Patent Publication Number: US-2022217873-A1

Title: Pressure based regulating design in fluid conditioning and distribution system

Description:
FIELD OF THE INVENTION 
     Embodiments of the present invention relate generally to data center cooling. More particularly, embodiments of the invention relate to a buffer unit design for cooling of electronics devices such as data center, IT system design, and system control. 
     BACKGROUND 
     Cooling is a prominent factor in a computer system and data center design. The number of high performance electronics components such as high performance processors packaged inside servers has steadily increased, thereby increasing the amount of heat generated and dissipated during the ordinary operations of the servers. The reliability of servers used within a data center decreases if the environment in which they operate is permitted to increase in temperature over time. Maintaining a proper thermal environment is critical for normal operations of these servers in data centers, as well as the server performance and lifetime. It requires more effective and efficient cooling solutions especially in the cases of cooling these high performance servers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         FIG. 1  is a block diagram illustrating an example of a data center facility according to one embodiment. 
         FIG. 2  is a block diagram illustrating an example of an electronic rack according to one embodiment. 
         FIG. 3  shows an example cooling system according to an embodiment of the application. 
         FIG. 4  is a flow diagram of an example process for a cooling system according to an embodiment of the application. 
         FIG. 5  shows another example cooling system according to an embodiment of the application. 
         FIG. 6  is another flow diagram of an example process for a cooling system according to an embodiment of the application 
         FIG. 7A  shows another example cooling system according to an embodiment of the application. 
         FIG. 7B  shows another example cooling system according to an embodiment of the application. 
         FIG. 7C  is another flow diagram of an example process for a cooling system according to an embodiment of the application 
         FIG. 8A  shows another example cooling system according to an embodiment of the application. 
         FIG. 8B  is another flow diagram of an example process for a cooling system according to an embodiment of the application. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments and aspects of the inventions will be described with reference to details discussed below, and the accompanying drawings will illustrate the various embodiments. The following description and drawings are illustrative of the invention and are not to be construed as limiting the invention. Numerous specific details are described to provide a thorough understanding of various embodiments of the present invention. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present inventions. 
     Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in conjunction with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification do not necessarily all refer to the same embodiment. 
     Cooling is critical to IT Hardware industry due to many reasons, besides ensuring normal operation and function. For example, not only does it play a crucial role in the hardware&#39;s infrastructure capability, service quality and availability, but it&#39;s also significantly cheaper. This directly impacts the profit of a service provider. This industry is one of the core competitors of the internet, cloud computing, high performance computing, AI based businesses, and any related other businesses that use computational, storage and internet hardware platforms, or infrastructures. For instance, for the rapidly growing cloud computing business, the performance and cost (both capital cost and operation cost) of compute and storage hardware systems, clusters, and infrastructures directly impact the success of a business. All these markets require continuous innovation and creation. Furthermore, a robust system architecture, or control and operation strategy may also benefit service providers in multiple aspects long term. 
     The goal is to provide increasingly advanced services by innovating and developing compute and storage infrastructures, and platforms with high resilience and flexible configurations to accommodate the dynamic variations in software, application, and business setting while simultaneously decreasing TCO. The system architecture design and control both play significant roles in this process. 
     The current disclosure introduces a system design and operation method for fluid conditioning and distribution using pressure. The design aims to enable a higher performance and better controlled fluid environment for an IT system thermal management and fluid management. In addition, this solution can be cross applied to handle multiple variations and dynamics in a liquid based cooling loop. 
     One of the challenges in the system design is to handle different types of normal and abnormal variations in a fluid based heat transfer system. This may include the variations in the heat load and cooling capacity as well as system failure, and other services. The system design, as well as the corresponding operation and control, should be robust and simple to accommodate these changes and anomalies. 
     Reliability presents another challenge. The current disclosure introduces a buffer loop together with its control feature enabled to provide reliable maintenance capabilities, minimizing the impact on the fluid, including the fluid pressure and temperature. Since the reliability become increasingly critical for modern IT cluster and hardware equipment, corresponding cooling fluid must be better controlled and regulated. 
     The system needs to be in high resilience, meaning it should be adjustable for different cooling loop arrangements and configurations in different use cases. Not only does this require a high resilience in hardware and system design, but this also requires advanced control and operation strategy to enable a full system functioning synergistically. 
     Self-regulating control is an important feature for modern clusters and systems. While a robust control design should be less dependent on sensors and complex software/algorithm, it must also provide designed operation conditions such as fluid conditions and distribution within the system and for the load. Thus, self-regulating features for components and system loops are one of the key technical directions in this field. 
