JP2000105029A - Two-stage cascade refrigerating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the pressure of high-pressure refrigerant upon defrosting operation so as to be the optimum value. SOLUTION: A two-stage cascade refrigerating device is provided with a high-temperature side refrigerating circuit constituted of a compressor, a four-way switching valve, a condenser, an expansion valve and the evaporating unit of a refrigerant heat exchanger 11 which are connected sequentially. The refrigerating device is provided with a first low-temperature side refrigerating circuit 3A, in which the compressor 31, the four-way switching valve 33, the condensing unit of the refrigerant heat exchanger 11, the expansion valve EV21 and the evaporator 5a are connected sequentially. When a predetermined condition is achieved after starting the defrosting operation of the first low-temperature side refrigerating circuit 3A by switching the four-way switching valve 33 of first low-temperature side refrigerating circuit 3A upon starting the defrosting operation, the four-way switching valve in the high- temperature side refrigerating circuit is switched. When a predetermined condition is achieved after re-opening the cooling operation of the high-temperature side refrigerating circuit by switching the four-way switching valve of the high-temperature side refrigerating circuit upon finishing the defrosting, the four-way switching valve 33 of the first low-temperature side refrigerating circuit 3A is switched to re-open the cooling operation of the first low- temperature side refrigerating circuit 3A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binary refrigeration system, and more particularly to a measure against defrost operation.

[0002]

2. Description of the Related Art Conventionally, a binary refrigeration system is disclosed in
As disclosed in Japanese Patent No. 210515, a primary refrigerant circuit and a secondary refrigerant circuit that individually perform refrigeration operation are provided. This binary refrigeration apparatus is used to obtain a low temperature of minus several tens of degrees, and can be used in a high efficiency from a high compression ratio to a low compression ratio, which is advantageous in energy saving.

[0003] The primary side refrigerant circuit of the above-mentioned two-way refrigeration system is configured by connecting a compressor, a condenser, an expansion valve, and an evaporator of a refrigerant heat exchanger in this order. Also, the secondary refrigerant circuit is
The compressor, the condensing part of the refrigerant heat exchanger, the expansion valve, and the evaporator are sequentially connected. In the refrigerant heat exchanger, the heat of condensation of the secondary refrigerant circuit and the heat of evaporation of the primary refrigerant circuit are exchanged.

[0004]

In addition to the above-described two-stage refrigeration system, the conventional two-stage refrigeration system forms frost on the evaporator of the secondary refrigerant, so that, for example, a defrost operation is performed every predetermined time. ing. For this defrost operation, a method has been proposed in which the refrigerant circulation directions of the primary refrigerant circuit and the secondary refrigerant circuit are reversed in cycle.

That is, a four-way switching valve is provided in each of the primary side refrigerant circuit and the secondary side refrigerant circuit, and the primary side refrigerant circuit causes the refrigerant to flow from the compressor in the order of the refrigerant heat exchanger, the expansion valve, and the condenser. Circulate back to machine. On the other hand, the secondary-side refrigerant circuit flows the refrigerant from the compressor in the order of the evaporator, the expansion valve, and the refrigerant heat exchanger, and circulates the refrigerant back to the compressor. As a result, the frost on the evaporator in the secondary refrigerant circuit is melted by the high-temperature refrigerant from the compressor.

[0006] During the above-mentioned defrost operation, the condenser of the primary refrigerant circuit functions as an evaporator, and the evaporator of the refrigerant heat exchanger functions as a condenser. On the other hand, in the secondary refrigerant circuit, the evaporator functions as a condenser, and the condensing part of the refrigerant heat exchanger functions as an evaporator.

Therefore, if the four-way switching valves of the primary refrigerant circuit and the secondary refrigerant circuit are simultaneously switched during the defrost operation, there is a problem that the high-pressure refrigerant pressure cannot be controlled to an appropriate value.

Specifically, when the four-way switching valves of the primary refrigerant circuit and the secondary refrigerant circuit are simultaneously switched at the start of the defrost operation, the condensing portion of the refrigerant heat exchanger in the secondary refrigerant circuit evaporates. At the same time as switching to the function, the evaporating section of the refrigerant heat exchanger in the primary refrigerant circuit switches to the condensation function. In this case, the temperature is high immediately before the condensing section of the secondary-side refrigerant circuit is switched, so that the evaporating section of the primary-side refrigerant circuit serving as the condenser cannot sufficiently release heat.
As a result, the high-pressure refrigerant pressure in the primary refrigerant circuit excessively increases,
High pressure abnormality occurs.

At the end of the defrost operation, when the cooling operation is restarted, if the four-way switching valves of the primary refrigerant circuit and the secondary refrigerant circuit are simultaneously switched, the refrigerant heat exchanger in the primary refrigerant circuit is switched. Returns from the condensing function to the evaporating function, while the condensing part of the refrigerant heat exchanger in the secondary refrigerant circuit returns from the evaporating function to the condensing function. In this case, since the temperature is in a high temperature state just before the evaporating section of the primary refrigerant circuit is switched, the condensing section of the secondary refrigerant circuit that returns to the condensing function cannot sufficiently radiate heat. As a result, the high-pressure refrigerant pressure in the secondary-side refrigerant circuit excessively increases, and a high-pressure abnormality occurs.

The present invention has been made in view of the above, and has as its object to control the high-pressure refrigerant pressure during defrost operation to an appropriate value.

[0011]

Means for Solving the Problems-Summary of the Invention-The present invention is to shift the switching timing of the four-way switching valve between the primary refrigerant circuit and the secondary refrigerant circuit during the defrost operation.

