Patent Publication Number: US-11384975-B2

Title: Refrigerator and control method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage application under 35 U.S.C. § 371 of International Application No. PCT/KR2017/012729, filed on Nov. 10, 2017, which claims the benefit of Korean Application No. 10-2016-0149484, filed on Nov. 10, 2016. The disclosures of the prior applications are incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a refrigerator and a control method thereof, and more particularly, to a refrigerator capable of determining a time to defrost an evaporator using a plurality of temperature sensors and a control method thereof. 
     BACKGROUND ART 
     In general, a refrigerator includes a machinery compartment, which is located at the lower part of a main body of the refrigerator. The machinery compartment is generally installed at the lower part of the refrigerator in consideration of the center of gravity of the refrigerator and in order to improve assembly efficiency and to achieve vibration reduction. 
     A refrigeration cycle device is installed in the machinery compartment of the refrigerator in order to keep the interior of the refrigerator frozen/refrigerated using the property of a refrigerant, which absorbs external heat when a low-pressure liquid refrigerant is changed to a gaseous refrigerant, whereby food is kept fresh. 
     The refrigeration cycle device of the refrigerator includes a compressor for changing a low-temperature, low-pressure gaseous refrigerant to a high-temperature, high-pressure gaseous refrigerant, a condenser for changing the high-temperature, high-pressure gaseous refrigerant, changed by the compressor, to a low-temperature, low-pressure liquid refrigerant, and an evaporator for changing the low-temperature, high-pressure liquid refrigerant, changed by the condenser, to a gaseous refrigerant in order to absorb external heat. Of course, the evaporator is installed in a separate space, not in the machinery compartment. 
     Operation of the evaporator cause heat exchange with the air inside the storage compartment to cool the air inside the storage compartment, and ice is formed on the evaporator over time. A heater may be periodically driven to remove the ice, but frequent operation of the heater only increases power consumption. 
     In this regard, it is necessary to reduce power consumption in the refrigerator by increasing reliability of determination of the ice removal time to remove ice formed on the evaporator. 
     DISCLOSURE 
     Technical Problem 
     An object of the present invention devised to solve the problem lies on a refrigerator capable of improving reliability of determination of a defrosting time, and a control method thereof. 
     Technical Solution 
     The object of the present invention can be achieved by providing a refrigerator including a cabinet having a storage compartment, a chamber having an evaporator configured to cool air, a discharge duct through which cold air heat-exchanged by the evaporator is supplied to the storage compartment, and an introduction duct through which air in the storage compartment is guided to the evaporator, a first temperature sensor configured to measure a temperature of the evaporator, a second temperature sensor configured to measure a temperature of the storage compartment, a third temperature sensor configured to measure a temperature of the air supplied from the chamber to the storage compartment, and a controller configured to determine a time to defrost the evaporator based on the temperatures measured by the first temperature sensor, the second temperature sensor, and the third temperature sensor. 
     The refrigerator may further include a heater configured to supply heat to the evaporator to defrost the evaporator, wherein the controller may derive the heater when defrosting is started. 
     The first temperature sensor may be disposed to contact the evaporator. 
     The first temperature sensor may be disposed at a portion of a duct positioned in the chamber, the duct guiding a refrigerant to the evaporator. 
     The first temperature sensor may be positioned at a corresponding portion within half of an entire path of movement of the refrigerant in the evaporator after the refrigerant is moved to the evaporator. 
     The second temperature sensor may measure a temperature of the air flowing into the chamber from the storage compartment. 
     The second temperature sensor may be installed in the storage compartment. 
     The second temperature sensor may be installed at an introduction port through which the introduction duct contacts the storage compartment. 
     The third temperature sensor may be disposed at a discharge port through which the discharge duct contacts the storage compartment. 
     The discharge duct may be provided with a fan configured to guide the air in the chamber to the storage compartment. 
     The third temperature sensor may be disposed between the discharge port and the fan, the discharge duct contacting the storage compartment through the discharge port. 
     The set value may be measured after defrosting of the evaporator is terminated. 
     The set value may be measured with a compressed refrigerant supplied to the evaporator. 
