Abstract:
A refrigerator that includes a compressor configured to compress a refrigerant; a condenser configured to condense the refrigerant; a first evaporator that is configured to evaporate the refrigerant, the evaporated refrigerant being configured to cool a refrigerating compartment; a second evaporator that is configured to evaporate the refrigerant, the evaporated refrigerant being configured to cool a freezing compartment; a first heat exchanger; a refrigerating-compartment expansion device that is coupled to the first heat exchanger and that is configured to expand the refrigerant and provide the expanded refrigerant to the first heat exchanger; a second heat exchanger coupled to the second evaporator; and a freezing-compartment expansion device that is coupled to the second heat exchanger and that is configured to expand the refrigerant and provide the expanded refrigerant to the second heat exchanger, wherein the first heat exchanger is configured to cool the second heat exchanger is disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The application claims priority under 35 U.S.C. §119 and 35 U.S.C. §365 to Korean Patent Application No. 10-2016-0000950 filed on Jan. 5, 2016 and Korean Patent Application No. 10-2016-0072600 filed on Jun. 10, 2016, the entire content of the prior applications is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present application generally relates to refrigerator control technology. 
       BACKGROUND 
       [0003]    In general, a refrigerator includes a plurality of storage compartments for storing a storage to be refrigerated or frozen, and one surface of each of the storage compartments is opened such that food can be inserted and withdrawn. The plurality of storage compartments includes a freezing compartment for freezing food and a refrigerating compartment for refrigerating food. 
         [0004]    In a refrigerator, a freezing system in which refrigerant is circulated is driven. An apparatus configuring the freezing system includes a compressor, a condenser, an expansion device and an evaporator. The evaporator may include a first evaporator provided at one side of the refrigerating compartment and a second evaporator provided at one side of the freezing compartment. 
         [0005]    Recently, a refrigerator including evaporators and expansion devices individually provided in freezing and refrigerating compartments was developed. This refrigerator controls each expansion device to adjust the amount of refrigerant supplied to each evaporator in a compressor, thereby respectively maintaining the internal temperatures of the freezing and refrigerating compartments at freezing and refrigerating temperatures. 
       SUMMARY 
       [0006]    The present disclosure is related to a refrigerator for selectively performing load shift according to the load thereof and a method of controlling the same. 
         [0007]    In general, one innovative aspect of the subject matter described in this specification can be embodied in a refrigerator including a compressor configured to compress a refrigerant; a condenser configured to condense the refrigerant; a first evaporator that is configured to evaporate the refrigerant condensed by the condenser, the evaporated refrigerant being configured to cool a refrigerating compartment; a second evaporator that is configured to evaporate the refrigerant condensed by the condenser, the evaporated refrigerant being configured to cool a freezing compartment; a first heat exchanger coupled to the first evaporator; a refrigerating-compartment expansion device that is coupled to the first heat exchanger and that is configured to expand the refrigerant and provide the expanded refrigerant to the first heat exchanger; a second heat exchanger coupled to the second evaporator; and a freezing-compartment expansion device that is coupled to the second heat exchanger and that is configured to expand the refrigerant and provide the expanded refrigerant to the second heat exchanger, wherein the first heat exchanger is configured to cool the second heat exchanger. 
         [0008]    The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In particular, one embodiment includes all the following features in combination. The freezing-compartment expansion device includes: a first expansion device coupled to an inlet side of the second heat exchanger, and a second expansion device coupled to an outlet side of the second heat exchanger, and wherein the refrigerant expanded by the second expansion device passes through the second evaporator. The refrigerator further includes a suction pipe that is configured to couple the second evaporator to the compressor, wherein the first expansion device, the second expansion device, and the suction pipe exchange heat with each other. A first surface of the first heat exchanger and a first surface of the second heat exchanger are coupled together. The refrigerator further includes a valve device that couples the condenser to the second heat exchanger and that is configured to control an amount of the refrigerant provided from the condenser to the second heat exchanger. The refrigerator further includes a first expansion device that is coupled to a first outlet side of the valve device and that is configured to expand the refrigerant that is provided to the second heat exchanger; and a second expansion device that is coupled to an outlet side of the second heat exchanger and that is configured to expand the refrigerant that is output from the second heat exchanger. The refrigerator further includes a third expansion device that is coupled to a second outlet side of the valve device and that is configured to expand the refrigerant that bypasses the second heat exchanger. Each of the first expansion device, the second expansion device, and the third expansion devices includes a respective capillary tube, and wherein a diameter of the capillary tube of the third expansion device is greater than a diameter of the capillary tube of the first expansion device or a diameter of the capillary tube of the second expansion device. The valve device includes a first valve including a first inlet, a first outlet, and a second outlet, and wherein the first valve is coupled to a first flow channel that extends from the first outlet of the first valve and that is coupled to the first expansion device, the second expansion device, and the second heat exchanger; and a second flow channel that extends from the second outlet of the first valve and that is coupled to the third expansion device. The refrigerator further includes: a coupler that couples the first flow channel to the second flow channel, wherein the coupler is coupled to an inlet side of the second evaporator. The compressor includes a first compressor configured to draw first refrigerant of the refrigerant and compress the first refrigerant, and a second compressor configured to draw second refrigerant of the refrigerant and compress the second refrigerant, and wherein the condenser includes a first condenser that is coupled to an outlet side of the first compressor and that is configured to condense the first refrigerant, and a second condenser that is coupled to an outlet side of the second compressor and that is configured to condense the second refrigerant. The compressor includes a first compressor, and a second compressor configured to draw second refrigerant of the refrigerant and compress the second refrigerant, and wherein the first compressor is configured to (i) draw first refrigerant of the refrigerant, the first refrigerant being evaporated by the first evaporator and (ii) compress the first refrigerant and the second refrigerant. The refrigerator further includes a second valve that includes a first inlet, a first outlet, a second outlet, and a third outlet, wherein the second valve is coupled to a first flow channel that extends from the first outlet of the second valve to the first heat exchanger; a second flow channel that extends from the second outlet of the second valve to the second heat exchanger; and a third flow channel that extends from the third outlet of the second valve to the second evaporator. The refrigerator further includes a refrigerating-compartment expansion device that is provided in the first flow channel and that is coupled to the first heat exchanger; a first expansion device that is provided in the second flow channel and that is coupled to the second heat exchanger; and a second expansion device that is provided in the second flow channel and that is coupled to the second heat exchanger. The refrigerator further includes: a third expansion device provided in the third flow channel. 
