide pump is installed on the pipeline between the low-pressure carbon dioxide liquid tank and the cold storage tank.

[0009] The carbon dioxide outlet of the cold storage tank is connected to the return port of the low-pressure carbon dioxide liquid tank, and an intelligent pressure regulating valve is installed in the pipeline between the return port of the low-pressure carbon dioxide liquid tank and the inlet of the variable frequency carbon dioxide compressor matrix.

[0010] Furthermore, it also includes an oil separator, which comprises a first oil separator disposed at the outlet of the variable frequency carbon dioxide compressor matrix.

[0011] Furthermore, the oil separator also includes a second oil separator and a third oil separator; the second oil separator is disposed on the pipeline between the return port of the low-pressure carbon dioxide liquid tank and the cold storage tank; the third oil separator is disposed on the pipeline between the outlet of the high-pressure liquid carbon dioxide receiving tank and the first-stage expansion valve.

[0012] Furthermore, it also includes a primary evaporator, the inlet of which is connected in parallel with the outlet of the primary expansion valve, and its outlet is connected to a pipeline between the return port of the low-pressure carbon dioxide tank and / or the inlet of the intelligent pressure regulating valve.

[0013] Furthermore, the primary evaporator is a fan-type cooling heat exchanger.

[0014] Furthermore, a secondary evaporator is also provided in the cold storage tank, serving as a cooling heat exchanger. The inlet of the first flow channel of the secondary evaporator is connected to the outlet of the cold storage tank, and its outlet is connected to the outlet of the low-pressure carbon dioxide liquid tank.

[0015] Furthermore, it also includes a hot water tank, the inlet of which is connected to the second flow channel outlet of the liquid refrigeration condenser.

[0016] Furthermore, the variable frequency carbon dioxide compressor matrix includes multiple variable frequency carbon dioxide compressors connected in parallel and series. Each variable frequency carbon dioxide compressor is controlled by a frequency controller, which adjusts the operating status of each compressor based on sensor signals from multiple sensing points in the system.

[0017] Furthermore, the intelligent pressure regulating valve is coupled to the control system of the variable frequency carbon dioxide compressor matrix, and can adjust the opening degree according to the pressure and temperature signals of the sensing point.

[0018] Furthermore, the cold storage tank is equipped with a cooling ice-heat exchanger, which functions as a secondary evaporator in the system.

[0019] The beneficial effects of this invention are as follows: By using environmentally friendly and natural carbon dioxide as the working fluid and combining it with its direct expansion phase change refrigeration cycle, the system's operating energy efficiency is significantly improved and the throttling losses of traditional cycles are effectively reduced. Furthermore, by integrating an intelligently controlled compressor matrix and a multi-stage heat exchange process, dynamic and precise matching of cooling and heating capacity and efficient recovery and utilization of condensation heat are achieved, thereby achieving the goal of a single system coordinating to meet diverse cooling and heating needs and significantly improving the overall energy utilization efficiency. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the overall structure of a specific embodiment of a direct expansion liquid carbon dioxide circulation system according to an embodiment of the present invention;

[0022] In the diagram: 1. Variable frequency carbon dioxide compressor matrix; 2. Low-pressure carbon dioxide liquid tank; 3. Intelligent pressure regulating valve; 4. High-pressure liquid carbon dioxide receiving tank; 4-1. First oil separator; 4-2. Second oil separator; 4-3. Third oil separator; 5. Hot water tank; 6. First-stage expansion valve; 7. Second-stage expansion valve; 8. Liquid carbon dioxide pump; 9. Cooling heat exchanger; 10. First-stage evaporator; 11. Cold storage tank; 12. Cold water pump; 13. Circulation pump; 14. Liquid refrigeration condenser; P1. First sensing point; P2. Second sensing point; P3. Third sensing point; P4. Fourth sensing point; P5. Fifth sensing point. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0024] It should be understood that in the description of the embodiments of the present invention, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are used only for the convenience of describing the embodiments of the present invention and for simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of the embodiments of the present invention, "several" means two or more, unless otherwise explicitly specified.