     In another aspect of the present invention, provided herein is a method for controlling a refrigerator, including a first defrosting step of defrosting an evaporator, an operation step of supplying a compressed refrigerant to the evaporator to cool a storage compartment, and a second defrosting step of defrosting the evaporator, wherein the operation step includes a first step of setting a set value based on values measured by a first temperature sensor configured to measure a temperature of the evaporator, a second temperature sensor configured to measure a temperature of the storage compartment, and a third temperature sensor configured to measure a temperature of air supplied from a chamber to the storage compartment, and a second step of determining whether the measured values have reach the set value, wherein, when the set value is reached in the second step, the operation step is terminated and the second defrosting step is performed. 
     A heater configured to heat the evaporator may be driven in the first defrosting step and the second defrosting step. 
     The first temperature sensor may be positioned at a corresponding portion within half of an entire path of movement of the refrigerant in the evaporator after the refrigerant is moved to the evaporator. 
     The second temperature sensor may be installed at an introduction port through which an introduction duct contacts the storage compartment, air in a storage compartment being guided to the evaporator through the introduction duct. 
     A fan may be provided in a discharge duct, cold air heat-exchanged by the evaporator being supplied to the storage compartment through the discharge duct, wherein the third temperature sensor may be disposed between a discharge port and the fan, the discharge duct contacting the storage compartment through the discharge port. 
     The first defrosting step may be terminated when the temperature measured by the first temperature sensor reaches a set temperature. 
     The second defrosting step may be terminated when the temperature measured by the first temperature sensor reaches a set temperature. 
     Advantageous Effects 
     According to the present invention, a defrosting time, which is a time when ice formed on an evaporator is to be removed, may be accurately determined. After defrosting is performed, heat exchange efficiency of the evaporator may be improved, and thus cooled air may be smoothly supplied into the storage compartment. 
     When defrosting is not required, the heater may not be driven, thereby preventing energy from being excessively consumed. The energy consumed in the entire refrigerator may be reduced, thereby improving the overall energy efficiency of the refrigerator. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a front view of a refrigerator with doors opened according to an embodiment of the present invention. 
         FIG. 2  is a schematic view showing main parts of the present invention. 
         FIG. 3  is a control block diagram according to an embodiment of the present invention. 
         FIG. 4  depicts change in temperature according to the amount of ice formed on an evaporator. 
         FIG. 5  illustrates a method of calculating a set value. 
         FIG. 6  is a diagram illustrating a control flow according to an embodiment. 
         FIG. 7  is a view illustrating an installation position of a first temperature sensor. 
     
    
    
     BEST MODE 
     Generally, a refrigerator is an appliance that defines a food storage space capable of blocking infiltration of heat from the outside by a cabinet and doors, the inside of which is filled with an insulation material, and has a refrigeration device, which includes an evaporator configured to absorb heat from the food storage space and a heat dissipation device configured to dissipate collected heat out of the food storage space. The food storage space is maintained in a low temperature range, where the microorganisms are difficult to survive and proliferate, in order to keep the stored food in good condition for a long time. 
     The refrigerator is divided into a refrigeration compartment for storing food at a temperature above zero and a freezer compartment for storing food at a temperature below zero. Refrigerators are classified into a top freezer refrigerator, which has a freezer compartment on a refrigeration compartment, and a bottom freezer refrigerator, which has a freezer compartment under a refrigeration compartment, and a side-by-side refrigerator, which has a freezer compartment and a refrigeration compartment on the left and right sides, depending on arrangement of the refrigeration compartment and the freezer compartment. 
     To allow a user to place food in the food storage space or retrieve stored food from the food storage space with ease, the refrigerator is provided with multiple shelves and drawers in the food storage space. 
     Hereinafter, preferred embodiments of the present invention capable of realizing the above object will be described with reference to the accompanying drawings. 
     It will be appreciated that for simplicity and clarity of illustration, the dimensions or shapes of some of the elements shown in the drawings may be exaggerated. In addition, terms specifically defined in consideration of the configuration and operation of the present invention may be replaced by other terms based on intensions of the user or operator, customs, or the like. The terms used herein should be construed based on the whole content of this specification. 
