JPH11166784A - Electric refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent dew formation at the circumferential fringe part of the opening of each room in an electric refrigerator having a plurality of rooms of different conditions of dew formation. SOLUTION: An antisweating heater 5N is provided at the circumferential fringe part of the opening of each room in an electric refrigerator and a sensor 1 for detecting the relative humidity around an electric refrigerator is provided. Relative humidity characteristics for the ambient temperature of the humidity sensor 1 are matched with the ambient temperature-relative humidity characteristics for the conditions of dew formation of the electric refrigerator. A drive circuit drives the antisweating heater 5N provided for each room depending on the easiness of dew formation when a steam humidity sensor detects a predetermined output reference value for a predetermined time continuously based on the detection output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric refrigerator provided with a heater for preventing dew.

[0002]

2. Description of the Related Art In a conventional electric refrigerator, a high-pressure and high-temperature pipe in a refrigerating cycle is stretched around the opening periphery of each storage room such as a freezing room, a refrigerator room, a vegetable room, and the like. Due to the heat generation, the above-mentioned peripheral portion of the opening is prevented from dew condensation. However, due to the relationship between the ambient temperature and the relative humidity of the electric refrigerator, even under conditions in which the dew does not dew at the opening periphery, if the refrigeration cycle operates, heat is generated from the high-temperature and high-pressure pipe, and this heat is generated as a heat load. As a result, the temperature in the refrigerator rises and dew is released.

[0003] Therefore, instead of a high-temperature and high-pressure pipe, a heater for dew-proofing is provided around the periphery of the opening.
The relative humidity around the electric refrigerator is detected, and at that relative humidity, it is determined whether or not the peripheral edge of the opening of the storage room is under the dew condition. An electric refrigerator for preventing dew has been proposed in Japanese Patent Application Laid-Open No. 8-136110.

FIGS. 10 and 11 show the structure of a conventional dew-proof system for an electric refrigerator. The microcomputer 10 shown in FIG. 11 is a humidity sensor 11 for detecting the relative humidity of the surroundings.
And the signal of the outside temperature thermistor 12 is detected, the temperature of the relative humidity indicated by the humidity sensor 11 is corrected by the value of the outside temperature thermistor, and the current relative humidity is determined. Based on the result, it is determined whether or not the condition is the dew condition based on the table data stored in the microcomputer 10 in advance. If the condition is the dew condition, each of the refrigerator compartment 13, the freezing compartment 14, the vegetable compartment 15 and the like shown in FIG. The dew-proof heater 16 provided on the periphery of the opening of the storage room is energized for a certain time.

[0005]

The humidity sensor generally has a temperature characteristic, and if the ambient temperature changes with respect to a certain electric resistance value, the relative humidity value indicated also changes. Therefore, when relative humidity is detected from the electric resistance value indicated by the humidity sensor, temperature correction is required.Use a humidity sensor that includes a temperature correction thermistor, or separately as in the conventional example described above. The ambient temperature is detected by the provided outside air temperature thermistor, and the above-described temperature correction processing is required at the time of determination by a microcomputer or the like. In the former case, the cost of the humidity sensor will increase,
In the latter case, it is necessary to separately provide a temperature correction thermistor, which leads to an increase in cost and a problem that the judgment process becomes complicated.

Electric refrigerators are often installed in kitchens, and there are many pots, electric pots, rice cookers and the like that generate steam around the electric refrigerator. These vapors may temporarily affect the electric refrigerator and erroneously detect that the humidity sensor has detected the dew-deposition condition.

[0007] Further, depending on the set temperature in the refrigerator, there are places where dew is easily generated and places where dew is hardly formed. If the dew-proof heater is arranged uniformly over the entire electric refrigerator, heat is similarly generated at a place where the heat generated by the dew-proof heater is not so required, which leads to an increase in the heat load in the refrigerator. Further, there is a problem that energization of the dew-proof heater beyond the amount of heat required for dew-proofing leads to an increase in the heat load in the refrigerator.

[0008]

In order to solve the above-mentioned problems, a first aspect of the present invention is to provide a relative humidity sensor for detecting a relative humidity around the refrigerator, and based on a detection output of the relative humidity sensor, the refrigerator is provided with a relative humidity sensor. By operating the dew-proof heater provided on the peripheral edge of the opening of the storage room, in the electric refrigerator to perform dew-proofing of the peripheral edge of the opening, the humidity sensor has a relative humidity characteristic with respect to the ambient temperature of the humidity sensor, It is characterized by being suitable for the relative humidity characteristic with respect to the ambient temperature, which is the dew condition of the refrigerator.

