Transcritical direct cooling CO2 heat pipe chip backboard cooling system and method

Abstract

The invention provides a transcritical direct cooling CO2 heat pipe chip backboard cooling system and method. The system comprises a three-stage cooling CO2 air cooler, a liquid cooling distribution unit, a heat pipe module, a compressor and a control module. The three-stage cooling CO2 air cooler is configured to provide cooling capacity to the liquid cooling distribution unit; the liquid cooling distribution unit is configured to transmit the CO2 working medium to the heat pipe module; the heat pipe module is configured to exchange heat with a CO2 working medium; the control module is configured to obtain temperature data; according to the temperature data, a first fan unit, a second fan unit, a first water pump, a second water pump, an electric throttle valve, a switching value electric stop valve and a compressor are controlled to operate in a preset mode, so that the superheat degree of the CO2 working medium at the air return end of the heat pipe module is within a preset range; the problems that an existing data center cooling scheme is insufficient in heat dissipation capacity, poor in environment compatibility, complex in system and low in energy efficiency are solved.

Description

Technical Field

[0001] The present application relates to the technical field of refrigeration equipment, and in particular to a transcritical direct-cooling CO2 heat pipe chip backplane cooling system and method. Background Art

[0002] With the rapid development of digital technology, the scale of data centers continues to expand, and the heat generated by chips has increased sharply. Currently, liquid cooling technology (such as cold plate / immersion) is generally used for heat dissipation.

[0003] While deionized water, widely used in cold plate liquid cooling, offers high thermal conductivity, it can dissolve trace impurities and regain conductivity over time, posing a risk of short circuits. It can also corrode metal pipes or electronic components, requiring water quality monitoring and the addition of corrosion inhibitors to maintain stability, increasing operational complexity. While fluorinated fluids (such as Novec) used in immersion liquid cooling offer excellent insulation and chemical inertness, their high cost limits large-scale deployment. The global warming potential (GWP) of some fluorinated fluids faces regulatory pressure. For example, Novec 7100 (perfluorinated ether) has a GWP of approximately 320, while Novec 649 (hydrofluoroether) has a GWP of approximately 210. Furthermore, their low boiling point can easily lead to volatile losses, requiring a highly sealed system design to prevent leaks. Furthermore, long-term exposure can corrode rubber or plastic sealing materials, accelerating equipment aging. Both systems share common challenges, including high waste liquid disposal costs and large initial investment in customized systems.

[0004] In summary, current data center cooling solutions have problems such as insufficient heat dissipation capacity, poor environmental compatibility, complex systems and low energy efficiency. Summary of the Invention

[0005] The present application provides a transcritical direct-cooling CO2 heat pipe chip backplane cooling system and method to solve the technical problems of existing data center cooling solutions such as insufficient heat dissipation capacity, poor environmental compatibility, complex system and low energy efficiency.

[0006] In a first aspect, the present application provides a transcritical direct-cooling CO2 heat pipe chip backplane cooling system, comprising:

[0007] Three-stage cooling CO2 air cooler, liquid cooling distribution unit, at least one heat pipe module, compressor, control module; the heat pipe module includes: CO2 power heat pipe module, CO2 gravity heat pipe module;

[0008] The three-stage cooling CO2 air cooler includes: a first air unit, a second air unit, a first water pump, and a second water pump; the three-stage cooling CO2 air cooler is configured to provide cooling to the liquid cooling distribution unit;

[0009] The liquid cooling distribution unit is connected to the three-stage cooling CO2 air cooler and the heat pipe module through an electric throttle valve and a switch electric stop valve; the liquid cooling distribution unit is configured to transmit the CO2 working medium to the heat pipe module;

[0010] The heat pipe module is configured to perform heat exchange with the CO2 working medium;

[0011] The control module is configured to:

[0012] Acquire temperature data; the temperature data includes: ambient dry-bulb temperature, ambient wet-bulb temperature and air cooler outlet temperature;

[0013] Based on the temperature data, the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, the on-off electric stop valve, and the compressor are controlled to operate in a preset mode so that the superheat of the CO2 working medium at the return air end of the heat pipe module is within a preset range; the preset modes include: transcritical operation mode, subcritical operation mode, natural cooling wet mode, and natural cooling dry mode.

[0014] In some embodiments, the control module is further configured to:

[0015] When the air cooler outlet temperature is greater than or equal to 31°C and the ambient wet-bulb temperature is greater than or equal to 16°C, controlling the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, the on-off electric stop valve, and the compressor to operate in the transcritical operation mode;

[0016] Wherein, when in the transcritical operation mode, the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, and the compressor are turned on, and the switch electric stop valve is closed.

[0017] In some embodiments, the control module is further configured to:

[0018] When the air cooler outlet temperature is less than 31°C and greater than 26°C, and the ambient wet-bulb temperature is greater than or equal to 16°C, controlling the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, the on-off electric stop valve, and the compressor to operate in the subcritical operation mode;

[0019] Wherein, when in the subcritical operation mode, the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, and the compressor are turned on, and the switch electric stop valve is closed.

[0020] In some embodiments, the control module is further configured to:

[0021] When the ambient wet-bulb temperature is less than 16°C and the ambient dry-bulb temperature is greater than 8°C, controlling the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, the on-off electric stop valve, and the compressor to operate in the natural cooling wet mode;

[0022] Among them, when in the natural cooling wet mode, the first fan group, the second fan group, the first water pump, the second water pump, and the switch electric stop valve are turned on, and the electric throttle valve and the compressor are turned off.

[0023] In some embodiments, the control module is further configured to:

[0024] When the ambient dry-bulb temperature is less than or equal to 8°C, the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, the on-off electric stop valve, and the compressor are controlled to operate in the natural cooling dry mode;

[0025] Among them, when in the natural cooling dry mode, the first fan unit, the second fan unit, and the switch electric stop valve are turned on, and the first water pump, the second water pump, the electric throttle valve, and the compressor are turned off.

