Patent Publication Number: US-2021190436-A1

Title: Refrigeration device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2018-169898, filed on Sep. 11, 2018 and International Patent Application No. PCT/JP2019/029757, filed on Jul. 30, 2019, the entire content of each of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates to refrigeration devices, and particularly to a refrigeration device that condenses a refrigerant and then evaporates the refrigerant to exert a cooling effect. 
     Description of the Related Art 
     There has been conventionally known a refrigeration device that performs heat exchange between a refrigerator and a storage chamber via a thermosiphon connected to a cooling unit of the refrigerator (see Patent Literature 1, for example). In the refrigeration device disclosed in Patent Literature 1, a pipe of a thermosiphon includes two paths, and each of the paths is structured to extend downward along a different half circumference of a storage chamber. In this refrigeration device, by increasing the inclination angle of each pipe path, prevention of the flow of the refrigerant in the pipe can be avoided even when the low-temperature storage is tilted. 
     [Patent Literature 1] Japanese Unexamined Patent Application Publication No. 2005-156011 
     A storage chamber of a low-temperature storage is required to stably maintain the low-temperature state. Accordingly, in such a low-temperature storage, various measures are adopted in order to restrain temperature rise within the storage chamber. For example, the storage chamber is covered with a thermal insulation material having high thermal insulation properties. Also, a door through which storage objects are transferred into and from the storage chamber is configured as a double door. The inner door is divided into multiple parts such that the area of an opening used for transfer of a storage object is reduced. Also, an alarm is set to sound when the door remains open for a predetermined period of time or longer, so as to alert the user. Further, as a countermeasure to a temporary power failure, an auxiliary cooling source, such as liquefied gas, is provided to restrain temperature rise within the storage chamber. 
     As a result of intensive study regarding refrigeration devices mounted on low-temperature storages, the inventors have found that, with regard to conventional refrigeration devices, there is room for improvement in stably maintaining the temperatures in the low-temperature storages. 
     SUMMARY OF THE INVENTION 
     The subject application has been made in view of such a situation, and a purpose thereof is to provide a technology for further stabilizing the temperature in a low-temperature storage. 
     In response to the above issue, one embodiment in the subject application is a refrigeration device. The refrigeration device includes: a refrigerator; and a heat pipe that includes a condensation unit, a pipe unit, and an evaporation unit, in which the condensation unit is connected with the refrigerator such that heat exchange therewith can be performed to condense a refrigerant, the pipe unit circulates the refrigerant between the condensation unit and the evaporation unit, and the evaporation unit extends along wall surfaces of a storage chamber, which houses a preservation object, and is attached to the wall surfaces such that heat exchange therewith can be performed to evaporate the refrigerant. The evaporation unit includes a first pipe conduit and a second pipe conduit. The first pipe conduit includes a first near-end part located closer to the condensation unit, a first far-end part located opposite to the first near-end part, and a first long circumference part, a first short circumference part, and a first junction part that are arranged between the first near-end part and the first far-end part. The second pipe conduit includes a second near-end part located closer to the condensation unit, a second far-end part located opposite to the second near-end part, and a second long circumference part, a second short circumference part, and a second junction part that are arranged between the second near-end part and the second far-end part. The first near-end part in the first pipe conduit is positioned higher than the second near-end part, and, in the first pipe conduit, the first long circumference part is located closer to the first near-end part, the first short circumference part is located closer to the first far-end part, and the first junction part is located between the first long circumference part and the first short circumference part. The first long circumference part extends around the storage chamber from the first near-end part side toward the first far-end part side in a first circumference direction, and also extends along more wall surfaces than the first short circumference part. The first junction part includes at least one first turning part that changes the circumference direction of the first pipe conduit. The first short circumference part extends around the storage chamber from the first near-end part side toward the first far-end part side, extends in the first circumference direction when the number of the first turning parts is even, extends in a second circumference direction, which is opposite to the first circumference direction, when the number of the first turning parts is odd, and extends along fewer wall surfaces than the first long circumference part. The second near-end part in the second pipe conduit is positioned lower than the first near-end part, and, in the second pipe conduit, the second short circumference part is located closer to the second near-end part, the second long circumference part is located closer to the second far-end part, and the second junction part is located between the second short circumference part and the second long circumference part. The second short circumference part extends around the storage chamber from the second near-end part side toward the second far-end part side in the first circumference direction, and also extends along fewer wall surfaces than the second long circumference part. The second junction part includes a second turning part that changes the circumference direction of the second pipe conduit and that is equal in number to the first turning part. The second long circumference part extends around the storage chamber from the second near-end part side toward the second far-end part side, extends in the first circumference direction when the number of the second turning parts is even, extends in the second circumference direction when the number of the second turning parts is odd, and extends along more wall surfaces than the second short circumference part. The first turning part positioned N-th counted from the first near-end part side and the second turning part positioned N-th counted from the second near-end part side are disposed respectively on wall surfaces facing each other, where N is an integer greater than or equal to 1. 
     Optional combinations of the aforementioned constituting elements, and implementation of the present invention, including the expressions, in the form of methods, apparatuses, or systems may also be practiced as additional modes of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which: 
         FIG. 1  is a perspective view of a low-temperature storage provided with a refrigeration device according to a first embodiment; 
         FIG. 2  is a rear view of the low-temperature storage; 
         FIG. 3  is a perspective view of a storage chamber and an evaporation unit; 
         FIG. 4  is a perspective view of the evaporation unit; 
         FIG. 5  is a schematic diagram used to describe a method for fabricating a first pipe conduit and a second pipe conduit; 
         FIGS. 6A, 6B, 6C, 6D, 6E, and 6F  are schematic diagrams that each illustrate a state where wall surfaces of a storage chamber are developed; 
         FIGS. 7A, 7B, 7C, and 7D  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed; 
         FIGS. 8A, 8B, 8C, and 8D  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed; 
         FIG. 9  is a perspective view of a low-temperature storage provided with a refrigeration device according to a second embodiment; 
         FIG. 10A  is a perspective view of a storage chamber and evaporation units, and  FIG. 10B  is a perspective view of the evaporation units; 
         FIG. 11  is a schematic diagram used to describe a postural relationship between the evaporation unit of a first heat pipe and the evaporation unit of a second heat pipe; 
         FIGS. 12A, 12B, 12C, 12D, 12E, and 12F  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed; 
         FIGS. 13A, 13B, 13C, and 13D  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed; 
         FIGS. 14A, 14B, 14C, and 14D  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed; and 
         FIG. 15  is a perspective view used to describe connecting pipes provided in a refrigeration device according to a first modification. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present invention, but to exemplify the invention. 
     In the following, the present invention will be described based on preferred embodiments with reference to the drawings. The embodiments are intended to be illustrative only and not to limit the invention, so that it should be understood that not all of the features or combinations thereof described in the embodiments are necessarily essential to the invention. Like reference characters denote like or corresponding constituting elements, members, and processes in each drawing, and repetitive description will be omitted as appropriate. Also, the scale or shape of each component shown in each drawing is defined for the sake of convenience to facilitate the explanation and is not to be regarded as limitative unless otherwise specified. When the terms “first”, “second”, and the like are used in the present specification or claims, such terms do not imply any order or degree of importance and are used to distinguish one configuration from another, unless otherwise specified. Further, in each drawing, part of a member less important in describing embodiments may be omitted. 
     First Embodiment 
       FIG. 1  is a perspective view of a low-temperature storage provided with a refrigeration device according to a first embodiment.  FIG. 2  is a rear view of the low-temperature storage.  FIG. 2  illustrates a state in which the inside of the low-temperature storage is transparently viewed. Also, the evaporation unit of the heat pipe is only partially illustrated. A low-temperature storage  1  ( 1 A) is used for low-temperature preservation of biological materials, such as cells and body tissues, drugs, and reagents, for example. The low-temperature storage  1  includes a thermally insulated box  2  of which an upper surface is open, and a machine chamber  4  disposed adjacent to the thermally insulated box  2 . 
     The thermally insulated box  2  includes an outer box  2   a  and an inner box  2   b  of which upper surfaces are both open. A space between the outer box  2   a  and the inner box  2   b  is filled with a thermal insulation material, which is not illustrated. The thermal insulation material may be a polyurethane resin, glass wool, or a vacuum insulation material, for example. A space within the inner box  2   b  constitutes a storage chamber  6 . The storage chamber  6  is a space for housing a preservation object. A target temperature inside the storage chamber  6  (hereinafter, referred to as a storage inside temperature, as appropriate) may be −50 degrees C. or lower, for example. 
     On the upper surface of the thermally insulated box  2 , a thermally insulated door  8  is provided via a packing. The thermally insulated door  8  is fixed at one end to the thermally insulated box  2  and provided to be rotatable about the one end. Accordingly, the opening of the storage chamber  6  is covered such as to be openable and closable. On the other end side of the thermally insulated door  8 , a handle part  10  is provided and used for open and close operations for the thermally insulated door  8 . On wall surfaces  26  on the thermal insulation material side of the inner box  2   b , an evaporation unit  24  of a heat pipe  16 , which will be described later, is provided. The inside of the storage chamber  6  is cooled by means of evaporation of a refrigerant in the evaporation unit  24 . 
     The machine chamber  4  is a space for housing a refrigeration device  12  of the present embodiment. However, part of a pipe unit  22  and the evaporation unit  24  of the heat pipe  16  in the refrigeration device  12  are arranged within the thermally insulated box  2 . Since the structures of the thermally insulated box  2  and the machine chamber  4  are publicly known, further detailed description therefor will be omitted. 
     The refrigeration device  12  is a device capable of cooling the inside of the storage chamber to an ultra-low temperature of −50 degrees C. or lower. The refrigeration device  12  includes a refrigerator  14  and the heat pipe  16 . 