According to a second aspect of the present invention, in the electric refrigerator according to the first aspect, when it is detected based on the detection output of the humidity sensor that the peripheral portion of the opening of the refrigerator has approached the dew bleeding condition, this detection is performed. A timer is provided for detecting that the state has continued for a predetermined time from the time point, and energization of the dew-proof heater is started in response to detection of the continuation of the predetermined time by the timer.

According to a third aspect of the present invention, there is provided a dew-proof heater provided at a periphery of an opening of a refrigerator compartment based on a detection output of the relative humidity sensor for detecting a relative humidity around the refrigerator. In an electric refrigerator which is operated to perform dew-proofing of the opening peripheral part, the dew-proof heater is separately provided for each opening peripheral part of each refrigerator compartment of the refrigerator, and the dew-proof heater emits when energized. As the anti-condensation heater provided at the periphery of the opening that is easy
A drive circuit for controlling energization to each of the dew-proof heaters is provided.

According to a fourth aspect of the present invention, in the electric refrigerator according to the third aspect, when a temperature setting of a certain storage room in the storage room is switched to a low temperature, during the low temperature setting period, The present invention is characterized in that the duty ratio of the dew-proof heater provided at the periphery of the opening of a certain storage room is controlled so as to be set to a value higher than the set value before switching to a low temperature by the drive circuit.

According to a fifth aspect of the present invention, there is provided a relative humidity sensor for detecting a relative humidity around the refrigerator, and a dew-proof heater provided at the periphery of the opening of the refrigerator compartment based on the detection output of the relative humidity sensor. In the electric refrigerator, which is operated to perform dew-proofing on the peripheral edge of the opening, the dew-proof heater provided on the peripheral edge of the opening of each of the compartments depends on the ease with which the peripheral edge of the opening of each compartment is released. Characterized by having a calorific value distribution.

According to a sixth aspect of the present invention, in the electric refrigerator according to the first to fifth aspects, the dew-proof heater is a heater having a positive temperature characteristic.

[0014]

According to the above invention, the humidity sensor whose temperature characteristic with respect to the output reference value of the relative humidity sensor indicating that the dew condition is approaching matches the characteristic of ambient temperature-relative humidity which is the dew condition of the electric refrigerator. , The output value of the humidity sensor is suitable for the dew conditions of the electric refrigerator without temperature correction, and it is easy to prevent dew condensation at the periphery of the opening of the storage room by the anti-dew heater. It can be performed with a simple configuration.

Further, according to the present invention, when it is detected that the dew condition has been approached in response to an output signal from the humidity sensor, a timer is activated, and the timer sets the same state to a predetermined state from the time when the above state is detected. When it is confirmed that the time has elapsed, the power supply to the dew-proof heater is started. As a result, the dew-proof heater can be reliably operated in the vicinity of the dew condition, and the stable operation of the dew-proof heater without any malfunction is performed. Can be done.

Further, according to the present invention, a dew-proof heater is provided separately for each opening peripheral portion of each compartment of the electric refrigerator, and when it is necessary to energize the dew-proof heater, a drive circuit is used to control the dew-proof heater. The amount of electricity supplied to each of the dew-proof heaters is controlled such that the more the dew-proof heaters are provided at the periphery of the opening of the storage room where the heaters easily emit water, the higher the duty ratio becomes. Therefore, the amount of heat generated by the dew-proof heater increases in the opening edge of the storage room where dew condensation is likely to occur, and it is possible to effectively prevent dew condensation at the opening edge of each storage room.

Further, according to the present invention, when the temperature setting of a certain storage room is switched to a low temperature, during the low-temperature setting period, the drive circuit turns on the dew-proof heater provided at the periphery of the opening of the storage room. The rate is controlled to be higher than the current set value. Therefore, in the periphery of the opening of the storage room set to low temperature, it is difficult to form dew condensation even if the storage room is set to low temperature. Variations in dew condensation occurrence conditions at the peripheral portion can be suppressed, and efficient dew condensation can be prevented by the dew-proof heater.

Further, according to the present invention, the dew-proof heater provided for each opening peripheral portion of each storage room of the electric refrigerator is provided with a calorific value distribution according to the ease of dew formation in each storage room. Therefore, the amount of heat generated for each compartment can be generated from the dew-proof heater simply by turning on electricity without individually controlling the amount of electricity supplied to the dew-proof heaters provided at the periphery of the opening of each compartment. With such a configuration, it is possible to effectively prevent dew condensation on the peripheral edge of the opening of each compartment.

