Patent Publication Number: US-2012043054-A1

Title: Air-conditioning apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an air-conditioning apparatus that efficiently performs cooling and heating using a plurality of such as indoor units. 
     BACKGROUND ART 
     Hitherto, an air-conditioning apparatus that performs cooling, heating, and simultaneous cooling and heating requires a cycle that performs cooling and a cycle that performs heating, and therefore requires a number of pipes connected to indoor units, making the apparatus excessively large and intricate. Meanwhile, there is an apparatus in which heating energy and cooling energy are generated simultaneously in a primary cycle, the resulting difference in heat quantity is compensated by an air heat exchanger and a compressor, and the cooling energy and the heating energy are conveyed to a secondary cycle (see Patent Literature 1, for example). 
     There is another problem in that, in either case of cooling and heating, different temperatures may be required at a time by individual loads (for example, heating air conditioning and floor heating, or perimeter air conditioning and interior air conditioning) and cycles based on separate systems are therefore necessary, making the apparatus excessively large and intricate. Meanwhile, there is an apparatus in which each heat exchanger that exchanges heat between a primary cycle and a secondary cycle is equipped with adjusting valves on the upstream and downstream sides on the primary-refrigerant side thereof so that the pressure and the flow rate during the heat-exchanging operation are adjusted, whereby the primary cycle is established by itself (see Patent Literature 2, for example). 
     On the other hand, as an energy-saving operation of controlling a secondary cycle, a minimum-resistance control operation is known in which the amount of electricity consumed by a pump that circulates a medium through to indoor units is minimized. In this minimum-resistance control operation, the air-conditioning flow rate of the pump is controlled such that the opening-degree of a control valve provided in a path for supplying the medium to the indoor units becomes the maximum, that is, the pressure loss occurring at the control valve is minimized. Opening-degree-controlling means calculates the required loads of the respective indoor units, or many sensing objects, in all branches. In a case of building air conditioning such as zoning air conditioning in which the number of branches is small in spite of the large scale and the operation pattern is relatively stable, the calculation can be handled even in a strict feedforward control operation (see Patent Literature 3, for example). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Examined Patent Application Publication No. 59-2832 (pages 2 to 4, and FIGS. 2 and 3) 
     Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2007-183045 (pages 4 to 6 and FIG. 1) 
     Patent Literature 3: Japanese Unexamined Patent Application Publication No. 2004-317000 (pages 8 to 14 and FIG. 1) 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the known example disclosed by Patent Literature 1, however, when simultaneously generating heating energy and cooling energy on the primary side, since a bypass is provided on the primary side of a heat exchanger provided between the primary cycle and the secondary cycle, the amounts of heating energy and cooling energy generated are adjusted by adjusting the flow rates on the primary side and in the bypass. Therefore, the primary cycle is complicated. 
     Meanwhile, in the known example disclosed by Patent Literature 2, in the heating operation, the higher one of the pressures of the heat exchangers provided between the primary cycle and the secondary cycle is taken as the discharge pressure. Therefore, although there are pressure-increasing operations for the two heat exchangers at different pressures, the operation for the circulation through the heat exchanger at the lower pressure is useless. Moreover, no explicit measures for a case where a plurality of loads are provided are provided. 
     Meanwhile, in the known example disclosed by Patent Literature 3, control parameters include an adjustment parameter, and air-conditioning units need to be individually adjusted on site in accordance with the pipe lengths and the fan coil capacities thereof. If the personnel in charge of on-site adjustment do not know the specifications of the secondary cycle, it takes more time to perform the adjustment. Moreover, if a plurality of indoor units are provided, it takes a long time to perform strict calculation and inter-device communication, and a costly processing apparatus is necessary. Such a situation may not be completely managed with an inexpensive processing apparatus. 
     The present invention is made to solve the above problems and to provide an air-conditioning apparatus capable of generating cooling energy, heating energy, and cooling energy and heating energy simultaneously with a simple configuration, and including a primary cycle that generates even cooling energy or heating energy alone in accordance with loads of different types and a secondary cycle that is efficient and is stabilized in a short time even if there are changes in the loads. 
     Solution to Problem 
     An air-conditioning apparatus according to the present invention includes a first cycle through which a first medium circulates, a second cycle through which a second medium circulates, and a third cycle through which the second medium circulates. The first cycle includes a loop in which a compressor, a first heat exchanger, a first reducing valve, a second heat exchanger in which the first medium circulating through the first cycle and the second medium circulating through the second cycle exchange heat therebetweeh, a second reducing valve, a third heat exchanger in which the first medium circulating through the first cycle and the second medium circulating through the third cycle exchange heat therebetween, and a flow-path switcher that switches the direction of flow of the first medium between forward and backward directions are sequentially connected to one another with pipes. The second cycle includes the second heat exchanger, a first pump that drives the second medium, a first path that connects the second heat exchanger and the first pump, and at least one first branch path having one end thereof connected to one end of the first path and the other end thereof connected to the other end of the first path. The third cycle includes the third heat exchanger; a second pump that drives the second medium, a second path that connects the third heat exchanger and the second pump, and at least one second branch path having one end thereof connected to one end of the second path and the other end thereof connected to the other end of the second path. Each first branch path and second branch path includes flow-path-switching valves, an indoor unit and a flow-rate-adjusting valve. The flow-path-switching valves have a first flow-path-switching valve that connects each first branch path and second branch path to one ends of the first path and the second path respectively, and that switches so as to communicate with at least one of the second cycle and the third cycle and a second flow-path-switching valve that connects to the other ends of the first path and the second path and that switches so as to communicate with at least one of the second cycle and the third cycle. The apparatus further includes switching-controlling means that switches the flow-path-switching valves such that an indoor unit performing a cooling operation connects to one of the cycles which has one of the second heat exchanger and the third heat exchanger in which the pressure of the first medium thereof is relatively low, and which exchanges heat with the first cycle and 
     such that an indoor unit performing a heating operation connects to one of the cycles which has one of the second heat exchanger and the third heat exchanger in which the pressure of the first medium thereof is relatively high, and which exchanges heat with the first cycle. 
     Advantageous Effects of Invention 
     According to the present invention, an efficient supply of heat source is realized with a simple configuration in accordance with various loads requiring heating energy, heating energy at different temperatures, cooling energy, cooling energy at different temperatures, and simultaneous heating energy and cooling energy. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1 . is a circuit diagram illustrating the configuration of an air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 2  is a circuit diagram illustrating an operation of the air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 3  is a circuit diagram illustrating an operation of the air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 4  is a circuit diagram illustrating the configuration of an air-conditioning apparatus according to a form of Embodiment 1 of the present invention. 
         FIG. 5  is a circuit diagram illustrating the configuration of an air-conditioning apparatus according to a form of Embodiment 1 of the present invention. 
         FIG. 6  is a schematic diagram illustrating the configuration of the air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 7  is a flowchart illustrating an operation of a control apparatus  100  according to Embodiment 1 of the present invention. 
