JPH01131879A - Refrigerator - Google Patents

Abstract

PURPOSE: To suppress the frosting of a low-temp. show case by operating so that a second and third evaporators work to cool while a first evaporator is defrosted and the first and third evaporator work to cool while the second one is defrosted. CONSTITUTION: Between the case of feeding a low-pressure liq. refrigerant to a first and second evaporators 14, 15 to work cooling and the case of working the second and third evaporators 15, 19 to cool while the first one 14 is defrosted, the feed rate of the liq. refrigerant in the refrigerator is unchanged but approximately const. Hence even when one evaporator is defrosted and two evaporators work to cool, the extreme down of the refrigerant evaporating temp. in the evaporator working to cool and great increase of frost due to this refrigerant evaporating temp. down can be prevented previously.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a refrigeration system used in low-temperature showcases, refrigerators, etc., and is equipped with three evaporators.

(b) Conventional technology A refrigeration system used in a low-temperature showcase is equipped with at least two evaporators and is equipped with at least two evaporators to suppress the temperature rise in the storage room during defrosting. While doing
Increasingly, a combination of defrosting and cooling methods are being adopted in which the other evaporator is cooled.

This combined defrosting and cooling method includes a method in which all of a plurality of evaporators connected in parallel are placed in an inner layer for cold air circulation, and a method in which one evaporator is placed in an inner layer and the other evaporator is placed in an inner layer for circulating cold air. There is a method of placing it in the outer layer for protective air circulation.

The former method is disclosed in Japanese Patent Publication No. 62-25952, Japanese Patent Application Laid-Open No. 60-256773, and U.S. Patent No. 46336.
No. 77, and examples of the latter method include Japanese Patent Publication No. 60-12542 and U.S. Pat. No. 4,648,247.

(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. During defrosting operation of one evaporator, because it is arranged in the inner layer so that it is at the same height,
Since the adjacent evaporator is operated for cooling, each evaporator is mutually susceptible to the influence of the temperature of the other evaporator.

For this reason, if the set temperature of the storage room is set below 0℃,
Considering that the temperature of the air curtain that closes the product storage and removal openings increases, it is necessary to set the refrigerant evaporation temperature of the evaporator operated for cooling to below -10"C. In order to use high-pressure liquid refrigerant, which undergoes heat exchange and becomes supercooled liquid in the evaporator, as a defrosting heat source, the temperature of the evaporator during cooling operation is low, so the amount of heat in the defrosting heat source is insufficient, and the setting A problem arose in that the frost on the evaporator that was being operated was not completely removed during the defrosting time, for example, 20 minutes.Also, another cause of residual frost was that the three evaporators After the cooling operation of the two evaporators, one evaporator is switched to the defrosting operation to reduce the number of evaporators that are being cooled. The evaporation temperature of the refrigerant in the evaporator is extremely low, 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, is insufficient, causing evaporation during defrosting operation. This will leave frost residue on the container.

Also, Japanese Patent Application Laid-open No. 60-256773 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 parallel to each other, one of which is connected to the inner passage and the other to the outer passage. After cooling the two evaporators, the cooling operation of one evaporator is continued, while the other evaporator is switched to defrosting operation.
Similar to the publication, the refrigerant evaporation temperature of the evaporator during cooling operation drops extremely, and the amount of frost on the evaporator during cooling operation increases. This causes a problem in that frost remains on the evaporator during defrosting operation.

