Refrigeration system

Abstract

To provide a refrigeration system that can smoothly supply liquid-phase refrigerant to a full-liquid evaporator. [Solution] A refrigeration system according to one aspect of the present invention comprises a refrigeration unit, a liquid-filled evaporator having a coil filled with liquid-phase refrigerant generated by the refrigeration unit and cooling the internal air by heat exchange between the internal air and the refrigerant, a supply line connected to the upstream end of the coil and through which the refrigerant flowing into the evaporator flows, an expansion valve provided in the supply line, a gas-liquid two-phase line connected to the downstream end of the coil and through which the gas-liquid two-phase refrigerant flowing out of the evaporator flows, a gas-liquid separator connected to the gas-liquid two-phase line and separating the refrigerant flowing out of the evaporator into liquid and gas phases, and a liquid line connecting the lower end of the gas-liquid separator and the portion of the supply line located between the expansion valve and the evaporator. The lower end of the gas-liquid separator is located above the upstream end of the coil.

Description

Technical Field

[0001] The present invention relates to a refrigeration system.

Background Art

[0002] For storing fish such as tuna and bonito, for example, it is necessary to maintain an ultra-low temperature (below -45°C) inside a refrigerated warehouse. As a refrigeration system for maintaining an ultra-low temperature inside a refrigerated warehouse, a so-called flooded evaporator in which the inside of a coil is filled with a liquid-phase refrigerant may be adopted. For example, Patent Document 1 below discloses a configuration in which a surge tank for storing a liquid-phase refrigerant is provided between an expansion valve and an evaporator. According to this configuration, the liquid-phase refrigerant stored in the surge tank is supplied to the evaporator by the self-weight of the liquid-phase refrigerant (the head difference between the surge tank and the evaporator).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the prior art, it has been difficult to smoothly supply the refrigerant to the evaporator due to the influence of pressure loss and the like. In particular, when liquid is supplied to the surge tank from a state where the amount of the liquid-phase refrigerant in the surge tank has decreased due to defrosting (a process of heating the evaporator to remove frost adhering to the evaporator), a desired head difference does not occur between the surge tank and the evaporator, and the refrigerant liquid is not supplied to the evaporator, and the refrigerant may return from the surge tank to the compressor in a liquid phase without evaporating. Thus, it is not preferable that the liquid-phase refrigerant returns to the compressor because it causes damage to the compressor.

[0005] It is also conceivable to increase the volume of the surge tank so that its lower end is below the inlet of the evaporator. However, this would lead to an increase in the amount of refrigerant circulating within the refrigeration system and a larger refrigeration system overall.

[0006] The present invention provides a refrigeration system that can smoothly supply liquid-phase refrigerant to a full-liquid evaporator. [Means for solving the problem]

[0007] To solve the above problems, the present invention employs the following embodiments. A refrigeration system according to one aspect of the present invention comprises a refrigeration unit, a liquid-filled evaporator having a coil filled with liquid-phase refrigerant generated by the refrigeration unit and installed in a cold storage warehouse to cool the air inside the warehouse by exchanging heat between the air inside the warehouse and the refrigerant, a supply line connected to the upstream end of the coil and through which the refrigerant flowing into the evaporator flows, an expansion valve provided in the supply line, a gas-liquid two-phase line connected to the downstream end of the coil and through which the gas-liquid two-phase refrigerant flowing out of the evaporator flows, a gas-liquid separator connected to the gas-liquid two-phase line and for separating the refrigerant flowing out of the evaporator into a liquid phase and a gas phase, and a liquid line connecting the lower end of the gas-liquid separator and the portion of the supply line located between the expansion valve and the evaporator, wherein the lower end of the gas-liquid separator is located above the upstream end of the coil.

