Pump unit

Abstract

We provide a pump unit that reduces the effort required for installation work. [Solution] The pump unit 101 has large-diameter header pipes 1, 2, 3, 4, a pump 5, and a pump control unit 6, and cools the primary refrigerant of the data center 11 by circulating a secondary refrigerant (e.g., cooling water) between the heat exchanger 13 of the data center 11 and the cooling unit 12. Multiple pipes (four each in the illustrated example) 21, 22, 23, 24 are connected to the corresponding header pipes 1, 2, 3, 4. The header pipes 1, 2, 3, 4 are all set to have a much larger diameter than the pipes 21, 22, 23, 24. The pump unit 101 has a portable frame (stand) on which the header pipes 1, 2, 3, 4, the flow paths 41, 42, 51, 61 connected between them, and the pump 5 are installed.

Description

Technical Field

[0001] The present invention relates to a pump unit used for circulating a refrigerant for cooling hardware installed in a data center.

Background Art

[0002] Data centers where AI (Artificial Intelligence) servers and the like are installed generate an enormous amount of heat, and the current air-cooling method cannot cope with the situation. There were no legal regulations, but the industry has continued to take the stance that it is impossible to supply cooling water to computers. However, since systems imported from abroad such as Google are already water-cooled, an agreement to allow water-cooling has finally been reached in the industry, and 2025 is considered the "Year of Water Cooling."

[0003] Since hardware such as computers cannot directly touch the cooling water, even in a water-cooling system, a refrigerant with electrical insulation is used as the primary refrigerant for directly cooling the hardware. Then, the primary refrigerant is cooled by a secondary refrigerant such as cooling water through a heat exchanger (CDU; Coolant Distribution Unit; Cooling Distribution Unit). In this way, in a water-cooling system, the hardware in the data center is indirectly cooled by the cooling water by using the cooling water as the secondary refrigerant.

[0004] In such a water-cooling system, installing a pump unit for circulating cooling water as the secondary refrigerant in a data center is a major task that requires a lot of effort. Therefore, it was predicted that a pump unit that could reduce the labor of the installation work was potentially eagerly awaited.

[0005] Furthermore, technologies related to the present invention are disclosed in Patent Documents 1 to 5. Patent Documents 1 and 2 disclose a cooling system intended for application to data centers. A header pipe for branching the refrigerant is disclosed, but it is provided in the flow path of the primary refrigerant that directly cools the heat-generating semiconductor device, and not in the flow path of the secondary refrigerant. In particular, Patent Document 2 discloses a containerized data center, but it is not just the cooling system that is containerized, but the data center itself is also containerized.

[0006] Patent documents 3 to 5 do not mention "data centers" and disclose cooling systems for information processing equipment or electronic equipment. Of these, patent document 4 describes a primary cooling system in which the supply amount of refrigerant is controlled by two pumps that individually circulate refrigerant to two radiators. Patent document 5 describes a primary cooling system in which the number of operating pumps is controlled according to the temperature difference between the inflowing and outflowing water. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2025-110953 [Patent Document 2] Japanese Patent Publication No. 2025-027789 [Patent Document 3] Japanese Patent Publication No. 2007-272294 [Patent Document 4] Patent No. 4544527 [Patent Document 5] Japanese Patent Publication No. 2003-029879 [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention has been made in view of the above-mentioned problems, and aims to provide a pump unit that can reduce the effort required for installation work. [Means for solving the problem]

