Method and system for cooling electronic equipment

Abstract

A system includes electronic equipment, a device arranged to cool air using a refrigerant, the device secured to one of a top side and a bottom side of the electronic equipment, and a housing arranged to enclose the electronic equipment and the device, where the cooled air is propagated from one of the top side and the bottom side of the electronic equipment to the other one of the top side and the bottom side of the electronic equipment.

Description

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a typical server room.

FIG. 2 shows a typical technique for cooling electronic equipment.

FIG. 3A shows a cooling system in accordance with an embodiment of the invention.

FIG. 3B shows a cooling system in accordance with an embodiment of the invention.

FIG. 4A shows a cooling system in accordance with an embodiment of the invention.

FIG. 4B shows a cooling system in accordance with an embodiment of the invention.

FIG. 5 shows a cooling system in accordance with an embodiment of the invention.

FIG. 6 shows a flowchart for cooling a cooling system in accordance with an embodiment of the invention.

FIG. 7 shows a server room in accordance with an embodiment of the invention.

FIG. 8 shows a cooling system in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Exemplary embodiments of the invention will be described with reference to the accompanying figures. Like items in the figures are shown with the same reference numbers. Further, the use of “ST” in the figures is equivalent to the use of “Step” in the detailed description below.

In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention.

Embodiments of the invention relate to a system and method for cooling electronic equipment. More specifically, one or more embodiments of the invention relate to electronic equipment that is cooled by air that flows from or to a top side of the electronic equipment to or from a bottom side of the electronic equipment, where the air is cooled by a heat exchanger secured to at least one of a top side and a bottom side of the electronic equipment.

FIG. 3A shows an exemplary system in accordance with an embodiment of the invention. Specifically, FIG. 3A shows a section of a cross-sectional front view of a housing 310. In one or more embodiments if the invention, housing 310 is a cabinet containing one or more server racks. The housing 310 houses blowing devices 302, heat exchanger 304, and electronic equipment 306. Connected to heat exchanger 304 are refrigerant lines 312 and 314.

In FIG. 3A, blowing devices 302 direct air downward, as indicated by arrows, in a channel enclosed by the walls of housing 310, through heat exchanger 304 and electronic equipment 306. Blowing devices 302 may be, for example, fans used to propagate air in the channel in housing 310. One skilled in the art will appreciate that while two (2) blowing devices 302 are shown in the exemplary embodiment of FIG. 3A, any number of blowing devices may be present. Additionally, if air is forced through housing 310 by an external source, blowing devices 302 may not be present.

Air is directed by blowing devices 302 to an air-liquid heat exchanger 304 secured to a top side of the electronic equipment 306. The air-liquid heat exchanger 304 uses a refrigerant supplied to it through refrigerant line 312 to cool air directed to the air-liquid heat exchanger 304. This process results in (i) heating the entering refrigerant, where the resulting warm refrigerant is directed away from the air-liquid heat exchanger 304 through refrigerant line 314 and (ii) returning cold air to the channel in housing 310. The resulting cold air flows to a top side of electronic equipment 306. Blowing devices 302 direct this cold air through electronic equipment 306 and out a bottom side of electronic equipment 306.

A refrigerant used in one or more embodiments of the invention may be a liquid or a gas. For example, a refrigerant may be air, ammonia, water, or carbon dioxide.

As shown in FIG. 3A, a technique for cooling electronic equipment in an embodiment of the invention involves the flow of air from a top side of the electronic equipment to a bottom side of the electronic equipment. Those skilled in the art will note that in such an embodiment, the front and back sides of the electronic equipment are accessible without disrupting air flow in components of the electronic equipment whether or not being accessed.

One skilled in the art will appreciate that while air flow in FIG. 3A is from top to bottom, air may also flow from bottom to top in a housing. Further, one skilled in the art will appreciate that a server rack or other housing of electronic equipment may have multiple electronic components or groups of electronic components that need to be cooled. In other words, electronic components may be stacked serially, on top of each other. The number of electronic components to be cooled is limited only by be the size of the housing and the cooling requirements of each component. Thus, if the cooling requirements of multiple electronic components may be met by a single blower unit, multiple electronic components may be stacked serially, with or without one or more heat exchangers and/or fans.

