Patent Publication Number: US-2023145285-A1

Title: Relay unit and air-conditioning apparatus including the same

Description:
TECHNICAL FIELD 
     The present disclosure relates to a relay unit configured to exchange heat between refrigerant and a heat medium and to an air-conditioning apparatus including the relay unit. 
     BACKGROUND ART 
     A known air-conditioning apparatus includes an outdoor unit, an indoor unit, and a heat medium relay unit provided between the outdoor unit and the indoor unit (see, for example, Patent Literature 1). A primary heat medium circulates between the outdoor unit and the heat medium relay unit. A secondary heat medium circulates between the indoor unit and the heat medium relay unit. The heat medium relay unit exchanges heat between the primary heat medium and the secondary heat medium. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: International Publication No. 2014/192139 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the case of the heat medium relay unit disclosed in Patent Literature 1, refrigerant pipes through which the primary heat medium circulates between the outdoor unit and the heat medium relay unit and heat medium pipes through which the secondary heat medium circulates between the indoor unit and the heat medium relay unit are attached to respective sides of a casing of the heat medium relay unit. Accordingly, to extend these pipes in an upward direction of the casing of the heat medium relay unit, it is necessary to temporarily extend the pipes in respective sideward directions of the casing and thereafter extend the pipes in the upward direction, thus resulting in an increase in the pipe length. 
     The present disclosure has been made to solve such a problem and an object thereof is to provide a relay unit configured to prevent pipes to be connected thereto from being lengthened and an air-conditioning apparatus including the relay unit. 
     Solution to Problem 
     A relay unit according to an embodiment of the present disclosure is a relay unit to be connected between a heat source side unit and a load side unit and includes: a heat medium heat exchanger that is to be connected to the heat source side unit via refrigerant pipes and that is to be connected to the load side unit via heat medium pipes; a casing containing the heat medium heat exchanger; a first refrigerant pipe connection port to be connected to one of the refrigerant pipes, the refrigerant pipes including a refrigerant pipe through which refrigerant flows from the heat source side unit into the heat medium heat exchanger and a refrigerant pipe through which the refrigerant flows out from the heat medium heat exchanger into the heat source side unit; a second refrigerant pipe connection port to be connected to an other of the refrigerant pipes; a first heat medium pipe connection port to be connected to one of the heat medium pipes, the heat medium pipes including a heat medium pipe through which a heat medium flows from the load side unit into the heat medium heat exchanger and a heat medium pipe through which the heat medium flows out from the heat medium heat exchanger into the load side unit; and a second heat medium pipe connection port to be connected to an other of the heat medium pipes. The first refrigerant pipe connection port, the second refrigerant pipe connection port, the first heat medium pipe connection port, and the second heat medium pipe connection port are provided on a top surface of the casing and face in a direction opposite to a direction of gravity. 
     An air-conditioning apparatus according to another embodiment of the present disclosure includes: a heat source side unit configured to generate a heat source; a load side unit configured to use the heat source generated by the heat source side unit; and the relay unit. 
     Advantageous Effects of Invention 
     According to the embodiments of the present disclosure, the port serving as a part to be connected to each of the refrigerant pipes and the heat medium pipes to be connected to the relay unit is provided on the top surface of the casing, and each port faces in the direction opposite to the direction of gravity. Thus, the refrigerant pipes and the heat medium pipes are connected, from above the casing, to the respective pipes connected to the heat medium heat exchanger. Accordingly, when the refrigerant pipes and the heat medium pipes extend in the upward direction from the top surface of the casing, it is possible to inhibit an increase in the pipe length compared with a configuration in which refrigerant pipes and heat medium pipes are attached to a side of a casing. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an external front view illustrating a configuration example of a relay unit according to Embodiment 1. 
         FIG.  2    is an external perspective view of the relay unit illustrated in  FIG.  1   . 
         FIG.  3    is a schematic diagram illustrating the relay unit illustrated in  FIG.  2    when viewed from above. 
         FIG.  4    is a circuit diagram illustrating a configuration example of an air-conditioning apparatus including the relay unit according to Embodiment 1. 
         FIG.  5    is an external front view schematically illustrating the state of the inside of each heat medium pipe of the relay unit illustrated in  FIG.  1   . 
         FIG.  6    is an external perspective view illustrating a configuration example of a relay unit according to Embodiment 2 to which pipes are connected. 
         FIG.  7    is an external perspective view illustrating a configuration example of a relay unit according to Embodiment 3. 
         FIG.  8    is an external perspective view illustrating the relay unit illustrated in  FIG.  7    whose drain pan is drawn out. 
         FIG.  9    is an external perspective view of the relay unit illustrated in  FIG.  7    when viewed in a different direction. 
         FIG.  10    is an external perspective view illustrating a configuration example of the drain pan illustrated in  FIG.  8   . 
         FIG.  11    is a schematic diagram illustrating a horizontal section of the relay unit illustrated in  FIG.  7    taken at the position at the height of the drain pan. 
         FIG.  12    is a layout illustrating an example in which the relay unit according to Embodiment 3 is installed. 
         FIG.  13    is a layout illustrating another example in which the relay unit according to Embodiment 3 is installed. 
         FIG.  14    is a layout illustrating still another example in which the relay unit according to Embodiment 3 is installed. 