[0009] To achieve the above objective, a first aspect of the present invention is a pump unit used in connection with a heat exchanger that performs heat exchange with a primary refrigerant to cool hardware installed in a data center, and a cooling unit that cools a secondary refrigerant that performs heat exchange with the primary refrigerant through the heat exchanger. This pump unit comprises first to fourth header pipes and first to second flow paths. The first header pipe has a plurality of first ports to which a plurality of first pipes that supply the secondary refrigerant to the cooling unit can be connected, and is larger in diameter than the plurality of first pipes. The second header pipe has a plurality of second ports to which a plurality of second pipes that return the secondary refrigerant after passing through the cooling unit can be connected, and is larger in diameter than the plurality of second pipes. The third header pipe has a plurality of third ports to which a plurality of third pipes that supply the secondary refrigerant to the heat exchanger can be connected, and is larger in diameter than the plurality of third pipes. The fourth header pipe has a plurality of fourth ports to which a plurality of fourth pipes that return the secondary refrigerant after passing through the heat exchanger can be connected, and is larger in diameter than the plurality of fourth pipes. The first flow path transports the secondary refrigerant from the fourth header pipe to the first header pipe. The second flow path transports the secondary refrigerant from the second header pipe to the third header pipe. One of the first and second flow paths has a pump to deliver the secondary refrigerant.

[0010] In this configuration, the first and second pipes connected to the cooling unit are connected to the first and second ports, respectively, and the third and fourth pipes connected to the heat exchanger are connected to the third and fourth ports, respectively, thereby achieving cooling of the hardware installed in the data center. Since there are multiple pipes for each of the first to fourth pipes, it is possible to use pipes with small diameters for each individual pipe. This makes it easy to install the pipes and connect them to the corresponding header pipes. In other words, the effort required for installation work is reduced. Even if multiple corresponding pipes are connected to each header pipe, the header pipe has a larger diameter than the pipes it is connected to, so the pressure difference of the secondary refrigerant between the multiple connected pipes is mitigated or eliminated. In other words, the flow rate difference of the secondary refrigerant between the multiple pipes is suppressed. Furthermore, since each header pipe has a larger diameter than the pipes it is connected to, each header pipe acts as a buffer to mitigate temperature changes in the secondary refrigerant returning from the heat exchanger due to fluctuations in the heat load of hardware cooling. This slows down the rate of change in the cooling unit's load, creating more leeway in the control of the cooling unit.

[0011] A second aspect of the present invention is a pump unit according to the first aspect, further comprising the first to fourth header pipes, the first flow path, the second flow path, and a portable frame on which the pump is installed.

[0012] The pump unit with this configuration can be transported to the data center as a complete assembly, frame and all, and can be put into use on-site by connecting the first to fourth piping lines.

[0013] A third aspect of the present invention is a pump unit according to the second aspect, wherein the first to fourth header pipes are arranged horizontally and parallel to each other, and two of each are arranged in two upper and lower tiers, with the heights of each tier being the same as those of the other tier.

[0014] This configuration allows for a lower height for the large-diameter header pipes, thereby improving portability and maintainability.

[0015] A fourth aspect of the present invention is a pump unit according to any of the first to third aspects, further comprising a first bypass passage for bypassing the secondary refrigerant from the first header pipe to the second header pipe. The first bypass passage has a first bypass valve for opening and closing the first bypass passage.

[0016] With this configuration, when it is necessary to reduce the flow rate of secondary refrigerant to the cooling unit for maintenance of a part of the cooling unit, the first bypass valve can be opened appropriately to bypass a portion of the secondary refrigerant, thereby reducing the flow rate of secondary refrigerant to the cooling unit without changing the pump flow rate.

[0017] A fifth aspect of the present invention is a pump unit according to any of the first to fourth aspects, further comprising a second bypass passage for bypassing the secondary refrigerant from the third header pipe to the fourth header pipe. The second bypass passage has a second bypass valve for opening and closing the second bypass passage.

[0018] With this configuration, when the flow rate of refrigerant to the heat exchanger should be reduced according to the scale of the heat exchanger to which the secondary refrigerant should be supplied, a portion of the secondary refrigerant can be bypassed by appropriately opening the second bypass valve. This allows the flow rate of the secondary refrigerant to the heat exchanger to be reduced without changing the pump flow rate.