-Solution Means- Specifically, as shown in FIG. 2, a first solution means is a compressor (21), a condenser (22), an expansion mechanism (EV11), a refrigerant heat exchanger, The evaporator of (11) is connected in order, and comprises a primary refrigerant circuit (20) through which the primary refrigerant circulates, while the compressor (31) and the condenser of the refrigerant heat exchanger (11) The expansion mechanism (EV21) and the evaporator (5a) are connected in order, and the secondary refrigerant circulates, and the primary refrigerant and the secondary refrigerant exchange heat in the refrigerant heat exchanger (11). It is premised on a binary refrigeration system including at least one secondary refrigerant circuit (3A).

The at least one secondary refrigerant circuit (3A) and the primary refrigerant circuit (20) are provided with a four-way switching valve (24) so that the refrigerant circulation direction is reversible between a forward cycle and a reverse cycle. , 33) are provided. Further, the primary refrigerant circuit (20) and a reversible secondary refrigerant circuit (3A) for circulating the refrigerant.
And a defrost means (72) for controlling the defrost operation by making the refrigerant circulation in a reverse cycle. In addition, upon receiving the defrost start signal from the defrost means (72), the four-way switching valve (33) of the secondary refrigerant circuit (3A) is switched to start the defrost operation of the secondary refrigerant circuit (3A). Thereafter, when a predetermined condition is satisfied, the four-way switching valve (2
A start control means (73) is provided for starting the defrost operation of the primary-side refrigerant circuit (20) by switching 4).

Further, the second solution means is based on a binary refrigeration apparatus having a primary refrigerant circuit and a secondary refrigerant circuit similar to the first solution means. Then, the at least one secondary refrigerant circuit (3A) and the primary refrigerant circuit (2
0) is provided with a four-way switching valve (24, 33) so that the refrigerant circulation direction is reversible between a forward cycle and a reverse cycle. Further, a defrost means (72) is provided for controlling the defrost operation by reversing the refrigerant circulation of the primary refrigerant circuit (20) and the reversible refrigerant circuit (3A) of the refrigerant circulation. Upon receiving the defrost end signal from the defrost means (72), the four-way switching valve (24) of the primary side refrigerant circuit (20) is switched to restart the cooling operation of the primary side refrigerant circuit (20). Then, a termination control means (74) for switching the four-way switching valve (33) of the secondary refrigerant circuit (3A) to restart the cooling operation of the secondary refrigerant circuit (3A) is provided.

Further, the third solving means is the same as the first solving means, except that the second solving means is provided with a second solving means end control means (74).

In a fourth aspect of the present invention, in the first aspect, the start control means (73) receives a defrost start signal, receives a defrost start signal, or receives a defrost start signal. After a certain period of time, when the condition that the superheat degree of the suction side refrigerant of the compressor (21) in the primary side refrigerant circuit (20) becomes equal to or less than a predetermined value is satisfied, the four-way switching valve ( 24) is configured to be switched.

According to a fifth aspect of the present invention, in the second aspect, the end control means (74) receives a defrost end signal, receives a defrost end signal, or receives a defrost end signal. After a certain period of time, when the condition that the superheat degree of the suction side refrigerant of the compressor (21) in the primary side refrigerant circuit (20) becomes equal to or less than a predetermined value is satisfied, the four-way switching valve of the secondary side refrigerant circuit (3A) (33) is switched.

The sixth means for solving the above problems is the first or second aspect.
In the above solution, a plurality of refrigerant heat exchangers (11, 11) are provided. The evaporating sections of the refrigerant heat exchangers (11, 11) are connected in parallel with each other to form a primary refrigerant circuit (20).
On the other hand, secondary-side refrigerant circuits (3A, 3B) are connected to the refrigerant heat exchangers (11, 11), respectively. Furthermore, at least one secondary refrigerant circuit (3A) of the plurality of secondary refrigerant circuits (3A, 3B) is configured so that refrigerant circulation is reversible. In addition, the evaporators (5a, 5b) of the respective secondary-side refrigerant circuits (3A, 3B) are integrally formed.

According to the above-mentioned specific items, in the present solution, when performing the defrost operation, the refrigerant circulation directions of the primary side refrigerant circuit (20) and the secondary side refrigerant circuit (3A) are both set to reverse cycles. Will be In particular, in the sixth solution, only one secondary-side refrigerant circuit (3A) performs the defrost operation.

The secondary refrigerant in the secondary refrigerant circuit (3A) is discharged from the compressor (31), flows through the evaporator (50), heats the evaporator (50), and heats the evaporator (50). Thaw frost). Thereafter, the secondary refrigerant evaporates in the condensing part of the refrigerant heat exchanger (11) via the receiver (34), and returns to the compressor (31).
This cycle is repeated.

On the other hand, the primary refrigerant of the primary refrigerant circuit (20) is discharged from the compressor (21), flows through the evaporating section of the refrigerant heat exchanger (11), and flows through the secondary refrigerant circuit (3A) of the secondary refrigerant circuit (3A). Heat the refrigerant. Thereafter, the primary refrigerant flowing through the refrigerant heat exchanger (11) passes through the receiver (25), evaporates in the condenser (22), and returns to the compressor (21). This cycle is repeated.

When the defrost operation is started, the first and third solutions first switch the four-way switching valve (33) of the secondary refrigerant circuit (3A). Thereafter, in a fourth solution, when the degree of superheat of the suction-side refrigerant of the primary-side refrigerant circuit (20) falls below a predetermined value and a predetermined condition is satisfied, the four-way switching valve ( Switch 24).

On the other hand, when terminating the defrost operation, the second and third solving means include a primary refrigerant circuit (2
Switch the four-way switching valve (24) of (0). Thereafter, in a fifth solution means, when the degree of superheat of the suction-side refrigerant of the primary-side refrigerant circuit (20) drops below a predetermined value and a predetermined condition is satisfied, the four-way switching valve of the secondary-side refrigerant circuit (3A) Switch (33).