         FIG.  15    is an external perspective view illustrating a configuration example of a drain pan to be provided in a relay unit according to Embodiment 4. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     The configuration of a relay unit in Embodiment 1 will be described.  FIG.  1    is an external front view illustrating a configuration example of the relay unit according to Embodiment 1.  FIG.  2    is an external perspective view of the relay unit illustrated in  FIG.  1   . As illustrated in  FIGS.  1  and  2   , a relay unit  4  includes a casing  5 , which has a cuboid shape. The casing  5  has a top surface  5   a,  a first side  5   b,  a second side  5   c,  a third side  5   d,  a fourth side  5   e,  and a bottom surface  5   f.  The second side  5   c  faces the first side  5   b.  The fourth side  5   e  faces the third side  5   d.  In Embodiment 1, the first side  5   b  is a front panel of the relay unit  4 , and the second side  5   c  is a rear panel of the relay unit  4 . The first side  5   b,  which is a front panel, is configured to be detached from the casing  5  to enable an operator to perform maintenance of the relay unit  4 . 
     As illustrated in  FIGS.  1  and  2   , a first refrigerant pipe connection port  6 , a second refrigerant pipe connection port  7 , first heat medium pipe connection ports  8   a  to  8   f,  and second heat medium pipe connection ports  9   a  to  9   f  are provided on the top surface  5   a  of the casing  5 . The first refrigerant pipe connection port  6 , the second refrigerant pipe connection port  7 , the first heat medium pipe connection ports  8   a  to  8   f,  and the second heat medium pipe connection ports  9   a  to  9   f  each face in the direction opposite to the direction of gravity (direction of an arrow of the Z axis). In addition, refrigerant pipe connection ports  11 , which serve as options, and heat medium pipe connection ports  10 , which serve as options, are provided on the top surface  5   a  of the casing  5 . The refrigerant pipe connection ports  11  and the heat medium pipe connection ports  10 , which serve as options, each also face in the direction opposite to the direction of gravity. 
     The configuration illustrated in  FIGS.  1  and  2    enables all refrigerant pipes and heat medium pipes to be each connected to extend in an upward direction (direction of the arrow of the Z axis) from the top surface  5   a  of the casing  5 . Even when refrigerant pipes or heat medium pipes have to be connected as options, the refrigerant pipes and the heat medium pipes that are connected as options are each also connected to extend in the upward direction from the top surface  5   a  of the casing  5 . Thus, it is possible to prevent pipes from extending in sideward directions of the casing  5  from any of the first side  5   b  to the fourth side  5   e.    
     In addition, a first opening  12  for a power supply line and a second opening  13  for a transmission line are formed in the top surface  5   a.  A power supply line and a transmission line (not illustrated) are each also connected to extend from the top surface  5   a  of the casing  5 . Thus, it is possible to prevent cables including a power supply line and a transmission line from extending in sideward directions of the casing  5  from any of the first side  5   b  to the fourth side  5   e.    
     In addition, this configuration is a configuration in which pipes and cables extend upward from the top surface  5   a  of the casing  5 . Thus, when an operator performs maintenance of the relay unit  4 , the operator can easily perform operations by detaching the first side  5   b.    
     As illustrated in  FIGS.  1  and  2   , the first heat medium pipe connection ports  8   a  to  8   f  are provided at respective positions in the top surface  5   a  closer to the first side  5   b,  and the second heat medium pipe connection ports  9   a  to  9   f  are provided at respective positions in the top surface  5   a  closer to the second side  5   c.  As illustrated in  FIG.  1   , the height of the first heat medium pipe connection ports  8   a  to  8   f  is lower than the height of the second heat medium pipe connection ports  9   a  to  9   f.  That is, the height of the first heat medium pipe connection ports  8   a  to  8   f  and the height of the second heat medium pipe connection ports  9   a  to  9   f  differ from each other. 
       FIG.  3    is a schematic diagram illustrating the relay unit illustrated in  FIG.  2    when viewed from above. For convenience of description,  FIG.  3    does not illustrate the first opening  12  and the second opening  13 , which are illustrated in  FIG.  2   . When referring to  FIG.  3   , the first heat medium pipe connection ports  8   a  to  8   f  are disposed to be spaced and to be parallel to a first edge  61 , which is an edge where the top surface  5   a  and the first side  5   b  illustrated in  FIG.  2    are in contact with each other. In addition, the second heat medium pipe connection ports  9   a  to  9   f  are disposed to be spaced and to be parallel to the first edge  61 . 
     In  FIG.  3   , the positions of the first heat medium pipe connection ports  8   a  to  8   f  in the direction along the first edge  61  (direction of an arrow of the X axis) and the positions of the second heat medium pipe connection ports  9   a  to  9   f  in the direction along the first edge  61  are shifted from each other relative to one vertex  62 , the vertex  62  and a vertex  63  being located at respective ends of the first edge  61 . That is, the positions where the second heat medium pipe connection ports  9   a  to  9   f  are disposed are shifted, in the direction along the first edge  61 , from the positions where the first heat medium pipe connection ports  8   a  to  8   f  are disposed. 
     Next, a configuration example of an air-conditioning apparatus including the relay unit  4  in Embodiment 1 will be described.  FIG.  4    is a circuit diagram illustrating a configuration example of an air-conditioning apparatus including the relay unit according to Embodiment 1. As illustrated in  FIG.  4   , an air-conditioning apparatus  1  includes a heat source side unit  2 , load side units  3   a  to  3   f,  and the relay unit  4 , which is connected between the heat source side unit  2  and the load side units  3   a  to  3   f.    
     The configuration example illustrated in  FIG.  4    illustrates a case in which the air-conditioning apparatus  1  includes six load side units  3   a  to  3   f.  However, the number of load side units is not limited to six and may be one. Detailed descriptions of the configurations of the heat source side unit  2  and the load side units  3   a  to  3   f  are omitted in Embodiment 1. In addition, detailed descriptions of the refrigerant flow between the heat source side unit  2  and the relay unit  4  and the heat medium flow between the relay unit  4  and the load side units  3   a  to  3   f  are omitted in Embodiment 1. 