         FIG. 8  is a circuit diagram illustrating the configuration of an air-conditioning apparatus according to Embodiment 2 of the present invention. 
         FIG. 9  is a flowchart illustrating an operation of the control apparatus  100  according to Embodiment 2 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     Embodiment 1 of the present invention will now be described.  FIG. 6  is a schematic diagram of an air-conditioning apparatus according to Embodiment 1 of the present invention. Reference numeral  90  denotes a building that is an object of air conditioning, the building including living spaces  91   a  to  c  and non-living spaces  92   a  to  c.  An air-conditioning apparatus  1  includes a heat source unit  2 , a relay unit  3 , and load units  4   a  to  4   f.  The heat source unit  2  and the relay unit  3  are connected to each other with two pipes, which are a first extension pipe  13  and a second extension pipe  18 , whereby a first cycle  5  is formed. The relay unit  3  and each of the load units  4   a  to  4   f  are connected to each other with two pipes, which are a corresponding one of third extension, pipes  33   a,  to  f  and a corresponding one of fourth extension pipes  36   a  to  f,  whereby a second cycle  6  or a third cycle  7  is formed. The heat source unit  2  is provided in a machine room on the rooftop, on the outside, in the basement, or so forth in the building. The load units  4   a  to  f  are in or near rooms. The relay unit  3  may be provided near the rooms as illustrated in  FIG. 6  or may be provided next to the heat source unit  2 . 
     Thus, unlike a chiller, the air-conditioning apparatus  1  does not include many pipes and is not intricate. Therefore, air conditioning can be controlled easily, and installation work and adjustment can be performed easily. 
     Furthermore, by utilizing different media such that a second medium filling the second cycle and the third cycle abutting the room spaces is water or brine and a first medium filling the first cycle not abutting the room spaces is carbon dioxide, even if a leakage of the medium should occur, the probability of the, occurrence of adverse influence is low. Even if the first medium is a flammable refrigerant that contains a refrigerant having a low GWP (global warming potential); the same effect is provided. Furthermore, in the present embodiment, since there are a plurality of cycles and a plurality of media, the amount of the first medium to be filled is smaller than in a case of a direct-expansion air-conditioning apparatus that includes one cycle filled with one medium. In a case where the first medium is a fluorocarbon refrigerant having, in general, a high ozone depletion potential, even if the first medium should leak, the amount to be filled is small and the degree of adverse influence on the environment is therefore low. 
     Furthermore, a flow-path-switching mechanism, which is in the form of a so-called four-way valve, may include a plurality of components. For example, any mechanism such as a flow-path-switching mechanism including a combination of four openable/closable valves or a flow-path-switching mechanism including a combination of two three-way valves is acceptable, as long as the mechanism has a function of switching flow paths. 
       FIG. 1  is a circuit diagram of the air-conditioning apparatus according to Embodiment 1 of the present invention. 
     Furthermore, the air-conditioning apparatus  1  includes the first cycle  5  through which the first medium circulates, the second cycle  6  through which the second medium circulates, and the third cycle  7  through which the second medium circulates. The first medium is carbon dioxide. The second medium is water, water with an additive such as an antiseptic substance, or brine. 
     The first cycle  5  is configured such that a compressor  9 , a flow-path switcher  10 , a first heat exchanger  11  and a fan  12  provided thereto, the first extension pipe  13 , a first reducing valve  14 , a second heat exchanger  15 , a second reducing valve  16 , a third heat exchanger  17 , the second extension pipe  18 , the flow-path switcher  10 , an accumulator  19 , and the compressor  9  are sequentially connected to one another. The second cycle  6  is configured such that the second heat exchanger  15 , a first pump  21 , a first branching path  40 , a plurality of branch paths  8   a  to  8   c,  a first combining path  41 , and the second heat exchanger  15  are sequentially connected to one another. The third cycle  7  is configured such that the third heat exchanger  17 , a second pump  22 , a second branching path  42 , the plurality of branch paths  8   a  to  8   c,  a second combining path  43 , and the third heat exchanger  17  are sequentially connected to one another. The plurality of branch paths  8   a  to  8   c  include first flow-path-switching valves  31   a  to  31   c,  flow-rate-adjusting valves  32   a  to  32   c,  the third extension pipes  33   a  to  33   c,  indoor units  34   a  to  34   c  and indoor-unit fans  35   a  to  35   c  provided thereto, the fourth extension pipes  36   a  to  36   c,  and second flow-path-switching valves  37   a  to  37   c.  Reference numerals  51  to  57  denote pressure sensors, and reference numerals  61  to  66 ,  67   a  to  67   c,  and  68   a  to  68   c  denote temperature sensors. 
     Note that a control apparatus  100  functions as compressor-rotation-speed-controlling means that controls the rotation speed of the compressor  9 ; fan-rotation-speed-controlling means that controls the rotation speeds of the fan provided to the first heat exchanger  11  and the indoor-unit fans  35   a  to  35   c  provided to the indoor units  34   a  to  34   c;  switching-controlling means, that controls the switching of the flow-path switcher  10 , the first flow-path-switching valves  31   a  to  31   c,  and the second flow-path-switching valves  37   a  to  37   c;  flow-rate-adjusting means that adjusts the flow rates of the first reducing valve  14  and the second reducing valves  32   a  to  32   c;  and rotation-speed-controlling means that controls the rotation speeds of the first pump  21  and the second pump  22 . 
     Next, an operation according to Embodiment 1 will be described. 
       FIG. 2  is a circuit diagram illustrating an operation of the air-conditioning apparatus according to Embodiment 1 of the present invention, in which the circuit illustrated by bold lines represents a circuit through which the second refrigerant flows, and the circuit illustrated by thin lines represents a line through which the second refrigerant does not flow (a non-connected line). 
     The operation according to Embodiment 1 will be described for the following six different cases: 
     (1) A case of a cooling-only operation, (2) a case of a cooling-only operation at different required temperatures, (3) a case of a cooling-main operation, (4) a case of a heating-only operation, (5) a case of a heating-only operation at different required temperatures, and (6) a case of a heating- main operation. 
     (1) Case of Cooling-Only Operation 
     A case of a cooling-only operation will now be described with reference to  FIG. 2 . 
     In the air-conditioning apparatus  1 , the flow-path switcher  10  is connected on the solid-line side. The first medium compressed by the compressor  9  and thus having a high pressure and a high temperature flows through the flow-path switcher  10  into the first heat exchanger  11 , and dissipates the heat thereof into the outside air supplied by the fan  12 , whereby the first medium comes to have a high pressure and a low temperature. The first medium flows through the first extension pipe  13 , and the pressure thereof is reduced by the first reducing valve  14 , whereby the first medium comes to have a low pressure and a low degree of dryness. The first medium further flows sequentially through the second heat exchanger  15 , the second reducing valve  16 , and the third heat exchanger  17 . The second reducing valve  16  is fully open, and the pressure loss is small. Furthermore, in the second heat exchanger  15 , since heat is exchanged between the first cycle  5  and the second cycle  6 , the first medium supplies the cooling energy thereof to the second medium. In the third heat exchanger  17 , since heat is exchanged between the first cycle  5  and the third cycle  7 , the first medium supplies the cooling energy thereof to the second medium. Thus, the first medium evaporates and comes to have a low pressure and a high degree of dryness, or becomes a low-pressure superheated gas. Then, the first medium sequentially flows through the second extension pipe  18 , the flow-path switcher  10 , and the accumulator  19 , and returns to the compressor  9 . 
     Here, the control apparatus  100  operates as follows. The control apparatus  100  controls the rotation speed of the compressor  9  such that the pressure in the intake-side pressure sensor  51  becomes constant. 
     The control apparatus  100  also controls the rotation speed of the outdoor-unit fan  12  such that the pressure at the discharge-side pressure sensor  52  becomes constant. Thus, the processing capacity of the first heat exchanger  11  is appropriately controlled. 
     The control apparatus  100  also controls the opening-degree of the first reducing valve  14  such that the result of Equation (1) below becomes constant. 
       (Exit superheat) of third heat exchanger 17=(Detected value of temperature sensor 64)−(Reduced saturation temperature at intake-side pressure sensor 51)   (1)
 