FIG. 3B shows an exemplary system in accordance with an embodiment of the invention where air is directed from bottom to top. In FIG. 3B, blowing devices 316 direct air upward, as indicated by arrows, in the channel enclosed by walls of housing 322. This may be accommodated by, for example, reversing the direction of flow of blowing devices 316, or by reversing the orientation of blowing devices 316.

Similar to the system shown in FIG. 3A, housing 322 houses blowing devices 316, heat exchanger 320, and electronic equipment 318a, 318b. Refrigerant lines 324 and 326 are connected to heat exchanger 320. In this embodiment, blowing devices 316 direct air upward in a channel enclosed by the walls of housing 322, after having passed through heat exchanger 320 and electronic equipment 318a, 318b. As discussed with respect to FIG. 3A, one skilled in the art will appreciate that while two (2) blowing devices 316 are shown in the exemplary embodiment of FIG. 3B, any number of blowing devices may be present. Additionally, if air is forced through housing 310 by an external source, blowing devices 302 may not be necessary.

Air is directed by blowing devices 316 to air-liquid heat exchanger 304 secured to a bottom side of the electronic equipment 306. The air-liquid heat exchanger 320 uses a refrigerant supplied to it through refrigerant line 324 to cool air directed to the air-liquid heat exchanger 320. As discussed with reference to FIG. 3A, this process results in (i) heating the entering refrigerant, where the resulting warm refrigerant is directed away from the air-liquid heat exchanger 320 through refrigerant line 326 and (ii) returning cold air to the channel in housing 322. The resulting cold air flows to a bottom side of electronic equipment 318a. Blowing devices 316 direct this cold air through electronic equipment 318a, out a top side of electronic equipment 318a, and to a bottom side of electronic equipment 318b. Air then flows through electronic equipment 318ba and out a top side of electronic equipment 318b.

As shown above, a server rack or other housing of electronic equipment may have multiple electronic components or groups of electronic components that need to be cooled. Similarly, multiple blowing units and heat exchangers may be present in a given housing. Further, electronic components may be stacked serially, on top of other electronic components. While the devices in FIGS. 3A and 3B are shown in a particular order, one skilled in the art will appreciate that electronic components 306, 318a, 318b may still be cooled when the devices are placed in a different order. For example, in FIG. 3A, electronic equipment 306 may be placed on top of heat exchanger 304, which may be placed on top of blowing devices 302, with air flow still passing from top to bottom in housing 322. Similarly, other configurations are possible with respect to FIGS. 3A and 3B which do not depart from the scope of the invention.

FIG. 4A shows cross-sectional side view of a cooling system in accordance with an embodiment of the invention. In this embodiment, a housing 408 houses multiple groups of electronic equipment 406a, 406b, and 406c. To accommodate for the additional electronic equipment, additional cooling devices and blowing devices may be necessary.

Similar to the system shown in FIG. 3B, housing 408 houses blowing devices 402a, 402b, 402c, heat exchangers 404a, 404b, 404c, 404d, and electronic equipment 406a, 4026, 406c. Refrigerant lines (not shown) are connected to heat exchangers 404a, 404b, 404c, 404d. In this embodiment, blowing devices 402a, 402b, 402c direct air upward in a channel enclosed by the walls of housing 408, after having passed through heat exchangers 404a, 404b, 404c, and electronic equipment 406a, 4026, 406c, respectively. As discussed with respect to FIG. 3A, one skilled in the art will appreciate that while two (2) blowing devices (e.g., 402c) are shown in the exemplary embodiment of FIG. 3B, any number of blowing devices may be present. Additionally, if air is forced through housing 408 by an external source, blowing devices (e.g., 402c) may not be necessary.

In FIG. 4A, air enters the bottom side of housing 408, as indicated by arrows. Air is directed by blowing devices 402a to air-liquid heat exchanger 404a secured to a bottom side of electronic equipment 406a. The air-liquid heat exchanger 404a uses a refrigerant supplied to it through a refrigerant line (not shown) to cool air directed to the air-liquid heat exchanger 404a. As discussed with reference to FIG. 3A, this process results in (i) heating the entering refrigerant, where the resulting warm refrigerant is directed away from the air-liquid heat exchanger 404a through another refrigerant line (not shown) and (ii) returning cold air to the channel in housing 408. The resulting cold air flows to a bottom side of electronic equipment 406a. Blowing devices 402a direct this cold air through electronic equipment 406a and out a top side of electronic equipment 406a.