[0024]

Therefore, according to the first, third and sixth means for solving the problems, at the start of the defrost operation, the four-way switching valve (33) of the secondary refrigerant circuit (3A) is switched, and then the primary refrigerant is switched. Since the four-way switching valve (24) of the side refrigerant circuit (20) is switched, the condensing section of the refrigerant heat exchanger (11) in the secondary side refrigerant circuit (3A) is brought to a low temperature state where the evaporation function is exhibited. After that, the four-way switching valve (24) of the primary refrigerant circuit (20) can be switched.

As a result, the evaporating portion of the refrigerant heat exchanger (11) of the primary refrigerant circuit (20) can radiate heat as a condenser, so that the high-pressure refrigerant pressure in the primary refrigerant circuit (20) rises excessively. Can be reliably prevented. Therefore, the high-pressure refrigerant pressure during the defrost operation can be reliably controlled to an appropriate value.

According to the second, third and sixth means for solving the problem, at the end of the defrost operation, after switching the four-way switching valve (24) of the primary refrigerant circuit (20), the secondary refrigerant Since the four-way switching valve (33) of the circuit (3A) is switched, the refrigerant heat exchanger (1) in the primary refrigerant circuit (20) is switched.
After the evaporating section 1) is in a low temperature state in which the evaporating function is exhibited, the four-way switching valve (33) of the secondary refrigerant circuit (3A) can be switched.

As a result, since the condenser of the refrigerant heat exchanger (11) of the secondary refrigerant circuit (3A) can surely radiate heat, the pressure of the high-pressure refrigerant in the secondary refrigerant circuit (3A) becomes excessive. Ascent can be reliably prevented. Therefore, the high-pressure refrigerant pressure during the defrost operation can be reliably controlled to an appropriate value.

According to the fourth and fifth solutions,
At the start and end of the defrost operation, if the degree of superheat of the suction-side refrigerant of the primary-side refrigerant circuit (20) decreases, the four-way switching valve (24) and the secondary-side refrigerant circuit of the primary-side refrigerant circuit (20) Since the four-way switching valve (33) of (3A) is switched, it is possible to accurately detect a state in which heat can be released from the refrigerant heat exchanger (11), and to prevent an excessive rise in high-pressure refrigerant pressure. .

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIGS. 1 and 2, the binary refrigeration system (10) cools a refrigerator or a freezer.
An outdoor unit (1A), a cascade unit (1B), and a cooling unit (1C) are provided. The outdoor unit (1A) and a part of the cascade unit (1B) constitute a high-temperature refrigeration circuit (20). on the other hand,
Two low-temperature side refrigeration circuits (3A, 3B) are constituted by the cascade unit (1B) and the cooling unit (1C).

The high temperature side refrigeration circuit (20) constitutes a primary side refrigerant circuit capable of reversible operation by switching the refrigerant circulation direction between a forward cycle and a reverse cycle. The high temperature side refrigeration circuit (20) includes a compressor (21), a condenser (22),
And an evaporator of two refrigerant heat exchangers (11, 11).

A first gas pipe (40) is connected to the discharge side of the compressor (21), and a second gas pipe (41) is connected to the suction side. The first gas pipe (40) includes a compressor (21)
, An oil separator (23) and a four-way switching valve (24) are connected in order, and connected to one end of the condenser (22). One end of a liquid pipe (42) is connected to the other end of the condenser (22). The liquid pipe (42) has a main pipe (4a) and two branch pipes (4b,
4c). Each branch pipe (4b, 4c) is connected to each evaporator of the two refrigerant heat exchangers (11, 11).

The main pipe (4a) of the liquid pipe (42) is connected to a branch pipe (4b, 4b) from the condenser (22) via a receiver (25).
c) is connected to. On the other hand, the branch pipe (4b, 4c)
Is provided with a cooling electric expansion valve (EV11) as an expansion mechanism.

The second gas pipe (41) is a main pipe (4d)
And two branch pipes (4e, 4f). The main pipe (4d) of the second gas pipe (41) connects the accumulator (26) and the four-way switching valve (24) in order from the compressor (21), while the branch pipes (4e, 4f) Is connected to the evaporator of each refrigerant heat exchanger (11, 11). That is, the evaporating sections of the two refrigerant heat exchangers (11, 11) are connected in parallel in the high-temperature side refrigeration circuit (20).

The branch pipes (4b, 4c, 4e, 4f) of the liquid pipe (42) and the second gas pipe (41) are provided in the cascade unit (1B).

The first gas pipe (40) and the receiver (25)
A gas passage (43) is connected between the two. One end of the gas passage (43) is connected between the four-way switching valve (24) and the condenser (22) in the first gas pipe (40), and the other end is connected to the upper part of the receiver (25). Have been. And
The gas passage (43) is provided with an on-off valve (SVGH), and is configured to perform high-pressure control during a cooling operation.

An oil return passage (44) having a capillary tube (CP) is connected between the oil separator (23) and the suction side of the compressor (21). An unload passage (45) of a compressor (21) including a capillary tube (CP) and an on-off valve (SVRH) is connected between a discharge side and a suction side of the compressor (21). The middle of the unload passage (45) is connected to the compressor (21).

The first gas pipe (40) on the discharge side of the compressor (21) has a high-pressure pressure sensor (SPH1) for detecting high-pressure refrigerant pressure, and a predetermined high-pressure High pressure switch (HPS1) that outputs an off signal when it reaches the value
Are provided. Further, a low-pressure pressure sensor (SPL1) for detecting a low-pressure refrigerant pressure is provided in the second gas pipe (41) on the suction side of the compressor (21).

Further, in the second gas pipe (41) on the suction side of the compressor (21), a suction temperature sensor (Th11) for detecting a suction side refrigerant temperature is provided with a four-way switching valve (24) and an accumulator (26). ).