[0026] In some embodiments, the control module is further configured to:

[0027] In the transcritical operation mode, a first target exhaust pressure value of the three-stage cooling CO2 air cooler is determined according to the air cooler outlet temperature; the first target exhaust pressure value is:

[0028] Pg=(2.778-0.0157×t o )×t gc +(0.381×t o -9.34)-1;

[0029] Where, t o Set the evaporation temperature value for the optimal exhaust pressure calculation, t gc is the air cooler outlet temperature;

[0030] The electric throttle valve is PID-adjusted according to the air cooler outlet temperature and the first target exhaust pressure value.

[0031] In some embodiments, the control module is further configured to:

[0032] Determine subcritical operation subcooling;

[0033] In the subcritical operation mode, the second target exhaust pressure value of the three-stage cooling CO2 air cooler is determined according to the air cooler outlet temperature and the subcritical operation subcooling degree; the second target exhaust pressure value is:

[0034] Pg = 4 × 10 -5 ×(t a +t l )3+0.0092×(t a +t l )2+0.9259×(t a +t l )+33.821;

[0035] Where, t a is the subcritical temperature, t l Subcooling for subcritical operation;

[0036] The electric throttle valve is PID-adjusted according to the air cooler outlet temperature and the second target exhaust pressure value.

[0037] In some embodiments, the liquid cooling distribution unit is connected to the heat pipe module via a CO2 working fluid pump; the number of the CO2 working fluid pumps is: N+1; N is the number of heat pipe modules.

[0038] In some embodiments, the CO2 power heat pipe module is configured with several chip cold plates, which are power heat pipes; the CO2 gravity heat pipe module is configured with a backplate heat exchanger, which is a CO2 gravity heat pipe, and the flow channel in the CO2 gravity heat pipe is set to enter from the bottom and exit from the top.

[0039] A second aspect of the present application provides a transcritical direct-cooling CO2 heat pipe chip backplane cooling method, which is applied to a transcritical direct-cooling CO2 heat pipe chip backplane cooling system according to any one of the first aspects above, comprising:

[0040] Acquire temperature data; the temperature data includes: ambient dry-bulb temperature, ambient wet-bulb temperature and air cooler outlet temperature;

[0041] Based on the temperature data, the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, the on-off electric stop valve, and the compressor are controlled to operate in a preset mode so that the superheat of the CO2 working medium at the return air end of the heat pipe module is within a preset range; the preset modes include: transcritical operation mode, subcritical operation mode, natural cooling wet mode, and natural cooling dry mode.

[0042] The present application provides a transcritical direct-cooling CO2 heat pipe chip backplane cooling system and method, the system comprising: a three-stage cooling CO2 air cooler, a liquid cooling distribution unit, at least one heat pipe module, a compressor, and a control module; the heat pipe module comprises: a CO2 power heat pipe module and a CO2 gravity heat pipe module; the three-stage cooling CO2 air cooler comprises: a first air unit, a second air unit, a first water pump, and a second water pump; the three-stage cooling CO2 air cooler is configured to provide cooling to the liquid cooling distribution unit; the liquid cooling distribution unit is connected to the three-stage cooling CO2 air cooler and the heat pipe module through an electric throttle valve and a switch electric stop valve; the liquid cooling distribution unit is configured to transfer the CO2 working medium to the heat pipe module; the heat pipe module is Configured to perform heat exchange with the CO2 working medium; the control module is configured to: obtain temperature data; the temperature data includes: ambient dry-bulb temperature, ambient wet-bulb temperature and air cooler outlet temperature; according to the temperature data, control the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, the on-off electric stop valve, and the compressor to operate in a preset mode, so that the superheat of the CO2 working medium at the return air end of the heat pipe module is within a preset range; the preset modes include: transcritical operation mode, subcritical operation mode, natural cooling wet mode and natural cooling dry mode, so as to improve the heat exchange efficiency, reduce the heat exchange temperature difference, reduce the system complexity and reduce the energy efficiency of the system through the transcritical direct cooling CO2 heat pipe chip backplane cooling system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0044] Figure 1 This is a schematic diagram of the structure of the transcritical direct cooling CO2 heat pipe chip backplane cooling system in this application;

[0045] Figure 2 Schematic diagram of the structure of the heat pipe module in this application.

[0046] Description of reference numerals:

[0047] 1-Three-stage cooling CO2 air cooler; 11-First air unit; 12-Second air unit; 13-First water pump; 14-Second water pump; 2-Liquid cooling distribution unit; 21-Electric throttle valve; 22-On / off electric shut-off valve; 23-CO2 working fluid pump; 3-CO2 power heat pipe module; 31-Chip cold plate; 4-CO2 gravity heat pipe module; 41-Back plate heat exchanger; 5-Compressor; 51-Pressure reducing valve; 6-Control module; 7-Shut-off valve; 8-Low-pressure circulation barrel; 9-Pressure reducing valve; 10-Pressure sensor; 20-Plate heat exchanger; 30-Electromagnetic pump; 40- Temperature sensor; 50-electric regulating valve; 101-air inlet; 102-fin heat exchanger; 103-first heat exchanger; 104-PVC filler; 105-second heat exchanger; 106-liquid outlet; 107-first air inlet; 108-water collector; 109-second air inlet; 110-third air inlet; 111-water spray tray; 112-spiral water distributor; 113-wound fin dew-point heat exchanger; 114-water side connecting port; 115-water side overflow port; 116-first nozzle; 117-first water tray; 118-second water tray; 119-second nozzle. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0049] For example, with the rapid development of digital technology, the scale of data centers continues to expand, and the heat generated by chips has increased dramatically. Current heat dissipation methods are gradually unable to meet the dual requirements of high efficiency and environmental protection. Current heat dissipation methods include air cooling and liquid cooling technology (such as cold plate / immersion).

[0050] Specifically, air cooling relies on air convection and fin heat conduction, which has high thermal resistance and low efficiency, and is difficult to handle over 100W / cm 2 In high heat flux density scenarios, fan power consumption accounts for 20% to 30% of the total energy consumption of the data center.

