JPH0470546B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a low-temperature show case equipped with three evaporators.

(b) Prior art In order to suppress the temperature rise in the storage room when defrosting a low-temperature storage case, at least two evaporators are provided, and while one evaporator is being defrosted, the other evaporator is not being defrosted. Increasingly, a combination of defrosting and cooling methods are being adopted.

As a combined method for defrosting and cooling, there is a method in which all of a plurality of evaporators connected in parallel are arranged in an inner layer for circulating cold air. Publication, JP-A No. 60-256773,
Adopted in US Pat. No. 4,633,677.

(c) Problems to be solved by the invention The low-temperature show case shown in the above-mentioned Japanese Patent Publication No. 62-25952 has three evaporators stacked one on top of the other in the front and back direction, and the air inlet and air outlet surfaces of each are at the same height. Due to the fact that it is placed on the inner layer so that
If the depth of the low-temperature storage case is fixed, there is a problem that the inner layer reduces the depth of the storage chamber, and during defrosting operation of one evaporator, the adjacent evaporator must be Because of the cooling operation, each evaporator is mutually susceptible to the influence of the temperature of the other evaporator. For this reason, when the set temperature of the storage room is set to 0°C or lower, the refrigerant evaporation temperature of the evaporator that is operated for cooling is set to - It is necessary to set the temperature to 10℃ or less, and therefore, in order to use the high-pressure liquid refrigerant that undergoes heat exchange in the evaporator under defrosting operation and becomes supercooled liquid as the defrosting heat source, the temperature must be set at 10℃ or lower. Due to the low temperature, the amount of heat from the defrosting heat source is insufficient,
A problem has arisen in which the defrost cannot be completely removed from the evaporator during the defrosting operation during the set defrosting time, for example, 20 minutes. Another cause of residual frost is that after three evaporators are in cooling operation, two evaporators are connected to cooling operation, one evaporator is switched to defrosting operation, and then one evaporator is switched to defrosting operation. In order to reduce the number of evaporators used for cooling, the refrigerant evaporation temperature of the evaporator during cooling operation drops dramatically, and the amount of frost on the evaporator during cooling operation increases. The amount of heat in the high-pressure liquid refrigerant becomes insufficient, resulting in residual frost on the evaporator during defrosting operation.

Also, Japanese Patent Application Laid-Open No. 60-256773 and U.S. Patent No.
The low-temperature case shown in No. 4633677 both divides a part of the inner layer into an inner passage and an outer passage, and has two evaporators connected in parallel with each other, one of which is placed in the inner passage.
The other evaporator is placed in the outer path, and after cooling operation of the two evaporators, the cooling operation of one evaporator is kept connected and the other evaporator is switched to defrosting operation. - Similar to Publication No. 25952, the refrigerant evaporation temperature of the evaporator during cooling operation is extremely low, and the amount of frost on the evaporator during cooling operation is increasing. There is a problem in that the amount of heat is insufficient and frost remains on the evaporator during defrosting operation.

Incidentally, under the conditions of the ambient temperature of the low-temperature case at 27°C and the ambient humidity of 70%, the refrigerant evaporation temperature of both the first and second evaporators is set to -13°C, and source pressure liquid refrigerant is supplied to both evaporators for cooling. After the evaporator is activated, if the reduced pressure liquid refrigerant is continuously supplied to one evaporator and the supply of the reduced pressure liquid refrigerant to the other evaporator is alternately interrupted,
As shown in Figure 8, the refrigerant evaporation temperature of the evaporator to which the reduced pressure liquid refrigerant is supplied drops to about -20°C, so the amount of frost on the evaporator increases during the cooling action, and the refrigerant is circulated. Since the cold air flow also becomes low temperature, the defrosting of the evaporator during the defrosting operation when the supply of reduced pressure liquid refrigerant is interrupted does not progress, and overall, the problem is that the amount of frost on the low-temperature case increases. arise.

