Minimization of cooling air preheat for maximum packaging density

[0001] The never-ending explosion in computing processing power has led to an even greater explosion in demands on that power, forcing the designers of computer systems to package vast amounts of electronic equipment into relatively small areas. In addition to the cost of acquiring and maintaining the electronic equipment itself, large and complex computer systems, such as server farms and large data centers, carry additional infrastructure costs, including the costs of real-estate and cooling systems. Because these infrastructure costs are often very high, the owners of these large systems are moving towards ever higher packaging densities, placing as much computing power as possible in each square foot of space.

[0002] The owners of complex systems such as server farms and data centers achieve high packaging density by packing more computer equipment in both horizontal and vertical directions. By way of example, the 5380 Server system produced by NCR Corporation is delivered with up to 512 computing nodes, each with as many as four CPUs, stacked in a cabinet that is only 77 inches tall by 24.5 inches wide by 40 inches deep.

[0003] While packing computer components this densely solves many of the problems facing the owners of such systems, it also creates another set of challenges, in particular the proper cooling of heat-generating components, especially the CPUs, within such systems. In attempting to alleviate these cooling problems, designers of this type of equipment use forced-air cooling techniques that are aimed at moving cold air from a cold-air source to the hot components inside the cabinet. Forced-air cooling comes in two basic forms—front-to-back cooling and bottom-to-top cooling. The form that is most appropriate in any particular hardware environment and configuration is governed by how the pieces of equipment are physically packaged and electrically connected together.

[0004] FIG. 1 is a side view of a server rack 100 that uses bottom-to-top cooling to accommodate the particular packaging needs of the components in the rack. As shown here, the rack 100 includes four vertically mounted rows of printed circuit assemblies, or electronic assemblies 110_{1 . . . N}, each having one or more heat-generating components, such as the central processing units (CPUs) 115_{1 . . . M}. Thermal energy dissipated by the CPUs 115_{1 . . . M} and other active and heat-dissipating integrated circuit devices on the electronic assemblies 110_{1 . . . N} is removed from the electronic assemblies 110_{1 . . . N} by a flow 160 of cooling air that moves from the bottom of the rack 100 to the top. As the air flows past these devices, the temperature of the air rises, so that the air at the top of the cabinet is considerably warmer than the air at the bottom. The cooling effect of the air is bolstered by fan trays 140_{1 . . . K} that serve to pull greater volumes of cool air through the rack, thereby increasing air-flow velocity over the CPUs 115_{1 . . . M} and other components on the electronic assemblies 110_{1 . . . N}. Nevertheless, the air passing over the components at the top of the rack 100 is considerably warmer, and thus has less cooling capacity, than the air passing over components at the bottom of the rack 100. With electronic components, particularly CPUs, growing increasingly hotter with normal operation, cooling is quickly becoming the deciding factor in determining the vertical density of a server rack.

[0005] An electronic hardware cabinet includes a forced-air component positioned to force a stream of air to move through the cabinet, and at least two electronic assemblies, mounted within the cabinet, each of which includes a heat-generating component. The electronic assemblies are positioned so that a portion of the stream of air is heated by a first one of the heat-generating components and, thereafter, that portion of the stream of air moves toward a second one of the heat-generating components. An airflow diverter is positioned between the electronic assemblies to deflect that portion of the stream of air heated by the first heat-generating component to prevent it from reaching the second heat-generating component.

[0006] In some systems, the airflow diverter is positioned to direct the portion of the stream of air heated by the heat-generating component into a hot-air path in the cabinet, and it often includes one or more walls or surfaces that taper toward the hot-air path. This hot-air path often includes a channel that is formed between at least one of the electronic assemblies and a wall of the cabinet. The cabinet often includes a hot-air exhaust port through which air in the hot-air path exits the cabinet.

[0007] In other systems, the airflow diverter is positioned also to direct that portion of the stream of air toward the first one of the heat-generating components before the first one of the heat-generating components heats it. Often that portion of the stream of air is directed from a cool-air path. This cool-air path often includes a channel that is formed between at least one of the electronic assemblies and a wall of the cabinet. The cabinet often includes of a cool-air inlet port through which the portion of the stream of air in the cool-air path enters the cabinet.