       FIG. 1  is a front view of a refrigerator with doors opened according to an embodiment of the present invention. 
     The refrigerator according to an embodiment is equally applicable to a top mount-type refrigerator in which a freezer compartment and a refrigeration compartment for storing food are partitioned into upper and lower parts such that the freezer compartment is disposed on the refrigeration compartment, and a side-by-side-type refrigerator in which a freezer compartment and a refrigeration compartment are partitioned into left and right parts. 
     In this embodiment, descriptions will be given based on a bottom freezer-type refrigerator in which a freezer compartment and a refrigeration compartment are partitioned into upper and lower parts such that the freezer compartment is disposed under the refrigeration compartment. 
     The cabinet of the refrigerator includes an outer case  10  for defining an overall outer appearance of the refrigerator seen to the user and an inner case  12  for defining a storage compartment  22  in which food is stored. A predetermined space may be formed between the outer case  10  and the inner case  12  to provide a passage through which cooled air can circulate. In addition, an insulation material may fill the space between the outer case  10  and the inner case  12  to maintain the interior of the storage compartment  22  at a low temperature, compared to the exterior of the storage compartment  22 . 
     In addition, a refrigeration cycle device configured to circulate a refrigerant to cool the air is installed in a machinery compartment (not shown) formed in the space between the outer case  10  and the inner case  12 . The refrigeration cycle device may be used to maintain the interior of the refrigerator at a low temperature to maintain the food stored in the refrigerator in a fresh state. The refrigeration cycle device may include a compressor configured to compress the refrigerant. 
     The refrigerator is provided with doors  20  and  30  for opening and closing the storage compartment. Herein, the doors may include a freezer compartment door  30  and a refrigeration compartment door  20 . One end of each of the doors is pivotably installed at the cabinet of the refrigerator. There may be a plurality of freezer compartment doors  30  and a plurality of refrigeration compartment doors  20 . That is, as shown in  FIG. 1 , the freezer compartment doors  30  and the refrigeration compartment doors  20  may be installed so as to be opened forward about both edges of the refrigerator. 
     The space between the outer case  10  and the inner case  12  may be filled with a foaming agent to insulate the storage compartment  22 . 
     An insulated space is formed in the storage compartment  22  by the inner case  12  and the doors  20 . Once the storage compartment  22  is closed by the doors  20 , an isolated and insulated space may be formed therein. In other words, the storage compartment  22  may be a space isolated from the outside by an insulation wall formed by the doors  20  and an insulation wall formed by the cases  10  and  12 . 
     Since cooled air can flow around in the storage compartment  22 , food stored in the storage compartment  22  may be maintained at a low temperature. 
     The storage compartment  22  may include a shelf  40  on which food items are placed. Herein, the storage compartment  22  may include a plurality of shelves  40 , and food items may be placed on each of the shelves  40 . The shelves  40  may be horizontally arranged to partition the interior of the storage compartment. 
     The storage chamber  22  is provided with a drawer  50  which can be drawn in or drawn out. Food and the like are accommodated and stored in the drawer  50 . Two drawers  50  may be disposed side by side in the storage compartment  22 . The user may open the left door of the storage compartment  22  to reach the drawer disposed on the left side. On the other hand, the user may open the right door of the storage compartment  22  to reach the drawer disposed on the right side. 
     The interior of the storage compartment  22  may be partitioned into a space positioned over the shelves  40 , a space formed by the drawers  50 , and the like. Thereby, a plurality of partitioned spaces to store food may be provided. 
     The cooled air supplied to one storage compartment is not allowed to freely move to the other storage compartments, but it is allowed to freely move to the partitioned spaces in one storage compartment. That is, the cooled air positioned over the shelves  40  is allowed to move into the space formed by the drawers  50 . 
       FIG. 2  is a schematic view showing main parts of the present invention. 
     Referring to  FIG. 2 , a chamber  70  is formed between the inner case  12  and the outer case  10 . 
     The chamber  70  is provided with an evaporator  80 , which is supplied with a compressed refrigerant capable of heat exchange with air to cool the air. The evaporator  80  is provided with a plurality of fins to increase the area of heat exchange with the air. 