The resultant cooling of electronic equipment 406a means the air that leaves the top side of electronic equipment 406a has been heated, and must be cooled again before it can be used to cool electronic equipment. Thus, a second air-liquid heat exchanger 404b is used to cool air that leaves the top side of electronic equipment 406a. Blowing devices 402a and 402b direct air that leaves the top side of electronic equipment 406a to second air-liquid heat exchanger 404a. From this point, the remaining components function in a manner similar to heat exchanger 404a, electronic equipment 406a, and blowing devices 402a, as discussed above. Air that leaves electronic equipment 406c may additionally pass through blowers 402c and heat exchanger 404d depending on requirements for the housing 408 or the room in which housing 408 is located. Alternatively, these components may not be present.

Further, while air is shown as being directed from bottom to top in the exemplary embodiment of the invention shown in FIG. 4A, one skilled in the art will appreciate that, as discussed with respect to FIG. 3A, components shown in FIG. 4A may be configured such that air flows from top to bottom in housing 408. Heat exchanger 404d allows air to be cooled before entering electronic equipment 406c in such a case.

In one or more embodiments of the invention, one or more air plenums may be implemented along the top and/or the bottom sides of a housing. Particularly, FIG. 4B shows a cross-sectional side view of a housing 418 having a plenum 410 located at the top of housing 418. The housing 418 contains electronic equipment 416a, 416b, 416c, heat exchangers 414a, 414b, 414c, 414d, and blowing units 412a, 412b, 412c, 412d, 412e, 412f. Within the front half of housing 418, air heated by heat dissipation from the electronic equipment 416a, 416b, 416c is directed by blowing devices 412a, 412b, 412c to air-liquid heat exchangers 414a, 414b, 414c. The air-liquid heat exchangers 414a, 414b, 414c use cold refrigerant to cool the hot air directed to the air-liquid heat exchanger 414a, 414b, 414c. This process results in (i) heating the entering refrigerant, where the resulting warm refrigerant is directed away from the housing 418 and (ii) returning cold air to a front side of the housing 418.

After passing through the front half of electronic equipment 416c and cooling the front half of electronic equipment 416c, the resultant heated air flows to the front side of heat exchanger 414d and is cooled as described above. Then, the cold air flows back around (via an air plenum 410 along a top side of the housing 418) to a rear side of the housing 418. Blowing devices 412c, 412d direct the cold air captured in the air plenum implemented along the front side of the housing 418 to the rear side of heat exchanger 414d and through electronic equipment 416c, from top to bottom.

After passing through the rear side of electronic equipment 416c and cooling the rear half of electronic equipment 416c, the resultant heated air flows to the rear side of heat exchanger 414c and is cooled. The air-liquid heat exchanger 414c uses a refrigerant supplied to it through a refrigerant line (not shown) to cool air directed to the air-liquid heat exchanger 414c. This process continues similarly with the rear halves of electronic equipment 416b and 416a. After passing through the rear half of electronic equipment 416a and cooling the rear half of electronic equipment 416a, the resultant heated air flows to the front side of heat exchanger 414a and is cooled as described above. Air then exits the housing 418 through the bottom of housing 418 after passing through heat exchanger 414a.

One skilled in the art will appreciate that a partition may be implemented in order to separate air channels in a housing and facilitate better air circulation. Further, one skilled in the art will appreciate that like plenum 410, a plenum may similarly be implemented on the bottom side of housing 418. Thus, air may enter the top of a housing, circulate from top to bottom through one portion of a housing, pass through a plenum at the bottom of the housing, and circulate from bottom to top through another portion of the housing. After passing through the housing in such a circuit, air may leave the top of the housing.