     The pressure control for the system proposed is a novel design. The previous solution may require multiple control signals for the entire system, and the previous solution may not consider the system and operation proposed in the current disclosure. The bypass loop design with either a buffer unit or/and an expansion system combined with different types of valves and advanced control for the individual components all contribute to the innovation feature in multiple scenarios. 
     A pressure based system design and operation is proposed in the current disclosure. The system includes a heat exchanger unit to exchange heat between the first fluid and the second fluid. The system design enables it to pump, distribute, condition, and regulate the first fluid based on the needs and variations in the system. Different types of system design are proposed with different components and loops in configuring the buffering loop, including using 4-way valve, pressure triggered valve as well as different types of buffering loops and systems. In addition, the system operation and control for each individual component and the system design are introduced and provided. Fluid pressure is measured and used as the key metrics, by either controlling the hydraulic parts directly or indirectly through the controller, for proper fluid conditioning and distribution with the variations in the fluid pressure. The approach enables a self-regulating system for fluid and thermal management. 
     In an embodiment, a cooling system includes an inlet port and an outlet port to be coupled to one or more electronic devices, a main loop having a heat exchanger coupled to the inlet port and the outlet port, and a buffer loop coupled to the inlet port and the outlet port. 
     For example, the main loop having a heat exchanger to receive fluid from the inlet port, to extract the heat which is generated by the electronic devices and carried by the fluid, and to return the fluid to the electronic devices via the outlet. 
     In an embodiment, a cooling system includes a buffer loop, configured in parallel with the main loop, with a buffer unit to temporarily buffer at least a portion of the fluid, and a first pressure controllable valve, coupled to the main loop and the buffer loop, to selectively distribute at least a portion of the fluid to at least one of the main loop or the buffer loop based on a fluid pressure of the fluid. 
     In an embodiment, a cooling system includes a bypass loop coupled between the first pressure controllable valve and the outlet port to operate as a direct bypass loop from the inlet port to the outlet port, bypassing the heat exchanger and the buffer unit. 
     In an embodiment, the first pressure controllable valve in the cooling system is a four-way valve to selective to distribute the fluid received from the inlet port to at least one of the first loop, the second loop, or the third loop. 
     In an embodiment, the first pressure controllable valve in the cooling system includes a first valve coupled between the inlet port and an inlet of the heat exchanger to control fluid flowrate of a first fluid flowing into the heat exchanger based on the fluid pressure, a second valve coupled between the inlet port and an inlet of the buffer unit to control fluid flowrate of a second fluid flowing into the buffer unit, and a third valve coupled between the inlet port and the direct bypass loop to control fluid flowrate of a third fluid flowing through the direct bypass loop based on the fluid pressure 
     In an embodiment, the first valve in the cooling system is triggered to open in response to the fluid pressure being above a first pressure threshold. In an embodiment, the second valve is triggered to open in response to the fluid pressure being above a second pressure threshold. In an embodiment, the third valve is triggered to open in response to the fluid pressure being above a third pressure threshold. In an embodiment, the first pressure threshold, the second pressure threshold, and the third pressure threshold are different. 
     In an embodiment, the buffer loop further includes a second pressure controllable valve disposed between an outlet of the buffer unit and the outlet port to control a flowrate of fluid from the outlet of the buffer unit to the outlet port. For example, the second pressure controllable valve is controlled based on a fluid pressure obtained from a pressure sensor within the buffer unit or a fluid pressure obtained from a pressure sensor disposed near the inlet port. 
     In an embodiment, the bypass loop further includes a fourth valve coupled between the third valve and the outlet port. For example, the second pressure controllable valve is coupled between the buffer unit and a connecting point between the third valve and the fourth valve. 
     In an embodiment, a cooling system includes a fluid pump couple between an outlet of the heat exchanger and the outlet port to pump the fluid towards the outlet port. 
     In an embodiment, a cooling system includes a bidirectional path coupled between the connecting point and an inlet of the fluid pump. 
     In an embodiment, a cooling system includes an external loop coupled with the heat exchanger, a fifth pressure controllable valve and an external outlet port. For example, the heat exchanger is to receive external fluid from the external inlet port and to return the external fluid via the external outlet port. 