[0008] In some systems the airflow diverter is positioned also to direct another portion of the stream of air toward the second heat-generating component.

[0009] In another aspect, an electronic hardware cabinet includes a forced-air component positioned to force a stream of air to move through the cabinet, and at least two vertically stacked electronic assemblies, mounted within the cabinet, each of which include a heat-generating component. The electronic assemblies are stacked so that a portion of the stream of air is heated by a first heat-generating component on a lower electronic assembly, and, thereafter, that portion of the stream of air moves towards a second heat-generating component on a higher electronic assembly. An airflow diverter is positioned to deflect that portion of the stream of air, heated by the first heat-generating component, to prevent it from reaching the second heat-generating component.

[0010] In some systems, the airflow diverter is positioned beside the lower electronic assembly, while in other systems it is positioned between the lower electronic assembly and the higher electronic assembly. In both of these systems, the airflow diverter is positioned to direct the portion of the stream of air heated by the first heat-generating component along a hot-air path in the cabinet.

[0011] In another aspect, an electronic hardware cabinet includes a forced-air component positioned to force a stream of air to move through the cabinet and at least two groups of electronic assemblies stacked vertically within the cabinet, one above the other. Each of the electronic assemblies in each group has at least one heat-generating component. Multiple airflow diverters are placed among the electronic assemblies to deflect a portion of the stream of air, heated by the heat-generating components in one group, to prevent it from reaching the heat-generating components in the other group.

[0012] In some systems the airflow diverters are positioned between the electronic assemblies in the group that is lower in the cabinet, while in other systems, the airflow diverters are positioned between the two groups of electronics assemblies.

[0013] In other aspects, an electronic hardware cabinet includes a forced-air component positioned to force a stream of air through the cabinet and a first and second electronic assembly, both having a heat-generating component. A first airflow diverter is positioned to direct at least a first portion of the stream of air over the heat-generating component on the first electronic assembly, thereby heating the first portion of the stream of air. The airflow diverter is positioned such that the air stream, after it is heated, is directed away from the second assembly.

[0014] In some systems, the first airflow diverter directs the heated first portion of the stream of air into a hot-air path in the cabinet. Often the cabinet also includes a third electronic assembly having a third heat-generating component and a second airflow diverter. This second airflow diverter is positioned to direct a second portion of the stream of air over the heat-generating component on the second electronic assembly, thereby heating the second portion of the stream of air. After the second portion of the stream of air is heated, the second airflow diverter directs it away from the third electronic assembly and into the hot air path.

[0020] FIG. 2 shows a hardware cabinet 200 that includes a housing 205 and one or more electronic-component assemblies, or simply “electronic assemblies” 210_{1 . . . N}, mounted within the housing 205. The cabinet 200 includes a mounting frame 220, or “rack,” to which the electronic assemblies 210_{1 . . . N} mount. In most systems, the electronic assemblies 210_{1 . . . N} are mounted in groups 230_{1 . . . R}, side-by-side, at various heights within the cabinet 200. For each of the groups 230_{1 . . . R} of electronic assemblies, the cabinet 200 includes an airflow-assistance mechanism, such as an array of fans, or fan tray 240_{1 . . . K}, which forces cool air over the electronic assemblies 210_{1 . . . N} in the group. In most systems, the fan trays 240_{1 . . . K} sit below one of the groups 230_{1 . . . R} of electronic assemblies.

[0021] Between each of the groups 230_{1 . . . R} of electronic assemblies is an airflow diverter, such as one of the airflow baffles 250_{1 . . . P}, that directs air flowing through the electronic assemblies 210_{1 . . . N} along desired paths. In general, a stream 260 of cold air enters the cabinet through an opening, or intake port 270, in the housing 205 and passes through a cold-air chimney 275. The fan trays 240_{1 . . . K} siphon cold air from the cold-air stream 260 and force the cold air over the electronic assemblies 210_{1 . . . N} in each of the corresponding groups 230_{1 . . . R}. As the cold air moves over the electronic assemblies 210_{1 . . . N} in the each of the groups 230_{1 . . . R}, the air removes heat that is generated by active components within the electronic assemblies. In doing so, the air itself heats up, typically to the point that it retains little or no cooling potential. However, instead of allowing this heated air to pass over electronic assemblies elsewhere in the cabinet 200, the airflow baffles 250_{1 . . . P} direct the heated air away from the other assemblies and into a hot-air stream 280 that forms within a hot-air chimney 285. The hot-air stream 280 exits the cabinet 200 through another opening, an exhaust port 290, formed in the housing 205.

