Abstract:
A refrigerating apparatus for keeping an inside of a storage at a predetermined low-temperature state includes first and second refrigerant circuits including compressors, condensers, decompressors, and evaporators, connected circularly with pipings to form refrigerating cycles, the circuit having a first or second refrigerant sealed therein as a working refrigerant, a first sensor which detects a temperature of a cascade condenser constituted by integrating the evaporator of the first refrigerant circuit and the condenser of the second refrigerant circuit in a heat exchangeable manner, first and second controllers which control operation performances of the first and second compressors in a variable manner based on first and second sensor detected temperatures in order that the first and second sensor detected temperatures are first and second temperatures, respectively, and a second sensor which detects a temperature inside the storage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of International Patent Application No. PCT/JP2009/066118 filed Sep. 16, 2009, which claims the benefit of priority to Japanese Patent Application Nos. 2008-237039 and 2009-211299, filed Sep. 16, 2008 and filed Sep. 14, 2009, respectively. The full contents of the International Patent Application are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a refrigerating apparatus. 
     2. Description of the Related Art 
     As a refrigerating apparatus configured to cool an inside of a low-temperature storage which stores storage objects such as refrigerated articles, for example, a dual refrigerating apparatus is known. The dual refrigerating apparatus includes a high-temperature side refrigerant circuit in which a first refrigerant is sealed and a low-temperature side refrigerant circuit in which a second refrigerant whose boiling point is lower than that of the first refrigerant is sealed. Also, an evaporator of the high-temperature side refrigerant circuit (hereinafter referred to as a high-temperature side evaporator) and a condenser of the low-temperature side refrigerant circuit (hereinafter referred to as a low-temperature side condenser) form a cascade condenser so as to mutually exchange heat. As a result, the second refrigerant is condensed by a cooling effect of the high-temperature side refrigerant circuit and the inside of the storage is cooled by the cooling effect of the low-temperature side refrigerant circuit. A cooling temperature inside the storage is detected by a sensor. In accordance with the detected cooling temperature of the inside of the storage, rotation speeds of a compressor of the high-temperature side refrigerant circuit (hereinafter referred to as a high-temperature side compressor) and a compressor of the low-temperature side refrigerant circuit (hereinafter referred to as a low-temperature side compressor) are controlled, respectively, and the inside of the storage is brought to a target cooling temperature (e.g., see Japanese Patent Laid-Open No. 5-142294). 
     In a case where control is made in such a manner that the cooling temperature inside the storage becomes constant, a temperature of the cascade condenser is preferably at a constant temperature. However, if specifications of the high-temperature side compressor and the low-temperature side compressor are different or their performances vary even if the specifications are the same, despite the fact that operations of the both compressors are simultaneously controlled by a detection output of the sensor, timings at which an evaporation temperature of the high-temperature side evaporator and a condensation temperature of the low-temperature side condenser are changed might not match, or rates of the change of the evaporation temperature of the high-temperature side evaporator and the condensation temperature of the low-temperature side condenser might be biased more than necessary. In this case, if the cooling temperature inside the storage changes, there was a possibility that time required until the temperature of the cascade condenser comes to a constant temperature becomes longer and the time until the cooling temperature in the storage comes to the constant temperature becomes longer. 
     SUMMARY OF THE INVENTION 
     A refrigerating apparatus, which keeps a temperature inside a storage at a predetermined low-temperature state, according to an aspect of the present invention, comprises:
         a first refrigerant circuit including a first compressor, a first condenser, a first decompressor, and a first evaporator, connected circularly with a first piping to form a refrigerating cycle, the first refrigerant circuit having a first refrigerant sealed therein as a working refrigerant;   a second refrigerant circuit including a second compressor, a second condenser, a second decompressor, and a second evaporator, connected circularly with a second piping to form a refrigerating cycle, the second refrigerant circuit having a second refrigerant sealed therein as a working refrigerant;   a first sensor configured to detect a temperature of a cascade condenser constituted by integrating the first evaporator and the second condenser in a heat exchangeable manner;   a first controller configured to control an operation performance of the first compressor in a variable manner based on the temperature detected by the first sensor in order that the temperature detected by the first sensor is a first temperature;   a second sensor configured to detect a temperature inside the storage; and   a second controller configured to control an operation performance of the second compressor in a variable manner based on the temperature detected by the second sensor in order that the temperature detected by the second sensor is a second temperature.       