[0008] According to this embodiment, the liquid-phase refrigerant flowing through the supply line is supplied directly to the evaporator after passing through the expansion valve. This allows for a smoother supply of liquid-phase refrigerant to the evaporator compared to the conventional configuration in which liquid-phase refrigerant is supplied to the evaporator via a surge tank. In this case, even immediately after the defrost mode, for example, liquid-phase refrigerant is supplied sequentially from the refrigeration unit, thus avoiding a refrigerant shortage in the evaporator and allowing for a quick transition to the normal cooling mode. Furthermore, since there is no need to enlarge the surge tank to ensure head difference, an increase in refrigerant volume and an increase in the size of the refrigeration system can be suppressed. Furthermore, in this embodiment, since the gas-liquid separator is connected to the evaporator downstream of the evaporator via a gas-liquid two-phase line, the gas-liquid separator is supplied with a highly dehydrated gas-liquid two-phase refrigerant that has been used for heat exchange in the evaporator. Therefore, the gas-liquid separator can easily separate the gas-liquid two-phase refrigerant into the gas phase and the liquid phase.

[0009] Furthermore, in this embodiment, the lower end of the gas-liquid separator is located above the upstream end of the coil. This configuration allows for a more compact gas-liquid separator and reduces the amount of refrigerant in the liquid phase stored within the separator, thereby suppressing the need for larger equipment and increased manufacturing costs. As a result, a compact and simple configuration ensures cooling performance through the evaporator, making it easier to maintain the desired temperature in a refrigerated warehouse.

[0010] In the refrigeration system according to the above embodiment, it is preferable that the system includes a first liquid level sensor provided in the gas-liquid separator for detecting the liquid level of the liquid phase refrigerant stored in the gas-liquid separator, and a control unit that controls the opening degree of the expansion valve based on the detection result of the first liquid level sensor, wherein the evaporator and the gas-liquid separator are each arranged within a dimensional range including a first height in the vertical direction, and the control unit adjusts the opening degree of the expansion valve based on the detection result of the first liquid level sensor so that the liquid level in the gas-liquid separator is maintained at the first height. According to this embodiment, since the evaporator and the gas-liquid separator are each positioned within a dimensional range that includes a first height, the liquid level of the liquid phase refrigerant stored in the evaporator and the gas-liquid separator is maintained at the same level. This allows the liquid level of the refrigerant in the evaporator (coil) to be controlled based on the liquid level of the refrigerant in the gas-liquid separator. Specifically, by adjusting the opening of the expansion valve so that the liquid level in the gas-liquid separator is maintained at a first height based on the detection result of the first liquid level sensor, the liquid level in the evaporator is maintained at a first height. This makes it possible to provide a smaller and lower-cost refrigeration system compared to a configuration in which refrigerant is supplied to the evaporator by a separate refrigerant pump or the like.

[0011] In the refrigeration system according to the above embodiment, a second liquid level sensor is provided in the gas-liquid separator below the first liquid level sensor, and it is preferable that the control unit reduces the opening of the expansion valve when it determines, based on the detection result of the first liquid level sensor, that the liquid level in the gas-liquid separator is at the first height, and increases the opening of the expansion valve when it determines, based on the detection result of the second liquid level sensor, that the liquid level in the gas-liquid separator is at a second height lower than the first height. According to this embodiment, the timing of adjusting the opening degree of the expansion valve can be controlled with greater precision compared to the case where the timing is determined solely by the first height.

[0012] In the refrigeration system according to the above embodiment, the refrigerant circulating in the refrigeration system contains oil, which has a lower specific gravity than the refrigerant. Therefore, it is preferable that an oil recovery line for discharging oil contained in the refrigerant within the gas-liquid separator is connected to the portion of the gas-liquid separator located at the same position as the first height or below the first height, and that an oil separator for storing oil flowing through the oil recovery line is provided in the portion located below the connection portion (oil discharge opening) between the gas-liquid separator and the oil recovery line. In this embodiment, the gas-liquid separator stores two layers of liquid, with the refrigerant in the lower layer and oil in the upper layer. In this case, when the oil in the upper layer reaches the same height as the oil discharge opening, it is discharged from the gas-liquid separator through the oil discharge opening. The oil discharged from the gas-liquid separator is stored in the oil separator. In other words, lubricating oil can be removed from the evaporator even while the refrigeration system is in operation. As a result, the decrease in heat transfer efficiency due to oil can be suppressed, and cooling efficiency can be easily maintained.