     The heat source side unit  2  and the relay unit  4  are connected by refrigerant pipes  51  and  52 . Refrigerant circulates between the heat source side unit  2  and the relay unit  4  via the refrigerant pipes  51  and  52 . The load side unit  3   a  and the relay unit  4  are connected by heat medium pipes  32   a  and  33   a.  A heat medium such as water or brine circulates between the load side unit  3   a  and the relay unit  4  via the heat medium pipes  32   a  and  33   a.  The load side unit  3   b  and the relay unit  4  are connected by heat medium pipes  32   b  and  33   b.  A heat medium circulates between the load side unit  3   b  and the relay unit  4  via the heat medium pipes  32   b  and  33   b.    
     The load side unit  3   c  and the relay unit  4  are connected by heat medium pipes  32   c  and  33   c.  A heat medium circulates between the load side unit  3   c  and the relay unit  4  via the heat medium pipes  32   c  and  33   c.  The load side unit  3   d  and the relay unit  4  are connected by heat medium pipes  32   d  and  33   d.  A heat medium circulates between the load side unit  3   d  and the relay unit  4  via the heat medium pipes  32   d  and  33   d.  The load side unit  3   e  and the relay unit  4  are connected by heat medium pipes  32   e  and  33   e.  A heat medium circulates between the load side unit  3   e  and the relay unit  4  via the heat medium pipes  32   e  and  33   e.  The load side unit  3   f  and the relay unit  4  are connected by heat medium pipes  32   f  and  33   f.  A heat medium circulates between the load side unit  3   f  and the relay unit  4  via the heat medium pipes  32   f  and  33   f.    
     The heat source side unit  2  includes a compressor  21 , a heat source side heat exchanger  22 , a four-way valve  23 , an accumulator  24 , an expansion valve  25 , and a controller  20 , which is configured to control the air-conditioning apparatus  1 . The compressor  21 , the heat source side heat exchanger  22 , the four-way valve  23 , the accumulator  24 , and the expansion valve  25  are connected via refrigerant pipes  26 . 
     The load side unit  3   a  includes a load side heat exchanger  31   a.  The load side unit  3   b  includes a load side heat exchanger  31   b.  The load side unit  3   c  includes a load side heat exchanger  31   c.  The load side unit  3   d  includes a load side heat exchanger  31   d.  The load side unit  3   e  includes a load side heat exchanger  31   e.  The load side unit  3   f  includes a load side heat exchanger  31   f.    
     The relay unit  4  includes a pump  41 , a heat medium heat exchanger  42 , and flow control valves  44   a  to  44   f.  The heat medium heat exchanger  42 , the pump  41 , and the flow control valves  44   a  to  44   f  are connected via heat medium pipes  46 . One of two refrigerant pipe connection ports of the heat medium heat exchanger  42  is connected to the expansion valve  25  of the heat source side unit  2  via refrigerant pipes  45  and  51 . The other of the two refrigerant pipe connection ports of the heat medium heat exchanger  42  is connected to the four-way valve  23  of the heat source side unit  2  via refrigerant pipes  45  and  52 . 
     One of two heat medium pipe connection ports of the heat medium heat exchanger  42  is connected to the flow control valves  44   a  to  44   f  via the heat medium pipes  46  forming six branches. The other of the two heat medium pipe connection ports of the heat medium heat exchanger  42  is connected to a heat medium discharge port of the pump  41  via heat medium pipes  46 . The flow control valve  44   a  is connected to the load side heat exchanger  31   a  via the heat medium pipe  32   a.  The flow control valve  44   b  is connected to the load side heat exchanger  31   b  via the heat medium pipe  32   b.  The flow control valve  44   c  is connected to the load side heat exchanger  31   c  via the heat medium pipe  32   c,  The flow control valve  44   d  is connected to the load side heat exchanger  31   d  via the heat medium pipe  32   d.  The flow control valve  44   e  is connected to the load side heat exchanger  31   e  via the heat medium pipe  32   e.  The flow control valve  44   f  is connected to the load side heat exchanger  31   f  via the heat medium pipe  32   f.  The heat medium pipes  46  located closer to a heat medium suction port of the pump  41  form six branches and are connected to the heat medium pipes  33   a  to  33   f.    
     Next, the pipe connection configuration between the relay unit  4  illustrated in  FIG.  2    and each of the heat source side unit  2  and the load side units  3   a  to  3   f  illustrated in  FIG.  4    will be described. 
     One of the refrigerant pipes  51  and  52  illustrated in  FIG.  4    is connected to the first refrigerant pipe connection port  6  illustrated in  FIG.  2   . The other of the refrigerant pipes  51  and  52  illustrated in  FIG.  4    is connected to the second refrigerant pipe connection port  7 . The first heat medium pipe connection port  8   a  illustrated in  FIG.  2    is connected to one of the heat medium pipes  32   a  and  33   a  illustrated in  FIG.  4   . The second heat medium pipe connection port  9   a  illustrated in  FIG.  2    is connected to the other of the heat medium pipes  32   a  and  33   a  illustrated in  FIG.  4   . The first heat medium pipe connection port  8   b  illustrated in  FIG.  2    is connected to one of the heat medium pipes  32   b  and  33   b  illustrated in  FIG.  4   . The second heat medium pipe connection port  9   b  illustrated in  FIG.  2    is connected to the other of the heat medium pipes  32   b  and  33   b  illustrated in  FIG.  4   . 
