Patent Publication Number: US-2022235975-A1

Title: Support system that supports design or construction of a refrigerant cycle apparatus

Description:
BACKGROUND 
     Technical Field 
     The present disclosure relates to a support system for supporting one of or both design and construction of a refrigerant cycle apparatus. 
     Related Art 
     Patent Literature 1 discloses an air conditioning system including a refrigerant shut-off valve. The refrigerant shut-off valve is closed when leakage of a refrigerant is detected. The refrigerant shut-off valve is disposed on a refrigerant connection pipe connecting a heat source-side unit and a utilization-side unit. 
     PATENT LITERATURE 
     Patent Literature 1: JP 2017-009267 A 
     In a refrigerant cycle apparatus of an air conditioning system or the like, the use of a shut-off valve is effective in case of occurrence of leakage of a refrigerant from a utilization-side unit into a space where someone is present. 
     However, heretofore, an idea of blocking a refrigerant at a location as close as possible to a utilization-side unit has become a common-sense approach, and no specific consideration has been given to arrangement of a shut-off unit for blocking the refrigerant. No consideration has been given to arrangement of a shut-off unit particularly in a refrigerant cycle apparatus including a common shut-off unit for a plurality of utilization-side units. 
     SUMMARY 
     One or more embodiments provide a support system for supporting one of or both design and construction of a refrigerant cycle apparatus. The refrigerant cycle apparatus includes a plurality of utilization-side units, a heat source-side unit, a connection pipe group, and a refrigerant shut-off unit. Each of the utilization-side units includes a first refrigerant circuit. The heat source-side unit includes a second refrigerant circuit. The connection pipe group is a group of connection pipes connecting the first refrigerant circuit and the second refrigerant circuit. The refrigerant shut-off unit is disposed between the first refrigerant circuit and the second refrigerant circuit, and is configured to block (shut off) a refrigerant flowing through the connection pipe group. The plurality of utilization-side units include a first utilization-side unit group. The first utilization-side unit group is a group of N (N: an integer equal to or more than two) utilization-side units. The refrigerant shut-off unit includes a first refrigerant shut-off unit. The first refrigerant shut-off unit is configured to block a flow of the refrigerant between the first refrigerant circuit in the first utilization-side unit group and the second refrigerant circuit. The connection pipe group includes a first connection pipe group. The first connection pipe group is a group of connection pipes connecting the first refrigerant circuit in the first utilization-side unit group and the first refrigerant shut-off unit. 
     The support system according to one or more embodiments includes an information acquisition unit and a presentation unit. The information acquisition unit is configured to acquire at least two of first information, second information, and third information. The first information concerns arrangement of the first refrigerant shut-off unit. The second information concerns each of the utilization-side units in the first utilization-side unit group. The third information concerns one of or both a length and an internal volume of the first connection pipe group. The presentation unit presents useful information based on at least the information acquired by the information acquisition unit. 
     (1) When the information acquisition unit acquires two of the first information, the second information, and the third information, the presentation unit calculates one of the first information, the second information, and the third information, which is not acquired by the information acquisition unit, and presents the calculated information as the useful information. 
     (2) When the information acquisition unit acquires the first information, the second information, and the third information, the presentation unit makes a determination as to appropriateness of the first information, second information, and third information, in view of allowable leakage of the refrigerant into a space where a corresponding one or more utilization-side units in the first utilization-side unit group is installed, and presents a result of the determination as the useful information. 
     (3) When the information acquisition unit acquires the first information, the second information, and the third information, the presentation unit calculates a first refrigerant amount as a sum of an amount of the refrigerant in the first refrigerant circuit in the first utilization-side unit group and an amount of the refrigerant in the first connection pipe group, and presents the first refrigerant amount as the useful information. 
     In the support system according to one or more embodiments, the presentation unit presents the useful information (1), the useful information (2), or the useful information (3). This configuration therefore enables one of or both design and construction of the refrigerant cycle apparatus, using the useful information. In particular, the support system according to one or more embodiments appropriately or simply fixes (determines) arrangement of the first refrigerant shut-off unit. 
     In the support system according to one or more embodiments, the second information includes installation space information and refrigerant amount information. The installation space information concerns the space where the corresponding one or more utilization-side units in the first utilization-side unit group is installed. The refrigerant amount information concerns the amount of the refrigerant in the first refrigerant circuit in the first utilization-side unit group. When the information acquisition unit acquires the second information and the third information, the presentation unit calculates the arrangement of the first refrigerant shut-off unit, as the first information. The presentation unit calculates the arrangement of the first refrigerant shut-off unit such that the first refrigerant amount is smaller than an allowable refrigerant leak amount in the space where the corresponding one or more utilization-side units in the first utilization-side unit group is installed. The first refrigerant amount corresponds to the sum of the amount of the refrigerant in the first refrigerant circuit in the first utilization-side unit group and the amount of the refrigerant in the first connection pipe group. 
     In the support system according to one or more embodiments, the arrangement of the first refrigerant shut-off unit is acquired as the useful information. 
     In the support system according to one or more embodiments, the second information includes installation space information and refrigerant amount information. The installation space information concerns the space where the corresponding one or more utilization-side units in the first utilization-side unit group is installed. The refrigerant amount information concerns the amount of the refrigerant in the first refrigerant circuit in the first utilization-side unit group. When the information acquisition unit acquires the first information, the second information, and the third information, the presentation unit makes a determination as to appropriateness of the first information, second information, and third information. The presentation unit makes the determination as to the appropriateness of the first information, second information, and third information, by determining whether the first refrigerant amount is smaller than an allowable refrigerant leak amount in the space where the corresponding one or more utilization-side units in the first utilization-side unit group is installed. The first refrigerant amount corresponds to the sum of the amount of the refrigerant in the first refrigerant circuit in the first utilization-side unit group and the amount of the refrigerant in the first connection pipe group. 
     In the support system according to one or more embodiments, a result of the determination as to the appropriateness of the first information, second information, and third information is acquired as the useful information. 
     In the support system according to one or more embodiments, when the information acquisition unit acquires the first information, the second information, and the third information, the presentation unit calculates the amount of the refrigerant in the first refrigerant circuit in the first utilization-side unit group and the amount of the refrigerant in the first connection pipe group based on a thermal environment of a place where the refrigerant cycle apparatus is installed, and calculates the first refrigerant amount as the sum of the calculated amounts. 
     In the support system according to one or more embodiments, the first refrigerant amount is calculated based on the thermal environment of the place where the refrigerant cycle apparatus is installed. This case enables acquisition of, as the useful information, an appropriate calculation result of the first refrigerant amount according to an installation place, as compared with a case where the first refrigerant amount is calculated based on a condition of an excessive thermal environment. 
     In the support system according to one or more embodiments, the refrigerant flowing through the first refrigerant circuit, the second refrigerant circuit, and the connection pipe group has flammability. The allowable refrigerant leak amount in the space where the corresponding one or more utilization-side units in the first utilization-side unit group is installed corresponds to an allowable refrigerant leak amount in a first room. The first room has a smallest spatial volume among one or more rooms where one of the utilization-side units in the first utilization-side unit group is or the utilization-side units in the first utilization-side unit group are installed. The allowable refrigerant leak amount in the first room is set such that a concentration of the refrigerant in the first room is within LFL (a lower flammability limit) of the refrigerant/safety factor. 
     In the support system according to one or more embodiments, the refrigerant flowing through the first refrigerant circuit, the second refrigerant circuit, and the connection pipe group is a mildly flammable refrigerant, a lower flammability refrigerant, or a higher flammability refrigerant. The mildly flammable refrigerant is classified as “Class 2L” in U.S. ANSI/ASHRAE Standard 34-2013. The lower flammability refrigerant is classified as “Class 2” in U.S. ANSI/ASHRAE Standard 34-2013. The higher flammability refrigerant is classified as “Class 3” in U.S. ANSI/ASHRAE Standard 34-2013. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic configuration diagram of an air conditioning apparatus that is an example of a refrigerant cycle apparatus according to one or more embodiments. 
         FIG. 2A  is a functional block diagram of the air conditioning apparatus. 
         FIG. 2B  is a flowchart of control upon leakage of a refrigerant. 
         FIG. 3A  is a diagram of exemplary arrangement A of a heat source-side unit, utilization-side units, and relay units. 
         FIG. 3B  is a diagram of exemplary arrangement B of the heat source-side unit, the utilization-side units, and the relay units. 
         FIG. 3C  is a diagram of exemplary arrangement C of the heat source-side unit, the utilization-side units, and relay units. 
         FIG. 3D  is a diagram of exemplary arrangement D of the heat source-side unit, the utilization-side units, and a relay unit. 
         FIG. 3E  is a diagram of exemplary arrangement E of the heat source-side unit, the utilization-side units, and the relay unit. 
         FIG. 4  is a schematic configuration diagram of a design support system for supporting design of the air conditioning apparatus. 
         FIG. 5  is a flowchart of a design method using the design support system. 
         FIG. 6  is a diagram of an exemplary basic configuration of an air conditioning apparatus designed using the design support system. 
         FIG. 7A  is a diagram of an exemplary display screen by a computer program in the design support system. 
         FIG. 7B  is a diagram of an exemplary display screen by the computer program in the design support system. 
         FIG. 7C  is a partially enlarged diagram of  FIG. 7B . 
         FIG. 7D  is a diagram of an exemplary display screen by the computer program in the design support system. 
         FIG. 7E  is a diagram of an exemplary display screen by the computer program in the design support system. 
         FIG. 7F  is a diagram of an exemplary display screen by the computer program in the design support system. 
         FIG. 7G  is a diagram of an exemplary display screen by the computer program in the design support system. 
         FIG. 8  is a control block diagram of a control unit in an air conditioning apparatus according to Modification 11. 