         [0009]    In general, another innovative aspect of the subject matter described in this specification can be embodied in a method of controlling a refrigerator that includes (i) a first compressor, a first condenser, a first heat exchanger, and a first evaporator for a refrigerating-compartment cycle and (ii) a second compressor, a second condenser, a second heat exchanger, a freezing-compartment expansion device, and a second evaporator for a freezing-compartment cycle, wherein the first heat exchanger is configured to cool the second heat exchanger, the method including operations of sensing a temperature of an indoor space of the refrigerator; sensing cooling capacity of the second compressor; and controlling an amount of a refrigerant provided to the second heat exchanger based on the temperature of the indoor space or the cooling capacity of the second compressor. 
         [0010]    The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In particular, one embodiment includes all the following features in combination. The method further includes determining that the cooling capacity of the second compressor satisfies a threshold cooling capacity; providing the refrigerant to the second heat exchanger based on the determination that the cooling capacity of the second compressor satisfies the threshold cooling capacity; and providing the refrigerant to the second evaporator based on the determination that the cooling capacity of the second compressor satisfies the threshold cooling capacity. The method further includes decompressing the refrigerant that is provided to the second heat exchanger; and decompressing the refrigerant that is provided to the second evaporator. The method further includes exchanging heat among (i) a suction pipe that extends from the second evaporator to the second compressor and (ii) one or more expansion devices of the freezing-compartment expansion device. The method further includes providing the refrigerant into two different channels using a three-way valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagram illustrating an example refrigerator. 
           [0012]      FIG. 2  is a diagram illustrating an example freezing cycle of a refrigerator. 
           [0013]      FIG. 3  is a diagram illustrating an example heat exchanger. 
           [0014]      FIG. 4  is a diagram illustrating example arrangements of refrigerant pipes. 
           [0015]      FIG. 5  is a diagram illustrating an example refrigerator. 
           [0016]      FIG. 6  is a graph illustrating an example P-H curve with reference to  FIG. 2 . 
           [0017]      FIG. 7  is a diagram illustrating an example refrigeration cycle of a refrigerator. 
           [0018]      FIG. 8  is a diagram illustrating an example refrigerator. 
           [0019]      FIG. 9  is a block diagram illustrating an example refrigerator. 
           [0020]      FIG. 10  is a flowchart of an example process for controlling a refrigerator. 
           [0021]      FIG. 11  is a diagram illustrating an example freezing cycle of a refrigerator. 
           [0022]      FIG. 12  is a diagram illustrating an example refrigerator. 
           [0023]      FIG. 13  is a graph illustrating an example P-H curve with reference to  FIG. 11 . 
           [0024]      FIG. 14  is a diagram illustrating an example freezing cycle of a refrigerator. 
       
    
    
       [0025]    Like reference numbers and designations in the various drawings indicate like elements 
       DETAILED DESCRIPTION 
       [0026]      FIG. 1  illustrates an example refrigerator. Referring to  FIG. 1 , a refrigerator  1  includes a main body  11  having an openable front surface and forming storage compartments  12  and  13 . The storage compartments include the refrigerating compartment  12  and the freezing compartment  13 , and the refrigerating compartment  12  and the freezing compartment  13  may be partitioned by a partition  14 . The refrigerating compartment  12  and the freezing compartment  13  may be referred to as a “first storage compartment” and a “second storage compartment”, respectively. 
         [0027]    The main body  11  may include an outer case  15  forming the appearance of the refrigerator  1 , a refrigerating-compartment inner case  16  provided inside the outer case  15  and forming the inside of the refrigerating compartment  12  and a freezing-compartment inner case (not shown) provided inside the outer case  15  and forming the inside of the freezing compartment  13 . An insulation material may be provided in a space between the outer case  15  and the freezing-compartment inner case  16  and a space between the outer case  15  and the freezing-compartment inner case. 
         [0028]    In addition, the refrigerator  1  may further include a freezing-compartment door  21  and a refrigerating-compartment door  22  coupled to the front side of the main body  11  to selectively shield the freezing compartment  13  and the refrigerating compartment  12 . 
         [0029]    In some implementations, for example, a bottom freezer type refrigerator in which a freezing compartment is provided under a refrigerating compartment will be described. However, the present application is not limited to the bottom freezer type refrigerator and is applicable to a top mount type refrigerator in which a freezing compartment is provided on a refrigerating compartment and a side-by-side type refrigerator in which a freezing compartment and a refrigerating compartment are provided side by side. 
         [0030]    The refrigerating compartment  12  may include a cool-air discharger  18  for discharging air cooled in a first evaporator  140  to the refrigerating compartment  12 . The cool-air discharger  18  may be provided on the rear surface of the refrigerating compartment  12  and may be formed on a refrigerating-compartment cover plate  23 . A freezing-compartment cover plate (not shown), on which a cool-air discharger (not shown) for discharging cool air is formed, may be provided on the rear surface of the freezing compartment  13 . 
         [0031]      FIG. 2  illustrates an example freezing cycle of a refrigerator.  FIG. 3  illustrates an example heat exchanger.  FIG. 4  illustrates example arrangements of refrigerant pipes.  FIG. 5  illustrates an example refrigerator.  FIG. 6  illustrates a graph showing an example P-H curve with reference to  FIG. 2 . 
         [0032]    First, referring to  FIG. 2 , the refrigerator  1  includes a refrigerating-compartment cycle  10  for operating the refrigerating cycle for cooling the refrigerating compartment  12  and a freezing-compartment cycle  20  for operating the refrigerating cycle for cooling the freezing compartment  13 . First refrigerant may be circulated in the refrigerating-compartment cycle  10  and second refrigerant may be circulated in the freezing-compartment cycle  20 . The first and second refrigerants are not mixed or distributed to form independent cycles. 
         [0033]    More specifically, the freezing-compartment cycle  10  includes a first compressor  100  as a “refrigerating-compartment compressor” for compressing the first refrigerant into high-temperature, high-pressure refrigerant, a first condenser  110  for condensing the high-temperature, high-pressure first refrigerant compressed by the first compressor  100  through heat radiation, a refrigerating-compartment expansion device  120  for decompressing the refrigerant condensed by the first condenser  110 , and a first evaporator  140  for evaporating the refrigerant decompressed by the refrigerating-compartment expansion device  120 . 
         [0034]    The first condenser  110  may be provided in a mechanical compartment located at the rear side of the freezing compartment  13  as a “refrigerating-compartment condenser”. A first condensing fan  110   a  may be provided at one side of the first condenser  110 . The first condensing fan  110   a  may operate such that air in the mechanical compartment or air in an indoor space provided in the refrigerator flows toward the first condenser  110 . 