(d) Means for Solving the Problems The present invention aims to solve the above problems, and as a means thereof, first to third evaporators are connected in parallel to each other, and the first evaporator When the evaporator is being defrosted, both the second and third evaporators have a cooling effect, and when the second evaporator has been defrosted, both the first and third evaporators have a cooling effect. , a blower fan, a part of which is divided into an inner and outer layer by a dividing plate, and an inner layer having an inner path in which the first evaporator is disposed and an outer path in which the second evaporator is disposed; an outer layer having the third evaporator, the second evaporator is located between the first evaporator and the third evaporator, and the inner half is the outer half of the first evaporator. A low-temperature show case is provided, the outer half of which is arranged to overlap the inner half of the third evaporator.

(e) Effect According to the embodiment, only the air temperature A of the inner passage 28 rises rapidly due to heating of the first electric heater 16 as defrosting of the first evaporator 14 starts; 28, the first electric heater 16
The air that has been heated and has a raised temperature, and the air that has passed through the outer path 29 and been cooled by the second evaporator 15 and has a lower temperature, merge in the inner layer 6, and are blown out to the opening 2 as an air curtain GA. Since the temperature of the cold air stream is suppressed to below 0°C from the early to middle stages of defrosting, the air temperature (A) is also suppressed to below 0°C, and the air that has passed through the third evaporator 19 from the middle to late stages of defrosting is also suppressed to below 0°C. is blown out into the opening 2 as a cold air flow of 0°C or less and acts as a guard air curtain GA that lowers the temperature of the air curtain CA. It can be suppressed to ℃.

Also, since the partition plate 4 and the dividing plate 27 are both formed with inclined portions 21 and 30 in the same direction, the arrangement of the first to third evaporators 14, 15, 19 is viewed from above. , the rear half of the second evaporator 15 overlaps the front half of the third evaporator 19, and the second evaporator 15
The rear half of the first evaporator 14 overlaps the front half of the first evaporator 14, and although three evaporators 14, 15, and 19 are arranged, there are actually two evaporators 1
3 evaporators 14,1 in a space of 4,19
5 and 19 can be placed.

(F) Embodiments Below, embodiments of the present invention will be described based on the drawings. 1 shown in FIG. 1 has a main body made up of a heat insulating wall 3 having an opening 2 for storing and taking out products on the front side. In the low-temperature case, by sequentially disposing the first and second partition plates 4 and 5 at an appropriate distance from the inner wall of the heat insulating wall 3, an inner layer 6 for circulating cold air is formed.
, an outer layer 7 for protective airflow circulation, a storage chamber 9 equipped with a plurality of shelves 8, and air outlets 10, 11 of both the inner and outer layers 6, 7 along the longitudinal direction of the upper edge of the opening 2;
The air outlet 1 along the longitudinal direction of the lower edge of the opening 2
Suction ports 12 and 13 of both the inner and outer layers 6 and 7 facing the inner and outer layers 6 and 7 are formed.

In the inner layer 6, there are first and second evaporators 14 and 15 which are plate-fin shaped and have the same heat exchange capacity.
and first and second electric heaters 16 and 17 that are provided on the lower surfaces of the two evaporators on the air inlet side and are energized during defrosting of the corresponding evaporators 14 and 15,
As shown by the solid line arrow in FIG. 1, an axial type first blower fan 18 for forcibly circulating the cold air flow in the inner layer 6 is arranged.
Further, a third evaporator 19 in the form of a plate fin and a second axial blower fan 20 for forcibly circulating the protective air flow in the outer layer 7 are disposed in the outer layer 7, as indicated by the dashed line arrow in FIG. There is. Both the first and second blowing fans 18 and 20 are constantly operated, and in order to make the amount of air blown by the first blowing fan 18 larger and the wind speed faster than the second blowing fan 20, the first blowing fan 1
8 is made larger than the number of second blowing fans 20.