Alternatively, a plenum may be implemented at the top and at the bottom of a housing. FIG. 5 shows an exemplary housing in accordance with one embodiment of the invention. Specifically, FIG. 5 shows a front cross-sectional view of a housing 500 having a plenum 510 at the top of the housing 500 and a plenum 512 at the bottom of the housing. Additionally, housing 500 includes a partition 514 separating a right portion of electronic equipment 506a, 506b, 506c, heat exchangers 504a, 504b, 504c, 504d, 504e, 504f, and blowing units 502a, 502b, 502c, 502d from a left portion of electronic equipment 506d, 506e, 506f, heat exchangers 504g, 504h, 504i, 504j, 504k, 504l, and blowing units 502e, 502f, 502g, 502h.

In FIG. 5, air passes through the heat exchangers and electronic equipment as shown by arrows and as described above with reference to FIGS. 3A and 3B. For example, in FIG. 5, blowing devices 502c and 502d direct cold air through a first channel, from top to bottom, to electronic equipment 506c. Air that cools electronic equipment 506c exits a bottom side of electronic equipment 506c. This air, which is heated by electronic equipment 506c, passes through heat exchanger 504f and is cooled. Blowing devices 502d and 502e direct air through air plenum 512 from a right side of housing 500 to a left side of housing 500. Thus, air is then directed from bottom to top in a second channel. This air is directed through heat exchanger 504g, where it is cooled. The process of cooling electronic equipment continues until air reaches heat exchanger 504l. After leaving heat exchanger 504l, air is directed by blowing units 502h, 502a through plenum 510, from a left side of cabinet 500 to a right side of cabinet 500, where it re-enters the first channel on the right side of housing 500.

In FIG. 5, partition 514 separates a top-to-bottom airflow on the right side of the cabinet 500 from a bottom-to-top airflow on the left side of the cabinet 500. Further, when air reaches the end of a channel, it passes through a plenum to another channel, where the direction of air flow is reversed. In this manner, a closed loop of circulating air may be contained in housing 500. One skilled in the art will appreciate that while air circulates in a clockwise direction in the exemplary embodiment of the invention shown in FIG. 5, blowing units, heat exchangers, and/or electronic equipment may be configured such that air passes through a housing in a counterclockwise direction.

One skilled in the art will appreciate that a single housing may be partitioned into front and rear halves as well as right and left halves, depending on the size of the housing and the cooling requirements of the electronic equipment contained therein.

FIG. 6 shows a flowchart in accordance with an embodiment of the invention. Specifically, FIG. 6 shows a method for cooling electronic equipment in accordance with an embodiment of the invention. Initially, refrigerant is supplied to a heat exchanger in a first channel of a housing associated with particular electronic equipment (Step 602). Air in the channel or air that has recently entered the housing passes vertically through the heat exchanger to cool the air (Step 604). As discussed above, for example, with reference to FIGS. 3A and 3B, air may pass from bottom to top or from top to bottom through a heat exchanger. After passing through the heat exchanger, air is directed in the same direction through electronic equipment in the housing to cool the electronic equipment (Step 606). One skilled in the art will appreciate that air that passes through the electronic equipment to cool the electronic equipment results in the air being heated in the process.

If a second heat exchanger is associated with the electronic equipment (Step 608), refrigerant is supplied to the second heat exchanger (Step 610) in the same manner as refrigerant is supplied to the first heat exchanger. Similarly, air passes through the second heat exchanger (Step 612) as described in Step 604. Even if a second heat exchanger is not present (Step 608), a plenum may exist in the housing. If a plenum does not exist in the housing (Step 614), the process ends. If a plenum is present (Step 614), air is directed through the plenum to a second channel in the housing (Step 616). In one or more embodiments of the invention, the plenum is designed such that after air passes through the plenum, air moves in a direction opposite the direction of the air in the first channel. Once the above process ends, it may be repeated as necessary to adequately cool all electronic equipment in the housing.

In one or more embodiments of the invention, air flow through some components in electronic equipment may be from top to bottom, while air flow through other components in the electronic equipment may be from bottom to top. This may be achieved by, for example, creating particular air plenums to force the direction of air in the housing.

Those skilled in the art will note that in one or more embodiments of the invention, a component in electronic equipment in a housing may be accessed without disrupting the cooling air flow of other components in the electronic equipment. As described above, in conventional front-to-back air flow cooling, a server room has to be equipped with adequate air conditioning so as to maintain cooling of even those components that are not being accessed when a front or back door of the housing is opened to access a particular component.