     The present invention has an object to improve controllability of a temperature inside the storage. 
     Other features of the present invention will become apparent from descriptions of this specification and of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For more thorough understanding of the present invention and advantages thereof, the following description should be read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a front view of a refrigerating apparatus  1  according to an embodiment; 
         FIG. 2  is a side view of the refrigerating apparatus  1  in  FIG. 1  when seen from the right side (−X side in  FIG. 1 ); 
         FIG. 3  is a circuit diagram illustrating an example of a refrigerant circuit  100  according to the embodiment; 
         FIG. 4  is a block diagram illustrating an example of a control circuit  200  according to the embodiment; 
         FIG. 5  is a flowchart illustrating an example of a processing procedure of a microcomputer  210  in a case where the refrigerating apparatus  1  controls a rotation speed of a first compressor  111  in accordance with a temperature of a cascade condenser  130 ; and 
         FIG. 6  is a flowchart illustrating an example of the processing procedure of the microcomputer  210  in a case where the refrigerating apparatus  1  controls a rotation speed of a second compressor  121  in accordance with a temperature inside the storage. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     At least the following details will become apparent from descriptions of this specification and of the accompanying drawings. 
     Configuration of the Refrigerating Apparatus 
     &lt;Overall Configuration&gt; 
     An example of an overall configuration of a refrigerating apparatus  1  according to the present embodiment will be described with reference to  FIGS. 1 and 2 .  FIG. 1  is a front view of the refrigerating apparatus  1  according to this embodiment.  FIG. 2  is a side view illustrating the refrigerating apparatus  1  in  FIG. 1  when seen from the right side (−X side in  FIG. 1 ). 
     The refrigerating apparatus  1  includes an insulation housing  2  having an opening in a front face (+Y side face), an insulation door  3  configured to open and close the opening of the insulation housing  2 , and a machine chamber  4  at a lower side (−Z side) of the insulation housing  2 . 
     The insulation housing  2  includes an outer box  21  and an inner box  22  which are made of metal, for example, and a foaming insulation material (not shown) including an insulation material made of a synthetic resin or a vacuum insulation material. The inner box  22  has an opening in a front face and stores refrigerated articles or the like inside. The inside of the inner box  22  will be referred to as an inside the storage. The outer box  21  has an opening in a front face and accommodates the inner box  22  inside. The foaming insulation material is filled between the outer box  21  and the inner box  22  and improves an insulation effect inside the storage. The inner box  22  is provided with an inner door  23  configured to open and close the opening thereof. The inner door  23  is made of a resin, for example, and improves the insulation effect inside the storage. 
     The insulation door  3  has an outer plate  32  and an inner plate  31  which are made of metal, for example, and is configured in such a manner that a foaming insulation material (not shown) is filled in a space between the two plates  31  and  32 . The insulation door  3  opens and closes the opening of the insulation housing  2  through a hinge  33 . On the insulation door  3 , a handle  34  with which a user opens and closes the door  3  is provided. The handle  34  has a lock mechanism (not shown) for fixing a state in which the insulation door  3  closes the opening of the insulation housing  2  or for releasing the fixation. Also, on a front face of the outer plate  32  of the insulation door  3 , a control panel  35  is provided. The control panel  35  has a control board  201 , a keyboard  35   a , a display  35   b  and the like, which will be described later. The keyboard  35   a  is configured to set a temperature inside the storage (second temperature, for example, which will be described later) by a user, for example, and the display  35   b  is configured to display this temperature setting, for example. 