       FIG. 1  is a block diagram illustrating an example of a data center or data center unit according to one embodiment. In this example,  FIG. 1  shows a top view of at least a portion of a data center. Referring to  FIG. 1 , according to one embodiment, data center system  100  includes one or more rows of electronic racks of information technology (IT) components, equipment or instruments  101 - 102 , such as, for example, computer servers or computing nodes that provide data services to a variety of clients over a network (e.g., the Internet). In this embodiment, each row includes an array of electronic racks such as electronic racks  110 A- 110 N. However, more or fewer rows of electronic racks may be implemented. Typically, rows  101 - 102  are aligned in parallel with frontends facing towards each other and back ends facing away from each other, forming aisle  103  in between to allow an administrative person walking therein. However, other configurations or arrangements may also be applied. For example, two rows of electronic racks may back to back face each other without forming an aisle in between, while their frontends face away from each other. The back ends of the electronic racks may be coupled to the room cooling liquid manifolds. 
     In one embodiment, each of the electronic racks (e.g., electronic racks  110 A- 110 N) includes a housing to house a number of IT components arranged in a stack operating therein. The electronic racks can include a cooling liquid manifold, a number of server slots (e.g., standard shelves or chassis configured with an identical or similar form factor), and a number of server chassis (also referred to as server blades or server shelves) capable of being inserted into and removed from the server slots. Each server chassis represents a computing node having one or more processors, a memory, and/or a persistent storage device (e.g., hard drive HD, solid state drive SSD), where a computing node may include one or more servers operating therein. At least one of the processors is attached to a liquid cold plate (also referred to as a cold plate assembly) to receive cooling liquid. In addition, one or more optional cooling fans are associated with the server chassis to provide air cooling to the computing nodes contained therein. Note that the cooling system  120  may be coupled to multiple data center systems such as data center system  100 . 
     In one embodiment, cooling system  120  includes an external liquid loop connected to a cooling tower or a dry cooler external to the building/housing container. The cooling system  120  can include, but is not limited to evaporative cooling, free air, rejection to large thermal mass, and waste heat recovery designs. Cooling system  120  may include or be coupled to a cooling liquid source that provide cooling liquid. 
     In one embodiment, each server chassis is coupled to the cooling liquid manifold modularly, such that a server chassis can be removed from the electronic rack without affecting the operations of remaining server chassis in the electronic rack and the cooling liquid manifold. In another embodiment, each server chassis is coupled to the cooling liquid manifold through a quick-release coupling assembly having a server liquid intake connector and a server liquid outlet connector coupled to a flexible hose to distribute the cooling liquid to the processors. The server liquid intake connector is to receive cooling liquid via a rack liquid intake connector from a cooling liquid manifold mounted on a backend of the electronic rack. The server liquid outlet connector is to emit warmer or hotter liquid carrying the heat exchanged from the processors to the cooling liquid manifold via a rack liquid outlet connector and then back to a coolant distribution unit (CDU) within the electronic rack. 
     In one embodiment, the cooling liquid manifold disposed on the backend of each electronic rack is coupled to liquid supply line  132  (also referred to as a room supply manifold) to receive cooling liquid from cooling system  120 . The cooling liquid is distributed through a liquid distribution loop attached to a cold plate assembly on which a processor is mounted to remove heat from the processors. A cold plate is configured similar to a heat sink with a liquid distribution tube attached or embedded therein. The resulting warmer or hotter liquid carrying the heat exchanged from the processors is transmitted via liquid return line  131  (also referred to as a room return manifold) back to cooling system  120 . 
     Liquid supply/return lines  131 - 132  are referred to as data center or room liquid supply/return lines (e.g., global liquid supply/return lines), which supply cooling liquid to all of the electronic racks of rows  101 - 102 . The liquid supply line  132  and liquid return line  131  are coupled to a heat exchanger of a CDU located within each of the electronic racks, forming a primary loop. The secondary loop of the heat exchanger is coupled to each of the server chassis in the electronic rack to deliver the cooling liquid to the cold plates of the processors. 
     In one embodiment, data center system  100  further includes an optional airflow delivery system  135  to generate an airflow to cause the airflow to travel through the air space of the server chassis of the electronic racks to exchange heat generated by the computing nodes due to operations of the computing nodes (e.g., servers) and to exhaust the airflow exchanged heat to an external environment or a cooling system (e.g., air-to-liquid heat exchanger) to reduce the temperature of the airflow. For example, air supply system  135  generates an airflow of cool/cold air to circulate from aisle  103  through electronic racks  110 A- 110 N to carry away exchanged heat. 
     The cool airflows enter the electronic racks through their frontends and the warm/hot airflows exit the electronic racks from their back ends. The warm/hot air with exchanged heat is exhausted from room/building or cooled using a separate cooling system such as an air-to-liquid heat exchanger. Thus, the cooling system is a hybrid liquid-air cooling system, where a portion of the heat generated by a processor is removed by cooling liquid via the corresponding cold plate, while the remaining portion of the heat generated by the processor (or other electronics or processing devices) is removed by airflow cooling. 