     The control apparatus  100  also makes the opening-degree of the second reducing valve  16  fully open. Thus, an appropriate cooling capacity is realized in accordance with the number of operating indoor units  34 . 
     The control apparatus  100  also controls the opening-degree of the flow-rate-adjusting valves  32   a  to  32   c  such that the result of Equation (2) below becomes constant. 
       (Temperature difference between entrance and exit) of indoor unit 34=(Detected value of temperature sensor 67)−(Detected value of temperature sensor 68)   (2)
 
     The control apparatus  100  also controls the rotation speed of the first pump  21  such that the result of Equation (3) below becomes constant. 
       (First pressure difference)=(Detected value of pressure sensor 55)−(Detected value of pressure sensor 54)   (3)
 
     The control apparatus  100  further controls the rotation speed of the second pump  22  such that the result of Equation (4) below becomes constant. 
       (Second pressure difference)=(Detected value of pressure sensor 57)−(Detected value of pressure sensor 56)   (4)
 
     Thus, the second medium can be made to appropriately circulate through the indoor units  34   a  to  34   c.    
     In the second cycle  6  to which cooling energy has been supplied from the first cycle  5  in the second heat exchanger  15 , the second medium has a low temperature, is circulated by the first pump  21 , and is allowed to flow into the branch paths  8   a  and  8   b  by the first flow-path-switching valves  31   a  and  31   b.  In the branch paths  8   a  and  8   b,  the flow rates of the second medium that is to flow therethrough are determined by the levels of resistances at the flow-rate-adjusting valves  32   a  and  32   b.  Subsequently, the second medium flows through the third extension pipes  33   a  and  33   b  into the indoor units  34   a  and  34   b.  In the indoor units  34   a  and  34   b,  the second medium supplies the cooling energy thereof to the load side by exchanging heat with the room air with the aid of the indoor-unit fans  35   a  and  35   b,  whereby the second medium comes to have a high temperature. Subsequently, the second medium flows through the fourth extension pipes  36   a  and  36   b  and the second flow-path-switching valves  37   a  and  37   b,  is combined into the first combining path  41 , and returns to the second heat exchanger  15 . 
     In the third cycle  7  to which cooling energy has been supplied from the first cycle  5  in the third heat exchanger  17 , the second medium has a low temperature, is circulated by the second pump  22 , and is allowed to flow into the branch path  8   c  by the first flow-path-switching valve  31   c.  In the branch path  8   c,  the flow rate of the second medium that is to flow therethrough is determined by the level of resistance at the flow-rate-adjusting valve  32   c.  Subsequently, the second medium flows through the third extension pipe  33   c  into the indoor unit  34   c.  In the indoor unit  34   c,  the second medium supplies the cooling energy thereof to the load side by exchanging heat with the room air with the aid of the indoor-unit fan  35   c,  whereby the second medium comes to have a high temperature. Subsequently, the second medium flows through the fourth extension pipe  36   c  and the second flow-path-switching valve  37   c,  and returns to the third heat exchanger  17 . 
     If there are any nonoperating indoor units  34 , the control apparatus  100  fully closes the flow-rate-adjusting valves  32  in the branch paths  8  having the nonoperating indoor units  34 , or switches the flow-path-switching valves  31  and  37  so as not to be connected to either of the second cycle  6  and the third cycle  7 . 
     Next, the operation of controlling the pump performed by the control apparatus  100  will be described in detail. If the required capacity of the air-conditioning apparatus has been determined, the required flow rate of the second medium is determined, and the flow rate of the pump is determined. However, unless the pump head is minimized, the pump input becomes larger than necessary, and the cooling/heating efficiency of the air-conditioning apparatus is reduced. Particularly, in building air conditioning, this is more pronounced in an air-conditioning apparatus having a small required capacity. To minimize the head, however, it is important in terms of minimizing the control operation to identify the flow-path resistances in a plurality of intricate branch paths (including the extension pipes  33  and  36  and the indoor units  34 ) provided in the case of building air conditioning or the like. 
       FIG. 7  is a flowchart illustrating the operational flow of the control apparatus  100  according to Embodiment 1. When the control apparatus  100  is first activated in Step S 101 , the control apparatus  100  fully opens all flow-rate-adjusting valves  32  in Step S 102 . Subsequently, the control apparatus  100  sets the rotation speed of the pump to the maximum in Step S 103  and activates the pump in Step S 104 . Subsequently, after a specific period of time, which is a short time, has elapsed in Step S 105 , the control apparatus  100  starts a branch-resistance-measuring operation in Step S 106 . First, the control apparatus  100  performs the branch-resistance-measuring operation for a first indoor unit  34 . That is, in Step S 107 , the control apparatus  100  opens the flow-path-switching valves  31  and  37  for the first indoor unit  34  and closes the flow-path-switching valves  31  and  37  for the other. indoor units  34  excluding those for the first indoor unit  34 , thereby allowing the second medium to flow only into the first indoor unit  34 . After a specific period of time has elapsed in Step S 108 , the control apparatus  100  acquires the detected values of the pressure sensors  54  to  57  in Step S 109  and calculates the flow-path resistance of a first branch path in Step S 110 . In this calculation, the current flow rate is identified from the correlation equation between the head and flow rate of the pump, which is known in advance from the design, and from the head, whereby the flow-path resistance of the first branch path is calculated. 
     Subsequently, the control apparatus  100  performs the same operation for a second first indoor-unit  34  in Step S 111  so as to calculate the flow-path resistance of a second branch path. 
     Furthermore, the control apparatus  100  repeats the same operation, including the operation for the last (n-th) indoor unit  34  in Step S 120  so as to calculate the flow-path resistance of an n-th branch path, whereby the required capacities of all indoor units  34  are calculated. Accordingly, the flow rate of the pump is determined from the required capacities of all indoor units  34 . 
     Note that while  FIG. 7  illustrates the case where the flow-path resistances of all branch paths are calculated by the first pump  21  alone, the calculation may be performed by dividing the group of branch paths between the first pump  21  and the second pump  22 . In that case, the identification time can be shortened. 
     Subsequently, in Step S 121 , the control apparatus  100  starts a regular control operation and the operation of the first cycle  5 . Subsequently, in Step S 122 , the control apparatus  100  judges whether or not a specific period of time has elapsed, and, if not, the control apparatus  100  controls the rotation speed of the pump in Step S 123  such that the target head is realized on the basis of Equation (3). If the specific period of time has elapsed in Step S 122 , the control apparatus  100  finds in Step S 124  the branch path (herein denoted by I) having the flow-rate-adjusting valve  32  whose opening-degree is the highest in the second cycle  6 . If the opening-degree of the branch path I is at or above the target maximum opening-degree in Step S 125 , the control apparatus  100  increases the target head in Step S 126  because the head of the pump is low. The increment may be a fixed value. If the opening-degree of the branch path I is at or below the target maximum opening-degree in Step S 125 , the control apparatus  100  reduces the target head in Step S 127  because the head of the pump is too high. The reduction method is as follows: 
       (New target head)=(Current target head)/(Calculated flow-path resistance of relevant branch path)×((Calculated flow-path resistance of relevant branch path)−((Flow-path resistance of flow-rate-adjusting valve at current opening-degree)−(Flow-path resistance of flow-rate-adjusting valve at target maximum opening-degree)))
 
     With such a configuration, no personnel for on-site adjustment are necessary, and minimization of the pump input is realized easily because the control apparatus  100  identifies the flow-path resistances and reflects the resistances in the control operation that is being performed. Furthermore, by reflecting this information in controlling the opening-degrees of the flow-rate-adjusting valves  32  on the basis of Equation (2), the controllability is further stabilized. 
     Note that while the above description concerns the first pump  21  in the second cycle  6 , the same applies to the first pump  22  in the third cycle  7 . Furthermore, while one pump is equipped with two pressure sensors on the upstream and downstream sides thereof, the head may be alternatively checked with the pressure sensor on the exit side of the pump because the pressure on the entrance side of the pump does not change substantially. Furthermore, if flow-rate sensors are provided instead of the pressure sensors, the head and the flow-path resistances are obtained from the characteristic between the head and the flow rate of the pump and the detected value of the flow-rate sensor, and the same effect is therefore provided. 
     Next, control of the flow-path-switching valves  31  performed by the control apparatus  100  will be further described. The indoor units  34  are all performing a cooling operation, and the first medium flows through the second heat exchanger  15  and thus comes to have a low pressure and two phases (a low pressure and a low degree of dryness), as described above. Subsequently, the first medium flows through the third heat exchanger  17  and thus becomes a low-pressure superheated gas having an (exit superheat). Since the heat transfer characteristic is superior in the two-phase state than in the superheated-gas state, the second heat exchanger  15  has higher heat exchangeability than the third heat exchanger  17 . Therefore, if an indoor unit  34  having a relatively large capacity is connected to the second cycle  6  (the second heat exchanger  15 ), the capacity is exerted without excess or loss. In a relevant branch path, the control apparatus  100  switches the first flow-path-switching valve  31  to open so as to be connected to the first branching path  40  and to closed so as not to be connected to the second branching path  42 , and switches the second flow-path-switching valve  37  to open so as to be connected to the first combining path  41  and to closed so as not to be connected to the second combining path  43 . 
     Furthermore, in an indoor unit  34  connected to a flow-rate-adjusting valve  32  whose opening-degree is high, the flow rate of the second medium is high, and a large capacity is therefore required. Accordingly, such an indoor unit  34  connected to a flow-rate-adjusting valve  32  whose opening-degree is high is preferably connected to the second cycle  6  (the second heat exchanger  15 ), and the relevant first flow-path-switching valve  31  and second flow-path-switching valve  37  are to be controlled as described above. 
     (2) Case of Cooling-Only Operation at Different Required Temperatures 
     A case of a cooling-only operation at different required temperatures will now be described with reference to  FIG. 2 . 
     In the air-conditioning apparatus  1 , the flow-path switcher  10  is connected on the solid-line side. The first medium compressed by the compressor  9  and thus having a high pressure and a high temperature flows through the flow-path switcher  10  into the first heat exchanger  11 , and dissipates heat into the outside air supplied by the fan  12 , whereby the first medium turns into high pressure and low temperature stage. The first medium flows through the first extension pipe  13 , and the pressure thereof is reduced by the first reducing valve  14 , whereby the first medium comes to have a low pressure and a low degree of dryness. The first medium further flows sequentially through the second heat exchanger  15 , the second reducing valve  16 , and the third heat exchanger  17 . In the second reducing valve  16 , the pressure of the first medium drops, and the reduced saturation temperatures at the pressures before and after the passage therethrough correspond to the required temperatures. This is because of the following reason. The opening-degree of the second reducing valve  16  and the degrees of drops in the pressure and temperature of the first medium correspond to each other at a ratio of 1 to 1. Hence, if the opening-degree of the second reducing valve is determined, the degrees of drops in the pressure and temperature of the first medium are automatically determined. Therefore, the control apparatus  100  controls the opening-degree of the second reducing valve  16  in accordance with the temperatures required by the indoor units  34 , whereby the temperature of the first medium can be adjusted. 
     Furthermore, in the second heat exchanger  15 , since heat is exchanged between the first cycle  5  and the second cycle  6 , the first medium supplies the cooling energy thereof to the second medium. In the third heat exchanger  17 , since heat is exchanged between the first cycle  5  and the third cycle  7 , the first medium supplies the cooling energy thereof to the second medium. Thus, the first medium evaporates and comes to have a low pressure and a high degree of dryness, or becomes a low-pressure superheated gas. Then, the first medium sequentially flows through the second extension pipe  18 , the flow-path switcher  10 , and the accumulator  19 , and returns to the compressor  9 . 
     Here, the control apparatus  100  operates as follows. The control apparatus  100  controls the rotation speed of the compressor  9  such that the pressure at the intake-side pressure sensor  51  becomes constant. 
     The control apparatus  100  also controls the rotation speed of the outdoor-unit fan  12  such that the pressure at the discharge-side pressure sensor  52  becomes constant. Thus, the processing capacity of the first heat exchanger  11  is appropriately controlled. 
     The control apparatus  100  also controls the opening-degree of the first reducing valve  14  such that the result of Equation (5) below becomes constant. 
       (Exit superheat) of third heat exchanger 17=(Detected value of temperature sensor 64)−(Reduced saturation temperature at intake-side pressure sensor 51)   (5)
 