     
    
    
     DETAILED DESCRIPTION 
     (1) Configuration of Air Conditioning Apparatus 
       FIG. 1  illustrates a schematic configuration of an air conditioning apparatus  1  that is an example of a refrigerant cycle apparatus. The air conditioning apparatus  1  is configured to cool and heat the interiors of rooms in a building or the like by a vapor compression refrigeration cycle. The air conditioning apparatus  1  mainly includes a heat source-side unit  2 , a plurality of utilization-side units  3   a,    3   b,    3   c,  and  3   d,  a relay units  4 A,  4 B connected to the utilization-side units  3   a,    3   b,    3   c  and  3   d,  refrigerant connection pipes  5  and  6 , and a control unit  19  (see  FIG. 2A ). The plurality of utilization-side units  3   a,    3   b,    3   c,  and  3   d  are connected to the heat source-side unit  2  in parallel. The refrigerant connection pipes  5  and  6  connect the heat source-side unit  2  to the utilization-side units  3   a,    3   b,    3   c,  and  3   d  via the relay units  4 A and  4 B. The control unit  19  controls constituent elements of the heat source-side unit  2 , utilization-side units  3   a,    3   b,    3   c,  and  3   d,  and relay units  4 A and  4 B. The air conditioning apparatus  1  includes a vapor compression refrigerant circuit  10 . The refrigerant circuit  10  is configured by connecting a heat source-side refrigerant circuit  12  of the heat source-side unit  2 , utilization-side refrigerant circuits  13   a,    13   b,    13   c,  and  13   d  of the utilization-side units  3   a,    3   b,    3   c,  and  3   d,  the relay units  4 A and  4 B, and the refrigerant connection pipes  5  and  6 . 
     The refrigerant circuit  10  is filled with R32 as a refrigerant. Leakage of R32 from the refrigerant circuit  10  into rooms (spaces where the utilization-side units are installed) in high concentrations may cause a combustion accident due to the flammability of the refrigerant. It has been required to prevent this combustion accident. 
     In the air conditioning apparatus  1 , the heat source-side unit  2  includes a switching mechanism  22  configured to switch between a cooling operation and a heating operation of each of the utilization-side units  3   a,    3   b,    3   c,  and  3   d.    
     (1-1) Refrigerant Connection Pipes 
     The liquid-side refrigerant connection pipe  5  mainly includes a main pipe portion  5 X extending from the heat source-side unit  2 , a plurality of branched pipe portions  5 Y branching off from the main pipe portion  5 X before the relay units  4 A and  4 B, and downstream pipe portions connecting the relay units  4 A and  4 B and the utilization-side units  3   a,    3   b,    3   c,  and  3   d.    
     The gas-side refrigerant connection pipe  6  mainly includes a main pipe portion  6 X extending from the heat source-side unit  2 , a plurality of branched pipe portions  6 Y branching off from the main pipe portion  6 X before the relay units  4 A and  4 B, and downstream pipe portions connecting the relay units  4 A and  4 B and the utilization-side units  3   a,    3   b,    3   c,  and  3   d.    
     As illustrated in  FIG. 1 , the downstream pipe portions of the liquid-side refrigerant connection pipe  5  and the downstream pipe portions of the gas-side refrigerant connection pipe  6  include a first connection pipe group  5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b  connecting the relay unit  4 A and the utilization-side units  3   a  and  3   b.  The first connection pipe group  5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b  includes common pipes  5   ab,    6   ab  extending from the relay unit  4 A to the utilization-side units  3   a  and  3   b,  most-downstream pipes  5   a,    6   a  branching off from the common pipes  5   ab,    6   ab  and extending to the utilization-side refrigerant circuit  13   a  of the utilization-side unit  3   a,  and most-downstream pipes  5   b,    6   b  branching off from the common pipe  5   ab,    6   ab  and extending to the utilization-side refrigerant circuit  13   b  of the utilization-side unit  3   b.    
     The liquid refrigerant flowing through the liquid-side refrigerant connection pipe  5  is in a liquid phase or has a larger ratio of a liquid phase than that of a gas phase. The gas refrigerant flowing through the gas-side refrigerant connection pipe  6  is in a gas phase or has a larger ratio of a gas phase than that of a liquid phase. 
     (1-2) Utilization-Side Units 
     The utilization-side units  3   a,    3   b,    3   c,  and  3   d  are installed in rooms of a building or the like. As described above, the utilization-side refrigerant circuits  13   a,    13   b,    13   c,  and  13   d  of the utilization-side units  3   a,    3   b,    3   c,  and  3   d  are connected to the heat source-side unit  2  via the liquid-side refrigerant connection pipe  5 , the gas-side refrigerant connection pipe  6 , and the relay units  4 A and  4 B, and each serves as a part of the refrigerant circuit  10 . 
     Next, a description will be given of a configuration of each of the utilization-side units  3   a,    3   b,    3   c,  and  3   d.  Since the utilization-side unit  3   a  is similar in configuration to the utilization-side units  3   b,    3   c,  and  3   d,  a description will be given of only the configuration of the utilization-side unit  3   a.  The components of the utilization-side units  3   b,    3   c,  and  3   d  are not described since the components can be understood in such a way that the alphabet “a” in the reference signs representing the respective components of the utilization-side unit  3   a  is replaced with the alphabets “b”, “c”, and “d”. 
     The utilization-side unit  3   a  mainly includes a utilization-side expansion valve  51   a  and a utilization-side heat exchanger  52   a.  The utilization-side unit  3   a  also includes a utilization-side liquid refrigerant pipe  53   a  connecting a liquid-side end of the utilization-side heat exchanger  52   a  and the liquid-side refrigerant connection pipe  5  (here, the most-downstream pipe  5   a ), and a utilization-side gas refrigerant pipe  54   a  connecting a gas-side end of the utilization-side heat exchanger  52   a  and the gas-side refrigerant connection pipe  6  (here, the most-downstream pipe  6   a ). 
     The utilization-side expansion valve  51   a  is an electric expansion valve which is capable of adjusting a flow rate of the refrigerant flowing through the utilization-side heat exchanger  52   a  while decompressing the refrigerant. The utilization-side expansion valve  51   a  is disposed on the utilization-side liquid refrigerant pipe  53   a.    
     The utilization-side heat exchanger  52   a  functions as a refrigerant evaporator to cool indoor air, or functions as a refrigerant radiator to heat the indoor air. The utilization-side unit  3   a  includes a utilization-side fan  55   a.  The utilization-side fan  55   a  provides, to the utilization-side heat exchanger  52   a,  the indoor air serving as a cooling source or a heating source for the refrigerant flowing through the utilization-side heat exchanger  52   a.  The utilization-side fan  55   a  is driven by a utilization-side fan motor  56   a.    
     The utilization-side unit  3   a  includes various sensors. Specifically, the utilization-side unit  3   a  includes a utilization-side heat exchange liquid-side sensor  57   a  that detects a temperature of the refrigerant at the liquid-side end of the utilization-side heat exchanger  52   a,  a utilization-side heat exchange gas-side sensor  58   a  that detects a temperature of the refrigerant at the gas-side end of the utilization-side heat exchanger  52   a,  and an indoor air sensor  59   a  that detects a temperature of the indoor air sucked into the utilization-side unit  3   a.  The utilization-side unit  3   a  also includes a refrigerant leakage detection unit  79   a  that detects leakage of the refrigerant. Examples of the refrigerant leakage detection unit  79   a  may include, but not limited to, a semiconductor gas sensor and a detection unit configured to detect a rapid refrigerant pressure drop in the utilization-side unit  3 a. In a case where the refrigerant leakage detection unit  79   a  is a semiconductor gas sensor, the refrigerant leakage detection unit  79   a  is connected to a utilization-side control unit  93   a  (see  FIG. 2A ). In a case where the refrigerant leakage detection unit  79   a  is a detection unit configured to detect a rapid refrigerant pressure drop, a pressure sensor is disposed on a refrigerant pipe, and the utilization-side control unit  93   a  is equipped with a detection algorithm for determining leakage of the refrigerant from a change of the sensor value. 
     In one or more embodiments, the utilization-side unit  3   a  includes the refrigerant leakage detection unit  79   a.  The refrigerant leakage detection unit  79   a  may alternatively be incorporated in a remote controller for operating the utilization-side unit  3   a  or installed in, for example, an indoor space to be subjected to air conditioning by the utilization-side unit  3   a.    
     (1-3) Heat Source-Side Unit 
     The heat source-side unit  2  is installed outdoors, for example, on the rooftop of a building or on the ground. As described above, the heat source-side refrigerant circuit  12  of the heat source-side unit  2  is connected to the utilization-side units  3   a,    3   b,    3   c,  and  3   d  via the liquid-side refrigerant connection pipe  5 , the gas-side refrigerant connection pipe  6 , and the relay units  4 A and  4 B, and serves as a part of the refrigerant circuit  10 . 
     The heat source-side unit  2  mainly includes a compressor  21  and a heat source-side heat exchanger  23 . The heat source-side unit  2  also includes the switching mechanism  22  as a mechanism configured to switch between the cooling operation and the heating operation. The switching mechanism  22  switches between a cooling operation state in which the heat source-side heat exchanger  23  functions as a refrigerant radiator and each of the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  functions as a refrigerant evaporator and a heating operation state in which the heat source-side heat exchanger  23  functions as a refrigerant evaporator and each of the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  functions as a refrigerant radiator. A suction refrigerant pipe  31  connects the switching mechanism  22  and a suction side of the compressor  21 . An accumulator  29  is disposed on the suction refrigerant pipe  31 . The accumulator  29  temporarily stores the refrigerant to be sucked into the compressor  21 . A discharge refrigerant pipe  32  connects a discharge side of the compressor  21  and the switching mechanism  22 . A first heat source-side gas refrigerant pipe  33  connects the switching mechanism  22  and a gas-side end of the heat source-side heat exchanger  23 . A heat source-side liquid refrigerant pipe  34  connects a liquid-side end of the heat source-side heat exchanger  23  and the liquid-side refrigerant connection pipe  5 . A second heat source-side gas refrigerant pipe  35  connects the switching mechanism  22  and the gas-side refrigerant connection pipe  6 . 
     The compressor  21  is configured to compress the refrigerant. The compressor  21  to be used herein is, for example, a closed compressor in which a displacement, such as rotary or scroll, compression element (not illustrated) is driven to rotate by a compressor motor  21   a.    
     The switching mechanism  22  is, for example, a four-way switching valve capable of switching a flow of the refrigerant in the refrigerant circuit  10 . In the case where the heat source-side heat exchanger  23  functions as a refrigerant radiator and each of the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  functions as a refrigerant evaporator (hereinafter, this case will be referred to as the “cooling operation state”), the switching mechanism  22  connects the discharge side of the compressor  21  to the gas side of the heat source-side heat exchanger  23  (see a solid line on the switching mechanism  22  illustrated in  FIG. 1 ). In the case where the heat source-side heat exchanger  23  functions as a refrigerant evaporator and each of the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  functions as a refrigerant radiator (hereinafter, this case will be referred to as the “heating operation state”), the switching mechanism  22  connects the suction side of the compressor  21  to the gas side of the heat source-side heat exchanger  23  (see a broken line on the first switching mechanism  22  illustrated in  FIG. 1 ). 