On the other hand, the first low temperature side refrigeration circuit (3A)
A secondary-side refrigerant circuit capable of reversible operation by switching the refrigerant circulation direction between a forward cycle and a reverse cycle is configured. The first low-temperature refrigeration circuit (3A) includes a compressor (31), a condensing section of a first refrigerant heat exchanger (11), and an evaporating heat transfer tube (5a).
And

The discharge side of the compressor (31) is connected to a first refrigerant heat exchanger (11) via a first gas pipe (60) via an oil separator (32) and a four-way switching valve (33). Is connected to one end of the condenser section. The other end of the condenser is connected to a liquid pipe (61)
Evaporating heat transfer tube (5a) via check valve (CV), receiver (34) and cooling expansion valve (EV21) as an expansion mechanism
Is connected to one end. The other end of the evaporating heat transfer tube (5a) is connected to a compressor (31) via a check valve (CV), a four-way switching valve (33) and an accumulator (35) by a second gas pipe (62). Connected to the suction side.

Then, the first refrigerant heat exchanger (11)
Is a cascade condenser, which is mainly configured to exchange heat between evaporation heat of the high-temperature side refrigeration circuit (20) and condensation heat of the first low-temperature side refrigeration circuit (3A).

The cooling expansion valve (EV21) is a temperature-sensitive expansion valve, and the temperature-sensitive cylinder (TS) is connected to the second gas pipe (62) on the outlet side of the evaporation heat transfer tube (5a). Is provided.

Since the first low temperature side refrigeration circuit (3A) is configured to perform a reverse cycle defrost operation, it is provided with a drain pan passage (63), a gas bypass passage (64), and a pressure reduction passage (65). I have. The drain pan passage (63) is connected to both ends of the check valve (CV) in the second gas passage (62), and is provided with a drain pan heater (6a) and a check valve (CV). ) Is configured to flow.

The gas bypass passage (64) is connected to both ends of the cooling expansion valve (EV21) in the liquid pipe (61), and is provided with a check valve (CV). (EV21).

The pressure reducing passage (65) is connected to both ends of the check valve (CV) in the liquid pipe (61) and includes an on-off valve (SVDL). The on-off valve (SVDL) is set to be slightly smaller than the diameter of the pressure reducing passage (65), and is configured to reduce the pressure of the liquid refrigerant during the defrost operation.

An upper end of the receiver (34) is connected to one end of a gas vent passage (66). The gas vent passage (66) includes an on-off valve (SVGL) and a capillary tube (CP), and the other end is connected to the second gas pipe (62) upstream of the accumulator (35).

An oil return passage (67) having a capillary tube (CP) is connected between the oil separator (32) and the suction side of the compressor (31).

The first gas pipe (60) on the discharge side of the compressor (31) has a high-pressure pressure sensor (SPH2) for detecting high-pressure refrigerant pressure and a predetermined high-pressure High pressure switch (HPS2) that outputs an off signal when the value reaches
Are provided. The second gas pipe (62) on the suction side of the compressor (31) is provided with a low pressure sensor (SPL2) for detecting a low pressure refrigerant pressure.

The second low-temperature refrigeration circuit (3B) has substantially the same configuration as the first low-temperature refrigeration circuit (3A), but includes a secondary refrigerant circuit that performs only a cooling operation without performing a defrost operation. Make up. The second low-temperature refrigeration circuit (3B)
The four-way switching valve (24) in the low temperature side refrigeration circuit (3A) is not provided, and further, the drain pan passage (63), the gas bypass passage (64), and the pressure reducing passage (65) are not provided. That is, the second low-temperature side refrigeration circuit (3B) includes the compressor (31), the condensing part of the second refrigerant heat exchanger (11), the receiver (34), the cooling expansion valve (EV21), and the evaporating transmission. The heat pipe (5b) and the accumulator (35) are sequentially connected by a first gas pipe (60), a liquid pipe (61), and a second gas pipe (62).

The cooling expansion valve (EV21) is a temperature-sensitive expansion valve, and a temperature-sensitive cylinder is provided in the second gas pipe (62) on the outlet side of the heat transfer tube (5b) for evaporation. I have. The second
The refrigerant heat exchanger (11) is a cascade condenser and is configured to exchange heat between the evaporation heat of the high-temperature refrigeration circuit (20) and the condensation heat of the second low-temperature refrigeration circuit (3B). .

While the heat transfer tubes for evaporation (5a, 5b), the expansion valve for cooling (EV21) and the drain pan passage (63) in the two low-temperature side refrigeration circuits (3A, 3B) are provided in the cooling unit (1C), Are provided in the cascade unit (1B).

The evaporating heat transfer tubes (5a, 5b) of the two low-temperature side refrigeration circuits (3A, 3B) constitute evaporators as shown in FIG. 2, but in this embodiment, they are integrated. One evaporator (50) is formed. Specifically, each of the low-temperature side refrigeration circuits (3A, 3B) includes n heat transfer tubes (5a, 5b), and the evaporator (50) has 2n heat transfer tubes (5a, 5B).
a, 5b), that is, 2n passes are formed.

A liquid temperature sensor (Th21) for detecting the temperature of the liquid refrigerant is provided in the first low-temperature side refrigeration circuit (3A) in front of the evaporating heat transfer pipe (5a) of the liquid pipe (61). On the other hand, the evaporator (50) is provided with an evaporator temperature sensor (Th22) for detecting the temperature of the evaporator (50).

The high-temperature refrigeration circuit (20) and both low-temperature refrigeration circuits (3A, 3B) are controlled by a controller (70). The controller (70) includes a high-pressure pressure sensor (SP
H1 and SPH2), while the compressor (2
1, 31). The controller (70) is provided with defrost means (72), defrost operation start control means (73), and end control means (74), in addition to the cooling means (71) for controlling the cooling operation. .

The defrost means (72) is configured to perform a defrost operation every predetermined time. That is, the defrost means (72) stops the operation of the second low-temperature refrigeration circuit (3B), while the first low-temperature refrigeration circuit (3
A) and four-way switching valve (24, 33) between high temperature side refrigeration circuit (20)
Is switched to the dashed line in FIGS. 1 and 2, and the refrigerant is circulated in the reverse cycle of the refrigerant circulation direction.