Further, according to the present invention, since the dew-proof heater provided at the peripheral edge of the opening of each storage room has a positive temperature characteristic, the dew-proof heater according to the ambient temperature and the relative humidity of the electric refrigerator is provided. Control of energization is simplified.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a data table of the result of an experiment performed to determine whether or not dew condensation occurs when the electric refrigerator is operated under a certain environmental condition. The dew formation region with respect to the relative humidity when the ambient temperature of the electric refrigerator changes is shown. FIG. In the figure, the values of the intersections indicated by ○ or × are omitted, but are the dew point temperatures under the respective conditions, where ○ indicates an area where no dew occurs and X indicates a dew occurrence area. That is, when the ambient temperature is 35 ° C., the relative humidity is 5
When the ambient temperature is 0 Rh% or more and the ambient temperature is 10 ° C., the dew is emitted at a relative temperature of 80 Rh% or more, and when the ambient temperature changes even at the same relative humidity, the dew-development condition changes.

FIG. 2 shows the structure of the humidity sensor used in the present invention. The humidity sensor 1 comprises a substrate 2 and the substrate 2
It comprises a moisture sensitive material 3 formed thereon and a pair of opposing electrodes 4 formed on the moisture sensitive material 3.

(Embodiment 1) FIGS. 3 to 5 illustrate Embodiment 1 of the present invention, and correspond to Claim 1. FIG.
FIG. 3 is a configuration diagram of a drive circuit that controls energization of the dew-proof heater 5 of the electric refrigerator using the humidity sensor 1 shown in FIG. In FIG. 3, reference numeral 6 denotes a microcomputer for outputting a control signal to the photocoupler 7 based on the output of the humidity sensor 1, and reference numeral 8 denotes a refrigerator 13 and a freezer 14 of the electric refrigerator via the output of the photocoupler 7. , Vegetable room 15
It is a power supply for supplying electric power to the dew-proof heater 5 provided at the periphery of the opening of each storage room. The installation of this dew-proof heater 5
As in the case of the conventional example, it may be formed in series at the periphery of the opening of each storage room.

According to the experimental results of the dew formation condition shown in FIG. 1, the microcomputer 6 determines that the time when the ambient temperature is 20 ° C. and the relative humidity is 60 Rh% is the state immediately before the dew condition, An output reference value R1 is set as a threshold value for on / off control of the dew-proof heater 5. Usually, the humidity sensor 1 has a temperature characteristic as shown in FIG. From the characteristics shown in FIG. 4, if the ambient temperature decreases, the relative humidity increases even if the humidity sensor 1 indicates the same electric resistance value, for example, the output reference value R1, and if the ambient temperature increases, Even if the humidity sensor 1 indicates the same output reference value, the relative humidity is low.

This temperature characteristic is similar to that of the occurrence of dew shown in FIG. Therefore, the humidity sensor 1 used in the control circuit of the dew-proof heater 5 shown in FIG. 3 shows the temperature characteristics with respect to the output reference value R1 set as described above, and the relationship between the ambient temperature and the relative humidity as shown in FIG. It shall be adjusted to the value of the dew-development condition shown in. As a result, the temperature characteristic itself of the humidity sensor 1 includes the characteristic serving as the dew condition, and it is determined whether or not the humidity condition is immediately before the dew condition.
For one input value of two humidity sensors,
A thermistor for temperature correction as in the conventional example is not required, and the dew prevention system can be simplified.

The ease with which water is released at the periphery of the opening of each compartment of the electric refrigerator differs depending on the compartments such as the refrigerator compartment 13, the freezing compartment 14, and the vegetable compartment 15. Therefore, the distribution of the heat generated by the dew-proof heater 5 is provided so that the amount of heat generated by the dew-proof heater 5 installed at the peripheral portion of the opening of each storage room where dew condensation is likely to occur is higher. That is, the freezer compartment 14 and the refrigerator compartment 1
3. In the order of the vegetable compartment 15, the calorific value of the dew-proof heater 5 installed on the periphery of the opening is increased. Thereby, it is possible to efficiently perform the dew prevention in each of the compartments having different dew conditions with a simple configuration.