         [0035]    The refrigerating-compartment expansion device  120  may include a capillary tube. The capillary tube has a relatively small diameter. The capillary tube may act as resistance to the flow of the refrigerant when the refrigerant passes through the capillary tube, thereby expanding the refrigerant. A first heat exchanger  130  may be provided between the refrigerating-compartment expansion device  120  and the first evaporator  140 . That is, the refrigerating-compartment expansion device  120  may be provided at the inlet side of the first heat exchanger  130  and the first evaporator  140  may be provided at the outlet side of the first heat exchanger  130 . 
         [0036]    The first evaporator  140  may be provided at the rear side of the refrigerating compartment  12  as a “refrigerating-compartment evaporator”. A first evaporation fan  140   a  may be provided at one side of the first evaporator  140 . The first evaporation fan  140   a  may operate such that cool air in the refrigerating compartment  12  flows toward the first evaporator  140 . Air cooled while passing through the first evaporator  140  may flow into the refrigerating compartment  12  again. 
         [0037]    The freezing-compartment cycle  20  includes a second compressor  200  as a “freezing-compartment compressor” for compressing the second refrigerant into high-temperature, high-pressure refrigerant, a second condenser  210  for condensing the high-temperature, high-pressure second refrigerant compressed by the second compressor  200  through heat radiation, freezing-compartment expansion devices  220  and  240  for decompressing the refrigerant condensed by the second condenser  210  and a second evaporator  250  for evaporating the refrigerant decompressed by the freezing-compartment expansion devices  220  and  240 . 
         [0038]    The second condenser  210  may be provided in a mechanical compartment located at the rear side of the freezing compartment  13  as a “freezing-compartment condenser”. A second condensing fan  210   a  may be provided at one side of the second condenser  210 . The second condensing fan  210   a  may operate such that air in the mechanical compartment or air in an indoor space provided in the refrigerator flows toward the second condenser  210 . 
         [0039]    The freezing-compartment expansion devices  220  and  240  include a plurality of expansion devices. The plurality of expansion devices includes the first expansion device  220  and the second expansion device  240 . Each of the first and second expansion devices  220  and  240  may include a capillary tube. A second heat exchanger  230  is provided between the first expansion devices  220  and  240 . That is, the first expansion device  220  may be provided at the inlet side of the second heat exchanger  230  and the second expansion device  240  may be provided at the outlet side of the second heat exchanger  230 . 
         [0040]    The second evaporator  250  may be provided at the rear side of the freezing compartment  12  as a “freezing-compartment evaporator”. A second evaporation fan  250   a  may be provided at one side of the second evaporator  250 . The second evaporation fan  250   a  may operate such that cool air in the freezing compartment  13  flows toward the second evaporator  250 . Air cooled while passing through the second evaporator  250  may flow into the freezing compartment  12  again. The first evaporator  140  may be referred to as a “refrigerating-compartment evaporator” and the second evaporator  250  may be referred to as a “freezing-compartment evaporator”. 
         [0041]    The refrigerator  1  may further include a device for shifting a load required for the freezing-compartment cycle  20  to the refrigerating-compartment cycle  10 . More specifically, the refrigerator  1  further includes an intermediate heat exchange unit  330  for exchanging heat between the refrigerating-compartment cycle  10  and the freezing-compartment cycle  20 . 
         [0042]    The intermediate heat exchange unit  330  includes a first heat exchanger  130  provided in the refrigerating-compartment cycle  10  and a second exchanger  230  provided in the freezing-compartment cycle  20 . Heat may be exchanged between the first refrigerant passing through the first heat exchanger  130  and the second refrigerant passing through the second heat exchanger  230 . 
         [0043]    The first heat exchanger  130  is provided at the outlet side of the refrigerating-compartment expansion device  120 . The first evaporator  140  may be provided at the outlet side of the first heat exchanger  130 . The temperature of the first refrigerant decompressed by the refrigerating-compartment expansion device  120  may be less than that of the second refrigerant flowing in the second heat exchanger  230 . 
         [0044]    Accordingly, the first refrigerant may absorb heat from the second heat exchanger  230  while passing through the first heat exchanger  130 . In this process, the first refrigerant may be evaporated. Accordingly, the first heat exchanger  130  may be referred to as an “auxiliary evaporator”. 
         [0045]    The second heat exchanger  230  may be provided at the outlet side of the freezing-compartment expansion device  220 . The second expansion device  240  may be provided at the outlet side of the second heat exchanger  230 . The second refrigerant decompressed by the freezing-compartment expansion device  220  may pass through the second heat exchanger  230  to radiate heat toward the first heat exchanger  130 . In this process, the second refrigerant may be supercooled. Accordingly, the second heat exchanger  230  may be referred to as an “auxiliary condenser”. 
         [0046]    The first and second heat exchangers  130  and  230  may be provided adjacent to each other to perform heat exchange. More specifically, the first and second heat exchangers  130  and  230  may exchange heat using a conduction method according to mutual contact. For example, as shown in  FIG. 3 , the first and second heat exchangers  130  and  230  may contact each other. The outer circumferential surface of the refrigerant pipe  135  of the first heat exchanger  130  and the outer circumferential surface of the refrigerant pipe  235  of the second heat exchanger  230  may be soldered. 
         [0047]    The diameter of the first refrigerant pipe  135  of the first heat exchanger  130  may be greater than the refrigerant pipe  235  of the second heat exchanger  230 . More specifically, the refrigerant of the first refrigerant pipe  135  may be evaporated by heat exchange and the refrigerant of the second refrigerant pipe  235  is condensed. The volume of gaseous refrigerant is greater than that of liquefied refrigerant. When the diameter of the pipe in which the gaseous refrigerant flows is too small, drop of the pressure of the gaseous refrigerant increases and thus heat exchange efficiency may deteriorate. Accordingly, by increasing the diameter of the first refrigerant pipe  135  to be greater than that of the second refrigerant pipe  235 , it is possible to improve heat exchange efficiency of the intermediate heat exchange unit  330 . 
         [0048]    As shown in  FIGS. 2 and 3 , the first refrigerant flowing in the first heat exchanger  130  may flow in a direction opposite to the direction of the second refrigerant flowing in the second heat exchanger  230 . More specifically, some of the second refrigerant of the second refrigerant pipe  235  is condensed while heat is delivered to the first refrigerant of the first refrigerant pipe  135 . When the refrigerant flow directions of the first and second refrigerant pipes  135  and  235  are opposite to each other, the amount of condensed second refrigerant gradually increases toward the downstream side of the second refrigerant pipe  235 , thereby improving heat exchange efficiency. 