[0013] In the refrigeration system according to the above embodiment, the refrigerant is preferably carbon dioxide. According to this aspect, by using a so-called flooded evaporator, there is no need to consider superheat like in a dry evaporator. Therefore, when using carbon dioxide as the refrigerant, it is easy to lower the supply temperature of the refrigerant to the evaporator. As a result, it is easy to maintain the inside of the refrigerated warehouse at an ultra-low temperature. Also, using a natural refrigerant such as carbon dioxide is desirable from the perspective of the global environment such as the GWP (Global Warming Potential).

Effect of the Invention

[0014] According to each of the above aspects, the liquid-phase refrigerant can be smoothly supplied to the flooded evaporator.

Brief Description of the Drawings

[0015] [Figure 1] It is a schematic configuration diagram of a refrigeration device according to an embodiment. [Figure 2] It is a front view of an evaporator according to an embodiment. [Figure 3] It is a cross-sectional view of the evaporator corresponding to the line III-III in FIG. 2. [Figure 4] It is a configuration diagram showing an evaporator and a gas-liquid separator according to an embodiment.

Modes for Carrying Out the Invention

[0016] Next, embodiments of the present invention will be described based on the drawings. In the embodiments and modifications described below, corresponding configurations may be denoted by the same reference numerals and description thereof may be omitted. In the following description, expressions indicating relative or absolute arrangements such as "parallel", "orthogonal", "center", "coaxial", etc. not only strictly represent such arrangements, but also represent states in which they are relatively displaced with tolerances and angles or distances that can obtain the same function. Also, in this embodiment, "opposite" includes not only the case where the orthogonal directions (normal directions) of two surfaces coincide with each other, but also the case where the orthogonal directions intersect.

[0017] [Refrigeration System 1] FIG. 1 is a schematic configuration diagram of the refrigeration system 1. The refrigeration system 1 shown in Fig. 1 is an ultra-low temperature refrigeration system 1 used for storing fish such as tuna and bonito (hereinafter referred to as refrigeration objects). The refrigeration system 1 includes a refrigerated warehouse 10, a refrigeration device 11, a defrosting device 12, and a control unit 13.

[0018] <Refrigerated warehouse 10> The refrigerated warehouse 10 has refrigeration objects carried in and out through an entrance / exit (not shown), and stores the carried-in refrigeration objects in a predetermined temperature range. In the present embodiment, it is preferable that the inside of the refrigerated warehouse 10 is maintained at an ultra-low temperature (-45°C or lower).

[0019] <Refrigeration device 11> The refrigeration device 11 cools the inside of the refrigerated warehouse 10 by heat-exchanging a refrigerant and the air inside the refrigerated warehouse 10. In the present embodiment, carbon dioxide (CO2) is used as the refrigerant. However, a refrigerant other than carbon dioxide (for example, ammonia (NH3) or alternative Freon, etc.) may be used for the refrigeration device 11.

[0020] The refrigeration device 11 includes a refrigeration unit 20, an evaporator 21, a gas-liquid separator 22, and an oil separator 23. The refrigeration unit 20, the evaporator 21, and the gas-liquid separator 22 are provided in order in the refrigerant main flow path 25 in the refrigerant flow direction.

[0021] The refrigeration unit 20 is a so-called direct expansion type condensing unit. In the refrigeration unit 20, mainly the gaseous-phase refrigerant among the gas-liquid two-phase refrigerant that has passed through the evaporator 21 is returned, and by compressing and heat-exchanging (condensing) the gaseous-phase refrigerant, etc., a high-pressure liquid-phase refrigerant is generated. The upstream end of a feed line 30 is connected to the outlet portion of the refrigeration unit 20. The feed line 30 constitutes a part of the refrigerant main flow path 25. In the feed line 30, the liquid-phase refrigerant generated by the refrigeration unit 20 flows toward the evaporator 21. An expansion valve 31 is provided in the feed line 30.