The back part of the first partition plate 4 is formed with a sloped part 21 that slopes backward, and the bottom wall part is formed with a vertical rising part 22, so that the inner and outer layers 6, 7 are Enlarged passages 23, 24, 25, 26 are formed in the back area and bottom area of the inner layer 6, and the enlarged passages 23 in the back area of the inner layer 6 are provided with both first and second evaporators 14, 15, A third evaporator 19 is installed in the enlarged channel 24 in the back area of the outer layer 7 and the inner layer 6
A first blower fan 18 is installed in the expanded channel 25 in the bottom area of the
A second blower fan 20 is arranged in each of the enlarged channels 26 in the bottom area of the outer layer 7 .

27 is disposed within the enlarged channel 23 of the inner layer 6, and connects the enlarged channel 23 to an inner channel 28 and an outer channel 29.
A dividing plate made of metal such as stainless steel, in the center of which is formed an inclined part 30 that slopes downward from the rear.
Further, an extending portion 32 having a flange 31 facing the lower surface of the first evaporator 14 is formed at a lower portion extending below the first electric heater 16 . Since the dividing plate 27 forms the inclined portion 30, the lower part of the inner passage 28 and the upper part of the outer passage 29 become widened passages 33, 34 for arranging the first and second evaporators 14, 15. On the other hand, medial tract 2
The upper part of 8 and the lower part of the outer passage 29 form narrow passages 35 and 36 for constricting the cold air flow. Also, the dividing plate 27
Therefore, the entrance width of the inner passage 28 is approximately twice the entrance width of the outer passage 29, while the exit width of the outer passage 29 is approximately twice the exit width of the inner passage 28, so that no frost is formed. The amount of ventilation of both evaporators 14 and 15 is kept constant.

Since the first partition plate 4 and the dividing plate 27 are both formed with inclined portions 21 and 30 in the same direction, the arrangement of the first to third evaporators 14, 15, 19 is viewed from above. Then, the rear half of the second evaporator 15 overlaps the front half of the third evaporator 19, and the rear half of the first evaporator 14 overlaps the front half of the second evaporator 15, so that three evaporators 14, 15, and 19, three evaporators 1 are actually installed in the space for two evaporators 14, 19.
4, 15, and 19 can be arranged.

Reference numeral 37 denotes a third partition plate made of metal such as stainless steel and placed in front of the first evaporator 14. Due to the arrangement of this partition plate, there is a space between the upper part and the lower part of the back wall 38 of the second partition plate 5. is open, and a side channel 39 whose lower part is closed is formed. Reference numeral 40 designates a number of holes formed in the lower part of the back wall 38 to communicate the side passage 39 with the lower area of the storage chamber 9.

FIG. 2 shows a refrigeration system for cooling the low-temperature show case 1, which includes a refrigerant compressor 41, an air-cooled condenser 42, a liquid receiver 43, and a dryer 4.
4, sight glass 45, first to third solenoid valves 4
6, 47, 48, first to third expansion valves 49, 50, 51 which are pressure reducing devices, first to third evaporators 14, 15, 19, gas-liquid separator 52 to high pressure gas pipe 53, High pressure liquid pipe 54, three high pressure liquid pipes 55, 56, 57 whose inlets are connected to this high pressure liquid pipe,
By connecting three low pressure liquid pipes 58, 59, 60, three low pressure gas branch pipes 61, 62, 63, and a low pressure gas pipe 64 to which the outlet of each low pressure gas branch pipe is connected in an annular manner, the above-mentioned Each of the first to third evaporators 14,
15, 19 correspond to each of the first to third solenoid valves 4
6, 47, 48 and expansion valves 49, 50, 51 in series, and are configured as a closed circuit in parallel with each other.

FIG. 3 shows another embodiment of the refrigeration system, in which the first to third solenoid valves 46, 47 shown in FIG.
48 and each of the first to third expansion valves 49, 50, 51
Instead, first to third electronic expansion valves 65, 66, and 67 may be used, each of which has an opening/closing function and a pressure reducing function, and whose valve shaft can be moved forward and backward in the vertical direction by a stepping motor.