The start control means (73) receives the defrost start signal from the defrost means (72) and switches the four-way switching valve (33) of the secondary refrigerant circuit (3A) to switch the secondary refrigerant circuit (33). After the defrost operation of 3A) is started, when a predetermined condition is satisfied, the four-way switching valve (24) of the primary refrigerant circuit (20) is switched to start the defrost operation of the primary refrigerant circuit (20). Have been.

Further, the start control means (73) determines whether a condition that a predetermined time elapses after receiving the defrost start signal or a predetermined time after receiving the defrost start signal, in the primary refrigerant circuit (20). When the condition that the superheat degree of the suction-side refrigerant of the compressor (21) becomes equal to or less than a predetermined value is satisfied, the four-way switching valve (24) of the primary-side refrigerant circuit (20) is switched.

The termination control means (74) receives the defrost termination signal from the defrost means (72) and switches the four-way switching valve (24) of the primary refrigerant circuit (20) to switch the primary refrigerant circuit (20). After restarting the cooling operation of
The four-way switching valve (33) of the secondary refrigerant circuit (3A) is switched to restart the cooling operation of the secondary refrigerant circuit (3A).

Further, the predetermined condition of the termination control means (74) may be a condition that a predetermined time elapses after receiving the defrost termination signal, or a predetermined time after receiving the defrost termination signal, the primary refrigerant circuit ( When the condition that the superheat degree of the suction side refrigerant of the compressor (21) in 20) becomes equal to or less than a predetermined value is satisfied, the four-way switching valve (33) of the secondary side refrigerant circuit (3A) is switched. .

The degree of superheat is determined by the suction temperature sensor (Th
11) is derived from the temperature difference (TSH-TEH) between the suction side refrigerant temperature TSH detected by the low pressure pressure sensor (SPL2) and the equivalent saturation temperature TEH of the low pressure refrigerant pressure detected by the low pressure pressure sensor (SPL2). Is set to

-Operation of Binary Refrigeration Unit- Next, the operation of the binary refrigeration unit (10) will be described.

First, when performing the cooling operation, the compressor (21) of the high-temperature side refrigeration circuit (20) and both low-temperature side refrigeration circuits (3A, 3A)
B) The two compressors (31, 31) are driven together. In this state, in the high-temperature side refrigeration circuit (20), the four-way switching valve (24) is switched to the solid line in FIG. 1, and the opening degree of the electric expansion valve for cooling (EV11) is controlled.

The compressor (21) of the high-temperature side refrigeration circuit (20)
The primary refrigerant discharged from the condenser is condensed in the condenser (22) to become a liquid refrigerant and flows to the cascade unit (1B). Then, the liquid refrigerant is divided into two branch pipes (4b, 4c), and the pressure is reduced by the electric cooling expansion valve (EV11). Thereafter, the liquid refrigerant evaporates in each evaporating section of the two refrigerant heat exchangers (11, 11) to become gas refrigerant and returns to the compressor (21). This cycle is repeated.

On the other hand, in the first low-temperature side refrigeration circuit (3A), the four-way switching valve (33) is switched to the solid line in FIG. 2, while the on-off valve (SVDL) of the pressure reducing passage (65) is fully closed, and Controls the degree of superheating of the expansion valve (EV21). In the second low-temperature refrigeration circuit (3B), the degree of superheat of the cooling expansion valve (EV21) is controlled.

In the two low-temperature refrigeration circuits (3A, 3B), the secondary refrigerant discharged from the compressors (31, 31) is condensed in the condensing section of the refrigerant heat exchanger (11, 11) to become a liquid refrigerant. The pressure of the liquid refrigerant is reduced by the expansion valves for cooling (EV21, EV21).
Thereafter, the liquid refrigerant evaporates in the evaporating heat transfer tubes (5a, 5b) to become gas refrigerant and returns to the compressors (31, 31). This cycle is repeated.

In each of the refrigerant heat exchangers (11, 11), the heat of evaporation of the high-temperature side refrigeration circuit (20) and the heat of condensation of each of the low-temperature side refrigeration circuits (3A, 3B) exchange heat. The secondary refrigerant in the side refrigeration circuits (3A, 3B) is cooled and condensed. on the other hand,
In the evaporator (50), the secondary refrigerant evaporates to generate cooling air, thereby cooling the inside of the refrigerator.

The binary refrigeration system (10) performs a defrost operation. This defrost operation is performed every 6 hours during the refrigeration operation and every 12 hours during the freezing operation. The defrost operation is performed by the second low-temperature refrigeration circuit (3B)
Is stopped, while the refrigerant circulation direction of the first low-temperature refrigeration circuit (3A) and the high-temperature refrigeration circuit (20) is reversed.

Specifically, in the first low-temperature side refrigeration circuit (3A), the four-way switching valve (33) is switched to the broken line in FIG.
Fully open the on-off valve (SVDL) and fully close the cooling expansion valve (EV21) of the pressure reducing passage (65).

The secondary refrigerant discharged from the compressor (31) passes through the four-way switching valve (33), passes through the drain pan passage (63), and heats the drain pan with the drain pan heater (6a).
Subsequently, the secondary refrigerant flows through the evaporator heat transfer tube (5a) to heat the evaporator (50), thereby melting the frost on the evaporator (50). Thereafter, the secondary refrigerant flowing through the heat transfer tube for evaporation (5a) flows through the gas bypass passage (64), flows through the pressure reducing passage (65) via the receiver (34), and is depressurized by the on-off valve (SVDL). Subsequently, the secondary refrigerant evaporates in the condensing section of the refrigerant heat exchanger (11), and returns to the compressor (31) via the four-way switching valve (33) and the accumulator (35). This cycle is repeated.