[0025] like Figure 1 As shown, a direct expansion liquid carbon dioxide circulation system according to an embodiment of the present invention includes a variable frequency carbon dioxide compressor matrix 1; the outlet of the variable frequency carbon dioxide compressor matrix 1 is connected to the inlet of the first flow channel of a liquid refrigeration condenser 14; a high-pressure liquid carbon dioxide receiving tank 4 is connected to the outlet of the first flow channel of the liquid refrigeration condenser 14; the outlet of the high-pressure liquid carbon dioxide receiving tank 4 is connected to the inlet of a first-stage expansion valve 6; the outlet of the first-stage expansion valve 6 is connected to the inlet of a first-stage evaporator 10; the liquid inlet of a low-pressure carbon dioxide liquid tank 2 is connected to the outlet of a second-stage expansion valve 7; a cold storage tank 11 is connected to the outlet of the low-pressure carbon dioxide liquid tank 2; and a liquid carbon dioxide pump 8 is installed on the pipeline between the low-pressure carbon dioxide liquid tank 2 and the cold storage tank 11.

[0026] The carbon dioxide outlet of the cold storage tank 11 is connected to the return port of the low-pressure carbon dioxide liquid tank 2, and an intelligent pressure regulating valve 3 is installed in the pipeline between the return port of the low-pressure carbon dioxide liquid tank 2 and the inlet of the variable frequency carbon dioxide compressor matrix 1.

[0027] According to an embodiment of the present invention, a direct expansion liquid carbon dioxide circulation system further includes an oil separator in a specific embodiment. The oil separator includes a first oil separator 4-1 disposed at the outlet of the variable frequency carbon dioxide compressor matrix 1.

[0028] According to an embodiment of the present invention, a direct expansion liquid carbon dioxide circulation system is provided. In a specific embodiment, the oil separator further includes a second oil separator 4-2 and a third oil separator 4-3. The second oil separator 4-2 is disposed on the pipeline between the return port of the low-pressure carbon dioxide liquid tank 2 and the cold storage tank 11. The third oil separator 4-3 is disposed on the pipeline between the outlet of the high-pressure liquid carbon dioxide receiving tank 4 and the first-stage expansion valve 6.

[0029] According to an embodiment of the present invention, a direct expansion liquid carbon dioxide circulation system further includes a primary evaporator 10 in a specific embodiment. The inlet of the primary evaporator 10 is connected in parallel with the outlet of the primary expansion valve 6, and its outlet is connected to a pipeline between the return port of the low-pressure carbon dioxide tank 2 and / or the inlet of the intelligent pressure regulating valve 3.

[0030] According to an embodiment of the present invention, in a specific embodiment of a direct expansion liquid carbon dioxide circulation system, the primary evaporator 10 is a fan-type cooling heat exchanger.

[0031] According to an embodiment of the present invention, a direct expansion liquid carbon dioxide circulation system further includes a cooling ice-heat exchanger 9 in a specific embodiment. The inlet of the first flow channel of the secondary evaporator 9 is connected to the outlet of the primary evaporator 10, and its first flow channel outlet is connected to the inlet of the low-pressure carbon dioxide liquid tank 2.

[0032] According to an embodiment of the present invention, a direct expansion liquid carbon dioxide circulation system further includes a hot water tank 5 in a specific embodiment, wherein the inlet of the hot water tank 5 is connected to the second flow channel outlet of the liquid refrigeration condenser 14.

[0033] According to an embodiment of the present invention, a direct expansion liquid carbon dioxide circulation system is provided. In a specific embodiment, the variable frequency carbon dioxide compressor matrix 1 includes multiple variable frequency carbon dioxide compressors connected in parallel and series. Each variable frequency carbon dioxide compressor is controlled by a frequency controller. The frequency controller adjusts the operating state of each compressor based on sensor signals from multiple sensing points P1, P2, P3, P4, and P5 in the system.

[0034] According to an embodiment of the present invention, in a specific embodiment of a direct expansion liquid carbon dioxide circulation system, the intelligent pressure regulating valve 3 is coupled to the control system of the variable frequency carbon dioxide compressor matrix 1, and can adjust the opening degree according to the pressure and temperature signals of the sensing point.

[0035] According to an embodiment of the present invention, in a specific embodiment of a direct expansion liquid carbon dioxide circulation system, the cold storage tank 11 is equipped with a cooling ice-heat exchanger, which functions as a secondary evaporator in the system.

[0036] To facilitate understanding of the above technical solutions of the present invention, the following detailed description of the above technical solutions of the present invention will be provided through specific usage methods.

