JPH01131874A - Low-temperature showcase - Google Patents

Abstract

PURPOSE: To suppress the frosting of a low-temperature showcase by providing an inner layer with an inner path where a first evaporator is arranged and an outer path where a second evaporator is arranged and an outer layer with a blowing fan and a third evaporator, and arranging the second evaporator so that the inner half overlaps with the outer half of the first evaporator and the outer half overlaps with the inner half of the third evaporator. CONSTITUTION: Only the air temperature of an inner path 28 rapidly increases due to the heating of a first electrical heater 16 as a first evaporator 14 starts defrosting. However, since air whose temperature is increased by heating the first electrical heater 16 and air whose temperature is reduced due to cooling by a second evaporator 15 caused by passing through an outer path 29 merge in an inner layer 6, the temperature of a cold air flow being discharged from an opening 2 as an air curtain CA is suppressed to 0 deg.C or less from the initial to middle stages of defrosting. Also, air passing through a third evaporator 19 from the middle to later stages of defrosting is discharged to the opening 2 as a cold air liquid, thus reducing the temperature of the air curtain CA and hence suppressing the increase in an air temperature A to a temperature deg.C striding over 0 deg.C-1 deg.C.

Description

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

(Example) Conventional technology When defrosting a low-temperature showcase, at least two evaporators are provided in order to suppress the temperature rise in the storage room, and while one evaporator is defrosting, the other evaporator is 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.
No. 60-256773, and U.S. Pat. No. 4,633,677.

(c) Problems to be solved by the invention The low-temperature showcase 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, so that the air inlet surface and air outlet surface of each are the same. If the depth of the low-temperature showcase is fixed at the time of design, there is a problem that the depth of the storage chamber is reduced by the inner layer, and one evaporation During the TJ operation of the evaporator, since the other adjacent evaporator is operated for cooling, each evaporator is 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 should be adjusted, taking into consideration that the temperature of the air curtain that closes the openings for storing and taking out products will rise. 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 evaporator under cooling operation must be Due to the low temperature of the evaporator, the amount of heat from the defrosting heat source is insufficient, resulting in the problem that the defrost from the evaporator cannot be completely removed during the set defrosting time, for example, 20 minutes. Ta. In addition, other causes of frost residue include:
After performing cooling operation on three evaporators, one evaporator is switched to defrosting operation while continuing cooling operation on two evaporators to reduce the number of evaporators operated on cooling operation. The refrigerant evaporation temperature of the evaporator during cooling operation drops extremely, and the amount of frost on the evaporator increases during cooling operation.In addition, the amount of heat in the high-pressure liquid refrigerant, which is the defrosting heat source, becomes insufficient, and the defrosting Residual frost will occur in the evaporator during M operation.

Also, Japanese Patent Application Laid-open No. 50-256773 and U.S. Patent No. 4
The low-temperature showcase shown in No. 633677 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 and the other is placed in the outer passage. After cooling the two evaporators, one evaporator is kept in cooling operation, while the other evaporator is switched to defrosting operation. Similarly, the refrigerant evaporation temperature of the evaporator in the evaporator during cooling operation drops dramatically, and the amount of B frost on the evaporator during cooling operation increases, and the amount of heat in the high-pressure liquid refrigerant, which serves as the defrosting heat source, becomes insufficient. , a problem arises in that frost remains on the evaporator during defrosting operation.

Incidentally, the ambient temperature of the low-temperature showcase is 27°C, and the ambient humidity is 7.
Under the condition of 0%, the first. After setting the refrigerant evaporation temperature of both second evaporators to -13°C and supplying reduced pressure liquid refrigerant to both evaporators to have a cooling effect, continuously supplying reduced pressure liquid refrigerant to one evaporator, and When the supply of reduced pressure liquid refrigerant to the other evaporator is alternately interrupted, the refrigerant evaporation temperature of the evaporator to which the reduced pressure liquid refrigerant is supplied drops to about 120°C, as shown in Figure 8, and cooling is interrupted. Not only does the amount of contamination on the evaporator during operation increase, but also the temperature of the circulating cold air stream becomes low, so that defrosting of the evaporator during defrosting operation when the supply of vacuum liquid refrigerant is interrupted does not proceed. First, overall, a problem arises in that the amount of frost on the low-temperature showcase increases.