     The refrigerator  14  is a device for cooling a condensation unit  20  of the heat pipe  16 . As the refrigerator  14 , a conventionally well-known refrigerator may be used, such as a Gifford-McMahon (GM) refrigerator, a pulse tube refrigerator, a Stirling refrigerator, a Solvay refrigerator, a Claude cycle refrigerator, and a Joule-Thomson (JM) refrigerator. The refrigerator  14  includes a cooling unit  18  that absorbs external heat. Since the structure of the refrigerator  14  is publicly known, further detailed description therefor will be omitted. 
     The heat pipe  16  is a device for cooling an object to be cooled by means of the heat of vaporization of a refrigerant. The heat pipe  16  mediates heat exchange between the cooling unit  18  of the refrigerator  14  and the inside of the storage chamber  6 . The heat pipe  16  includes the condensation unit  20 , the pipe unit  22 , and the evaporation unit  24 . 
     The condensation unit  20  is connected with the cooling unit  18  of the refrigerator  14  such that heat exchange therewith can be performed. The heat exchange between the condensation unit  20  and the cooling unit  18  cools the refrigerant within the condensation unit  20 , so that the refrigerant is condensed to liquid. For example, the condensation unit  20  may include a condensation fin connected to the cooling unit  18  and also include a refrigerant passage constituted by grooves of the condensation fin. The cold of the cooling unit  18  is transmitted, via the condensation fin, to the refrigerant flowing through the refrigerant passage. The gaseous refrigerant liquefies in the refrigerant passage. As the refrigerant, a refrigerant gas, such as R740 (argon), R50 (methane), R14 (tetrafluoromethane), and R170 (ethane), may be used. 
     One end of the pipe unit  22  is connected to the condensation unit  20 . More specifically, one end of the pipe unit  22  is connected to the refrigerant passage of the condensation unit  20 . Also, the other end of the pipe unit  22  is connected to the evaporation unit  24 . The refrigerant within the heat pipe  16  is circulated between the condensation unit  20  and the evaporation unit  24  through the pipe unit  22 . 
     The evaporation unit  24  is connected thermally to the inside of the storage chamber  6  such that heat exchange therewith can be performed. More specifically, the evaporation unit  24  has a tubular shape and extends along the wall surfaces  26  on the thermal insulation material side of the inner box  2   b , i.e., the wall surfaces  26  of the storage chamber  6 . The evaporation unit  24  is attached to the wall surfaces  26  such that heat exchange therewith can be performed, so as to evaporate the refrigerant. The evaporation unit  24  may be fixed to the wall surfaces  26  directly or via a heat transfer material, for example. 
     The refrigerant liquefied in the condensation unit  20  flows into the evaporation unit  24  through the pipe unit  22 . The refrigerant in the evaporation unit  24  then absorbs heat from the inside of the storage chamber  6  to evaporate. Such evaporation of the refrigerant cools the inside of the storage chamber  6 . The refrigerant gasified in the evaporation unit  24  flows into the refrigerant passage of the condensation unit  20  through the pipe unit  22 . Thereafter, the refrigerant in the condensation unit  20  is condensed again to liquid. 
     The evaporation unit  24  includes a first pipe conduit  28  and a second pipe conduit  30 . Also, the pipe unit  22  includes a first pipe  32  and a second pipe  34 . To the condensation unit  20 , one end of the first pipe  32  and one end of the second pipe  34  are connected. Further, the other end of the first pipe  32  is connected to one end of the first pipe conduit  28 , and the other end of the second pipe  34  is connected to one end of the second pipe conduit  30 . Thus, the first pipe conduit  28  and the second pipe conduit  30  are connected to the same refrigerator  14 . The boundary between the pipe unit  22  and the evaporation unit  24  corresponds to a boundary between an area where the heat pipe  16  is in contact with the wall surfaces  26  and an area where the heat pipe  16  is not in contact with the wall surfaces  26 , for example. In other words, in the piping of the heat pipe  16 , a portion in contact with the wall surfaces  26  corresponds to the evaporation unit  24 , and a portion not in contact with the wall surfaces  26  corresponds to the pipe unit  22 . The other end of the first pipe conduit  28  and the other end of the second pipe conduit  30  are connected with each other via a connecting pipe  50 , which will be described later. 
     Part of the refrigerant from the condensation unit  20  flows into the first pipe conduit  28  of the evaporation unit  24  through the first pipe  32 . The part of the refrigerant exchanges heat with wall surfaces  26  overlapped by the first pipe conduit  28  to reach an end part located opposite to the pipe unit  22  side. Part of the refrigerant that has evaporated and gasified during the process returns to the condensation unit  20  through the first pipe  32 . Accordingly, the liquid refrigerant and the gaseous refrigerant flow in the opposite directions within the first pipe conduit  28  and the first pipe  32 . At the time, the liquid refrigerant flows near the outer side of the pipe, and the gaseous refrigerant flows near the center of the pipe. 
     Meanwhile, another part of the refrigerant from the condensation unit  20  flows into the second pipe conduit  30  of the evaporation unit  24  through the second pipe  34 . The another part of the refrigerant exchanges heat with wall surfaces  26  overlapped by the second pipe conduit  30  to reach an end part located opposite to the pipe unit  22  side. Part of the refrigerant that has evaporated and gasified during the process returns to the condensation unit  20  through the second pipe  34 . Accordingly, the liquid refrigerant and the gaseous refrigerant flow in the opposite directions within the second pipe conduit  30  and the second pipe  34 . At the time, the liquid refrigerant flows near the outer side of the pipe, and the gaseous refrigerant flows near the center of the pipe. Thus, the refrigeration device  12  includes a first refrigerant circulation passage including the first pipe  32  and the first pipe conduit  28 , and a second refrigerant circulation passage including the second pipe  34  and the second pipe conduit  30 . 
     In the following, the structure of the evaporation unit  24  will be described in detail.  FIG. 3  is a perspective view of the storage chamber and the evaporation unit.  FIG. 4  is a perspective view of the evaporation unit. As described previously, the evaporation unit  24  includes the first pipe conduit  28  and the second pipe conduit  30 . The first pipe conduit  28  includes: a first near-end part  36   a  located closer to the condensation unit  20 ; a first far-end part  38   a  located opposite to the first near-end part  36   a ; and a first long circumference part  40   a , a first short circumference part  42   a , and a first junction part  44   a  that are arranged between the first near-end part  36   a  and the first far-end part  38   a.    
     The second pipe conduit  30  includes: a second near-end part  36   b  located closer to the condensation unit  20 ; a second far-end part  38   b  located opposite to the second near-end part  36   b ; and a second long circumference part  40   b , a second short circumference part  42   b , and a second junction part  44   b  that are arranged between the second near-end part  36   b  and the second far-end part  38   b.    
     The first near-end part  36   a  in the first pipe conduit  28  is positioned higher than the second near-end part  36   b . The first pipe conduit  28  includes the first long circumference part  40   a  located closer to the first near-end part  36   a , the first short circumference part  42   a  located closer to the first far-end part  38   a , and the first junction part  44   a  located between the first long circumference part  40   a  and the first short circumference part  42   a . Accordingly, in the first pipe conduit  28 , the first near-end part  36   a , the first long circumference part  40   a , the first junction part  44   a , the first short circumference part  42   a , and the first far-end part  38   a  are arranged in this order from the condensation unit  20  side. 
     The first long circumference part  40   a  extends around the storage chamber  6  from the first near-end part  36   a  side toward the first far-end part  38   a  side in a first circumference direction, and also extends along more wall surfaces  26  than the first short circumference part  42   a . The first junction part  44   a  includes at least one first turning part  46   a  that changes the circumference direction of the first pipe conduit  28 . The first short circumference part  42   a  also extends around the storage chamber  6  from the first near-end part  36   a  side toward the first far-end part  38   a  side. The first short circumference part  42   a  extends in the first circumference direction when the number of first turning parts  46   a  is even, and extends in a second circumference direction, which is opposite to the first circumference direction, when the number of first turning parts  46   a  is odd. Also, the first short circumference part  42   a  extends along fewer wall surfaces  26  than the first long circumference part  40   a.    
     The second near-end part  36   b  in the second pipe conduit  30  is positioned lower than the first near-end part  36   a . The second pipe conduit  30  includes the second short circumference part  42   b  located closer to the second near-end part  36   b , the second long circumference part  40   b  located closer to the second far-end part  38   b , and the second junction part  44   b  located between the second short circumference part  42   b  and the second long circumference part  40   b . Accordingly, in the second pipe conduit  30 , the second near-end part  36   b , the second short circumference part  42   b , the second junction part  44   b , the second long circumference part  40   b , and the second far-end part  38   b  are arranged in this order from the condensation unit  20  side. 
     The second short circumference part  42   b  extends around the storage chamber  6  from the second near-end part  36   b  side toward the second far-end part  38   b  side in the first circumference direction, similarly to the first long circumference part  40   a . Also, the second short circumference part  42   b  extends along fewer wall surfaces  26  than the second long circumference part  40   b . The second junction part  44   b  includes a second turning part  46   b  that changes the circumference direction of the second pipe conduit  30  and that is equal in number to the first turning part  46   a . The second long circumference part  40   b  also extends around the storage chamber  6  from the second near-end part  36   b  side toward the second far-end part  38   b  side. The second long circumference part  40   b  extends in the first circumference direction when the number of second turning parts  46   b  is even, and extends in the second circumference direction when the number of second turning parts  46   b  is odd. Also, the second long circumference part  40   b  extends along more wall surfaces  26  than the second short circumference part  42   b.    
     When the number of wall surfaces  26  overlapped by the first long circumference part  40   a  is defined as m, and the number of wall surfaces  26  overlapped by the first short circumference part  42   a  is defined as n, the number m+n of wall surfaces  26  overlapped by the first long circumference part  40   a  or the first short circumference part  42   a  is greater than or equal to the total number of wall surfaces  26  that define the storage chamber  6 . The same applies to the second long circumference part  40   b  and the second short circumference part  42   b . Also, in the present embodiment, the number of wall surfaces  26  overlapped by the first long circumference part  40   a  is equal to that overlapped by the second long circumference part  40   b , and the number of wall surfaces  26  overlapped by the first short circumference part  42   a  is equal to that overlapped by the second short circumference part  42   b . The “overlap” means that, when viewed from a normal direction of each wall surface  26 , the first pipe conduit  28  or the second pipe conduit  30  overlaps the wall surface  26 . 