     The control apparatus  100  also controls the opening-degree of the second reducing valve  16  such that the result of Equation (6) below becomes the required temperature difference. 
       (Temperature difference)=(Reduced saturation temperature at pressure sensor 53)−(Reduced saturation temperature at intake-side pressure sensor 51)   (6)
 
     Thus, an appropriate cooling capacity is realized in accordance with the number of operating indoor units  34 . 
     Meanwhile, since the second cycle  6  to which cooling energy has been supplied from the first cycle  5  in the second heat exchanger  15  exchanges heat in the second heat exchanger  15  with the first cycle  5  filled with the first medium that is yet to flow through the reducing valve  14  and has a relatively high pressure, the evaporating temperature of the second medium in the second cycle  6  is higher than in the third cycle  7 , and the blowoff temperatures of corresponding ones of the indoor units  34  are high. 
     Furthermore, since the third cycle  7  to which cooling energy has been supplied from the first cycle  5  in the third heat exchanger  17  exchanges heat in the third heat exchanger  17  with the first cycle  5  filled with the first medium that has flowed through the reducing valve  14  and has a relatively low pressure, the evaporating temperature of the second medium in the third cycle  7  is lower than in the second cycle  6 , and the blowoff temperatures of corresponding ones of the indoor units  34  are low. 
     This is because of the following reason. In the cooling operation, since the second heat exchanger  15  in the first cycle  5  is connected on the upstream side with respect to the second reducing valve  16 , the first medium flowing through the second heat exchanger  15  has a temperature obtained before the pressure reduction by the second reducing valve  16 . In contrast, since the third heat exchanger  17  in the first cycle  5  is connected on the downstream side with respect to the second reducing valve  16 , the first medium flowing through the third heat exchanger  17  has a temperature that has dropped after the pressure reduction by the second reducing valve  16 . Therefore, the temperature of the first medium in the second heat exchanger  15  is higher than the temperature of the first medium in the third heat exchanger  17 . Accordingly, the second medium in the second cycle  6  that has exchanged heat with the first medium in the second heat exchanger  15  has a higher temperature than the second medium in the third cycle  7  that has exchanged heat with the first medium having a lower temperature in the third heat exchanger  17 . This is the reason. 
     Note that if there are any nonoperating indoor units  34 , the control apparatus  100  fully closes the flow-rate-adjusting valves  32  in the branch paths having the nonoperating indoor units  34 , or switches the flow-path-switching valves  31  and  37  so as not to be connected to either of the second cycle  6  and the third cycle  7 . 
     Here, the control apparatus  100  operates as follows. The control apparatus  100  controls the opening-degrees of the flow-rate-adjusting valves,  32   a  to  32   c  such that the result of Equation (7) below becomes constant. 
       (Temperature difference between entrance and exit)=(Detected value of temperature sensor 67)−(Detected value of temperature sensor 68)   (7)
 
     The control apparatus  100  also controls the rotation speed of the first pump  21  such that the result of Equation (8) below becomes constant. 
       (First pressure difference)=(Detected value of pressure sensor 55)−(Detected value of pressure sensor 54)   (8)
 
     The control apparatus  100  also controls the rotation speed of the second pump  22  such that the result of Equation (9) below becomes constant. 
       (Second pressure difference)=(Detected value of pressure sensor 57)−(Detected value of pressure sensor 56)   (9)
 
     Thus, the second medium can be made to appropriately circulate through the indoor units  34 . 
     As described above, since cooling energy can be supplied at two different temperatures through the second heat exchanger  15  and the third heat exchanger  17  that are connected in series, the air-conditioning apparatus  1  operates with an increased efficiency without any excessive compressing operation. Furthermore, since cooling energy is supplied at the two different temperatures with one heat source, interior air conditioning and perimeter air conditioning in building air conditioning or the like are realized simultaneously. 
       FIG. 3  is a circuit diagram illustrating an operation of the air-conditioning apparatus according to Embodiment 1 of the present invention, in which the circuit illustrated by bold lines represents a circuit through which the second refrigerant flows, and the circuit illustrated by thin lines represents a line through which the second refrigerant does not flow (a non-connected line). 
     (3) Case of Cooling-Main Cooling/Heating Operation 
     Now, a “cooling-main operation” in which cooling and heating are performed simultaneously and the cooling capacity is larger than the heating capacity will be described with reference to  FIG. 3 . 
     In the air-conditioning apparatus  1 , the flow-path switcher  10  is connected on the solid-line side. The first medium compressed by the compressor  9  and thus having a high pressure and a high temperature flows through the flow-path switcher  10  into the first heat exchanger  11 , and dissipates the heat thereof into the outside air supplied by the fan  12 , whereby the first medium, if the pressure thereof is at or above the critical value, comes to have a high pressure and a medium temperature. The first medium further flows sequentially through the first extension pipe  13 , the first reducing valve  14 , and the second heat exchanger  15 . The first reducing valve  14  is fully open, and the pressure loss is small. Furthermore, in the second heat exchanger  15 , since heat is exchanged between the first cycle  5  and the second cycle  6 , the first medium supplies the heating energy thereof to the second medium, thereby having a high pressure and a low temperature. Subsequently, the pressure of the first medium is reduced by the second reducing valve  16 , and the first medium comes to have a low pressure and a low degree of dryness. Subsequently, when the first medium flows through the third heat exchanger  17 , since heat is exchanged between the first, cycle and the third cycle, the first medium supplies the cooling energy thereof to the second medium, whereby the first medium evaporates and comes to have a low pressure and a high degree of dryness, or becomes a low-pressure superheated gas. Then, the first medium sequentially flows through the second extension pipe  18 , the flow-path switcher  10 , and the accumulator  19 , and returns to the compressor  9 . 
     Here, the control apparatus  100  operates as follows. The control apparatus  100  controls the rotation speed of the compressor  9  such that the pressure at the intake-side pressure sensor  51  becomes constant, and also controls the rotation speed of the outdoor-unit fan  12  such that the pressure at the discharge-side pressure sensor  52  becomes constant, whereby the processing capacity of the first heat exchanger  11  is controlled. 
     The control apparatus  100  also makes the opening-degree of the first reducing valve  14  fully open. 
     The control apparatus  100  also controls the opening-degree of the second reducing valve  16  such that the result of Equation (10) below becomes constant. 
       (Exit superheat) of third heat exchanger 17=(Detected value of temperature sensor 64)−(Reduced saturation temperature at intake-side pressure sensor 51)   (10)
 
