Abstract:
A hot/cold aisle air containment room includes a plurality of electronic equipment enclosures at least partially defining an interior aisle, a frame structure supporting one or more ceiling panels above the interior aisle, and a door assembly. The door assembly includes a sliding door and an unpowered door closer mechanism adapted to move the sliding door from an open state to a closed state, thereby providing controlled access to the interior aisle and minimizing intermixing of hot air and cold air between an environment external to the hot/cold aisle air containment room and an environment internal to the hot/cold aisle air containment room.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a U.S. non-provisional patent application of, and claims priority under 35 U.S.C. §119(e) to, U.S. provisional patent application Ser. No. 61/597,301, filed Feb. 10, 2012, which is expressly incorporated herein by reference in its entirety. Additionally, each of the following commonly-assigned U.S. patent applications, including any application publication thereof, is expressly incorporated herein by reference in its entirety:
       (a) U.S. provisional patent application Ser. No. 61/411,359, filed Nov. 8, 2010 and entitled, “ADJUSTABLE WALL ASSEMBLY FOR HOT/COLD AISLE CONTAINMENT SYSTEM,” attached hereto as Appendix A, which itself is expressly incorporated herein by reference in its entirety;   (b) U.S. provisional patent application Ser. No. 61/568,692, filed Dec. 9, 2011 and entitled, “DATA PROCESSING EQUIPMENT STRUCTURE;” and   (c) U.S. non-provisional patent application Ser. No. 13/707,521, filed Dec. 6, 2012 and entitled, “DATA PROCESSING EQUIPMENT STRUCTURE.”       
 
     
    
     COPYRIGHT STATEMENT 
       [0005]    All of the material in this patent document is subject to copyright protection under the copyright laws of the United States and other countries. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in official governmental records but, otherwise, all other copyright rights whatsoever are reserved. 
       BACKGROUND OF THE PRESENT INVENTION 
       [0006]    1. Field of the Present Invention 
         [0007]    The present invention relates generally to door assemblies for electronic equipment hot/cold aisle air containment rooms, and, in particular, to door assemblies having a door closer mechanism. 
         [0008]    2. Background 
         [0009]    Racks, frames and enclosures for mounting and storing computer and other electronic components or equipment have been well known for many years. Racks and frames are typically simple rectangular frameworks on which electronic components may be mounted, or on which other mounting members, such as shelves or brackets, may be mounted which in turn may support the electronic components. Enclosures are typically frames on which panels or doors, or both, are hung to provide aesthetic improvement, to protect the components from external influences, to provide security for the components stored inside, or for other reasons. 
         [0010]    Racks, frames and enclosures have been built in many different sizes and with many different proportions in order to best accommodate the components which they are designed to support and store. Components stored in these enclosures may include audio and video equipment and the like, but quite frequently include computer equipment and related peripheral devices. These components typically include housings enclosing internal operative elements. 
         [0011]    As is also well known, the electronic equipment mounted in these structures tends to generate large amounts of thermal energy that needs to be exhausted away from the equipment effectively in order to maintain the equipment in proper operating order or to prevent damage thereto. The problem can be especially significant when the components are enclosed in enclosures, because thermal energy generated thereby can concentrate within the equipment enclosure and cause the components to overheat and shut down. As equipment becomes more densely packed with electronics, the quantities of thermal energy have continued to increase in recent years, and thermal energy management has become a significant issue confronting today&#39;s rack, enclosure, frame and enclosure manufacturers, the manufacturers of the electronic equipment, and the users of such equipment. 
         [0012]    Typically, multiple racks, frames, enclosures, and the like (sometimes collectively referred to hereinafter as “enclosures”) are housed together in a data center room. Because of the overheating problem, and particularly with multiple enclosures being placed in a single room, thermal management of the data center room is very important. A goal of data center thermal management is to maximize the performance, uptime and life expectancy of the active components being housed in the room. Toward this end, data center rooms are often arranged so as to increase efficiency and optimize performance. 