     The first heat medium pipe connection port  8   c  illustrated in  FIG.  2    is connected to one of the heat medium pipes  32   c  and  33   c  illustrated in  FIG.  4   . The second heat medium pipe connection port  9   c  illustrated in  FIG.  2    is connected to the other of the heat medium pipes  32   c  and  33   c  illustrated in  FIG.  4   . The first heat medium pipe connection port  8   d  illustrated in  FIG.  2    is connected to one of the heat medium pipes  32   d  and  33   d  illustrated in  FIG.  4   . The second heat medium pipe connection port  9   d  illustrated in  FIG.  2    is connected to the other of the heat medium pipes  32   d  and  33   d  illustrated in  FIG.  4   . The first heat medium pipe connection port  8   e  illustrated in  FIG.  2    is connected to one of the heat medium pipes  32   e  and  33   e  illustrated in  FIG.  4   . The second heat medium pipe connection port  9   e  illustrated in  FIG.  2    is connected to the other of the heat medium pipes  32   e  and  33   e  illustrated in  FIG.  4   . The first heat medium pipe connection port  8   f  illustrated in  FIG.  2    is connected to one of the heat medium pipes  32   f  and  33   f  illustrated in  FIG.  4   . The second heat medium pipe connection port  9   f  illustrated in  FIG.  2    is connected to the other of the heat medium pipes  32   f  and  33   f  illustrated in  FIG.  4   . 
     The ports for connecting the respective refrigerant pipes and the ports for connecting the respective heat medium pipes are not gathered on any of the first side  5   b  to the fourth side  5   e  of the casing  5  but on the top surface  5   a.  In addition, as illustrated in  FIG.  3   , similarly to the arrangement of the first heat medium pipe connection port  8   a  and the second heat medium pipe connection port  9   a,  the heat medium pipes are arranged, in the direction of the arrow of the X axis from the vertex  62 , alternately at the positions in the top surface  5   a  closer to the first side  5   b  and the positions in the top surface  5   a  closer to the second side  5   c.  The spaces between the connection ports adjacent to each other are wide. Thus, when an operator connects the heat medium pipes to the relay unit  4 , the operator can easily perform pipe connection operations. Furthermore, the height of the first heat medium pipe connection ports  8   a  to  8   f  and the height of the second heat medium pipe connection ports  9   a  to  9   f  differ from each other, thus improving the ease of connecting the heat medium pipes to the relay unit  4 . 
     Next, a trial operation of the installed air-conditioning apparatus  1  in Embodiment 1 will be described. An operator installs the air-conditioning apparatus  1  illustrated in  FIG.  4    and then fills a heat medium into the heat medium pipes  32   a  to  32   f,    33   a  to  33   f,  and  46 . Subsequently, the operator has to purge air from the heat medium pipes  32   a  to  32   f,    33   a  to  33   f,  and  46 . Air remaining in a heat medium can result in malfunction of the pump  41  in addition to impairment of heat exchange efficiency. 
     In the relay unit  4  in Embodiment 1, air is easily purged from a heat medium filled in the heat medium pipes  46  compared with a horizontal pipe structure in which heat medium pipes are attached to a side of a casing in a sideward direction. This will be described with reference to  FIG.  5   .  FIG.  5    is an external front view schematically illustrating the state of the inside of each heat medium pipe of the relay unit illustrated in  FIG.  1   .  FIG.  5    schematically illustrates the heat medium pipe  46  connected to each of the second heat medium pipe connection ports  9   b  and  9   d.    
     For example, when the heat medium is water and water is filled in the heat medium pipes  46  of the relay unit  4 , as illustrated in  FIG.  5   , air  101  moves in the heat medium pipes  46  in the direction opposite to the direction of gravity (direction of the arrow of the Z axis) because the air  101  has a density lower than that of water. It is clear that provision of an air purge valve above each of the second heat medium pipe connection ports  9   b  and  9   d  enables the air  101  to be easily purged from the heat medium pipe  46 . 
     The first refrigerant pipe connection port  6 , the second refrigerant pipe connection port  7 , the first heat medium pipe connection ports  8   a  to  8   f,  and the second heat medium pipe connection ports  9   a  to  9   f  are provided on the top surface  5   a  of the casing  5  of the relay unit  4  in Embodiment 1. The first refrigerant pipe connection port  6 , the second refrigerant pipe connection port  7 , the first heat medium pipe connection ports  8   a  to  8   f,  and the second heat medium pipe connection ports  9   a  to  9   f  each face in the direction opposite to the direction of gravity. 
     According to Embodiment 1, the port serving as a part to be connected to each of the refrigerant pipes and the heat medium pipes to be connected to the relay unit  4  is provided on the top surface  5   a  of the casing  5 , and each port faces in the direction opposite to the direction of gravity. Thus, the refrigerant pipes and the heat medium pipes are connected, from above the casing  5 , to the respective pipes connected to the heat medium heat exchanger  42 . When the refrigerant pipes and the heat medium pipes extend in the upward direction from the top surface  5   a  of the casing  5 , it is possible to inhibit an increase in the pipe length compared with an existing relay unit in which refrigerant pipes and heat medium pipes are attached to a side of a casing. 
     In addition, in the relay unit  4  in Embodiment 1, pipes such as a refrigerant pipe and cables such as a power supply line are not connected to the first side  5   b,  which is the front side of the casing  5 . Accordingly, an operator can use the front side of the casing  5  as a maintenance space for the relay unit  4  and easily detach the first side  5   b,  thus improving maintenance efficiency. 
     Furthermore, the first heat medium pipe connection ports  8   a  to  8   f  and the second heat medium pipe connection ports  9   a  to  9   f  are provided on the top surface  5   a  of the casing  5  of the relay unit  4  in Embodiment 1, and each port faces in the direction opposite to the direction of gravity. Thus, as described with reference to  FIG.  5   , when the air  101  is purged from a heat medium filled in heat medium pipes such as the heat medium pipes  46 , the air  101  easily moves in the upward direction of the casing  5 . As a result, since air is easily purged from the heat medium pipes compared with a horizontal pipe structure, an operator can purge air in a short time. 