     In the present embodiment, the storage chamber  6  includes four wall surfaces  26 . The wall surfaces  26  are surfaces extending in a vertical direction. Hereinafter, the four wall surfaces  26  are defined as a first wall surface  26   a , a second wall surface  26   b , a third wall surface  26   c , and a fourth wall surface  26   d . The first wall surface  26   a  through the fourth wall surface  26   d  are arranged in this order in the counterclockwise direction and define the storage chamber  6 . Accordingly, the first wall surface  26   a  and the third wall surface  26   c  face each other, and the second wall surface  26   b  and the fourth wall surface  26   d  face each other. The counterclockwise direction and the clockwise direction in the present embodiment mean the circling directions when the storage chamber  6  is viewed from the upper side in a vertical direction. 
     The first near-end part  36   a  is disposed to overlap the first wall surface  26   a . For example, the first near-end part  36   a  is disposed near the side of the first wall surface  26   a  in contact with the fourth wall surface  26   d . The first long circumference part  40   a  extends around the storage chamber  6  from the first near-end part  36   a  side toward the first far-end part  38   a  side in the counterclockwise direction (first circumference direction), and also extends along the first wall surface  26   a  through the fourth wall surface  26   d , i.e., four wall surfaces  26 . 
     The number of first turning parts  46   a  is even, and more specifically is two. The first turning part  46   a  positioned first and closer to the first long circumference part  40   a  side is disposed to overlap the fourth wall surface  26   d , and the first turning part  46   a  positioned second and closer to the first short circumference part  42   a  side is disposed to overlap the third wall surface  26   c . The first junction part  44   a  includes a first turning pipe conduit  48   a  that connects the two first turning parts  46   a . The first junction part  44   a  has a pipe shape snaking in a substantial S-shape. 
     Each first turning part  46   a  has a substantial U-shape, and the first turning part  46   a  positioned first changes the circumference direction of the first pipe conduit  28  from the counterclockwise direction to the clockwise direction (second circumference direction). From the first turning part  46   a  positioned first, the first turning pipe conduit  48   a  extends in the clockwise direction along the fourth wall surface  26   d  and the third wall surface  26   c , i.e., two wall surfaces  26 , to reach the first turning part  46   a  positioned second. The first turning part  46   a  positioned second changes the circumference direction of the first pipe conduit  28  from the clockwise direction to the counterclockwise direction. 
     The first short circumference part  42   a  extends around the storage chamber  6  from the first near-end part  36   a  side toward the first far-end part  38   a  side in the counterclockwise direction, similarly to the first long circumference part  40   a , and also extends along the third wall surface  26   c  and the fourth wall surface  26   d , i.e., two wall surfaces  26 . Thus, in the present embodiment, the number of wall surfaces  26  overlapped by the first junction part  44   a  is equal to that overlapped by the first short circumference part  42   a.    
     As with the first near-end part  36   a , the second near-end part  36   b  is also disposed to overlap the first wall surface  26   a . The second short circumference part  42   b  extends around the storage chamber  6  from the second near-end part  36   b  side toward the second far-end part  38   b  side in the counterclockwise direction, similarly to the first long circumference part  40   a , and also extends along the first wall surface  26   a  and the second wall surface  26   b , i.e., two wall surfaces  26 . Thus, the number of wall surfaces  26  overlapped by the second short circumference part  42   b  is equal to that overlapped by the first short circumference part  42   a.    
     The number of second turning parts  46   b  is even, and more specifically is two. The second turning part  46   b  positioned first and closer to the second short circumference part  42   b  side is disposed to overlap the second wall surface  26   b , and the second turning part  46   b  positioned second and closer to the second long circumference part  40   b  side is disposed to overlap the first wall surface  26   a . The second junction part  44   b  includes a second turning pipe conduit  48   b  that connects the two second turning parts  46   b . The second junction part  44   b  has a pipe shape snaking in a substantial S-shape. 
     Each second turning part  46   b  has a substantial U-shape, and the second turning part  46   b  positioned first changes the circumference direction of the second pipe conduit  30  from the counterclockwise direction to the clockwise direction. From the second turning part  46   b  positioned first, the second turning pipe conduit  48   b  extends in the clockwise direction along the second wall surface  26   b  and the first wall surface  26   a , i.e., two wall surfaces  26 , to reach the second turning part  46   b  positioned second. The second turning part  46   b  positioned second changes the circumference direction of the second pipe conduit  30  from the clockwise direction to the counterclockwise direction. Thus, in the present embodiment, the number of wall surfaces  26  overlapped by the second junction part  44   b  is equal to that overlapped by the second short circumference part  42   b.    
     The second long circumference part  40   b  extends around the storage chamber  6  from the second near-end part  36   b  side toward the second far-end part  38   b  side in the counterclockwise direction, similarly to the first short circumference part  42   a , and also extends along the first wall surface  26   a  through the fourth wall surface  26   d , i.e., four wall surfaces  26 . Thus, the number of wall surfaces  26  overlapped by the second long circumference part  40   b  is equal to that overlapped by the first long circumference part  40   a.    
     The first turning part  46   a  positioned N-th counted from the first near-end part  36   a  side (N is an integer greater than or equal to 1) and the second turning part  46   b  positioned N-th counted from the second near-end part  36   b  side are disposed respectively on wall surfaces  26  facing each other, i.e., wall surfaces  26  extending parallel with each other. These first turning part  46   a  and second turning part  46   b  are disposed at nearly the same height position in a vertical direction. In the present embodiment, the first turning part  46   a  positioned first counted from the first near-end part  36   a  side is disposed on the fourth wall surface  26   d , and the second turning part  46   b  positioned first counted from the second near-end part  36   b  side is disposed on the second wall surface  26   b  that faces the fourth wall surface  26   d . These first turning part  46   a  and second turning part  46   b  are disposed at nearly the same height position in a vertical direction. Similarly, the first turning part  46   a  positioned second counted from the first near-end part  36   a  side is disposed on the third wall surface  26   c , and the second turning part  46   b  positioned second counted from the second near-end part  36   b  side is disposed on the first wall surface  26   a  that faces the third wall surface  26   c . These first turning part  46   a  and second turning part  46   b  are also disposed at nearly the same height position in a vertical direction. 
     The heat pipe  16  in the present embodiment is a so-called thermosiphon, which circulates a refrigerant by gravity. Accordingly, the condensation unit  20  is disposed higher than the evaporation unit  24 . Also, the first pipe conduit  28  and the second pipe conduit  30  are tilted to extend gradually downward from the near-end parts ( 36   a ,  36   b ) to the far-end parts ( 38   a ,  38   b ), respectively. The refrigerant liquefied in the condensation unit  20  is transferred to the evaporation unit  24  by gravity and then flows from the near-end parts ( 36   a ,  36   b ) toward the far-end parts ( 38   a ,  38   b ). Accordingly, even when inner surfaces of pipes constituting the heat pipe  16  have simply flat and smooth shapes, such a liquid refrigerant can be transferred to the evaporation unit  24 . 
     The heat pipe  16  in the present embodiment includes the connecting pipe  50  that connects the first far-end part  38   a  and the second far-end part  38   b . The liquid refrigerant flowing through the first pipe conduit  28  gradually evaporates while flowing from the first near-end part  36   a  toward the first far-end part  38   a , but the refrigerant partially remains liquid to reach the first far-end part  38   a . Similarly, the liquid refrigerant flowing through the second pipe conduit  30  also partially remains liquid to reach the second far-end part  38   b.    
     Since the first far-end part  38   a  and the second far-end part  38   b  are connected by the connecting pipe  50 , the liquid refrigerant that has reached each far-end part can flow into the other pipe conduit side. Accordingly, between the first pipe conduit  28  and the second pipe conduit  30 , the liquid refrigerant can be transferred from the pipe conduit in which a larger amount of the liquid refrigerant flows, to the pipe conduit in which a smaller amount of the liquid refrigerant flows. This can equalize the amounts of the liquid refrigerant in the first pipe conduit  28  and the second pipe conduit  30 . 
     Also, the heat pipe  16  in the present embodiment does not include a device that locally changes the refrigerant pressure in the pipe conduits, such as a compressor and an expansion valve, or a structure that changes the refrigerant pressure in the pipe conduits due to pipe blockage by the liquid, such as a narrow tube and a capillary. Accordingly, in the heat pipe  16  of the present embodiment, the refrigerant pressure in the pipe conduits is equal at any portion. 
     The heat pipe  16  may be structured to include a number of narrow grooves, called wicks, extending in a longitudinal direction of the pipe and provided along the outer circumference inside the pipe, so as to transfer a liquid refrigerant by means of capillary forces exerted between the grooves and the liquid refrigerant. The heat pipe  16  may also be structured to circulate a refrigerant using a device that controls the refrigerant pressure in the pipe conduits, such as a compressor. In this case, the first pipe conduit  28  is used as a forward part, the second pipe conduit  30  is used as a return part, and a circulation passage for the refrigerant is constituted by connecting the compressor, the condensation unit  20 , the first pipe  32 , the evaporation unit  24 , and the second pipe  34  in this order, for example. 
     More specifically, within the heat pipe  16 , the refrigerant is compressed by the compressor and flows, as a high-pressure gas, into the condensation unit  20 . The refrigerant within the condensation unit  20  is cooled by the refrigerator  14  to be condensed to liquid and then flows into the first pipe  32 . At the time, since the refrigerant within the condensation unit  20  has a high pressure, the refrigerant is condensed to liquid even at a high temperature. Accordingly, the refrigerator  14  can be constituted by a simple device, such as a blower. Therefore, the configuration of the “refrigerator” in the subject application is not particularly limited as long as the refrigerant can be condensed in the condensation unit, and may be a simple device, such as a blower. The liquid refrigerant flowing in the first pipe  32  flows into the first pipe conduit  28  of the evaporation unit  24  through the first pipe  32 . 