FIG. 4 shows an electric circuit for operating the refrigeration system, and each phase of the 3-phase 200V power supply is connected to a contact 52Ca of an electromagnetic contactor 52C for the compressor, which will be described later.
The compressor motor CM is connected through. The operation switch SW is connected to the S phase, and the R,
A duty cycle (hereinafter referred to as D) timer T is connected between the S and both phases. This timer T for D is, for example, a 30 minute cycle timer,
The contact Ta is closed for 25 minutes from the start of driving, the contact Ta is opened for the remaining 5 minutes, and after the 5 minutes have passed, the device is reset to the initial state.
Incidentally, the length of the closing and opening times of the contact Ta can be arbitrarily changed depending on the set temperature of the storage chamber 9 to be controlled. TH is a temperature switch such as a thermostat that controls the temperature of the storage chamber 9;
It constitutes a series circuit with Ta and relay X, and is connected in parallel to the D timer T. For example, this temperature switch TH is ±6°C to +5°C.
It is a mechanism that opens and closes with a differential of 0.5℃, but due to the characteristics of the temperature switch TH, it cannot immediately follow changes in cold air temperature.
Even if the set temperature was set at -3℃ (lower limit set temperature -3.5℃, upper limit set temperature -2.5℃), the experiment was performed by opening at -4℃ and closing at -1℃.
Control to an average temperature of °C. 52C is compressor motor
This is an electromagnetic contactor for driving the CM, and forms a series circuit with both the high-voltage and low-voltage switches 63H and 63L of the refrigeration system, and is connected in parallel to the D timer T. ST is a defrost timer (hereinafter referred to as S timer), and each of the 1st to 4th normally open contacts
It includes STa ₁ , STa ₂ , STa ₃ , STa ₄ and both first and second normally closed contacts STb ₁ and STb ₂ . This S timer ST consists of a 6-hour timer, for example.
After 2 hours and 45 minutes from the start of operation, the first 15 minute
Open normally closed contact STb ₁ , both 1st and 3rd normally open contacts
The first output that closes STa ₁ and STa ₃ is output, and when 5 hours and 45 minutes have passed from the start of driving, the second normally closed contact STb ₂ is opened for 15 minutes, and both the second and fourth normally open contacts STa ₂ ,
The second output that closes STa ₄ is output, and after 6 hours, it is reset to the initial state, and from then on, the first,
It has a mechanism that outputs the second output. The first solenoid valve 46 is the first normally closed contact of the S timer ST.
A series circuit is formed with STb ₁ and the normally open contact Xa of the relay X, and the second solenoid valve 47 is connected to the S
It is connected in series with the second normally closed contact STb ₂ of the timer ST, and in parallel with the first normally closed contact STb ₁ and the first solenoid valve 46 . Also, the third
The solenoid valve 48 is connected in series with the normally closed contact Xb of the relay X. This normally closed contact Xb includes the third and fourth normally open contacts STa ₃ and STa ₄ of the S timer ST.
are connected in parallel. The first electric heater 16 is a first electrical heater that is opened and closed based on the first normally open contact STa ₁ of the S timer ST and the temperature of the first evaporator 14 or the temperature of the air that has passed through the evaporator 14. The second electric heater 17 is connected in series with the high temperature return thermoswitch DT ₁ , and the second electric heater 17 is connected to the second normally open contact STa ₂ of the S timer ST and the temperature of the third evaporator 15 or the temperature of the air passing through this evaporator. It is connected in series with a second high temperature return thermoswitch DT ₂ that opens and closes based on temperature. Both the first and second high temperature return thermoswitches DT ₁ and DT ₂ are opened at temperatures above 5°C to cut off both the first and second electric heaters 16 and 17, and closed at temperatures below 5°C. Both the first and second electric heaters 16 and 17 are enabled to be energized. Incidentally, both the first and second blowing fans 18, 20
is connected to operate continuously when the operation switch SW is turned on.

Next, the operation of the low-temperature show case 1 will be explained with reference to FIGS. 1 to 4.