     In the machine chamber  4 , a refrigerant circuit  100  excluding a second evaporator  125 , which will be described later, is accommodated. As exemplified by a dot line in  FIG. 2 , a pipe made of, for example, copper or aluminum which forms the second evaporator  125  is attached to an outer face of the inner box  22  in a thermally conductive manner and cools the inside of the inner box  22  with a heat absorption action which occurs when a refrigerant is evaporated by the second evaporator  125 . 
     &lt;Refrigerant Circuit and Control Circuit&gt; 
     A configuration example of the refrigerant circuit  100  and a control circuit  200  provided in the refrigerating apparatus  1  according to this embodiment will be described below with reference to  FIGS. 3 and 4 .  FIG. 3  is a circuit diagram illustrating an example of the refrigerant circuit  100  according to the present embodiment.  FIG. 4  is a block diagram illustrating an example of the control circuit  200  according to the present embodiment. 
     The refrigerant circuit  100  includes, as exemplified in  FIG. 3 , a first refrigerant circuit  110  in which a first refrigerant is sealed and a second refrigerant circuit  120  in which a second refrigerant whose boiling point (evaporation temperature) is lower than that of the first refrigerant is sealed. 
     The first refrigerant circuit  110  includes a first compressor  111  configured to compress the first refrigerant to a high-temperature/high-pressure gas refrigerant and to discharge it, a first upstream-stage condenser (first condenser)  112  and a first downstream-stage condenser (first condenser)  113  which are configured to cool the first refrigerant discharged from the first compressor  111  and to condense it to a low-temperature and high-pressure refrigerant, a first decompressor (flow-passage variable valve, a capillary tube and the like)  114 , and a first evaporator  115  configured to evaporate the first refrigerant which has been brought to a low-temperature and high-pressure, which are connected circularly with a first piping  116 . 
     A suction side of the first compressor  111  is connected to the first evaporator  115 , and a discharge side of the first compressor  111  is connected to the first upstream-stage condenser  112 . In  FIGS. 3 and 4 , “H” means a high-temperature side compressor representing the first compressor  111  in the first refrigerant circuit  110 , while “L” means a low-temperature side compressor (a second compressor  121  in the second refrigerant circuit  120 ), which will be described later. 
     The first upstream-stage condenser  112  is a condenser formed by meandering a pipe made of, for example, copper or aluminum which is configured to cool the first refrigerant compressed by the first compressor  111  and may be formed as a portion of the first condenser. The first upstream-stage condenser  112  may be used as a heat source for evaporating drain water generated from the evaporator or used as a heat source for preventing condensation on a portion where the insulation door  3  or the inner door  23  or the like is in contact with the outer box  21  and the inner box  22 . 
     The first downstream-stage condenser  113  is a condenser formed by meandering a pipe made of, for example, copper or aluminum, which is configured to further cool the first refrigerant which radiated heat in the first upstream-stage condenser  112  and whose temperature has been decreased. 
     To the first upstream-stage condenser  112  and the first downstream-stage condenser  113 , air is blown by, for example, a fan  118  having a fan motor  117  which will be described later, through a filter (not shown) for removing dusts. As a result, heat radiation from the first refrigerant to the air in the condensers  112  and  113  is promoted, and the refrigerant is condensed in the first downstream-stage condenser  113  and becomes a low-temperature and high-pressure refrigerant. 
     A first decompressor  114  is, for example, a capillary tube configured to decompress the first refrigerant which has been condensed by the first downstream-stage condenser  113 . A flow-rate control valve capable of adjusting a flow rate of the refrigerant may be used. 