[0019] A sixth aspect of the present invention is a pump unit according to any of the first to fifth aspects, further comprising a pump control unit for controlling the pump. Furthermore, of the first and second flow paths, the flow path containing the pump further comprises a flow meter for detecting the flow rate of the secondary refrigerant flowing through that flow path. The control unit controls the pump by referring to the flow rate detected by the flow meter so that the flow rate of the secondary refrigerant becomes a predetermined constant amount.

[0020] According to this configuration, the flow rate of the secondary refrigerant pumped by the pump can be maintained at a predetermined constant value.

[0021] A seventh aspect of the present invention is a pump unit according to the sixth aspect, wherein the pump has three or more unit pumps connected in parallel. And the control unit performs rotation control to drive a plurality of unit pumps in order so that at least one unit pump is sequentially stopped.

[0022] According to this configuration, in a data center where constant cooling is required without interruption, maintenance (repair and inspection) of the pump can be performed without changing the flow rate of the secondary refrigerant.

[0023] An eighth aspect of the present invention is a cooling system according to the seventh aspect, further comprising a temperature sensor for detecting the air temperature. And when the air temperature detected by the temperature sensor is lower than a predetermined temperature, the pump control unit operates all of the three or more unit pumps.

[0024] According to this configuration, when the secondary refrigerant is, for example, cooling water and the air temperature is lower than, for example, 5°C, all unit pumps can be operated, thereby preventing the secondary refrigerant from freezing.

Advantages of the Invention

[0025] As described above, according to the present invention, a pump unit that can reduce the labor of installation work is realized.

Brief Description of the Drawings

[0026] [Figure 1] It is a schematic diagram illustrating the configuration of a pump unit according to an embodiment of the present invention. [Figure 2] It is a schematic diagram illustrating the connection form of each pipe to each header pipe of the pump unit in FIG. 1. [Figure 3] It is a schematic diagram illustrating the circulation path of the secondary refrigerant transported by the pump unit in FIG. 1. [Figure 4] This is an external view illustrating the specific configuration of the pump unit shown in Figure 1. [Figure 5] This is a schematic diagram showing another example of the header pipe arrangement for the pump unit in Figure 1. [Modes for carrying out the invention]

[0027] Figure 1 is a schematic diagram illustrating the configuration of a pump unit according to one embodiment of the present invention. This pump unit 101 is a system that cools hardware such as AI servers in the data center 11 through a heat exchanger (CDU) 13 in the data center 11. For this reason, the pump unit 101 is installed and used inside the building of the data center 11. As already mentioned, an electrically insulating refrigerant is used as the primary refrigerant to directly cool the hardware in the data center 11. The pump unit 101 cools the primary refrigerant with a secondary refrigerant such as cooling water via the heat exchanger 13.

[0028] The pump unit 101 includes large-diameter header pipes 1, 2, 3, and 4, a pump 5, and a pump control unit 6. The header pipes 1, 2, 3, and 4 are connected to the heat exchanger 13 and the cooling unit 12 in the data center 11, which are external devices of the pump unit 101, via pipes 21, 22, 23, and 24. The cooling unit 12 is a device that cools the secondary refrigerant. The pump 5 is installed in the flow path connecting the header pipes 1, 2, 3, and 4 and pumps out the secondary refrigerant. The pump control unit 6 controls the pump 5, for example, by incorporating an inverter.

[0029] In this way, the pump unit 101 cools the primary refrigerant of the data center 11 by circulating a secondary refrigerant between the heat exchanger 13 of the data center 11 and the cooling unit 12. The secondary refrigerant circulated by the pump unit 101 is, for example, the simplest cooling water.

[0030] Figure 2 is a schematic diagram illustrating the piping configuration of the pump unit 101 to header pipes 1, 2, 3, and 4. Piping 21, 22, 23, and 24 are connected to header pipes 1, 2, 3, and 4, respectively. Piping 21 is a pipe that sends cooling water, which is the secondary refrigerant, from header pipe 1 to the cooling unit 12. Piping 22 is a pipe that returns the cooling water cooled by the cooling unit 12 back to header pipe 2. Piping 23 is a pipe that sends the cooling water that has returned to header pipe 2 from header pipe 3 to the heat exchanger 13 of the data center 11. A flow path 41 is open between header pipe 2 and header pipe 3.