(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. When the container is being defrosted, the second. Both the third evaporator performs the cooling function, and when the second evaporator is defrosted, the first evaporator. Both third evaporators are equipped with a refrigeration device that performs a cooling action, and a blower fan, a part of which is divided into an inner and outer part by a dividing plate, and an inner path in which the first evaporator is misplaced, and an inner path in which the second evaporator is an inner layer having an outer tract disposed;
an outer layer including a blower fan and the third evaporator, the second evaporator being located between the first evaporator and the third evaporator, and an inner half of the second evaporator having an inner half of the first evaporator. The third evaporator is provided with a low-temperature syszy case arranged so as to overlap the outer half of the third evaporator and the outer half overlap the inner half of the third evaporator.

(*) According to the working example, the inner path (28
) only the air temperature (A) rises rapidly, but in the inner passage (
28), the air is heated by the first electric heater (16) and the temperature is increased, and the air that is cooled by the second evaporator (15) and lowered in temperature by passing through the outer path (29) forms the inner layer. (6), the temperature of the cold air flow blown out to the opening (2) as an air curtain (CA) is suppressed to below 0℃ from the early to mid-stage of defrosting, so the air temperature (A) is also The air that has been suppressed to below 0°C and has passed through the third evaporator (19) during the middle to late stages of defrosting is blown out to the opening (2) as a cold air flow of below 0°C, and is blown out of the air curtain (CA). Because it acts as a guard air curtain (GA) that lowers the temperature, the increase in air temperature (A) is reduced from -℃ to 1℃ over 0℃.
can be suppressed to

In addition, since the partition plate (4) and the dividing plate (27) are both formed with inclined parts (21) (30) in the same direction, the first to third evaporators (14) (15) ( 19), the rear half of the second evaporator (15) overlaps the front half of the third evaporator (19).
), the rear half of the first evaporator (14) overlaps with the front half of the evaporators (14
) (19) in the installation space of three evaporators (14) (1
5) (19) can be placed.

(F) Example The present invention will be explained in detail based on the drawings below. (1) not shown in Figure 1 is an opening (2) for storing and taking out products on the front side.
This is a low-temperature showcase whose main body is composed of a heat insulating wall (3) formed with a first wall at an appropriate interval from the inner wall of the heat insulating wall (3). By sequentially arranging the second partition plates (4) and (5), an inner layer (6) for circulating cold air, an outer layer (7) for circulating protective air, and a plurality of shelves (8) are provided. a storage chamber (9), an air outlet (10) (11) of both the inner and outer layers (6) < 7 along the longitudinal direction of the upper edge of the opening (2), and a longitudinal direction of the lower edge of the opening (2); along the direction of the air outlet (10) (
Suction ports (12) and (13) of both the inner and outer Wj (6) and (7) facing the inner and outer Wj (6) and (7) are formed.

The inner layer (6) has a first layer having a plate-fin shape and having the same heat exchange capacity. Both the second evaporators (14) and (15), and the first evaporator, which is provided on the lower surface of the two evaporators on the air inlet side and is energized when the corresponding evaporator (14><15) is defrosted. 27th! Air heaters (16) (17) and a first axial blower fan (18) for forcibly circulating the cold air flow in the inner layer (6) as shown by the solid line arrows in FIG.
) includes a third evaporator (19) in the form of a plate fin;
A second axial blower fan (20) for forcibly circulating the protective airflow of the outer layer (7) is arranged as indicated by the dashed-dotted line arrow in FIG. Said 1st. 2nd double blower fan (18) (20)
is constantly operated, and in order to increase the amount of air blown by the first fan (18) and to increase the speed of air than the second fan (20), the number of the first fan (18) is changed to the number of the second fan (18). 20).