     At the time, the refrigerant pressure in the pipe conduit increased by the compressor is reduced in the first pipe  32 , so that the heat exchange in the evaporation unit  24  can be efficiently performed. Specifically, the diameter of the first pipe  32  may desirably be locally narrower such that only the refrigerant in the liquid state can flow into the first pipe  32 . For example, the first pipe  32  may be constituted by a narrow pipe, such as a capillary. Also, a narrow pipe having a diameter of 2.5 mm or less may be used as the first pipe  32 , for example. Accordingly, only the refrigerant in the liquid state can flow into the first pipe  32 , so that the refrigerant pressure in the pipe conduit can be efficiently reduced by means of friction within the pipe. 
     Thereafter, the liquid refrigerant that has flowed into the first pipe conduit  28  of the evaporation unit  24  gradually evaporates as the heat exchange between the evaporation unit  24  and the storage chamber  6  is performed. The refrigerant is then gasified while flowing through the first pipe conduit  28 , the connecting pipe  50 , and the second pipe conduit  30  and flows into the second pipe  34 . The gaseous refrigerant that has flowed into the second pipe  34  then flows into the compressor again to be compressed and flows, as a high-pressure gas, into the condensation unit  20 . 
     In the present embodiment, the first pipe conduit  28  and the second pipe conduit  30  have the identical entire length. Accordingly, the contact length between the first pipe conduit  28  and the storage chamber  6  can be made equal to the contact length between the second pipe conduit  30  and the storage chamber  6 . Therefore, the thermal load applied on each of the first pipe conduit  28  and the second pipe conduit  30  is nearly identical, so that the inside of the storage chamber  6  can be uniformly cooled. Also, the first pipe conduit  28  and the second pipe conduit  30  can be manufactured more easily.  FIG. 5  is a schematic diagram used to describe a method for fabricating the first pipe conduit and the second pipe conduit. In  FIG. 5 , each dotted line a indicates a position at which a pipe material  52  is bent to fabricate the first pipe conduit  28 . Also, each dotted line b indicates a position at which the pipe material  52  is bent to fabricate the second pipe conduit  30 . 
     As illustrated in  FIG. 5 , when the entire length of the first pipe conduit  28  is identical with the entire length of the second pipe conduit  30 , each of the first pipe conduit  28  and the second pipe conduit  30  can be manufactured using the pipe material  52  in common. Also, in the first pipe conduit  28  and the second pipe conduit  30  of the present embodiment, the first long circumference part  40   a  and the second long circumference part  40   b  have the identical length, the first short circumference part  42   a  and the second short circumference part  42   b  have the identical length, and the first junction part  44   a  and the second junction part  44   b  have the identical length. Accordingly, the pipe material  52  can be used in common, with the first turning parts  46   a  or the second turning parts  46   b  already formed therein. More specifically, the first pipe conduit  28  and the second pipe conduit  30  can be fabricated using a snaking pipe in common, by making the bending positions (positions at which the pipe is bent to extend along each wall surface  26 ) thereof different. 
     Also, in the present embodiment, the number of first turning parts  46   a  and the number of second turning parts  46   b  are both even. Accordingly, bending directions of the snaking pipe can be made identical. More specifically, the pipe material  52  can be bent in the same way at all the dotted lines a or all the dotted lines b, either to form inverted V shapes or V shapes. Also, the angle between the first long circumference part  40   a  and the gravity direction, i.e., the inclination to the gravity direction, is identical with the angle between the second short circumference part  42   b  and the gravity direction. Similarly, the angle between the first short circumference part  42   a  and the gravity direction is identical with the angle between the second long circumference part  40   b  and the gravity direction. Further, the angle between a portion of the first junction part  44   a  winding in the first circumference direction and the gravity direction is identical with the angle between a portion of the second junction part  44   b  winding in the first circumference direction and the gravity direction. The same applies to the portions of the first junction part  44   a  and the second junction part  44   b  winding in the second circumference direction. Accordingly, the first pipe conduit  28  and the second pipe conduit  30  in contact with the storage chamber  6  follow similar trajectories in a vertical direction. Therefore, the storage chamber  6  can be uniformly cooled. Also, all of the portions of the first pipe conduit  28  and the second pipe conduit  30  winding in the first circumference direction and the portions of the first pipe conduit  28  and the second pipe conduit  30  winding in the second circumference direction may be configured such that the angle between each of the portions and the gravity direction becomes identical. This can cool the storage chamber  6  more uniformly. 
     When the number of wall surfaces  26  of the storage chamber  6  is defined as A, in each of the first pipe conduit  28  and the second pipe conduit  30 , the short circumference part ( 42   a ,  42   b ) extends along wall surfaces  26  of which the number is A/2×B (B is an integer greater than or equal to 1), and the difference between the number of wall surfaces  26  along which the short circumference part ( 42   a ,  42   b ) extends and the number of wall surfaces  26  along which the long circumference part ( 40   a ,  40   b ) extends is A/2. In other words, when the number of wall surfaces is defined as A, the number of wall surfaces overlapped by a short circumference part is defined as C, and the number of wall surfaces overlapped by a long circumference part is defined as D, the conditions of C=A/2×B (B is an integer greater than or equal to 1) and D−C=A/2 are satisfied. Accordingly, the total number of pipe portions in the first pipe conduit  28  and the second pipe conduit  30  overlapping each wall surface  26  can be made equal. Consequently, each wall surface  26  is equally cooled, so that the inside of the storage chamber  6  can be cooled more uniformly. 
     Also, in the present embodiment, the number of wall surfaces  26  along which the first turning pipe conduit  48   a  (or the first junction part  44   a ) extends is equal to the number of wall surfaces  26  along which the second turning pipe conduit  48   b  (or the second junction part  44   b ) extends; when the number of such wall surfaces is defined as E, the condition of E=A/2 is satisfied. Accordingly, all the wall surfaces  26  can be cooled by means of the first turning pipe conduit  48   a  and the second turning pipe conduit  48   b , so that the inside of the storage chamber  6  can be uniformly cooled. 
       FIGS. 6A-6F  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed. In  FIGS. 6A-6F , A as the number of wall surfaces  26  is four. Also, the number of first turning parts  46   a  and the number of second turning parts  46   b  are both even in  FIGS. 6A-6C  and are both odd in  FIGS. 6D-6F . 
     In  FIGS. 6A and 6D , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps four wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps two wall surfaces  26 . 
     Accordingly, the number of wall surfaces along which a short circumference part extends is 2, which satisfies the requirement of A/2×B (=4/2×1=2). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 4, and the number of wall surfaces along which a short circumference part extends, i.e., 2, is 2, which satisfies the requirement of A/2 (=4/2=2). In this case, the number of pipe portions overlapping each wall surface  26  becomes equal. 
     In  FIGS. 6B and 6E , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps five wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps three wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 3, which does not satisfy the requirement of A/2×B (or the requirement of “B is an integer greater than or equal to 1”). Meanwhile, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 5, and the number of wall surfaces along which a short circumference part extends, i.e., 3, is 2, which satisfies the requirement of A/2 (=4/2=2). In this case, the number of pipe portions overlapping each wall surface  26  is not equal. 
     In  FIGS. 6C and 6F , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps six wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps four wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 4, which satisfies the requirement of A/2×B (=4/2×2=4). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 6, and the number of wall surfaces along which a short circumference part extends, i.e., 4, is 2, which satisfies the requirement of A/2 (=4/2=2). In this case, the number of pipe portions overlapping each wall surface  26  becomes equal. 
       FIGS. 7A-7D  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed. In  FIGS. 7A-7D , A as the number of wall surfaces  26  is six. Also, the number of first turning parts  46   a  and the number of second turning parts  46   b  are both even. 
     In  FIG. 7A , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps six wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps three wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 3, which satisfies the requirement of A/2×B (=6/2×1=3). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 6, and the number of wall surfaces along which a short circumference part extends, i.e., 3, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  becomes equal. 
     In  FIG. 7B , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps seven wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps four wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 4, which does not satisfy the requirement of A/2×B (or the requirement of “B is an integer greater than or equal to 1”). Meanwhile, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 7, and the number of wall surfaces along which a short circumference part extends, i.e., 4, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is not equal. 
     In  FIG. 7C , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps eight wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps five wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 5, which does not satisfy the requirement of A/2×B (or the requirement of “B is an integer greater than or equal to 1”). Meanwhile, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 8, and the number of wall surfaces along which a short circumference part extends, i.e., 5, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is not equal. 
     In  FIG. 7D , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps nine wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps six wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 6, which satisfies the requirement of A/2×B (=6/2×2=6). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 9, and the number of wall surfaces along which a short circumference part extends, i.e., 6, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  becomes equal. 
       FIGS. 8A-8D  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed. In  FIGS. 8A-8D , A as the number of wall surfaces  26  is six. Also, the number of first turning parts  46   a  and the number of second turning parts  46   b  are both odd. 
     In  FIG. 8A , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps six wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps three wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 3, which satisfies the requirement of A/2×B (=6/2×1=3). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 6, and the number of wall surfaces along which a short circumference part extends, i.e.,  3 , is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  becomes equal. 
     In  FIG. 8B , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps seven wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps four wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 4, which does not satisfy the requirement of A/2×B (or the requirement of “B is an integer greater than or equal to 1”). Meanwhile, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 7, and the number of wall surfaces along which a short circumference part extends, i.e., 4, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is not equal. 