[0022] The airflow baffles 250_{1 . . . P} are mounted within the cabinet 200 in any one of a variety of ways. For instance, in some systems the airflow baffles 250_{1 . . . P} comprise an integral part of the mounting frame 220. In other systems, an existing mounting frame 220 is retrofitted with airflow baffles 250_{1 . . . P}. Alternatively, in many systems, one end of the airflow baffle 250_{1 . . . P} fastens to one or more of the electronic assemblies 210_{1 . . . N} within one of the groups 230_{1 . . . R} and the opposing end of the airflow baffle 250_{1 . . . P} fastens to the adjacent fan tray 240_{1 . . . K}. Mounting the airflow baffles 250_{1 . . . P} within the cabinet 200 in a manner such as these provides an effective mechanism for ensuring that each of the groups 230_{1 . . . R} of electronic assemblies, regardless of its location within the cabinet, has access to cold air from the cold-air stream 260 without interference from the hot exhaust air generated elsewhere in the cabinet.

[0023] FIG. 3 also shows a hardware cabinet 300 that includes a housing 305 and one or more electronic assemblies 310_{1 . . . N} mounted within the housing 305. This cabinet also includes a mounting frame, or “rack” 320, to which the electronic assemblies 310_{1 . . . N} mount. The electronic assemblies 310_{1 . . . N} are mounted in groups 330_{1 . . . R} side-by-side, at various levels within the cabinet 300, and for each of the groups 330_{1 . . . R} an airflow assistance mechanism, such as one of the fan trays 340_{1 . . . K}, forces cool air over the electronic assemblies 310_{1 . . . N} of that group. The fan trays 340_{1 . . . K} typically sit below the electronic assemblies 310_{1 . . . N} of each of the groups 330_{1 . . . R}.

[0024] Mounted on each of the electronic assemblies 310_{1 . . . N} is at least one heat-dissipating component, such as one of the CPUs 315_{1 . . . M}. In terms of CPU placement, all the electronic assemblies 310_{1 . . . N} are typically (though not always) identical or nearly identical. An airflow diverter, such as one of the airflow baffles 350_{1 . . . P} is positioned adjacent to each electronic assembly to form a duct around the corresponding CPU 315_{1 . . . M}. The duct formed by each of the airflow baffles 350_{1 . . . P} directs cool air over one of the CPUs 315_{1 . . . M} and then away from that CPU and the corresponding electronic assembly. At least some portion of each of each of the airflow baffles 350_{1 . . . P} is angled to direct the air that is heated by the CPU 315_{1 . . . M} away form other CPUs sitting higher in the cabinet 300. While the system described here shows airflow baffles 350_{1 . . . P} around all CPUs 315_{1 . . . M} at all levels in the cabinet, some systems do not include airflow baffles for all the CPUs.

[0025] As with the system in FIG. 2, a stream of cold air 360 enters the cabinet 300 of FIG. 3 through one or more openings in the bottom of the housing 305, and the fan trays 340_{1 . . . K} drive cold air from the cold air stream 360 over the electronic assemblies 310_{1 . . . N}. As the cold air moves over the electronic assemblies 310_{1 . . . N} in each of the groups 330_{1 . . . R}, the airflow baffles 350_{1 . . . P} direct cool air over each of the CPUs 315_{1 . . . M} to remove heat generated by those components. The design of the airflow baffles 350_{1 . . . P} in FIG. 3 allows each airflow baffle to direct the newly heated air away from other CPUs and heat-generating components at higher levels in the cabinet 300 and into a hot-air stream 380 that bypasses those components. Ultimately, the heated air from the hot-air stream 380 exits the cabinet 300 through one or more openings formed in the housing 305, usually at the top of the housing.