The back portion of the first partition plate (4) has a sloped portion (21) that slopes downward toward the rear, and the bottom wall portion has a vertical raised portion (22). Both J!
Widened channels (23), (24), (25), and (26) are formed in the back area and the bottom area of the inner layer (6) to widen the passage width, and the widened channels in the back area of the inner layer (6) are formed. (23) both first and second evaporators (14) (15), a third evaporator (19) in the widening channel (24) of the back area of the outer layer (7), and a third evaporator (19) in the inner layer (6). A first blower fan (18) is provided in the expansion passage (25) in the bottom area of the outer layer (7), and an expansion passage (26) in the bottom area of the outer layer (7)
A second blower fan (20) is disposed at each of the two.

(27) is arranged in the widened channel (23) of the inner layer (6), and connects this widened channel (23) to the inner channel (28) and the outer channel (29).
It is a dividing plate made of metal such as stainless steel that is divided into two parts, the inside and outside, and in the center thereof there is formed an inclined part (30) that slopes downward from the rear, and in the lower part that extends downward from the first electric heater (16). , an extension part (32) having a flange (31) facing the lower surface of the first evaporator (14) is formed. Since the dividing plate (27) forms the inclined part (30), the lower part of the inner passage (28) and the upper part of the outer passage (29) are the same as those of the first. The upper part of the inner passage (28) and the lower part of the outer passage (29) serve as widened passages (33) and (34) for arranging the second evaporators (14) and (15), while the upper part of the inner passage (28) and the lower part of the outer passage (29) are used to narrow the cold air flow. It becomes a narrow road (35) (36). Also, the entrance width of the inner passage (28) is changed by the dividing plate (27) to the outer passage (29).
), while the outlet width of the outer passageway (29) is about twice the outlet width of the inner passageway (28);
The ventilation volume of both evaporators (14) and (15) in a non-frosted state is kept constant.

Since the first partition plate (4) and the dividing plate (27) are both formed with inclined portions <21> (30) in the same direction, each of the first to third evaporators (14) (15) (19) when viewed in plan, the rear half of the second evaporator (15) overlaps the front half of the third evaporator (19), and the second evaporator (19) overlaps the front half of the second evaporator (19).
The rear half of the first evaporator (14) overlaps the front half of the first evaporator (15), and although three evaporators (14) (15 bar 19) are arranged, there are actually two evaporators (1
4) Three evaporators <14>(
15) (19) can be placed.

(37) is a third partition plate made of metal such as stainless steel and placed in front of the first evaporator (14). Along with the arrangement of this partition plate, the back wall ( 38) A side channel (39) is formed between the lower part and the upper part to be open and the lower part to be closed. Numerous holes (40) are formed in the lower part of the back wall (38) and 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 showcase (1), and this refrigeration system includes a refrigerant compressor (41),
Air-cooled condenser (42), liquid receiver (43), dryer (44)
), sight glass (45), first to third solenoid valves (4
6) (47) (48) The first to third pressure reducing devices
Each expansion valve (49) (50) (51), the first to third
Each evaporator (14) (15) (19), gas-liquid separator (52
) into a high-pressure gas pipe (53), a high-pressure supply pipe (54), and three high-pressure liquid branch pipes (55) (5) whose inlets are connected to this high-pressure liquid pipe.
6) (57), 3 low pressure liquid pipes (58) (59) (60
), 3 low pressure gas branch pipes (61) (62) (63),
The low pressure gas pipe to which one outlet of each low pressure gas branch pipe is connected (
64) in an annular manner, the first to third
The first to third solenoid valves (46) (47) (48) and expansion valves (4) corresponding to each evaporator (14) (15) (19)
9) (50) and (51) are connected in series and are configured as a closed circuit in parallel relationship with each other.