Furthermore, the low-temperature showcase shown in Japanese Patent Publication No. 60-12542 and U.S. Patent No. 4,648,247 has two evaporators connected in parallel, one of which is arranged in the inner layer and the other in the outer layer, After heat exchange is performed using a high-pressure refrigerant such as hot gas or high-pressure liquid refrigerant as a de-weighting heat source for the inner layer evaporator, this refrigerant is depressurized and guided to the outer layer evaporator during cooling operation. Since the condensation temperature of the refrigerant changes according to the season, that is, the temperature change of the ambient conditions in which the low-temperature showcase is installed, the amount of heat given to the evaporator from the defrosting heat source per unit time decreases during seasons such as winter when the outside air temperature is low. There is a problem that the frost on the evaporator cannot be completely removed within the defrosting time, and conversely, in seasons such as summer when the outside temperature is high, the amount of water supplied to the evaporator from the de-duty heat source per unit During the latter stages of defrosting, when the fog melts and the surface of the evaporator is exposed to the circulating airflow, the defrosting heat source becomes larger than the cooling heat source, and the temperature in the storage room increases rapidly. An increasing number of problems arose.

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 the inner lid generator for a cooling effect, the reduced pressure liquid refrigerant is continuously supplied to one evaporator. At the same time, 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 being supplied decreases to 120°C as shown in FIG.
Not only does the amount of frost on the evaporator during the cooling process increase as the temperature decreases, but also the circulating cold air flow becomes lower in temperature. The defrosting process does not progress, and overall, the problem arises 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 refrigerant supply is stopped and the equipment is being defrosted, the second. Both the third evaporator performs the cooling action, and when the second evaporator is defrosted with the refrigerant supply stopped, the first evaporator performs the cooling action. A refrigeration system is provided in which both third evaporators perform a cooling action.

(n) According to the working example, the first. Second double evaporator (14) (15)
Two evaporators (14) (15) are supplied with reduced pressure liquid refrigerant to
is performing a cooling action, the first evaporator (14) is performing a defrosting action, and the second evaporator (14) is performing a defrosting action. When both third evaporators (15) and (19) are performing a cooling action, and when the second evaporator (15) is performing a defrosting action,
1st. When both the third evaporators (14) and (19) are performing a cooling action, the reduced pressure liquid refrigerant is constantly supplied to both evaporators, so the supply amount of the reduced pressure liquid refrigerant in the refrigeration system is becomes approximately constant.

(f) Example The present invention will be explained in detail below based on the drawings. (1) shown in Fig. 3 is an opening (2) for storing and taking out products on the front side.
A low-temperature showcase whose main body is composed of a heat insulating wall (3) formed with a first heat insulating wall (3) 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 B (6) for circulating cold air, an outer layer (7) for circulating protective air, and multiple shelves (8) can be arranged. a storage chamber (9) equipped with a storage chamber (9), an air outlet (10) (11) of both the inner and outer layers (6) and (7) along the longitudinal direction of the upper edge of the opening (2), and a lower edge of the opening (2). The air outlet (10) (
The suction ports (
12) and (13) 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, 15) and the first evaporator, which is provided on the lower surface of the air inlet side of the two evaporators and is energized when the corresponding evaporators (14, 15) are defrosted. A second electric heater (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 arrow in FIG. 7)
A third evaporator (19) in the form of a plate fin and a second axial blower fan (20) for forcibly circulating the protective airflow of the outer layer (7) are arranged as indicated by the dashed line arrow in Fig. 3. has been done. Said 1st. Both the second blower fans (18) and (20) are fully operational at all times, and in order to increase the amount of air blown by the first blower fan (18) and to increase the wind speed than the second blower fan (20), the first blower fan (18) is operated at full capacity. (18) is made larger than the number of second blowing fans (20).

The back portion of the first partition plate (4) is formed with a sloped portion (21) that slopes backward, and the bottom wall portion is formed with a vertical raised portion (22), so that the inside and outside of the Both layers (
6) A path (23) (24) < 25) (26) with a wider passageway width is formed in the back area and bottom area in (7), and the path (23) in the back area of the inner layer (6) is the first,
A second double evaporator (14) (15), a third evaporator (19) in the path (24) of the back area of the outer layer (7), a third evaporator (19) in the path (25) of the bottom area of the inner layer (6); The first ventilation fan (
18), second blowing fans (two) are respectively arranged in the passages (26) of the bottom area of said outer layer (7).