     Embodiment 2 
     Embodiment 2 is an example in which heat medium pipes are connected to the relay unit  4  described in Embodiment 1. In Embodiment 2, the same components as those described in Embodiment 1 have the same reference signs, and detailed descriptions thereof are omitted. 
     The configuration of the relay unit  4  in Embodiment 2 will be described.  FIG.  6    is an external perspective view illustrating a configuration example of a relay unit according to Embodiment 2 to which pipes are connected. In the configuration example illustrated in  FIG.  6   , the heat medium pipe  32   a  illustrated in  FIG.  4    is connected to the first heat medium pipe connection port  8   a  illustrated in  FIG.  2   . The heat medium pipe  32   b  illustrated in  FIG.  4    is connected to the first heat medium pipe connection port  8   b  illustrated in  FIG.  2   . The heat medium pipe  32   c  illustrated in  FIG.  4    is connected to the first heat medium pipe connection port  8   c  illustrated in  FIG.  2   . The heat medium pipe  32   d  illustrated in  FIG.  4    is connected to the first heat medium pipe connection port  8   d  illustrated in  FIG.  2   . The heat medium pipe  32   e  illustrated in  FIG.  4    is connected to the first heat medium pipe connection port  8   e  illustrated in  FIG.  2   . The heat medium pipe  32   f  illustrated in  FIG.  4    is connected to the first heat medium pipe connection port  8   f  illustrated in  FIG.  2   . 
     In the configuration example illustrated in  FIG.  6   , the heat medium pipes  32   a  to  32   f  and  33   a  to  33   f  extend in the direction of the arrow of the X axis. However, the direction in which pipes are disposed is not limited to that illustrated in  FIG.  6   . In addition,  FIG.  6    illustrates an example in which heat medium pipes  35  are connected to the respective heat medium pipe connection ports  10  illustrated in  FIG.  2   . However, when the heat medium pipe connection ports  10  are not used, the heat medium pipes  35  do not have to be provided. 
     In the configuration example illustrated in  FIG.  6   , the heat medium pipe  33   a  illustrated in  FIG.  4    is connected to the second heat medium pipe connection port  9   a  illustrated in  FIG.  2   . The heat medium pipe  33   b  illustrated in  FIG.  4    is connected to the second heat medium pipe connection port  9   b  illustrated in  FIG.  2   . The heat medium pipe  33   c  illustrated in  FIG.  4    is connected to the second heat medium pipe connection port  9   c  illustrated in  FIG.  2   . The heat medium pipe  33   d  illustrated in  FIG.  4    is connected to the second heat medium pipe connection port  9   d  illustrated in  FIG.  2   . The heat medium pipe  33   e  illustrated in  FIG.  4    is connected to the second heat medium pipe connection port  9   e  illustrated in  FIG.  2   . The heat medium pipe  33   f  illustrated in  FIG.  4    is connected to the second heat medium pipe connection port  9   f  illustrated in  FIG.  2   . 
     An air purge valve  14   a  is provided at a place in the heat medium pipe  33   a  located above the second heat medium pipe connection port  9   a  illustrated in  FIG.  2   . An air purge valve  14   b  is provided at a place in the heat medium pipe  33   b  located above the second heat medium pipe connection port  9   b  illustrated in  FIG.  2   . An air purge valve  14   c  is provided at a place in the heat medium pipe  33   c  located above the second heat medium pipe connection port  9   c  illustrated in  FIG.  2   . 
     An air purge valve  14   d  is provided at a place in the heat medium pipe  33   d  located above the second heat medium pipe connection port  9   d  illustrated in  FIG.  2   . An air purge valve  14   e  is provided at a place in the heat medium pipe  33   e  located above the second heat medium pipe connection port  9   e  illustrated in  FIG.  2   . An air purge valve  14   f  is provided at a place in the heat medium pipe  33   f  located above the second heat medium pipe connection port  9   f  illustrated in  FIG.  2   . 
     In the configuration example illustrated in  FIG.  6   , an on-off valve  15  is provided at each of the first heat medium pipe connection ports  8   a  to  8   f  and the second heat medium pipe connection ports  9   a  to  9   f  illustrated in  FIG.  2   . As described in Embodiment 1 with reference to  FIG.  1   , the height of the first heat medium pipe connection ports  8   a  to  8   f  and the height of the second heat medium pipe connection ports  9   a  to  9   f  differ from each other. The second heat medium pipe connection ports  9   a  to  9   f  are higher than the first heat medium pipe connection ports  8   a  to  8   f,  and the levels thereof thus differ from each other. Accordingly, space is formed between the heat medium pipes  32   a  to  32   f  and the heat medium pipes  33   a  to  33   f,  facilitating operation of the on-off valve  15  of each of the second heat medium pipe connection ports  9   a  to  9   f.    
     Although not illustrated in  FIG.  6   , an air purge valve may be provided at each of the heat medium pipes  32   a  to  32   f.  The heat medium pipes  33   a  to  33   f  are located higher than the heat medium pipes  32   a  to  32   f.  Thus, even when air purge valves (not illustrated) are provided on the respective heat medium pipes  32   a  to  32   f,  the air purge valves do not interfere with the heat medium pipes  33   a  to  33   f.    