On the other hand, in the high-temperature side refrigeration circuit (20), the four-way switching valve (24) is switched to the dashed line in FIG. 1, and the cooling electric expansion valve (EV11) is fully opened.

The primary refrigerant discharged from the compressor (21) passes through the four-way switching valve (24) to the first refrigerant heat exchanger (11).
And heats the secondary refrigerant of the first low-temperature side refrigeration circuit (3A). Thereafter, the primary refrigerant flowing through the evaporating section of the refrigerant heat exchanger (11) passes through the receiver (25), and then enters the condenser (2).
Evaporated in 2), the four-way switching valve (24) and the accumulator (2
After 6), return to the compressor (21). This cycle is repeated.

In the defrost operation, the liquid temperature sensor (Th21) detects a refrigerant temperature of 35 ° C., for example, and the evaporator temperature sensor (Th22) detects an evaporator temperature of 5 ° C. Alternatively, when the high-pressure pressure sensor (SPH2) of the first low-temperature side refrigeration circuit (3A) detects a high-pressure refrigerant pressure of, for example, 18 kg / cm ² , the process ends. Note that the above defrost operation ends even with a one-hour guard timer.

In the cooling operation in addition to the defrost operation, the on-off valve (SVGL) of the gas vent passage (66) in each of the low-temperature refrigeration circuits (3A, 3B) is opened, and the receiver (34)
The liquid refrigerant accumulated in the compressor is returned to the low-temperature side compressor (31).

The gas passage (43) in the high-temperature side refrigeration circuit (20) opens the on-off valve (SVGH) when the pressure of the high-pressure refrigerant detected by the high-pressure pressure sensor (SPH1) decreases during the cooling operation. Then, the high-pressure refrigerant is supplied to the receiver (25) to increase the high-pressure refrigerant pressure.

Next, the switching operation of the four-way switching valves (24, 33) in the high-temperature side refrigeration circuit (20) and the first low-temperature side refrigeration circuit (3A), which is a feature of the present invention, will be described with reference to FIGS. explain.

First, FIG. 3 shows a first low-temperature side refrigeration circuit (3A).
After receiving the defrost signal (defrost signal) (step ST11), the pump-down operation is performed for 20 seconds (step ST12), and then the four-way switching valve (33) is switched (step ST13). In this case, as described later, the four-way switching valve (33) of the first low-temperature side refrigeration circuit (3A) is switched earlier than the four-way switching valve (24) of the high-temperature side refrigeration circuit (20).

Thereafter, after performing the defrost operation as described above (step ST14), it is determined whether or not the defrost is to be terminated (step ST15). Then, when the defrost ends, an end signal is transmitted to the high temperature side refrigeration circuit (20) (step ST16), and the four-way switching valve (33) is switched (step ST17). In this case, as described later, the four-way switching valve (33) of the first low-temperature side refrigeration circuit (3A) is switched after the four-way switching valve (24) of the high-temperature side refrigeration circuit (20). Thereafter, the operation returns to the cooling operation (step ST18), and the above operation is repeated.

FIG. 4 shows the operation of the high-temperature side refrigeration circuit (20). After receiving a defrost signal (defrost signal) (step ST21), the cooling operation is continued (step ST22). Switch the directional control valve (24) (step ST2
3). In this case, as described later, the high-temperature side refrigeration circuit (2
0) is connected to the first low-temperature side refrigeration circuit (3A)
After the four-way switching valve (33).

Thereafter, after performing the defrost operation as described above (step ST24), when a defrost end signal is received (step ST25), the four-way switching valve (24) is switched (step ST26). In this case, as described later, the four-way switching valve (24) of the high-temperature side refrigeration circuit (20) is switched earlier than the four-way switching valve (33) of the first low-temperature side refrigeration circuit (3A). Thereafter, the operation returns to the cooling operation (step ST17), and the above operation is repeated.

The switching control of the four-way switching valve (24) of the high temperature side refrigeration circuit (20) will be described with reference to FIG.

The step ST23 in FIG. 4 will be described in detail. As shown in FIG. 5, when the defrost operation is started, first,
The four-way switching valve (33) of the first low-temperature refrigeration circuit (3A) is switched (see step ST13 in FIG. 3). In this case, the high-temperature refrigeration circuit (20) determines whether two minutes have elapsed in step ST31. The cooling operation is continued (step ST in FIG. 4).
22). Until two minutes have elapsed, the process proceeds to step ST32, where it is determined whether one minute has elapsed and the superheat degree of the suction-side refrigerant of the primary-side refrigerant circuit (20) has dropped below 5 ° C. (T
SH-TEH <5). Until the condition such as the decrease in the degree of superheat is satisfied, the flow returns to the step ST31.
Move to ST33 and switch the four-way switching valve (24).

That is, the four-way switching valve (33) of the first low-temperature refrigeration circuit (3A) is switched, and after the condensing part of the refrigerant heat exchanger (11) is switched to the evaporation function, the high-temperature refrigeration circuit (3) is switched. Two
The evaporating section of the refrigerant heat exchanger (11) of (0) continues the cooling operation as it is. In this state, the refrigerant in the high-temperature side refrigeration circuit (20) does not evaporate. If this state is continued, the liquid refrigerant returns to the compressor (21) in a wet operation. The four-way switching valve (24) of the circuit (20) is switched.

On the other hand, when terminating the defrost operation, the high temperature side refrigeration circuit (20) switches the four-way switching valve (24) as shown in FIG. During the defrost operation, in step ST41, the on-off valve (SVR) of the unload passage (45)
H) is opened, and the on-off valve (SVGH) of the gas passage (43) is closed. Thereafter, the process proceeds to step ST42, where it is determined whether or not there is a defrost end signal from the first low-temperature side refrigeration circuit (3A). The process waits in step ST42 until the end signal is received, and when the end signal is received, Moving to step ST43, the four-way switching valve (24) is switched (see step ST26 in FIG. 4).