       FIG. 2  is block diagram illustrating an electronic rack according to one embodiment. Electronic rack  200  may represent any of the electronic racks as shown in  FIG. 1 , such as, for example, electronic racks  110 A- 110 N. Referring to  FIG. 2 , according to one embodiment, electronic rack  200  includes, but is not limited to, CDU  201 , rack management unit (RMU)  202 , and one or more server chassis  203 A- 203 E (collectively referred to as server chassis  203 ). Server chassis  203  can be inserted into an array of server slots (e.g., standard shelves) respectively from frontend  204  or backend  205  of electronic rack  200 . Note that although there are five server chassis  203 A- 203 E shown here, more or fewer server chassis may be maintained within electronic rack  200 . Also note that the particular positions of CDU  201 , RMU  202 , and/or server chassis  203  are shown for the purpose of illustration only; other arrangements or configurations of CDU  201 , RMU  202 , and/or server chassis  203  may also be implemented. In one embodiment, electronic rack  200  can be either open to the environment or partially contained by a rack container, as long as the cooling fans can generate airflows from the frontend to the backend. 
     In addition, for at least some of the server chassis  203 , an optional fan module (not shown) is associated with the server chassis. Each of the fan modules includes one or more cooling fans. The fan modules may be mounted on the back ends of server chassis  203  or on the electronic rack to generate airflows flowing from frontend  204 , traveling through the air space of the sever chassis  203 , and existing at backend  205  of electronic rack  200 . 
     In one embodiment, CDU  201  mainly includes heat exchanger  211 , liquid pump  212 , and a pump controller (not shown), and some other components such as a liquid reservoir, a power supply, monitoring sensors and so on. Heat exchanger  211  may be a liquid-to-liquid heat exchanger. Heat exchanger  211  includes a first loop with inlet and outlet ports having a first pair of liquid connectors coupled to external liquid supply/return lines  131 - 132  to form a primary loop. The connectors coupled to the external liquid supply/return lines  131 - 132  may be disposed or mounted on backend  205  of electronic rack  200 . The liquid supply/return lines  131 - 132 , also referred to as room liquid supply/return lines, may be coupled to cooling system  120  as described above. 
     In addition, heat exchanger  211  further includes a second loop with two ports having a second pair of liquid connectors coupled to liquid manifold  225  (also referred to as a rack manifold) to form a secondary loop, which may include a supply manifold (also referred to as a rack liquid supply line or rack supply manifold) to supply cooling liquid to server chassis  203  and a return manifold (also referred to as a rack liquid return line or rack return manifold) to return warmer liquid back to CDU  201 . Note that CDUs  201  can be any kind of CDUs commercially available or customized ones. Thus, the details of CDUs  201  will not be described herein. 
     Each of server chassis  203  may include one or more IT components (e.g., central processing units or CPUs, general/graphic processing units (GPUs), memory, and/or storage devices). Each IT component may perform data processing tasks, where the IT component may include software installed in a storage device, loaded into the memory, and executed by one or more processors to perform the data processing tasks. Server chassis  203  may include a host server (referred to as a host node) coupled to one or more compute servers (also referred to as computing nodes, such as CPU server and GPU server). The host server (having one or more CPUs) typically interfaces with clients over a network (e.g., Internet) to receive a request for a particular service such as storage services (e.g., cloud-based storage services such as backup and/or restoration), executing an application to perform certain operations (e.g., image processing, deep data learning algorithms or modeling, etc., as a part of a software-as-a-service or SaaS platform). In response to the request, the host server distributes the tasks to one or more of the computing nodes or compute servers (having one or more GPUs) managed by the host server. The compute servers perform the actual tasks, which may generate heat during the operations. 
     Electronic rack  200  further includes optional RMU  202  configured to provide and manage power supplied to servers  203 , and CDU  201 . RMU  202  may be coupled to a power supply unit (not shown) to manage the power consumption of the power supply unit. The power supply unit may include the necessary circuitry (e.g., an alternating current (AC) to direct current (DC) or DC to DC power converter, battery, transformer, or regulator, etc.) to provide power to the rest of the components of electronic rack  200 . 
     In one embodiment, RMU  202  includes optimization module  221  and rack management controller (RMC)  222 . RMC  222  may include a monitor to monitor operating status of various components within electronic rack  200 , such as, for example, computing nodes  203 , CDU  201 , and the fan modules. Specifically, the monitor receives operating data from various sensors representing the operating environments of electronic rack  200 . For example, the monitor may receive operating data representing temperatures of the processors, cooling liquid, and airflows, which may be captured and collected via various temperature sensors. The monitor may also receive data representing the fan power and pump power generated by the fan modules  231  and liquid pump  212 , which may be proportional to their respective speeds. These operating data are referred to as real-time operating data. Note that the monitor may be implemented as a separate module within RMU  202 . 