     The heat source-side heat exchanger  23  functions as a refrigerant radiator or a refrigerant evaporator. The heat source-side unit  2  includes a heat source-side fan  24 . The heat source-side fan  24  provides outdoor air to the heat source-side unit  2 . The heat source-side unit  2  sucks therein the outdoor air, and the heat source-side heat exchanger  23  causes the outdoor air to exchange heat with the refrigerant. The outdoor air is then discharged from the heat source-side unit  2 . The heat source-side fan  24  is driven by a heat source-side fan motor. 
     In the cooling operation of the air conditioning apparatus  1 , the refrigerant flows from the heat source-side heat exchanger  23  to the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  each functioning as a refrigerant evaporator, through the liquid-side refrigerant connection pipe  5  and the relay units  4 A and  4 B. In the heating operation of the air conditioning apparatus  1 , the refrigerant flows from the compressor  21  to the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  each functioning as a refrigerant radiator, through the gas-side refrigerant connection pipe  6  and the relay units  4 A and  4 B. In the cooling operation, the switching mechanism  22  switches to the cooling operation state. The heat source-side heat exchanger  23  functions as a refrigerant radiator. The refrigerant flows from the heat source-side unit  2  to the utilization-side units  3   a,    3   b,    3   c,  and  3   d  through the liquid-side refrigerant connection pipe  5  and the relay units  4 A and  4 B. In the heating operation, the switching mechanism  22  switches to the heating operation state. The refrigerant flows from the utilization-side units  3   a,    3   b,    3   c,  and  3   d  to the heat source-side unit  2  through the liquid-side refrigerant connection pipe  5  and the relay units  4 A and  4 B. The heat source-side heat exchanger  23  functions as a refrigerant evaporator. 
     A heat source-side expansion valve  25  is disposed on the heat source-side liquid refrigerant pipe  34 . The heat source-side expansion valve  25  is electrically driven to decompress the refrigerant in the heating operation. The heat source-side expansion valve  25  is disposed near the liquid-side end of the heat source-side heat exchanger  23  on the heat source-side liquid refrigerant pipe  34 . 
     The heat source-side unit  2  includes various sensors. Specifically, the heat source-side unit  2  includes a discharge pressure sensor  36  that detects a pressure (a discharge pressure) of the refrigerant discharged from the compressor  21 , a discharge temperature sensor  37  that detects a temperature (a discharge temperature) of the refrigerant discharged from the compressor  21 , and a suction pressure sensor  39  that detects a pressure (a suction pressure) of the refrigerant sucked into the compressor  21 . The heat source-side unit  2  also includes a heat source-side heat exchange liquid-side sensor  38  that detects a temperature (a heat source-side heat exchange outlet temperature) of the refrigerant at the liquid-side end of the heat source-side heat exchanger  23 . 
     (1-4) Relay Units 
     The relay units  4 A and  4 B are installed indoors, for example, in attic spaces of rooms and passageways in a building. The relay units  4 A and  4 B are interposed together with the liquid-side refrigerant connection pipe  5  and the gas-side refrigerant connection pipe  6  between the utilization-side units  3   a,    3   b,    3   c,  and  3   d  and the heat source-side unit  2 , and each serves as a part of the refrigerant circuit  10 . The relay units  4 A and  4 B function as refrigerant shut-off units that block the flows of the refrigerant between the utilization-side units  3   a,    3   b,    3   c,  and  3   d  and the heat source-side unit  2 . The relay units  4 A,  4 B may be disposed near the utilization-side units  3   a,    3   b,    3   c,    3   d.  Alternatively, the relay units  4 A,  4 B may be disposed away from the utilization-side units  3   a,    3   b,    3   c,    3   d.  Still alternatively, the relay units  4 A and  4 B may be collectively disposed at one place. 
     Next, a description will be given of a configuration of each of the relay units  4 A and  4 B. Since the relay unit  4 A is similar in configuration to the relay unit  4 B, a description will be given of only the configuration of the relay unit  4 A. The components of the relay unit  4 B are not described since the components can be understood in such a way that the alphabet “A” in the reference signs representing the respective components of the relay unit  4 A is replaced with the alphabet “B”. 
     The relay unit  4 A mainly includes a liquid connection pipe  61 A and a gas connection pipe  62 A. 
     The liquid connection pipe  61 A has a first end connected to one of the branched pipe portions  5 Y of the liquid-side refrigerant connection pipe  5  and a second end connected to the common pipe  5   ab  of the liquid-side refrigerant connection pipe  5 . A liquid relay shut-off valve  41 A is disposed on the liquid connection pipe  61 A. The liquid relay shut-off valve  41 A is an electric expansion valve. 
     The gas connection pipe  62 A has a first end connected to one of the branched pipe portions  6 Y of the gas-side refrigerant connection pipe  6  and a second end connected to the common pipe  6   ab  of the gas-side refrigerant connection pipe  6 . A gas relay shut-off valve  42 A is disposed on the gas connection pipe  62 A. The gas relay shut-off valve  42 A is an electric expansion valve. 
     In the cooling operation and the heating operation, each of the liquid relay shut-off valve  41 A and the gas relay shut-off valve  42 A is in a fully open state. 
     (1-5) Control Unit 
     As illustrated in  FIG. 2A , the control unit  19  includes a heat source-side control unit  92 , relay-side control units  94 A and  94 B connected to the heat source-side control unit  92  via a transmission line  95 , and utilization-side control units  93   a,    93   b,    93   c,  and  93   d  connected to the relay-side control units  94 A and  94 B via a transmission line  96 . The heat source-side control unit  92  controls the constituent components of the heat source-side unit  2 . The relay-side control unit  94 A controls the constituent components of the relay unit  4 A, and the relay-side control unit  94 B controls the constituent components of the relay unit  4 B. The utilization-side control unit  93   a  controls the constituent components of the utilization-side unit  3   a,  the utilization-side control unit  93   b  controls the constituent components of the utilization-side unit  3   b,  the utilization-side control unit  93   c  controls the constituent components of the utilization-side unit  3   c,  and the utilization-side control unit  93   d  controls the constituent components of the utilization-side unit  3   d.  The heat source-side control unit  92  of the heat source-side unit  2 , the relay-side control units  94 A and  94 B of the relay units  4 A and  4 B, and the utilization-side control units  93   a,    93   b,    93   c,  and  93   d  of the utilization-side units  3   a,    3   b,    3   c,  and  3   d  exchange information such as control signals with one another via the transmission lines  95  and  96 . 
     The heat source-side control unit  92  includes a control board having electric components such as a microcomputer and a memory mounted thereon. The heat source-side control unit  92  is connected to the various constituent components  21 ,  22 ,  24 , and  25  and various sensors  36 ,  37 ,  38 , and  39  of the heat source-side unit  2 . Each of the relay-side control units  94 A and  94 B includes a control board having electric components such as a microcomputer and a memory mounted thereon. The relay-side control unit  94 A is connected to the gas relay shut-off valve  42 A and liquid relay shut-off valve  41 A of the relay unit  4 A. The relay-side control unit  94 B is connected to the gas relay shut-off valve  42 B and liquid relay shut-off valve  41 B of the relay unit  4 B. The relay-side control units  94 A and  94 B are connected to the heat source-side control unit  92  via the first transmission line  95 . Each of the utilization-side control units  93   a,    93   b,    93   c,  and  93   d  includes a control board having electric components such as a microcomputer and a memory mounted thereon. The utilization-side control unit  93   a  is connected to the various constituent components  51   a  and  55   a  and various sensors  57   a,    58   a,    59   a,  and  79   a  of the utilization-side unit  3   a.  The utilization-side control unit  93   b  is connected to the various constituent components  51   b  and  55   b  and various sensors  57   b,    58   b,    59   b,  and  79   b  of the utilization-side unit  3   b.  The utilization-side control unit  93   c  is connected to the various constituent components  51   c  and  55   c  and various sensors  57   c,    58   c,    59   c,  and  79   c  of the utilization-side unit  3   c.  The utilization-side control unit  93   d  is connected to the various constituent components  51   d  and  55   d  and various sensors  57   d,    58   d,    59   d,  and  79   d  of the utilization-side unit  3   d.  The utilization-side control units  93   a,    93   b,    93   c,  and  93   d  are connected to the relay-side control units  94 A and  94 B via the second transmission line  96 . 
     In this way, the control unit  19  controls the operation of the entire air conditioning apparatus  1 . Specifically, the control unit  19  controls the various constituent components  21 ,  22 ,  24 ,  25 ,  51   a  to  51   d,    55   a  to  55   d,    41 A,  41 B,  42 A, and  42 B of the air conditioning apparatus  1  (here, the heat source-side unit  2 , utilization-side units  3   a,    3   b,    3   c,  and  3   d,  and relay units  4 A and  4 B), based on, for example, detection signals from the various sensors  36 ,  37 ,  38 ,  39 ,  57   a  to  57   d,    58   a  to  58   d,    59   a  to  59   d,  and  79   a  to  79   d.    
     (2) Basic Operation of Air Conditioning Apparatus 
     Next, a description will be given of a basic operation of the air conditioning apparatus  1 . The basic operation of the air conditioning apparatus  1  includes the cooling operation and the heating operation as described above. The basic operation of the air conditioning apparatus  1  to be described below is performed by the control unit  19  that controls the constituent components of the air conditioning apparatus  1  (the heat source-side unit  2 , utilization-side units  3   a,    3   b,    3   c,  and  3   d,  and relay units  4 A and  4 B). 
     (2-1) Cooling Operation 
     In the cooling operation, for example, in a case where all the utilization-side units  3   a,    3   b,    3   c,  and  3   d  perform the cooling operation (in which all the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  function as a refrigerant evaporator, and the heat source-side heat exchanger  23  functions as a refrigerant radiator), the switching mechanism  22  switches to the cooling operation state (the state indicated by the solid line on the switching mechanism  22  illustrated in  FIG. 1 ), so that the compressor  21 , the heat source-side fan  24 , and the utilization-side fans  55   a,    55   b,    55   c,  and  55   d  are driven. In addition, the liquid relay shut-off valve  41 A and gas relay shut-off valve  42 A of the relay unit  4 A are fully opened, and the liquid relay shut-off valve  41 B and gas relay shut-off valve  42 B of the relay unit  4 B are fully opened. 
     In the cooling operation, the high-pressure refrigerant discharged from the compressor  21  flows into the heat source-side heat exchanger  23  through the switching mechanism  22 . When the refrigerant flows into the heat source-side heat exchanger  23 , the heat source-side heat exchanger  23  functioning as a refrigerant radiator cools the refrigerant by heat exchange with the outdoor air provided by the heat source-side fan  24  to condense the refrigerant. The refrigerant flows out of the heat source-side unit  2  through the heat source-side expansion valve  25 . 