Accordingly, in one or more embodiments of the invention, separate air conditioning may not be required as components not being accessed remain air cooled by the same process occurring when the housing doors are closed. FIG. 7 shows an exemplary server room 706 in accordance with an embodiment of the invention. In FIG. 7, server room 706 has two housings 702, 704. Each of the housings 702, 704 is connected to refrigerant lines 710, 712 that are connected to a chiller unit 708. As discussed above, air may recirculate within the housings or in the room in which the housings are located.

Further, in one or more embodiments of the invention, if a refrigerant is not available in a particular server room, the electronic equipment may still be situated in the server room by removing any air-liquid heat exchangers. In such embodiments, air in the housing would flow from the top/bottom of the electronic equipment to the bottom/top of the electronic equipment using, for example, fans implemented with the electronic equipment and/or fans implemented within the server room.

Further, one or more embodiments of the invention described above may be used in conjunction with one or more other means of cooling electronic equipment. For example, as shown in FIG. 8, a housing 810 in accordance with one or more embodiments of the invention houses blowing devices 802, heat exchanger 804, and electronic equipment 806. Connected to heat exchanger 804 are refrigerant lines 812 and 814. Also within housing 810 are air flow channels 814a, 814b, separated by a baffle. Further, within electronic equipment 806 is liquid cooler 816.

Operatively, blowing devices 802, heat exchanger 804, and electronic equipment 806 function similarly to blowing devices 302, heat exchanger 304, and electronic equipment 306, described with reference to FIG. 3A. In one or more embodiments of the invention, air flow channels 818a, 818b are configured to allow air to flow from front to back or from back to front in housing 810, and liquid cooler 816 is configured to cool individual electronic components (e.g., a processor in the electronic equipment 806). Thus, in one or more embodiments of the invention, air flow channels 818a, 818b may cool electronic devices near the sides of housing 810, and liquid cooler 816 may cool individual electronic components, in conjunction with blowing devices 802, heat exchanger 804, and electronic equipment 806. One skilled in the art will appreciate that air flow channels 818a, 818b may be used independently from liquid cooler 816, and additionally that other similar means of cooling electronic equipment may be used in conjunction with the aforementioned components.

Advantages of the invention may include one or more of the following. In one or more embodiments of the invention, electronic equipment is cooled using air that is cooled using an air-liquid heat exchange in a housing.

In one or more embodiments of the invention, the ability to air cool electronic equipment using cooled air may be used to cool electronic equipment having increased heat dissipation.

In one or more embodiments of the invention, because electronic equipment is cooled from top-to-bottom or bottom-to-top, space on the sides of the electronic equipment that would be used to facilitate other methods of cooling (e.g., space needed for air holes) may be instead used for connectors (e.g., power connections, input/output connections), or may be removed to reduce the footprint of the housing (i.e., the surface area used on the floor of the room in which the housing is located). Further, in one or more embodiments of the invention, an air plenum may be removed from one or more sides, a top or a bottom of a housing. Further, in one or more embodiments of the invention, typical data center requirements such as cooling coils and raised floor or ceiling space or air plenums may not be necessary.

In one or more embodiments of the invention, because air holes are not needed in a housing in which air contained within the housing flows from one side to another side of electronic equipment in the housing, electromagnetic interference may be better contained.

In one or more embodiments of the invention, because electronic equipment is cooled from top-to-bottom or bottom-to-top, one or more components of the electronic equipment may be stacked, and one or more components of the electronic equipment may be serviced/accessed without disrupting air flow in other components. This obviates the need for a separate air cooling mechanism to cool those other components were air flow directed from one side of the electronic equipment to another side of the electronic equipment.

In one or more embodiments of the invention, because electronic equipment is cooled from top-to-bottom or bottom-to-top, a smaller volume of air is moved. Further, in one or more embodiments of the invention, because electronic equipment is cooled from top-to-bottom or bottom-to-top, less air needs to be circulated to cool electronic equipment. Further, in one or more embodiments of the invention, because electronic equipment is cooled from top-to-bottom or bottom-to-top, air may be reused in a given stack of electronic equipment.

In one or more embodiments of the invention, because electronic equipment is housed in a housing that uses air to cool the electronic equipment, where the air is contained within the housing, noise suppression of the electronic housing may be improved.