     Based on the operating data, optimization module  221  performs an optimization using a predetermined optimization function or optimization model to derive a set of optimal fan speeds for fan modules  231  and an optimal pump speed for liquid pump  212 , such that the total power consumption of liquid pump  212  and fan modules  231  reaches minimum, while the operating data associated with liquid pump  212  and cooling fans of the fan modules are within their respective designed specifications. Once the optimal pump speed and optimal fan speeds have been determined, RMC  222  configures liquid pump  212  and cooling fans of fan modules  231  based on the optimal pump speeds and fan speeds. 
     As an example, based on the optimal pump speed, RMC  222  communicates with a pump controller of CDU  201  to control the speed of liquid pump  212 , which in turn controls a liquid flow rate of cooling liquid supplied to the liquid manifold  225  to be distributed to at least some of server chassis  203 . Similarly, based on the optimal fan speeds, RMC  222  communicates with each of the fan modules to control the speed of each cooling fan of the fan modules  231 , which in turn control the airflow rates of the fan modules. Note that each of fan modules may be individually controlled with its specific optimal fan speed, and different fan modules and/or different cooling fans within the same fan module may have different optimal fan speeds. 
     Note that the rack configuration as shown in  FIG. 2  is shown and described for the purpose of illustration only; other configurations or arrangements may also be applicable. For example, CDU  201  may be an optional unit. The cold plates of server chassis  203  may be coupled to a rack manifold, which may be directly coupled to room manifolds  131 - 132  without using a CDU. Although not shown, a power supply unit may be disposed within electronic rack  200 . The power supply unit may be implemented as a standard chassis identical or similar to a sever chassis, where the power supply chassis can be inserted into any of the standard shelves, replacing any of server chassis  203 . In addition, the power supply chassis may further include a battery backup unit (BBU) to provide battery power to server chassis  203  when the main power is unavailable. The BBU may include one or more battery packages and each battery package include one or more battery cells, as well as the necessary charging and discharging circuits for charging and discharging the battery cells. 
       FIG. 3  shows an example cooling system  400  according to an embodiment of the application. The cooling system may be implemented as part of cooling system  120  of FIG.  1  or as part of CDU  201  of  FIG. 2 . For example,  FIG. 3  shows a schematic representation of the fluid conditioning and distribution system. In an embodiment, the cooling system includes two fluid streams ( 433 ,  451 ) exchanging thermal energy. For example, the main fluid  433  inlet and outlet are port #1 ( 421 ) and port #2 ( 423 ), and the external/heat exchanger fluid  451  inlet and outlet are port #3 ( 427 ) and port #4 ( 425 ). Inlet port  421  may be coupled to a cold plate attached to an electronic device that generates heat to receive the fluid carrying the heat. Outlet port  423  may supply the fluid back to the cold plate of the electronic device or to a cold plate of another electronic device. An electronic device may be a processor or other IT component within an electronic rack as described above. In an embodiment, the heat is exchanged between the two fluids ( 433 ,  451 ) through the heat exchanger (HX) unit  437 . In an embodiment, the main function of the system is used for regulating and controlling of the pressure, temperature and flowrate of the main fluid  433  by adjusting the entire system and components. 
     In  FIG. 3 , in an embodiment, the valve  453  is used for regulating the flowrate of the second/external fluid  451  of the external loop of the heat exchanger  437 , and this valve  453  in  FIG. 3  system is controlled by the temperature sensor  431 . In an embodiment, the pump  419  is used for pulling or pushing the fluid through the system. In an embodiment, the two-way loop  455  enables the main fluid  433  moving in either direction. 
     In an embodiment, the key design in the system is the design of the bypass loop  453  and this is the core focus in this disclosure. In an embodiment, key components of the bypass loop  453  are a buffer unit  401  and its corresponding loop  413 . For example, the buffer unit  401  buffers the variations in pressure and fluid volume happened due to multiple reasons. In an embodiment, another loop is a direct bypass loop  453  without any components used on the system according to an embodiment. In an embodiment, the main focus of the current disclosure is on the buffer unit loop  413 . 