[0026] The airflow baffles 350_{1 . . . P} mount to the electronic assemblies 310_{1 . . . N}, forming an angled duct around each of the CPUs 315_{1 . . . M}. The airflow baffles 350_{1 . . . P} are mounted in any one of a variety of ways. For instance, in some systems each of the airflow baffles 350_{1 . . . P} may consist of two individual wall portions mounted to one of the electronic assemblies 310_{1 . . . N}, one on either side of the CPU. The individual wall portions extend from each of the electronic assemblies 310_{1 . . . N} to the backside of an adjacent electronic assembly, defining an air duct around each of the CPUs 315_{1 . . . M}. In other systems, each of the airflow baffles 350_{1 . . . P} consists of a housing mounted to each of the electronic assemblies 310_{1 . . . N} over the corresponding CPU 315_{1 . . . M} to form a duct around that CPU. Alternatively, in some systems the airflow baffles 350_{1 . . . P} mount directly to the component rack 320 and not to the electronic assemblies 310_{1 . . . N} themselves. Mounting the airflow baffles 350_{1 . . . P} in these or equivalent manners provides an effective mechanism for ensuring that each of the CPUs 315_{1 . . . M} on each of the electronic assemblies 310_{1 . . . N}, regardless of its location within the cabinet 300, has access to cold air without interference from the hot exhaust air generated by CPUs 315_{1 . . . M} lower in the cabinet.

[0027] FIG. 4 shows a hardware cabinet 400 that includes a housing 405, a rack 420, electronic assemblies 410_{1 . . . N} mounted in groups 430_{1 . . . R}, CPUs 415_{1 . . . M} and fan trays 440_{1 . . . K}, all of which are arranged identically to the corresponding components of FIG. 3. FIG. 4 also depicts airflow diverters, or airflow baffles 450_{1 . . . P}, associated with each of the electronic assemblies 410_{1 . . . N}.

[0028] At each level in the cabinet, the airflow baffles 450_{1 . . . P} force a cool air stream 460 to flow over the CPUs 415_{1 . . . M} at that level, which in turn heat the air flowing in the stream. Instead of allowing this heated air to pass over other CPUs higher in the cabinet 400, however, the airflow baffles 450_{1 . . . P} direct the heated air into a hot-air stream 480 that forms with in a hot-air chimney 485. The hot-air chimney 485 isolates the hot-air stream 480 from other CPUs and heat-generating components, directing the heated air from the hot-air stream 480 to exit the cabinet 400 through one or more exit ports formed in the housing 405, usually at the top of the housing.

[0029] The airflow baffles 450_{1 . . . P} in this embodiment form both an angled air duct 465_{1 . . . J} around each of the CPUs 415_{1 . . . M} and a hot-air chimney portion. The hot-air chimney portions formed by the airflow baffles 450_{1 . . . P} are interconnected with each other to form a hot-air chimney 485 that extends upward through the rack.

[0030] The airflow baffles 450_{1 . . . P} are mounted within the cabinet 400 in any one of a variety of ways. For instance, in some systems, each of the airflow baffles 450_{1 . . . P} may consist of three individual wall portions mounted to each of the electronic assemblies 410_{1 . . . N}. Two outer portions, or the tapered portion 452 and the chimney portion 454, define the outer boundary of each of the airflow baffles 450_{1 . . . P}. The tapered portion 452 tapers toward the chimney portion 454 for directing air into the hot-air chimney 485. The third individual wall portion, or inner wall 456, resides between the other two, defining a barrier between the angled air duct 465_{1 . . . J} on one side and the hot-air chimney 485 on the other side. These three individual wall portions typically extend from each of the electronic assemblies 410_{1 . . . N} to the backside of an adjacent electronic assembly, defining an air duct around each of the CPUs 415_{1 . . . M} and a hot-air chimney portion extending away from the electronic assembly.