     The inner case  12  is provided with the storage compartment  22  in which foods can be stored. The storage compartment  22  is surrounded by the inner case  12  to form a sealed space, such that the food stored therein can be maintained at a low temperature. 
     The chamber  70  is provided with a discharge duct  72  through which the air located in the chamber  70  can be guided to the storage compartment  22 . The discharge duct  72  allows the chamber  70  and the storage compartment  22  to communicate with each other. 
     The exhaust duct  72  may be provided with a fan  140  to generate wind capable of guiding the air inside the chamber  70  to the storage compartment  22 . 
     A discharge port  74  may be formed at a portion where the discharge duct  72  communicates with the storage compartment  22 , and accordingly the air guided through the discharge duct  72  may be introduced into the storage compartment  22  after passing through the discharge port  74 . 
     The chamber  70  is provided with an introduction duct  82  such that the air located in the storage compartment  22  can be moved to the chamber  70 . An introduction port  84  may be formed at a portion where the introduction duct  82  contacts the storage compartment  22 , and accordingly the air in the storage compartment  22  may be guided to the chamber  70  after passing through the introduction port  84  and the introduction duct  82 . 
     The introduction duct  82  may be provided with a separate fan. However, since a pressure change occurs when the fan  140  causes the air in the chamber  70  to be supplied to the storage compartment  22 , air can move from the storage compartment  22  to the chamber  70  even if the introduction duct  82  is not provided with a separate fan. 
     The chamber  70  may be provided with a heater  150  capable of removing ice formed on the evaporator  80 . The heater  150  may generate heat to increase the temperature inside the chamber  70 , such that the temperature of the evaporator  80  can increase. 
     In some implementations, a first temperature sensor  110  configured to measure a temperature T 1  of the evaporator  80  is provided. The first temperature sensor  110  is disposed to be in contact with the evaporator  80  and may thus directly measure the temperature of the evaporator  80 . 
     Since the compressed refrigerant moves in the evaporator  80 , the temperature of the evaporator  80  is lowered while the refrigerant is moving. 
     In addition, a second temperature sensor  120  configured to measure a temperature of the storage compartment  22  is provided. The second temperature sensor  120  may be installed in the storage compartment to measure the temperature of the storage compartment. 
     The second temperature sensor  120  measures the temperature of the air in the storage compartment  22  before the air undergoes heat exchange with the evaporator  80 . 
     Alternatively, the second temperature sensor  120  may be installed at the introduction port  84  through which the introduction duct  82  contacts the storage compartment  22 . The second temperature sensor  120  may measure the temperature of the air flowing into the chamber  70  from the storage compartment  22 . Since the second temperature sensor  120  is fixedly disposed at a specific position, the temperature at the specific position may be measured. 
     When the fan  140  is driven, air in the storage compartment  22  is entirely mixed and guided to the introduction duct  82 . Accordingly, since the air in the storage compartment  22  is guided to the introduction duct  82  after being mixed, the internal temperature of the storage compartment  22  may be measured more accurately even if the second temperature sensor  120  is at a specific position,. 
     The third temperature sensor  130  may be disposed at the discharge port  74  through which the discharge duct  72  contacts the storage compartment  22 . That is, the third temperature sensor  130  may be disposed between the discharge port  74 , through which the discharge duct  72  contacts the storage compartment  22 , and the fan  140 . 
     In the chamber  70 , the air having undergone heat exchange with the evaporator  80  is guided to the discharge duct  72  by the blowing force of the fan  140 , and is finally discharged to the storage compartment  22  through the discharge port  74 . Accordingly, when the third temperature sensor  130  is disposed at the discharge duct  72 , the third temperature sensor  130  may measure the temperature of the air supplied from the chamber  70  to the storage compartment  22 . 
     The third temperature sensor  130  measures the temperature of the air having undergone heat exchange with the evaporator  80 . Since the temperature can be measured while the air having undergone heat exchange with the evaporator  80  and the air that has not undergone heat exchange with the evaporator  80  are mixed with each other by the fan  140 , the temperature of the air before the air is discharged into the storage compartment  22  may be measured. 