(27) is arranged in the path (23) of the inner layer (6), and connects this path (23) with the inner path (28) and the outer path (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 connected to both the first and second evaporators (14) and (15). The upper part of the inner passage (28) and the lower part of the outer passage (29) serve as narrow passages (35) (36) for narrowing the cold air flow. . 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) and (30) in the same direction, each of the first to third evaporators (14) and (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 even though three evaporators (14>(15) and (19)) are arranged, 2 evaporators (
14) Three evaporators (14>) in the installation space of (19)
(15) and (19) can be arranged.

(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 passage (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. 1 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), each of the first to third expansion valves (49), (50), and (51) that are pressure reducing devices, each of the first to third evaporators (14>(15) (19), Gas-liquid separator (52)
A high pressure gas pipe (53), a high pressure liquid pipe (54), and three high pressure liquid branch pipes (55 bar 56) whose inlets are connected to this high pressure liquid pipe.
(57), three low pressure liquid pipes (58) (59) (60),
Three low-pressure gas branch pipes (61), (62), and (63), and a low-pressure gas pipe (64) to which the outlet of each low-pressure gas branch pipe is connected.
By connecting the first to third evaporators (14), (15), and (19) in an annular manner, the first to third electromagnetic valves (46), (47), and expansion valves (46), (47, and 49)(
50) and (51), and are configured as closed circuits that are in a parallel relationship with each other.

FIG. 2 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 reducing 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 (52Ca) of a compressor electromagnetic contactor (52C), which will be described later. An operation switch (SW) is connected to the S phase, and a duty cycle timer (T) is connected between both phases of R9S. This D timer (T) is, for example, a 30-minute cycle timer, which closes its contact (Ta) for 25 minutes from the start of driving, and closes its contact (Ta) for the remaining 5 minutes.
It is a mechanism that resets to the initial state after 5 minutes have passed. Incidentally, the length of both the closing time and the interval time of the contact point (Ta) can be arbitrarily changed depending on the set temperature of the storage chamber (9) to be controlled. (TI) is the storage room (
9) A temperature switch such as a thermos cloth for controlling the temperature constitutes a series circuit with the contact (Ta) and the relay (X), and is connected in parallel to the above-mentioned timer (T). This temperature switch (TI) is for example -6℃ to +5℃
It is a mechanism that opens and closes with a differential of ±0.5℃ in the range of ℃, but due to the characteristics of the temperature switch (TI), it cannot immediately follow changes in cold air temperature.
Even if the set temperature is -3°C (lower limit set temperature -3.5°C, upper limit set temperature -2.5°C), it actually opens at -4°C, -
The closing operation is performed at 1°C and the storage chamber (9) is controlled to an average temperature of approximately -3°C. (52C) is the compressor motor (CM
), which constitutes a series circuit with both the high-voltage and low-voltage switches (631) (63L) of the refrigeration system, and is connected in parallel to the above-described timer (T).

(ST) is a timer for defrosting (hereinafter referred to as S use), and the first to fourth normally open contacts (STa+) (STa, ) (STa,
) (STa,) and the first. 2nd both side closing contact (STb I
) (STb*). This S timer (ST) is composed of, for example, a 6-hour timer, and when 2 hours and 45 minutes have passed from the start of operation, it opens the first normally closed contact (STb,) for 15 minutes, and the first and third domestic contact points (STb, ) are opened for 15 minutes. STa r
) (STa s ) is output, and when 5 hours and 45 minutes have elapsed from the start of driving, the second normally closed contact (STb, ) is opened for 15 minutes, and the second normally closed contact (STb, ) is closed. 4th each normally open contact (STa
=) (STa, ) is output to close the second output, and when 6 hours have elapsed, it is reset to the initial state, and from then on, the first output. It is a mechanism that outputs the second output. The first solenoid valve (4
6) is the first normally closed contact (srb) of the S timer (ST).
+) and the normally closed contact (Xa) of the relay (X) constitute a series circuit, and the second solenoid valve (47)
It is connected in series with the second normally closed contact (STh, ) of the timer (ST), and in parallel with the first normally closed contact (STb, ) and the first solenoid valve (46). Further, the third solenoid valve (48) is connected to the normally closed contact (X) of the relay (X).
b) are connected in series. This normally closed contact (Xb) is connected to the third point of the S timer (ST). The 4th intercity point (ST
a s ) (STa = ) are connected in parallel.