     When the refrigerant flows out of the heat source-side unit  2 , the refrigerant then flows into the relay units  4 A and  4 B in a branched manner through the liquid-side refrigerant connection pipe  5  (the main pipe portion  5 X and branched pipe portions  5 Y). When the refrigerant flows into the relay units  4 A and  4 B, the refrigerant then flows out of the relay units  4 A and  4 B through the liquid relay shut-off valves  41 A and  41 B. 
     When the refrigerant flows out of the relay units  4 A and  4 B, the refrigerant then flows into the utilization-side units  3   a,    3   b,    3   c,  and  3   d  through the common pipes  5   ab  and  5   cd  and the most-downstream pipes  5   a,    5   b,    5   c,  and  5   d.  When the refrigerant flows into the utilization-side units  3   a,    3   b,    3   c,  and  3   d,  each of the utilization-side expansion valves  51   a,    51   b,    51   c,  and  51   d  decompresses the refrigerant. The refrigerant then flows into the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d.  When the refrigerant flows into the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d,  the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  each functioning as a refrigerant evaporator heat the refrigerant by heat exchange with indoor air supplied from the rooms by the utilization-side fans  55   a,    55   b,    55   c,  and  55   d  to evaporate the refrigerant. The refrigerant thus evaporated flows out of the utilization-side units  3   a,    3   b,    3   c,  and  3   d.  On the other hand, the indoor air cooled in the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  is supplied to the rooms to cool the interiors of the rooms. 
     When the refrigerant flows out of the utilization-side units  3   a,    3   b,    3   c,  and  3   d,  the refrigerant then flows into the relay units  4 A and  4 B through the most-downstream pipes  6   a,    6   b,    6   c,  and  6   d  and common pipes  6   ab  and  6   cd  of the gas-side refrigerant connection pipe  6 . When the refrigerant flows into the relay units  4 A and  4 B, the refrigerant then flows out of the relay units  4 A and  4 B through the gas relay shut-off valves  42 A and  42 B. 
     When the refrigerant flows out of the relay units  4 A and  4 B, the refrigerant then flows into the heat source-side unit  2  in a merged state through the gas-side refrigerant connection pipe  6  (the main pipe portion  6 X and branched pipe portions  6 Y). When the refrigerant flows into the heat source-side unit  2 , the refrigerant is then sucked into the compressor  21  via the switching mechanism  22  and the accumulator  29 . 
     (2-2) Heating Operation 
     In the heating operation, for example, in a case where all the utilization-side units  3   a,    3   b,    3   c,  and  3   d  perform the heating operation, the switching mechanism  22  switches to the heating operation state (the state indicated by the broken line on the switching mechanism  22  illustrated in  FIG. 1 ), so that the compressor  21 , the heat source-side fan  24 , and the utilization-side fans  55   a,    55   b,    55   c,  and  55   d  are driven. In addition, the liquid relay shut-off valve  41 A and gas relay shut-off valve  42 A of the relay unit  4 A are fully opened, and the liquid relay shut-off valve  41 B and gas relay shut-off valve  42 B of the relay unit  4 B are fully opened. 
     The high-pressure refrigerant discharged from the compressor  21  flows out of the heat source-side unit  2  through the switching mechanism  22 . 
     When the refrigerant flows out of the heat source-side unit  2 , the refrigerant then flows into the relay units  4 A and  4 B through the gas-side refrigerant connection pipe  6  (the main pipe portion  6 X and branched pipe portions  6 Y). When the refrigerant flows into the relay units  4 A and  4 B, the refrigerant then flows out of the relay units  4 A and  4 B through the gas relay shut-off valves  42 A and  42 B. 
     When the refrigerant flows out of the relay units  4 A and  4 B, the refrigerant then flows into the utilization-side units  3   a,    3   b,    3   c,  and  3   d  through the common pipes  6   ab  and  6   cd  and the most-downstream pipes  6   a,    6   b,    6   c,  and  6   d.  When the refrigerant flows into the utilization-side units  3   a,    3   b,    3   c,  and  3   d,  the refrigerant then flows into the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d.  When the high-pressure refrigerant flows into the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d,  the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  each functioning as a refrigerant radiator cool the refrigerant by heat exchange with indoor air supplied from the rooms by the utilization-side fans  55   a,    55   b,    55   c,  and  55   d,  to condense the refrigerant. Each of the utilization-side expansion valves  51   a,    51   b,    51   c,  and  51   d  decompresses the refrigerant thus condensed. The refrigerant then flows out of the utilization-side units  3   a,    3   b,    3   c,  and  3   d.  On the other hand, the indoor air heated in the utilization-side heat exchangers  52   a,    52   b,    52   c,  and  52   d  is supplied to the rooms to heat the interiors of the rooms. 
     When the refrigerant flows out of the utilization-side units  3   a,    3   b,    3   c,  and  3   d,  the refrigerant then flows into the relay units  4 A and  4 B through the most-downstream pipes  5   a,    5   b,    5   c,  and  5   d  and the common pipes  5   ab  and  5   cd.  When the refrigerant flows into the relay units  4 A and  4 B, the refrigerant then flows out of the relay units  4 A and  4 B through the liquid relay shut-off valves  41 A and  41 B. 
     When the refrigerant flows out of the relay units  4 A and  4 B, the refrigerant then flows into the heat source-side unit  2  in a merged state through the liquid-side refrigerant connection pipe  5  (the main pipe portion  5 X and branched pipe portions  5 Y). When the refrigerant flows into the heat source-side unit  2 , the refrigerant then flows into the heat source-side expansion valve  25 . When the refrigerant flows into the heat source-side expansion valve  25 , the heat source-side expansion valve  25  decompresses the refrigerant. The refrigerant thus decompressed then flows into the heat source-side heat exchanger  23 . When the refrigerant flows into the heat source-side heat exchanger  23 , the heat source-side heat exchanger  23  heats the refrigerant by heat exchange with outdoor air provided by the heat source-side fan  24  to evaporate the refrigerant. The refrigerant thus evaporated is sucked into the compressor  21  via the switching mechanism  22  and the accumulator  29 . 
     (3) Operation of Air Conditioning Apparatus upon Leakage of Refrigerant 
     With reference to  FIG. 2B , next, a description will be given of an operation of the air conditioning apparatus  1  upon leakage of the refrigerant. As will be described below, the control unit  19  that controls the constituent components of the air conditioning apparatus  1  performs the operation of the air conditioning apparatus  1  upon leakage of the refrigerant, in a manner similar to that for the foregoing basic operation. 
     Since the control unit  19  performs the similar control even when the leakage of the refrigerant occurs at any of the utilization-side units  3   a,    3   b,    3   c,  and  3   d,  a description will be given of a case where, for example, the leakage of the refrigerant occurs at the room where the utilization-side unit  3   a  is installed. 
     As illustrated in  FIG. 2B , in step S 1 , the control unit  19  determines whether any one of the refrigerant leakage detection units  79   a,    79   b,    79   c,  and  79   d  of the utilization-side units  3   a,    3   b,    3   c,  and  3   d  detects leakage of the refrigerant. When the refrigerant leakage detection unit  79   a  of the utilization-side unit  3   a  detects the leakage of the refrigerant into the space (i.e., the interior of the room) where the utilization-side unit  3   a  is installed, the processing proceeds to step S 2 . 
     In step S 2 , next, the utilization-side unit  3   a  causing the leakage of the refrigerant issues a warning to a person in the space where the utilization-side unit  3   a  is installed, using an alarm (not illustrated) configured to sound a buzzer and to turn a light on. 
     In step S 3 , next, the control unit  19  closes the liquid relay shut-off valve  41 A and gas relay shut-off valve  42 A of the relay unit  4 A for the utilization-side unit  3   a  causing the leakage of the refrigerant. The control unit  19  thus separates the upstream side and downstream side (where the utilization-side units  3   a  and  3   b  are provided) of the relay unit  4 A from each other to stop the flow of the refrigerant via the relay unit  4 A. The refrigerant thus never flows from the heat source-side unit  2  or the other utilization-side units  3   c  and  3   d  to the utilization-side units  3   a  and  3   b.    
     (4) Arrangement of Relay Unit Functioning as Refrigerant Shut-Off Unit 
     (4-1) Importance of Arrangement of Relay Unit 
     As described above, if the refrigerant leaks from, for example, the utilization-side refrigerant circuit  13   a  of the utilization-side unit  3   a,  the control unit  19  closes the liquid relay shut-off valve  41 A and gas relay shut-off valve  42 A of the relevant relay unit  4 A. The amount of the refrigerant that leaks into the space where the utilization-side unit  3   a  is installed therefore takes a maximum value equal to a total value of the amounts of the refrigerant in the utilization-side refrigerant circuit  13   a  of the utilization-side unit  3   a,  the utilization-side refrigerant circuit  13   b  of the utilization-side unit  3   b,  the common pipes  5   ab  and  6   ab,  and the most-downstream pipes  5   a,    6   a,    5   b,  and  6   b  on the downstream side of the relay unit  4 A. As described in the foregoing item (1-1), a part of the liquid-side refrigerant connection pipe  5  and a part of the gas-side refrigerant connection pipe  6  located closer to the utilization-side units  3   a  and  3   b  than to the relay unit  4 A are called the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). 
     In other words, a sum of the amount of the refrigerant in the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) and the amount of the refrigerant in the utilization-side refrigerant circuits  13   a  and  13   b  of the utilization-side units  3   a  and  3   b  corresponds to a maximum value of the amount of the refrigerant that leaks into the space where the utilization-side unit  3   a  causing the leakage of the refrigerant is installed. The maximum refrigerant leak amount is referred to as a refrigerant amount Q. 
     As illustrated in  FIG. 3A , it is assumed herein that the utilization-side unit  3   a  is installed on the ceiling of a small office kitchenette, the utilization-side unit  3   b  is installed on the ceiling of a large boardroom, the utilization-side unit  3   c  is installed on the ceiling of a first drawing room of a medium size, and the utilization-side unit  3   d  is installed on the ceiling of a second drawing room of a medium size. The heat source-side unit  2  is installed at a place slightly away from the four rooms. It is also assumed herein that there is an on-the-job demand to install the relay units  4 A and  4 B on the attic of a passageway adjacent to the four rooms and arrange the relay units  4 A and  4 B side by side as illustrated in  FIG. 3A  in consideration of maintainability. 