     As described in Embodiment 1, the first opening  12  and the second opening  13  are formed in the top surface  5   a  of the casing  5 . As illustrated in  FIG.  6   , a power supply line  71  extends from the first opening  12  and is connected to a power supply (not illustrated). A transmission line  72  extends from the second opening  13  and is connected to the controller  20  illustrated in  FIG.  4   . The transmission line  72  serves to transmit a control signal output from the controller  20 . The power supply line  71  and the transmission line  72  are disposed along the heat medium pipe  32   a  and are fastened to the heat medium pipe  32   a  with a cable tie  73 . In the casing  5 , the power supply line  71  is connected to the pump  41  and the flow control valves  44   a  to  44   f  illustrated in FIG. 
       4 . In the casing  5 , the transmission line  72  is connected to the pump  41  and the flow control valves  44   a  to  44   f  illustrated in  FIG.  4   . 
     In the relay unit  4  in Embodiment 2, the first heat medium pipe connection ports  8   a  to  8   f  are provided at the respective positions closer to the first side  5   b,  and the second heat medium pipe connection ports  9   a  to  9   f  are provided at the respective positions closer to the second side  5   c.  The height of the first heat medium pipe connection ports  8   a  to  8   f  is lower than the height of the second heat medium pipe connection ports  9   a  to  9   f.  Since the height of the second heat medium pipe connection ports  9   a  to  9   f  located closer to the rear side of the casing  5  is higher than the height of the first heat medium pipe connection ports  8   a  to  8   f  located closer to the front side of the casing  5 , an operator can easily operate the on-off valve  15  attached to each of the second heat medium pipe connection ports  9   a  to  9   f  and easily attach the air purge valves  14   a  to  14   f  above the second heat medium pipe connection ports  9   a  to  9   f.  In this manner, Embodiment 2 facilitates attachment of air purge valves, and hangers necessary for a horizontal pipe structure do not have to be provided, thus improving workability and serviceability. 
     In addition, in Embodiment 2, the relay unit  4  may include the power supply line  71  extending from the inside of the casing  5  via the first opening  12  formed in the top surface  5   a  of the casing  5 . Furthermore, the relay unit  4  may include the transmission line  72  extending from the inside of the casing  5  via the second opening  13  formed in the top surface  5   a  of the casing  5 . 
     Since the first opening  12  and the second opening  13  are formed in the top surface  5   a  of the casing  5 , it is possible to draw out, through the top surface  5   a  of the casing  5 , the power supply line  71  and the transmission line  72  connected to the inside of the relay unit  4 . Thus, it is possible to route the power supply line  71  and the transmission line  72  along pipes such as the heat medium pipe  32   a  extending toward a ceiling. 
     Embodiment 2 enables pipes such as refrigerant pipes and heat medium pipes and cables including the power supply line  71  and the transmission line  72  to be bundled together and to be fixed to the top surface  5   a  of the casing  5 . Thus, such cables are not attached to the front side. Accordingly, when an operator detaches the front panel to perform maintenance of the relay unit  4 , the operator does not have to beware of cutting cables compared with an example in which cables are attached to the front of a casing. In addition, since cables are not attached to the front side of the casing  5 , the operator can use the front side of the casing  5  as a maintenance space, thus improving maintenance efficiency. 
     Embodiment 3 
     Embodiment 3 is an example in which the relay unit  4  described in Embodiment 1 includes a drain pan. In Embodiment 3, the same components as those described in Embodiments 1 and 2 have the same reference signs, and detailed descriptions thereof are omitted. 
     The configuration of the relay unit  4  in Embodiment 3 will be described.  FIG.  7    is an external perspective view illustrating a configuration example of a relay unit according to Embodiment 3.  FIG.  8    is an external perspective view illustrating the relay unit illustrated in  FIG.  7    whose drain pan is drawn out. 
     As illustrated in  FIG.  8   , the relay unit  4  includes a drain pan  18 .  FIG.  8    illustrates a state in which the drain pan  18  is drawn out from the casing  5 .  FIG.  7    illustrates a state in which the drain pan  18  is housed in the casing  5 . In  FIG.  7   , the drain pan  18  illustrated in  FIG.  8    is disposed above the bottom surface  5   f.  The drain pan  18  serves to store dew condensation water generated when condensation occurs on a surface of the heat medium heat exchanger  42  illustrated in  FIG.  4   . 
     As illustrated in  FIG.  8   , the drain pan  18  includes a first drain port  17   a  and a second drain port  17   b.  In the state in which the drain pan  18  is housed in the casing  5 , a first drain socket  16   a  is formed in the part of the first side  5   b  located at the position equivalent to the first drain port  17   a,  and a second drain socket  16   b  is formed in the part of the third side  5   d  located at the position equivalent to the second drain port  17   b.  In Embodiment 3, as illustrated in  FIG.  8   , the first side  5   b  includes a drawer panel  50 , which is a part configured to be separate. An operator can slide the drain pan  18  and draw out the drain pan  18  from the casing  5  by drawing the drawer panel  50  in the direction opposite to the direction of an arrow of the Y axis. An operator can slide the drain pan  18  and house the drain pan  18  in the casing  5  by pushing the drawer panel  50  in the direction of the arrow of the Y axis. 
       FIG.  9    is an external perspective view of the relay unit illustrated in  FIG.  7    when viewed in a different direction. As illustrated in  FIG.  9   , a third drain socket  16   c  is formed in the part of the second side  5   c  located at the position equivalent to the height of the drain pan  18  housed in the casing  5 , and a fourth drain socket  16   d  is formed in the part of the fourth side  5   e  located at the position equivalent to the height of the drain pan  18  housed in the casing  5 . 