[0051] Specifically, consider liquid cooling technologies (such as cold plate / immersion cooling): While the deionized water widely used in cold plate liquid cooling offers high thermal conductivity, it can dissolve trace impurities and regain conductivity over time, posing a risk of short circuits. This can also corrode metal pipes or electronic components, requiring water quality monitoring and the addition of corrosion inhibitors to maintain stability, increasing operational complexity. While fluorinated fluids (such as Novec) used in immersion liquid cooling offer excellent insulation and chemical inertness, their high cost limits large-scale deployment. The global warming potential (GWP) of some fluorinated fluids faces regulatory pressure, such as Novec 7100 (perfluorinated ether) with a GWP of approximately 320 and Novec 649 (hydrofluoroether) with a GWP of approximately 210. Furthermore, their low boiling point can easily lead to volatile losses, requiring a highly sealed system design to prevent leaks. Furthermore, long-term exposure can corrode rubber or plastic sealing materials, accelerating equipment aging. Both technologies share common challenges, including high wastewater disposal costs and significant initial investment in customized systems.

[0052] For example, CO2 has a low boiling point, is non-toxic, non-flammable, and non-explosive, and can be used with various lubricants. Its low viscosity and density can reduce flow resistance and system pipe diameters, further miniaturizing the system and saving machine room space. Furthermore, CO2 has excellent heat exchange properties, reducing the heat exchange area of ​​evaporators and gas coolers, making the system more compact. Finally, CO2 is a component of nature with an ODP of 0 and a GWP of 1.

[0053] For example, while heat pipes can transfer heat quickly, their condensing end relies on an external cooling system, limiting their heat dissipation capacity when used independently. Inadequate coordination with the main refrigeration system reduces heat transfer efficiency. Furthermore, current system regulation methods are rigid and unable to dynamically respond to load changes. Safety monitoring and emergency response mechanisms under high-pressure conditions are also incomplete, limiting the reliability of the technology.

[0054] In summary, current data center cooling solutions generally suffer from insufficient heat dissipation capacity, poor environmental compatibility, system complexity, and low energy efficiency. While both CO2 cooling and heat pipe technologies have their own potential, there is a lack of system designs that deeply integrate the two. This is particularly true for chip-level direct cooling, where the coordinated optimization of high-voltage safety, dynamic control, and high heat flux management has yet to be achieved.

[0055] Because some data center cooling solutions have problems such as insufficient heat dissipation capacity, poor environmental compatibility, complex systems, and low energy efficiency in some technologies, in order to solve these technical problems, this application provides a transcritical direct-cooling CO2 heat pipe chip backplane cooling system and method. The transcritical direct-cooling CO2 heat pipe chip backplane cooling system and method are described below:

[0056] like Figure 1, which is a schematic structural diagram of the transcritical direct cooling CO2 heat pipe chip backplane cooling system in this application.

[0057] In a first aspect, the present application provides a transcritical direct-cooling CO2 heat pipe chip backplane cooling system, comprising:

[0058] A three-stage cooling CO2 air cooler 1, a liquid-cooling distribution unit 2, at least one heat pipe module, a compressor 5, and a control module 6; the heat pipe module includes: a CO2 power heat pipe module 3, a CO2 gravity heat pipe module 4; the three-stage cooling CO2 air cooler 1, the liquid-cooling distribution unit 2, at least one heat pipe module, the compressor 5, and the control module 6 are connected through a refrigeration pipe and a valve arranged on the refrigeration pipe.

[0059] Specifically, the CO2 power heat pipe module 3 is configured with several chip cold plates 31, which are power heat pipes; the CO2 gravity heat pipe module 4 is configured with a backplate heat exchanger 41, which is a CO2 gravity heat pipe, and the flow channel in the CO2 gravity heat pipe is set to enter from the bottom and exit from the top.

[0060] Among them, when using the CO2 chip cold plate 31, the resistance of multiple chip cold plates 31 is unbalanced and too large. If a gravity heat pipe is used, the gravity heat siphon cycle cannot be formed. Therefore, a power heat pipe is used to control the on and off frequency of the electromagnetic pump according to the return air superheat of the chip cold plate 31 to achieve a return air superheat of 1k.

[0061] The backplate heat exchanger 41 uses a CO2 gravity heat pipe. Its flow path is a bottom-in, top-out microchannel heat exchanger. This allows for smoother CO2 flow within the microchannels, making it more suitable for gravity heat pipe thermosiphon heat exchange. The electric control valve opening is adjusted based on the return air superheat of the microchannel heat exchanger to achieve a return air superheat of 1K.

[0062] The three-stage cooling CO2 air cooler 1 includes: a first air unit 11, a second air unit 12, a first water pump 13, and a second water pump 14; the three-stage cooling CO2 air cooler 1 is configured to provide cooling to the liquid cooling distribution unit 2.

[0063] Among them, the three-stage cooling CO2 air cooler 1 includes: 101 air inlet, D10×1 stainless steel tube stainless steel fin heat exchanger 102 (1st section air cooler / sensible heat section), D10×1 small diameter stainless steel tube first heat exchanger 103 (2nd section air cooler / latent heat section), PVC filler 104, D10×1 small diameter stainless steel tube second heat exchanger 105 (3rd section air cooler / subcooling section), liquid outlet 106, EC first fan unit 11, first air inlet 107, water collector 108, second air inlet 109, third air inlet 110, water spray tray 111, spiral water distributor 112, spiral plate dew point heat exchanger 113, water side connecting port 114, water side overflow port 115, EC second fan unit 12, first water pump 13, first nozzle 116, second water pump 14, first water tray 117, second water tray 118, second nozzle 119.

[0064] The liquid cooling distribution unit 2 is connected to the three-stage cooling CO2 air cooler 1 and the heat pipe module through the electric throttle valve 21 and the switch electric stop valve 22; the liquid cooling distribution unit 2 is configured to transmit the CO2 working medium to the heat pipe module.

[0065] The liquid cooling distribution unit CDU includes: an electric throttle valve 21, a switching electric stop valve 22, a low-pressure circulation barrel 8, a pressure reducing valve 9, a CO2 working fluid pump 23, and a pressure sensor 10.

[0066] Specifically, the gaseous high-temperature CO2 working medium starts from the low-pressure circulation barrel 8, passes through the pipeline where the compressor 5 and the pressure reducing valve 9 are located, and is connected to the three-stage cooling CO2 air cooler 1. After being cooled by the three-stage cooling CO2 air cooler 1 to become liquid low-temperature CO2 working medium, it is throttled and reduced in pressure by the electric throttle valve 21 and then returns to the low-pressure circulation barrel 8. The liquid low-temperature CO2 working medium then flows to the CO2 power heat pipe module 3 and the CO2 gravity heat pipe module 4 through the action of the CO2 working medium pump 23.