(Embodiment 2) FIG. 6 is a flowchart for explaining Embodiment 2 of the present invention, and corresponds to claim 2. The microcomputer 6 shown in FIG. 3 first determines in step S1 whether or not the anti-dew heater 5 is in an energized state. If the dew-proof heater 5 is energized, the energizing time is counted in advance by the microcomputer 6, and it is determined in step S4 whether or not the energizing time has passed 30 minutes. If the energization time of the dew-proof heater has passed 30 minutes, the power supply to the dew-proof heater 5 is cut off in step S5 and the process returns to the start. If not, the process returns to the start in the energized state.

If it is determined in step S1 that the dew-proof heater 5 is not energized, the process proceeds to step S2 to determine whether or not the ON condition in which the detection output of the humidity sensor 1 is approaching the output reference value R1 is being counted. Judge. This is for starting the energization of the dew-proof heater 5 when the relative humidity sensor 1 detects that the dew condition has been reached, that is, the ON condition, for a certain period of time, in this embodiment, continuously for 10 minutes. This is for improving the accuracy of the energization control of the dew-proof heater 5.

If it is determined in step S2 that the ON condition is not being counted, it is determined in step S3 whether or not the counting for 10 minutes is completed. If not, the process returns to the start. If completed, the next step is performed. Humidity sensor 1 in S6
The detection signal is read. Also, the above step S2
If the ON condition is being counted, the process proceeds to step S6.
The detection output of the humidity sensor at that time is read. As described above, in the present embodiment, the microcomputer 6 reads the output signal of the humidity sensor 1 at intervals of 10 minutes.

In step S7, it is determined whether or not the output signal of the humidity sensor 1 read into the microcomputer 6 in step S6 is higher than the output reference value R1 preset in the microcomputer 6 as described above. In this step S7, when the output signal of the humidity sensor 1 is smaller than the output reference value R1 at that time, it is determined that the state is close to the dew condition, and from the time when this state is first detected in the next step S9, The counting of the continuation time of this state (the state where the dew-proof heater 1 is on) is started.

Until the count time in step S9 elapses 2 minutes, the process returns to the start, and the output signal of the humidity sensor 1 is read at any time in steps S2 and S6. In the above step S9, the ON condition is continuously 2
If it is determined that the minutes have elapsed, the process proceeds to step S10, and the power supply 8 starts supplying power to the dew-proof heater 5.

If it is determined in step S7 that the output signal of the humidity sensor 1 is smaller than the output reference value R1 before the on-condition has continuously passed for two minutes, it is determined in step S8 that the dew-condition is not a dew-release condition. Is stopped, the process returns to the start, and returns to the process of monitoring every 10 minutes again. As described above, turning off the dew-proof heater 1 is performed after energization for a certain period of time from the time when energization is performed in steps S4 and S5. Here, it is turned off when 30 minutes have passed, and again
It returns to the process of monitoring every 0 minutes.

According to the second embodiment, the humidity sensor 1
When the state is continued for a certain period of time (10 minutes in this embodiment) after reaching the output reference value R1 for energizing the dew-proof heater 5, the dew-proof heater 5 is energized for the first time. Even if steam generated from placed pots, electric pots, rice cookers, etc. may temporarily affect the operation, the dew-proof heater 5 is not accidentally energized, preventing malfunctions of dew prevention. Can be.

(Embodiment 3) FIGS. 7 and 8 show the configuration of Embodiment 3 of the present invention, and correspond to Claims 3 and 4 of the present invention. 7 and 8, the dew-proof heater 5 has a dew-proof heater 5-1 for the refrigerating room and a defrost-proof heater for the freezing room on the periphery of the opening of each of the refrigerator compartment 13, the freezing compartment 14, and the vegetable compartment 15. Dew heater 5-2, dew prevention heater 5 for vegetable room
3 are provided separately. 7-1, 7-2, 7
Reference numeral -3 denotes a photocoupler for controlling the energization of each of the above-mentioned dew-proof heaters 5-1, 5-2 and 5-3 by a control signal from the microcomputer 6, and reference numeral 8 denotes the photocouplers 7-1 and 7-.
2, 7-3, each anti-dew heater 5-1, 5-2, 5
-3.

In an electric refrigerator, the ease with which water is released varies from room to room due to the difference in temperature from outside air depending on the set temperature of each room. It is the freezer compartment 14 that emits dew most easily, followed by the refrigerator compartment 13 and the vegetable compartment 15 in that order. The microcomputer 6 determines whether or not it is necessary to energize each of the above dew-proof heaters 5-1, 5-2, and 5-3 by the microcomputer 6 for each dew-proof heater.
This is performed in the same manner as in the first and second embodiments. The energization to the dew-proof heaters 5-1, 5-2, and 5-3 is performed, for example, by
The dew-proof heater 5-2 for the freezer compartment is turned on for all 30 minutes, which is the power supply period.