When the operation switch (SW) is closed, timer T for D and timer ST for S are driven.
The electromagnetic contactor 52C is excited, and both the first and second blowing fans 18, 20 are operated. As the electromagnetic contactor 52C is energized, the contact 52Ca is closed, the compressor motor CM is driven, the compressor 41 is operated, and refrigerant circulation is started. Also, at the same time as the D timer T is energized, the contact Ta closes.
Relay X is energized through temperature switch TH and normally open contact Xa is closed, and normally closed contact Xb _{is opened} . The third solenoid valve 48 is de-energized and closed while being energized and opened through STb ₂ and the normally open contact Xa. As both the first and second solenoid valves 46, 47 are opened, the cooling operation of the first and second evaporators 14, 15, that is, the first mode is started, and both the first and second expansion valves 49, 50 are opened. The reduced pressure liquid refrigerant is supplied to both the first and second evaporators 14 and 15 through the evaporators 14 and 15, respectively, and exchanges heat with the cold air flow that is being forcedly circulated through the inner layer 6. By repeating this heat exchange, the temperature of the cold air stream gradually decreases, and the air curtain CA formed in the opening 2 also becomes cold due to this cold air stream, as shown in FIG. Incidentally, since the reduced pressure liquid refrigerant is not supplied to the third evaporator 19, the protective air flow forced to circulate through the outer layer 7 is not supplied to the third evaporator 19.
When a guard air curtain GA is formed outside the CA, the temperature will be lowered slightly due to the influence of the cold air flow. During the cooling operation of both the first and second evaporators 14 and 15, the temperature of the cold air reaches the lower limit setting of the temperature switch TH, and the temperature switch is turned off.
When the thermo-off time is reached when TH is open, or when the duty-off time of timer T for D is reached, contact Ta is opened.
When in the second mode, in which the relay 47 are de-energized and closed together, while the third solenoid valve 48 is energized and opened through the normally closed contact Xb. Both the first and second solenoid valves 46, 4
Due to the closure of 7, both the first and second evaporators 14, 15
The supply of vacuum liquid refrigerant to the third
The reduced pressure liquid refrigerant is supplied to the evaporator 19 and undergoes heat exchange with the protective air flow that is forcedly circulated through the outer layer 7 . By repeating this heat exchange during the thermo-off time or duty-off time, the temperature of the protective airflow gradually decreases, and the guard air curtain GA formed by this protective airflow also becomes colder, approaching the temperature of the air curtain GA caused by the cold airflow. It turns out. During this time, both the first and second evaporators 14 and 15 are subjected to off-cycle defrosting with a cold air flow forced to be circulated by the first blower fan 18. Note that the frost adhering to the third evaporator 19 is defrosted in the off-cycle by the protective air flow during the thermo-on time and the duty-on time.

Then, when the cold air temperature reaches the upper limit setting of the temperature switch TH and the temperature switch TH is closed, and the duty ion time is reached and the contact Ta is closed, the relay X is energized and the normally open contact Xa is closed.
When the normally closed contact Xb opens, both the first and second solenoid valves 4
6 and 47 are energized and opened, while the third solenoid valve 48
is closed and de-energized, and the cooling operation by both the first and second evaporators 14 and 15 described above, that is, returns to the first mode. It should be noted that during this cooling operation, the above-mentioned second mode, that is, the thermo-off time or duty-off time is taken several times.

As the cooling operation progresses, both the first and second evaporators 14,
15, the start of the cooling operation, that is, the S timer ST
When 2 hours and 45 minutes have passed since the S timer
15 minutes from ST both 1st and 3rd normally open contacts STa ₁ ,
A first output that closes STa ₃ and opens the first normally closed contact STb ₁ is output, energizing the first electric heater 16 and connecting the third solenoid valve 4 through the third normally open contact STa ₃ .
8 is energized and opened, on the other hand, the first solenoid valve 46 is de-energized and closed, and the supply of reduced pressure liquid refrigerant to the first evaporator 14 is interrupted, and the first evaporator 14 is in defrosting operation, that is, in the third mode. Become. During this defrosting operation, the third solenoid valve 48 is opened and the third evaporator 19 is operated for cooling regardless of the operation of the D timer T, and the second evaporator 15 is also operated for cooling, and the outer layer 7 Protective airflow that is forced to circulate through the outer passage 2 of the inner layer 6
The temperature of the cold air flowing through the inner passage 28 of the inner layer 6 in which the first evaporator 14 is arranged is gradually increased by the heating of the first electric heater 16. . That is, in conjunction with the defrosting operation of the first evaporator 14, both the second and third evaporators 15 and 19 are operated for cooling, and during this period, the opening operation of the D timer T does not work effectively.