         [0049]    The second expansion device  240  is provided at the outlet side of the second heat exchanger  230  to decompress the refrigerant supercooled by the second heat exchanger  230 . The refrigerant decompressed by the second heat exchanger  230  may be evaporated by the second evaporator  250 . The first evaporator  140  is provided at the outlet side of the first heat exchanger  130  and the refrigerant evaporated by the first heat exchanger  130  may be additionally evaporated by the first evaporator  140 . 
         [0050]    The refrigerating-compartment cycle  10  further includes a first suction pipe  145  extending from the outlet side of the first evaporator  140  to the first compressor  100 . The first suction pipe  145  may exchange heat with the refrigerating-compartment expansion device  120 . For example, the first suction pipe  145  and the refrigerating-compartment expansion device  120  may be coupled to each other through soldering to perform heat exchange using the conduction method. The first suction pipe  145  and the refrigerating-compartment expansion device  120  form a first suction line heat exchange unit  160 . 
         [0051]    Low-temperature refrigerant flowing in the first suction pipe  145  and relatively-high-temperature refrigerant passing through the refrigerating-compartment expansion device  120  exchange heat with each other, thereby increasing refrigerant overheating degree of the first suction pipe  145  and increasing the refrigerant supercooling degree of the refrigerating-compartment expansion device  120 . As a result, it is possible to improve operational efficiency of the refrigerating-compartment cycle  10 . 
         [0052]    The freezing-compartment cycle  20  further includes a second suction pipe  255  extending from the outlet side of the second evaporator  250  to the second compressor  200 . The second suction pipe  255  may exchange heat with the first and second expansion devices  220  and  240 . For example, the second suction pipe  255  and the first and second expansion devices  220  and  240  may be coupled to each other through soldering to perform heat exchange using the conduction method. The second suction pipe  255  and the first and second expansion devices  220  and  240  form a second suction line heat exchange unit  260 . 
         [0053]    Low-temperature refrigerant flowing in the second suction pipe  255  and relatively-high-temperature refrigerant passing through the first and second expansion devices  220  and  240  exchange heat with each other, thereby increasing refrigerant overheating degree of the second suction pipe  255  and increasing the refrigerant supercooling degree of the first and second expansion devices  220  and  240 . As a result, it is possible to improve operational efficiency of the freezing-compartment cycle  20 . 
         [0054]    The flow of the refrigerant will be briefly described. First, the refrigerant is compressed by the first compressor  100  and the compressed refrigerant is condensed by the first condenser  110 . The condensed refrigerant is guided to the first heat exchanger  130  after passing through the refrigerating-compartment expansion device  120 . At this time, the refrigerating compartment expansion device  120  is soldered to the first suction pipe  145  connecting the first evaporator  140  to the first compressor  110  in the first suction line heat exchange unit  160  to exchange heat with each other, as shown in  FIG. 5 . 
         [0055]    The first heat exchanger  130  functions as an evaporator while exchanging heat with the second heat exchanger  230  in the intermediate heat exchange unit  330  and the refrigerant in the first heat exchanger  130  may be vaporized. The refrigerant may cool ambient air while passing through the first evaporator  140  to supply cool air to the refrigerating compartment  12 . 
         [0056]    The refrigerant passing through the first evaporator  140  may be sucked into and compressed by the first compressor  100  through the first suction pipe  145 . 
         [0057]    In some implementations, the refrigerant compressed by the second compressor  200  is guided into the second condenser  210 . The refrigerant is guided to the first expansion device  220  after passing through the second condenser  210  and the first expansion device  220  exchanges heat with the second suction pipe  255  connecting the first evaporator  250  to the second compressor  220  in the second suction line heat exchange unit  260 . 
         [0058]    The refrigerant passing through the first expansion device  220  may flow into the second heat exchanger  230  and exchange heat with the first heat exchanger  130 . In this process, the refrigerant of the second heat exchanger  230  may be condensed. 
         [0059]    Here, the condensation capacity of the refrigerant additionally condensed in the second heat exchanger  230  may correspond to a part “A” of  FIG. 6 . By the part “A”, the load of the cooling cycle of the second compressor  200  is shifted to the cooling cycle of the first compressor  100 , thereby improving operational efficiency of the refrigerator. That is, since the refrigerant compressed by the second compressor  200  is additionally condensed in the part “A”, more cool air may be generated in the second evaporator  250 . 
         [0060]    The refrigerant passing through the second heat exchanger  230  is guided to the second evaporator  250  after passing through the second expansion device  240 . At this time, the second expansion device  240  exchanges heat with the second suction pipe  255  in the second suction line heat exchange unit  260 . 
         [0061]    The second evaporator  250  may exchange heat with ambient air passing therethrough to generate cool air and to supply the generated cool air to the freezing compartment. The refrigerant passing through the second evaporator  250  may be sucked into and compressed by the second compressor  200  through the second suction pipe  255 . 
         [0062]    The intermediate exchange unit  330  including the first heat exchanger  130  and the second heat exchanger  230  may be provided at the rear side of the first evaporator  140 . More specifically, the intermediate heat exchanger unit  330  is manufactured in a refrigerant pipe structure shown in  FIG. 5  and is provided between the outer case  15  and the refrigerating-compartment inner case  16 , the ends of the refrigerant pipes are connected to the other refrigerant pipes and then the refrigerant pipes are embedded by injecting an insulation material. The intermediate heat exchanger unit  330  is embedded in the insulation material such that heat exchange between the two refrigerant pipes is possible but heat exchange with ambient air is impossible. 
         [0063]    If the intermediate heat exchange unit  330  is provided behind the second evaporator  250 , the second evaporator  250  is used to supply cool air to the freezing compartment and, at this time, the intermediate heat exchange unit  330  may function as a load of the freezing compartment. Accordingly, the intermediate heat exchange unit  330  is preferably provided behind the first evaporator  140 . 
         [0064]    As compared to a refrigerator without the intermediate heat exchange unit  330 , cooling efficiency of the refrigerator can be improved. 
         [0065]      FIG. 7  illustrates an example refrigeration cycle of a refrigerator.  FIG. 8  illustrates an example refrigerator. Referring to  FIGS. 7 and 8 , the refrigerator  1   a  includes a refrigerating-compartment cycle  10   a  and a freezing-compartment cycle  20   a.    