FIG. 3 shows another embodiment of the refrigeration system, in which the first to third electromagnetic valves (46), (47), and (48) and the first to third expansion valves (49) shown in FIG. Instead of (50) and (51), it is also possible to use the first to third electronic expansion valves (65), (66), and (67), which have an opening/closing function and a pressure reduction function, and whose valve shafts can be moved up and down by a stepping motor. good.

FIG. 4 shows an electric circuit for operating the refrigeration device,
A compressor motor (CM) is connected to each of the R, S, and T phases of the three-phase 200V power supply via a contact (szca) of a compressor magnetic contactor (52C), which will be described later. The operation switch (SW) is connected, and a duty cycle timer (T) is connected between both R2S phases.
is connected. This D timer (T) is, for example, 30
The contact (Ta) is closed for 25 minutes from the start of driving, and the contact (Ta) is closed for the remaining 5 minutes.
) is opened, and after 5 minutes have elapsed, the device is reset to its initial state. In addition, the closing of the contact (1'a),
The length of the time period can be arbitrarily changed depending on the set temperature of the storage chamber (9) to be controlled. (TI) is a temperature switch such as a thermostat that controls the temperature of the storage room (9), and constitutes a series circuit with the contact (Ta) and relay (X), and is parallel to the timer (1'). The connection is broken. This temperature switch (TI) is for example -66C
The mechanism opens and closes with a differential of ±0.5°C in the range of ~ +5°C, but the temperature switch (T
Due to the characteristics of H), it is not possible to immediately follow changes in cold air temperature, so the set temperature is set at -3°C (lower limit set temperature -3.5°C,
Even though the upper limit temperature is set at -2.5°C, the opening operation is actually performed at -4°C and the closing action is at -1°C, and the storage chamber (9) is kept at about -3°C.
Control to an average temperature of °C. (52C) is an electromagnetic contactor for driving the compressor motor (CM>), which forms a series circuit with both the high-pressure and low-pressure switches (63H) and (63L) of the refrigeration system. are connected in parallel.

(ST) is a timer for defrosting (hereinafter referred to as S use), and the first to fourth normally open contacts (STa+) (STa, > (STa,
>(STaa) and the first. 2nd both side closing contact (STb l
) (STb, ). This S timer (ST) is composed of, for example, a 6-hour timer, and when 2 hours and 45 minutes have passed since the start of driving, the first normally closed contact (STb, ) is opened for 15 minutes, and the first and fourth normally open contacts are opened. (ST
aI) < STa s ) is output, and when 5 hours and 45 minutes have passed from the start of driving, the second
Open the normally closed contact (STb,) and open the second. The 4th intercity point (S
The second output that closes Ta * ) (STa = ) is output, and after 6 hours, it is reset to the initial state, and from then on, the first output is output in the same way. It is a mechanism that outputs the second output. The first solenoid valve (46) has a first normally closed contact (STb, ) of the S timer (ST) and a normally closed contact (STb, ) of the relay (X).
Xa) constitutes a series circuit with the second solenoid valve (
47) is the second normally closed contact (ST) of the S timer (ST).
b, ), and the first normally closed contact ′
(STb,) and the first voltage high valve (46) are connected in parallel. Further, the third solenoid valve (48) is connected in series with the normally closed contact (Xb) of the relay (X). This normally closed contact (Xb) is connected to the third point of the S timer (ST).
The fourth two city points (STa, ) (STa, ) are connected in parallel. Further, the first electric heater (16) controls the temperature of the first regular contact point (STa+> of the S tie 7 (ST) and the first evaporator (14) or the air that has passed through this evaporator (14). The second electric heater (17) is connected in series with a first high temperature return thermoswitch (DTI) that opens and closes based on the temperature of the S timer (ST). ) and a second high temperature return thermoswitch (DTI) which is opened and closed based on the temperature of the third evaporator (15) or the temperature of the air passing through this evaporator. Both high temperature return thermoswitch <D
TI) (DTI) becomes open at 5°C or higher, and the first. Second
Both electric heaters (16) and (17) are cut off, and 5°
C, it becomes closed and the first. Both second electric heaters (16) (
17) It makes it possible to conduct electricity. In addition, the first
, the second blower fan (18) (2Q) is operated by pressing the operation switch (
It is connected to operate continuously as the switch (SW) is turned on.