[0067] The heat pipe module is configured to perform heat exchange with the CO2 working medium; the heat pipe module includes: a CO2 power heat pipe module 3 and a CO2 gravity heat pipe module 4.

[0068] The CO2 powered heat pipe module 3 includes an electric throttle valve 21 , a pressure sensor 10 , a plate heat exchanger 20 , an electromagnetic pump 30 , a chip cold plate 31 , and a temperature sensor 40 .

[0069] Specifically, the liquid low-temperature CO2 working medium enters the CO2 power heat pipe module 3 through the delivery pipeline under the drive of the CO2 working medium pump 23. The CO2 working medium first flows through the electric throttle valve 21 for pressure regulation, and then exchanges heat with the CO2 working medium in the power heat pipe circulation system through the plate heat exchanger 20. When the system is equipped with a CO2 chip cold plate 31, in view of the technical bottleneck that the flow resistance characteristics of multiple parallel chip cold plates 31 are significantly different and the overall flow resistance coefficient is relatively large, the gravity heat pipe is not applicable because it cannot establish an effective thermal siphon effect, so an active circulation power heat pipe solution is adopted. The system constructs a closed-loop control system by integrating the pressure sensor 10 and the temperature sensor 40, and implements PID regulation on the electromagnetic pump 30 based on the working condition parameters collected in real time, accurately maintaining the working medium superheat at the return air end of the chip cold plate 31 stable within the 1K threshold range.

[0070] The CO2 gravity heat pipe module 4 includes: an electric throttle valve 21 , a pressure sensor 10 , a plate heat exchanger 20 , a temperature sensor 40 , an electric regulating valve 50 , and a back plate heat exchanger 41 .

[0071] Specifically, the liquid low-temperature CO2 working medium, driven by the CO2 working medium pump 23, enters the CO2 gravity heat pipe module 4 through a delivery pipeline. The working medium first undergoes pressure step regulation through the electric throttle valve 21, then undergoes heat exchange with the CO2 working medium in the gravity heat pipe circulation loop within the plate heat exchanger 20. Specifically, the backplate heat exchanger 41 utilizes a gravity heat pipe architecture. The CO2 working medium flows through an electric control valve 50 equipped with a dynamic adjustment function before entering a microchannel evaporator with a bottom-inlet, top-outlet flow design. This microchannel structure effectively adapts to the thermosiphon phase change heat transfer mechanism of the gravity heat pipe by improving capillary transport efficiency. The system integrates a pressure sensor 10 and a temperature sensor 40 to form a closed-loop feedback mechanism. Based on real-time data collected on the saturated vapor pressure difference and temperature gradient, a PID control algorithm is used to dynamically adjust the flow cross-section of the electric control valve 50, precisely controlling the working medium superheat at the return air end of the microchannel heat exchanger to the design value of 1K while maintaining the spontaneous circulation characteristics of the thermosiphon effect.

[0072] The control module 6 is configured to:

[0073] Acquire temperature data; the temperature data includes: ambient dry-bulb temperature, ambient wet-bulb temperature and air cooler outlet temperature;

[0074] According to the temperature data, the first fan unit 11, the second fan unit 12, the first water pump 13, the second water pump 14, the electric throttle valve 21, the switch electric stop valve 22, and the compressor 5 are controlled to operate in a preset mode so that the superheat of the CO2 working medium at the return air end of the heat pipe module is within a preset range; the preset modes include: transcritical operation mode, subcritical operation mode, natural cooling wet mode and natural cooling dry mode.

[0075] In this embodiment, the control module 6 is further configured to:

[0076] When the air cooler outlet temperature is greater than or equal to 31°C and the ambient wet-bulb temperature is greater than or equal to 16°C, the first fan unit 11, the second fan unit 12, the first water pump 13, the second water pump 14, the electric throttle valve 21, the on-off electric stop valve 22, and the compressor 5 are controlled to operate in the transcritical operation mode;

[0077] In the transcritical operation mode, the first fan unit 11, the second fan unit 12, the first water pump 13, the second water pump 14, the electric throttle valve 21, and the compressor 5 are turned on, and the switch electric stop valve 22 is closed.

[0078] Specifically, during CO2 transcritical operation, air enters from the first air inlet 107 and undergoes heat and moisture exchange with the water in the first water pan 117 that is sent to the first nozzle 116 by the first water pump 13, thereby cooling the CO2 refrigerant inside the D10×1 small-diameter stainless steel pipe first heat exchanger 103 (2-stage air cooler / latent heat section). After the heat and moisture exchange, the air passes through the water collector 108 and then cools the CO2 refrigerant inside the heat exchanger at the D10×1 stainless steel pipe stainless steel fin heat exchanger 102 (1-stage air cooler / sensible heat section), and is finally discharged through the EC first air unit 11. The sprayed water that has undergone heat and moisture exchange at the D10×1 small-diameter stainless steel pipe first heat exchanger 103 (2-stage air cooler / latent heat section) continues to fall and undergoes heat and moisture exchange again with the air entering through the second air inlet 109 on the PVC filler 104, thereby lowering the water temperature. After the heat and moisture exchange, the air is discharged from the second air unit 12 after passing through the water collector 108; part of the water in the water spray tray 111 is passed into the spiral water distributor 112, and part of it flows through the PVC filler 104 again. The spiral water distributor 112 sprays part of the water into the spiral dew-point heat exchanger 113 for heat exchange with the incoming air, and the other part of the water is sprayed into the PVC filler 104 for heat and moisture exchange with the air flowing out of the spiral dew-point heat exchanger 113. After the heat and moisture exchange, the air undergoes heat and moisture exchange with the water sprayed from the second nozzle 119 by the second water pump 14 outside the second heat exchanger 105 (3-stage air cooler / subcooling stage) of the D10×1 small-diameter stainless steel pipe, thereby cooling the CO2 refrigerant inside the heat exchanger; a water-side connecting port 114 is provided in the second water tray 118, and a water-side overflow port 115 is provided between the first water tray 117 and the second water tray 118.