         [0013]    One common way of organizing a data center room to meet these objectives involves arranging individual enclosures in rows, with the air intake of each enclosure facing toward one side of the row and the heated air exhaust of each enclosure facing toward the other side of the row. Rows of enclosures are arranged in back-to-back relationship so that enclosures of two separate rows receive cool intake air from a common “cold” aisle between the rows, exhaust heated air into a common “hot” aisle between the rows, or utilize a combination thereof. Various permutations of these arrangements are well known. 
         [0014]    When “cold” or “hot” aisle approaches are utilized, they must still accommodate human access into the aisle so as to access the enclosures themselves. In older implementations, no special walls or other structures are utilized to maximize separation of the aisles from the environment, but more recently, the cold and hot aisle effect has been enhanced through the use of such structures. In these implementations, it has become more necessary to provide doors for access to the interior of the aisles. This, in turn, has created a need for improvements in door assemblies to address such issues as doors being left open accidentally, but without creating additional power requirements. This and other needs are addressed by the present invention. 
       SUMMARY OF THE PRESENT INVENTION 
       [0015]    The present invention comprises a hot/cold aisle air containment room. Broadly defined, the present invention according to a first aspect includes a hot/cold aisle air containment room substantially as shown and described. 
         [0016]    Broadly defined, the present invention according to a second aspect includes a hot/cold aisle air containment room, having a door closer mechanism, substantially as shown and described. 
         [0017]    Broadly defined, the present invention according to a third aspect includes a hot/cold aisle air containment room that includes a pair of rows of electronic equipment enclosures defining an interior aisle therebetween, a frame structure supporting one or more ceiling panels above the interior aisle, and a door assembly. The door assembly includes one or more doors and has a door closer mechanism to provide controlled access to the interior aisle. 
         [0018]    In features of this aspect, the interior aisle may be a cold aisle; and/or the interior aisle may be a hot aisle. 
         [0019]    In further features of this aspect, the door closer mechanism may include a belt/pulley assembly supported by a rail extrusion of the door assembly; the belt/pulley assembly may include a damper pulley, a free pulley, and a timing belt routed around the damper pulley and the free pulley; the timing belt may be toothed; each of the damper pulley and the free pulley may include a cylindrical bearing surface having a series of teeth that interlock with the toothed timing belt; the one or more doors may be attached to the timing belt via a splice bracket and a belt splice plate, thereby allowing the one or more doors to be controlled relative to the timing belt; the door assembly may further include a return spring mounted on a spool to provide resistance to the one or more doors; a biasing force of the return spring may be resisted by the damper pulley; the damper pulley may be permitted to rotate freely in one direction and is damped in the other direction; the damper pulley may be permitted to rotate freely when the one or more doors are being opened; and/or the damper pulley may be damped when the one or more doors are being closed. 
         [0020]    Broadly defined, the present invention according to a fourth aspect includes a method of opening and closing one or more doors in a hot/cold aisle air containment room, substantially as shown and described. 
         [0021]    Broadly defined, the present invention according to a fifth aspect includes a hot/cold aisle air containment room. The hot/cold aisle air containment room includes a plurality of electronic equipment enclosures at least partially defining an interior aisle, a frame structure supporting one or more ceiling panels above the interior aisle, and a door assembly. The door assembly includes a sliding door and am unpowered door closer mechanism adapted to move the sliding door from an open state to a closed state, thereby providing controlled access to the interior aisle and minimizing intermixing of hot air and cold air between an environment external to the hot/cold aisle air containment room and an environment internal to the hot/cold aisle air containment room. 
         [0022]    In features of this aspect, the hot/cold aisle air containment room may be disposed within a room in a building; the interior aisle may be a cold aisle; and/or the interior aisle may be a hot aisle. 