     The first evaporator  115  is an evaporator configured to evaporate the first refrigerant which has been decompressed by the first decompressor  114  and forms a cascade condenser  130  together with a second downstream-stage condenser  123  of the second refrigerant circuit  120 . The cascade condenser  130  is constituted by integrating the first evaporator  115  and the second downstream-stage condenser  123  in a heat exchangeable manner, and a double tube or a plate-shaped heat exchanger may be used, for example. That is, by means of a heat absorption action which occurs when the first refrigerant is evaporated by the first evaporator  115 , the second refrigerant of the second downstream-stage condenser  123  is cooled. The first refrigerant is evaporated by the first evaporator  115  and then, is circulated through the first refrigerant circuit  110  by being sucked into the first compressor  111  again. 
     Substantially similarly to the first refrigerant circuit  110 , the second refrigerant circuit  120  includes the second compressor  121 , a second upstream-stage condenser  122 , the second downstream-stage condenser (second condenser)  123 , a second decompressor  124 , and the second evaporator  125 , which are circularly connected by a second piping  126 . 
     The second compressor  121  compresses the second refrigerant. The second upstream-stage condenser  122  has a configuration similar to that of the first upstream-stage condenser of the first refrigerant circuit  110  and works similarly. The second downstream-stage condenser  123  forms a part of the above-mentioned cascade condenser  130  and is cooled by a heat absorption action of the first refrigerant evaporated by the first evaporator. The second decompressor  124  has a configuration similar to that of the first decompressor  114  of the first refrigerant circuit  110  and works similarly. The second evaporator  125  evaporates the second refrigerant decompressed by the second decompressor  124 . By means of the heat absorption action which occurs when the second refrigerant is evaporated by the second evaporator  125 , the inside of the storage is cooled through the inner box  22 . The second refrigerant is evaporated by the second evaporator  125  and then, is circulated through the second refrigerant circuit  120  by being sucked into the second compressor  121  again. 
     The above-mentioned refrigerant circuit  100  is controlled by the control circuit  200 . The control circuit  200  has, as exemplified in  FIG. 4 , a first sensor  206 , a second sensor  207 , the control board  201  on which the microcomputer  210  is mounted, a first inverter  204 , and a second inverter  205 . 
     The first sensor  206  detects a temperature of the cascade condenser  130 . A temperature detected by the first sensor  206  is hereinafter referred to as a first detected temperature. The first sensor  206  is mounted so as to detect a piping temperature in the vicinity of an outlet of the first evaporator  115  constituting the cascade condenser  130  or a temperature of the first refrigerant in the vicinity of the outlet. The temperature sensor  206  may be mounted in such a manner that a temperature of the first refrigerant in the first evaporator  115  constituting the evaporator in the cascade condenser  130 , that is, an evaporation temperature of the first refrigerant can be detected. Also, it is possible to modify control, which will be described below, on the basis of a temperature difference between a temperature of the piping (or the first refrigerant) in the vicinity of an inlet of the first evaporator and a temperature of the piping (or the first refrigerant) in the vicinity of the outlet thereof, and it is also possible to use a temperature of the piping (or the first refrigerant) in the vicinity of the inlet of the evaporator, a temperature of the piping (or the first refrigerant) in the vicinity of the inlet of the second downstream-stage condenser  123 , and a temperature of the piping (or the first refrigerant) in the vicinity of the outlet thereof. 
     The second sensor  207  detects a temperature inside the storage. A temperature detected by the second sensor  207  will be hereinafter referred to as a second detected temperature. 
     The microcomputer  210  mounted on the control board  201  compares the first detected temperature with a first temperature determined in advance and outputs a first control signal for controlling the number of revolutions of the first compressor  111  to the first inverter  204  in accordance with a comparison result. Also, the microcomputer  210  compares the second detected temperature with a second temperature determined in advance and outputs a second control signal for controlling the number of revolutions of the second compressor  121  to the second inverter  205  in accordance with a comparison result. The control board  201  is supplied with electric power from a switching power source  202  and the switching power source  202  is supplied with electric power through a power cable  203 . 