[0079] Specifically, when CO2 is transcritical, the CO2 exhaust pressure is above the CO2 critical pressure, the exhaust pressure is high, the exhaust temperature is high, and it is in transcritical sensible heat exchange. A three-stage cooling CO2 air cooler 1 is adopted. The D10×1 stainless steel tube stainless steel fin heat exchanger 102 (1st section air cooler / sensible heat section) mainly reduces the exhaust temperature to the CO2 temperature of the ambient dry bulb temperature + 10°C. The D10×1 small diameter stainless steel tube first heat exchanger 103 (2nd section air cooler / latent heat section) reduces the outlet temperature of the D10×1 stainless steel tube stainless steel fin heat exchanger 102 (1st section air cooler / sensible heat section) to the wet bulb temperature +3°C. The D10×1 small diameter stainless steel tube second heat exchanger 105 (3rd section air cooler / supercooling section) reduces the outlet temperature of the D10×1 small diameter stainless steel tube first heat exchanger 103 (2nd section air cooler / latent heat section) to the wet bulb temperature -3°C. The first D10×1 small-diameter stainless steel pipe heat exchanger 103 (two-stage air cooler / latent heat section) uses wet-bulb evaporative cooling to reduce the outlet temperature to +3°C wet-bulb temperature. The second D10×1 small-diameter stainless steel pipe heat exchanger 105 (three-stage air cooler / subcooling section) uses dew-point evaporative cooling to reduce the outlet temperature to -3°C wet-bulb temperature. The air-cooled + wet curtain adiabatic air cooler can reduce the outlet temperature to +5°C wet-bulb temperature, while the three-stage CO2 air cooler 1 can reduce the air cooler outlet temperature to -3°C wet-bulb temperature, which is 8°C lower than the outlet temperature of the wet curtain adiabatic air cooler, greatly improving cooling efficiency.

[0080] Specifically, when the outlet temperature of the three-stage CO2 air cooler 1 is t gc ≥31℃, ambient wet bulb temperature t s When the temperature is ≥16℃, the cooling system operates in transcritical mode, and the target exhaust pressure is controlled according to the outlet temperature of the second CO2 air cooler 1 of the third-stage cooling system. The target exhaust pressure value is Pg (gauge pressure bar), and the evaporation temperature is t0. Pg=(2.778-0.0157×t0)×t gc +(0.381×t0-9.34)-1, PID adjustment is performed on the electric throttle valve opening according to the three-stage cooling CO2 air cooler 1 and the target exhaust pressure value.

[0081] In this embodiment, the control module 6 is further configured to:

[0082] When the air cooler outlet temperature is less than 31°C and greater than 26°C, and the ambient wet-bulb temperature is greater than or equal to 16°C, the first fan group 11, the second fan group 12, the first water pump 13, the second water pump 14, the electric throttle valve 21, the switch electric stop valve 22, and the compressor 5 are controlled to operate in the subcritical operation mode; wherein, when in the subcritical operation mode, the first fan group 11, the second fan group 12, the first water pump 13, the second water pump 14, the electric throttle valve 21, and the compressor 5 are turned on, and the switch electric stop valve 22 is closed.

[0083] Specifically, when CO2 is operating subcritically, the D10×1 stainless steel tube stainless steel fin heat exchanger 102 (1st section air cooler / sensible heat section) discharges heat in the sensible heat section, the D10×1 small diameter stainless steel tube first heat exchanger 103 (2nd section air cooler / latent heat section) discharges heat in the condensing section, and the D10×1 small diameter stainless steel tube second heat exchanger (3rd section air cooler / subcooling section) 105 discharges heat in the subcooling section.

[0084] Specifically, when the outlet temperature of the three-stage cooling CO2 air cooler 1 is 26℃<t gc <31℃, ambient wet bulb temperature t s When the temperature is ≥16℃, the cooling system operates in subcritical mode, and the exhaust pressure is controlled according to the subcooling degree. The subcritical operation subcooling degree t l , when tgc≤26℃, the target exhaust pressure value is pg (gauge pressure bar), Pg=4×10(-5)×(t a +t l )3+0.0092×(t a +t l )2+0.9259×(t a +t l )+33.821, perform PID adjustment on the electric throttle valve opening according to the three-stage cooling CO2 air cooler 1 and the target exhaust pressure value.

[0085] In this embodiment, the control module 6 is further configured to:

[0086] When the ambient wet-bulb temperature is less than 16°C and the ambient dry-bulb temperature is greater than 8°C, the first fan group 11, the second fan group 12, the first water pump 13, the second water pump 14, the electric throttle valve 21, the switch electric stop valve 22, and the compressor 5 are controlled to operate in the natural cooling wet mode; wherein, when in the natural cooling wet mode, the first fan group 11, the second fan group 12, the first water pump 13, the second water pump 14, and the switch electric stop valve 22 are turned on, and the electric throttle valve 21 and the compressor 5 are turned off.

[0087] Specifically, the natural cooling wet mode mainly relies on turning on the EC first fan unit 11, the EC second fan unit 12, and the first water pump 13. The fresh air outside the unit enters from the first air inlet 107 and the second air inlet 109, and flows through the D10×1 small-diameter stainless steel tube first heat exchanger 103 (2-stage air cooler / latent heat section), the water collector 108, the D10×1 stainless steel tube stainless steel fin heat exchanger 102 (1-stage air cooler / sensible heat section), and the PVC filler 104, and is finally discharged by the EC first fan unit 11.

[0088] Specifically, when the ambient wet-bulb temperature ts is less than 16° C. and the dry-bulb temperature tg is greater than 8° C., the cooling system operates in the natural cooling wet mode, closes the electric throttle valve group, closes the carbon dioxide compressor group, and opens the switch electric stop valve 22 .

[0089] In this embodiment, the control module 6 is further configured to:

[0090] When the ambient dry-bulb temperature is less than or equal to 8°C, the first fan group 11, the second fan group 12, the first water pump 13, the second water pump 14, the electric throttle valve 21, the switch electric stop valve 22, and the compressor 5 are controlled to operate in the natural cooling dry mode; wherein, when in the natural cooling dry mode, the first fan group 11, the second fan group 12, and the switch electric stop valve 22 are turned on, and the first water pump 13, the second water pump 14, the electric throttle valve 21, and the compressor 5 are turned off.