         [0066]    The refrigerating-compartment cycle  10   a  further includes a valve device  290  provided at the outlet side of the second condenser  210  to control the flow of refrigerant such that the refrigerant passing through the second condenser  210  selectively flows into the second heat exchanger  230 . For example, the valve device  290  may include a three-way valve having one inlet and two outlets. 
         [0067]    The freezing-compartment cycle  20   a  includes a first flow channel  294  extending from the first inlet  290   a  of the valve device  290  to the second heat exchanger  230  and a second flow channel  295  extending from the second outlet  290   b  of the valve device  290  to a coupler  276  of the first flow channel  294 . According to the control state of the valve device  290 , the refrigerant may flow through at least one of the first and second flow channels  294  and  295 . 
         [0068]    When the valve device  290  is controlled such that the first flow channel  294  is opened and the second flow channel  295  is closed, the refrigerant flows into the second heat exchanger  230  to perform heat exchange in the intermediate heat exchange unit  330 . That is, the load of the freezing-compartment cycle  20   a  is shifted to the refrigerating-compartment cycle  10   a,  thereby obtaining supercooling effect of the refrigerating-compartment cycle  10   a.  The load of the refrigerating compartment is less than that of the freezing compartment and the operational efficiency of the refrigerating-compartment cycle  10   a  is higher than that of the freezing-compartment cycle  20   a,  thereby improving the operation performance of the refrigerator. 
         [0069]    In some implementations, when the valve device  290  is controlled such that the second flow channel  295  is opened and the first flow channel  294  is closed, the refrigerant may bypass the second heat exchanger  230  and flow toward the inlet side of the second evaporator  250 . That is, the shift of the load of the refrigerating-compartment cycle  10   a  to the freezing-compartment cycle  20   a  is restricted, thereby improving the cooling speed of the refrigerating compartment  12 . 
         [0070]    In the first flow channel  294 , the first expansion device  220 , the second heat exchanger  230  and the second expansion device  240  may be provided. Accordingly, the refrigerant flowing in the first flow channel  294  may flow into the second evaporator  250  through the first expansion device  220 , the second heat exchanger  230  and the second expansion device  240 . 
         [0071]    In the second flow channel  295 , a third expansion device  275  may be provided. The third expansion device  275  may be understood as a refrigerating-compartment expansion device. For example, the third expansion device  275  may include a capillary tube. 
         [0072]    Accordingly, the refrigerant flowing in the second flow channel  295  may flow into the second evaporator  250  through the third expansion device  275  and the coupler  276 . The coupler  276  is a point where the first flow channel  294  and the second flow channel  295  meet and may be provided at the inlet side of the second evaporator  250 . 
         [0073]    The length or diameter of the refrigerating-compartment expansion device  120  may be determined such that the decompression level of the refrigerating-compartment expansion device  120  is greater than that of the first expansion device  220 . For example, the diameter of the refrigerating-compartment expansion device  120  may be less than that of the first expansion device  220 . The length of the refrigerating-compartment expansion device  120  may be greater than that of the first expansion device  220 . 
         [0074]    The diameter of the third expansion device  275  may be greater than that of the first expansion device  220  or the second expansion device  240 . For example, the diameter of the third expansion device  275  may be 0.9 mm and the diameter of the first and second expansion devices  220  and  240  may be 0.7 mm. 
         [0075]    Accordingly, the flow resistivity of the refrigerant passing through the second flow channel  295  may be less than that of the refrigerant passing through the first flow channel  294 . As a result, the amount of refrigerant flowing when the second flow channel  295  is opened may be greater than that of refrigerant flowing when the first flow channel  294  is opened. 
         [0076]    The valve device  290  may be controlled based on a load required for the refrigerator. For example, upon cooling operation or cooling-after-defrosting operation of the refrigerator, that is, if the load of the refrigerator is high, the valve device  290  is controlled to prevent heat exchange in the intermediate heat exchange unit  330 . That is, the valve device  290  is controlled such that the first outlet  290   a  is closed and the second outlet  290   b  is opened. Therefore, the refrigerant may flow in the second flow channel. 
         [0077]    In this example, the amount of refrigerant flowing into the second evaporator  250  through the second flow channel  295  may increase, and the load of the freezing-compartment cycle  20   a  may not be shifted to the refrigerating-compartment cycle  10   a,  thereby rapidly performing cooling of the refrigerating compartment  12 . 
         [0078]    In some implementations, if a stable cooling cycle is performed after cooling operation or cooling-after-defrosting operation of the refrigerator, that is, if the load of the refrigerator is low, the valve device  290  is controlled such that heat exchange is performed in the intermediate heat exchange unit  330 . That is, the valve device  290  is controlled such that the second outlet  290   b  is closed and the first outlet  290   a  is opened. Thus, the refrigerant may flow in the first flow channel  294 . 
         [0079]    In this example, the amount of refrigerant flowing into the second evaporator  250  through the first flow channel  294  may be slightly low but the load of the freezing-compartment cycle  20 ′ may be shifted to the refrigerating-compartment cycle  10 ′, thereby improving the supercooling degree of the freezing-compartment cycle  20 ′. 
         [0080]    The second suction pipe  255  may exchange heat with the first to third expansion devices  220 ,  240  and  275 . For example, the second suction pipe  255  and the first to third expansion devices  220 ,  240  and  275  are coupled to each other through soldering to perform heat exchange according to the conduction method. The second suction pipe  255  and the first to third expansion devices  220 ,  240  and  275  form a second suction line heat exchange unit  260 . 
         [0081]    Here, the third expansion device  275  may lengthily extend to be coupled with the first and second expansion devices  220  and  240  and the second suction pipe  255 . More specifically, the third expansion device  275  may include a first expansion part  275   a  coupled with the first expansion device  220  and the second suction pipe  255  and a second expansion part  275   b  coupled with the second expansion device  240  and the second suction pipe  255  as illustrated in  FIG. 8 . 
         [0082]      FIG. 9  illustrates an example refrigerator.  FIG. 10  is a flowchart of an example process for controlling a refrigerator. 
         [0083]    Referring to  FIG. 9 , the refrigerator  1   a  includes an indoor temperature sensor  351  for sensing the temperature of an indoor space where the refrigerator  1   a  is provided, an indoor humidity sensor  352  for sensing the humidity of the indoor space and a compressor stroke sensor  353  for sensing the stroke of the second compressor  200 . The compressor stroke sensor  353  senses the stroke of reciprocal motion of a piston of the second compressor  200 . The stroke may be used to determine the cooling capacity of the second compressor  200 . Accordingly, the compressor stroke sensor  353  is understood as a “cooling capacity sensor”. 