     Preferably, the third temperature sensor  130  is installed at a position where the sensor is insensitive to change in flow rate and sensitive to the temperature according to heat exchange with the evaporator  80 . 
       FIG. 3  is a control block diagram according to an embodiment of the present invention. 
     Referring to  FIG. 3 , a controller  100  may receive temperature information measured by the first temperature sensor  110 , the second temperature sensor  120 , and the third temperature sensor  130 . 
     In the conventional technology, defrosting of the evaporator is monotonously performed using information on the time the when user opened the door, the time when the compressor was driven, and the like. Accordingly, defrosting is performed without considering the external environment in which the refrigerator is used or the type of food stored in the refrigerator. 
     Accordingly, an environment where frequent defrosting is required due to more frequent frosting of the evaporator than in other environments, or an environment where frequent defrosting is not necessary due to less frequency frosting of the evaporator than in other environments has not been considered. That is, even if defrosting is not necessary, defrosting may be performed, causing waste of energy. In addition, defrosting may not be performed even when defrosting is needed, which may cause inconvenience to the user. 
     In this embodiment, the execution time for defrosting can be individually determined using the temperature information measured by the first temperature sensor  110 , the second temperature sensor  120 , and the third temperature sensor  130 . Accordingly, the time at which defrosting is required may be more accurately determined. Further, defrosting may not be performed in situations where defrosting is not needed, and thus energy efficiency may be improved. 
     The controller  100  may drive the fan  140 . The fan  140  may be driven when the air cooled by the evaporator  70  is to be supplied to the storage compartment  22  in order to cool the storage compartment  22 . 
     In addition, during the operation of the fan  140 , mixed air moves at positions where the temperature is measured by the second temperature sensor  120  and the third temperature sensor  130 . Accordingly, the temperature may be more accurately measured by the second temperature sensor  120  and the third temperature sensor  130 . 
     The controller  100  drives the heater  150  upon determining that defrosting of the evaporator is necessary. The controller stops driving the heater  150  upon determining that defrosting of the evaporator is completed. 
     The controller  100  drives the compressor  160  to compress the refrigerant upon determining that the storage compartment  22  needs to be cooled. The refrigerant compressed by the compressor  160  may be moved to the evaporator, and thus the air in contact with the evaporator may be cooled. 
       FIG. 4  depicts change in temperature according to the amount of ice formed on an evaporator. 
     In  FIG. 4 , the top line depicts the temperature measured by the second temperature sensor  120 , the middle line depicts the temperature measured by the third temperature sensor  130 , and the lowermost line depicts the temperature measured by the first temperature sensor  110 . 
     As the time for which the refrigerator is used increases, the amount of ice formed on the evaporator is also increases. This is because ice is formed on the evaporator as moisture contained in the food is moved to the chamber with the food stored in the storage compartment while the evaporator is not defrosted. 
     When the amount of ice formed on the evaporator increases, the evaporator is kept from directly contacting the air in the chamber because ice is positioned on the exterior of the evaporator. 
     As a result, heat exchange performance of the evaporator performing heat exchange with air is degraded. Then, the temperature of the air cooled through heat exchange with the evaporator is increased, and the air at a relatively high temperature is supplied to the storage compartment. 
     That is, as the amount of ice formed on the evaporator is increased (toward the right side on the x-axis in  FIG. 4 ), the evaporator cannot easily exchange heat with the air, and accordingly the temperature T 1  of the evaporator is lowered. 
     As the amount of ice formed on the evaporator is increased, the temperature T 2  of the storage compartment rises because the air supplied to the storage compartment is not the air sufficiently cooled by the evaporator. 
     As the amount of ice formed on the evaporator is increased, efficiency of heat exchange between the evaporator and the air is lowered, and accordingly the temperature T 3  of the air supplied from the chamber to the storage compartment is increased. 
     In this embodiment, the time at which defrosting of the evaporator is necessary may be determined based on the above-described pattern of change in temperature. 