         [0023]    In further features of this aspect, the plurality of electronic equipment enclosures may be arranged in a row, wherein the interior aisle includes two sides and two ends, and wherein the row of electronic equipment enclosures defines one side of the interior aisle; and/or the plurality of electronic equipment enclosures may be arranged in a pair of rows, and wherein the pair of rows of electronic equipment enclosures define opposite sides of the interior aisle. 
         [0024]    In further features of this aspect, the hot/cold aisle air containment room may further include one or more wall panels; the wall panels may at least partially define at least one end or side of the interior aisle; and/or the wall panels may be a part of the door assembly. 
         [0025]    In further features of this aspect, the door assembly may be disposed at one end of the interior aisle; the sliding door may be a first sliding door, wherein the door assembly includes a second sliding door, and wherein the unpowered door closer mechanism is adapted to move the first sliding door and the second sliding door simultaneously from an open state to a closed state; and/or the door closer mechanism may include a belt/pulley assembly supported by a rail assembly. 
         [0026]    In further features of this aspect, the belt/pulley assembly may include a damper pulley, a free pulley, and a belt routed around the damper pulley and the free pulley, wherein the sliding door is attached to the belt, thereby allowing the sliding door to be controlled relative to the belt; the belt may be a synchronous belt; the synchronous belt may be toothed; and/or each of the damper pulley and the free pulley may include a cylindrical bearing surface having a series of teeth that interlock with the toothed synchronous belt. 
         [0027]    In further features of this aspect, the hot/cold aisle air containment room may further include a pulley tensioning device; the sliding door may be attached to the belt via a splice bracket and a belt splice plate; the door assembly may further include a return spring mounted on a spool to provide resistance to the sliding door; and/or a biasing force of the return spring may be resisted by the damper pulley. 
         [0028]    In further features of this aspect, the damper pulley may be permitted to rotate freely in one direction and is damped in the other direction; the damper pulley may be permitted to rotate freely when the sliding door is being opened; and/or the damper pulley may be damped when the sliding door is being closed. 
         [0029]    In further features of this aspect, the rail assembly may include a main rail extrusion supporting at least one roller bracket assembly; each roller bracket assembly may include at least one roller that rides along a portion of the main rail extrusion and that supports a roller bracket which supports the sliding door; and/or the at least one roller may ride in a roller cavity in the main rail extrusion. 
         [0030]    In still further features of this aspect, a spring bracket may be attached at one end of the rail assembly, wherein a structure is provided that engages the spring bracket when the sliding door is moved to a fully open state; the structure may be disengageable from the spring bracket by pulling the door closed; and/or the hot/cold aisle air containment room may further include a roller bracket assembly that carries the door, wherein the structure is a portion of the roller bracket assembly. 
         [0031]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    Further features, embodiments, and advantages of the present invention will become apparent from the following detailed description with reference to the drawings, wherein: 
           [0033]      FIG. 1  is a front isometric view of a containment room having a double door assembly with a door closer mechanism in accordance with one or more preferred embodiments of the present invention; 
           [0034]      FIG. 2  is a rear isometric view of the containment room of  FIG. 1 , illustrating a single door assembly with a door closer mechanism in accordance with one or more preferred embodiments of the present invention; 
           [0035]      FIG. 3  is a front view of the double door assembly of  FIG. 1 , shown with the front cover of the rail assembly removed; 
           [0036]      FIG. 4  is a front view of the double door assembly of  FIG. 3 , shown with the doors in an open state; 
           [0037]      FIG. 5  is a fragmentary side cross sectional view of the rail assembly of  FIG. 4 , taken along line  5 - 5 ; 
           [0038]      FIG. 6  is a partially exploded isometric view of one of the roller bracket assemblies of  FIG. 3 ; 
           [0039]      FIG. 7  is an orthogonal view of the door closer mechanism of  FIG. 3 ; 
           [0040]      FIG. 8  is an exploded isometric view of the door closer mechanism of  FIG. 7 ; 
           [0041]      FIG. 9  is an isometric view of the damper pulley of  FIG. 8 ; 
           [0042]      FIG. 10  is an exploded isometric view of the damper pulley of  FIG. 9 ; 
           [0043]      FIG. 11  is an isometric view of the free pulley of  FIG. 8 ; 
           [0044]      FIG. 12  is an exploded isometric view of the free pulley of  FIG. 11 ; 
           [0045]      FIG. 13  is an isometric view of one of the belt splice brackets of  FIG. 8 ; 
           [0046]      FIG. 14  is an isometric view of one of the belt splice plates of  FIG. 8 ; 
           [0047]      FIG. 15  is an isometric view of the return spring of  FIG. 8 ; 
           [0048]      FIG. 16  is an isometric view of the return spring spool of  FIG. 8 ; 
           [0049]      FIG. 17  is an exploded fragmentary rear isometric view of portions of the left end of the rail assembly of  FIG. 4 ; and 
           [0050]      FIGS. 18 and 19  are enlarged fragmentary front cross-sectional views of the rail assembly of  FIG. 5 , taken along line  18 - 18 . 