     The first inverter  204  converts a single-phase alternating-current voltage from the power cable  203  to a three-phase alternating-current voltage and applies it to a three-phase coil motor (not shown) of the first compressor  111 . The first inverter  204  has a configuration in which a plurality of power transistors (not shown) and the like configured to supply power to the first compressor  111  are connected in a three-phase bridge state, for example. When each of the plurality of power transistors is turned on/off by the above-mentioned first control signal, the number of revolutions of the first compressor  111  is controlled. That is, by means of the first inverter  204  and the microcomputer  210  (the first controller), the number of revolutions of the first compressor  111  is controlled in order that the temperature of the cascade condenser  130  is the above-mentioned first temperature. 
     The second inverter  205  converts the single-phase alternating-current voltage from the power cable  203  to the three-phase alternating-current voltage and applies it to a three-phase coil motor (not shown) of the second compressor  121 . Similarly to the first inverter  204 , the second inverter  205  includes a plurality of power transistors (not shown) and the like configured to supply power to the second compressor  121 , for example. When each of the plurality of power transistors is turned on/off by the above-mentioned second control signal, the number of revolutions of the second compressor  121  is controlled. That is, by means of the second inverter  205  and the microcomputer  210  (the second controller), the number of revolutions of the second compressor  121  is controlled in order that the temperature inside the storage is the above-mentioned second temperature. 
     According to the exemplification in  FIG. 4 , the control circuit  200  further has a third sensor  208  and a fourth sensor  209 . The third sensor  208  detects a temperature around the first upstream-stage condenser  112  and the first downstream-stage condenser  113 , for example. The fourth sensor  209  is a filter sensor configured to detect clogging of the above-mentioned filter which is configured to remove dusts. The microcomputer  210  determines a failure of the fan motor  117  or the like on the basis of a detection result of the third sensor  208  and the fourth sensor  209  and notifies the result to a user through the display  35   b  or the like, for example. 
     &lt;Operation of the Refrigerating Apparatus&gt; 
     An operation of the refrigerating apparatus  1  provided with the above-mentioned configuration will be described below with reference to  FIGS. 5 and 6 .  FIG. 5  is a flowchart illustrating an example of a processing procedure of the microcomputer  210  with which the refrigerating apparatus  1  controls the number of revolutions of the first compressor  111  in accordance with the temperature (first detected temperature) of the cascade condenser  130 .  FIG. 6  is a flowchart illustrating an example of the processing procedure of the microcomputer  210  with which the refrigerating apparatus  1  controls the number of revolutions of the second compressor  121  in accordance with the temperature (second detected temperature) inside the storage. 
     As exemplified in  FIG. 5 , when the refrigerating apparatus  1  is powered on through the power cable  203 , the microcomputer  210  first drives the first compressor  111  at a predetermined number of revolutions (S 100 ). Since the first refrigerant starts circulating through the first refrigerant circuit  110  by the operation of the first compressor  111 , the temperature of the cascade condenser  130  is decreased by the cooling action which occurs when the first refrigerant is evaporated by the first evaporator  115 . 
     Subsequently, the microcomputer  210  compares the first detected temperature and the first temperature and determines whether or not the first detected temperature is lower than or equal to the first temperature (S 101 ). The first temperature is a temperature determined in advance by a type of the second refrigerant or performance (efficiency or specification) or the like of the second compressor  121 , and specifically, it is a temperature of the cascade condenser  130  optimal for condensing the second refrigerant by the second downstream-stage condenser  123 . 
     If it is determined that the first detected temperature is higher than the first temperature (S 101 : NO), the microcomputer  210  executes the process of Step  101  again. 
     If it is determined that the first detected temperature is lower than or equal to the first temperature (S 101 : YES), the microcomputer  210  drives the second compressor  121  at a predetermined number of revolutions (S 102 ). 