[0022] The refrigerant discharged from the refrigeration unit 20 contains lubricating oil (refrigeration oil). The lubricating oil is used to lubricate the compressor (not shown) installed in the refrigeration unit 20. In other words, the main refrigerant flow path 25 contains the lubricating oil that flows out with the refrigerant when it is discharged from the compressor's outlet. The lubricating oil used has a lower specific gravity than the refrigerant and is incompatible with the refrigerant, however, if it separates in the evaporator 21 or the gas-liquid separator 22 and accumulates at the top, a compatible lubricating oil may be used.

[0023] The evaporator 21 cools the air inside the storage unit by exchanging heat between the liquid-phase refrigerant supplied from the refrigeration unit 20 and the air inside the storage unit. The downstream end of the supply line 30 is connected to the inlet of the evaporator 21. In other words, the liquid-phase refrigerant is supplied directly to the evaporator 21 through the supply line 30 without passing through the gas-liquid separator 22. When carbon dioxide is used as the refrigerant, the temperature of the refrigerant at the inlet of the evaporator 21 is set to a temperature near the triple point of carbon dioxide (for example, -55°C), but not below the triple point (-56.6°C).

[0024] The upstream end of the gas-liquid two-phase line 32 is connected to the outlet of the evaporator 21. The gas-liquid two-phase line 32 constitutes part of the refrigerant main flow path 25. The gas-liquid two-phase refrigerant used to cool the air inside the chamber in the evaporator 21 flows through the outlet of the evaporator 21 to the gas-liquid separator 22 via the gas-liquid two-phase line 32. The detailed configuration of the evaporator 21 will be described later.

[0025] The gas-liquid separator 22 is located at the downstream end of the gas-liquid two-phase line 32. The gas-liquid separator 22 separates the gas-liquid two-phase refrigerant discharged from the evaporator 21 into a gas phase refrigerant and a liquid phase refrigerant. A first gas return line 35 is connected to the gas-liquid separator 22. The first gas return line 35 constitutes part of the refrigerant main flow path 25 and connects the gas-liquid separator 22 to the refrigeration unit 20. Of the gas-liquid two-phase refrigerant that flows into the gas-liquid separator 22, the gas phase refrigerant flows towards the inlet of the refrigeration unit 20 (compressor suction port) through the first gas return line 35.

[0026] A liquid return line 36 is connected to the gas-liquid separator 22. The liquid return line 36 connects the portion of the supply line 30 located between the expansion valve 31 and the evaporator 21 to the gas-liquid separator 22. In this embodiment, the liquid return line 36 keeps the evaporator 21 and the gas-liquid separator 22 in constant communication. Of the refrigerant that flows into the gas-liquid separator 22, the liquid phase refrigerant flows towards the supply line 30 through the liquid return line 36. That is, the liquid phase refrigerant flowing through the liquid return line 36 merges with the liquid phase refrigerant flowing through the supply line 30 and is then supplied back to the evaporator 21. Furthermore, because the evaporator 21 and the gas-liquid separator 22 are constantly in communication through the supply line 30 and the liquid return line 36, a flow of liquid phase refrigerant from the evaporator 21 to the gas-liquid separator 22 is also possible. The detailed configuration of the gas-liquid separator 22 will be described later.

[0027] The oil separator 23 stores the lubricating oil contained in the refrigerant. The oil separator 23 is formed as a cylinder with its vertical direction as the axial direction, and comprises a container with both its upper and lower ends closed. The oil separator 23 is positioned below the gas-liquid separator 22.

[0028] The oil separator 23 is connected to an oil recovery line 40, an oil return line 42, and a second gas return line 43.

[0029] The oil recovery line 40 connects the gas-liquid separator 22 and the oil separator 23. Specifically, the upstream end of the oil recovery line 40 is connected to a portion of the gas-liquid separator 22 that is below the connection portion of the gas-liquid two-phase line 32 and above the connection portion of the liquid return line 36. The downstream end of the oil recovery line 40 is connected to the upper part of the oil separator 23. The oil separator 23 is located below the connection portion of the gas-liquid separator 22 with the oil recovery line 40. Therefore, the lubricating oil present in the gas-liquid separator 22 flows towards the oil separator 23 in the oil recovery line 40 due to its own gravity (head difference between the gas-liquid separator 22 and the oil separator 23).