Further, the first electric heater (16) is connected to the S timer (S
T)'s first regular contact point (STa I) and the first evaporator (1
4) or the temperature of the air that has passed through the evaporator (14).
17) is the second constant contact point (ST) of the S timer (ST).
a*) and a second high temperature return thermoswitch (DTx) which is opened and closed based on the temperature of the second evaporator (15) or the temperature of the air that has passed through this evaporator. Said 1st. 2nd high temperature return thermo switch (DT, ) (o
'rz) becomes open at 5°C or higher and becomes the first. Both the second electric heaters (16) and (17) are cut off, and the first and second electric heaters are closed when the temperature is lower than 5°C. Both second electric heaters (16) and (17) are enabled to be energized. Incidentally, both the first and second blower fans (18) and (20) are connected to be operated continuously when the operation switch (S-ken) 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 (Sl') are driven, and at the same time, the electromagnetic contactor (52C) is excited, and the first... Both the second blower fans (18) and (20) are now fully operational. As the electromagnetic contactor (52C) is energized, the contact (52Ca) closes, the compressor motor (CM) is driven, the compressor (41) is operated, and refrigerant circulation is started. Also, the D timer (T)
The contact (Ta) closes at the same time as the current is applied to the contact (Ta).
) and temperature switch (TI), the relay (X) is energized to close the normally closed contact (Xa), and the normally closed contact (
Xb) opens and the first. The second two solenoid valves (46) and (47) have the first and second solenoid valve points (srb t > (srb t
) and the normally closed contact (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. The cooling operation, that is, the first mode, of both the second evaporators (14) and (15) is started, and the first mode. Second double expansion valve (49) (
50) to the first and second evaporators (14) and (15), respectively.
) is supplied with reduced pressure liquid refrigerant and exchanges heat with the cold air flow that is 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 of A), the temperature will be lowered slightly due to the influence of the cold air flow. Said 1st. Second double evaporator (14)
(15) During the cooling operation, the cold air temperature changes to the temperature switch (TH).
) is reached and the temperature switch (TH) is opened during the thermo-off time, or when the duty-off time of the D timer (T) is reached and the contact (Ta) is opened.
In mode, the relay (X) is de-energized, the normally closed contact (Xa) is open, and the normally closed contact (Xb) is idle, and along with this opening/closing operation, the first. Second solenoid valve (46) (47)
are de-energized and closed together, while the third solenoid valve (4
8) 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. Protection in which 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 the outer layer (7). Heat is exchanged with the airflow. 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 expanded into 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 (TI), the temperature switch (TH) is closed, and the duty-on time has come and the contact (Ta) is closed, the relay (
X) is energized, the normally closed contact (Xa) is closed, and the normally closed contact (Xb
) becomes open and the first. Both the second solenoid valves (46) and (47) are energized and opened, while the third solenoid valve (48) is de-energized and closed. The cooling operation using the second evaporators (14) and (15) 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, the first Both second evaporators (14) (15
), that is, after 2 hours and 45 minutes have elapsed since the S timer (ST) was started, the first 1. Third domestic demand contact point (STa, ) (
STa, ) is closed and the first normally closed contact (sTb+) is opened.The first output is output, which energizes the first electric heater (16) and connects the third electromagnetic through the third normal contact (STas). While the valve (48) is energized and opened, the first solenoid valve (46)
is de-energized and the supply of reduced pressure liquid refrigerant to the first evaporator (14) is interrupted, and the first evaporator (14) enters a defrosting operation, that is, a third mode. During this defrosting operation, the D timer (
Regardless of the operation of I'), the third solenoid valve (48) is opened and the third evaporator (19) is operated for cooling, and the second evaporator (15) is also operated for cooling, and the outer layer (7) Protective airflow is forced to circulate through the outer channel (2) of the inner layer (6).
The cold air stream passing through the first evaporator (9) is cooled and the first evaporator (
The cold air flow passing through the inner channel (28) of the inner layer (6) in which the inner layer (6) is arranged is gradually heated by heating by the first electric heater (16). That is, with the defrosting 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 (DTs) is opened. 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).
<15> While both cooling operations are in the first mode,
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 (5 units)
After 5 hours and 45 minutes have passed since the drive of the S tie? (ST
) for 15 minutes. 4th intercity point (SIa,) <S
A second output is output that closes the terminal (la, ) and opens the second normally closed contact (SIbz), energizes the second electric heater (17), and connects the third normally closed contact (STa a ) to While the solenoid valve (48) is energized and opened, the second solenoid valve (47)
) is de-energized and the supply of the reduced pressure liquid refrigerant to the second evaporator (15) is interrupted, and the second evaporator (15) enters the defrosting operation, that is, the fourth mode. During this defrosting operation, the third solenoid valve (48) is opened regardless of the operation of the D timer (T), the third evaporator (19) is operated for cooling, and the first evaporator (14) is continuously operated. ) is also in cooling operation, with protective air being forcedly circulated through the outer layer (7) and the inner passage (2) of the inner layer (6).
The cold air stream passing through the second evaporator (
The cold air flow passing through the outer channel (29) of the inner layer (6) in which the structure (15) is arranged is gradually heated by 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) have completed their cooling operation, and during this time, 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 (D) is activated. When the second electric heater (17) is opened, the second electric heater (17) 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 second evaporator (15)
A reduced pressure liquid refrigerant is supplied to both the first and second evaporators (14).
(15) While both cooling operations are in the first mode,
The supply of vacuum liquid refrigerant to the third evaporator (19) can be interrupted, and the frost adhering to the third evaporator (19) will be defrosted in the off-cycle by the protective airflow 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. , 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. Both second evaporators (14) (
15) refrigerant evaporation temperature to -13°C1 third evaporator (19
) When operating with the refrigerant evaporation temperature set at -8°C, and the set temperature of the storage chamber (9) set at -3°C (upper limit set temperature -2,5°C, lower limit set temperature -3,5°C), the first mode Then, the evaporation temperatures of each evaporator (14), (15), and (19) have the characteristics shown in FIG. That is, 1st. Second double evaporator (14) (1
5) is lowered to -136C during thermo-on and duty-on times when reduced pressure liquid refrigerant is supplied, but on the other hand,
During the thermo-off or duty-on time when the supply of vacuum liquid refrigerant is interrupted, the temperature rises to -12°C. On the other hand, the third evaporator (
19) is lowered to 18°C during thermo-off and duty-off times when reduced pressure liquid refrigerant is supplied;
During the thermo-on and duty-on times when the supply of vacuum liquid refrigerant is interrupted, the temperature rises to +1.5°C.