Thereafter, the process proceeds to step ST44, in which the open / close valve (SVRH) of the unload passage (45) and the open / close valve (SVGH) of the gas passage (43) are left as it is, and proceeds to step ST45 to determine whether one minute has elapsed. Is determined. Until this one minute has elapsed, the process proceeds to step ST46, where it is determined whether 10 seconds have elapsed and the degree of superheat of the suction side refrigerant of the primary side refrigerant circuit (20) has dropped below 5 ° C (TSH-TEH). <5). The process returns to step ST45 until the condition such as a decrease in the degree of superheat is satisfied, and when the above-described one minute elapses or the condition such as the decrease in the degree of superheat is satisfied, the process proceeds to step ST47 and the first low-temperature side refrigeration circuit The switching signal of the four-way switching valve (33) is transmitted to (3A), and the cooling operation is restarted.

On the other hand, the first low-temperature side refrigeration circuit (3A)
The four-way switching valve (33) is switched as shown in FIG. First, during the defrost operation, in step ST51, the on-off valve (SVDL) of the pressure reducing passage (65) is opened, and in step ST52, it is determined whether or not the defrost is completed, and the process waits in step ST52 until the defrost is completed. After that, when the defrost ends, the process moves to step ST53, and transmits an end signal to the high-temperature side refrigeration circuit (20) (see step ST16 in FIG. 3).

As described above, the transmission of the end signal causes the high-temperature side refrigeration circuit (20) to switch the four-way switching valve (24) (see step ST26 in FIG. 4 and step ST26 in FIG. 6).
43). On the other hand, the first low-temperature side refrigeration circuit (3A) continues the defrost operation, and determines in step ST54 whether or not a switching signal of the four-way switching valve (24) of the high-temperature side refrigeration circuit (20) has been received. , Wait until receiving the switching signal,
When the switching signal is received, the process proceeds to step ST55, closes the on-off valve (SVDL) of the pressure reducing passage (65), and switches the four-way switching valve (33) in step ST56 (step in FIG. 1).
ST17), restart the cooling operation.

That is, the four-way switching valve (24) of the high-temperature side refrigeration circuit (20) is switched to return the evaporating section of the refrigerant heat exchanger (11) from the condensation function to the evaporation function. The condensing section of the refrigerant heat exchanger (11) of (3A) continues the evaporation function of the defrost operation as it is. In this state, the refrigerant in the high-temperature side refrigeration circuit (20) does not evaporate. If this state is continued, the liquid refrigerant returns to the compressor in a wet operation.
When this wet operation is detected, the first low-temperature side refrigeration circuit (3A)
Of the four-way switching valve (33).

As described above, according to the present embodiment, at the start of the defrost operation, after the four-way switching valve (33) of the first low-temperature side refrigeration circuit (3A) is switched, the high-temperature switching is performed. Since the four-way switching valve (24) of the side refrigeration circuit (20) is switched, the condensing section of the refrigerant heat exchanger (11) in the first low temperature side refrigeration circuit (3A)
After the low-temperature state in which the evaporation function is exhibited, the four-way switching valve (24) of the high-temperature side refrigeration circuit (20) can be switched.

As a result, since the evaporating section of the refrigerant heat exchanger (11) of the high-temperature side refrigeration circuit (20) can radiate heat as a condenser, the high-pressure refrigerant pressure in the high-temperature side refrigeration circuit (20) rises excessively. Can be reliably prevented. Therefore, the high-pressure refrigerant pressure during the defrost operation can be reliably controlled to an appropriate value.

At the end of the defrost operation, after switching the four-way switching valve (24) of the high temperature side refrigeration circuit (20),
Since the four-way switching valve (33) of the first low-temperature side refrigeration circuit (3A) is switched, the evaporating section of the refrigerant heat exchanger (11) in the high-temperature side refrigeration circuit (20) operates at a low temperature where the evaporating function is exhibited. After the state, the four-way switching valve (33) of the first low-temperature side refrigeration circuit (3A) can be switched.

As a result, the condensing portion of the refrigerant heat exchanger (11) of the first low-temperature side refrigeration circuit (3A) can reliably radiate heat, and the high-pressure refrigerant pressure of the first low-temperature side refrigeration circuit (3A) can be reduced. Excessive rise can be reliably prevented. Therefore, the high-pressure refrigerant pressure during the defrost operation can be reliably controlled to an appropriate value.

When the degree of superheat of the refrigerant on the suction side of the high-temperature side refrigeration circuit (20) decreases at the start and end of the defrost operation, the four-way switching valve (24) and the four-way switching valve (24) of the high-temperature side refrigeration circuit (20) Four-way switching valve (3
Since 3) is switched, it is possible to accurately detect the state in which heat can be released from the refrigerant heat exchanger (11), and to prevent an excessive increase in the high-pressure refrigerant pressure.

[0094]

In another embodiment of the present invention,
Although the low temperature side refrigeration circuit (3A, 3B) was provided, the present invention
It may have one low-temperature refrigeration circuit (3A), and conversely, three or more first low-temperature refrigeration circuits (3A, 3B,
...).

[Brief description of the drawings]

FIG. 1 is a refrigerant circuit diagram showing a main part of a high temperature side refrigeration circuit of the present invention.

FIG. 2 is a refrigerant circuit diagram showing a low-temperature side refrigeration circuit of the present invention.

FIG. 3 is a control flowchart showing a defrost operation of a first low-temperature side refrigeration circuit.

FIG. 4 is a control flowchart showing a defrost operation of the high-temperature side refrigeration circuit.

FIG. 5 is a control flow chart showing a switching operation of a four-way switching valve at the start of defrost in the high-temperature side refrigeration circuit.