[0031] Piping 24 is a pipe that returns the cooling water heated by the heat exchanger 13 to the header pipe 4. A passage 42 is open between the header pipe 4 and the header pipe 1 (see Figure 1). A pump 5 is installed in the passage 42, and when the pump 5 operates, the cooling water that has returned to the header pipe 4 is returned to the header pipe 1 via the passage 42. Then, the cooling water is sent again from the header pipe 1 to the cooling unit 12 through piping 21. In this way, the cooling water, which is the secondary refrigerant, circulates between the heat exchanger 13 of the data center 11 and the cooling unit 12 via the pump unit 101.

[0032] Multiple pipes 21, 22, 23, and 24 are connected to the corresponding header pipes 1, 2, 3, and 4. This allows the required flow rate to be secured while keeping the diameter of each individual pipe constituting pipes 21, 22, 23, and 24 small. Because the diameter of each pipe in pipes 21, 22, 23, and 24 is kept small, the work of installing pipes 21, 22, 23, and 24, and connecting them to header pipes 1, 2, 3, and 4, is easier.

[0033] Header pipes 1, 2, 3, and 4 are all set to have a much larger diameter than pipes 21, 22, 23, and 24. As a result, for example, pressure differences in the cooling water are eliminated among the multiple pipes 21 that are commonly connected to header pipe 1, so that the flow rate of the cooling water is uniform among these multiple pipes 21. The same applies to the other header pipes 2, 3, and 4, and pipes 22, 23, and 24.

[0034] Since header pipes 1, 2, 3, and 4 have a much larger diameter than the connected pipes 21, 22, 23, and 24, header pipes 1, 2, 3, and 4 act as buffers to mitigate temperature changes in the cooling water returning from the heat exchanger 13 of the data center 11 due to fluctuations in the heat load for hardware cooling. As a result, the rate of change in the load on the cooling unit 12 becomes slower, and there is more leeway in controlling the cooling unit 12.

[0035] Each side wall of header pipes 1, 2, 3, and 4 is provided with multiple openings (four in the illustrated example) (referred to as "ports" in this application) for detachably connecting pipes 21, 22, 23, and 24. Preferably, a detachable coupling structure is used at the connection between the ports of header pipes 1, 2, 3, and 4 and pipes 21, 22, 23, and 24. Furthermore, it is preferable that flexible hoses be used for pipes 21, 22, 23, and 24. This makes the process of connecting pipes 21, 22, 23, and 24 to header pipes 1, 2, 3, and 4 even easier.

[0036] In the illustrated example, pipes 21, 22, 23, and 24 are connected to larger diameter pipes 31, 32, 33, and 34, respectively. Through pipes 31, 32, 33, and 34, pipes 21, 22, 23, and 24 are connected to the heat exchanger 13 or cooling unit 12 of the data center 11.

[0037] Figure 3 is a schematic diagram illustrating the circulation path of the cooling water transported by the pump unit 101. A bypass channel 51 is installed between header pipe 1 and header pipe 2. The bypass channel 51 bypasses the cooling water from header pipe 1 to header pipe 2. A bypass valve 52 and a flow meter 53 are installed in the bypass channel 51. The bypass valve 52 opens and closes the bypass channel 51. The flow meter 53 measures the flow rate of the cooling water flowing through the bypass channel 51.

[0038] In the illustrated example, the bypass valve 52 is operated manually. For example, when the flow rate of cooling water to the cooling unit 12 needs to be reduced by a predetermined amount for maintenance of part of the cooling unit 12, the operator can bypass a portion of the cooling water by appropriately opening the bypass valve 52 while visually monitoring the flow meter 53. This allows the flow rate of cooling water to the cooling unit 12 to be reduced without changing the flow rate of the pump 5. The amount of reduction in the flow rate of cooling water to the cooling unit 12 is the same as the flow rate of cooling water flowing through the bypass channel 51 displayed by the flow meter 53.