     Thus, appropriate cooling and heating capacities are realized in accordance with the number of operating indoor units  34 . 
     In the second cycle  6  to which heating energy has been supplied from the first cycle  5  in the second heat exchanger  15 , the second medium has a relatively high temperature, is circulated by the first pump  21 , and is allowed to flow into the branch path  8   a  by the first flow-path-switching valve  31   a.  In the branch path  8   a,  the flow rate of the second medium that is to flow therethrough is determined by the level of resistance at the flow-rate-adjusting valve  32   a.  Subsequently, the second medium flows through the third extension pipe  33   a  into the indoor unit  34   a.  In the indoor unit  34   a,  the second medium supplies the heating energy thereof to the load side by exchanging heat with the room air with the aid of the indoor-unit fan  35   a,  whereby the second medium comes to have a low temperature. Subsequently, the second medium flows through the fourth extension pipe  36   a,  the second flow-path-switching valve  37   a,  and the first combining path  41 , and returns to the second heat exchanger  15 . 
     In the third cycle  7  to which cooling energy has been supplied from the first cycle  5  in the third heat exchanger  17 , the second medium has a relatively low temperature, is circulated by the second pump  22 , and is allowed to flow into the branch paths  8   b  and  8   c  by the first flow-path-switching valves  31   b  and  31   c.  In the branch paths  8   b  and  8   c,  the flow rates of the second medium that is to flow therethrough are determined by the levels of resistances at the flow-rate-adjusting valves  32   b  and  32   c.  Subsequently, the second medium flows through the third extension pipes  33   b  and  33   c  into the indoor units  34   b  and  34   c.  In the indoor units  34   b  and  34   c,  the second medium supplies the cooling energy thereof to the load side by exchanging heat with the room air with the aid of the indoor-unit fans  35   b  and  35   c,  whereby the second medium comes to have a high temperature. Subsequently, the second medium flows through the fourth extension pipes  36   b  and  36   c  and the second flow-path-switching valves  37   b  and  37   c,  is combined into the second combining path  43 , and returns to the third heat exchanger  17 . 
     As described above, since relatively mild heating energy and relatively strong cooling energy can be supplied from the second heat exchanger  15  and the third heat exchanger  17 , respectively, that are connected in series, an efficient cooling/heating operation is realized by connecting some operating indoor units  34  in a relatively small number or having relatively small heating capacities to the second heat exchanger  15  and connecting the other operating indoor units  34  in a relatively large number or having relatively large cooling capacities to the third heat exchanger  17 . 
     (4) Case of Heating-Only Operation 
     A case of a heating-only operation will now be described with reference to  FIG. 2 . 
     In the air-conditioning apparatus  1 , the flow-path switcher  10  is connected on the broken-line side. The first medium compressed by the compressor  9  and thus having a high pressure and a high temperature flows through the flow-path switcher  10 , the second extension pipe  18 , the third heat exchanger  17 , the second reducing valve  16 , and the second heat exchanger  15 . The second reducing valve  16  is fully open, and the loss is small. Furthermore, in the third heat exchanger  17 , since heat is exchanged between the first cycle  5  and the third cycle  7 , the first medium supplies the heating energy to the second medium. In the second heat exchanger  15 , since heat is exchanged with the second cycle  6 , the first medium supplies the heating energy to the second medium. Thus, the first medium comes to have a high pressure and a low temperature. By flowing through the first reducing valve  14 , the first medium comes to have a low pressure and a low degree of dryness. The first medium flows through the first extension pipe  13  into the first heat exchanger  11 , and absorbs heat from the outside air supplied by the fan  12 , whereby the first medium comes to have a low pressure and a high degree of dryness. Subsequently, the first medium flows through the flow-path switcher  10  and the accumulator  19 , and returns to the compressor  9 . In general, in indoor units  34  intended for buildings, the amount of refrigerant is easier to become excessive in the heating operation than in the cooling operation depending on the sizes of the heat exchangers and the arrangement of the extension pipes and the reducing valves. Therefore, by storing this in the accumulator  19 , the liquid refrigerant is prevented from being taken into the compressor  9 , and the reliability is thus provided. 
     Here, the control apparatus  100  operates as follows. The control apparatus  100  controls the rotation speed of the compressor  9  such that the pressure at the discharge-side pressure sensor  52  becomes constant, and also controls the rotation speed of the outdoor-unit fan  12  such that the pressure at the intake-side pressure sensor  51  becomes constant, whereby the processing capacity of the first heat exchanger  11  is appropriately controlled. 
     The control apparatus  100  also makes the opening-degree of the second reducing valve  16  fully open. 
     The control apparatus  100  also controls the opening-degree of the first reducing valve  14  such that the result of Equation (11) below becomes constant. 
     (If the detected value of the pressure sensor  51  is at or above the critical pressure of the first medium) 
       (Exit temperature) of third heat exchanger 17=(Detected value of temperature sensor 61) 
     (If the detected value of the pressure sensor  51  is below the critical pressure of the first medium) 
       (Exit subcooling) of third heat exchanger 17=(Reduced saturation temperature at discharge-side pressure sensor 52)−(Detected value of temperature sensor 61)   (11)
 
     Thus, an appropriate heating capacity is realized in accordance with the number of operating indoor units  34 . 
     In the third cycle  7  to which heating energy has been supplied from the first cycle  5  in the third heat exchanger  17 , the second medium has a high temperature, is circulated by the second pump  22 , and is allowed to flow into the branch path  8   c  by the first flow-path-switching valve  31   c.  In the branch path  8   c,  the flow rate of the second medium that is to flow therethrough is determined by the level of resistance at the flow-rate-adjusting valve  32   c.  Subsequently, the second medium flows through the third extension pipe  33   c  into the indoor unit  34   c.  In the indoor unit  34   c,  the second medium supplies the heating energy thereof to the load side by exchanging heat with the room air with the aid of the indoor-unit fan  35   c,  whereby the second medium comes to have a low temperature. Subsequently, the second medium flows through the fourth extension pipe  36   c  and the second flow-path-switching valve  37   c,  and returns to the third heat exchanger  17 . 
     In the second cycle  6  to which heating energy has been supplied from the first cycle  5  in the second heat exchanger  15 , the second medium has a high temperature, is circulated by the first pump  21 , and is allowed to flow into the branch paths  8   a  and  8   b  by the first flow-path-switching valves  31   a  and  31   b.  In the branch paths  8   a  and  8   b,  the flow rates of the second medium that is to flow therethrough are determined by the levels of resistances at the flow-rate-adjusting valves  32   a  and  32   b.  Subsequently, the second medium flows through the third extension pipes  33   a  and  33   b  into the indoor units  34   a  and  34   b.  In the indoor units  34   a  and  34   b,  the second medium supplies the heating energy thereof to the load side by exchanging heat with the room air with the aid of the indoor-unit fans  35   a  and  35   b,  whereby the second medium comes to have a low temperature. Subsequently, the second medium flows through the fourth extension pipes  36   a  and  36   b  and the second flow-path-switching valves  37   a  and  37   b,  is combined into the first combining path  41 , and returns to the second heat exchanger  15 . 
     If there are any nonoperating indoor units  34 , the control apparatus  100  fully closes the flow-rate-adjusting valves  32  in the branch paths  8  having the nonoperating indoor units  34 , or switches the flow-path-switching valves  31  and  37  so as not to be connected to either of the second cycle  6  and the third cycle  7 . 
     Here, the control apparatus  100  operates as follows. The control apparatus  100  controls the opening-degrees of the flow-rate-adjusting valves  32   a  to  32   c  such that the result of Equation (12) below becomes constant. 
       (Temperature difference between entrance and exit)=(Detected value of temperature sensor 67)−(Detected value of temperature sensor 68)   (12)
 
     The control apparatus  100  also controls the rotation speed of the first pump  21  such that the result of Equation (13) below becomes constant. 
       (First pressure difference)=(Detected value of pressure sensor 55)−(Detected value of pressure sensor 54)   (13)
 
     The control apparatus  100  also controls the rotation speed of the second pump  22  such that the result of Equation (14) below becomes constant. 
       (Second pressure difference)=(Detected value of pressure sensor 57)−(Detected value of pressure sensor 56)   (14)
 
     Thus, the second medium can be made to appropriately circulate through the indoor units  34 . 
     (5) Case of Heating-Only Operation at Different Required Temperatures 
     A case of a heating-only operation at different required temperatures will now be described with reference to  FIG. 3 . 
     In the air-conditioning apparatus  1 , the flow-path switcher  10  is connected on the broken-line side. The first medium compressed by the compressor  9  and thus having a high pressure and a high temperature sequentially flows through the flow-path switcher  10 , the second extension pipe  18 , the third heat exchanger  17 , the second reducing valve  16 , and the second heat exchanger  15 . In the second reducing valve  16 , the pressure drops, and the reduced saturation temperatures at the pressures before and after the passage therethrough correspond to the required temperatures. Furthermore, in the third heat exchanger  17 , since heat is exchanged between the first cycle  5  and the third cycle  7 , the first medium supplies the heating energy thereof to the second medium. In the second heat exchanger  15 , since heat is exchanged between the first cycle  5  and the second cycle  6 , the first medium supplies the heating energy thereof to the second medium. Thus, the first medium comes to have a high pressure and a low temperature. The first medium further flows through the first reducing valve  14 , thereby having a low pressure and a low degree of dryness. The first medium flows through the first extension pipe  13  into the first heat exchanger  11 , and absorbs heat from the outside air supplied by the fan  12  in the first heat exchanger  11 , whereby the first medium comes to have a low pressure and a high degree of dryness. Subsequently, the first medium flows through the flow-path switcher  10  and the accumulator  19 , and returns to the compressor  9 . In general, in indoor units  34  intended for buildings, the amount of refrigerant is easier to become excessive in the heating operation than in the cooling operation depending on the sizes of the heat exchangers and the arrangement of the extension pipes and the reducing valves. Therefore, by storing this in the accumulator  19 , the liquid refrigerant is prevented from being taken into the compressor, and the reliability is thus provided. 
     Here, the control apparatus  100  operates as follows. The control apparatus  100  controls the rotation speed of the compressor  9  such that the pressure at the discharge-side pressure sensor  52  becomes constant. 
     The control apparatus  100  also controls the rotation speed of the outdoor-unit fan  12  such that the pressure at the intake-side pressure sensor  51  becomes constant. Thus, the processing capacity of the first heat exchanger  11  is controlled. 
     The control apparatus  100  also controls the opening-degree of the second reducing valve  16  such that the result of Equation (15) below becomes the required temperature difference. 
     (If the detected value of the pressure sensor  51  is at or above the critical pressure of the first medium) 
       (Pressure difference)=(Detected value of discharge-side pressure sensor 52)−(Detected value of pressure sensor 53)
 