     Next, the overall configuration of the drain pan  18  illustrated in  FIG.  8    will be described.  FIG.  10    is an external perspective view illustrating a configuration example of the drain pan illustrated in  FIG.  8   . The drain pan  18  includes a plate  81 , which has a rectangular shape corresponding to the shape of the bottom surface  5   f,  and four frame portions  82   a  to  82   d,  which are provided around the plate  81 . The four frame portions  82   a  to  82   d  prevent dew condensation water from leaking out from the plate  81 . Of the two frame portions  82   a  and  82   b  adjacent to each other, the first drain port  17   a  is formed at the position in one frame portion, that is, the frame portion  82   a,  at a first distance xi from a second edge  64 , where the two frame portions  82   a  and  82   b  are in contact with each other, and the second drain port  17   b  is formed at the position in the other frame portion, that is, the frame portion  82   b,  at a second distance y 1  from the second edge  64 .  FIG.  9    illustrates an example in which the drain pan  18  is inserted into the casing  5  such that the frame portion  82   c  is located closer to the second side  5   c  of the casing  5  illustrated in  FIG.  8   . 
     Next, the positional relationships between the first drain socket  16   a  to the fourth drain socket  16   d  illustrated in  FIGS.  8  and  9    will be described.  FIG.  11    is a schematic diagram illustrating a horizontal section of the relay unit illustrated in  FIG.  7    taken at the position at the height of the drain pan. 
     In  FIG.  11   , an edge where the first side  5   b  and the third side  5   d  are in contact with each other is a third edge  65 , and an edge where the second side  5   c  and the fourth side  5   e  are in contact with each other is a fourth edge  66 . The rectangular shape illustrated in  FIG.  11    corresponds to the shape of the bottom surface  5   f.  A centroid  67  of the rectangular shape illustrated in  FIG.  11    overlaps the centroid of the bottom surface  5   f  on the Z axis. As illustrated in  FIG.  11    the first drain socket  16   a  is formed at the position in the first side  5   b  at the first distance x 1  from the third edge  65 , and the second drain socket  16   b  is formed at the position in the third side  5   d  at the second distance y 1  from the third edge  65 . 
     In addition, the third drain socket  16   c  is formed at a position in the second side  5   c,  the position in the second side  5   c  and the position of the first drain socket  16   a  being symmetrical relative to the centroid  67  as the symmetry center point. That is, the third drain socket  16   c  is formed at the position in the second side  5   c  at the first distance x 1  from the fourth edge  66 . The fourth drain socket  16   d  is formed at a position in the fourth side  5   e,  the position in the fourth side  5   e  and the position of the second drain socket  16   b  being symmetrical relative to the centroid  67  as the symmetry center point. 
     The fourth drain socket  16   d  is formed at the position in the fourth side  5   e  at the second distance y 1  from the fourth edge  66 . 
     The configuration illustrated in  FIG.  11    enables the drain pan  18  to be inserted into the casing  5  such that the frame portion  82   c  is located closer to the second side  5   c  of the casing  5  and such that the frame portion  82   a  is located closer to the second side  5   c  of the casing  5 . When the drain pan  18  is housed in the casing  5  such that the frame portion  82   c  is located closer to the second side  5   c  of the casing  5 , either of the first drain socket  16   a  and the second drain socket  16   b  can be chosen as a drain port. In addition, when the drain pan  18  is housed in the casing  5  such that the frame portion  82   a  is located closer to the second side  5   c  of the casing  5 , either of the third drain socket  16   c  and the fourth drain socket  16   d  can be chosen as a drain port. In this manner, an operator can choose a drain port from the first drain socket  16   a  to the fourth drain socket  16   d  of the first side  5   b  to the fourth side  5   e.    
     Next, an example in which the relay unit  4  is installed beside walls will be described.  FIG.  12    is a layout illustrating an example in which the relay unit according to Embodiment 3 is installed.  FIG.  12    illustrates an example in which the second side  5   c,  the third side  5   d,  and the fourth side  5   e  are surrounded by walls with the first side  5   b  located beside an open space. In this example, an operator houses the drain pan  18  in the casing  5  as illustrated in  FIG.  7    and can then connect a drain hose  55  to the first drain port  17   a  and the first drain socket  16   a  as illustrated in  FIG.  12   . 
       FIG.  13    is a layout illustrating another example in which the relay unit according to Embodiment 3 is installed.  FIG.  13    illustrates an example in which the second side  5   c  and the fourth side  5   e  are surrounded by walls with the first side  5   b  and the third side  5   d  located beside an open space. An operator houses the drain pan  18  in the casing  5  as illustrated in  FIG.  7    and then connects the drain hose  55  to the second drain port  17   b  and the second drain socket  16   b  as illustrated in  FIG.  13   . In this example, it is possible to make space for maintenance in front of the first side  5   b  of the casing  5 . 
       FIG.  14    is a layout illustrating still another example in which the relay unit according to Embodiment 3 is installed.  FIG.  14    illustrates an example in which the second side  5   c  and the third side  5   d  are surrounded by walls with the first side  5   b  and the fourth side  5   e  located beside an open space. An operator houses the drain pan  18  in the casing  5  such that the frame portion  82   a  illustrated in  FIG.  10    of the drain pan  18  is located closer to the second side  5   c  and then connects the drain hose  55  to the second drain port  17   b  and the fourth drain socket  16   d  as illustrated in  FIG.  14   . In this example, it is possible to make space for maintenance in front of the first side  5   b  of the casing  5 . 
     In this manner, even when the casing  5  is installed beside walls, an operator can choose a port for the drain hose  55  according to the layout of walls and a maintenance area, for example. 