[0039] A bypass channel 61 is installed between header pipe 3 and header pipe 4. The bypass channel 61 bypasses cooling water from header pipe 3 to header pipe 4. A bypass valve 62 and a flow meter 63 are installed in the bypass channel 61. The bypass valve 62 opens and closes the bypass channel 61. The flow meter 63 measures the flow rate of cooling water flowing through the bypass channel 61.

[0040] In the illustrated example, the bypass valve 62 is operated manually. For example, when the flow rate of cooling water supplied to the heat exchanger (CDU) 13 of the data center 11 needs to be reduced depending on the scale of the CDU 13 to which the cooling water should be supplied, the operator can bypass a portion of the cooling water by appropriately opening the bypass valve 62 while visually monitoring the flow meter 63. This allows the flow rate of cooling water to the heat exchanger 13 to be reduced without changing the flow rate of the pump 5 or the flow rate of cooling water to the cooling unit 12. The amount of reduction in the flow rate of cooling water supplied to the heat exchanger 13 is the same as the flow rate of cooling water flowing through the bypass channel 61 displayed by the flow meter 63.

[0041] Figure 1 illustrates the flow rates in pipes 21, 22, 23, and 24 when the discharge rate of pump 5 is maintained at 960 L / min, and the bypass valve 62 (see Figure 4) is opened appropriately to bypass cooling water at a flow rate of 360 L / min through the bypass passage 61 (see Figure 4). The flow rate of cooling water flowing through cooling unit 12 is 960 L / min, and the flow rate of cooling water flowing through heat exchanger 13 is 600 L / min (= 960 L / min - 360 L / min). In this example, cooling unit 12 is specified to maintain a cooling water flow rate at a predetermined value (960 L / min) during normal operation, and it is assumed that the scale of AI servers etc. that the heat exchanger 13 of the data center 11 is responsible for cooling is smaller than the capacity of cooling unit 12, so a cooling water flow rate of 600 L / min, which is lower than 960 L / min, is sufficient. In this way, by opening and closing the bypass valve 62, the cooling unit 12 can accommodate various sizes of equipment to be cooled by the heat exchanger 13, within the range of its capacity.

[0042] In the examples shown in Figures 1 and 3, a flow meter 73 is installed in the flow path 42 to measure the flow rate of the cooling water flowing through the flow path 42. The measurement data from the flow meter 73 is transmitted to the pump control unit 6. The pump control unit 6 controls the pump 5 so that the flow rate of the cooling water flowing through the flow path 42 is constant, for example, 960 L / min, by referring to the measurement data from the flow meter 73.

[0043] In the illustrated example, pump 5 has three unit pumps connected in parallel. The pump control unit 6, for example, drives only two unit pumps at a time, leaving the remaining one idle, and rotates the idled unit pump among the three in sequence. By performing this rotation control, maintenance of pump 5 can be carried out without changing the flow rate of cooling water that the data center 11 constantly requires. This also contributes to extending the lifespan of pump 5.

[0044] A temperature sensor 81 is installed in header pipe 1. The temperature sensor 81 measures the temperature of the cooling water in header pipe 1, that is, the temperature of the cooling water returning from the heat exchanger 13 (the temperature of the cooling water sent to the cooling unit 12). A temperature sensor 82 is installed in header pipe 2. The temperature sensor 82 measures the temperature of the cooling water in header pipe 2, that is, the temperature of the cooling water sent to the heat exchanger 13 (the temperature of the cooling water cooled by the cooling unit 12). The measurement data from temperature sensors 81 and 82 is sent to a control device 90 (see Figure 1) attached to the cooling unit 12. The control device 90, for example, refers to the measurement data from temperature sensors 81 and 82 to perform modular control and control the cooling unit 12 so as to maintain the temperature of the cooling water sent to the heat exchanger 13 at 23°C. The cooling unit 12 illustrated in Figures 1 and 2 has multiple cooling modules. The control device 90 controls the number of operating modules according to the load, for example, by operating only one unit when the cooling load is light, and by operating all units at full capacity when the load is heavy. This type of control is called "module control".