[0031] In other systems, each of the airflow baffles 450_{1 . . . P} is a housing mounted to one of the electronic assemblies 410_{1 . . . N} over one of the CPUs 415_{1 . . . M} to form a duct around that CPU which leads to a hot-air chimney portion. In other systems, the airflow baffles 450_{1 . . . P} mount directly to the component rack 420. Mounting the baffles in a manner such as these provides an effective mechanism for ensuring that each of the CPUs 415_{1 . . . M} on each of the electronic assemblies 410_{1 . . . N}, regardless of its location within the cabinet 400, has access to cold air without interference from the hot exhaust air generated by CPUs lower in the cabinet.

[0032] FIG. 5 shows a hardware cabinet 500 that includes a housing 505, a rack 520, electronic assemblies 510_{1 . . . N} mounted in groups 530_{1 . . . R}, CPUs 515_{1 . . . M} and fan trays 540_{1 . . . K}, all of which are arranged identically to the corresponding components of FIG. 3 and FIG. 4. In most systems, associated with each of the electronic assemblies 510_{1 . . . N} is an airflow diverter, such as one of the airflow baffles 550_{1 . . . P} that forces air to flow over each of the corresponding CPUs 515_{1 . . . M} and then diverts the air into a hot-air stream 580 that forms within a hot-air chimney 585. The hot-air chimney 585 is formed between the cabinet wall 507 and the outer perimeter of the groups 530_{1 . . . R} of electronic assemblies, so that the hot-air stream 580 passes through a gap between the electronic assemblies 510_{1 . . . N} and the cabinet wall 507 and not over the electronic assemblies themselves. The hot-air stream 580 exits the cabinet 500 through one or more openings, such as an exhaust port 590, formed in the housing 505.

[0033] The airflow baffles 550_{1 . . . P} are mounted within the cabinet 500 in any one of a variety of ways. For instance, in some systems, the airflow baffles 550_{1 . . . P} comprise an integral part of the mounting frame 520, or an existing mounting frame 520 can be retrofitted with airflow baffles 550_{1 . . . P}. Alternatively, in other systems, the airflow baffles 550_{1 . . . P} include an individual angled wall portion mounted to each of the electronic assemblies 510_{1 . . . N} on the side of the CPU opposite the hot-air chimney 585. The individual wall portion extends from the each of the electronic assemblies 510_{1 . . . N} to the backside of an adjacent electronic assembly, defining a barrier between the CPU 515_{1 . . . M} on that electronic assembly and CPUs at higher levels within the hardware cabinet 500. In other systems, the each of the airflow baffles 550_{1 . . . P} consists of a housing mounted to each of the electronic assemblies 510_{1 . . . N} over each of the corresponding CPUs 515_{1 . . . M} to form a duct around the CPU. Mounting the airflow baffles 550_{1 . . . P} within the cabinet 500 in a manner such as these provides an effective mechanism for directing hot-air into the hot-air chimney 585 and for ensuring that each of the groups 530_{1 . . . R} of electronic assemblies, regardless of its location within the cabinet, has access to cold air from the cold-air stream 560 without interference from the hot exhaust air generated elsewhere in the cabinet.

[0034] The text above describes one or more specific embodiments of a broader invention. The invention also is carried out in a variety of alternative embodiments and thus is not limited to those described here.

[0035] For example, while the systems shown here are described in terms of cooling CPUs, the cooling techniques described are useful in cooling any type of heat-dissipating component in a hardware cabinet.

[0036] Also, while the systems shown here each include a fan tray for each group of electronic assemblies, the described techniques work just as well for systems having a single fan tray of single fan for the entire cabinet. In such an embodiment, the single fan or single fan tray can be located at any suitable location, either inside or outside of the cabinet.

[0037] Likewise, while the systems shown here all involve a flow of air from the bottom to the top of the cabinet, the described techniques are equally useful for systems in which air flows in other directions, such as front to back. Also, while the embodiments of FIG. 3, FIG. 4 and FIG. 5 are all described separately, the structures they show are equally useful when used in any combination within a single hardware cabinet.

[0038] Moreover, while several of the specific embodiments indicate using cool air or cold air, a person skilled in the art will understand that these terms include not only air that has been mechanically and/or chemically cooled, but also air that is taken from the surrounding ambient environment.

[0039] Many other embodiments are also within the scope of the following claims.