     In  FIG. 8C , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps eight wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps five wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 5, which does not satisfy the requirement of A/2×B (or the requirement of “B is an integer greater than or equal to 1”). Meanwhile, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 8, and the number of wall surfaces along which a short circumference part extends, i.e., 5, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is not equal. 
     In  FIG. 8D , each of the first long circumference part  40   a  and the second long circumference part  40   b  overlaps nine wall surfaces  26 , and each of the first short circumference part  42   a  and the second short circumference part  42   b  overlaps six wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 6, which satisfies the requirement of A/2×B (=6/2×2=6). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 9, and the number of wall surfaces along which a short circumference part extends, i.e., 6, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  becomes equal. 
     As described above, the refrigeration device  12  according to the present embodiment includes: the refrigerator  14 ; and the heat pipe  16  that includes the condensation unit  20  connected with the refrigerator  14  such that heat exchange therewith can be performed to condense a refrigerant, the evaporation unit  24  that extends along the wall surfaces  26  of the storage chamber  6  housing a preservation object and that is attached to the wall surfaces  26  such that heat exchange therewith can be performed to evaporate the refrigerant, and the pipe unit  22  through which the refrigerant is circulated between the condensation unit  20  and the evaporation unit  24 . The evaporation unit  24  includes the first pipe conduit  28  and the second pipe conduit  30 . 
     The first pipe conduit  28  includes: the first near-end part  36   a  located closer to the condensation unit  20 ; the first far-end part  38   a  located opposite to the first near-end part  36   a ; and the first long circumference part  40   a , the first short circumference part  42   a , and the first junction part  44   a  that are arranged between the first near-end part  36   a  and the first far-end part  38   a . The second pipe conduit  30  includes: the second near-end part  36   b  located closer to the condensation unit  20 ; the second far-end part  38   b  located opposite to the second near-end part  36   b ; and the second long circumference part  40   b , the second short circumference part  42   b , and the second junction part  44   b  that are arranged between the second near-end part  36   b  and the second far-end part  38   b.    
     The first near-end part  36   a  in the first pipe conduit  28  is positioned higher than the second near-end part  36   b , and the first pipe conduit  28  includes the first long circumference part  40   a  located closer to the first near-end part  36   a , the first short circumference part  42   a  located closer to the first far-end part  38   a , and the first junction part  44   a  located between the first long circumference part  40   a  and the first short circumference part  42   a . The first long circumference part  40   a  extends around the storage chamber  6  from the first near-end part  36   a  side toward the first far-end part  38   a  side in the first circumference direction, and also extends along more wall surfaces  26  than the first short circumference part  42   a . The first junction part  44   a  includes at least one first turning part  46   a  that changes the circumference direction of the first pipe conduit  28 . The first short circumference part  42   a  also extends around the storage chamber  6  from the first near-end part  36   a  side toward the first far-end part  38   a  side. The first short circumference part  42   a  extends in the first circumference direction when the number of first turning parts  46   a  is even, and extends in the second circumference direction, which is opposite to the first circumference direction, when the number of first turning parts  46   a  is odd. Also, the first short circumference part  42   a  extends along fewer wall surfaces  26  than the first long circumference part  40   a.    
     The second near-end part  36   b  in the second pipe conduit  30  is positioned lower than the first near-end part  36   a , and the second pipe conduit  30  includes the second short circumference part  42   b  located closer to the second near-end part  36   b , the second long circumference part  40   b  located closer to the second far-end part  38   b , and the second junction part  44   b  located between the second short circumference part  42   b  and the second long circumference part  40   b . The second short circumference part  42   b  extends around the storage chamber  6  from the second near-end part  36   b  side toward the second far-end part  38   b  side in the first circumference direction, and also extends along fewer wall surfaces  26  than the second long circumference part  40   b . The second junction part  44   b  includes the second turning part  46   b  that changes the circumference direction of the second pipe conduit  30  and that is equal in number to the first turning part  46   a . The second long circumference part  40   b  also extends around the storage chamber  6  from the second near-end part  36   b  side toward the second far-end part  38   b  side. The second long circumference part  40   b  extends in the first circumference direction when the number of second turning parts  46   b  is even, and extends in the second circumference direction when the number of second turning parts  46   b  is odd. Also, the second long circumference part  40   b  extends along more wall surfaces  26  than the second short circumference part  42   b.    
     The first turning part  46   a  positioned N-th counted from the first near-end part  36   a  side (N is an integer greater than or equal to 1) and the second turning part  46   b  positioned N-th counted from the second near-end part  36   b  side are disposed respectively on wall surfaces  26  facing each other. With such a configuration, compared to the case where the entire pipe is wound along the wall surfaces of the storage chamber in the same direction from one end part to the other end part, the number of pipe portions provided on each wall surface can be increased, and vertical intervals between pipe portions can be narrowed. This can make the temperature in the low-temperature storage  1  more stable. 
     Also, in the present embodiment, the first pipe conduit  28  and the second pipe conduit  30  can be provided, without intersection therebetween, on the wall surfaces  26  of the storage chamber  6 . When pipe conduits intersect, one of the pipe conduits is spaced away from the wall surface  26  at the intersection. Accordingly, the efficiency of cooling the storage chamber  6  is reduced by the pipe conduit spaced away at the intersection. In the present embodiment, on the other hand, such reduction in the cooling efficiency can be avoided. Therefore, the storage chamber  6  can be cooled more uniformly, so that the temperature in the low-temperature storage  1  can be made more stable. 
     In the present embodiment, the first long circumference part  40   a  and the second short circumference part  42   b  as a pair mainly cool an upper area of the storage chamber  6 . Also, the first short circumference part  42   a  and the second long circumference part  40   b  as a pair mainly cool a lower area of the storage chamber  6 . Further, the first junction part  44   a  and the second junction part  44   b  as a pair mainly cool a middle area of the storage chamber  6 . Accordingly, the entirety of the storage chamber  6  can be cooled in a balanced manner. 
     Also, in the present embodiment, the heat pipe  16  is a thermosiphon, in which each of the first pipe conduit  28  and the second pipe conduit  30  extends gradually downward in a vertical direction from the near-end part to the far-end part. Accordingly, providing the first pipe conduit  28  and the second pipe conduit  30 , without intersection therebetween, around the storage chamber  6  can be achieved more easily. Also, the first pipe conduit  28  and the second pipe conduit  30  are connected to the same refrigerator  14 . This can simplify the structure of the low-temperature storage  1 . 
     Also, the number of first turning parts  46   a  and the number of second turning parts  46   b  are both even, the first junction part  44   a  includes a first turning pipe conduit  48   a  that connects two adjacent first turning parts  46   a , and the second junction part  44   b  includes a second turning pipe conduit  48   b  that connects two adjacent second turning parts  46   b . Accordingly, in each pipe conduit, the long circumference part and the short circumference part can be provided to extend in the same circumference direction. 
     When the number of wall surfaces  26  of the storage chamber  6  is defined as A, in each of the first pipe conduit  28  and the second pipe conduit  30 , the short circumference part extends along wall surfaces  26  of which the number is A/2×B (B is an integer greater than or equal to 1), and the difference between the number of wall surfaces  26  along which the short circumference part extends and the number of wall surfaces  26  along which the long circumference part extends is A/2. Accordingly, the number of pipe portions overlapping each wall surface  26 , i.e., the number of times the first pipe conduit  28  and the second pipe conduit  30  pass along each wall surface  26 , can be made equal. Consequently, the storage chamber  6  can be cooled more uniformly, so that the temperature in the low-temperature storage  1  can be made more stable. 
     Also, the first pipe conduit  28  and the second pipe conduit  30  have the identical entire length. Accordingly, each of the first pipe conduit  28  and the second pipe conduit  30  can be fabricated using the pipe material  52  in common. Therefore, the manufacturing cost of the refrigeration device  12  can be reduced. Also, in the first pipe conduit  28  and the second pipe conduit  30 , the first long circumference part  40   a  and the second long circumference part  40   b  have the identical length, the first short circumference part  42   a  and the second short circumference part  42   b  have the identical length, and the first junction part  44   a  and the second junction part  44   b  have the identical length. Accordingly, the pipe material  52  can be used in common, with the first turning parts  46   a  or the second turning parts  46   b  already formed therein. Further, the number of first turning parts  46   a  and the number of second turning parts  46   b  are both even. Accordingly, bending directions of the snaking pipe can be made identical. Therefore, the processes for manufacturing the refrigeration device  12  can be further simplified. 
     The heat pipe  16  includes the connecting pipe  50  that connects the first far-end part  38   a  and the second far-end part  38   b . This can equalize the amounts of the liquid refrigerant in the first pipe conduit  28  and the second pipe conduit  30 . As a result, the storage chamber  6  can be cooled more uniformly, so that the temperature in the low-temperature storage  1  can be made more stable. 
     Second Embodiment 
     The second embodiment includes a configuration basically in common with the first embodiment, except that the structure of the refrigeration device  12  is different. In the following, the present embodiment will be described mainly for configurations different from those in the first embodiment, and description of configurations in common will be briefly given or may be omitted.  FIG. 9  is a perspective view of a low-temperature storage provided with a refrigeration device according to the second embodiment.  FIG. 10A  is a perspective view of the storage chamber and evaporation units.  FIG. 10B  is a perspective view of the evaporation units. 
     The refrigeration device  12  according to the present embodiment mounted on a low-temperature storage  1  ( 1 B) includes multiple sets of a refrigerator and a heat pipe. As an example, there will be described the refrigeration device  12  that includes a first system  12 I as a first set and a second system  12 II as a second set. The number of systems is not limited to two. In the following description and drawings, the reference numeral of each configuration included in the first system  12 I is provided with “I” at the end, and the reference numeral of each configuration included in the second system  12 II is provided with “II” at the end. 
     The first system  12 I includes a first refrigerator  14 I and a first heat pipe  16 I. The first refrigerator  14 I is the refrigerator  14  in the first embodiment, and the first heat pipe  16 I is the heat pipe  16  in the first embodiment. 