     (If the detected value of the pressure sensor  51  is below the critical pressure of the first medium) 
       (Temperature difference)=(Reduced saturation temperature at discharge-side pressure sensor 52)−(Reduced saturation temperature at pressure sensor 53) tm (15)
 
     The control apparatus  100  also controls the opening-degree of the first reducing valve  14  such that the result of Equation (16) below becomes constant. 
     (If the detected value of the pressure sensor  51  is at or above the critical pressure of the first medium) 
       (Exit temperature) of third heat exchanger 17=(Detected value of temperature sensor 61) 
     (If the detected value of the pressure sensor  51  is below the critical pressure of the first medium) 
       (Exit subcooling) of third heat exchanger 17=(Reduced saturation temperature at discharge-side pressure sensor 52)−(Detected value of temperature sensor 61)   (16)
 
     Thus, an appropriate heating capacity is realized in accordance with the number of operating indoor units  34 . 
     Meanwhile, since the third cycle  7  to which heating energy has been supplied from the first cycle  5  in the third heat exchanger  17  exchanges heat in the third heat exchanger  17  with the first cycle  5  filled with the first medium that is yet to flow through the reducing valve  14  and has a relatively high pressure, the evaporating temperature of the second medium in the third cycle  7  is higher than in the second cycle  6 , and the blowoff temperatures of corresponding ones of the indoor units  34  are high. 
     Furthermore, since the second cycle  6  to which heating energy has been supplied from the first cycle  5  in the second heat exchanger  15  exchanges heat in the second heat exchanger  15  with the first cycle  5  filled with the first medium that has flowed through the reducing valve  14  and has a relatively low pressure, the evaporating temperature of the second medium in the second cycle  6  is lower than in the third cycle  7 , and the blowoff temperatures of corresponding ones of the indoor units  34  are low. 
     This is because of the following reason. In the heating operation, since the third heat exchanger  17  in the first cycle  5  is connected on the upstream side with respect to the second reducing valve  16 , the first medium flowing through the third heat exchanger  17  has a temperature obtained before the pressure reduction by the second reducing valve  16 . In contrast, since the second heat exchanger  15  in the first cycle  5  is connected on the downstream side with respect to the second reducing valve  16 , the first medium flowing through the second heat exchanger  15  has a temperature that has dropped after the pressure reduction by the second reducing valve  16 . Therefore, the temperature of the first medium in the third heat exchanger  17  is higher than the temperature of the first medium in the second heat exchanger  15 . Accordingly, the temperature of the second medium in the third cycle  7  that has exchanged heat with the first medium in the third heat exchanger  17  is higher than the temperature of the second medium in the second cycle  6  that has exchanged heat with the first medium having a lower temperature in the second heat exchanger  15 . This is the reason. 
     Note that if there are any nonoperating indoor units  34 , the control apparatus  100  fully closes the flow-rate-adjusting valves  32  in the branch paths having the nonoperating indoor units  34 , or switches the flow-path-switching valves  31  and  37  so as not to be connected to either of the second cycle  6  and the third cycle  7 . 
     Here, the control apparatus  100  operates as follows. The control apparatus  100  controls the opening-degrees of the flow-rate-adjusting valves  32   a  to  32   c  such that the result of Equation (17) below becomes constant. 
       (Temperature difference between entrance and exit)=(Detected value of temperature sensor 67)−(Detected value of temperature sensor 68)   (17)
 
     The control apparatus  100  also controls the rotation speed of the first pump  21  such that the result of Equation (18) below becomes constant. 
       (First pressure difference)=(Detected value of pressure sensor 55)−(Detected value of pressure sensor 54)   (18)
 
     The control apparatus  100  also controls the rotation speed of the second pump  22  such that the result of Equation (19) below becomes constant. 
       (Second pressure difference)=(Detected value of pressure sensor 57)−(Detected value of pressure sensor 56)   (19)
 
     Thus, the second medium can be made to appropriately circulate through the indoor units  34 . 
     As described above, since heating energy can be supplied at two different temperatures through the second heat exchanger  15  and the third heat exchanger  17  that are connected in series, the air-conditioning apparatus operates with an increased efficiency without any excessive compressing operation. Furthermore, since heating energy is supplied at two different temperatures with one heat source, interior air conditioning and perimeter air conditioning in building air conditioning or the like are realized simultaneously. 
     (6) Case of Heating-Main Cooling/Heating Operation 
     Now, a “heating-main operation” in which cooling and heating are performed simultaneously and the heating capacity is larger than the cooling capacity will be described with reference to  FIG. 3 . 
     In the air-conditioning apparatus  1 , the flow-path switcher  10  is connected on the broken-line side. The first medium compressed by the compressor  9  and thus having a high pressure and a high temperature flows through the flow-path switcher  10 , the second extension pipe  18 , and the third heat exchanger  17 . When the first medium flows through the third heat exchanger  17 , heat is exchanged between the first cycle  5  and the third cycle  7 , whereby the first medium supplies the heating energy thereof to the second medium and comes to have a high pressure and a low temperature. Subsequently, the pressure of the first medium is reduced by the second reducing valve  16 , whereby the first medium comes to have a low pressure and a low degree of dryness. Subsequently, when the first medium flows through the second heat exchanger  15 , heat is exchanged between the first cycle  5  and the second cycle  6 , whereby the first medium supplies the cooling energy thereof to the second medium and comes to have a low pressure and two phases. Subsequently, although the first medium flows through the first reducing valve  14 , since the first reducing valve  14  is fully open, the pressure loss is small. Subsequently, the first medium flows through the first extension pipe  13  into the first heat exchanger  11 . Here, the first medium absorbs heat from the outside air supplied by the fan  12 . Thus, the first medium comes to have a low pressure and a high degree of dryness. The first medium subsequently flows through the flow-path switcher  10  and the accumulator  19 , and returns to the compressor  9 . In general, in indoor units  34  intended for buildings, the amount of refrigerant is easier to become excessive in the heating operation than in the cooling operation depending on the sizes of the heat exchangers and the arrangement of the extension pipes and the reducing valves. Therefore, by storing this in the accumulator  19 , the liquid refrigerant is prevented from being taken into the compressor  9 , and the reliability is thus provided. 
     Here, the control apparatus  100  operates as follows. The control apparatus  100  controls the rotation speed of the compressor  9  such that the pressure at the discharge-side pressure sensor  52  becomes constant, and also controls the rotation speed of the outdoor-unit fan  12  such that the pressure at the intake-side pressure sensor  51  becomes constant, whereby the processing capacity of the first heat exchanger  11  is controlled. 
     The control apparatus  100  also controls the opening-degree of the second reducing valve  16  such that the result of Equation (20) below becomes constant. 
     (If the detected value of the pressure sensor  51  is at or above the critical pressure of the first medium) 
       (Exit temperature) of third heat exchanger 17=(Detected value of temperature sensor 63) 
     (If the detected value of the pressure sensor  51  is below the critical pressure of the first medium) 
       (Exit subcooling) of third heat exchanger 17=(Reduced saturation temperature at discharge-side pressure sensor 52)−(Detected value of temperature sensor 63)   (20)
 