Next, referring to Figures 1 to 4, the low temperature showcase (1
) operation will be explained.

When the operation switch (SW) is closed, the D timer (T) and the S timer (ST) are driven, and the electromagnetic contactor (52C) is energized. Both second blower fans (1B) (20) are operated. The electromagnetic contactor (
52C), the contact (52Ca) closes, the compressor motor (CM) is driven, the compressor (41) is operated, and refrigerant circulation is started. Also, the contact (Ta) closes at the same time as the D timer (T) is energized, and this contact (Ta)
The relay (X) is energized through the temperature switch (TH) and the normally open contact (Xa) closes, and the normally closed contact (X
b) opens and the first. The second solenoid valves (46, 47) are energized and opened through the first and second solenoid valve points (from S) (STbl) and normally open contacts (Xa), and the third solenoid valve (48) is de-energized and closed. Said 1st. As both the second solenoid valves (46) and (47) open, the first solenoid valve (46) and (47) open. Second
The cooling operation of both evaporators (14) and (15), that is, the first mode is started, and the first mode. A cold air flow in which decompressed liquid refrigerant is supplied to the first and second evaporators (14, 15) through the second expansion valves (49, 50), respectively, and is forcedly circulated through the inner layer (6). Heat exchanged. By repeating this heat exchange, the temperature of the cold air stream gradually decreases, and this cold air stream forms an air curtain (CA) in the opening (2) as shown in Figure 1.
It also gets cold. Incidentally, since the reduced pressure liquid refrigerant is not supplied to the third evaporator (19), the protective airflow being forcedly circulated through the outer layer (7) is transferred to the guard air curtain (GA) outside the air curtain (CA). When it is completely formed, the temperature will be lowered slightly due to the effect of the cold air flow. Said 1st. During the cooling operation of both second evaporators (14) and (15), when the cold air temperature reaches the lower limit set value of the temperature switch (TI) and the temperature switch (TI) is opened during the thermo-off time, or when the D timer ( In the second mode, when the duty-off time of T) has reached and the contact (Ta) is open, the relay (X) is de-energized and the normally open contact (Xa) is open.
is opened, the normally closed contact (Xb) is closed, and along with this opening/closing operation, the first. Both the second solenoid valves (46, 47) are de-energized and closed, while the third solenoid valve (48) is energized and opened through the normally closed contact (Xb). Said 1st. As both the second solenoid valves (46) and (47) close, the first solenoid valve (46) and (47) close. The supply of reduced pressure liquid refrigerant to both second evaporators (14) and (15) is interrupted, and reduced pressure liquid refrigerant is instead supplied to the third evaporator (19) and forcedly circulated through outside M3 (7). Heat exchanged with the protective air stream. By repeating this heat exchange during the thermo-off time or duty-off time, the temperature of the protective air stream gradually decreases, and the guard air curtain (GA) formed by this protective air stream also becomes cold, resulting in an air curtain (CA) formed by the cold air stream. The temperature will approach .

During this time, the 1st. Both second evaporators (14, 15) are off-cycle defrosted with a forced circulation of cold air 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.