     The second system  12 II includes a second refrigerator  14 II provided separately from the first refrigerator  14 I, and a second heat pipe  16 II connected to the second refrigerator  14 II. The heat pipes ( 16 I,  16 II) of the respective systems ( 12 I,  12 II) are provided around the same storage chamber  6 . In other words, two refrigeration units are provided for one storage chamber  6 . 
     For the second refrigerator  14 II, a refrigerator having the same configuration as the first refrigerator  14 I may be used. As with the first heat pipe  16 I, the second heat pipe  16 II includes a condensation unit  20 II, a pipe unit  22 II, and an evaporation unit  24 II. The condensation unit  20 II and the pipe unit  22 II are configured similarly to the condensation unit  20 I and the pipe unit  22 I in the first system  12 I. The evaporation unit  24 II includes a first pipe conduit  28 II and a second pipe conduit  30 II. The first pipe conduit  28 II and the second pipe conduit  30 II are connected to the condensation unit  20 II, respectively through a first pipe  32 II and a second pipe  34 II. 
     The first pipe conduit  28 II is structured similarly to the first pipe conduit  28 I. More specifically, the first pipe conduit  28 II includes: a first near-end part  36   a II located closer to the condensation unit  20 II; a first far-end part  38   a II located on the opposite side; and a first long circumference part  40   a II, a first short circumference part  42   a II, and a first junction part  44   a II that are arranged between the first near-end part  36   a II and the first far-end part  38   a II. 
     The second pipe conduit  30 II is structured similarly to the second pipe conduit  30 I. More specifically, the second pipe conduit  30 II includes: a second near-end part  36   b II located closer to the condensation unit  20 II; a second far-end part  38   b II located on the opposite side; and a second long circumference part  40   b II, a second short circumference part  42   b II, and a second junction part  44   b II that are arranged between the second near-end part  36   b II and the second far-end part  38   b II. 
     The first near-end part  36   a II in the first pipe conduit  28 II is positioned higher than the second near-end part  36   b II. The first pipe conduit  28 II includes the first long circumference part  40   a II located closer to the first near-end part  36   a II, the first short circumference part  42   a II located closer to the first far-end part  38   a II, and the first junction part  44   a II located between the first long circumference part  40   a II and the first short circumference part  42   a II. 
     The first long circumference part  40   a II extends around the storage chamber  6  from the first near-end part  36   a II side toward the first far-end part  38   a II side in the first circumference direction, and also extends along more wall surfaces  26  than the first short circumference part  42   a II. The first junction part  44   a II includes at least one first turning part  46   a II that changes the circumference direction of the first pipe conduit  28 II. The first short circumference part  42   a II also extends around the storage chamber  6  from the first near-end part  36   a II side toward the first far-end part  38   a II side. The first short circumference part  42   a II extends in the first circumference direction when the number of first turning parts  46   a II is even, and extends in the second circumference direction, which is opposite to the first circumference direction, when the number of first turning parts  46   a II is odd. Also, the first short circumference part  42   a II extends along fewer wall surfaces  26  than the first long circumference part  40   a II. 
     The second near-end part  36   b II in the second pipe conduit  30 II is positioned lower than the first near-end part  36   a II. The second pipe conduit  30 II includes the second short circumference part  42   b II located closer to the second near-end part  36   b II, the second long circumference part  40   b II located closer to the second far-end part  38   b II, and the second junction part  44   b II located between the second short circumference part  42   b II and the second long circumference part  40   b II. 
     The second short circumference part  42   b II extends around the storage chamber  6  from the second near-end part  36   b II side toward the second far-end part  38   b II side in the first circumference direction, similarly to the first long circumference part  40   a II. Also, the second short circumference part  42   b II extends along fewer wall surfaces  26  than the second long circumference part  40   b II. The second junction part  44   b II includes a second turning part  46   b II that changes the circumference direction of the second pipe conduit  30 II and that is equal in number to the first turning part  46   a II. The second long circumference part  40   b II also extends around the storage chamber  6  from the second near-end part  36   b II side toward the second far-end part  38   b II side. The second long circumference part  40   b II extends in the first circumference direction when the number of second turning parts  46   b II is even, and extends in the second circumference direction when the number of second turning parts  46   b II is odd. Also, the second long circumference part  40   b II extends along more wall surfaces  26  than the second short circumference part  42   b II. 
     In the present embodiment, the number of first turning parts  46   a II in the first pipe conduit  28 II is equal to the number of first turning parts  46   a I in the first pipe conduit  28 I. Also, the number of second turning parts  46   b II in the second pipe conduit  30 II is equal to the number of second turning parts  46   b I in the second pipe conduit  30 I. Further, the number of first turning parts  46   a II in the first pipe conduit  28 II is equal to the number of second turning parts  46   b II in the second pipe conduit  30 II, and the number of first turning parts  46   a I in the first pipe conduit  28 I is equal to the number of second turning parts  46   b I in the second pipe conduit  30 I. Thus, the first turning parts  46   a I, the first turning parts  46   a II, the second turning parts  46   b I, and the second turning parts  46   b II are equal in number. Accordingly, the first system  12 I and the second system  12 II include the same number of turning parts. 
     Also, in the present embodiment, the storage chamber  6  around which the first heat pipe  16 I and the second heat pipe  16 II are provided includes four wall surfaces  26 , which are specifically the first wall surface  26   a , the second wall surface  26   b , the third wall surface  26   c , and the fourth wall surface  26   d . The first wall surface  26   a  through the fourth wall surface  26   d  are arranged in this order in the counterclockwise direction and define the storage chamber  6 . 
     The first pipe conduit  28 II and the second pipe conduit  30 II have structures obtained by rotating the first pipe conduit  28 I and the second pipe conduit  30 I in the counterclockwise direction by 90 degrees. Accordingly, the first near-end part  36   a II is disposed to overlap the second wall surface  26   b . For example, the first near-end part  36   a II is disposed near the side of the second wall surface  26   b  in contact with the first wall surface  26   a . The first long circumference part  40   a II extends around the storage chamber  6  from the first near-end part  36   a II side toward the first far-end part  38   a II side in the counterclockwise direction, and also extends along the second wall surface  26   b  through the first wall surface  26   a , i.e., four wall surfaces  26 . 
     The number of first turning parts  46   a II is even, and more specifically is two. The first turning part  46   a II positioned first and closer to the first long circumference part  40   a II side is disposed to overlap the first wall surface  26   a , and the first turning part  46   a II positioned second and closer to the first short circumference part  42   a II side is disposed to overlap the fourth wall surface  26   d . The first junction part  44   a II includes a first turning pipe conduit  48   a II that connects the two first turning parts  46   a II. 
     Each first turning part  46   a II has a substantial U-shape, and the first turning part  46   a II positioned first changes the circumference direction of the first pipe conduit  28 II from the counterclockwise direction to the clockwise direction. From the first turning part  46   a II positioned first, the first turning pipe conduit  48   a II extends in the clockwise direction along the first wall surface  26   a  and the fourth wall surface  26   d , i.e., two wall surfaces  26 , to reach the first turning part  46   a II positioned second. The first turning part  46   a II positioned second changes the circumference direction of the first pipe conduit  28 II from the clockwise direction to the counterclockwise direction. 
     The first short circumference part  42   a II extends around the storage chamber  6  from the first near-end part  36   a II side toward the first far-end part  38   a II side in the counterclockwise direction, similarly to the first long circumference part  40   a II, and also extends along the fourth wall surface  26   d  and the first wall surface  26   a , i.e., two wall surfaces  26 . 
     As with the first near-end part  36   a II, the second near-end part  36   b II is also disposed to overlap the second wall surface  26   b . The second short circumference part  42   b II extends around the storage chamber  6  from the second near-end part  36   b II side toward the second far-end part  38   b II side in the counterclockwise direction, similarly to the first long circumference part  40   a II, and also extends along the second wall surface  26   b  and the third wall surface  26   c , i.e., two wall surfaces  26 . 
     The number of second turning parts  46   b II is even, and more specifically is two. The second turning part  46   b II positioned first and closer to the second short circumference part  42   b II side is disposed to overlap the third wall surface  26   c , and the second turning part  46   b II positioned second and closer to the second long circumference part  40   b II side is disposed to overlap the second wall surface  26   b . The second junction part  44   b II includes a second turning pipe conduit  48   b II that connects the two second turning parts  46   b II. 
     Each second turning part  46   b II has a substantial U-shape, and the second turning part  46   b II positioned first changes the circumference direction of the second pipe conduit  30 II from the counterclockwise direction to the clockwise direction. From the second turning part  46   b II positioned first, the second turning pipe conduit  48   b II extends in the clockwise direction along the third wall surface  26   c  and the second wall surface  26   b , i.e., two wall surfaces  26 , to reach the second turning part  46   b II positioned second. The second turning part  46   b II positioned second changes the circumference direction of the second pipe conduit  30 II from the clockwise direction to the counterclockwise direction. 
     The second long circumference part  40   b II extends around the storage chamber  6  from the second near-end part  36   b II side toward the second far-end part  38   b II side in the counterclockwise direction, similarly to the first short circumference part  42   a II, and also extends along the second wall surface  26   b  through the first wall surface  26   a , i.e., four wall surfaces  26 . 
     The first turning part  46   a II positioned N-th counted from the first near-end part  36   a II side (N is an integer greater than or equal to 1) and the second turning part  46   b II positioned N-th counted from the second near-end part  36   b II side are disposed respectively on wall surfaces  26  facing each other. In the present embodiment, the first turning part  46   a II positioned first counted from the first near-end part  36   a II side is disposed on the first wall surface  26   a , and the second turning part  46   b II positioned first counted from the second near-end part  36   b II side is disposed on the third wall surface  26   c  that faces the first wall surface  26   a . Similarly, the first turning part  46   a II positioned second counted from the first near-end part  36   a II side is disposed on the fourth wall surface  26   d , and the second turning part  46   b II positioned second counted from the second near-end part  36   b II side is disposed on the second wall surface  26   b  that faces the fourth wall surface  26   d.    