The dew-proof heater 5-1 for the refrigerating room is turned on only for 5 minutes out of 10 minutes at a current conduction rate of 50%, and this operation is repeated three times. Therefore, the dew-proof heater 5-1 is energized for half of the entire energizing time of 30 minutes for 15 minutes. Similarly, the dew-proof heater 5-3 for the vegetable room has an energization rate of 30% and is turned on for 3 minutes during 10 minutes, and this operation is repeated three times. Turn on electricity for only 9 minutes. As described above, the duty ratio of the dew-proof heater is varied according to the ease of dew formation, and control is performed so as not to generate heat more than necessary.

Here, in the case of a storage room in which the set temperature in the refrigerator can be set variably from the freezing temperature to the refrigeration temperature,
The dew-proof heater provided on the periphery of the opening of the storage compartment sets the energization rate to 100% as described above when the storage compartment is set to the freezing temperature, and sets the refrigerator to the refrigerator temperature. Is controlled by the microcomputer 6 so that the duty ratio is set to 50%. As described above, the set temperature in the refrigerator during the operation of the electric refrigerator can be changed to cope with a change in the ease of dew formation in the refrigerator. The specific numerical values shown in the present embodiment are not limited to these, and can be appropriately changed according to the design.

(Embodiment 4) FIG. 9 shows the configuration of Embodiment 4 of the present invention, and corresponds to claim 5 of the present invention.
9, the same reference numerals are given to the portions corresponding to FIGS. 1 to 8 in the above-described first to third embodiments, and the description will be omitted. In FIG. 9, the defrosting heater 5 for the refrigerator compartment provided at the periphery of each opening of the refrigerator compartment 13, the freezer compartment 14 and the vegetable compartment 15.
-1, The dew-proof heater 5-2 for the freezing room and the dew-proof heater 5-3 for the vegetable room are connected in parallel. Then, the dew-proof heaters connected in parallel are connected to a power supply 8 via a photocoupler 7.

Each of the above dew-proof heaters 5-1, 5-2, 5
For example, the dew-proof heater 5-2 for the freezer compartment is a heater of 30 to 40 W, and the dew-proof heater 5-1 for the refrigerator compartment is 20 to 3 for example.
0W heater, dewproofing heater 5-3 for vegetable room
0 to 20W. Then, each of the dew-proof heaters 5-1 and 5
-2 and 5-3 are arranged on the periphery of the opening of each corresponding storage room as described above, and are electrically connected in parallel.

With the above configuration, the control of the energization by the microcomputer 6 may be simply a control of turning on and off, and the amount of heat generated according to the ease of heat generation can be obtained from each of the dew-proof heaters. It is possible to efficiently prevent the dew condensation at the peripheral edge of the opening of each compartment having different conditions. In the fourth embodiment, as in the third embodiment, specific numbers can be appropriately changed.

The dew-proof heaters 5, 5-1, 5-2, and 5-3 used in the above-described embodiments have positive temperature characteristics (PTC characteristics), for example, a temperature of the dew-proof heater of 40 ° C. With the characteristic that the resistance value increases rapidly, the temperature of the dew-proof heater can be suppressed to about 40 ° C even when the dew-proof heater is connected and energized. The heat load inside can be reduced.
(Claim 6)

[0041]

Since the present invention has the above-described structure,
According to the first aspect, it is not necessary to perform temperature correction on the output value of the temperature sensor, and it is possible to determine whether or not the condition for energizing the dew-proof heater is obtained with one sensor and one input, thereby simplifying the system. Can be achieved.

According to the second aspect of the present invention, since a delay period is provided in the judgment before the dew-proof heater is energized, a pot, an electric pot, a rice cooker and the like are placed around the refrigerator and generated by these. Even if the generated steam temporarily flows toward the electric refrigerator, no malfunction occurs, and a stable dew-proof operation can be performed regardless of the surrounding conditions.

According to the third aspect of the present invention, the microcomputer controls the duty ratio of the dew-proof heaters provided at the periphery of the opening of each of the compartments having different dew-deposition conditions, and controls the duty ratio according to the ease of dew-dropping in each of the compartments. Since the generated heat is obtained, unnecessary heat load is reduced, and an efficient dew-proof operation can be performed.

Further, according to the present invention, even when the set temperature in the refrigerator is changed to a low temperature and the direction in which dew is easily emitted is set, the duty ratio of the dew-proof heater for the refrigerator is set to be high to control. Therefore, even when the set temperature is changed, it is possible to efficiently prevent dew condensation on the periphery of the opening of the storage room.