         [0084]    The refrigerator  1   a  further includes a controller  350  for controlling operation of the first and second compressors  100  and  200  or the valve device  290  based on the temperature information sensed by the indoor temperature sensor  351 . 
         [0085]    For example, if the indoor temperature sensed by the indoor temperature sensor  351  is equal to or greater than a predetermined temperature or if the refrigerator  1   a  initially operates, the controller  350  may regard the load of the refrigerator  1   a  as being high, increase the operating frequency of the first compressor  100  or the second compressor  200 , and increase the cooling capacity (stroke). 
         [0086]    The indoor temperature information and the operating frequencies and cooling capacities of the first and second compressors  100  and  200  may be mapped and pre-stored. The operation state of the refrigerator  1 , that is, the condition related to the cooling operation, cooling-after-defrosting operation or stabilization operation and the operating frequencies and cooling capacities of the first and second compressors  100  and  200  may be mapped and pre-stored. Here, the “stabilization operation” may be understood as a state in which the pressure ranges of the refrigerating-compartment cycle  10 ′ and the freezing-compartment cycle  20   a  reach a normal range to stably perform operation. 
         [0087]    The controller  350  may determine the load of the refrigerator  1   a  based on the cooling capacity sensed by the compressor stroke sensor  353  and adjust the control state of the valve device  290 . 
         [0088]    Referring to  FIG. 10 , the refrigerator  1   a  is powered on and the cooling operations of the refrigerating compartment  12  and the freezing compartment  13  may be performed (S 11 ). Then, the temperature or humidity of the indoor space where the refrigerator  1   a  is provided may be sensed (S 12 ). 
         [0089]    Along with the operation state of the refrigerator  1   a,  the cooling capacity of the second compressor  200  may be sensed. The cooling capacity of the second compressor  200  may be set to a value previously mapped based on the operation state of the refrigerator  1   a.    
         [0090]    For example, if the cooling operation or cooling-after-defrosting operation of the refrigerator  1  is performed, since a relatively high load is required, the cooling capacity of the second compressor  200  may be determined to output first cooling capacity. The first cooling capacity is the highest cooling capacity and may be greater than predetermined cooling capacity. 
         [0091]    In some implementations, if the cooling cycle of the refrigerator  1   a  is stabilized, since a relatively low load is required, the cooling capacity of the second compressor  200  may be determined to output second cooling capacity. The second cooling capacity is less than the first cooling capacity and may be less than the predetermined cooling capacity (S 13 ). 
         [0092]    Based on the operation state of the refrigerator  1   a  and the cooling capacity of the second compressor  200 , the control state of the valve device  290  is determined. The control state of the valve device  290  may include a “first control state” for opening the first flow channel  294  and closing the second flow channel  295 , a “second control state” for opening the second flow channel  295  and closing the first flow channel  294  and a “third control state” for opening the first and second flow channels  294  and  295 . 
         [0093]    Whether the condition of opening the first and second flow channels  294  and  295  is satisfied may be determined. For example, the condition may include the operation state from the start to the end of the defrosting operation after a rapid freezing operation is finished. At this time, the valve device  290  may be controlled to open the first and second outlets  290   a  and  290   b  and the operation of the second compressor  200  may be stopped (S 14  and S 21 ). 
         [0094]    If the condition of opening the first and second flow channels  294  and  295  is not satisfied, whether the condition of shifting the load from the freezing-compartment cycle  20  to the refrigerating-compartment cycle  10  is satisfied may be determined 
         [0095]    The condition that load shift is not performed may include the case where the second compressor  200  outputs the first cooling capacity, the case where the indoor temperature is relatively low or the case where the indoor humidity is relatively high. If the indoor temperature is relatively low, the density of the refrigerant circulated in the freezing-compartment cycle  20  may increase and thus the amount of gaseous refrigerant sucked into the first compressor  200  may decrease. Accordingly, the load of the refrigerator may increase and thus the amount of circulated refrigerant needs to increase. 
         [0096]    If the indoor humidity is relatively high, the load needs to increase in order to prevent dew from being formed in the refrigerator and thus the amount of circulated refrigerant needs to increase. 
         [0097]    In some implementations, load shift is not performed and the valve device  290  is switched to the second control state to close the first flow channel  294  and open the second flow channel  295 . Accordingly, the refrigerant may bypass the intermediate heat exchange unit  330  to flow toward the inlet side of the second evaporator  250 . As a result, since the refrigerant flows in the second flow channel  295  having relatively low flow resistivity, the amount of circulated refrigerant may increase (S 16 , S 19  and S 20 ). 
         [0098]    The condition of performing load shift includes conditions other than the condition of opening the first and second flow channels  294  and  295  and the condition that load shift is not performed. In this example, the load of the refrigerator is recognized as being relatively low. Accordingly, the valve device  290  may be switched to the first control state to open the first flow channel  294  and close the second flow channel  295 . Accordingly, the refrigerant flows into the intermediate heat exchange unit  330  and exchanges heat with the refrigerating-compartment cycle  10 , thereby increasing the supercooling degree (S 17  and S 18 ). 
         [0099]    According to the control method, by changing the control state of the valve device  290  according to the load of the refrigerator, the refrigerant may bypass the intermediate heat exchange unit  330  and flow in the second flow channel  295  having low flow resistivity if a large amount of refrigerant of the system is necessary, and the refrigerant may be guided to the intermediate heat exchange unit  330  if a large amount of refrigerant of the system is not necessary, thereby improving system performance and reducing power consumption. 
         [0100]      FIG. 11  illustrates an example freezing cycle of a refrigerator.  FIG. 12  illustrates an example refrigerator.  FIG. 13  illustrates a graph showing an example P-H curve with reference to  FIG. 11 . 
         [0101]    Referring to  FIGS. 11 to 13 , the refrigerator  1   b  includes a plurality of devices for driving the freezing cycle. 
         [0102]    More specifically, the refrigerator  1   b  includes a plurality of compressors  400  and  500  for compressing refrigerant, a condenser  510  for condensing the refrigerant compressed by the plurality of compressors  400  and  500 , a plurality of expansion devices  420 ,  520  and  540  for decompressing the refrigerant condensed by the condenser  510  and a plurality of evaporators  440  and  550  for evaporating the decompressed refrigerant by the plurality of expansion devices  420 ,  520  and  540 . 