When the cold air temperature reaches the upper limit set value of the temperature switch (TH), the temperature switch (TI) is closed, and the duty-on time has come and the contact (Ta) is closed, the relay (X) is energized and remains in the normal state. The open contact (Xa) is closed, the normally closed contact (Xb) is open, and the first. 2nd double solenoid valve (46)
(47) is energized and opened, while the third solenoid valve (48) is de-energized and closed. Second double evaporator (14)
(15) returns to the cooling operation, that is, 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, the first Both second evaporators (14) (15
), that is, after 2 hours and 45 minutes have elapsed since the S timer (Sff) was activated, the S timer (5 units)
15 minutes from the 1st. Point between the third city and city (STa r)
(STa,) is closed and the first normally closed contact (STb,) is opened, a first output is output, which energizes the first electric heater (16), and also through the third normally open contact (STa s). While the third solenoid valve (48) is fully energized, 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. 14) defrosting operation, that is, the third mode. During this defrosting operation, the third solenoid valve (48) is opened regardless of the operation of the D timer (T), and the third evaporator (19) is operated for cooling.
Subsequently, the second evaporator (15) is also operated for cooling, and the outer layer (7
) and the cold air flow passing through the outer channel (29) of the inner layer (6) are cooled, and the air flow of the inner layer (6) where the first evaporator (14) is arranged is cooled. Inner road 28)
The temperature of the cold air flowing through the first electric heater (16) gradually rises. That is, along with the M removal operation of the first evaporator (14), the second. Both the 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.

When the defrosting operation of the first evaporator (14) progresses and the temperature of the cold air flow passing through the first evaporator (14) reaches 5°C, the first high temperature return thermoswitch (DT+) opens. As a result, the first electric heater (16) is de-energized, and the time until the end of defrosting is a draining time for draining the condensate. After the set defrosting time has passed, the first evaporator (14)
A reduced pressure liquid refrigerant is supplied to both the first and second evaporators (14).
(is>Both cooling operation, that is, the first mode, while
The supply of vacuum liquid refrigerant to the third evaporator (19) will be interrupted, and the frost adhering to the third evaporator (19) will be defrosted in the off-cycle by the protective air flow during the thermo-on and duty-on periods. Become. 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.

The cooling operation further progresses to the first stage. Both second evaporators (14) (
15) Start of the cooling operation, that is, the S timer (ST)
After 5 hours and 45 minutes have passed since the drive of the S tie? (ST
) for 15 minutes. The 4th intercity point (Sraa) (S
Taa) is closed and the second normally closed contact (srb,) is opened.The second output is energized to the second electric heater (17), and the third normally open contact (SIa,) is energized. While the solenoid valve (48) is energized and opened, 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. ) defrosting operation, that is, the fourth mode. During this defrosting operation, the D timer (T
), the third solenoid valve (48) is opened and the third evaporator (19) is operated for cooling, and the first evaporator (14) is also operated for cooling, forcing the outer layer (7) Protective airflow being circulated and the inner channel (28) of the inner layer (6)
The cold air flow passing through the second evaporator (15
) The cold air flow passing through the outer channel (29) of the inner layer (6) in which the inner layer (6) is arranged is gradually heated by the heating of the second electric heater (17). That is, with the defrosting operation of the second evaporator (15), the first. Both the third evaporators (14) and (19) are operated for cooling, and during this period, the opening operation of the D timer (T) does not work effectively.

When the defrosting operation of the second evaporator (15) progresses and the temperature of the cold air flow passing through the second evaporator (15) reaches 5°C, the second high temperature return thermoswitch (DI switch) is opened. As a result, the second electric heater (17>) is de-energized, and the time until the end of defrosting is a draining time for draining the condensate.

When the set defrosting time has passed, the reduced pressure liquid refrigerant is supplied to the second evaporator (15), and both the first and second evaporators (14) (
15) While both cooling operations are in the first mode, the supply of reduced pressure liquid refrigerant to the third evaporator (19) is interrupted, and the frost attached to the third evaporator (19) is removed from the thermo-on and During the duty-on period, the off-cycle defrost will be terminated by the protective airflow. 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. , the second mode is performed within the first mode,
The time chart is shown in FIG.