       
    
    
     DETAILED DESCRIPTION 
       [0051]    As a preliminary matter, it will readily be understood by one having ordinary skill in the relevant art (“Ordinary Artisan”) that the present invention has broad utility and application. Furthermore, any embodiment discussed and identified as being “preferred” is considered to be part of a best mode contemplated for carrying out the present invention. Other embodiments also may be discussed for additional illustrative purposes in providing a full and enabling disclosure of the present invention. As should be understood, any embodiment may incorporate only one or a plurality of the above-disclosed aspects of the invention and may further incorporate only one or a plurality of the above-disclosed features. Moreover, many embodiments, such as adaptations, variations, modifications, and equivalent arrangements, will be implicitly disclosed by the embodiments described herein and fall within the scope of the present invention. 
         [0052]    Accordingly, while the present invention is described herein in detail in relation to one or more embodiments, it is to be understood that this disclosure is illustrative and exemplary of the present invention, and is made merely for the purposes of providing a full and enabling disclosure of the present invention. The detailed disclosure herein of one or more embodiments is not intended, nor is to be construed, to limit the scope of patent protection afforded the present invention, which scope is to be defined by the claims and the equivalents thereof. It is not intended that the scope of patent protection afforded the present invention be defined by reading into any claim a limitation found herein that does not explicitly appear in the claim itself. 
         [0053]    Thus, for example, any sequence(s) and/or temporal order of steps of various processes or methods that are described herein are illustrative and not restrictive. Accordingly, it should be understood that, although steps of various processes or methods may be shown and described as being in a sequence or temporal order, the steps of any such processes or methods are not limited to being carried out in any particular sequence or order, absent an indication otherwise. Indeed, the steps in such processes or methods generally may be carried out in various different sequences and orders while still falling within the scope of the present invention. Accordingly, it is intended that the scope of patent protection afforded the present invention is to be defined by the appended claims rather than the description set forth herein. 
         [0054]    Additionally, it is important to note that each term used herein refers to that which the Ordinary Artisan would understand such term to mean based on the contextual use of such term herein. To the extent that the meaning of a term used herein—as understood by the Ordinary Artisan based on the contextual use of such term—differs in any way from any particular dictionary definition of such term, it is intended that the meaning of the term as understood by the Ordinary Artisan should prevail. 
         [0055]    Regarding applicability of 35 U.S.C. §112, ¶6, no claim element is intended to be read in accordance with this statutory provision unless the explicit phrase “means for” or “step for” is actually used in such claim element, whereupon this statutory provision is intended to apply in the interpretation of such claim element. 
         [0056]    Furthermore, it is important to note that, as used herein, “a” and “an” each generally denotes “at least one,” but does not exclude a plurality unless the contextual use dictates otherwise. Thus, reference to “a picnic basket having an apple” describes “a picnic basket having at least one apple” as well as “a picnic basket having apples.” In contrast, reference to “a picnic basket having a single apple” describes “a picnic basket having only one apple.” 