[0045] In the example shown in Figure 1, the pump unit 101 further includes a temperature sensor 83. The temperature sensor 83 is installed, for example, near the pump 5 and detects the ambient temperature around the pump 5. The measurement data from the temperature sensor 83 is used by the pump control unit 6. When the temperature detected by the temperature sensor 83 falls below a predetermined temperature, the pump control unit 6 drives the pump 5 so that all three unit pumps operate. For example, when the temperature falls below 5°C, all unit pumps can be activated, preventing the start-up of idle unit pumps from being hindered by the freezing of the cooling water.

[0046] Figure 4 is an external view illustrating the specific configuration of the pump unit 101. In the illustrated example, the pump unit 101 has a portable frame (stand) 120. Header pipes 1, 2, 3, 4, flow channels 41, 42, 51, 61 connected between them, and a pump 5 are mounted on the frame 120. The pump unit 101, configured in this way, can be transported to the data center 11 along with the frame 120 in its assembled state, and can be put into use by connecting the piping 21, 22, 23, 24 at the site. Considering that conventional technology requires transporting the header pipes 1, 2, 3, 4, flow channels 41, 42, 51, 61, and pump 5 individually, and then assembling and connecting them at the data center 11 installation site, it is clear that this significantly improves work efficiency.

[0047] Figure 5 is a schematic diagram showing another example of the arrangement of header pipes 1, 2, 3, and 4 of the pump unit 101. In the example of Figure 5, the header pipes 1, 2, 3, and 4 are not only arranged so that their axes are horizontal and parallel to each other, as in the example of Figure 4, but are also arranged in two tiers vertically and horizontally. As a result, the overall height of the large-diameter header pipes 1, 2, 3, and 4 is kept low, thereby improving portability and maintainability.

[0048] Here, we will illustrate the main pipe diameters of the prototype pump unit 101. The unit of each diameter is millimeters. Header pipe 1 (first header pipe) (200A: outer diameter 225, inner diameter 184; or 300A: outer diameter 315, inner diameter 257.8) has multiple (four in the illustrated example) first ports (50A: outer diameter 63, inner diameter 51.4; or 100A: outer diameter 110, inner diameter 90) to which multiple (four in the illustrated example) pipes 21 (first pipes) that supply cooling water (secondary refrigerant) to the cooling unit 12 can be connected. The pipes 21 and the first ports are of the same diameter. Therefore, header pipe 1 is larger in diameter than each pipe 21. Header pipe 2 (second header pipe) (200A: outer diameter 225, inner diameter 184; or 300A: outer diameter 315, inner diameter 257.8) has multiple (four in the illustrated example) second ports (50A: outer diameter 63, inner diameter 51.4; or 100A: outer diameter 110, inner diameter 90) to which multiple (four in the illustrated example) pipes 22 (second pipes) that return the cooling water (secondary refrigerant) that has passed through the cooling unit 12 can be connected. The pipes 22 and the second ports are of the same diameter. Therefore, header pipe 2 is larger in diameter than each pipe 22. Header pipe 3 (third header pipe) (200A: outer diameter 225, inner diameter 184; or 300A: outer diameter 315, inner diameter 257.8) has multiple (four in the illustrated example) third ports (50A: outer diameter 63, inner diameter 51.4; or 100A: outer diameter 110, inner diameter 90) to which multiple (four in the illustrated example) pipes 23 (third pipes) that supply cooling water (secondary refrigerant) to the heat exchanger 13 can be connected. The pipes 23 and the third ports are of the same diameter. Therefore, header pipe 3 is larger in diameter than each pipe 23. Header pipe 4 (fourth header pipe) (200A: outer diameter 225, inner diameter 184; or 300A: outer diameter 315, inner diameter 257.8) has multiple (four in the illustrated example) fourth ports (50A: outer diameter 63, inner diameter 51.4; or 100A: outer diameter 110, inner diameter 90) to which multiple (four in the illustrated example) pipes 24 (fourth pipes) that return the cooling water (secondary refrigerant) that has passed through the heat exchanger 13 can be connected. The pipes 24 and the fourth ports have the same diameter. Therefore, header pipe 4 has a larger diameter than each pipe 24. [Explanation of Symbols]