FIG. 6 is a control flow chart showing a switching operation of a four-way switching valve at the end of defrost in the high-temperature side refrigeration circuit.

FIG. 7 is a control flowchart showing a switching operation of a four-way switching valve at the end of defrost in the first low-temperature side refrigeration circuit.

[Explanation of symbols]

 10 Binary refrigeration unit 11 Refrigerant heat exchanger 20 High temperature side refrigeration circuit (Primary side refrigerant circuit) 21 Compressor 22 Condenser 24 Four-way switching valve EV11 Electric expansion valve 3A, 3B Low temperature side refrigeration circuit (Secondary side refrigerant circuit) 31 Compressor 33 Four-way switching valve EV21 Expansion valve 50 Evaporator 5a, 5b Evaporator heat transfer tube (evaporator) 70 Controller 71 Cooling means 72 Defrost means 73 Start control means 74 End control means

Claims (6)

[Claims] 1. A compressor (21), a condenser (22), an expansion mechanism (EV11), and an evaporator of a refrigerant heat exchanger (11) are connected in order, and a primary refrigerant circulates. A primary refrigerant circuit (20), a compressor (31), and a condensing part of the refrigerant heat exchanger (11);
The expansion mechanism (EV21) and the evaporator (5a) are connected in order, and the secondary refrigerant circulates and at least heat exchanges between the primary refrigerant and the secondary refrigerant in the refrigerant heat exchanger (11). In a binary refrigeration system including one secondary-side refrigerant circuit (3A), the at least one secondary-side refrigerant circuit (3A) and the primary-side refrigerant circuit (20) have a refrigerant circulation direction in a normal cycle. While the four-way switching valve (24, 33) is provided so as to be reversible with the reverse cycle, the refrigerant circulation of the primary refrigerant circuit (20) and the reversible secondary refrigerant circuit (3A) of the refrigerant circulation is reversed. A defrost means (72) for controlling a defrost operation in a cycle, and a defrost start signal from the defrost means (72);
After the defrost operation of the secondary refrigerant circuit (3A) is started by switching the four-way switching valve (33) of the secondary refrigerant circuit (3A), when a predetermined condition is satisfied, the primary refrigerant circuit (20) is deactivated. A binary refrigeration system comprising: a start control means (73) for switching a path switching valve (24) to start a defrost operation of the primary refrigerant circuit (20). 2. A compressor (21), a condenser (22), an expansion mechanism (EV11), and an evaporator of a refrigerant heat exchanger (11) are sequentially connected to each other, and the primary refrigerant circulates. A primary refrigerant circuit (20), a compressor (31), and a condensing part of the refrigerant heat exchanger (11);
The expansion mechanism (EV21) and the evaporator (5a) are connected in order, and the secondary refrigerant circulates and at least heat exchanges between the primary refrigerant and the secondary refrigerant in the refrigerant heat exchanger (11). In the binary refrigeration system including one secondary-side refrigerant circuit (3A), the at least one secondary-side refrigerant circuit (3A) and the primary-side refrigerant circuit (20) have a refrigerant cycle direction of a normal cycle. While the four-way switching valve (24, 33) is provided so as to be reversible with the reverse cycle, the refrigerant circulation of the primary refrigerant circuit (20) and the reversible secondary refrigerant circuit (3A) of the refrigerant circulation is reversed. A defrost means (72) for controlling a defrost operation in a cycle, and a defrost end signal from the defrost means (72);
After switching the four-way switching valve (24) of the primary-side refrigerant circuit (20) to restart the cooling operation of the primary-side refrigerant circuit (20), when a predetermined condition is satisfied, the four-way of the secondary-side refrigerant circuit (3A) Switching valve (3
And a termination control means (74) for resuming the cooling operation of the secondary-side refrigerant circuit (3A) by switching 3). 3. The two-way refrigeration system according to claim 1, wherein the four-way switching valve (24) of the primary refrigerant circuit (20) is switched by receiving a defrost end signal of the defrost means (72). After resuming the cooling operation of the circuit (20), when a predetermined condition is reached, the four-way switching valve (33) of the secondary refrigerant circuit (3A)
And a termination control means (74) for switching over and restarting the cooling operation of the secondary-side refrigerant circuit (3A). 4. The two-stage refrigeration system according to claim 1, wherein the start control means (73) keeps a predetermined time after receiving the defrost start signal or a predetermined time after receiving the defrost start signal. When a condition that the superheat degree of the suction-side refrigerant of the compressor (21) in the primary-side refrigerant circuit (20) becomes equal to or less than a predetermined value is satisfied after a time, the four-way switching valve (24) of the primary-side refrigerant circuit (20) is switched. A binary refrigeration apparatus characterized by being configured as described above. 5. The two-stage refrigeration system according to claim 2, wherein the termination control means (74) keeps a predetermined time after receiving the defrost termination signal or a predetermined time after receiving the defrost termination signal. After a lapse of time, when the condition that the superheat degree of the suction side refrigerant of the compressor (21) in the primary side refrigerant circuit (20) becomes less than a predetermined value is satisfied, the four-way switching valve (33) of the secondary side refrigerant circuit (3A) is opened. A binary refrigeration system characterized by being configured to switch. 6. The binary refrigeration system according to claim 1, wherein a plurality of refrigerant heat exchangers (11, 11) are provided, and the evaporating portions of each of the refrigerant heat exchangers (11, 11) are arranged in parallel with each other. The refrigerant heat exchangers (11, 11) are connected to secondary refrigerant circuits (3A, 3B), respectively, while being connected to form the primary refrigerant circuit (20). At least one secondary-side refrigerant circuit (3A) of the side-side refrigerant circuits (3A, 3B) is configured so that refrigerant circulation is reversible, and the evaporator (3A, 3B) of each of the secondary-side refrigerant circuits (3A, 3B) A binary refrigeration apparatus, wherein 5a and 5b) are integrally formed.