[0091] Specifically, the natural cooling dry mode mainly relies on turning on the EC first fan unit 11 and the EC second fan unit 12, and turning off the first water pump 13 and the second water pump 14. The fresh air outside the unit enters from the first air inlet 107, flows through the D10×1 small-diameter stainless steel tube first heat exchanger 103 (2-stage air cooler / latent heat section), the water collector 108, the D10×1 stainless steel tube stainless steel fin heat exchanger 102 (1-stage air cooler / sensible heat section), and is finally discharged by the EC first fan unit 11.

[0092] Specifically, when the dry-bulb temperature tg≤8°C, the cooling system operates in natural cooling dry mode, closes the electric throttle valve group, turns off the carbon dioxide compressor group, opens the switch electric stop valve 22, turns off the first water pump 13 and the second water pump 14, and the three-stage cooling CO2 air cooler 1 only operates the first fan group 11 and the second fan group 12.

[0093] In this embodiment, the control module 6 is further configured to:

[0094] In the transcritical operation mode, the first target exhaust pressure value of the three-stage cooling CO2 air cooler 1 is determined according to the air cooler outlet temperature; the first target exhaust pressure value is:

[0095] Pg=(2.778-0.0157×t o )×t gc +(0.381×t o -9.34)-1;

[0096] Where, t o Set the evaporation temperature value for the optimal exhaust pressure calculation, t gc is the air cooler outlet temperature;

[0097] The electric throttle valve 21 is PID-adjusted according to the air cooler outlet temperature and the first target exhaust pressure value.

[0098] In this embodiment, the control module 6 is further configured to:

[0099] Determine subcritical operation subcooling;

[0100] In the subcritical operation mode, the second target exhaust pressure value of the three-stage cooling CO2 air cooler 1 is determined according to the air cooler outlet temperature and the subcritical operation subcooling degree; the second target exhaust pressure value is:

[0101] Pg = 4 × 10 -5 ×(t a +t l )3+0.0092×(t a +t l )2+0.9259×(t a +t l )+33.821;

[0102] Where, t a is the subcritical temperature, t l Subcooling for subcritical operation;

[0103] The electric throttle valve 21 is PID-adjusted according to the air cooler outlet temperature and the second target exhaust pressure value.

[0104] In this embodiment, the liquid cooling distribution unit 2 is connected to the heat pipe module via CO2 working fluid pumps 23. The number of CO2 working fluid pumps 23 is N+1, where N is the number of heat pipe modules. The CO2 working fluid pumps 23 operate in an N+1 standby mode. If any CO2 working fluid pump 23 fails, the standby pump automatically activates, ensuring safety and reliability. The CO2 working fluid pumps 23 operate at a constant pressure differential based on the difference between the pump outlet pressure and the pressure in the low-pressure circulation tank 8, maximizing energy savings.

[0105] This application provides a transcritical direct cooling CO2 heat pipe chip backplane cooling system, which, when in transcritical operation mode:

[0106] A portion of the CO2 gas above the low-pressure circulation barrel 8 enters the gas supply pipeline under the action of pressure, and becomes high-temperature and high-pressure gas after work by the carbon dioxide compressor unit. The CO2 gas passes through the valve and enters the fin heat exchanger 102 of the three-stage cooling CO2 air cooler 1. In the fin heat exchanger 102, the CO2 gas temperature drops to about 10°C higher than the ambient dry-bulb temperature. The CO2 gas then enters the first heat exchanger 103 of the three-stage cooling CO2 air cooler 1. In the first heat exchanger 103, the CO2 gas temperature drops to about 3°C ​​higher than the ambient wet-bulb temperature. The CO2 gas finally enters the second heat exchanger 105 of the three-stage cooling CO2 air cooler. In the first heat exchanger 103, the CO2 gas temperature drops to about 3°C ​​lower than the ambient wet-bulb temperature. The CO2 gas is discharged from the three-stage cooling CO2 air cooler 1 through the return pipe. In the return pipe, the CO2 gas passes through the valve, pressure sensor 10, temperature sensor 40 and electric throttle valve group. Under the throttling and pressure reduction action of the electric throttle valve group, the CO2 gas becomes low-temperature and low-pressure gas. The CO2 gas finally returns to the low-pressure circulation barrel 31 to release the cooling capacity, and the cycle continues.

[0107] A portion of the CO2 liquid below the low-pressure circulation barrel 8 enters the liquid supply pipe group under the action of pressure. In one of the liquid supply pipes in the liquid supply pipe group, the low-temperature CO2 liquid is pressurized by the CO2 working fluid pump 23, and then passes through the pressure sensor 10 and the pressure reducing valve 51. A portion of the CO2 liquid enters the cold plate liquid supply main pipe. The CO2 liquid is diverted to the CO2 power heat pipe module 3 by multiple cold plate liquid supply branches in the cold plate liquid supply main pipe. In the CO2 power heat pipe module 3, the CO2 liquid enters the chip cold plate 31 after being depressurized by the electric throttle valve 21. In the chip cold plate 31, the CO2 liquid quickly absorbs the heat generated by the chip when flowing through the microchannel in the chip cold plate 31 and vaporizes into CO2 gas, and then passes through the cold plate 31. The CO2 powered heat pipe module 3 is discharged after the pressure sensor 10 and temperature sensor 40 are installed on the plate return liquid branch pipe and the cold plate return liquid branch pipe, and the CO2 gas in the CO2 powered heat pipe module 3 is discharged and collected in the cold plate return liquid main pipe; at the same time, another part of the CO2 liquid enters the back plate liquid supply pipe, and enters the back plate heat exchanger 41 after being reduced in pressure by the electric throttle valve 21. In the microchannel of the back plate heat exchanger 41, the CO2 liquid absorbs heat and vaporizes into CO2 gas, and then passes through the back plate return liquid pipe and the pressure sensor 10 and temperature sensor 40 installed on the back plate return liquid pipe, and is collected with the CO2 gas from the cold plate return liquid main pipe into the return liquid pipeline, and returns to the low-pressure circulation barrel 8 through the return liquid pipeline, and the cycle is repeated.