         [0057]    When used herein to join a list of items, “or” denotes “at least one of the items,” but does not exclude a plurality of items of the list. Thus, reference to “a picnic basket having cheese or crackers” describes “a picnic basket having cheese without crackers,” “a picnic basket having crackers without cheese,” and “a picnic basket having both cheese and crackers.” Finally, when used herein to join a list of items, “and” denotes “all of the items of the list.” Thus, reference to “a picnic basket having cheese and crackers” describes “a picnic basket having cheese, wherein the picnic basket further has crackers,” as well as describes “a picnic basket having crackers, wherein the picnic basket further has cheese.” 
         [0058]    Referring now to the drawings, in which like numerals represent like components throughout the several views, one or more preferred embodiments of the present invention are next described. The following description of one or more preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0059]      FIG. 1  is a front isometric view of a containment room  10  having a double door assembly  20  with a door closer mechanism in accordance with one or more preferred embodiments of the present invention, and  FIG. 2  is a rear isometric view of the containment room  10  of  FIG. 1 , illustrating a single door assembly  120  with a door closer mechanism in accordance with one or more preferred embodiments of the present invention. As shown therein, two rows of equipment enclosures  12 , each of which may house a variety of data processing equipment, are arranged opposite each other along an interior aisle  14 . As used herein, the term “data processing equipment” refers to a wide range of electronic equipment as well as racks, frames, enclosures, and the like that are typically used to house such equipment. A frame structure  16  supports ceiling panels  18  above the interior aisle  14 . Access to the interior aisle  14  is provided at the front end by the double door assembly  20  and at the rear end by the single door assembly  120 . 
         [0060]    Together, the ceiling panels  18 , the door assemblies  20 , 120  and the equipment enclosures  12  themselves fully enclose the interior aisle  14 , and the entire structure of the containment room  10  may rest on the floor surface in a data center room (not shown). In many embodiments, cool air is supplied to the interior aisle  14 , where it is allowed to pass through doors or openings in the inward-facing sides of the equipment enclosures  12 . This type of arrangement is commonly referred to as a “cold” aisle. The air is used to cool equipment operating inside the enclosures  12 , and the heated air resulting from this process is exhausted out the rear or top of the enclosures  12 . However, in some embodiments, the heated air is exhausted out the bottoms of the enclosures  12 . Furthermore, in some embodiments, cool air is provided to the outward-facing sides of the equipment enclosures  12 , and heated air is exhausted to the interior aisle  14 , where it may be routed downward through the floor, upward through various overhead duct structures (not shown), or routed back to cooling units (not shown) located next to the enclosures  12  themselves. This type of arrangement is commonly referred to as a “hot” aisle. Various implementations of cold and hot aisles are described, for example, in commonly-assigned U.S. non-provisional patent application Ser. No. 13/707,521, filed Dec. 6, 2012, which is expressly incorporated herein by reference in its entirety. It will be appreciated that the door assemblies  20 , 120  and door closer mechanisms described and illustrated herein have applicability in any of these environments and applications. 
         [0061]    As shown in  FIG. 1 , the double door assembly  20  includes two doors  22 , two side wall panels  24 , a rail assembly  30 , and a door closer mechanism  50 .  FIG. 3  is a front view of the double door assembly  20  of  FIG. 1 , shown with the front cover  36  of the rail assembly  30  removed, and  FIG. 4  is a front view of the double door assembly  20  of  FIG. 3 , shown with the doors  22  in an open state. The rail assembly  30 , which may be mounted to the frame structure  16  of the containment room  10 , supports the door closer mechanism  50  (perhaps best shown in  FIG. 7 ) and the doors  22 , and further provides a mounting surface for the upper ends of the panels  24 . The lower ends of the panels  24  may be attached to the floor. In at least some embodiments, the lower ends of the panels  24  are also sealed to the floor to prevent air from passing underneath. In at least some embodiments, seals (not shown) are provided along the entire vertical lengths of the right and left edges of each door  22 . 