Under the conditions of the ambient temperature of the low temperature showcase (1) of 27° C. and the ambient humidity of 70%, the first. Second double evaporator (14) (1
5) Refrigerant evaporation temperature of -13°C1 third evaporator (19)
Set the refrigerant evaporation temperature in the storage room (9) to -2,5°C (upper limit set temperature -2,5 °C1 lower limit set temperature -
3.5° C.), the evaporation temperatures of each evaporator (14), (15), and (19) have the characteristics shown in FIG. 6 in the first mode. That is, 1st. Both second evaporators (14) (15
) is lowered to -113°C during thermo-on and duty-on times when reduced-pressure liquid refrigerant is supplied, but rises to -12°C during thermo-off and duty-on times when the supply of reduced-pressure liquid refrigerant is interrupted. On the other hand, the third evaporator (19
) is lowered to -18°C during thermo-off and duty-off times when vacuum liquid refrigerant is supplied, but rises to +1.5°C during thermo-on and duty-on times when supply of vacuum liquid refrigerant is interrupted.

The third evaporator (19) is the first evaporator (19). Second double evaporator (14)
In addition to setting the evaporation temperature higher than in (15), the supply time of reduced pressure liquid refrigerant to the third evaporator (19) is
．． Since the supply time of the reduced pressure liquid refrigerant to both the second evaporators (14) and (15) is shorter than the supply time of the reduced pressure liquid refrigerant to the second evaporators (14) and (15), the first. The evaporation temperature of the third evaporator (19) is higher than that of the second evaporators (14) and (15).
) will not become lower, but if the evaporation temperature of the third evaporator (19) is lower than that of the first evaporator (19). Second double evaporator (14) (1
5) Even if it becomes lower than the evaporation temperature of the third evaporator (
19) is arranged in the outer layer (7), which is a favorable situation from the point of view of lowering the temperature of the protective air flow passing through the outer layer (7).

Figure 7 shows the air temperature characteristics during defrosting of the first evaporator (14) in the third mode under the above-mentioned conditions of ambient temperature 27°C and ambient humidity 70%, and (A) shows the air temperature characteristics during defrosting of the first evaporator (14). ), (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), (D) is the air temperature in the third evaporator ( 19) through the opening (2
) is the temperature of the air blown out. According to the figure, the air temperatures (A) and (B) are the same as the first mode before starting the third mode. Second
Since both evaporators (14) and (15) are in the first mode with a cooling effect, the temperature is -5°C, but with the start of the third mode, the air temperature (A
) only rises rapidly, but the air whose temperature has increased by being heated by the first electric heater (16) by passing through the inner path (28), and the second air which has increased in temperature by passing through the outer path (29).
The air whose temperature has been lowered by being cooled by the evaporator (15) forms the inner layer (
6), the temperature of the cold air flow blown out to the opening (2) as an air curtain (CA) is suppressed to below 0°C from the beginning to the middle of the third mode, so the air temperature (A) temperature is also suppressed to below 0°C. Also, from the middle to the late stage of the third mode, the air that has passed through the third evaporator (19) is blown out to the opening (2) as a cold air flow of 0°C or less, thereby lowering the temperature of the air curtain (CA). (GA), the increase in air temperature (A) is -1°C to 1° above O'C.
It can be suppressed to C.

That is, while the latent heat of the first electric heater (16) is mostly used to defrost the first evaporator (14) from the beginning to the middle of the third mode, it also heats the air passing through the inner path (28). In addition, the amount of air passing through the inner passage (28) is small compared to the amount of air passing through the outer passage (29) because frost acts as a flow path resistance. , the air passing through the inner passage (28) and the outer passage (29).
) by merging with the air that has passed through the inner layer (6), a cold air flow of 0° C. or lower can be created, so the air temperature (A) can be suppressed to 0° C. or lower. Also, the latent heat of the first electric heater (16) is transferred to the first evaporator (16) from the middle to the late stage of the third mode.
In addition to the fact that the amount of warming the air passing through the first evaporator (14) gradually becomes larger than the amount of defrosting (14), the inner path (28) Since the amount of air passing through the inner layer (6) gradually increases, it is not possible to suppress the temperature rise of the cold air flow passing through the inner layer (6) from the initial to middle stages by merging the air that has passed through the outer layer (29). , the protective air flow blown out from the outer layer (7) to the opening (2) and forming a guard air curtain (GA") is O"CC.
An air curtain (CA) is installed at the opening (2) to
), it is possible to suppress the rise in air temperature (A) in the storage room (9) cooled by the air curtain (CA).