     The relay unit  4  in Embodiment 3 includes the drain pan  18 , which is configured to store dew condensation water and to be slid and drawn out from the casing  5 . Thus, the drain pan  18  is easy to clean. In addition, in Embodiment 3, a port for the drain hose  55  is provided in each of the first side  5   b  to the fourth side Se of the relay unit  4 , and drain ports are provided in two parts of the drain pan  18 . When an operator houses the drain pan  18  in the casing  5 , the operator can choose between two orientations of the drain pan  18  to be inserted into the casing  5  and choose, from four sides, that is, the first side  5   b  to the fourth side  5   e,  a surface to which the drain hose  55  is attached. 
     In Embodiment 3, a surface to which the drain hose  55  is attached can be chosen from four sides, that is, the first side  5   b  to the fourth side  5   e.  Thus, even when the relay unit  4  is installed beside walls, it is possible to attach the drain hose  55  to the relay unit  4  as long as a side located beside an open space is included in the four sides. 
     In addition, in Embodiment 3, two drain ports are provided in the drain pan  18 . Thus, one of the two drain ports can be used as a regular drain port, and the other of the two drain ports can be used as an emergency drain port. 
     Embodiment 4 
     In Embodiment 4, the relay unit  4  described in Embodiment 3 is formed to include a drain pan whose configuration is different. In Embodiment 4, the same components as those described in Embodiments 1 to 3 have the same reference signs, and detailed descriptions thereof are omitted. 
     The configuration of a drain pan to be provided in the relay unit  4  in Embodiment 4 will be described. Other than the drain pan, the relay unit  4  in Embodiment 4 has a configuration similar to that described in Embodiment 3, and detailed descriptions thereof are thus omitted.  FIG.  15    is an external perspective view illustrating a configuration example of a drain pan to be provided in a relay unit according to Embodiment 4. 
     A drain pan  18   a  includes the plate  81  and the four frame portions  82   a  to  82   d,  which are provided around the plate  81 . Of the two frame portions  82   a  and  82   b,  the first drain port  17   a  is formed at the position in one frame portion, that is, the frame portion  82   a,  at the first distance xi from the second edge  64 , where the two frame portions  82   a  and  82   b  are in contact with each other, and the second drain port  17   b  is formed at the position in the other frame portion, that is, the frame portion  82   b,  at the second distance y 1  from the second edge  64 . 
     A projection  56  is provided, between the first drain port  17   a  and the second drain port  17   b,  at a corner portion on the plate  81  where the second edge  64  is formed. In the configuration example illustrated in  FIG.  15   , the projection  56  is a quadrangular pyramid whose bottom surface is formed by two sides extending for the first distance x 1  and two sides extending for the second distance y 1 . Since the shape of the projection  56  is a quadrangular pyramid, dew condensation water formed on the periphery of the corner portion can easily flow, in directions toward the first drain port  17   a  and the second drain port  17   b,  along inclined surfaces of the quadrangular pyramid. 
     In the drain pan  18   a  illustrated in  FIG.  15   , the projection  56  is provided at the corner portion where the second edge  64  is formed. Thus, it is possible to prevent water collected on the plate  81  from remaining at the corner portion. In addition, even when one of the first drain port  17   a  and the second drain port  17   b  is closed, water collected on the plate  81  is discharged, along the projection  56 , to the outside from the other thereof that is open. 
     In the relay unit  4  in Embodiment 4, the projection  56  is provided, between the first drain port  17   a  and the second drain port  17   b,  at the corner portion on the plate  81  of the drain pan  18   a  where the second edge  64  is formed. Thus, even when one of the two drain ports is closed, water collected on the plate  81  is discharged, along the projection  56 , to the outside from the other thereof that is open. As a result, dew condensation water does not remain at the corner portion of the drain pan  18   a  Water does not remain at the corner portion of the drain pan  18   a,  thus inhibiting production of foreign matter such as dust and slime that causes clogging of a drain port. In addition, this structure is a structure in which water is unlikely to be collected in the drain pan  18   a  and can thus reduce rusting and water leakage. 
     REFERENCE SIGNS LIST 
       1 : air-conditioning apparatus,  2 : heat source side unit,  3   a  to  3   f:  load side unit,  4 : relay unit,  5 : casing,  5   a:  top surface,  5   b:  first side,  5   c:  second side,  5   d:  third side,  5   e:  fourth side,  5   f:  bottom surface,  6 : first refrigerant pipe connection port,  7 : second refrigerant pipe connection port,  8   a  to  8   f:  first heat medium pipe connection port,  9   a  to  9   f:  second heat medium pipe connection port,  10 : heat medium pipe connection port,  11 : refrigerant pipe connection port,  12 : first opening,  13 : second opening,  14   a  to  14   f:  air purge valve,  15 : on-off valve,  16   a:  first drain socket,  16   b:  second drain socket,  16   c:  third drain socket,  16   d:  fourth drain socket,  17   a:  first drain port,  17   b:  second drain port,  18 ,  18   a:  drain pan,  20 : controller,  21 : compressor,  22 : heat source side heat exchanger,  23 : four-way valve,  24 : accumulator,  25 : expansion valve,  26 : refrigerant pipe,  31   a  to  31   f:  load side heat exchanger,  32   a  to  32   f:  heat medium pipe,  33   a  to  33   f:  heat medium pipe,  35 : heat medium pipe,  41 : pump,  42 : heat medium heat exchanger,  44   a  to  44   f:  flow control valve,  45 : refrigerant pipe,  46 : heat medium pipe,  50 : drawer panel,  51 : refrigerant pipe,  55 : drain hose,  56 : projection,  61 : first edge,  62 : vertex,  64 : second edge,  65 : third edge,  66 : fourth edge,  67 : centroid,  71 : power supply line,  72 : transmission line,  73 : cable tie,  81 : plate,  82   a  to  82   d:  frame portion,  101 : air