     The control apparatus  100  also makes the opening-degree of the first reducing valve  14  fully open. 
     Thus, appropriate cooling and heating capacities are realized in accordance with the number of operating indoor units  34 . 
     In the third cycle  7  to which heating energy has been supplied from the first cycle  5  in the third heat exchanger  17 , the second medium turns into relatively high temperature state, is circulated by the second pump  22 , and flows into the branch paths  8   b  and  8   c  by the first flow-path-switching valves  31   b  and  31   c.  In the branch paths  8   b  and  8   c,  the flow rates of the second medium that is to flow therethrough are determined by the levels of resistances at the flow-rate-adjusting valves  32   b  and  32   c.  Subsequently, the second medium flows through the third extension pipes  33   b  and  33   c  into the indoor units  34   b  and  34   c.  In the indoor units  34   b  and  34   c,  the second medium supplies the heating energy thereof to the load side by exchanging heat with the room air with the aid of the indoor-unit fans  35   b  and  35   c,  whereby the second medium comes to have a low temperature. Subsequently, the second medium flows through the fourth extension pipes  36   b  and  36   c  and the second flow-path-switching valves  37   b  and  37   c,  is combined into the second combining path  43 , and returns to the third heat exchanger  17 . 
     In the second cycle  6  to which cooling energy has been supplied from the first cycle  5  in the second heat exchanger  15 , the second medium has a relatively low temperature, is circulated by the first pump  21 , and is allowed to flow into the branch path  8   a  by the first flow-path-switching valve  31   a.  In the branch path  8   a,  the flow rate of the second medium that is to flow therethrough is determined by the level of resistance at the flow-rate-adjusting valve  32   a.  Subsequently, the second medium flows through the third extension pipe  33   a  into the indoor unit  34   a.  In the indoor unit  34   a,  the second medium supplies the cooling energy thereof to the load side by exchanging heat with the room air with the aid of the indoor-unit fan  35   a,  whereby the second medium comes to have a high temperature. Subsequently, the second medium flows through the fourth extension pipe  36   a,  the second flow-path-switching valve  37   a,  and the first combining path  41 , and returns to the second heat exchanger  15 . 
     Here, the control apparatus  100  operates as follows. The control apparatus  100  controls the opening-degree of the flow-rate-adjusting valves  32   a  to  32   c  such that the result of Equation (21) below becomes constant. 
       (Temperature difference between entrance and exit)=(Detected value of temperature sensor 67)−(Detected value of temperature sensor 68)   (21)
 
     The control apparatus  100  also controls the rotation speed of the first pump  21  such that the result of Equation (22) below becomes constant. 
       (First pressure difference)=(Detected value of pressure sensor 55)−(Detected value of pressure sensor 54)   (22)
 
     The control apparatus  100  also controls the rotation speed of the second pump  22  such that the result of Equation (23) below becomes constant. 
       (Second pressure difference)=(Detected value of pressure sensor 57)−(Detected value of pressure sensor 56)   (23)
 
     Thus, the second medium can be made to appropriately circulate through the indoor units  34 . 
     By the above operations, the cooling-only operation, the heating-only operation, and the mixed cooling/heating operation are realized efficiently. 
     Note that while the opening-degree of each of the first reducing valve  14  and the second reducing valve  16  can be adjusted, the pressure loss drop in the case where the reducing valve is fully open may be reduced by providing an on-off valve in parallel with the reducing valve, and opening the on-off valve when the reducing valve is fully open and closing the on-off valve when the reducing valve is not fully open. Furthermore, the second heat exchanger  15  and the third heat exchanger  17  may be any of a plate heat exchanger, a double-pipe heat exchanger, and a microchannel heat exchanger. However, if the direction of flow is limited as in the plate heat exchanger, a switching valve or the like may be provided. 
     Furthermore, a bridge circuit such as the one illustrated in  FIG. 4  may be provided in either of the outdoor unit and the relay unit. Thus, even if the direction of the flow-path switcher  10  is reversed during an operation, a refrigerant sound and the like can be suppressed, and the stability in controlling the first medium is maintained. That is, in the circuit illustrated in  FIG. 1 , the direction of flow of the first medium in the first cycle is reversed when the flow-path switcher  10  is switched; whereas, in  FIG. 4 , the direction of flow of the first medium in the first extension pipe  13 , the first cycle in the relay unit  3 , and the second extension pipe  18  is constant. Furthermore, the direction of flow of the second medium does not change in the second cycle and the third cycle. Although a refrigerant sound is generated when the direction of flow of the first medium is reversed, such a refrigerant sound is not generated in and near the room spaces illustrated in  FIG. 6  because the direction of flow does not change near the room spaces (the refrigerant sound is generated in the heat source unit, naturally). 
     Furthermore, other than controlling the processing capacity of the first heat exchanger  11  by changing the rotation speed of the fan  12 , separate first heat exchangers  11   a  to  11   d  may be provided in parallel as illustrated in  FIG. 5 , whereby the processing capacity may be changed on the basis of the number of heat exchangers. This is effective in a case where only one fan  12  is provided and in a case where the rotation speed cannot be reduced as a matter of reliability of the fan motor. 
     Here, reference numerals  70   a  to  70   d  and  71   a  to  71   d  denote switching valves, which enable the heat exchanger  11  to be used partially by being opened/closed in accordance with the combinations summarized in Table 1. Thus, the heat transfer area can be reduced, and the processing capacity of the heat exchanger can be changed. 
     Exemplary situations where the rotation speed of the fan motor cannot be reduced include a case where the fan motor is also responsible for the cooling of the control apparatus  100 . Furthermore, in a case where the outside air is cool, heat needs to be exchanged even if the fan motor is stopped, because there is a temperature difference. In such a case, it is effective to adjust the heat transfer area as summarized in Table 1. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                 Heat 
                   
                   
               
               
                 Processing 
                 transfer 
                 Switching valve 
                 Heat exchanger 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 capacity 
                 area 
                 70a/71a 
                 70b/71b 
                 70c/71c 
                 70d/71d 
                 11a 
                 11b 
                 11c 
                 11d 
               
               
                   
               
               
                 Large 
                 Large 
                 Open 
                 Open 
                 Open 
                 Open 
                 Used 
                 Used 
                 Used 
                 Used 
               
               
                 ↓ 
                 ↓ 
                 Closed 
                 Open 
                 Open 
                 Open 
                 Not 
                 Used 
                 Used 
                 Used 
               
               
                 Small 
                 Small 
                   
                   
                   
                   
                 used 
                   
                   
                   
               
               
                   
                   
                 Closed 
                 Closed 
                 Open 
                 Open 
                 Not 
                 Not 
                 Used 
                 Used 
               
               
                   
                   
                   
                   
                   
                   
                 used 
                 used 
                   
                   
               
               
                   
                   
                 Closed 
                 Closed 
                 Closed 
                 Open 
                 Not 
                 Not 
                 Not 
                 Used 
               
               
                   
                   
                   
                   
                   
                   
                 used 
                 used 
                 used 
               
               
                   
               
            
           
         
       
     