Further, an inner passage (28) and an outer passage (29>) are formed independently in the inner layer (6), and first and second passages are formed on the upstream side of the confluence area of the air that has passed through the inner passage and the outer passage. Because both high-temperature return thermoswitches (DT,) (DT,) are provided, the first high-temperature return thermoswitch (DT,) opens when the temperature reaches 5°C in the latter half of the third mode, and the first electric heater (DT,) opens. 16), the temperature of the cold air flow blown out from the inner layer (6) is controlled by the first high temperature return thermoswitch (
DTI>, and therefore, when the first mode is restored, 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 evaporator (15) is defrosted.

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

■First. When both the second evaporators are supplied with reduced pressure liquid refrigerant and the two evaporators are performing a cooling action, the first evaporator is performing a defrosting action, and the second evaporator is performing a defrosting action. When both the third evaporators are performing a cooling action, the second evaporator is performing a defrosting action, and the first evaporator is performing a defrosting action. When both the third evaporators are performing a cooling action, since the reduced pressure liquid refrigerant is always supplied to both evaporators, the supply amount of the reduced pressure liquid refrigerant to the refrigeration system is approximately constant. As a result, even when one evaporator is performing a defrosting function and two evaporators are performing a cooling function, an extreme decrease in the refrigerant evaporation temperature occurs in the evaporator that is performing the cooling function, and this decrease in refrigerant evaporation temperature is caused. In addition to being able to avoid a significant increase in frost formation, it is also possible to suppress the temperature rise in the storage room during defrosting of one evaporator.

■If you look at the arrangement of the first to third evaporators in a plan view,
The rear half of the second evaporator overlaps the front half of the third evaporator, and the rear half of the first evaporator overlaps the front half of the second evaporator, so that three evaporators are arranged. Regardless,
Since three evaporators can be arranged in the space for actually two evaporators, the depth of the entire low-temperature showcase can be reduced by the length of one evaporator.

[Brief explanation of the drawing]

1 to 7 show an embodiment of the low temperature showcase of the present invention, FIG. 1 is a longitudinal sectional side view, FIG. 2 is a refrigerant circuit diagram, and FIG. 3 is a refrigerant circuit showing another embodiment. Figure 4 is an electric circuit diagram, Figure 5 is an operation time chart, Figure 6 is a characteristic diagram showing the refrigerant evaporation temperature, Figure 7 is for defrosting one evaporator, two
FIG. 8 is a characteristic diagram showing the air temperature in the low-temperature showcase when each evaporator is used for cooling. (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 tract, (29)...lateral tract.

Claims (1)

[Claims] 1. Equipped with first to third evaporators connected in parallel to each other,
When the first evaporator is defrosted, both the second and third evaporators perform a cooling action, and when the second evaporator is defrosted, both the first and third evaporators perform a cooling action. an inner layer comprising a refrigeration device and a blower fan, a part of which is divided into an inner and outer part by a dividing plate, and has an inner path in which the first evaporator is disposed, and an outer channel in which the second evaporator is disposed; an outer layer including a blower fan and the third evaporator, the second evaporator being located between the first evaporator and the third evaporator, and an inner half of the second evaporator having an inner half of the first evaporator. a low temperature showcase arranged so as to overlap the outer half of the third evaporator, and the outer half overlap the inner half of the third evaporator.