     In an embodiment, a pressure sensor P 1   429  is used at the inlet close to the port #1  421 . In an embodiment, a four-way valve  455  is used for manipulating and regulating fluid to the main loop  433 , the direct bypass loop  453 , and/or the buffer loop  413 . Valve  455  is configured to distribute same or different amount of fluid to loops  433 ,  453 , and/or  413 , dependent upon the fluid pressure sensed by pressure sensor  429 . The valve opening ratio of each way may be different, which may be opened, closed, or anywhere in between based on a specific pressure threshold. The detailed operation of using the four-way valve  455  in the system shown in  FIG. 3  are described in the next section  FIG. 4 . In addition, in an embodiment, the valve  409  is used on the buffer loop ( 413 ,  417 ) controlling the fluid on this loop. In an embodiment, valve  409  can be either controlled by a fluid pressure sensor  435  within the buffer unit  401  or/and the same pressure sensor P 1   429 . 
     In an embodiment, a cooling system  400  includes an external output loop  451  coupled with the heat exchanger  437 , a fifth pressure controllable valve  453  and an external outlet port  427 . For example, the heat exchanger  437  is to receive external fluid from the external inlet port  425  via an external input loop  461  and to return the external fluid via external output loop  451  to the external outlet port  427 . 
     Overall, the buffer unit/loop  413 , the direct loop  453  as well as the main/heat exchanger loop  433  are regulated by the four-way valve  455  to achieve the fluid distribution and conditioning. In an embodiment, the bypass loop  453  is extended and is parallel with the pump  419  in the system. 
       FIG. 4  is a flow diagram of an example process  500  for a cooling system according to an embodiment of the application. For example,  FIG. 4  shows the system operation for the one shown in  FIG. 3 . In an embodiment, the example process  500  includes two scenarios, which are the system pressure increasing or decreasing. For example, the key feature is controlling and switching the four-way valve  455  to manage main fluid conditions in the cooling system when the pressure varies caused by either during normal operations or abnormal operations, as well as to accommodate the unbalances between the cooling capacity and heating load. 
     At operation  501 , the four-way valve  455  is in position #1  411  with constant pump speed. In an embodiment, when the main/heat changer loop  433  disconnected or other scenarios, the system pressure P 1   421  will increase to cause a higher flowrate from Port #1  411 . In an embodiment, at operation  503 , in response to the system pressure P 1   429  increases, the four-way valve  455  changes the position #1  411  to position #2  435  and position #3  407 . At operation  505 , with remaining similar flowrate of Port #2  423 , the buffer unit  401  buffers the fluid with the valve  409  closed. 
     In an embodiment, when the main/heat changer loop  433  is plugged in or other scenarios, the system pressure P 1   421  will decrease to cause a lower flowrate from Port #1  411 . In an embodiment, at operation  507 , in response to the system pressure P 1   429  decreases, the four-way valve  455  changes the position from position #2  435  and #3  407  to partially #1  411  and #3  407 . At operation  509 , with remaining similar flowrate of Port #2  423 , the buffer unit  401  supplies the fluid with the valve  409  opened. At operation  511 , the four-way valve changes back to position #1  411 . 
     In an embodiment, when the pump  419  is disconnected or other scenarios, the system pressure P 1   421  will decrease to cause a lower flowrate from Port #1  411 . In an embodiment, at operation  513 , in response to the system pressure P 1   429  decreases, the four-way valve  455  changes the position to position #1  411  and #2  435 . At operation  515 , with remaining similar flowrate of Port #2  423 , the bypass loop  453  bypasses the fluid. At operation  517 , the four-way valve changes back to position #1  411 . 
     In an embodiment, when the pump  419  is plugged in or other scenarios, the system pressure P 1   421  will increase to cause a higher flowrate from Port #1  411 . In an embodiment, at operation  519 , in response to the system pressure P 1   429  increases, the four-way valve  455  changes to the position #1  411  and #3  407  with the valve  409  closed. At operation  521 , with remaining similar flowrate of Port #2  423 , the four-way valve  455  changes to the position #1  411  with the valve  409  opened. At operation  523 , the temperature control  431  can adjust the external fluid flowrate. 
       FIG. 5  shows another example cooling system  600  according to an embodiment of the application. For example,  FIG. 5  shows another bypass loop design for the system. The main functions of the system shown in  FIG. 5  are almost the same as the one shown in  FIG. 3 . The main difference is that instead of using a four-way valve  455  for regulating different loops, individual two-way valve is used. Each of valves  411 ,  435 , and  407  may be associated with the same or different thresholds to open or close the corresponding valve, fully or partially. 
     In an embodiment, valve  435  and valve  407  as well as valve  409  are pressure controlled and pressure trigger valve, which means that those valves can be opened by the fluid pressure once the fluid pressure is larger than these valves opening pressure. In an embodiment, the opening pressure can be also controlled by the pressure signal received by the valves. For example, valve  453  can be a regular valve for controlling the fluid within the heat exchanger loop  451 . In an embodiment, valve  409  is used for regulating the second fluid into the external loop  417 . In an embodiment, the valve  411  can also be controlled by the pressure P 1   429 . 