     Further, in the present embodiment, the first turning part  46   a I and the second turning part  46   b I positioned N-th counted from the condensation unit  20 I side of the first heat pipe  16 I (N is an integer greater than or equal to 1) and the first turning part  46   a II and the second turning part  46   b II positioned N-th counted from the condensation unit  20 II side of the second heat pipe  16 II are each disposed on a different wall surface. 
     In the present embodiment, the first turning part  46   a I and the second turning part  46   b I positioned first counted from the condensation unit  20 I side of the first heat pipe  16 I are disposed respectively on the fourth wall surface  26   d  and the second wall surface  26   b . Meanwhile, the first turning part  46   a II and the second turning part  46   b II positioned first counted from the condensation unit  20 II side of the second heat pipe  16 II are disposed respectively on the first wall surface  26   a  and the third wall surface  26   c . Thus, these four turning parts are disposed on different wall surfaces  26 . 
     Also, the first turning part  46   a I and the second turning part  46   b I positioned second counted from the condensation unit  20 I side of the first heat pipe  16 I are disposed respectively on the third wall surface  26   c  and the first wall surface  26   a . Meanwhile, the first turning part  46   a II and the second turning part  46   b II positioned second counted from the condensation unit  20 II side of the second heat pipe  16 II are disposed respectively on the fourth wall surface  26   d  and the second wall surface  26   b . Thus, these four turning parts are disposed on different wall surfaces  26 . 
     As with the first heat pipe  16 I, the second heat pipe  16 II is also a thermosiphon. Accordingly, the first pipe conduit  28 II and the second pipe conduit  30 II are tilted to extend gradually downward in a vertical direction from the near-end parts ( 36   a II,  36   b II) to the far-end parts ( 38   a II,  38   b II), respectively. The second heat pipe  16 II includes a connecting pipe  50 II that connects the first far-end part  38   a II and the second far-end part  38   b II. The second heat pipe  16 II may also be structured to circulate a refrigerant using a compressor or the like. 
     A connecting pipe  50 I has a substantial U-shape, and, when viewed from a normal direction of the fourth wall surface  26   d , the curved portion protrudes from the fourth wall surface  26   d . More specifically, when viewed from a normal direction of the fourth wall surface  26   d , the curved portion of the connecting pipe  50 I protrudes in a normal direction of the first wall surface  26   a  from the side of the fourth wall surface  26   d  in contact with the first wall surface  26   a . Accordingly, the connecting pipe  50 I includes an area not in contact with the fourth wall surface  26   d . Meanwhile, the second long circumference part  40   b II extends from the fourth wall surface  26   d  to the first wall surface  26   a  such as to be positioned within the portion of the connecting pipe  50 I protruding from the fourth wall surface  26   d . In other words, the portion of the connecting pipe  50 I protruding from the fourth wall surface  26   d  is provided across the second long circumference part  40   b II. Accordingly, the first heat pipe  16 I and the second heat pipe  16 II can be provided around the same storage chamber  6 , with minimized intersections among the pipe conduits. More specifically, the first pipe conduit  28 I, the first pipe conduit  28 II, the second pipe conduit  30 I, and the second pipe conduit  30 II do not intersect each other, so that the entirety of each pipe conduit is in contact with wall surfaces  26 . Only the connecting pipe  50 I is spaced away from the wall surfaces  26 . Accordingly, the storage chamber  6  can be cooled more uniformly, so that the temperature in the low-temperature storage  1  can be made more stable. In a configuration not provided with the connecting pipe  50 I, the first heat pipe  16 I and the second heat pipe  16 II can be provided, without intersection therebetween, around the same storage chamber  6  and also without structural ingenuity, such as a pipe partially protruding from a wall surface. 
     Also, in the present embodiment, the first pipe conduit  28 II and the second pipe conduit  30 II in the second heat pipe  16 II have shapes obtained by turning upside down the first pipe conduit  28 I and the second pipe conduit  30 I in the first heat pipe  16 I.  FIG. 11  is a schematic diagram used to describe a postural relationship between the evaporation unit of the first heat pipe and the evaporation unit of the second heat pipe. As illustrated in  FIG. 11 , the first pipe conduit  28 II and the second pipe conduit  30 II have shapes identical with those obtained by rotating the first pipe conduit  28 I and the second pipe conduit  30 I about an axis Z as the rotational axis by 180 degrees. The axis Z is the line of intersection between a virtual plane X, which is parallel to the second wall surface  26   b  and the fourth wall surface  26   d  facing each other and is positioned in the middle between the two wall surfaces, and a virtual plane Y, which is parallel to a bottom surface  26   e  (the lower surface) and a top surface  26   f  (the upper surface) of the storage chamber  6  and is positioned in the middle between the two surfaces. The top surface  26   f  is a plane that includes the upper ends of the first wall surface  26   a  through the fourth wall surface  26   d.    
     The first near-end part  36   a II of the first pipe conduit  28 II corresponds to the second far-end part  38   b I of the second pipe conduit  30 I. Also, the second near-end part  36   b II of the second pipe conduit  30 II corresponds to the first far-end part  38   a I of the first pipe conduit  28 I. When the first pipe conduit  28 I and the second pipe conduit  30 I are turned upside down and when the connecting pipe  50 I connected to the first far-end part  38   a I and the second far-end part  38   b I is connected to the first near-end part  36   a I and the second near-end part  36   b I instead, the evaporation unit  24 II can be obtained. Accordingly, the evaporation unit  24 I and the evaporation unit  24 II can be configured using identically shaped components. Therefore, each of the evaporation unit  24 I and the evaporation unit  24 II can equally exchange the heat with the storage chamber  6 . More specifically, in both the cases where each of the first system  12 I and the second system  12 II is solely driven and where both the first system  12 I and the second system  12 II are simultaneously driven, the storage chamber  6  can be cooled more uniformly. 
     Also, as with the first pipe conduit  28 I and the second pipe conduit  30 I, the first pipe conduit  28 II and the second pipe conduit  30 II have the identical entire length. Accordingly, each of the first pipe conduit  28 II and the second pipe conduit  30 II can be manufactured using the pipe material  52  in common. Further, in the first pipe conduit  28 II and the second pipe conduit  30 II, the first long circumference part  40   a II and the second long circumference part  40   b II have the identical length, the first short circumference part  42   a II and the second short circumference part  42   b II have the identical length, and the first junction part  44   a II and the second junction part  44   b II have the identical length. Accordingly, the pipe material  52  can be used in common, with the first turning parts  46   a II or the second turning parts  46   b II already formed therein. Also, the number of first turning parts  46   a II and the number of second turning parts  46   b II are both even. Accordingly, bending directions of the snaking pipe can be made identical. 
     Also, when the number of wall surfaces of the storage chamber  6  is defined as A, the number of wall surfaces overlapped by a short circumference part is defined as C, and the number of wall surfaces overlapped by a long circumference part is defined as D, the first pipe conduit  28 I and the second pipe conduit  30 I, and the first pipe conduit  28 II and the second pipe conduit  30 II satisfy the conditions of C=A/2×B (B is an integer greater than or equal to 1) and D−C=A/2. Accordingly, the number of pipe portions overlapping each wall surface  26  can be made equal in each of the first system  12 I and the second system  12 II. Also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  can be made equal. Therefore, in both the cases where each of the first system  12 I and the second system  12 II is solely driven and where both the first system  12 I and the second system  12 II are simultaneously driven, the storage chamber  6  can be cooled more uniformly. 
       FIGS. 12A-12F  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed. In  FIGS. 12A-12F , the first pipe conduit  28 I and the second pipe conduit  30 I in the first system  12 I are indicated by solid lines, and the first pipe conduit  28 II and the second pipe conduit  30 II in the second system  12 II are indicated by dotted lines. In  FIGS. 12A-12F , A as the number of wall surfaces  26  is four. Also, the number of each of the turning parts ( 46   a I,  46   b I,  46   a II,  46   b II) is even in  FIGS. 12A-12C  and is odd in  FIGS. 12D-12F . 
     In  FIGS. 12A and 12D , in both the first system  12 I and the second system  12 II, each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps four wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps two wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 2, which satisfies the requirement of A/2×B (=4/2×1=2). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 4, and the number of wall surfaces along which a short circumference part extends, i.e., 2, is 2, which satisfies the requirement of A/2 (=4/2=2). In this case, the number of pipe portions overlapping each wall surface  26  is equal in each of the first system  12 I and the second system  12 II. Accordingly, also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  becomes equal. 
     In  FIGS. 12B and 12E , in both the first system  12 I and the second system  12 II, each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps five wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps three wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 3, which does not satisfy the requirement of A/2×B (or the requirement of “B is an integer greater than or equal to 1”). Meanwhile, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 5, and the number of wall surfaces along which a short circumference part extends, i.e., 3, is 2, which satisfies the requirement of A/2 (=4/2=2). In this case, the number of pipe portions overlapping each wall surface  26  is not equal in each of the first system  12 I and the second system  12 II. 
     Also, as illustrated in  FIG. 12B , when the number of each of the turning parts ( 46   a I,  46   b I,  46   a II,  46   b II) is even, the number of pipe portions overlapping each wall surface  26  is not equal also in the first system  12 I and the second system  12 II as a whole. On the other hand, as illustrated in  FIG. 12E , when the number of each of the turning parts ( 46   a I,  46   b I,  46   a II,  46   b II) is odd, the number of pipe portions overlapping each wall surface  26  becomes equal in the first system  12 I and the second system  12 II as a whole. Accordingly, when the number of each of the turning parts is odd, the storage chamber  6  can be uniformly cooled when the first system  12 I and the second system  12 II are simultaneously driven. However, when only one of the systems is solely driven, the cooling uniformity is reduced. 