According to the fifth aspect of the present invention, the dew-proof heaters provided on the peripheral edge of the opening of each storage room have a calorific value distribution according to the ease of dew formation in the corresponding storage room. Unnecessary heat load can be reduced by a simple hardware configuration of the heater, and dew prevention corresponding to each storage room can be efficiently performed.

According to the sixth aspect of the present invention, since the dew-proof heater itself has the PTC characteristic, even if the energization is continued, unnecessary heat generation is suppressed and unnecessary heat generation is suppressed. The load can be reduced.

[Brief description of the drawings]

FIG. 1 is table data indicating whether or not dew has occurred under various environmental conditions of an electric refrigerator.

FIG. 2 is a configuration diagram of a temperature sensor in the electric refrigerator of the present invention.

FIG. 3 is a structural diagram of a control system in the electric refrigerator of the present invention.

FIG. 4 is a characteristic diagram of an output signal of a humidity sensor in the electric refrigerator of the present invention.

FIG. 5 is a temperature characteristic diagram of a humidity sensor used in the electric refrigerator of the present invention.

FIG. 6 is a flowchart illustrating a control method of a dew-proof system used in the present invention.

FIG. 7 is a view showing an arrangement of a dew-proof heater of the electric refrigerator of the present invention.

FIG. 8 is a configuration diagram of another control system of the electric refrigerator of the present invention.

FIG. 9 is a configuration diagram of still another control system of the electric refrigerator of the present invention.

FIG. 10 is a diagram showing an arrangement of a dew-proof heater of a conventional electric refrigerator.

FIG. 11 is a configuration diagram of a control system of a conventional electric refrigerator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Humidity sensor 5, 5-1 5-2, 5-3 Dew-proof heater 6 Microcomputer 7, 7-1, 7-2, 7-3 Photocoupler 8 Power supply 13 Refrigerator room 14 Freezer room 15 Vegetable room R1 Output reference value

Claims (6)

[Claims] A relative humidity sensor for detecting a relative humidity around a refrigerator is provided. Based on a detection output of the relative humidity sensor, a dew-proof heater provided at a peripheral portion of an opening of a refrigerator compartment is operated to open the opening. In the electric refrigerator configured to prevent dew condensation on the peripheral portion, the humidity sensor has a relative humidity characteristic with respect to an ambient temperature of the humidity sensor that matches a relative humidity characteristic with respect to an ambient temperature that is a dew-release condition of the refrigerator. An electric refrigerator. 2. Based on the detection output of the humidity sensor,
When detecting that the opening edge of the refrigerator has approached the dew condition, there is provided a timer for detecting that the same state has continued for a predetermined time from the time of the detection, and the protection is performed in response to the detection of the continuation of the predetermined time by the timer. 2. The electric refrigerator according to claim 1, wherein energization of the dew heater is started. 3. A relative humidity sensor for detecting a relative humidity around the refrigerator is provided, and a dew-proof heater provided at a peripheral portion of the opening of the refrigerator compartment is operated based on a detection output of the relative humidity sensor, and the peripheral portion of the opening is opened. In an electric refrigerator designed to perform dew-proofing, the dew-proof heater is provided separately for each opening edge of each refrigerator compartment of the refrigerator, and when the dew-proofing heater is energized, it is provided at an opening edge that is easy to emit dew. An electric refrigerator, comprising: a drive circuit for controlling power supply to each of the dew-proof heaters such that the dew-proof heater has a higher energization rate. 4. When the temperature setting of a certain storage room in the storage room is switched to a low temperature, during the low-temperature setting period, the energization rate of a dew-proof heater provided at the periphery of the opening of the certain storage room. 4. The electric refrigerator according to claim 3, wherein the drive circuit controls to set a value higher than a set value before switching to a low temperature. 5. A relative humidity sensor for detecting a relative humidity around the refrigerator is provided, and a dew-proof heater provided at a peripheral portion of the opening of the refrigerator compartment is operated based on a detection output of the relative humidity sensor, and the peripheral edge of the opening is opened. In the electric refrigerator configured to perform the dew-proofing of the compartments, the dew-prevention heater provided around the opening of each of the compartments has a calorific value distribution according to the ease of dew condensation at the periphery of the opening of each compartment. An electric refrigerator, comprising: 6. The electric refrigerator according to claim 1, wherein said dew-proof heater is a heater having a positive temperature characteristic.