     In an embodiment, for the valve  435  and valve  407 , they will be opened, fully or partially, by the fluid pressure  429  once the pressure as P 1   429  increases to a predetermined threshold. In an embodiment, the opening pressure P 1   429  for valve  435  and valve  407  may be different. For example, during normal operation, fluid only passes through the main/heat exchanger loop  433  since valve  435  and valve  407  are closed. In an embodiment, when the pressure P 1   429  increases, then the valve  435  and valve  407  can be triggered and status can be changed from close to open. Then, for example, the fluid can be distributed through the corresponding loop. 
     In addition, as mentioned above, in an embodiment, the corresponding opening pressure can be adjusted and tuned based on the system requirement. In an embodiment, the valve  409  can be controlled by the fluid pressure within the buffer unit  401  or/and the same pressure as valve  407 . In an embodiment, in the buffering mode, valve  407  is opened and valve  409  is closed. In an embodiment, in the releasing mode, valve  407  is closed and valve  409  is opened. In an embodiment, air pressure adjustment valve  415  is used for adjusting the pressure of the buffering section in the buffer unit system, for example, for discharging scenarios. 
       FIG. 6  is a flow diagram of an example process  610  for a cooling system according to an embodiment of the application. For example,  FIG. 6  shows the operation and control for the system shown in  FIG. 5  using the pressure sensor and the two way valves for the first fluid. 
     At operation  601 , the cooling system receives pressure P 1  measured from the sensor  429 . In an embodiment, at operation  603 , when the P 1   429  is in the design range, then moves to operation  605 . At operation  605 , the cooling system opens the valve  411 , closes the valves  407 ,  409  and  435 , and then moves back to operation  601 . 
     In an embodiment, at operation  603 , when the P 1  is not in the design range, then moves to operations  607  or  613 . For example, at operation  607 , when the P 1  is not in the design range and the received pressure P 1   429  increases, the cooling system opens valve  407 . At operation  609 , when the pressure P 1   429  increases and reaches to the P-high, the cooling system changes the valve  409  into the high pressure control mode. At operation  611 , when the pressure P 1   429  increases, the cooling system opens valve  407  and  409 . 
     Similar as above, for example, at operation  613 , when the P 1  is not in the design range and the received pressure P 1   429  decreases, the cooling system opens valve  435 . At operation  615 , when the pressure P 1   429  decreases and reaches to the P-law, the cooling system changes the valve  409  into the low pressure control mode. At operation  617 , when the pressure P 1   429  decreases, the cooling system opens valve  435  and valve  409 . 
       FIGS. 7A and 7B  show other example cooling systems ( 700 ,  710 ) according to embodiments of the application. For example,  FIGS. 7A and 7B  show full system regulating design using P 1 . In an embodiment,  FIG. 7A  shows that the pump  419  is used on the exit loop functioning as a pulling pump for the cooling system  700 . In an embodiment,  FIG. 7B  shows that the design that pump  441  is designed as a pushing pump for the cooling system  710 , and it may be treated as a pushing pump for the heat exchanger or the cooling system. For example, in the full system pressure regulating and controlling design, P 1   421  is also used for controlling valve  453 . In an embodiment valve  453  can be either a pressure controlled valve or a pressure triggered valve. For example, during variation of P 1   421 , when valve  435  and valve  407  are not triggered, an increasing of P 1   421  represents an increasing of a flowrate to the main/heat exchanger loop  433 . 
     In an embodiment, this requires an increasing on the external fluid  451  flowrate. For example, in this design, the pump ( 419 ,  441 ) maybe controlled by the fluid temperature in the loop. In an embodiment, the system fluid pressure measured by  429  is used for controlling several valves and fluid components, and this may require additional controller for tuning the input value of the P 1   429  and then provide different actual control signals for different valves to function differently. Therefore, in an embodiment, P 1   429  can be used as the original input, and each of the actual control output is calculated or processed based on the operation scenarios, system design and characteristics and so on. 
       FIG. 7C  is a flow diagram of an example process  720  for a cooling system according to an embodiment of the application. For example,  FIG. 7C  shows the operation and control for the system shown in  FIGS. 7A and 7B  using the pressure sensor and two way valves for both the main fluid  433  and the heat exchanger fluid  451 . 