     However, in a case where the utilization-side units  3   a  and  3   b  each have a large capacity and a total pipe length of the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) takes a large value, if the refrigerant leaks into the small office kitchenette, where the utilization-side unit  3   a  is installed, by the refrigerant amount Q, the concentration of the refrigerant R32 in the vicinity of a floor surface of the office kitchenette may increase to exceed a lower flammability limit (LFL)/safety factor (e.g., a safety factor of 4), depending on a spatial volume of the office kitchenette. The LFL refers to a minimum concentration of a refrigerant that enables propagation of flames with the refrigerant and air mixed evenly, in conformance with ISO817. 
     Therefore, if the concentration of the refrigerant that leaks into the small office kitchenette by the refrigerant amount Q exceeds the LFL/safety factor, it may be necessary to change the arrangement of the relay unit  4 A as illustrated in  FIG. 3B  in order to reduce the refrigerant amount Q. If the concentration still exceeds the LFL/safety factor even after the change in arrangement of the relay unit  4 A to the arrangement illustrated in  FIG. 3B , it may be conceivable to deploy one relay unit  4 D for the utilization-side unit  3   a  and to deploy one relay unit  4 C for the remaining utilization-side units  3   b,    3   c,  and  3   d  as illustrated in  FIG. 3C . In contrast, it is assumed herein that the utilization-side units  3   a,    3   b,    3   c,  and  3   d  are installed in large rooms. In a case where all the refrigerant in the utilization-side units  3   a,    3   b,    3   c,  and  3   d,  the refrigerant in the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ), and the refrigerant in a second connection pipe group connecting the relay unit  4 B and the utilization-side units  3   c  and  3   d  leak into one room (a room having the smallest spatial volume among the four rooms), if the concentration of the refrigerant in this room falls below the LFL/safety factor, it may be possible to achieve cost saving by installing one relay unit  4 E functioning as a refrigerant shut-off unit as illustrated in  FIGS. 3D and 3E . As described above, the arrangement of the relay unit is very important. 
     It should be noted that the relay units  4 C,  4 D, and  4 E illustrated in  FIGS. 3C to 3E  are similar in configuration to the relay unit  4 A described above. 
     (4-2) Air Conditioning Apparatus Designing Method Involving Fixing Arrangement of Relay Unit 
     As described above, particularly in the case of deploying one common relay unit for a plurality of utilization-side units, how to fix arrangement of the relay unit functioning as a refrigerant shut-off unit is very important from the viewpoint of safety and cost. Heretofore, however, an experienced designer who is familiar with various refrigerant characteristics and laws and regulations has spent a lot of time to calculate and fix arrangement of a refrigerant shut-off unit every time for each case. 
     The air conditioning apparatus  1  according to one or more embodiments is designed with a design support system  300  (see  FIG. 4 ). The design support system  300  is capable of designing the air conditioning apparatus  1  while testing various design variations, such as pipe diameters and lengths of refrigerant connection pipes relevant to arrangement of relay units, and changes in utilization-side units to be associated with each relay unit. 
     (4-2-1) Configuration of Design Support System 
     As illustrated in  FIG. 4 , the design support system  300  mainly includes a Web server  310  as a computer, a user terminal  330  capable of accessing the Web server  310  via a communication line  301  such as the Internet, and a database server  320  connected to the Web server  310 . 
     (4-2-1-1) Web Server 
     The Web server  310  includes a control processing device and a storage device (i.e., storage). The control processing device may be a processor such as a central processing unit (CPU) or a graphics processing unit (GPU). The control processing device reads a design support program from the storage device, and executes predetermined image processing and arithmetic processing in accordance with this program. In addition, the control processing device writes a result of the arithmetic processing into the storage device, and reads information from the storage device, in accordance with this program.  FIG. 4  illustrates various functional blocks implemented by the control processing device. 
     As illustrated in  FIG. 4 , the Web server  310  includes an information acquisition unit  312  and a useful information presentation unit  318  as an aggregate of functional blocks. When the user terminal  330  as a client accesses the Web server  310 , the Web server  310  receives information and settings from the user terminal  330 , and gives a screen including useful information and the like to the user terminal  330 . 
     (4-2-1-1-1) Information Acquisition Unit 
     The information acquisition unit  312  includes, as functional blocks, an installation space size information acquisition unit  313 , a first utilization-side unit group information acquisition unit  314 , a first connection pipe group information acquisition unit  315 , a thermal environment information acquisition unit  316 , and the like. 
     The installation space size information acquisition unit  313  acquires information such as an installation height of the air conditioning apparatus in a room as an installation space, and a floor area and a spatial volume of the room. 
     The first utilization-side unit group information acquisition unit  314  acquires information on a first utilization-side unit group corresponding to a plurality of utilization-side units disposed downstream (i.e., on the opposite side to the heat source-side unit  2 ) of one relay unit (e.g., the relay unit  4 A described above) including a shut-off valve. In the air conditioning apparatus illustrated in  FIG. 3A  and an air conditioning apparatus illustrated in  FIG. 6  (to be described later), the utilization-side units  3   a  and  3   b  disposed downstream of one relay unit  4 A are called a first utilization-side unit group  81 . The first utilization-side unit group information acquisition unit  314  acquires a volume, a capability (a capacity), model information, and the like of a refrigerant circuit in the first utilization-side unit group  81 . 
     The first connection pipe group information acquisition unit  315  acquires information on a connection pipe group connecting a plurality of utilization-side units disposed downstream of one relay unit and the relay unit. As described above, the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) connects the relay unit  4 A and the two utilization-side units  3   a  and  3   b  (the first utilization-side unit group  81 ). The first connection pipe group information acquisition unit  315  acquires information on pipe lengths and pipe sizes (e.g., inner diameters) in the first connection pipe group. 
     The thermal environment information acquisition unit  316  acquires a thermal environment of a place where the air conditioning apparatus is installed. Information on a thermal environment to be acquired by the thermal environment information acquisition unit  316  in a case where the air conditioning apparatus is installed in a cold region is different from a thermal environment to be acquired by the thermal environment information acquisition unit  316  in a case where the air conditioning apparatus is installed in a hot region such as a country near the equator. 
     (4-2-1-1-2) Useful Information Presentation Unit 
     The useful information presentation unit  318  calculates information useful for a user as a designer of the air conditioning apparatus, based on various kinds of information acquired by the information acquisition unit  312  and various kinds of information previously stored in the database server  320 , and presents the information thus calculated to the user. The useful information presentation unit  318  includes, as functional blocks, an acquired information appropriateness determination unit  318   a,  a relay unit arrangement restriction fixing unit  318   b,  a first utilization-side unit group refrigerant amount calculation unit  318   c,  a first connection pipe group refrigerant amount calculation unit  318   d,  and the like. 
     The acquired information appropriateness determination unit  318   a  determines whether acquired information is suitable for design of the air conditioning apparatus from the viewpoint of an allowable amount of the refrigerant leaking into the room where the air conditioning apparatus is installed, based on information acquired by the first utilization-side unit group information acquisition unit  314  and information acquired by the first connection pipe group information acquisition unit  315 . 
     The relay unit arrangement restriction fixing unit  318   b  fixes a restriction on arrangement of the relay unit for blocking the refrigerant, from the viewpoint of an allowable amount of the refrigerant leaking into the room where the air conditioning apparatus is installed, based on information acquired by the first utilization-side unit group information acquisition unit  314  and information acquired by the first connection pipe group information acquisition unit  315 . 
     The first utilization-side unit group refrigerant amount calculation unit  318   c  calculates a total amount of the refrigerant in the utilization-side refrigerant circuits of the utilization-side units in the first utilization-side unit group, based on information acquired by the first utilization-side unit group information acquisition unit  314  and information acquired by the thermal environment information acquisition unit  316 . Specifically, the first utilization-side unit group refrigerant amount calculation unit  318   c  assumes a state in which the largest amount of refrigerant flows through the utilization-side refrigerant circuits of the utilization-side units in the first utilization-side unit group, in accordance with a thermal environment, and calculates a total amount of the refrigerant in the utilization-side refrigerant circuits under such a severe condition. 
     The first connection pipe group refrigerant amount calculation unit  318   d  calculates a total amount of the refrigerant in the first connection pipe group, based on information acquired by the first connection pipe group information acquisition unit  315  and information acquired by the thermal environment information acquisition unit  316 . Specifically, the first connection pipe group refrigerant amount calculation unit  318   d  assumes a state in which the largest amount of refrigerant flows through the first connection pipe group, in accordance with a thermal environment, and calculates a total amount of the refrigerant in the first connection pipe group under such a severe condition. 
     (4-2-1-2) Database Server 
     The database server  320  stores therein, for example, connection pipe size information  321  on sizes (e.g., inner diameters) of various connection pipes, utilization-side unit internal volume information  322  on internal volumes of utilization-side refrigerant circuits in utilization-side units for each capacity and for each type, and refrigerant information  323  on an LFL fixed for each refrigerant. When a new utilization-side unit or a new refrigerant is added, the information in the database server  320  is updated. 
     (4-2-1-3) User Terminal 
     The user terminal  330  is, for example, a personal computer, a tablet terminal, or a smartphone which the user uses in a design room or a place where the air conditioning apparatus is installed. The user accesses the Web server  310  by means of the program installed in the user terminal  330 , an applet, or a browser to use the design support program in the Web server  310 . The user terminal  330  displays on its screen various kinds of information calculated and presented by the design support program in the Web server  310 . In other words, the Web server causes a display of the user terminal  330  to display information. 
     (4-2-2) Exemplary Design Using Design Support System 
     With reference to  FIG. 5 , next, a description will be given of exemplary design by the user of the design support system  300  with the design support program in the Web server  310 . 
     The foregoing items (1) to (4-1) regarding the air conditioning apparatus  1  each describe the air conditioning apparatus  1  including the two utilization-side units  3   a  and  3   b  (the first utilization-side unit group  81 ) disposed downstream of the relay unit  4 A and the two utilization-side units  3   c  and  3   d  disposed downstream of the relay unit  4 B (see  FIG. 3A ). In the following exemplary design by the user of the design support system  300 , on the assumption that the user designs the air conditioning apparatus illustrated in  FIG. 6 , a description will be given of how to use the design support system at the time when designing the air conditioning apparatus. It is assumed that an initial policy of designing the air conditioning apparatus illustrated in  FIG. 6  involves disposing the two utilization-side units  3   a  and  3   b  (the first utilization-side unit group  81 ) downstream of the relay unit  4 A, disposing three utilization-side units  3   c,    3   d,  and  3   e  downstream of the relay unit  4 B, and disposing one utilization-side unit  3   f  downstream of a relay unit  4 F. The relay unit  4 F is similar in configuration to the relay units  4 A and  4 B described above. The utilization-side units  3   e  and  3   f  are similar in configuration to the utilization-side units  3   a,    3   b,    3   c,  and  3   d  described above. The utilization-side unit  3   a,  the utilization-side unit  3   b,  the utilization-side unit  3   c,  the utilization-side unit  3   d,  the utilization-side unit  3   e,  and the utilization-side unit  3   f  are respectively installed on the ceiling of an office kitchenette, the ceiling of a boardroom, the ceiling of a second drawing room, the ceiling of a first drawing room, the ceiling of a third drawing room, and the ceiling of a fourth drawing room. 