         [0062]    The rail assembly  30  includes a main rail extrusion  32 , a pair of roller bracket assemblies  34 , the front cover  36 , and a pair of end caps  38 . Each door  22  has a support rail  26  mounted along the upper end thereof, and each support rail  26  may be attached to a respective roller bracket assembly  34 . The roller bracket assemblies  34  are carried by the main rail extrusion  32 . The doors  22  may be opened by pulling them apart, causing the roller bracket assemblies  34  to spread apart along the main rail extrusion  32 . 
         [0063]      FIG. 5  is a fragmentary side cross sectional view of the rail assembly  30  of  FIG. 4 , taken along line  5 - 5 , and  FIG. 6  is a partially exploded isometric view of one of the roller bracket assemblies  34  of  FIG. 3 . As shown therein, each roller bracket assembly  34  includes a bracket  42  and two sets of ball bearing rollers  44 . The support rail  26  of the door  22  is secured to a portion of the bracket  42  via fasteners  46 , and the top of the door  22  itself is secured to another portion of the bracket  42  via additional fasteners  48 . The two sets of ball bearing rollers  44 , preferably made from nylon or similar plastic material, are mounted at the upper edge of the bracket  42  and are arranged to ride in a roller cavity  40  in the main rail extrusion  32 , thus allowing the bracket  42  (and the door  22  which it carries) to roll back and forth. 
         [0064]      FIG. 7  is an orthogonal view of the door closer mechanism  50  of  FIG. 3 , and  FIG. 8  is an exploded isometric view of the door closer mechanism  50  of  FIG. 7 . As shown therein, the door closer mechanism  50  includes a belt/pulley assembly  60 , a mounting bracket  52 , a pair of belt splice brackets  54 , a pair of belt splice plates  56 , and a return spring assembly  58 , all supported by the main rail extrusion  32 . Primary operation is facilitated by the belt/pulley assembly  60 , which includes a timing or other synchronous belt  62 , a damper pulley  64 , and a free pulley  66 . The free pulley  66  may be mounted directly to the main rail extrusion  32 , while the damper pulley  64  may be fastened to one end of the mounting bracket  52 , which itself is fastened to the main rail extrusion  32 . The synchronous belt  62  is routed around the free pulley  66  and the damper pulley  64  and maintained in sufficient tension to enable operation, as further described below. The synchronous belt  62  is preferably made from polyurethane with steel cords, but other soft plastics may alternatively or additionally be used as well as other cord materials, such as fiberglass. Furthermore, in some embodiments, a flat belt could be used in place of the toothed belt with the inclusion of a pulley tensioning device; and still further, other types of belts, such as a vee belt, could also be used. 
         [0065]      FIGS. 9 and 10  are an isometric view and an exploded isometric view, respectively, of the damper pulley  64  of  FIG. 8 , and  FIGS. 11 and 12  are an isometric view and an exploded isometric view, respectively, of the free pulley  66  of  FIG. 8 . As perhaps best shown in  FIGS. 9 and 11 , the cylindrical bearing surface  68  of both pulleys  64 , 66  includes a series of teeth that interlock with the teeth on the synchronous belt  62 . Once the synchronous belt  62  is engaged around the pulleys  64 , 66  and properly adjusted, the respective rotations of the pulleys  64 , 66  are thus locked together. The damper pulley  64  and its operation will be further described hereinbelow. 