     In this embodiment, the temperatures of the inlet/outlet of the evaporator and the temperature of the refrigerant supplied to the evaporator may be measured to calculate the amount of heat exchange according to cooling by the evaporator in the total amount of heat exchange. Thus, by predicting the amount of ice formed on the evaporator, the time at which defrosting is ne necessary may be efficiently identified. That is, the amount of ice formed on the evaporator may be predicted using the ratio of the maximum amount of heat exchange by the evaporator and the actual amount of heat exchange, and the time to defrost the evaporator may be determined according to the prediction. 
       FIG. 5  illustrates a method of calculating a set value. 
     In this embodiment, the time at which the evaporator needs to be defrosted may be determined based on a value calculated according to the temperatures measured by the first temperature sensor, the second temperature sensor, and the third temperature sensor. 
     In this embodiment, two indicators calculated by the three temperature sensors are proposed. 
     As shown in  FIG. 5   a,  the time at which defrosting is necessary may be found using indicators  1  and  2 . 
     It can be seen from  FIG. 5 b    that the temperature of the air supplied from the chamber to the storage compartment as measured by the third temperature sensor undergoes the largest change in the initial state and after frosting. 
     Under these conditions, it was confirmed that indicator  2  can more easily detect changes in temperature at three points according to frosting than indicator  1 . That is, when indicator  1  is used, the change from a state before frosting to a state after frosting is relatively small. On the other hand, when indicator  2  is used, the change from a state before frosting to a state after frosting is large, and accordingly frosting detection capability could be improved. Therefore, when indicator  2  is used, the resolution for change in temperature may be improved, and the time at which defrosting is needed may be more accurately identified. 
     As described above, since the defrosting time can be more accurately identified by the three temperature sensors when indicator  2  is used than when indicator  1  is used, an embodiment of identifying the defrosting time using indicator  2  will be described below. 
     However, even when indicator  1  is used, the defrosting time may be identified by using a similar method, and the detailed description thereof will be omitted as it is similar to the description of the method based on indicator  2 . 
       FIG. 6  is a diagram illustrating a control flow according to an embodiment. 
     Referring to  FIG. 6 , the evaporator  80  is defrosted (S 10 ). Here, the defrosting start time may be based on the time for which the refrigerator is used, the time for which the door is opened, and the driving time of the compressor as in conventional cases. Alternatively, in this embodiment, the defrosting start time may be determined using the values measured by the three temperature sensors. 
     In S 10 , in performing the defrosting, current may be supplied to the heater  150  and heat may be supplied by the heater  150 . 
     It is determined whether a defrosting termination condition for terminating defrosting of the evaporator  80  is satisfied (S 12 ). 
     As the defrosting termination condition, the temperature of the evaporator  80  measured by the first temperature sensor  110  may be used. That is, if the temperature of the evaporator  80  according to the first temperature sensor  110  is raised to a specific temperature, it may be determined that the temperature of the evaporator  80  has risen enough to remove the frozen ice. Thus, defrosting of the evaporator  80  may be terminated. 
     If the defrosting termination condition is satisfied in S 12 , defrosting of the evaporator  80  is terminated (S 14 ). The defrosting may be terminated by stopping driving the heater  150 . 
     When defrosting is terminated, a normal operation for cooling the storage compartment  22  is performed (S 20 ). 
     The controller  100  causes the compressor  160  to compress the refrigerant, and the compressed refrigerant is supplied to the evaporator  80 . As the air in the chamber  70  undergoes heat exchange with the evaporator  80 , the air is cooled and the cooled air is guided to the discharge duct  72  by the blowing force of the fan  140 . 
     That is, as the fan  140  is driven, the air in the chamber  80  may be guided to the storage compartment  22  through the discharge duct  72 , thereby cooling the inside of the storage compartment  22 . 
     The controller  100  sets, as a set value, one of values calculated by indicator  2  using the temperature values measured by the first temperature sensor  110 , the second temperature sensor  120 , and the third temperature sensor  130  (S 22 ). 
     The controller  100  may calculate the set value using Equation 1 below. 
     
       
         
           
             
               
                 
                   
                     
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     where a is less than 1. 