[0049] 1,2,3,4 Header pipes (1st to 4th header pipes), 5 Pump, Control unit 6, 11 Data center, 12 Cooling unit, 13 Heat exchanger (CDU), 21,22,23,24 Piping (1st to 4th piping), 31,32,33,34 Piping, 41 Flow path (2nd flow path), 42 Flow path (1st flow path), 51 Bypass flow path, 52 Bypass valve, 53 Flow meter, 61 Bypass flow path, 62 Bypass valve, 63 Flow meter, 73 Flow meter, 81,82 Temperature sensors, 83 Ambient temperature sensor, 90 Control device, 101 Pump unit, 120 Frame (mounting base).

Claims

1. A pump unit used in connection with a heat exchanger that performs heat exchange with a primary refrigerant to cool hardware installed in a data center, and a cooling unit that cools a secondary refrigerant that performs heat exchange with the primary refrigerant through the heat exchanger, The cooling unit has a plurality of first ports to which a plurality of first pipes for supplying the secondary refrigerant can be connected, and a first header pipe having a larger diameter than the plurality of first pipes, Multiple second pipes that return the secondary refrigerant after passing through the cooling unit have multiple connectable second ports, and a second header pipe having a larger diameter than the multiple second pipes, The heat exchanger has a plurality of third ports to which a plurality of third pipes for supplying the secondary refrigerant can be connected, and a third header pipe having a larger diameter than the plurality of third pipes, It has a plurality of fourth ports to which a plurality of fourth pipes can be connected to return the secondary refrigerant that has passed through the heat exchanger, and a fourth header pipe that is larger in diameter than the plurality of fourth pipes, A first flow path for transporting the secondary refrigerant from the fourth header pipe to the first header pipe, The system includes a second flow path for transporting the secondary refrigerant from the second header pipe to the third header pipe, One of the first and second flow paths is a pump unit having a pump for supplying the secondary refrigerant.

2. The pump unit according to claim 1, further comprising the first to fourth header pipes, the first flow path, the second flow path, and a portable frame on which the pump is installed.

3. The pump unit according to claim 2, wherein the first to fourth header pipes are arranged horizontally and parallel to each other, and two of each are arranged in two upper and lower tiers, with the heights of each tier being the same as those of the other tier.

4. The system further includes a first bypass channel that bypasses the secondary refrigerant from the first header pipe to the second header pipe, The pump unit according to claim 1, wherein the first bypass passage has a first bypass valve for opening and closing the first bypass passage.

5. The system further includes a second bypass channel that bypasses the secondary refrigerant from the third header pipe to the fourth header pipe, The pump unit according to claim 1, wherein the second bypass passage has a second bypass valve for opening and closing the second bypass passage.

6. The pump control unit for controlling the aforementioned pump is further provided, Of the first and second flow paths, the one flow path having the pump further includes a flow meter for detecting the flow rate of the secondary refrigerant flowing through that one flow path. The pump control unit controls the pump so that the flow rate of the secondary refrigerant becomes a predetermined constant amount by referring to the flow rate detected by the flow meter, according to claim 1.

7. The aforementioned pump has three or more unit pumps connected in parallel. The pump control unit according to claim 6, wherein the pump control unit performs rotation control to drive multiple unit pumps in sequence so that at least one unit pump is stopped in sequence.

8. It is further equipped with a temperature sensor to detect the temperature, The pump control unit according to claim 7, wherein when the temperature detected by the temperature sensor falls below a predetermined temperature, the pump control unit activates all three or more unit pumps.

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