     Because of the above configuration, the path of the first cycle is simple in any kinds of operations. In a so-called direct-expansion air-conditioning apparatus in which a heat source unit  2  and load-side units  4  are provided in one cycle, the circuit is intricate because of a plurality of indoor units  34 , and the operation of controlling the first cycle is intricate because the operation is started and stopped repeatedly. Furthermore, the refrigerating machine oil, which is important in terms of the reliability of the compressor provided in the cycle, may be unevenly distributed or be accumulated in the cycle because such oil cannot be captured completely even with a high-performance oil separator. In contrast, in the present embodiment, since the first cycle has a simple path, the probability of occurrence of such uneven distribution or accumulation of the refrigerating machine oil is low, and sufficient reliability is provided. This is particularly effective in a case where the refrigerating machine oil is incompatible with the medium. Pumps to be used in the second cycle and the third cycle inherently have no possibility of discharging oil to the outside and are therefore highly reliable. 
     Furthermore, since the flow-rate-adjusting valves  32  are provided in the relay unit, even if any flow-rate-adjusting valves  32  fail, it is only necessary to perform a general recovery work (replacement or the like) for the relay unit alone. That is, since there is no need to do the recovery work for each of all the indoor units  34 , the work is less cumbersome. 
     With the above configuration, since the second heat exchanger  15  has a larger heat-exchanging capacity than the third heat exchanger  17  in the cooling-only operation or the cooling-main cooling/heating operation, by connecting indoor units  34  having relatively large cooling capacities to the second heat exchanger  15  and indoor units  34  having relatively small cooling capacities to the third heat exchanger  17 , a highly efficient air-conditioning apparatus with a simple configuration can be provided. 
     Furthermore, since the second heat exchanger  15  has a larger heat-exchanging capacity than the third heat exchanger  17 , by connecting the indoor units  34  connected to flow-rate-adjusting valves whose opening-degrees are almost fully open to one of the second cycle and the third cycle that has a heat exchanger in which the first medium has a relatively high pressure, a highly efficient air-conditioning apparatus with a simple configuration can be provided. 
     Furthermore, if the indoor units  34  are all performing a cooling-only operation or heating-only operation and are not of the rated loads, the control apparatus  100  may operate such that one of the second cycle and the third cycle that has the smaller input is used, regardless of whether the air-conditioning apparatus is operated with only one cycle or with two cycles. 
     Furthermore, the flow-rate characteristics of the respective branches may be identified by the control apparatus  100  during a test operation, so that the characteristics can be reflected in the normal operation. Thus, the operation of controlling the switching can be performed more efficiently. 
     Furthermore, while the first medium is carbon dioxide, the first medium may be a flammable refrigerant, a low GWP (global warming potential) refrigerant, or a fluorocarbon refrigerant. 
     Note that the control apparatus  100  (rotation-speed-controlling means) sets the difference between the entrance-side pressure and the exit-side pressure of the first pump  21  or the second pump  22  in the second cycle  6  or the third cycle  7  to the target value, which is such a value that the opening-degree of one of the plurality of flow-rate-adjusting valves  32  provided in the second cycle  6  or the third cycle  7  and having the highest valve-opening-degree becomes the maximum. That is, by minimizing the flow rate from the first pump  21  or the second pump  22  and maximizing the opening-degree of the flow-rate-adjusting valve  32  whose valve-opening-degree is the highest, an efficient operation is realized. 
     Note that the exit-side pressure of the first pump  21  or the second pump  22  in the second cycle  6  or the third cycle  7  may be set to the target value. 
     Embodiment 2 
     Next, an operation according to Embodiment 2 will be described. 
       FIG. 8  is a circuit diagram illustrating an operation of an air-conditioning apparatus according to Embodiment 2 of the present invention. Note that descriptions of elements identical with those in Embodiment 1 are omitted. The configuration is the same as that illustrated in  FIGS. 1 to 3 , except that the temperature sensors  67   a  to  c  and  68   a  to  c  provided for the load-side units  4  are substituted by temperature sensors  67   d  to  f  and  68   d  to  f  provided in the relay unit so that the temperatures of Medium 2 at those positions are measured, and that no pressure sensors are provided in the second cycle  6  and the third cycle  7 . 
     Next, an operation of controlling the pump performed by the control apparatus  100  will be described in detail. 
       FIG. 9  is a flowchart illustrating the operational flow of the control apparatus  100  according to Embodiment 2 . When the control apparatus  100  is first activated in Step S 201 , the control apparatus  100  fully opens all flow-rate-adjusting valves  32  in Step S 202 . Subsequently, the control apparatus  100  sets the rotation speed of the pump to the maximum in Step S 203  and activates the pump in Step S 204 . Subsequently, after a specific period of time, which is a short time, has elapsed in Step S 205 , the control apparatus  100  starts a branch-resistance-measuring operation in Step S 206 . First, the control apparatus  100  performs the branch-resistance-measuring operation for a first indoor unit  34 . That is, in Step S 207 , the control apparatus  100  opens the flow-path-switching valves  31  and  37  for the first indoor unit and closes the flow-path-switching valves  31  and  37  for the other indoor units  34  than the first indoor unit  34 , thereby allowing the second medium to flow only into the first indoor unit  34 . After a specific period of time has elapsed in Step S 208 , the control apparatus  100  acquires the detected value of the temperature sensor  68  in Step S 209  and lets the detected value be T1o. 
     Subsequently, in Step S 210 , the control apparatus  100  lowers the opening-degree of the flow-rate-adjusting valve  32  of the first indoor unit  34  from fully open to 50%. Note that the value 50% is not a fixed value but only needs to be such a value as to significantly change the resistance of the flow-rate-adjusting valve  32 . Subsequently, in Step S 211 , the control apparatus  100  starts time measurement. Subsequently, the control apparatus  100  acquires the detected value of the temperature sensor  68  and lets the detected value be T 1  in Step S 212 , and compares the absolute value of (T 1 −T 1   o ) and a set value in Step S 213 . If the result of the comparison shows that the absolute value of (T 1 −T 1   o ) is below the set value, the operation returns to Step S 212 . If the absolute value of (T 1 −T 1   o ) is above the set value, the operation proceeds to Step S 214 , in which the time measurement is ended. Subsequently, the flow-path resistance of the first branch path is calculated in Step S 215 . In this calculation, the flow rate of the first branch path is estimated on the basis of the correlation equation between the head and flow rate of the pump, which is known in advance from the design, and the time period from when the opening-degree of the flow-rate-adjusting valve  32  is lowered until when the detected value of the temperature sensor  68  changes. From the estimated flow rate, the flow-path resistance can be calculated. 
     Subsequently, in Step S 216 , the control apparatus  100  performs the same operation for a second indoor unit  34  so as to calculate the flow-path resistance of a second branch path. 
     Furthermore, the control apparatus  100  repeats the same operation, including the operation for the last (n-th) indoor unit  34  in Step S 217  so as to calculate the flow-path resistance of an n-th branch path. Thus, the required capacities of all the indoor units  34  are calculated, and the flow rate of the pump is therefore determined from the required capacities of all the indoor units  34 . 
     Note that while  FIG. 9  illustrates the case where the flow-path resistances of all branch paths are calculated on the basis of the first pump  21  alone, the calculation may be performed by dividing the group of branch paths between the first pump  21  and the second pump  22 . In that case, the identification time can be shortened. 
     Subsequently, in Step S 218 , the control apparatus  100  starts a regular control operation and the operation of the first cycle  5 . Subsequently, in Step S 219 , the control apparatus  100  judges whether or not a given period of time has elapsed, and if not, the control apparatus  100  controls the rotation speed of the pump in Step S 220  such that the target head is realized on the basis of Equation (3). If the specific period of time has elapsed in Step S 219 , the control apparatus  100  finds in Step S 221  the branch path (herein denoted by I) having the flow-rate-adjusting valve  32  whose opening-degree is the highest in the second cycle  6 . If the opening-degree of the branch path I is found to be at or above the target maximum opening-degree in Step S 222 , the control apparatus  100  increases the target head in Step S 223  because the head of the pump is low. The increment may be a fixed value. If the opening-degree of the branch path I is at or below the target maximum opening-degree in Step S 223 , the control apparatus  100  reduces the target head in Step S 224  because the head of the pump is too high. The reduction method is as follows: 
       (New target head)=(Current target head)/(Calculated flaw-path resistance of relevant branch path)×((Calculated flow-path resistance of relevant branch path)−((Flow-path resistance of flow-rate-adjusting valve at current opening-degree)−(Flow-path resistance of flow-rate-adjusting valve at target maximum opening-degree)))
 
     With such a configuration, no personnel for on-site adjustment are necessary, and minimization of the pump input is realized easily because the control apparatus  100  identifies the flow-path resistances and reflects the resistances in the control operation that is being performed. Furthermore, since the flow-path resistances are calculated by using the temperature sensors instead of using the pressure sensors, costs can be reduced. Furthermore, since the temperature sensors are provided in the relay unit  3  instead of being provided to the indoor units  34 , even if any temperature sensors fail, it is only necessary to perform a general recovery work (replacement or the like) for the relay unit alone. That is, there is no need to do the recovery work for each of all the indoor units  34 , and the ease of maintenance is therefore increased. 
     REFERENCE SIGNS LIST 
       1  air-conditioning apparatus 
       2  heat source unit 
       3  relay unit 
       4 ,  4   a  to 4 f  load unit 
       5  first cycle 
       6  second cycle 
       7  third cycle 
       8   a  to  8   c  branch path 
       9  compressor 
       10  flow-path switcher 
       11 ,  11   a  to  11   d  first heat exchanger 
       12  fan 
       13  first extension pipe 
       14  first reducing valve 
       15  second heat exchanger 
       16  second reducing valve 
       17  third heat exchanger 
       18  second extension pipe 
       19  accumulator 
       21  first pump 
       22  second pump 
       31 ,  31   a  to  31   c  first flow-path-switching valve 
       32 ,  32   a  to  32   c  flow-rate-adjusting valve 
       33   a  to  33   c  third extension pipe 
       34 ,  34   a  to  34   c  indoor unit 
       35   a  to  35   e  indoor-unit fan 
       36   a  to  36   c  fourth extension pipe 
       37   a  to  37   c  second flow-path-switching valve 
       40  first branching path 
       41  first combining path 
       42  second branching path 
       43  second combining path 
       51  intake-side pressure sensor 
       52  discharge-side pressure sensor 
       53 ,  54 ,  55 ,  56 ,  57  pressure sensor 
       61 ,  62 ,  63 ,  64 ,  65 ,  66 ,  67 ,  67   a  to  67   c ,  68 ,  68   a  to  68   c  temperature sensor 
       70   a  to  70   d ,  71   a  to  71   d  on-off valve  72   a  to  72   d  check valve 
       90  building 
       91  room space 
       92  non-room space 
       100  control apparatus