As the defrosting operation of the first evaporator 14 progresses, the first
When the temperature of the cold air flow that has passed through the evaporator 14 reaches 5°C, the first high temperature return thermoswitch DT ₁ is opened, the first electric heater 16 is de-energized, and the drain is turned off until the defrosting end time. This is the time to drain the water. When the set defrost time has passed,
A reduced pressure liquid refrigerant is supplied to the first evaporator 14;
Cooling operation of both the second evaporators 14 and 15, that is, the first
mode, the supply of reduced pressure liquid refrigerant to the third evaporator 19 is interrupted, and the third evaporator 1
9 will be defrosted off-cycle by the protective air flow during the thermo-on and duty-on periods. It should be noted that during this cooling operation, the above-mentioned second mode, that is, thermo-off or duty-off time will be taken several times.

As the cooling operation further progresses, both the first and second evaporators 1
4 and 15, the start of the cooling operation, that is, the S timer
When 5 hours and 45 minutes have passed since ST was driven, both the second and fourth normally open contacts STa ₂ ,
A second output that closes STa ₄ and opens the second normally closed contact STb ₂ is output, energizing the second electric heater 17 and connecting the third solenoid valve ₄ through the fourth normally open contact STa 4.
8 is energized and opened, while the second solenoid valve 47 is de-energized and closed, and the supply of reduced pressure liquid refrigerant to the second evaporator 15 is interrupted, and the second evaporator 15 is in defrosting operation, that is, in the fourth mode. Become. During this defrosting operation, the third solenoid valve 48 is opened and the third evaporator 19 is operated for cooling regardless of the operation of the D timer T, and the first evaporator 14 is also operated for cooling, and the outer layer 7 Protective airflow that is forced to circulate and the inner passage 2 of the inner layer 6
The cold air flow passing through the inner layer 6 is cooled, and the temperature of the cold air flow passing through the outer passage 29 of the inner layer 6 where the second evaporator 15 is arranged is gradually increased by heating by the second electric heater 17. do. That is, in conjunction with the defrosting operation of the second evaporator 15, both the first and third evaporators 14 and 19 are operated for cooling, and during this time, the opening operation of the D timer T does not work effectively.

As the defrosting operation of the second evaporator 15 progresses, the second
When the temperature of the cold air flow that has passed through the evaporator 15 reaches 5°C, the second high temperature return thermoswitch DT ₂ is opened, the second electric heater 17 is de-energized, and the drain is turned off until the end of defrosting. This is the time to drain the water. When the set defrost time has passed,
The reduced pressure liquid refrigerant is supplied to the second evaporator 15, and the first,
Cooling operation of both the second evaporators 14 and 15, that is, the first
mode, the third evaporator 19 interrupts the supply of reduced pressure liquid refrigerant, and the third evaporator 19
9 will be defrosted off-cycle by the protective air flow during the thermo-on and duty-on periods. It should be noted that during this cooling operation, the above-mentioned second mode, that is, thermo-off or duty-off time will be taken several times.

When the defrosting time of the second evaporator 15 ends, the S timer ST is reset to the initial state, and the above-mentioned first mode, third mode, first mode, and fourth mode are repeated, and the first mode second among
The mode is executed and the time chart shown in FIG. 5 is obtained.