         [0103]    The plurality of compressors  400  and  500  includes the first compressor  400  and the second compressor  500 . The second compressor  500  is a “low-pressure compressor” provided at a low pressure side to first-stage compress the refrigerant and the first compressor  400  is a “high-pressure compressor” for further compressing (second-stage compressing) the refrigerant compressed by the second compressor  500 . The second compressor  500  may be understood as a freezing-compartment cooling compressor and the second compressor  400  may be understood as a refrigerating-compartment cooling compressor. 
         [0104]    The plurality of evaporators  440  and  550  includes the first evaporator  440  for generating cool air to be supplied to the refrigerating compartment and the second evaporator  550  for generating cool air to be supplied to the freezing compartment. The refrigerator  1   b  may further include a condensation fan  510   a  provided at one side of the condenser  510  and first and second evaporation fans  440   a  and  550   a  provided at one sides of the first and second evaporators  440  and  550 . 
         [0105]    The refrigerator  1   b  further includes a second suction pipe  555  extending from the outlet side of the second evaporator  550  to the inlet side of the second compressor  500 . Accordingly, the refrigerant passing through the second evaporator  550  may be sucked into the second compressor  500 . 
         [0106]    The refrigerator  1   b  further includes a first suction pipe  445  extending from the outlet side of the first evaporator  440  to the inlet side of the first compressor  400  and a coupler  505  where the first suction pipe  445  and the outlet-side refrigerant pipe, that is, a low-pressure discharge pipe  570 , of the second compressor  500  are coupled. Accordingly, the first-stage compressed refrigerant flowing the low-pressure discharge pipe  570  is coupled with the refrigerant passing through the first evaporator  440  in the coupler  505  and is sucked into the first compressor  400 . The refrigerant sucked into the first compressor  400  flows into the condenser  510  after being compressed. 
         [0107]    The plurality of expansion devices  420 ,  520  and  540  includes a refrigerating-compartment expansion device  420  for expanding the refrigerant which will flow into the first evaporator  440 . The refrigerator  1   b  further includes a first heat exchanger  430  provided at the outlet side of the refrigerating-compartment expansion device  420 . The first evaporator  440  may be provided at the outlet side of the first heat exchanger  430 . The first heat exchanger  430  forms an intermediate heat exchange unit along with the second heat exchanger  530  and absorbs heat from the heat exchanger  530  to guide evaporation of the refrigerant. 
         [0108]    The first suction pipe  445  and the refrigerating-compartment expansion device  420  may exchange heat with each other. For example, the first suction pipe  445  and the refrigerating-compartment expansion device  420  may be coupled to each other through soldering. By heat exchange, the supercooling degree of the refrigerant flowing in the refrigerating-compartment expansion device  420  and the overheating degree of the refrigerant flowing in the first suction pipe  445  can be improved. The first suction pipe  445  and the refrigerating-compartment expansion device  420  form a first suction line heat exchange unit  460 . 
         [0109]    The plurality of expansion devices  420 ,  520  and  540  further includes the first expansion device  520  and the second expansion device  540 . The refrigerator  1   b  further includes a second heat exchanger  530  provided between the first and second expansion devices  520  and  540 . The refrigerant decompressed by the first expansion device  520  may be cooled by the second heat exchanger  530  and may be decompressed by the second expansion device  540  again. Then, the refrigerant decompressed by the second expansion device  540  may flow into the second evaporator  550 . 
         [0110]    The second heat exchanger  530  may faun the intermediate heat exchange unit along with the first heat exchanger  430  and radiate heat to the second heat exchanger  530  to guide supercooling of the refrigerant. 
         [0111]    The second suction pipe  555  and the freezing-compartment expansion devices  520  and  540  may exchange heat with each other. For example, the second suction pipe  555  and the freezing-compartment expansion devices  520  and  540  may be coupled to each other through soldering. By heat exchange, the supercooling degree of the refrigerant flowing in the freezing-compartment expansion devices  520  and  540  and the overheating degree of the refrigerant flowing in the second suction pipe  555  can be improved. The second suction pipe  555  and the freezing-compartment expansion devices  520  and  540  form a second suction line heat exchange unit  560 . 
         [0112]    The refrigerator  1   b  further includes a valve device  300  provided at the outlet side of the condenser  510  to control the flow of the refrigerant such that the refrigerant passing through the condenser  510  selectively flows into the first and second evaporators  440  and  550 . For example, the valve device  300  includes a three-way valve having one inlet and two outlets. 
         [0113]    The refrigerator  1   b  includes a first flow channel  301  extending from the first outlet  300   a  of the valve device  300  to the first heat exchanger  430  and a second flow channel  302  extending from the second outlet  300   b  of the valve device  300  to the second heat exchanger  530 . According to the control state of the valve device  600 , the refrigerant may flow through at least one of the first and second flow channels  301  and  302 . 
         [0114]    The refrigerant branched to the first flow channel  301  by the valve device  300  is guided to the first heat exchanger after passing through the refrigerating-compartment expansion device  420 . The refrigerant absorbs external heat while primarily evaporating in the first heat exchanger  430  and further evaporates after passing through the first evaporator  440 , thereby supplying cool air to the refrigerating compartment. The refrigerant passing through the first evaporator  440  may be sucked into and compressed by the first compressor  400  through the first suction pipe  445 . 
         [0115]    The refrigerant branched to the second flow channel  302  by the valve device  300  is guided to the first expansion device  520  and the first expansion device  520  exchanges heat with the second suction pipe  555  in the second suction line heat exchange unit  460 . 
         [0116]    The refrigerant passing through the first expansion device  520  flows into the second heat exchanger  530  and the second heat exchanger  530  exchanges heat with the first heat exchanger  430 . In this process, some of the refrigerant of the second heat exchanger  530  may be condensed while radiating heat. That is, as shown in  FIG. 13 , the refrigerant may be further condensed in a part “B” while passing through the second heat exchanger  530 . Since the load may be shifted upon cooling while the refrigerant passes through the part “B”, operational efficiency of the refrigerator can be improved. 
         [0117]    The refrigerant passing through the second heat exchanger  530  is guided to the second evaporator  550  for supplying cool air to the freezing compartment after passing through the second expansion device  540 . At this time, the second expansion device  540  exchanges heat with the second suction pipe  555 . The second evaporator  550  may exchange heat with ambient air passing therethrough to generate cool air and the generated cool air may be supplied to the freezing compartment. The refrigerant passing through the second evaporator  550  may be sucked into and compressed by the second compressor  500  through the second suction pipe  555 . 