In one or more embodiments of the invention, a housing is less dependent on an air flow rate or an air flow space of a server room than a housing which requires air flow in the server room to cool the electronic equipment in the housing either during normal operation or servicing.

In one or more embodiments of the invention, because electronic equipment in a housing is cooled by cold air, there may be less of a risk of water or refrigerant leakage.

In one or more embodiments of the invention, electronic equipment in a housing may be operated in a server room having only a power supply and a chiller unit (for communicating refrigerant with the housing).

In one or more embodiments of the invention, multiple cooling system components may be implemented to provide levels of redundancy for electronic equipment in a housing.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

1. A system, comprising: electronic equipment;a device arranged to cool air using a refrigerant, the device secured to one of a top side and a bottom side of the electronic equipment; anda housing arranged to enclose the electronic equipment and the device,wherein the cooled air is propagated from one of the top side and the bottom side of the electronic equipment to the other one of the top side and the bottom side of the electronic equipment.

2. The system of claim 1, the electronic equipment comprising: one or more computer systems; anda chassis arranged to support the one or more computer systems.

3. The system of claim 1, wherein the refrigerant is at least one of water, air, ammonia, and carbon dioxide.

4. The system of claim 1, the housing comprising a first door arranged to allow access to a front side of the electronic equipment, and a second door arranged to allow access to a rear side of the electronic equipment.

5. The system of claim 1, further comprising: at least one air flow channel separated from the cooled air by at least one baffle; anda liquid cooling unit configured to cool a processor in the electronic equipment.

6. The system of claim 1, further comprising: at least one blowing device implemented at one of the top side and the bottom side of the electronic equipment.

7. The system of claim 1, the housing comprising: an air plenum implemented along one or more of a top side and a bottom side of the housing.

8. The system of claim 1, further comprising: a chiller unit operatively connected to the housing, the chiller unit arranged to supply the refrigerant.

9. A method of cooling electronic equipment, comprising: supplying a refrigerant to a device secured to the electronic equipment in a first channel;generating cold air by using the device to cool air that passes vertically through the device;directing the cold air into one of a top side and a bottom side of the electronic equipment, wherein the cold air cools the electronic equipment; anddirecting air heated by the electronic equipment to the other of the top side and the bottom side of the electronic equipment.

10. The method of claim 9, further comprising: supplying refrigerant to a second device secured to the electronic equipment in the first channel; andgenerating cold air by using the device to cool the air heated by the electronic equipment that passes vertically through the device.

11. The method of claim 9, further comprising: directing one of heated air and cold air through a plenum to a second channel, wherein the air in the second channel moves in a direction opposite that of air in the first channel.

12. The method of claim 9, further comprising: propagating air from one of the top side and the bottom side of the electronic equipment to the other of the top side and the bottom side of the electronic equipment.

13. The method of claim 9, wherein the refrigerant is one of water, air, ammonia, and carbon dioxide.

14. The method of claim 9, wherein the electronic equipment is housed in a housing.

15. An apparatus, comprising: electronic equipment in a first channel of a housing; anda heat exchanger secured to one of a top side and a bottom side of the electronic equipment, the heat exchanger arranged to cool air entering the heat exchanger;wherein the housing is arranged to house the electronic equipment and the heat exchanger, andwherein cold air generated by the heat exchanger is arranged to flow within the housing from one of the top side and the bottom side of the electronic equipment to the other one of the top side and the bottom side of the electronic equipment.

16. The apparatus of claim 15, further comprising: at least one blowing device implemented at one or more of the top side and the bottom side of the electronic equipment arranged to propagate the air within the housing.

17. The apparatus of claim 15, further comprising: a plenum implemented along at least one of a top side and a bottom side of the housing connecting the first channel and a second channel, wherein air in the second channel moves in a direction opposite that of air in the first channel.

18. The apparatus of claim 15, the electronic equipment comprising: a plurality of servers; anda rack arranged to support the plurality of servers.

19. The apparatus of claim 15, wherein the heat exchanger cools air dependent on a refrigerant.

20. The apparatus of claim 15, further comprising a front door of the housing arranged to allow access to a front side of the electronic equipment without affecting air circulation.