[0037] In practical application, the direct expansion liquid carbon dioxide circulation system according to the present invention requires reasonable equipment selection and installation. The variable frequency carbon dioxide compressor matrix 1 should preferably consist of multiple parallel and series-connected fully enclosed or semi-enclosed CO2-specific variable frequency compressors, with their total capacity determined based on the design cooling and heating loads. The liquid refrigeration condenser 14 should employ a high-efficiency shell-and-tube or plate heat exchanger, with a design pressure meeting supercritical operating conditions. Both the high-pressure liquid carbon dioxide receiving tank 4 and the low-pressure carbon dioxide liquid tank 2 are pressure vessels, and their design pressure and operating temperature ranges must match the system design parameters. The primary expansion valve 6 and secondary expansion valve 7 are preferably electronic expansion valves for precise control. The cold storage tank 11 can be selected as a water-based or ice-based cold storage tank, with internal coils resistant to low-temperature corrosion. The intelligent control system should include a programmable logic controller (PLC), a frequency converter, pressure and temperature sensors P1-P5, and corresponding control algorithm software.

[0038] The system installation must follow strict process procedures. All refrigerant piping should be made of seamless stainless steel pipe, welded together, and undergo thorough purging and pressure testing. Oil separators 4-1, 4-2, and 4-3 must be installed vertically, ensuring the return oil line slope is correct. Heat exchangers must be installed horizontally with sufficient maintenance space. Sufficient straight pipe sections must be provided before and after the expansion valve. Sensors must be installed at representative measuring points, and signal cables must be properly shielded.

[0039] After the system is debugged, it can be put into operation. During startup, the liquid carbon dioxide pump 8 and the chilled water pump 12 are started first, and then the compressors in the variable frequency carbon dioxide compressor matrix 1 are started gradually. The system pressure is controlled by the intelligent pressure regulating valve 3 and the compressor frequency in a coordinated manner to gradually establish normal operating conditions.

[0040] In cooling mode, the system focuses on producing chilled water (5℃~10℃) for user use through the secondary evaporator 9, or providing cooling at a lower temperature (-40℃~-25℃) through the primary evaporator 10. At this time, the heat of condensation is recovered and stored in the hot water tank 5.

[0041] In heating mode, the system prioritizes ensuring the water supply temperature of hot water tank 5, and the liquid refrigeration condenser 14 serves as the main heat source to heat the room temperature water to 85°C.

[0042] In integrated mode, the intelligent control system dynamically adjusts the number and frequency of compressors, the opening degree of each expansion valve, and the flow rate of refrigerant / water based on real-time monitoring of cooling and heating load demands, so as to optimally allocate cooling and heating capacity and maximize energy utilization.

[0043] The cold storage cycle can operate during off-peak electricity periods or when cooling demand is low. Liquid carbon dioxide is throttled through the secondary expansion valve 7 and sent to the cold storage tank 11 to make ice or cool the refrigerant, storing the cold energy. During peak electricity demand or when the efficiency of the refrigeration unit decreases, the cold storage tank 11 can release the cold energy to meet the cooling demand, playing a role in peak shaving, valley filling, energy saving, and consumption reduction.

[0044] The entire operation is fully automated, monitored and regulated by an intelligent control system. Operators only need to set the target temperature and pressure or select the operating mode through the human-machine interface. The system has comprehensive automatic protection and fault diagnosis functions to ensure safe and reliable operation.

[0045] Regular maintenance is crucial for ensuring the long-term, efficient, and stable operation of the system. This includes periodically checking and replacing lubricating oil, cleaning heat exchanger fins and tube bundles, calibrating safety valves and sensors, and upgrading control software.

[0046] In summary, the technical solution of the present invention has the following beneficial effects:

[0047] By using environmentally friendly and natural carbon dioxide as the refrigerant and combining it with its direct expansion phase change refrigeration cycle, the system completely eliminates the potential for ozone layer depletion and significantly reduces the impact of the greenhouse effect. At the same time, it effectively avoids the inherent defects of traditional transcritical cycles, such as high exhaust temperature and excessive throttling loss, thereby achieving the goal of comprehensively improving the system's operating energy efficiency and reliability.