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 cooling effect, the temperature is -5°C, but with the start of the third mode, the air temperature (A) is increased by heating by the first electric heater (16).
However, by passing through the inner passage (28), the air heated by the first electric heater (16) and having a raised temperature, and by passing through the outer passage (29), the air is heated by the second evaporator (15). ) and the air whose temperature has decreased by being cooled in 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) is also The temperature is kept below 0°C. In addition, from the middle to the late stage of the third mode, the air that has passed through the third evaporator (19) is blown out into the opening (2) as a cold air flow of 0°C or less, and a guard air curtain (CA) lowers the temperature of the air curtain (CA). GA), the increase in air temperature (A) can be suppressed to a temperature of -1°C to 1°C, which is over 0°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, it also heats the air passing through the inner passage (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 it with the air that has passed through M(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. Moreover, the first electric heater (16)
The latent heat of the 3rd mode is due to the fact that the amount of warming the air passing through the first evaporator (14) gradually becomes larger than the amount of defrosting the first evaporator (14) from the middle to the late stage of the third mode. As the frost gradually melts, the amount of air passing through the inner layer (28) gradually increases, so the inner layer (6) is energized by merging the air that has passed through the outer layer (29). Although it is not possible to suppress the rise in temperature of the cold air flow from the initial to middle stage, the temperature of the protective air blown out from the outer layer (7) to the opening (2) and forming the guard air curtain (GA) is below 0°C. In 2) air curtain (CA
), 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 a first passageway (28) and an outer passage (29) are formed on the upstream side of the confluence area of the air that has passed through the inner passage and the outer passage. Since both second high temperature return thermoswitches (DTI) (D'I', ) are provided, the first high temperature return thermoswitch (o'r+) reaches 5°C and opens in the latter half of the third mode. Therefore, when the first electric heater (16) is de-energized, the inner layer (6)
The temperature of the cold air flow blown out from the DTI is lower than the temperature of the first high-temperature return thermoswitch (DTI), so when the first mode is returned, it takes a short time to lower the temperature of the storage chamber (9) to the set temperature. It gets faster.