Both the first and second evaporators 14,
The cooling evaporation temperature of the third evaporator 15 is -13°C, the cooling evaporation temperature of the third evaporator 19 is -8°C, and the set temperature of the storage chamber 9 is -13°C.
3℃ (upper limit set temperature -2.5℃, lower limit set temperature -3.5
℃), the evaporation temperatures of each evaporator 14, 15, and 19 have the characteristics shown in FIG. 6 in the first mode. That is, both the first and second evaporators 14 and 15 are lowered to -13°C during thermo-on and duty-on times when reduced-pressure liquid refrigerant is supplied, but on the other hand, during thermo-off or duty-on times when the supply of reduced-pressure liquid refrigerant is interrupted. The temperature rises to -2℃. On the other hand, the third evaporator 19 is -8°C during the thermo-off and duty-off times when the reduced pressure liquid refrigerant is supplied.
On the other hand, during thermo-on and duty-on times when the supply of reduced pressure liquid refrigerant is interrupted, +
The temperature rises to 1.5℃.

The third evaporator 19 includes both the first and second evaporators 1.
In addition to setting the evaporation temperature higher than 4 and 15, the supply time of reduced pressure liquid refrigerant to the third evaporator 19 is set to be shorter than the supply time of reduced pressure liquid refrigerant to both the first and second evaporators 14 and 15. The evaporation temperature of the third evaporator 19 will not be lower than the evaporation temperature of both the first and second evaporators 14 and 15, but if Temperature is first and second
Even if the evaporation temperature becomes lower than the evaporation temperature of both evaporators 14 and 15, the third evaporator 19 is arranged in the outer layer 7, which is a preferable condition from the viewpoint of lowering the temperature of the protective air flow passing through the outer layer 7.

Figure 7 shows the ambient temperature 27℃ and ambient humidity 70% as described above.
The third mode under the conditions of , that is, the first evaporator 1
4 shows the air temperature characteristics during defrosting, and A is storage room 9.
B is the air temperature immediately after passing through the first evaporator 14, C is the air temperature immediately after passing through the second evaporator 15, and D is the air temperature after passing through the third evaporator 19 and blown out into the opening 2. It's temperature. According to the figure, the air temperature A
and B are -5°C before the start of the third mode because both the first and second evaporators 14 and 15 are in the first mode performing a cooling action, but with the start of the third mode, the temperature in the first The air temperature A is increased by heating the electric heater 16.
The air that passes through the inner passage 28 is heated by the first electric heater 16 and its temperature rises, and the air that passes through the outer passage 29 and is cooled by the second evaporator 15 and whose temperature decreases. Since the cold air flows into the opening 2 as the air curtain CA, the temperature of the cold air stream blown out to the opening 2 as the air curtain CA is suppressed to below 0°C from the beginning to the middle of the third mode, so the air temperature A also becomes below 0°C. suppressed. or,
3rd evaporator 1 from middle to late stage of 3rd mode
The air passing through 9 is blown out into the opening 2 as a cold air flow below 0°C and acts as a guard air curtain GA that lowers the temperature of the air curtain CA. It can be suppressed to 1°C to 1°C.

That is, while the latent heat of the first electric heater 16 is largely used to defrost the first evaporator 14 from the beginning to the middle of the third mode, only a small amount is used to heat the air passing through the inner passage 28. In addition, the amount of air passing through the inner passage 28 is smaller than the amount of air passing through the outside 29 because frost acts as a flow path resistance. By merging the air that has passed through the passage 29 at the inner layer 6, a cold air flow with a temperature of 0° C. or lower can be created, so that the air temperature A can be suppressed to 0° C. or lower. or,
The amount of latent heat of the first electric heater 16 that loosens the air passing through the first evaporator 14 gradually becomes larger than the amount that defrosts the first evaporator 14 from the middle to the latter half of the third mode. In addition, since the amount of air passing through the inner passage 28 gradually increases as the frost gradually melts, the temperature of the cold air flow passing through the inner layer 6 can be increased by combining the air that has passed through the outer passage 29. Although the rise in temperature cannot be suppressed from the initial to middle stage, the protective airflow that is blown out from the outer layer 7 to the opening 2 and forms the guard air curtain GA is below 0°C, so the air curtain CA can be cooled at the opening 2. It is possible to suppress an increase in the air temperature A in the storage room 9 cooled by CA.