[0030] An oil recovery valve 51 is provided in the oil recovery line 40. The oil recovery valve 51 switches between communication and disconnection between the gas-liquid separator 22 and the oil separator 23 through the oil recovery line 40. A check valve 50 (non-return valve) is provided in the portion of the oil recovery line 40 located downstream of the oil recovery valve 51. The check valve 50 allows the flow of fluid (mainly lubricating oil) from the gas-liquid separator 22 to the oil separator 23 and suppresses the flow of fluid from the oil separator 23 to the gas-liquid separator 22.

[0031] The oil return line 42 connects the oil separator 23 and the first gas return line 35. Specifically, the upstream end of the oil return line 42 is connected to the portion of the oil separator 23 located below the connection portion of the oil recovery line 40. In the illustrated example, the upstream end of the oil return line 42 is connected to the bottom wall portion of the oil separator 23. The downstream end of the oil return line 42 is connected to the first gas return line 35. The oil return line 42 is provided with an oil return valve 52. The oil return valve 52 switches between communication and disconnection between the oil separator 23 and the first gas return line 35 through the oil return line 42. The oil return line 42 may also be provided with a temperature sensor 54 for detecting the temperature inside the oil return line 42.

[0032] The second gas return line 43 connects the oil separator 23 and the first gas return line 35. Specifically, the upstream end of the second gas return line 43 is connected to the portion of the oil separator 23 located above the connection portion of the oil recovery line 40. In the illustrated example, the upstream end of the second gas return line 43 is connected to the top wall portion of the oil separator 23. The downstream end of the second gas return line 43 is connected to the portion of the first gas return line 35 located upstream of the connection portion with the oil return line 42. The gaseous refrigerant present in the oil separator 23 flows through the second gas return line 43 toward the first gas return line 35. The second gas return line 43 is provided with a gas return valve 53. The gas return valve 53 switches between communication and disconnection between the oil separator 23 and the first gas return line 35 through the second gas return line 43.

[0033] A heater 55 is provided on the outer surface of the oil separator 23 and the oil return line 42. The heater 55 heats the inside of the oil separator 23 and the oil return line 42, making it easier to vaporize the liquid phase refrigerant contained in the lubricating oil.

[0034] <Evaporator 21> Figure 2 is a front view of the evaporator 21. Figure 3 is a cross-sectional view corresponding to line III-III in Figure 2. As shown in Figures 2 and 3, the evaporator 21 comprises a fin module 80, a refrigerant flow path 81, and a warm brine flow path 82. In this embodiment, the evaporator 21 is a so-called full-liquid type evaporator 21. A full-liquid type evaporator 21 is one in which heat exchange is performed between the liquid phase refrigerant and the air inside the chamber when a predetermined amount of liquid phase refrigerant is filled in the refrigerant flow path 81.

[0035] The fin module 80 is equipped with multiple fins 90. Each fin 90 is made of a material with excellent thermal conductivity, such as aluminum. Each fin 90 is formed in a thin plate shape with the thickness direction being the direction that intersects the vertical direction (hereinafter referred to as the X direction). Each fin 90 is arranged with spacing in the X direction. Air inside the chamber can pass between adjacent fins 90.

[0036] As shown in Figure 3, each fin 90 has a first refrigerant pore row 91, a second refrigerant pore row 92, and a warm brine pore row 93. In each fin 90, the corresponding refrigerant pore rows 91 and 92 and the warm brine pore rows 93 overlap each other when viewed from the X direction. Therefore, in the following description, the details of the refrigerant pore rows 91 and 92 and the warm brine pore row 93 will be explained using one fin 90 as an example.

[0037] The first refrigerant hole rows 91 and the second refrigerant hole rows 92 are arranged alternately with a gap between them in a direction that intersects the X direction when viewed from above (hereinafter referred to as the Y direction). Adjacent first refrigerant hole rows 91 and second refrigerant hole rows 92 constitute a pair of refrigerant hole sets 94. Therefore, in this embodiment, multiple refrigerant hole sets 94 are arranged in the Y direction.