     In this way, first, the first compressor  111  is started up, and when the first detected temperature becomes lower than or equal to the first temperature, the second compressor  121  is started up so that the second refrigerant in the cascade condenser  130  is cooled and can easily reach a predetermined temperature range. Thus, the temperature inside the storage can also easily reach a predetermined temperature mentioned below. 
     In a case where the second refrigerant starts circulating in the second refrigerant circuit  120  by the operation of the second compressor  121 , since the high-temperature second refrigerant is fed to the second downstream-stage condenser  123 , it works to increase the temperature of the cascade condenser  130 . On the other hand, since the second refrigerant is cooled by exchanging heat with the first refrigerant evaporated in the first evaporator  115 , it works to decrease the temperature of the cascade condenser  130 . The processing by the microcomputer  210 , which will be described below, is to maintain the temperature of the condenser  130  in the predetermined temperature range around the first temperature by controlling the latter action to decrease the temperature of the cascade condenser  130  through the first compressor  111 . 
     The microcomputer  210  compares the first detected temperature and a predetermined temperature higher than the first temperature (first temperature+α) and determines whether the first detected temperature is higher than “first temperature+α” or not (S 103 ). “First temperature+α” is a high-temperature side temperature in the temperature range suitable for condensing the second refrigerant in the cascade condenser  130 , for example. 
     If it is determined that the first detected temperature is higher than “first temperature+α” (S 103 : YES), the microcomputer  210  outputs the first control signal for raising the number of revolutions of the first compressor  111  to the first inverter  204  (S 104 ) and executes the process of Step S 103  again. As a result, an amount of the first refrigerant discharged per unit time from the first compressor  111  is increased and an evaporation amount of the refrigerant is increased, cooling capability of the first refrigerant circuit  110  is increased, and the temperature of the cascade condenser  130  is decreased toward an evaporation temperature of the first refrigerant. The microcomputer  210  repeatedly executes the process of Step S 103 : YES and S 104  until the first detected temperature becomes lower than or equal to “first temperature+α”. 
     If it is determined that the first detected temperature is lower than or equal to “first temperature+α” (S 103 : NO), the microcomputer  210  compares the first detected temperature and a predetermined temperature lower than the first temperature (first temperature−α) and determines whether or not the first detected temperature is lower than “first temperature−α” (S 105 ). “First temperature−α” is a low-temperature side temperature in the temperature range suitable for sufficiently condensing the second refrigerant in the cascade condenser  130 , for example. That is, in condensing the second refrigerant, the temperature of the cascade condenser  130  does not have to be lower than “first temperature−α”, and a value of α in “first temperature−α” may be the same value as or a different value from α which gives the above-mentioned upper-limit temperature of the cascade condenser  130 . 
     If it is determined that the first detected temperature is lower than “first temperature−α” (S 105 : YES), the microcomputer  210  outputs the first control signal for decreasing the number of revolutions of the first compressor  111  to the first inverter  204  (S 106 ) and executes the process of Step S 103  again. As a result, the amount of the first refrigerant discharged per unit time from the first compressor  111  is decreased and the cooling capability of the first refrigerant circuit  110  is lowered, and if the amount of the second refrigerant flowing through the second downstream-stage condenser  123  is large, the temperature of the cascade condenser  130  is increased. That is, the temperature of the first refrigerant gasified by the first evaporator  115  is increased by receiving radiation from the second downstream-stage condenser. The microcomputer  210  repeatedly executes the process of Step S 103 : NO, S 105 : YES, and S 106  until the first detected temperature becomes higher than or equal to “first temperature−α”. 
     If it is determined that the first detected temperature is higher than or equal to “first temperature−α” (S 105 : NO), the microcomputer  210  executes the process of Step S 103  again. That is, while the first detected temperature is maintained higher than or equal to “first temperature−α” and lower than or equal to “first temperature+α”, the microcomputer  210  repeatedly executes the process of Step S 103 : NO and S 105 : NO. 