     (4-2-2-1) Operation by User and Processing in Web Server 
       FIG. 5  illustrates a schematic flow of exemplary design using the design support system  300 . 
     First, the user inputs a system symbol of an air conditioning apparatus, in an input area A 11  on a screen (see  FIG. 7A ) displayed on a display of the user terminal  330 .  FIG. 7A  illustrates a data input and setting window W 1  provided by the design support program in the Web server  310 . The heat source-side unit  2  and the utilization-side units  3   a  to  3   f  illustrated in  FIG. 6  constitute one refrigerant system in the air conditioning apparatus, the air conditioning apparatus illustrated in  FIG. 6  one refrigerant system. In view of this, the user inputs a system symbol for identifying an air conditioning apparatus, in the input area A 11 . 
     In addition, the user selectively inputs a model number of an outdoor unit as the heat source-side unit  2  of the air conditioning apparatus, in an input area A 12  on the screen illustrated in  FIG. 7A . The user selectively inputs a model number of an outdoor unit, from a pulldown menu of model numbers stored in the database server  320 . 
     The user inputs a model number of an indoor unit as each of the utilization-side units of the air conditioning apparatus, in an input area A 13  on the screen illustrated in  FIG. 7A . The model number which the user inputs is acquired by the first utilization-side unit group information acquisition unit  314  of the Web server  310 . The first utilization-side unit group information acquisition unit  314  of the Web server  310  retrieves information relative to the model number of the indoor unit as the utilization-side unit, from the utilization-side unit internal volume information  322  stored in the database server  320 . 
     Next, when the user selects settings on a relay unit group, from a window (not illustrated) different from the data input and setting window W 1 , an input and setting area A 16  and a setting button B 16  concerning a relay unit are displayed on the data input and setting window W 1  as illustrated in  FIG. 7B . For example, if the user intends to make settings on the relay unit  4 B, the user performs data input concerning a relay unit group  4 B. In an input area A 16   a  on a screen illustrated in  FIG. 7C  (a partially enlarged diagram of  FIG. 7B ), when the user selects a utilization-side unit (an indoor unit) to be disposed downstream of the relay unit  4 B, the relay unit  4 B is associated with the utilization-side unit, so that a relay unit group is created. For example, when the user selects three utilization-side units and clicks the setting button B 16 , the relay unit  4 B and the three utilization-side units are registered as one group. 
     The foregoing input and setting operations correspond to step S 21  in  FIG. 5 . 
     Next, the user inputs a name of a room as a space where each of the utilization-side units (indoor units) is installed. The user inputs a name of a room in an input area A 14  on a screen illustrated in  FIG. 7D . For example, the user inputs a room name “second drawing room” to a box A 14   b  in the input area A 14 . 
     Next, the user inputs a floor area of each room and an installation height of the corresponding utilization-side unit (the indoor unit). In a state in which the user selects the box A 14   b  on the screen illustrated in  FIG. 7D , alternatives of a floor area and alternatives of an installation height of each utilization-side unit are displayed in an input area A 15  on the screen illustrated in  FIG. 7D . The user is able to perform data input by selecting one of the alternatives. The information on the floor area of each room and the information on the installation height of the corresponding utilization-side unit which the user inputs are acquired by the installation space size information acquisition unit  313  of the Web server  310 . 
     In a case where a utilization-side unit is installed on the ceiling of a room, the user inputs a height from the floor surface to the ceiling, as an installation height of the utilization-side unit. If the user intends to input the dimensions more specifically, the user inputs a height dimension from the floor surface to an assumed position at which leakage of a refrigerant occurs. 
     The foregoing input and setting operations correspond to step S 22  in  FIG. 5 . 
     Next, when the user clicks a button B 17  in the data input and setting window W 1  illustrated in  FIG. 7B , the data input and setting operations end. The design support program in the Web server  310  then causes the display of the user terminal  330  to display thereon a plotting window W 2  illustrated in  FIG. 7E . The plotting window W 2  displays images of the heat source-side unit  2 , relay units  4 A,  4 B, and  4 F, utilization-side units  3   a  to  3   f,  and refrigerant connection pipes which the user has already input. When the user clicks a button B 18  in the plotting window W 2 , input window W 3  of a new connection pipe length (a length of a refrigerant connection pipe) is opened as illustrated in  FIG. 7F . The user inputs a length of each gas-side refrigerant connection pipe and a length of each liquid-side connection pipe, in this input window W 3 . It should be noted that the design support program in the Web server  310  automatically fixes a pipe diameter (a pipe size) of a refrigerant connection pipe in accordance with a capacity of the heat source-side unit  2  and a capacity of each utilization-side unit. 
     When the user finishes the data input in the connection pipe length input window W 3  illustrated in  FIG. 7F , and then clicks a button B 19 , the input information is acquired by the first connection pipe group information acquisition unit  315  of the Web server  310 . A warning window W 4  illustrated in  FIG. 7G  is opened instead of the connection pipe length input window W 3 , on the display of the user terminal  330 . The warning window W 4  indicates that leakage of the refrigerant does not satisfy an allowable level in a predetermined room (“office kitchenette” in  FIG. 7G ) as a space where a corresponding one or more utilization-side units of the air conditioning apparatus is installed. In accordance with the warning window W 4 , the user determines that the number of utilization-side units to be disposed downstream of the relay unit  4 A is too large or determines that the total length of the refrigerant connection pipes (a first refrigerant connection pipe group) to be located downstream of the relay unit  4 A is too long. The user then returns the screen to the screen illustrated in  FIG. 7C  to change the number of utilization-side units to be disposed downstream of the relay unit  4 A, or returns the screen to the screen illustrated in  FIG. 7F  to change the lengths of the refrigerant connection pipes to be located downstream of the relay unit  4 A. The change in lengths of the refrigerant connection pipes to be located downstream of the relay unit  4 A means a change in arrangement of the relay unit  4 A. 
     As a matter of course, the warning window W 4  illustrated in  FIG. 7G  is not opened if the leakage of the refrigerant satisfies the allowable level in all the rooms as the spaces where the utilization-side units of the air conditioning apparatus are installed. 
     (4-2-2-2) Determination as to Whether Leakage of Refrigerant Satisfies Allowable Level, Using Design Support Program 
     The creation and display of the warning window W 4  ( FIG. 7G ) using the design support program in the Web server  310  are made by the corresponding functional blocks of the Web server  310  through the following calculations. With reference to  FIG. 6 , next, a description will be given of the calculations, with the first utilization-side unit group  81  (the utilization-side units  3   a  and  3   b ) located downstream of the relay unit  4 A as an example. 
     First, the acquired information appropriateness determination unit  318   a  of the Web server  310  selects the “office kitchenette” having the smallest floor area between the rooms where the first utilization-side unit group  81  (the utilization-side units  3   a  and  3   b ) are installed, as a room for which safety measures are should be taken. In one or more embodiments, a room having the smallest floor area is a room having the smallest spatial volume. Next, the Web server  310  calculates a volume V (m 3 ) of the internal space of the “office kitchenette”. The volume V (m 3 ) is calculated by multiplying the floor area of the office kitchenette and the ceiling height of the office kitchenette together. In one or more embodiments, the volume V (m 3 ) of the internal space of the “office kitchenette” is calculated from the values input in the input area A 15  on the screen illustrated in  FIG. 7D . 
     Next, the Web server  310  calculates an allowable refrigerant leak amount A (kg/m 3 ) per unit volume of the room. One of conditions for the calculation is a refrigerant type. The LFL described above changes depending on a refrigerant type (e.g., R32, R1234yf, etc.). A safety factor, which is one of the conditions for the calculation, is set at, for example, 4. In a case where each room is ventilated, a ventilation amount may be defined as one of the conditions for the calculation. 
     The allowable refrigerant leak amount A×V (kg) in the “office kitchenette” is calculated by multiplying the volume V (m 3 ) of the “office kitchenette” and the allowable refrigerant leak amount A (kg/m 3 ) per unit volume together. 
     The foregoing operations correspond to step S 23  in  FIG. 5 . 
     Next, the first utilization-side unit group refrigerant amount calculation unit  318   c  of the Web server  310  calculates a total amount M 1  (kg) of the refrigerant in the utilization-side refrigerant circuits  13   a  and  13   b  of the utilization-side units  3   a  and  3   b  in the first utilization-side unit group  81  illustrated in  FIG. 6 . This calculation is made using the internal volumes of the utilization-side refrigerant circuits  13   a  and  13   b  of the utilization-side units  3   a  and  3   b.  The internal volumes are stored in the database server  320 . The first utilization-side unit group refrigerant amount calculation unit  318   c  of the Web server  310  calculates the total amount M 1  (kg) of the refrigerant in the utilization-side refrigerant circuits  13   a  and  13   b,  on the assumption that the refrigerant is present in a predetermined state in each of the utilization-side refrigerant circuits  13   a  and  13   b  of the utilization-side units  3   a  and  3   b.  In this calculation, a thermal environment of a region where the air conditioning apparatus is installed is considered as described above. The thermal environment refers to, for example, an environment of a region where the air conditioning apparatus is installed, such as a hot country near the equator or a cold region where an outside temperature is below −10° C. in winter. An air conditioning operation differs between a region near the equator and a cold region. Specifically, a target refrigerant temperature at a utilization-side heat exchanger of a utilization-side unit differs between a region near the equator and a cold region. This results in changes in amounts of the refrigerant in the utilization-side refrigerant circuits  13   a  and  13   b  of the utilization-side units  3   a  and  3   b  and amount of the refrigerant in the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). In view of this, the amounts of the refrigerant in the utilization-side refrigerant circuits  13   a  and  13   b  are calculated based on a thermal environment of a region where the air conditioning apparatus is installed. Information on a thermal environment of a region where the air conditioning apparatus is installed is previously acquired by the thermal environment information acquisition unit  316  of the Web server  310 . For example, in the upper display screen of the data input and setting window W 1  illustrated in  FIG. 7A , the user inputs information on a thermal environment, in conjunction with information on an address and a name of a building in which the air conditioning apparatus is installed. 