         [0066]    Each door  22  is attached to the synchronous belt  62  via a combination of a belt splice bracket  54  and a belt splice plate  56 .  FIG. 13  is an isometric view of one of the belt splice brackets  54  of  FIG. 8 , and  FIG. 14  is an isometric view of one of the belt splice plates  56  of  FIG. 8 . As perhaps best shown in  FIG. 5 , the belt splice bracket  54  and belt splice plate  56  may be clamped together around the synchronous belt  62  and held together by a fastener  55 , as perhaps best illustrated in  FIGS. 5 and 8 . The belt splice bracket  54  is fastened to the bracket  42  of the roller bracket assembly  34 , as shown in  FIG. 5 . Thus, each door  22  is connected to the synchronous belt  62  (via the support rail  26 , roller bracket assembly  34 , and belt splice bracket/plate  54 , 56 ) at a particular location along the belt  62 , thereby allowing the position of the door  22  to be precisely controlled relative to the synchronous belt  62  and to each other. Notably, one door  22  is connected to the lower portion of the synchronous belt  62 , while the other door  22  is connected to the upper portion. As shown in  FIGS. 7 and 8 , this is accomplished by inverting the belt splice bracket  54  and belt splice plate  56  for the latter of the two doors  22 . Thus, movement of the belt  62  in one rotational direction causes the two belt splices to move apart (clockwise in  FIGS. 7 and 8 ), while movement of the belt  62  in the opposite rotational direction (counterclockwise in  FIGS. 7 and 8 ) causes the two belt splices to move toward each other. Put another way, separation of (opening) the two doors  22  causes the two belt splices to move apart, thereby causing the belt  62  to move in one rotational direction (clockwise in  FIGS. 7 and 8 ), while moving the two doors  22  toward each other (i.e., closing the doors) causes the two belt splices to move toward each other, thereby causing the belt  62  to move in the opposite rotational direction (counterclockwise in  FIGS. 7 and 8 ). 
         [0067]    A return spring  57 , mounted on a spool  59 , is mounted to one of the roller bracket assemblies  34 .  FIG. 15  is an isometric view of the return spring  57  of  FIG. 8 , and  FIG. 16  is an isometric view of the return spring spool  59  of  FIG. 8 . One end of the spring  57  itself is attached to the mounting bracket  52 . In the illustrated embodiment, the mounting bracket  52  is on the right, the damper pulley  64  is connected to the right end of the mounting bracket  52 , the return spring spool  59  is connected to the belt splice bracket  54  on the left, and the end of the spring  57  is attached to the left end of the mounting bracket  52 . It will be appreciated, however, that various of these elements and others may be rearranged while still accomplishing the same basic functionality. The spring  57  is preferably a constant-force spring which unrolls as the belt splice bracket  54 , to which it is attached, is moved away from the mounting bracket  52 . Thus, in  FIGS. 7 and 8 , movement of the lefthand belt splice bracket  54  to the left causes the return spring spool  59  to move to the left. Because the end of the spring  57  is attached to the mounting bracket  52 , which remains stationary, the spring  57  unwinds as the spool  59  moves, thus resisting the movement of the belt splice bracket  54  (and the door  22  to which it is attached). When the door  22  is released, the force of the spring  57  acts to pull the belt splice bracket  54 , and the door  22  to which it is attached, back toward the mounting bracket  52 . Furthermore, because both doors  22  are attached to the same synchronous belt  62 , movement of the lefthand belt splice bracket  54  effectuates synchronized movement of the righthand belt splice bracket  54  (and the righthand door  22 ) as well. 
         [0068]    The biasing force applied by the return spring  57  is resisted by the damper pulley  64 , whose construction and operation are described next with particular reference to  FIG. 10 . As shown therein, the damper pulley  64  includes a main body  72  and a cover  74 , which for convenience may be similar to the construction of the free pulley  66 , shown in  FIG. 12 . The main body  72  and the cover  74  define an interior compartment  76 . In the interior compartment of the damper pulley  64 , two sets of alternating discs  78 , 80  are arranged, separated by spacers  82 . Each of the discs  78  in the first set includes three guide teeth  79 , disposed around the periphery thereof, that are arranged to fit into corresponding grooves  83  on the interior of the main damper body  72  (visible in the interior of the main pulley body  72  in  FIG. 12 ). Each of the discs  80  in the second set includes two guide teeth  81 , disposed around the center opening thereof, that are arranged to fit into grooves  84  in the external surfaces of a hub  86 . A main axle  88  is inserted through two sets of bearings  90 , 92 , one set of which is press-fit into the hub  86 . The interior compartment  76  is filled with oil and the main body  72  and cover  74  are sealed together. 