Further, an inner passage 28 and an outer passage 29 are formed independently in the inner layer 6, and first and second high temperature return thermoswitches DT are provided upstream of the confluence area of the air that has passed through the inner passage and the outer passage. ₁ and DT ₂ , when the first high-temperature return thermoswitch DT ₁ reaches 5°C and opens to cut off the power supply to the first electric heater 16 in the latter half of the third mode, air is blown from the inner layer 6. The temperature of the cold air flow is lower than the temperature of the first high temperature return thermoswitch DT ₁ and therefore
When returning to the mode, it takes less time to lower the temperature of the storage chamber 9 to the set temperature.

Note that the same temperature characteristics as shown in FIG. 7 can be obtained also in the fourth mode in which the second evaporation period 15 is defrosted.

(g) Effects of the invention According to the present invention described above, the following effects are produced.

When the two evaporators are cooling by supplying reduced pressure liquid refrigerant to both the first and second evaporators, and
When the evaporator has a defrosting function and both the second and third evaporators have a cooling function, and when the second evaporator has a defrosting function and both the first and third evaporators have a cooling function. Because reduced pressure liquid refrigerant is always supplied to both evaporators, the amount of reduced pressure liquid refrigerant supplied to the refrigeration system is approximately constant, and as a result,
Even when one evaporator has a defrosting function and two evaporators have a cooling function, there is an extreme drop in the refrigerant evaporation temperature of the evaporator during the cooling function, and frost formation due to this drop in refrigerant evaporation temperature. In addition to being able to avoid a significant increase in the temperature, it is also possible to suppress the temperature rise in the storage room during defrosting of one evaporator.

When looking at the arrangement of the first to third evaporators in plan, the front half of the third evaporator overlaps the rear half of the second evaporator, and the front half of the second evaporator overlaps the rear half of the first evaporator. Although three evaporators are installed, the configuration is such that three evaporators can be installed in the space required for two evaporators. , it is possible to reduce the depth of the entire constant-temperature case by the length of one evaporator.

[Brief explanation of drawings]

1 to 7 show an embodiment of the low-temperature show case of the present invention, FIG. 1 is a longitudinal sectional side view, and FIG.
Figure 3 is a refrigerant circuit diagram, Figure 3 is a refrigerant circuit diagram showing another embodiment, Figure 4 is an electric circuit diagram, Figure 5 is an operation time chart, Figure 6 is a characteristic diagram showing refrigerant evaporation temperature, and Figure 7 is a diagram showing refrigerant evaporation temperature. The figure is a characteristic diagram showing the air temperature of a constant temperature show case when one evaporator is used for defrosting and two evaporators are used for cooling, and FIG. 8 is a characteristic diagram of the prior art corresponding to FIG. 6. 6...Inner layer, 7...Outer layer, 14...First evaporator, 15...Second evaporator, 18...Blower fan,
19...Third evaporator, 20...Blower fan, 27
...dividing plate, 28...medial path, 29...lateral path.

Claims (1)

[Claims] 1 Equipped with first to third evaporators connected in parallel to each other, when the first evaporator is defrosting, both the second and third evaporators perform a cooling action, and the second evaporator performs the defrosting function. When the first and third evaporators are used, the first and third evaporators are equipped with a refrigeration device and a blower fan,
One part is divided into inner and outer parts by a dividing plate, and the first part is divided into inner and outer parts by a dividing plate.
an inner layer having an inner channel in which an evaporator is disposed, an outer vessel in which the second evaporator is disposed, and an outer layer including a blower fan and the third evaporator;
The second evaporator is located between the first evaporator and the third evaporator, and the inner half overlaps the outer half of the first evaporator and the outer half overlaps the inner half of the third evaporator. A low-temperature case located in the.