     The set value may be a value measured for the first time during driving of the compressor  150  after defrosting is completed. Alternatively, the set value may be a value measured at the time when the compressor  150  is driven as the storage compartment  22  deviates from the set temperature range after the storage compartment is cooled by the set temperature. The set value may be an average of multiple values or a median value selected from among the multiple values. 
     In some implementations, ‘a’ in the set value may be a number less than 1, such as 0.8. To cause defrosting to frequently occur, a relatively small value may be selected as a. To cause defrosting not to frequently occur, a relatively large value may be selected as a. 
     In this embodiment, the set value is set in the operation step. That is, although the set value can be stored as an absolute value, a new set value is set every time the operation is performed. 
     That is, in the present embodiment, the set value is set every time by the temperature measured in the stable cycle after the defrosting is performed. Accordingly, errors caused by a sample and sensor deviation may be prevented. In this embodiment, the set value may be updated every time defrosting is terminated. Thereby, accuracy of the defrosting time may be improved, which may lead to improvements in terms of power consumption and defrosting reliability. 
     It is determined whether the value calculated using indicator  2  based on the temperature values measured by the first temperature sensor  110 , the second temperature sensor  120  and the third temperature sensor  130  reaches the set value (S 24 ). 
     When the set value is reached in S 24 , defrosting is started (S 30 ). 
     When the set value is reached, the controller  100  may drive the heater  150 , determining that defrosting of the evaporator  80  is necessary. 
     When the heater  150  is driven, the inside of the chamber  70  is heated by heat generated by the heater  150 . As the temperature of the evaporator  70  increases, ice formed on the evaporator  70  melts. 
     During the defrosting, the temperature of the evaporator  70  is measured by the first temperature sensor  110 . When it is determined by the first temperature sensor  110  that the temperature of the evaporator  70  has been sufficiently raised, the controller  100  stops driving the heater  150  and terminates defrosting (S 32  and S 34 ). 
       FIG. 7  is a view illustrating an installation position of a first temperature sensor. 
     The first temperature sensor  110  may be provided at a portion of a duct  109  that is located in the chamber  70  to guide the refrigerant to the evaporator  80 . 
     As shown in  FIG. 7 , the evaporator  80  takes the form of a pipe that is continuous as a whole. The evaporator is curved in zigzags and provided with a plurality of fins for increasing the heat exchange area. After passing through the expansion valve, the refrigerant is supplied to the evaporator  80 . 
     The first temperature sensor  110  may be provided at the front end of a portion of the evaporator  80  where the fins are formed, that is, a position to which the refrigerant moves immediately before the refrigerant reaches the portion of the evaporator  80  where the fins are positioned. 
     The temperature of a portion adjacent to the inlet of the evaporator  80  is generally lower than the temperatures at the other portions. As the refrigerant is introduced into the evaporator  80 , heat exchange occurs between the evaporator  80  and the external air. Generally, heat exchange between the portion corresponding to the inlet and the external air is not significant. 
     The portion at the lowest temperature in the evaporator  80  may be a portion that is easily frosted as ice is formed thereon. Accordingly, the first temperature sensor  110 , which is arranged to measure the temperature of the evaporator  80 , may be disposed at a portion of the evaporator  80  where the temperature is relatively low or frosting occurs relatively easily. 
     Of course, the first temperature sensor  110  may be positioned at a portion within half the entire path of movement of the refrigerant in the evaporator  80  after the refrigerant is moved to the evaporator  80 . 
     According to the result of an experiment conducted by the inventor, the temperature could be reliably measured despite the change of the external air or the operation condition until the refrigerant moved to a position corresponding to about half the path in the evaporator  80 . That is, even when the distributed assembly and component distribution of the product (distribution of sensor temperatures and distribution of the amount of refrigerant) occurred, the temperature of the evaporator  80  could be measured accurately at the corresponding position. 
     For example, when a temperature sensor was installed so as to deviate from the corresponding position, a temperature different from the actual temperature of the evaporator was detected relatively many times due to various unexpected factors. 
     It is to be understood that the present invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 
     INDUSTRIAL APPLICABILITY 
     The present invention provides a refrigerator capable of improving reliability of determination of a defrosting time, and a control method thereof.