     At operation  701 , the cooling system receives pressure P 1  measured from the sensor  429 . In an embodiment, at operation  703 , when the P 1   429  is not in the design range, then moves to operation  705 . At operation  705 , the cooling system enters the bypass loop operating mode. It needs to be mentioned that even the operations of  707 - 713  and  715 - 721  are two separate branches, they may be connected in an actual sequence. For example, when system is at operation  713 , it may continue to measure the P 1   429 , and then goes to process operation  715 . 
     In an embodiment, at operation  703 , when the P 1   429  is in the design range, then moves to operations  707  or  715 . For example, at operation  707 , when the received pressure P 1   429  increases, the cooling system increases the open ratio of the valve  411 . At operation  709 , the cooling system increases the flowrate of the main loop  433 . At operation  711 , the cooling system increases the open ratio of the valve  453  based on the pressure P 1   429 . At operation  713 , the cooling system enables a fully opening valve  453  at the maximum pressure P 1   429  within the design range. 
     For example, at operation  715 , when the received pressure P 1   429  decreases, the cooling system decreases the open ratio of the valve  411 . At operation  717 , the cooling system decreases the flowrate of the main loop  433 . At operation  719 , the cooling system decreases the open ratio of the valve  453  based on the pressure P 1   429 . At operation  721 , the cooling system enables the minimum opening valve  453  at the maximum pressure P 1   429  within the design range. It should be noted that the two loop control shown in the above two examples may require additional calculation and system tuning using the pressure data input from P 1   429 . 
       FIG. 8A  shows another example cooling system  800  according to an embodiment of the application. For example,  FIG. 8A  shows an expansion system used on the buffer loop  413 . In an embodiment, the expansion system has same valves in its inlet and outlet. In an embodiment, P 5   449  and P 4   447  can be understood as the control signal and the corresponding opening pressure for valve  407  and valve  409 , respectively. For example, the P 4   447  is controlled and connected with the air side  403  system in the expansion tank. In an embodiment, the air pressure adjustment functions are integrated on the expansion system for air side system pressure pre-charging and presetting, as well as for dynamic adjustment. In an embodiment, the pressure P 3   435  of the air section  403  can be adjusted by air pressure adjustment valve  415 . It needs to be mentioned that for two-phase system, the loops ( 413 ,  417 ) and corresponding port locations ( 457 ,  459 ) may follow certain requirement. For example, the port location  457  of the vapor loop  413  needs to be higher than the port location  459  the liquid loop  417 . 
       FIG. 8B  is a flow diagram of an example process  810  for a cooling system according to an embodiment of the application. For example,  FIG. 8B  shows the operation and control for the system with expansion unit on the buffer loop shown in  FIG. 8A  using the two way valves. For example, the pressure P 1   429  represents supply side pressure, the pressure P 2   443  represents the pressure of the fluid portion  405  in the expansion system  401 , the pressure P 3   435  represents the pressure of the air portion  403  in the expansion system  401 , the pressure P-set  445  represents the air charging pressure, the pressure P 4   447  represents the controlled pressure of valve  409 , and the pressure P 5   449  represents the controlled pressure of valve  407 . 
     At operation  801 , when pressure P 1   429  increases, the cooling system opens valve  407  based on P 5   449 ; when pressure P 3   435  greater or equal to P-set  445 , opens air pressure adjustment valve  415 ; when valve  407  opens, the fluid comes into the fluid portion  405  of the expansion system  401 ; when valve  409  is not open, the fluid can be stored in the fluid portion  405 , and the pressure builds up. 
     At operation  803 , in the buffering mode, the system control aims to enable as much as fluid into the fluid portion  405 ; P 3   435  is used for controlling the opening pressure P 4   447  for valve  409 ; and P 2   443  increases with fluid volume increases. 
     At operation  805 , the open pressure of P 4   447  for valve  409  is controlled larger than valve  407 ; the pressure P 3   435  and P-set  445  control how much higher P 4   447  over P 5   449 ; and P-set  445  is used for controlling and defining the opening of valve  409 . 
     At operation  807 , the pressure P 1   429  increases more than P 2   443  increases with fluid volume increases  405 . 
     At operation  809 , if the pressure P 2   443  is greater or equal to P 4   447 , then moves to operation  811 . At operation  911 , the cooling system opens valve  409 . At operation  813 , if the pressure P 2   443  is not less than P 4   447 , then moves back to operation  811  to open the valve  409 . At operation  813 , if the pressure P 2   443  is less than P 4   447 , then moves to operation  815  to close valve  409 , and then moves back to operation  807 . 
     At operation  809 , if the pressure P 2   443  is not greater or equal to P 4   447 , then moves to operation  815  to close valve  409  and then moves back to operation  807 . 
     In the foregoing specification, embodiments of the invention have been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.