[0038] The row of holes 93 for warm brine is provided between adjacent rows of holes 91 and 92 for refrigerant that constitute a single row of holes 94 for refrigerant. In this case, the row of holes 93 for warm brine is not provided between adjacent rows of holes 94 for refrigerant. However, the row of holes 93 for warm brine may be provided alternately for all rows of holes 91 and 92 for refrigerant.

[0039] The first refrigerant hole row 91 comprises a plurality of first refrigerant holes 95. The plurality of first refrigerant holes 95 are arranged in a straight line with spacing in the vertical direction. Each first refrigerant hole 95 penetrates the fin 90 in the X direction. Each first refrigerant hole 95 is a round hole formed with the same diameter D1. The plurality of first refrigerant holes 95 constituting the first refrigerant hole row 91 are arranged at equal intervals.

[0040] The second refrigerant hole row 92 comprises a plurality of second refrigerant holes 96. The plurality of second refrigerant holes 96 are arranged in a straight line with spacing in the vertical direction. Each second refrigerant hole 96 penetrates the fin 90 in the X direction. Each second refrigerant hole 96 is a round hole formed with a diameter D1 equivalent to that of each first refrigerant hole 95. The plurality of second refrigerant holes 96 constituting the second refrigerant hole row 92 are arranged at equal intervals. Note that the shape of each refrigerant hole 95,96 is not limited to a perfect circle, but can be changed as appropriate to an elliptical shape, etc.

[0041] In the first row of refrigerant holes 91 and the second row of refrigerant holes 92 that constitute a single refrigerant hole set 94, the first refrigerant holes 95 and the second refrigerant holes 96 are arranged with a half-pitch offset in the vertical direction. Specifically, the arrangement pitch of the first refrigerant holes 95 (the distance between adjacent first refrigerant holes 95 in the vertical direction) and the arrangement pitch of the second refrigerant holes 96 (the distance between adjacent second refrigerant holes 96 in the vertical direction) are equal. Furthermore, in the first row of refrigerant holes 91 and the second row of refrigerant holes 92 that constitute a single refrigerant hole set 94, the first refrigerant holes 95 and the second refrigerant holes 96 are arranged in a staggered (alternating) pattern when viewed from the X direction. However, the arrangement pitch of the multiple refrigerant holes 95 and 96 that constitute each refrigerant hole set 91 and 92 can be changed as appropriate.

[0042] The row of warm brine holes 93 comprises a plurality of warm brine holes 105. The plurality of warm brine holes 105 are arranged in a straight line with spacing in the vertical direction. Each warm brine hole 105 penetrates the fin 90 in the X direction. Each warm brine hole 105 is a round hole formed with a diameter D2 smaller than the diameter D1 of the refrigerant holes 95, 96. In this embodiment, the diameter D1 is set to, for example, 15.88 mm, and the diameter D2 is set to 12.70 mm. It is preferable that both diameters D1 and D2 are set in the range of 9 mm to 16 mm. The shape of the warm brine hole 105 is not limited to a perfect circle, but can be changed as appropriate to an elliptical shape, etc. In this case, it is sufficient that the opening area of ​​the warm brine hole 105 is smaller than the opening area of ​​the refrigerant holes 95, 96. Also, the warm brine hole 105 and the refrigerant holes 95, 96 do not necessarily have similar shapes.

[0043] Each of the warm brine holes 105 constituting a row of warm brine holes 93 is arranged at equal intervals. In this embodiment, the arrangement pitch of each warm brine hole 105 is greater than the arrangement pitch of the refrigerant holes 95 and 96. That is, the number of warm brine holes 105 constituting the row of warm brine holes 93 is less than the number of refrigerant holes 95 and 96 constituting the rows of refrigerant holes 91 and 92. In the illustrated example, the warm brine holes 105 are located between vertically adjacent first refrigerant holes 95 in the first row of refrigerant holes 91, and between vertically adjacent second refrigerant holes 96 in the second row of refrigerant holes 92. Therefore, each warm brine hole 105 is surrounded by four refrigerant holes 95 and 96.