         [0118]      FIG. 14  illustrates an example freezing cycle of a refrigerator. Referring to  FIG. 14 , the refrigerator  1   c  includes a plurality of compressors  400  and  500  for compressing refrigerant, a condenser  510  for condensing the refrigerant compressed by the plurality of compressors  400  and  500 , a plurality of expansion devices  420 ,  520 ,  540  and  575  for decompressing the refrigerant condensed by the condenser  510  and a plurality of evaporators  440  and  550  for evaporating the decompressed refrigerant by the plurality of expansion devices  420 ,  520 ,  540  and  575 . 
         [0119]    The plurality of expansion devices  420 ,  520 ,  540  and  575  includes the refrigerating-compartment expansion device  420  for expanding the refrigerant flowing into the first evaporator  440 , the first expansion device  530  and the second expansion device  540 . The plurality of expansion devices  420 ,  520 ,  540  and  575  further includes the third expansion device  575 . The third expansion device  575  configures a freezing-compartment expansion device along with the first and second expansion devices  520  and  540 . The refrigerator  1   c  further includes a valve device  600  provided at the outlet side of the condenser  510  to control the flow of the refrigerant such that the refrigerant passing through the condenser  510  selectively flows into the first and second evaporators  440  and  550 . For example, the valve device  600  includes a four-way valve having one inlet and three outlets. The valve device  600  may control the flow of the refrigerant such that the refrigerant selectively flows into the second heat exchanger  530 . 
         [0120]    The refrigerator  1   c  includes a first flow channel  601  extending from the first outlet  600   a  of the valve device  600  to the first heat exchanger  430 , a second flow channel  602  extending from the second outlet  600   b  of the valve device  600  to the second heat exchanger  530 , and a third flow channel  630  extending from the third outlet  600   c  of the valve device  600  to the coupler  576 . According to the control state of the valve device  600 , the refrigerant may flow through at least one of the first to third flow channels  610 ,  620  and  630 . When the valve device  600  is controlled such that the first and second flow channels  610  and  620  are opened and the third flow channel  630  is closed, the refrigerant may flow into the first and second heat exchangers  430  and  530  to perform heat exchange in the intermediate heat exchanger unit  330 . That is, the load of the freezing-compartment cycle  60  is shifted to the refrigerating-compartment cycle  50 , thereby obtaining supercooling effect of the refrigerating-compartment cycle  50 . 
         [0121]    In some implementations, when the valve device  600  is controlled such that the first and third flow channels  610  and  630  are opened and the second flow channel  620  is closed, some of the refrigerant may flow into the first heat exchanger  430  but the remaining refrigerant may bypass the second heat exchanger  530  and flow toward the inlet side of the second evaporator  250 . That is, the shift of the load of the freezing-compartment cycle  60  to the refrigerating-compartment cycle  20   a  is restricted, thereby improving the cooling speed of the refrigerating compartment  12 . 
         [0122]    If cooling of the refrigerating compartment  12  is not necessary, the first flow channel  610  may be closed and the third flow channel may be opened, thereby operating only the freezing-compartment cycle  60 . Of course, at this time, heat exchange in the intermediate heat exchange units  430  and  530  may be restricted. 
         [0123]    In the first flow channel  610 , the refrigerating-compartment expansion device  420  may be provided. Accordingly, the refrigerant flowing in the first flow channel  610  may flow into the first evaporator  440  through the refrigerating-compartment expansion device  420  and the first heat exchanger  430 . 
         [0124]    In the second flow channel  620 , the first and second expansion devices  520  and  540  may be provided. Accordingly, the refrigerant flowing in the second flow channel  620  may flow into the second evaporator  250  through the first expansion device  520 , the second heat exchanger  530  and the second expansion device  540 . 
         [0125]    In the third flow channel, the third expansion device  575  may be provided. 
         [0126]    The three outlets of the valve device  600  may include the first outlet  600   a  connected to the first flow channel  610 , the second outlet  600   b  connected to the second flow channel  620  and the third outlet  600   c  connected to the third flow channel  630 . The valve device  600  may be controlled to open at least one of the three outlets. The third flow channel  630  extends from the third outlet  600   c  to the coupler  576 . The coupler  576  is a point where the second and third flow channels  620  and  630  meet and may be provided at the inlet side of the second evaporator  250 . 
         [0127]    Each of the refrigerating-compartment expansion device  420  and the first to third expansion devices  520 ,  540  and  575  may include a capillary tube. 
         [0128]    The diameter of the third expansion device  575  may be greater than that of the first expansion device  520  or the second expansion device  540 . For example, the diameter of the third expansion device  575  may be 0.9 mm and the diameter of the first and second expansion devices  520  and  540  may be 0.7 mm. 
         [0129]    Accordingly, the flow resistivity of the refrigerant passing through the third flow channel  630  may be less than that of the refrigerant passing through the second flow channel  620 . As a result, the amount of refrigerant flowing when the third flow channel  630  is opened may be greater than that of refrigerant flowing when the second flow channel  620  is opened. 
         [0130]    Accordingly, in the refrigerator, to which a cooling system using two-stage compression is applied, the control state of the valve device  600  can be changed according to the load of the refrigerator. More specifically, if the load of the refrigerator is high and thus refrigerant flows in the third flow channel  630 , heat exchange in the intermediate heat exchange units  430  and  530  is not performed and the amount of refrigerant flowing into the second evaporator  550  through the third flow channel  630  may increase. As a result, since the load of the freezing-compartment cycle  60  is not shifted to the refrigerating-compartment cycle  50 , it is possible to rapidly perform cooling of the refrigerating compartment. 
         [0131]    In some implementations, if the load of the refrigerator is low and thus the refrigerant flows into the second flow channel  250 , the amount of refrigerant flowing into the second evaporator  250  may slightly decrease but the load of the load of the freezing-compartment cycle  60  is shifted to the refrigerating-compartment cycle  50 , thereby improving the supercooling degree of the freezing-compartment cycle  60 . 
         [0132]    The second suction pipe  555  and the freezing-compartment expansion devices  520 ,  540  and  575  may exchange heat with each other. The second suction pipe  555  and the freezing-compartment expansion devices  520 ,  540  and  575  may be coupled to each other through soldering. By heat exchange, the supercooling degree of the refrigerant flowing in the freezing-compartment expansion devices  520 ,  540  and  575  and the overheating degree of the refrigerant flowing in the second suction pipe  555  can be improved. 
         [0133]    The second suction pipe  555  and the freezing-compartment expansion devices  520 ,  540  and  575  form a second suction line heat exchange unit  560 .