     From the above, the temperature of the cascade condenser  130  is maintained in a temperature range suitable for condensing the second refrigerant by controlling the number of revolutions of the first compressor  111 . The temperature range is set in advance according to characteristics of the second refrigerant and the like, for example. If the condensation temperature of the second refrigerant is stable in such a temperature range, by slightly controlling the operation of, for example, the second compressor  121 , the evaporation temperature of the second evaporator  125  in the second refrigerant circuit  120  can be controlled to a constant temperature, and the temperature inside the storage can also be made stable with respect to load fluctuation in the storage. 
     In parallel with the above-mentioned process, the microcomputer  210  executes the following process in order to control the operation of the second compressor  121  whose driving has been started at Step S 102 . 
     As exemplified in  FIG. 6 , the microcomputer  210  compares the second detected temperature and a predetermined temperature higher than the second temperature (second temperature+α) and determines whether or not the second detected temperature is higher than “second temperature+α” (S 200 ). Here, “second temperature+α” is a cooling temperature inside the storage which is to be an upper limit when the inside of the storage is maintained in a predetermined temperature range around the second temperature. A value of α in “second temperature+α” may be the same value as or a different value from α which gives the above-mentioned high-temperature side temperature or low-temperature side temperature of the cascade condenser  130 . 
     If it is determined that the second detected temperature is higher than “second temperature+α” (S 200 : YES), the microcomputer  210  outputs a second control signal for increasing the number of revolutions of the second compressor  121  to the second inverter  205  (S 201 ) and executes the process of Step S 200  again. As a result, the amount of the second refrigerant discharged per unit time from the second compressor  121  is increased and the cooling capability of the second refrigerant circuit  120  is increased. The microcomputer  210  repeatedly executes the process of Step S 200 : YES and S 201  until the second detected temperature becomes less than or equal to “second temperature+α”. 
     If it is determined that the second detected temperature is less than or equal to “second temperature+α” (S 200 : NO), the microcomputer  210  compares the second detected temperature and a predetermined temperature lower than the second temperature (second temperature−α) and determines whether or not the second detected temperature is lower than “second temperature−α” (S 202 ). “Second temperature−α” is a lower-limit temperature in the above-mentioned predetermined temperature range, for example. A value of α in “second temperature−α” may be the same value as or a different value from α to give the above-mentioned upper-limit temperature in the predetermined temperature range. 
     If it is determined that the second detected temperature is lower than “second temperature−α” (S 202 : YES), the microcomputer  210  outputs the second control signal for decreasing the number of revolutions of the second compressor  121  to the second inverter  205  (S 203 ) and executes the process of Step S 200  again. As a result, the amount of the second refrigerant discharged per unit time from the second compressor  121  is decreased and the cooling capability of the second refrigerant circuit  120  is lowered. The microcomputer  210  repeatedly executes the process of Step S 200 : NO, S 202 : YES, and S 203  until the second detected temperature becomes higher than or equal to “second temperature−α”. 
     If it is determined that the second detected temperature is higher than or equal to “second temperature−α” (S 202 : NO), the microcomputer  210  executes the process of Step S 200  again. That is, while the second detected temperature is maintained higher than or equal to “second temperature−α” and lower than or equal to “second temperature+α”, the microcomputer  210  repeatedly executes the process of Step S 200 : NO and S 202 : NO. 
     As mentioned above, in a state in which the temperature of the cascade condenser  130  is maintained in the temperature range suitable for condensing the second refrigerant by the above-mentioned process in  FIG. 5 , by controlling the number of revolutions of the second compressor  121  in accordance with the process in  FIG. 6 , the temperature inside the storage is maintained in the predetermined temperature range on the basis of the specification of the refrigerating apparatus  1 . That is, the cooling temperature of the second refrigerant circuit  120  can reach the constant temperature more quickly. 
     The above embodiments of the present invention are simply for facilitating the understanding of the present invention and are not in any way to be construed as limiting the present invention. The present invention may variously be changed or altered without departing from its spirit and encompass equivalents thereof.