[0108] In subcritical operating mode:

[0109] The outlet temperature and target exhaust pressure of the three-stage CO2 air cooler 1 are used to PID-regulate the opening of the electric throttle valve group. A portion of the CO2 gas above the low-pressure circulation barrel 8 enters the gas supply pipeline under pressure. After work is performed by the carbon dioxide compressor group, it becomes high-temperature and high-pressure gas. It then passes through the valve and enters the finned tube heat exchanger 9 of the three-stage CO2 air cooler for pre-cooling. It then enters the second heat exchanger 105 of the three-stage CO2 air cooler 1 to condense into CO2 liquid. Finally, it enters the first heat exchanger 103 of the three-stage CO2 air cooler 1 for supercooling. It is discharged from the three-stage CO2 air cooler 1 through the return pipe. In the return pipe, it passes through the valve, pressure sensor 10, temperature sensor 40, and the electric throttle valve group. Under the throttling and pressure reduction action of the electric throttle valve group, the CO2 liquid becomes a low-temperature and low-pressure liquid. Finally, it returns to the low-pressure circulation barrel 8 to release the cooling capacity, and the cycle continues. The operating principles of the remaining devices are the same as those in the transcritical operation mode.

[0110] In Free Cooling Wet Mode:

[0111] Close the electric throttle valve assembly, shut down the CO2 compressor assembly, and open the on-off electric shut-off valve 22. A portion of the CO2 gas above the low-pressure circulation barrel 8 enters the gas supply pipeline under pressure, passes through pressure reducing valve 9 and the valve, enters the tertiary cooling CO2 air cooler 1, and is cooled. The return gas pipe then passes through the valve, pressure sensor 10, temperature sensor 40, and on-off electric shut-off valve 22 before returning to the low-pressure circulation barrel 8 to release the cooling energy, thus completing the cycle. The remaining operating principles of the device are the same as those in the transcritical operation mode.

[0112] In natural cooling dry mode:

[0113] Turn off the carbon dioxide compressor unit, open the switch electric stop valve 22, turn off the first water pump 13 and the second water pump 14, and the three-stage cooling CO2 air cooler 1 only runs the first fan unit 11 and the second fan unit 12. The operating principles of the remaining devices are the same as those in the natural cooling wet mode.

[0114] This application provides a transcritical direct-cooling CO2 heat pipe chip backplane cooling system, which has the following beneficial effects:

[0115] 1. Pure CO2 natural refrigerant, CO2 heat pipe has high heat exchange efficiency, large latent heat and small heat exchange temperature difference.

[0116] 2. The cooling system can operate in transcritical mode, subcritical mode, natural cooling wet mode and natural cooling dry mode according to the ambient dry-bulb temperature, wet-bulb temperature and air cooler outlet temperature to improve cooling efficiency.

[0117] 3. CO2 refrigerant has higher heat exchange efficiency than other HFO refrigerants, higher heat exchange sensitivity, and shorter heat exchange response time, which is more conducive to heat dissipation of high-power, fast, and high-heat-generating chips.

[0118] 4. The CO2 working fluid pump adopts N+1 backup mode. When any working fluid pump fails, the backup pump automatically starts. The CO2 working fluid pump uses a constant pressure differential frequency conversion based on the difference between the pump outlet pressure and the low-pressure circulation tank pressure to maximize energy saving.

[0119] 5. The CO2 compressor adopts a piston compressor, which has the characteristics of small pressure ratio and large pressure difference of CO2 and has high efficiency. The CO2 compressor adopts an oil-free small pressure ratio centrifugal compressor, and the refrigeration system runs oil-free, completely eliminating the trouble of oil film thermal resistance and oil return.

[0120] 6. When CO2 is transcritical, the outlet temperature of the air-cooled + wet curtain adiabatic air cooler drops to the wet bulb temperature + 5°C, while the three-stage cooling CO2 air cooler can drop the air cooler outlet temperature to the wet bulb temperature -3°C, which is 8°C lower than the outlet temperature of the wet curtain adiabatic air cooler, greatly improving the cooling efficiency.

[0121] A second aspect of the present application provides a transcritical direct-cooling CO2 heat pipe chip backplane cooling method, which is applied to a transcritical direct-cooling CO2 heat pipe chip backplane cooling system described in any of the above embodiments, comprising:

[0122] Acquire temperature data; the temperature data includes: ambient dry-bulb temperature, ambient wet-bulb temperature and air cooler outlet temperature;

[0123] Based on the temperature data, the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, the on-off electric stop valve, and the compressor are controlled to operate in a preset mode so that the superheat of the CO2 working medium at the return air end of the heat pipe module is within a preset range; the preset modes include: transcritical operation mode, subcritical operation mode, natural cooling wet mode, and natural cooling dry mode.

[0124] It is worth noting that the effects of the above method embodiments can be found in the effects of the above system embodiments, which will not be described in detail here.

[0125] The above specific implementation methods further explain in detail the purpose, technical solutions and beneficial effects of the embodiments of the present application. It should be understood that the above are only specific implementation methods of the embodiments of the present application and are not intended to limit the scope of protection of the embodiments of the present application. Any modifications, equivalent replacements, improvements, etc. made on the basis of the technical solutions of the embodiments of the present application should be included in the scope of protection of the embodiments of the present application.

Claims

1. A transcritical direct cooling CO2 heat pipe chip backplane cooling system, characterized in that: include: A three-stage cooling CO2 air cooler (1), a liquid cooling distribution unit (2), at least one heat pipe module, a compressor (5), and a control module (6); the heat pipe module comprises: a CO2 power heat pipe module (3) and a CO2 gravity heat pipe module (4); The three-stage cooling CO2 air cooler (1) comprises: a first air fan unit (11), a second air fan unit (12), a first water pump (13), and a second water pump (14); the three-stage cooling CO2 air cooler (1) is configured to provide cooling to the liquid cooling distribution unit (2); The liquid cooling distribution unit (2) is connected to the three-stage cooling CO2 air cooler (1) and the heat pipe module via an electric throttle valve (21) and a switch electric stop valve (22); the liquid cooling distribution unit (2) is configured to transmit the CO2 working medium to the heat pipe module; The heat pipe module is configured to perform heat exchange with the CO2 working medium; The control module (6) is configured to: Acquire temperature data; the temperature data includes: ambient dry-bulb temperature, ambient wet-bulb temperature and air cooler outlet temperature; According to the temperature data, the first fan unit (11), the second fan unit (12), the first water pump (13), the second water pump (14), the electric throttle valve (21), the on-off electric stop valve (22), and the compressor (5) are controlled to operate in a preset mode so that the superheat of the CO2 working medium at the return air end of the heat pipe module is within a preset range; the preset modes include: a transcritical operation mode, a subcritical operation mode, a natural cooling wet mode, and a natural cooling dry mode.