     Examples of the conditions for the calculation of the total amount M 1  (kg) of the refrigerant in the utilization-side refrigerant circuits  13   a  and  13   b  may include, but not limited to, a condition concerning a heating operation, a condition that a condensation temperature at a utilization-side heat exchanger is 46° C. in the heating operation, a condition that a target degree of subcooling is 5° C. in the heating operation, a condition concerning a density of the refrigerant in the liquid-side refrigerant connection pipe  5 , and a condition concerning a density of the refrigerant in the gas-side refrigerant connection pipe  6 . The condition concerning the heating operation refers to a condition of an operation that increases the amounts of the refrigerant in the utilization-side refrigerant circuits  13   a  and  13   b,  depending on a region. These conditions for each thermal environment are incorporated in the design support program in the Web server  310 . 
     The foregoing operations correspond to step S 24  in  FIG. 5 . 
     The first connection pipe group refrigerant amount calculation unit  318   d  of the Web server  310  also calculates an amount M 2  (kg) of the refrigerant in the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) connecting the relay unit  4 A and the first utilization-side unit group  81  (the utilization-side units  3   a  and  3   b ). This calculation is made by a conversion from the pipe diameter and pipe length of the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). The thermal environment of the region where the air conditioning apparatus is installed is also considered for the calculation of the amount M 2  (kg) of the refrigerant in the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). 
     The foregoing operations correspond to step S 25  in  FIG. 5 . 
     Next, the acquired information appropriateness determination unit  318   a  of the Web server  310  determines whether a sum of the total amount M 1  (kg) of the refrigerant in the first utilization-side unit group  81  and the amount M 2  (kg) of the refrigerant in the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) is larger or smaller than the allowable refrigerant leak amount A×V (kg) in the “office kitchenette”. In other words, the acquired information appropriateness determination unit  318   a  of the Web server  310  determines whether the following relationship (1) is satisfied. 
         M 1+ M 2≤ A×V    (1)
 
     When the relationship (1) is not satisfied, and the sum of M 1  and M 2  (kg) exceeds the allowable refrigerant leak amount A×V (kg), the acquired information appropriateness determination unit  318   a  of the Web server  310  determines that the leak of the refrigerant exceeds the allowable level. When the relationship (1) is satisfied, the acquired information appropriateness determination unit  318   a  of the Web server  310  determines that the leakage of the refrigerant is within a range of the allowable level. When the acquired information appropriateness determination unit  318   a  of the Web server  310  determines that the leak of the refrigerant exceeds the allowable level, the warning window W 4  ( FIG. 7G  described above) is created and displayed on the display of the user terminal  330 . 
     The foregoing operations correspond to steps S 26  and S 27  in  FIG. 5 . 
     (5) Features 
     (5-1) 
     As described above, a design support system  300  is a system for supporting design of an air conditioning apparatus as a refrigerant cycle apparatus. 
     As illustrated in, for example,  FIG. 6 , the air conditioning apparatus includes a plurality of utilization-side units  3   a  to  3   f,  a heat source-side unit  2 , refrigerant connection pipes  5  and  6 , and relay units  4 A,  4 B, and  4 F each serving as a refrigerant shut-off unit. The plurality of utilization-side units  3   a  to  3   f  include a first utilization-side unit group  81 . The first utilization-side unit group  81  is a group of two utilization-side units  3   a  and  3   b.  The relay unit  4 A blocks a flow of a refrigerant between utilization-side refrigerant circuits  13   a  and  13   b  in the first utilization-side unit group  81  and a heat source-side refrigerant circuit  12  of the heat source-side unit  2 . The refrigerant connection pipes  5  and  6  include a first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). The first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) is a group of connection pipes connecting the utilization-side refrigerant circuits  13   a  and  13   b  in the first utilization-side unit group  81  and the relay unit  4 A. 
     The design support system  300  includes an information acquisition unit  312  and a useful information presentation unit  318 . The information acquisition unit  312  includes a first utilization-side unit group information acquisition unit  314  that acquires information on each of the utilization-side units  3   a  and  3   b  in the first utilization-side unit group  81 . The information acquisition unit  312  includes a first connection pipe group information acquisition unit  315  that acquires information on a pipe length and a pipe size of the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). The useful information presentation unit  318  includes an acquired information appropriateness determination unit  318   a  that makes a determination as to appropriateness of design information which a user inputs (e.g., information on the utilization-side units  3   a  and  3   b,  information on the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ), size information on an installation space) in view of allowable leakage of the refrigerant in a space where a corresponding one of the utilization-side units  3   a  and  3   b  in the first utilization-side unit group  81  is installed, and presents a result of the determination as useful information (see  FIG. 7G ). 
     With this configuration, the user is able to design the air conditioning apparatus while testing various design variations, in fixing arrangement of the relay unit  4 A and fixing a type and a number of utilization-side units to be disposed downstream of the relay unit  4 A. For example, using the design support system  300 , the user changes the arrangement of the relay unit  4 A to change the length of the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) or changes the design such that the utilization-side unit  3   b  disposed downstream of the relay unit  4 A is disposed downstream of another relay unit, in accordance with the warning window W 4  on the screen illustrated in  FIG. 7G . The user then clicks the “check” button again to obtain a result of a determination as to whether a total amount (kg) of the refrigerant in the first utilization-side unit group and first connection pipe group disposed downstream of the changed relay unit  4 A falls below the allowable refrigerant leak amount A×V (kg) in the “office kitchenette”. 
     (5-2) 
     The design support system  300  includes a Web server  310  that stores therein a design support program involving calculation based on a thermal environment of a region where the air conditioning apparatus is installed, in finding (calculating) a total amount M 1  (kg) of the refrigerant in the utilization-side refrigerant circuits  13   a  and  13   b  and an amount M 2  (kg) of the refrigerant in the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). This calculation considers, for example, a condition concerning a heating operation, a condition that a condensation temperature at a utilization-side heat exchanger is 46° C. in the heating operation, a condition that a target degree of subcooling is 5° C. in the heating operation, a condition concerning a density of the refrigerant in the liquid-side refrigerant connection pipe  5 , and a condition concerning a density of the refrigerant in the gas-side refrigerant connection pipe  6 . Among the conditions, for example, the condition concerning the condensation temperature at the utilization-side heat exchanger in the heating operation differs between a thermal environment in a cold region and a thermal environment in a hot region. 
     Therefore, the design support system  300  configured to perform calculation based on information on a thermal environment acquired by a thermal environment information acquisition unit  316  of the Web server  310  attains a calculation result of an appropriate refrigerant amount according to a place where the air conditioning apparatus is installed, as compared with a case where the design support system  300  uniformly calculates the refrigerant amounts M 1  and M 2 , based on a condition of an excessive thermal environment. 
     (6) Modifications 
     (6-1) Modification 1 
     According to one or more embodiments, the acquired information appropriateness determination unit  318   a  of the design support system  300  makes a determination as to appropriateness of design information which the user inputs (e.g., information on the utilization-side units  3   a  and  3   b,  information on the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ), size information on the installation space), and presents a result of the determination to the user as useful information in the form of the warning window W 4  illustrated in  FIG. 7G . 
     In place of this configuration or in addition to this configuration, the design support system  300  may calculate a restriction on the arrangement of the relay unit  4 A as the refrigerant shut-off unit and present a result of the calculation to the user. 
     As illustrated in  FIG. 4 , the useful information presentation unit  318  of the Web server  310  includes the relay unit arrangement restriction fixing unit  318   b  as a functional block. The design support program in the Web server  310  of the design support system  300  may achieve presentation of useful information by the relay unit arrangement restriction fixing unit  318   b,  in place of presentation of useful information by the acquired information appropriateness determination unit  318   a.    
     After steps S 21  to S 24  in  FIG. 5  describe above, the relay unit arrangement restriction fixing unit  318   b  subtracts the total amount M 1  (kg) of the refrigerant in the utilization-side refrigerant circuits  13   a  and  13   b  of the utilization-side units  3   a  and  3   b,  from the allowable refrigerant leak amount A×V (kg) in the “office kitchenette”, thereby calculating a maximum value of the amount of the refrigerant that may be present in the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). The maximum value of the amount of the refrigerant in the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) refers to a restriction on the arrangement of the relay unit  4 A. This is because the arrangement of the relay unit  4 A is strongly related to the length of the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). When receiving the maximum value of the amount of the refrigerant in the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) from the relay unit arrangement restriction fixing unit  318   b,  the user searches for arrangement of the relay unit  4 A within a range of the restriction on the length of the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). 
     The design support system  300  may automatically plot appropriate arrangement of the relay unit  4 A as a refrigerant shut-off unit and present the arrangement to the user. In this case, for example, the design support system  300  puts a priority on maintainability of the plurality of relay units  4 A,  4 B, and  4 F and fixes the arrangement of the relay unit  4 A within the range of the restriction on the length of the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) such that the relay units  4 A,  4 B, and  4 F are closely disposed each other. 
     (6-2) Modification 2 
     According to one or more embodiments, the acquired information appropriateness determination unit  318   a  of the design support system  300  makes a determination as to appropriateness of design information which the user inputs (e.g., information on the utilization-side units  3   a  and  3   b,  information on the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ), size information on the installation space), and presents a result of the determination to the user as useful information in the form of the warning window W 4  illustrated in  FIG. 7G . 
     In place of this configuration, the useful information presentation unit  318  of the Web server  310  in the design support system  300  may present the refrigerant amounts M 1  and M 2  calculated in steps S 24  and S 25  describe above to the user as useful information. The useful information presentation unit  318  may alternatively present a sum of the refrigerant amounts M 1  and M 2  (a first refrigerant amount) to the user as useful information. 
     In accordance with numerical values of the refrigerant amounts M 1  and M 2 , a somewhat experienced designer is able to determine whether a problem arises in a case where a refrigerant leaks, in view of the sizes of rooms where the utilization-side units  3   a  and  3   b  are installed. 
     (6-3) Modification 3 
     According to Modification 1, the design support system  300  calculates the restriction on the arrangement of the relay unit  4 A as the refrigerant shut-off unit, and presents the result of the calculation to the user as the first information. 
     In place of this configuration, the design support system  300  may calculate a restriction on an internal volume of the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ) and present a result of the calculation to the user as third information. In accordance with this presentation, the user is able to make a choice of changing the length and pipe diameter of the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ). 