     In  FIGS. 12C and 12F , in both the first system  12 I and the second system  12 II, each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps six wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps four wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 4, which satisfies the requirement of A/2×B (=4/2×2=4). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 6, and the number of wall surfaces along which a short circumference part extends, i.e., 4, is 2, which satisfies the requirement of A/2 (=4/2=2). In this case, the number of pipe portions overlapping each wall surface  26  is equal in each of the first system  12 I and the second system  12 II. Accordingly, also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  becomes equal. 
       FIGS. 13A-13D  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed. In  FIGS. 13A-13D , the first pipe conduit  28 I and the second pipe conduit  30 I in the first system  12 I are indicated by solid lines, and the first pipe conduit  28 II and the second pipe conduit  30 II in the second system  12 II are indicated by dotted lines. In  FIGS. 13A-13D , A as the number of wall surfaces  26  is six. Also, the number of each of the turning parts ( 46   a I,  46   b I,  46   a II,  46   b II) is even. 
     In  FIG. 13A , each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps six wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps three wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 3, which satisfies the requirement of A/2×B (=6/2×1=3). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 6, and the number of wall surfaces along which a short circumference part extends, i.e., 3, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is equal in each of the first system  12 I and the second system  12 II. Accordingly, also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  becomes equal. 
     In  FIG. 13B , each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps seven wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps four wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 4, which does not satisfy the requirement of A/2×B (or the requirement of “B is an integer greater than or equal to 1”). Meanwhile, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 7, and the number of wall surfaces along which a short circumference part extends, i.e., 4, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is not equal in each of the first system  12 I and the second system  12 II. Also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  is not equal. 
     In  FIG. 13C , each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps eight wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps five wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 5, which does not satisfy the requirement of A/2×B (or the requirement of “B is an integer greater than or equal to 1”). Meanwhile, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 8, and the number of wall surfaces along which a short circumference part extends, i.e., 5, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is not equal in each of the first system  12 I and the second system  12 II. Also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  is not equal. 
     In  FIG. 13D , each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps nine wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps six wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 6, which satisfies the requirement of A/2×B (=6/2×2=6). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 9, and the number of wall surfaces along which a short circumference part extends, i.e., 6, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is equal in each of the first system  12 I and the second system  12 II. Accordingly, also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  becomes equal. 
       FIGS. 14A-14D  are schematic diagrams that each illustrate a state where the wall surfaces of a storage chamber are developed. In  FIGS. 14A-14D , the first pipe conduit  28 I and the second pipe conduit  30 I in the first system  12 I are indicated by solid lines, and the first pipe conduit  28 II and the second pipe conduit  30 II in the second system  12 II are indicated by dotted lines. In  FIGS. 14A-14D , A as the number of wall surfaces  26  is six. Also, the number of each of the turning parts ( 46   a I,  46   b I,  46   a II,  46   b II) is odd. 
     In  FIG. 14A , each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps six wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps three wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 3, which satisfies the requirement of A/2×B (=6/2×1=3). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 6, and the number of wall surfaces along which a short circumference part extends, i.e., 3, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is equal in each of the first system  12 I and the second system  12 II. Accordingly, also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  becomes equal. 
     In  FIG. 14B , each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps seven wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps four wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 4, which does not satisfy the requirement of A/2×B (or the requirement of “B is an integer greater than or equal to 1”). Meanwhile, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 7, and the number of wall surfaces along which a short circumference part extends, i.e., 4, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is not equal in each of the first system  12 I and the second system  12 II. Also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  is not equal. 
     In  FIG. 14C , each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps eight wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps five wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 5, which does not satisfy the requirement of A/2×B (or the requirement of “B is an integer greater than or equal to 1”). Meanwhile, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 8, and the number of wall surfaces along which a short circumference part extends, i.e., 5, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is not equal in each of the first system  12 I and the second system  12 II. Also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  is not equal. 
     In  FIG. 14D , each of the long circumference parts ( 40   a I,  40   b I,  40   a II,  40   b II) overlaps nine wall surfaces  26 , and each of the short circumference parts ( 42   a I,  42   b I,  42   a II,  42   b II) overlaps six wall surfaces  26 . Accordingly, the number of wall surfaces along which a short circumference part extends is 6, which satisfies the requirement of A/2×B (=6/2×2=6). Also, the difference between the number of wall surfaces along which a long circumference part extends, i.e., 9, and the number of wall surfaces along which a short circumference part extends, i.e., 6, is 3, which satisfies the requirement of A/2 (=6/2=3). In this case, the number of pipe portions overlapping each wall surface  26  is equal in each of the first system  12 I and the second system  12 II. Accordingly, also in the first system  12 I and the second system  12 II as a whole, the number of pipe portions overlapping each wall surface  26  becomes equal. 
     As described above, the refrigeration device  12  according to the present embodiment includes the first system  12 I including the first refrigerator  14 I and the first heat pipe  16 I, and the second system  12 II including the second refrigerator  14 II, provided separately from the first refrigerator  14 I, and the second heat pipe  16 II. The second heat pipe  16 II includes the condensation unit  20 II, the pipe unit  22 II, and the evaporation unit  24 II, which includes the first pipe conduit  28 II and the second pipe conduit  30 II, and the second heat pipe  16 II is connected to the second refrigerator  14 II. The heat pipes ( 16 I,  16 II) of the respective systems ( 12 I,  12 II) are provided around the same storage chamber  6 . Accordingly, even if one of the first system  12 I and the second system  12 II fails, the other system can be used to uniformly cool the storage chamber  6 . Therefore, the temperature in the low-temperature storage  1  can be made more stable. 
     Also, in the present embodiment, the heat pipes ( 16 I,  16 II) of the respective systems ( 12 I,  12 II) are provided around the storage chamber  6  having four wall surfaces  26 , and the number of each of the turning parts ( 46   a I,  46   b I,  46   a II,  46   b II) is even. Accordingly, the shapes of the first pipe conduit  28 II and the second pipe conduit  30 II in the second heat pipe  16 II can be made equal to the shapes obtained by turning upside down the first pipe conduit  28 I and the second pipe conduit  30 I in the first heat pipe  16 I. Consequently, in both the cases where the storage chamber  6  is cooled only with the first system  12 I and where the storage chamber  6  is cooled only with the second system  12 II, the storage chamber  6  can be equally cooled in a balanced manner. Also, the manufacturing cost of the refrigeration device  12  can be reduced, and the processes for manufacturing the refrigeration device  12  can be simplified. 
     Also, in the present embodiment, the first turning part  46   a I and the second turning part  46   b I positioned N-th counted from the condensation unit  20 I side of the first heat pipe  16 I (N is an integer greater than or equal to 1) and the first turning part  46   a II and the second turning part  46   b II positioned N-th counted from the condensation unit  20 II side of the second heat pipe  16 II are each disposed on a different wall surface  26 . Accordingly, the first heat pipe  16 I and the second heat pipe  16 II can be provided around the same storage chamber  6 , with minimized intersections among the pipe conduits. As a result, the storage chamber  6  can be cooled more uniformly, so that the temperature in the low-temperature storage  1  can be made more stable. 
     Exemplary embodiments of the present invention have been described in detail. Each of the abovementioned embodiments merely describes a specific example for carrying out the present invention. The embodiments are not intended to limit the technical scope of the present invention, and various design modifications, including changes, addition, and deletion of constituting elements, may be made to the embodiments without departing from the scope of ideas of the invention defined in the claims. Such an additional embodiment with a design modification added has the effect of each of the combined embodiments and modifications. In the aforementioned embodiments, matters to which design modifications may be made are emphasized with the expression of “of the present embodiment”, “in the present embodiment”, or the like, but design modifications may also be made to matters without such expression. Optional combinations of the abovementioned constituting elements may also be employed as additional aspects of the present invention. Also, the hatching provided on the cross sections in the drawings is not provided to limit the materials of the objects with the hatching. 
     First Modification 
       FIG. 15  is a perspective view used to describe connecting pipes provided in a refrigeration device according to a first modification. Each of the connecting pipes ( 50 I,  50 II) in the first modification includes a portion extending along the bottom surface  26   e  of the storage chamber  6 . The portions in contact with the bottom surface  26   e  are configured as the lowermost parts of the connecting pipes ( 50 I,  50 II), or the lowermost parts of the evaporation units ( 24 I,  24 II). Accordingly, the inside of the storage chamber  6  can be cooled also from the bottom surface  26   e . Also, since the portion in contact with the bottom surface  26   e  is the lowermost part of the evaporation unit  24 , even in a configuration in which a refrigerant is circulated by gravity, such as a thermosiphon, the refrigerant partially remains liquid to reach the portion in contact with the bottom surface  26   e . The liquid refrigerant is then retained uniformly in the portion in contact with the bottom surface  26   e , so that heat exchange with the storage chamber  6  can be performed. Accordingly, irrespective of the refrigerant circulation method, the inside of the storage chamber  6  can be cooled also from the bottom surface  26   e . Consequently, the storage chamber  6  can be cooled more uniformly, so that the temperature in the low-temperature storage  1  can be made more stable. 
     Others 
     The refrigeration device  12  may also include a refrigerant container that is connected to the heat pipe  16  and that stores a refrigerant for the heat pipe  16 . For example, the refrigerant container may be connected to the refrigerant passage of the condensation unit  20  via a pipe. The refrigerant can be transferred between the heat pipe  16  and the refrigerant container through the pipe. When the pressure within the heat pipe  16  is increased, the refrigerant partially flows from the heat pipe  16  to the refrigerant container. When the pressure within the heat pipe  16  is reduced, the refrigerant partially flows from the refrigerant container to the heat pipe  16 . Accordingly, the pressure within the heat pipe  16  can be modulated. 
     The embodiments may be defined by the following item. 
     [Item 1] A low-temperature storage ( 1 ), including: 
     a storage chamber ( 6 ) that houses a preservation object; and 
     a refrigeration device ( 12 ) that cools the storage chamber ( 6 ).