2. A transcritical direct cooling CO2 heat pipe chip backplane cooling system according to claim 1, characterized in that: The control module (6) is further configured to: When the air cooler outlet temperature is greater than or equal to 31° C. and the ambient wet-bulb temperature is greater than or equal to 16° C., the first fan unit (11), the second fan unit (12), the first water pump (13), the second water pump (14), the electric throttle valve (21), the on-off electric stop valve (22), and the compressor (5) are controlled to operate in the transcritical operation mode; Wherein, when in the transcritical operation mode, the first fan unit (11), the second fan unit (12), the first water pump (13), the second water pump (14), the electric throttle valve (21), and the compressor (5) are turned on, and the on-off electric stop valve (22) is closed.

3. The transcritical direct cooling CO2 heat pipe chip backplane cooling system according to claim 1, characterized in that: The control module (6) is further configured to: When the air cooler outlet temperature is less than 31° C. and greater than 26° C., and the ambient wet-bulb temperature is greater than or equal to 16° C., controlling the first fan unit (11), the second fan unit (12), the first water pump (13), the second water pump (14), the electric throttle valve (21), the on-off electric stop valve (22), and the compressor (5) to operate in the subcritical operation mode; Wherein, when in the subcritical operation mode, the first fan unit (11), the second fan unit (12), the first water pump (13), the second water pump (14), the electric throttle valve (21), and the compressor (5) are turned on, and the on-off electric stop valve (22) is closed.

4. The transcritical direct cooling CO2 heat pipe chip backplane cooling system according to claim 1, characterized in that: The control module (6) is further configured to: When the ambient wet-bulb temperature is less than 16° C. and the ambient dry-bulb temperature is greater than 8° C., the first fan unit (11), the second fan unit (12), the first water pump (13), the second water pump (14), the electric throttle valve (21), the on-off electric stop valve (22), and the compressor (5) are controlled to operate in the natural cooling wet mode; Wherein, when in the natural cooling wet mode, the first fan unit (11), the second fan unit (12), the first water pump (13), the second water pump (14), and the switch quantity electric stop valve (22) are turned on, and the electric throttle valve (21) and the compressor (5) are turned off.

5. The transcritical direct cooling CO2 heat pipe chip backplane cooling system according to claim 1, characterized in that: The control module (6) is further configured to: When the ambient dry-bulb temperature is less than or equal to 8° C., the first fan unit (11), the second fan unit (12), the first water pump (13), the second water pump (14), the electric throttle valve (21), the on-off electric stop valve (22), and the compressor (5) are controlled to operate in the natural cooling dry mode; Wherein, when in the natural cooling dry mode, the first fan unit (11), the second fan unit (12), and the switch electric stop valve (22) are turned on, and the first water pump (13), the second water pump (14), the electric throttle valve (21), and the compressor (5) are turned off.

6. The transcritical direct cooling CO2 heat pipe chip backplane cooling system according to claim 1, characterized in that: The control module (6) is further configured to: When in the transcritical operation mode, a first target exhaust pressure value of the three-stage cooling CO2 air cooler (1) is determined according to the air cooler outlet temperature; the first target exhaust pressure value is: Pg=(2.778-0.0157×t o )×t gc +(0.381×t o -9.34)-1; Where, t o Set the evaporation temperature value for the optimal exhaust pressure calculation, t gc is the air cooler outlet temperature; The electric throttle valve (21) is PID regulated according to the air cooler outlet temperature and the first target exhaust pressure value.

7. The transcritical direct cooling CO2 heat pipe chip backplane cooling system according to claim 1, characterized in that: The control module (6) is further configured to: Determine subcritical operation subcooling; When in the subcritical operation mode, the second target exhaust pressure value of the three-stage cooling CO2 air cooler (1) is determined according to the air cooler outlet temperature and the subcritical operation subcooling degree; the second target exhaust pressure value is: Pg=4×10 -5 ×(t a +t l )3+0.0092×(t a +t l )2+0.9259×(t a +t l )+33,821; Where, t a is the subcritical temperature, t l Subcooling for subcritical operation; The electric throttle valve (21) is PID regulated according to the air cooler outlet temperature and the second target exhaust pressure value.

8. The transcritical direct cooling CO2 heat pipe chip backplane cooling system according to claim 1, characterized in that: The liquid cooling distribution unit (2) is connected to the heat pipe module via a CO2 working fluid pump (23); the number of the CO2 working fluid pumps (23) is: N+1; N is the number of the heat pipe modules.

9. The transcritical direct cooling CO2 heat pipe chip backplane cooling system according to claim 1, characterized in that: The CO2 power heat pipe module (3) is configured with a plurality of chip cold plates (31), and the chip cold plates (31) are power heat pipes; the CO2 gravity heat pipe module (4) is configured with a back plate heat exchanger (41), and the back plate heat exchanger (41) is a CO2 gravity heat pipe, and the flow channel in the CO2 gravity heat pipe is configured to enter from the bottom and exit from the top.

10. A transcritical direct-cooling CO2 heat pipe chip backplane cooling method, applied to a transcritical direct-cooling CO2 heat pipe chip backplane cooling system according to any one of claims 1 to 9, characterized in that: include: Acquire temperature data; the temperature data includes: ambient dry-bulb temperature, ambient wet-bulb temperature and air cooler outlet temperature; Based on the temperature data, the first fan unit, the second fan unit, the first water pump, the second water pump, the electric throttle valve, the on-off electric stop valve, and the compressor are controlled to operate in a preset mode so that the superheat of the CO2 working medium at the return air end of the heat pipe module is within a preset range; the preset modes include: transcritical operation mode, subcritical operation mode, natural cooling wet mode, and natural cooling dry mode.

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