         [0069]    In operation, the damper pulley  64  rotates freely in one direction, but the damping mechanism limits the rotational speed significantly in the opposite direction. In the door closer mechanism  50 , the damper pulley  64  is allowed to rotate freely when the doors  22  are being opened (i.e., when the synchronous belt  62  is moved in the clockwise direction in  FIGS. 7 and 8 ), but the damping mechanism limits rotational speed when the doors  22  are being closed (i.e., when the synchronous belt  62  is moved in the counterclockwise direction in  FIGS. 7  and  8 ). Thus, although the return spring  57  tends to force the doors  22  closed any time the doors  22  are placed in an opened state, the force applied by the spring  57  is counterbalanced by the damping effect of the damping pulley  64 . However, the damping mechanism does not provide any resistance to the doors  22  being opened, and the resistance offered by the return spring  57  may be easily overcome by the user. 
         [0070]    Advantageously, the door closer mechanism  50  provides a convenient means for causing the doors  22  shown in  FIG. 1  to be closed automatically, but without risk of sudden or violent closings, and without the need for any electrical power or other power requirements. The constant force spring  57 , counterbalanced by the damping mechanism, causes the door to be closed at a near-constant speed that is conveniently slow. Furthermore, in the double door assembly  20 , both doors  22  may be opened with one hand. 
         [0071]    In at least some embodiments, a “hold open” feature may be provided to keep the doors  22  in an open state, if desired. Such a feature may be particularly useful, for example, to allow equipment to be carried in and out of the containment room  10 . In this regard,  FIG. 17  is an exploded fragmentary rear isometric view of portions of the left end of the rail assembly  30  of  FIG. 4 , and  FIGS. 18 and 19  are enlarged fragmentary front cross-sectional views of the rail assembly  30  of  FIG. 5 , taken along line  18 - 18 . As shown therein, a spring bracket  94  may be attached to one of the end caps  38  such that it protrudes into the roller cavity  40 . When the door  22  closest to the spring bracket  94  is opened to its fullest extent, a raised tooth  49  on the end of the roller bracket  42  carrying that door  22  is pushed past a bend in the spring bracket  94  and is caught behind it, thereby holding the door in its open state. This is shown in  FIG. 18 . In order to avoid slamming the door  22  against the end cap  38 , a bumper  96  may be provided as well. When the door  22  is to be closed again, a gentle tug will be sufficient to pull the trapped tooth  49  from behind the bend in the spring bracket  94 , as shown in  FIG. 19 , and the roller bracket  42  (and the door depending from it) may then operate as described previously. 
         [0072]    It will be appreciated that the same principles and elements used for the double door assembly  20  of  FIG. 1  may likewise be utilized on the single door assembly  120  shown in  FIG. 2 , except that only one belt splice (bracket  54  and plate  56 ) needs to be clamped to the synchronous belt  62  because only one door  22  is utilized. If necessary, the arrangement of the various elements may be reversed, particularly if it is desired to switch from a righthand door to a lefthand door. 
         [0073]    Based on the foregoing information, it will be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those specifically described herein, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing descriptions thereof, without departing from the substance or scope of the present invention. 
         [0074]    Accordingly, while the present invention has been described herein in detail in relation to one or more preferred embodiments, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for the purpose of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended to be construed to limit the present invention or otherwise exclude any such other embodiments, adaptations, variations, modifications or equivalent arrangements; the present invention being limited only by the claims appended hereto and the equivalents thereof.