[0048] By integrating a variable frequency compressor matrix and a multi-stage expansion heat exchange process, and introducing an intelligent collaborative control system, the system can dynamically match changing heating and cooling loads in real time, accurately adjust refrigerant flow and pressure distribution, and simultaneously achieve efficient recovery of condensation heat and preparation of high-temperature hot water. This results in a system that collaboratively meets diverse heating and cooling needs, significantly improves overall energy utilization efficiency and operational economy.

[0049] Through modular integrated design and energy storage tank configuration, the system combines multiple functions such as deep cooling, air conditioning, domestic hot water supply and cold energy storage, significantly reducing initial equipment investment and floor space, while enhancing the system's buffering capacity and operational stability in response to load fluctuations. This achieves the ideal effect of simplifying system architecture, broadening application scenarios and improving overall performance.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A direct expansion liquid carbon dioxide circulation system, characterized in that, The system includes a variable frequency carbon dioxide compressor matrix (1); the outlet of the variable frequency carbon dioxide compressor matrix (1) is connected to the first flow channel inlet of a liquid refrigeration condenser (14); the first flow channel outlet of the liquid refrigeration condenser (14) is connected to a high-pressure liquid carbon dioxide receiving tank (4); the outlet of the high-pressure liquid carbon dioxide receiving tank (4) is connected to the inlet of a primary expansion valve (6); the outlet of the primary expansion valve (6) is connected to a primary evaporator (10); the liquid inlet of a low-pressure carbon dioxide liquid tank (2) is connected to the outlet of a secondary expansion valve (7), and the inlet of the secondary expansion valve (7) is connected to another outlet of the high-pressure liquid carbon dioxide receiving tank (4); the outlet of the low-pressure carbon dioxide liquid tank (2) is connected to a cold storage tank (11); and a liquid carbon dioxide pump (8) is installed on the pipeline between the low-pressure carbon dioxide liquid tank (2) and the cold storage tank (11). The carbon dioxide outlet of the cold storage tank (11) is connected to the return port of the low-pressure carbon dioxide liquid tank (2), and an intelligent pressure regulating valve (3) is installed in the pipeline between the return port of the low-pressure carbon dioxide liquid tank (2) and the inlet of the variable frequency carbon dioxide compressor matrix (1). The outlet of the primary evaporator (10) is connected to the return port of the low-pressure carbon dioxide liquid tank (2) and / or the inlet of the intelligent pressure regulating valve (3) via a pipeline. The variable frequency carbon dioxide compressor matrix (1) includes multiple variable frequency carbon dioxide compressors connected in parallel and in series. Each variable frequency carbon dioxide compressor is controlled by a frequency controller. The frequency controller adjusts the operating status of each compressor based on sensor signals from multiple sensing points in the system. The intelligent pressure regulating valve (3) is coupled to the control system of the variable frequency carbon dioxide compressor matrix (1) and can adjust the opening degree according to the pressure and temperature signals of the sensing point. The cold storage tank (11) is a cold storage tank for storing ice and cooling.

2. The direct expansion liquid carbon dioxide circulation system according to claim 1, characterized in that, It also includes an oil separator, which includes a first oil separator (4-1) disposed at the outlet of the variable frequency carbon dioxide compressor matrix (1).

3. The direct expansion liquid carbon dioxide circulation system according to claim 2, characterized in that, The oil separator also includes a second oil separator (4-2) and a third oil separator (4-3); the second oil separator (4-2) is installed on the pipeline between the low-pressure carbon dioxide liquid tank (2) and the cold storage tank (11); the third oil separator (4-3) is installed on the pipeline between the outlet of the high-pressure liquid carbon dioxide receiving tank (4) and the first-stage expansion valve (6).

4. The direct expansion liquid carbon dioxide circulation system according to claim 1, characterized in that, The primary evaporator (10) is a fan-type cooling heat exchanger.

5. The direct expansion liquid carbon dioxide circulation system according to claim 1, characterized in that, It also includes a cooling ice-heat exchanger (9), which is installed in a cold storage tank (11); the first flow channel inlet of the cooling ice-heat exchanger (9) is connected to the circulating water channel, and its first flow channel outlet is connected to the inlet of the cooling circulation pump (12).

6. The direct expansion liquid carbon dioxide circulation system according to claim 1, characterized in that, It also includes a hot water tank (5), the inlet of which is connected to the second flow channel outlet of the liquid refrigeration condenser (14).

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