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.

In the present invention described above, 1. Second double evaporator (14) (1
5) to supply vacuum liquid refrigerant to the two evaporators (14) and (1).
5) has a cooling effect, the first evaporator (14) has a defrosting effect, and the second evaporator (14) has a defrosting effect. When both the third evaporators (15) and (19) are performing the cooling function, and when the second evaporator (15) is performing the defrosting function, the first evaporator (15) is performing the defrosting function. When both the third evaporators (14) and (19) are performing a cooling action, the reduced pressure liquid refrigerant is constantly supplied to both evaporators, so the supply amount of the reduced pressure liquid refrigerant in the refrigeration system is becomes approximately constant, and as a result, even when one evaporator is defrosting and two evaporators are cooling, there is an extreme drop in refrigerant evaporation temperature and this refrigerant evaporation occurs in the evaporator that is cooling. A significant increase in frost formation caused by a drop in temperature can be avoided.

(G) Effects of the Invention According to the present invention described above, in the refrigeration system equipped with three evaporators, the first evaporator. 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. A significant increase in frost formation can be avoided, and the number of times the refrigeration equipment must be defrosted can be reduced.

[Brief explanation of the drawing]

Figures 1 to 7 show embodiments of the refrigeration system of the present invention, Figure 1 is a refrigerant circuit diagram, Figure 2 is a refrigerant circuit diagram showing another embodiment, and Figure 3 is a diagram of the refrigeration system. A vertical side view of the low-temperature showcase equipped, Fig. 4 is an electric circuit diagram, Fig. 5 is an operation time chart, Fig. 6 is a characteristic diagram showing the refrigerant evaporation temperature, and Fig. 7 is a defrosting diagram of one evaporator. , a characteristic diagram showing the air temperature of the low-temperature showcase when two evaporators are cooled, and FIG. 8 is a characteristic diagram of the prior art corresponding to FIG. 6. (14)...first evaporator, (15)...second evaporator, (19)...third evaporator.

Claims (1)

[Claims] 1. Equipped with first to third evaporators connected in parallel to each other,
When the refrigerant supply to the first evaporator is stopped and the defrosting is being performed, both the second and third evaporators perform a cooling action, and when the refrigerant supply to the second evaporator is stopped and the defrosting is being performed, the first and third evaporators perform a cooling action. A refrigeration system in which both the third evaporator performs the cooling action.