     The design support system  300  may alternatively present a list of devices of different capacities, the devices being usable as the utilization-side units  3   a  and  3   b,  as the useful information (second information), based on a restriction on the internal volumes of the utilization-side refrigerant circuits  13   a  and  13   b  of the utilization-side units  3   a  and  3   b  rather than the restriction on the arrangement of the relay unit  4 A. In accordance with the presentation of the useful information, the user is able to make an examination as to whether the downsizing of the utilization-side unit  3   a  is possible, in consideration of, for example, a margin from the viewpoint of an air conditioning capacity as to a current capacity of the utilization-side unit  3   a  installed in the “office kitchenette”. 
     (6-4) Modification 4 
     According to one or more embodiments, the design support program in the Web server  310  of the design support system  300  causes the data input and setting window W 1  to display the input and setting area A 16  and the setting button B 16  regarding the relay unit as illustrated in  FIG. 7B . In the input area A 16   a,  when the user selects a utilization-side unit (an indoor unit) to be disposed downstream of the relay unit  4 B, the relay unit  4 B is associated with the utilization-side unit, so that a relay unit group is created. 
     In addition to this configuration, the rooms as spaces where utilization-side units (indoor units) are installed may also be grouped. The reason therefor is as follows. In a case where a partition between two or more rooms is an airy ventilated member such as a partial wall or a shade, an allowable refrigerant leak amount upon leakage of a refrigerant should be calculated by addition of spatial volumes of these rooms. The grouping of the rooms is effective also in a case where multiple utilization-side units (indoor units) are installed in one room. 
     (6-5) Modification 5 
     According to one or more embodiments, the warning window W 4  illustrated in  FIG. 7G  is opened when the user clicks the button B 19  on the connection pipe length input window W 3  illustrated in  FIG. 7F . In place of this configuration, when it is determined that the leakage of the refrigerant does not satisfy the allowable level, a warning message may be issued while input numerical values are highlighted red immediately even when the user is inputting the numerical values on the connection pipe length input window W 3  illustrated in  FIG. 7F . 
     (6-6) Modification 6 
     According to one or more embodiments, the design support system  300  is described with the designer of the air conditioning apparatus regarded as the user. In installing the air conditioning apparatus in a worksite (building), the design support system  300  may alternatively be used by a constructor who fixes a path of the connection pipes  5  and  6  and fixes arrangement of the relay units  4 A,  4 B, and  4 F at the worksite. In a case where the user who is the constructor of the air conditioning apparatus uses the design support system  300 , the design support system  300  serves as a system for supporting the construction in addition to the design. 
     (6-7) Modification 7 
     According to one or more embodiments, as illustrated in, for example,  FIG. 7E , the design support program in the Web server  310  of the design support system  300  allows display of the two-dimensional plotting window W 2 . In place of this configuration, the design support program in the Web server  310  of the design support system  300  may allow display of a three-dimensional plotting screen. 
     (6-8) Modification 8 
     According to one or more embodiment, the warning window W 4  illustrated in  FIG. 7G  is presented as the useful information to the user by the design support program in the Web server  310  of the design support system  300 . In place of this configuration, a series of information items and calculation results, such as the refrigerant amounts M 1  and M 2 , the allowable refrigerant leak amount A×V (kg) in the “office kitchenette”, and the input value of the length of the first connection pipe group ( 5   ab,    5   a,    5   b,    6   ab,    6   a,    6   b ), may be collectively output in the form of a graph or a chart. For example, if these information items are available in the form of a list, the user is able to make an examination on, for example, arrangement of the relay unit  4 A while checking the printed list. 
     (6-9) Modification 9 
     According to one or more embodiments, the database server  320  may further store information on design of an air conditioning apparatus for each region and past calculation results. In this case, the user is able to use information, such as calculation results, on an air conditioning apparatus already installed in a different building of a similar structure, for design of an air conditioning apparatus which the user designs. 
     (6-10) Modification 10 
     According to one or more embodiments, the user inputs the length of each gas-side refrigerant connection pipe and the length of each liquid-side refrigerant connection pipe, in the input window W 3  illustrated in  FIG. 7F , by the design support program in the Web server  310  of the design support system  300 . In the design support program in the Web server  310 , a default pipe size is previously fixed in accordance with a capacity of a heat source-side unit and a capacity of a utilization-side unit. 
     In place of this configuration, the user may further input a pipe size (a pipe diameter), in the input window W 3  illustrated in  FIG. 7F . 
     (6-11) Modification 11 
     According to one or more embodiments, the control unit  19  of the air conditioning apparatus  1  has the configuration in which the heat source-side control unit  92 , the relay-side control units  94 A and  94 B, and the utilization-side control units  93   a,    93   b,    93   c,  and  93   d  are connected via the transmission lines  95  and  96  as illustrated in  FIG. 2A . 
     The control unit  19  may alternatively employ a configuration in which the heat source-side control unit  92  and the relay-side control units  94 A and  94 B are connected via the utilization-side control units  93   a,    93   b,    93   c,  and  93   d  as illustrated in  FIG. 8 , in place of the configuration in which the heat source-side control unit  92  and the utilization-side control units  93   a,    93   b,    93   c,  and  93   d  are connected via the relay-side control units  94 A and  94 B as illustrated in  FIG. 2A . 
     (6-12) Modification 12 
     According to one or more embodiments, each of the liquid relay shut-off valve  41 A, the liquid relay shut-off valve  41 B, the gas relay shut-off valve  42 A, and the gas relay shut-off valve  42 B in the air conditioning apparatus  1  is an electric expansion valve, but may alternatively be an electromagnetic valve that switches between an open state and a closed state. 
     (6-13) Modification 13 
     According to one or more embodiments, the air conditioning apparatus  1  includes the relay units  4 A and  4 B each having the liquid-side configuration and the gas-side configuration. The air conditioning apparatus  1  may alternatively include a relay unit having the liquid-side configuration and a relay unit having the gas-side configuration. 
     (6-14) Modification 14 
     According to one or more embodiments, the refrigerant circuit  10  in the air conditioning apparatus  1  is filled with R32 as a refrigerant. However, the technique regarding the arrangement of the relay unit described above is also effective in a case where the refrigerant circuit  10  is filled with another flammable refrigerant. The technique regarding the arrangement of the relay unit described above is also effective in a case where the refrigerant circuit  10  is filled with a single refrigerant of a mildly flammable refrigerant such as R32, R1234yf, R1234ze, or R744, or a mixed refrigerant containing this refrigerant. It should be noted that R32 is difluoromethane (HFC-32), R1234yf is 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf), R1234ze is 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze), and R744 is carbon dioxide. 
     A mildly flammable refrigerant, a lower flammability refrigerant, or a higher flammability refrigerant is supposed to be used as a refrigerant with which the refrigerant circuit  10  is filled and which flows through the refrigerant circuit  10 . The mildly flammable refrigerant is classified as “Class 2L” in U.S. ANSI/ASHRAE Standard 34-2013. The lower flammability refrigerant is classified as “Class 2” in U.S. ANSI/ASHRAE Standard 34-2013. The higher flammability refrigerant is classified as “Class 3” in U.S. ANSI/ASHRAE Standard 34-2013. 
     U.S. ANSI/ASHRAE Standard 34-2013 is a standard of criteria for evaluation of flammable gas in the United States of America. Regulations on chemical materials are established in various countries around the world, and one of the regulations is the flammability of chemical materials. A standard is established for each country, and gas is classified into flammable gas and non-flammable gas under the criteria for evaluation in each country. In Japan, High Pressure Gas Safety Act defines an explosion limit value as one of criteria of flammable gas. Examples of the criteria of flammable gas may include ASHRAE34 and DOT as U.S. standards, EN378-1 and CLP Regulation as European standards, and GHS and ISO10156 as international standards. A European standard equivalent to U.S. ANSI/ASHRAE Standard 34-2013 is, for example, DIN EN378-1 (2008). DIN EN378-1 (2008) also specifies “Class 3: Higher Flammability”, “Class 2: Lower Flammability”, and “Class 2L: Mildly Flammable” as in U.S. ANSI/ASHRAE Standard 34-2013. Likewise, ISO/Final Draft International Standard (FDIS) 817 (2013) specifies “Class 3: Higher Flammability”, “Class 2: Lower Flammability”, and “Subclass 2L: Mildly Flammable”. 
     (6-15) Modification 15 
     According to one or more embodiments, the refrigerant circuit  10  in the air conditioning apparatus  1  is filled with mildly flammable R32 as a refrigerant. However, the technique regarding the arrangement of the relay unit described above is also effective in a case of employing, for example, a toxic refrigerant or a refrigerant that may cause a shortage of oxygen concentration if the refrigerant leaks in large amounts. For example, this technique is also applicable in a case of employing carbon dioxide as a refrigerant. 
     (6-16) Modification 16 
     While one or more embodiments have been described herein above, it is to be appreciated that various changes in form and detail may be made without departing from the spirit and scope of the present disclosure presently or hereafter claimed. 
     Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims. 
     REFERENCE SIGNS LIST 
       2 : heat source-side unit 
       3   a:  utilization-side unit (utilization-side unit in first utilization-side unit group) 
       3   b:  utilization-side unit (utilization-side unit in first utilization-side unit group) 
       3   c:  utilization-side unit 
       3   d:  utilization-side unit 
       3   e:  utilization-side unit 
       3   f:  utilization-side unit 
       4 A: relay unit (refrigerant shut-off unit; first refrigerant shut-off unit) 
       4 B: relay unit (refrigerant shut-off unit) 
       4 F: relay unit (refrigerant shut-off unit) 
       5 : liquid-side refrigerant connection pipe (connection pipe group) 
       5   a:  most-downstream pipe (first connection pipe group) 
       5   ab:  common pipe (first connection pipe group) 
       5   b:  most-downstream pipe (first connection pipe group) 
       6 : gas-side refrigerant connection pipe (connection pipe group) 
       6   a:  most-downstream pipe (first connection pipe group) 
       6   ab:  common pipe (first connection pipe group) 
       6   b:  most-downstream pipe (first connection pipe group) 
       12 : heat source-side refrigerant circuit (second refrigerant circuit) 
       13   a:  utilization-side refrigerant circuit (first refrigerant circuit) 
       13   b:  utilization-side refrigerant circuit (first refrigerant circuit) 
       81 : first utilization-side unit group 
       300 : design support system (support system) 
       312 : information acquisition unit 
       318 : useful information presentation unit (presentation unit)