[0044] As shown in Figures 2 and 3, the refrigerant flow path 81 constitutes a part of the main refrigerant flow path 25. The refrigerant flow path 81 is connected to the downstream end of the supply line 30 via an inlet header (not shown). On the other hand, the refrigerant flow path 81 is connected to the upstream end of the gas-liquid two-phase line 32 via an outlet header (not shown). The refrigerant flow path 81 is equipped with two coils (first coil 110 and second coil 111) for each row of refrigerant holes 91 and 92. Each coil 110 and 111 is a tubular material (heat transfer tube) having an outer diameter that can be pressed into each refrigerant hole 95 and 96. That is, the outer diameter of each coil 110 and 111 is formed to be equivalent to the diameter D1 of each refrigerant hole 95 and 96. In the following, the coils 110 and 111 provided in the first row of refrigerant holes 91 will be used as an example to explain the details of the coils 110 and 111, and the second row of refrigerant holes 92 will be given the same reference numerals as the coils 110 and 111 provided in the first row of refrigerant holes 91, and its explanation will be omitted.

[0045] Each coil 110, 111 penetrates the refrigerant holes 95 facing each other in the X direction between adjacent fins 90, and extends upward in a meandering manner in the X direction by being folded back on both sides in the X direction relative to the fin module 80. The lower end of each coil 110, 111 is connected to the inlet header. The upper end of each coil 110, 111 is connected to the outlet header. Each coil 110, 111 extends parallel to the same first row of refrigerant holes 91, forming a so-called double-circuit structure (parallel structure).

[0046] As shown in Figure 2, the first coil 110 comprises a first straight section 110a, a second straight section 110b, a first folded section 110c, and a second folded section 110d. The second coil 111 includes a third straight section 111a, a fourth straight section 111b, a third folded section 111c, and a fourth folded section 111d.

[0047] The first straight section 110a is assembled in a state where it is in contact with the inner periphery of the first through-hole 95a by being press-fitted into the first through-hole 95a of the first refrigerant hole 95. The first straight section 110a is provided between adjacent fins 90 so as to penetrate each of the first through-holes 95a that are facing each other in the X direction. The second straight section 110b is assembled in a state where it is in contact with the inner periphery of the second through-hole 95b by press-fitting it into the second through-hole 95b which is adjacent to the first through-hole 95a above the first refrigerant hole 95. The second straight section 110b is provided so as to penetrate each of the second through-holes 95b that are facing each other in the X direction between adjacent fins 90.

[0048] The third straight section 111a is assembled in a state where it is in contact with the inner periphery of the third through-hole 95c by press-fitting it into the third through-hole 95c, which is adjacent to the second through-hole 95b above the first refrigerant hole 95. The third straight section 111a is provided between adjacent fins 90 so as to penetrate each of the third through-holes 95c that are facing each other in the X direction. The fourth straight section 111b is assembled in a state where it is in contact with the inner periphery of the fourth through-hole 95d by press-fitting it into the fourth through-hole 95d, which is adjacent to the third through-hole 95c above among the first refrigerant holes 95. The fourth straight section 111b is provided so as to penetrate each of the fourth through-holes 95d that are facing each other in the X direction between adjacent fins 90.

[0049] In this embodiment, the first refrigerant holes 95 consist of two through-holes (first through-hole 95a and second through-hole 95b) through which the first coil 110 (first straight section 110a and second straight section 110b) passes, and two through-holes (third through-hole 95c and fourth through-hole 95d) through which the second coil 111 (third straight section 111a and fourth straight section 111b) passes, arranged alternately. In the following description, the first through-hole 95a and second through-hole 95b will be referred to as the first hole set 115, and the third through-hole 95c and fourth through-hole 95d will be referred to as the second hole set 116. In this case, the first refrigerant hole row 91 will consist of the first hole set 115 and the second hole set 116 arranged alternately in the vertical direction.

[0050] The first folded portion 110c is provided on one side (-X side) in the X direction relative to the fin module 80. The first folded portion 110c connects the X-direction ends of the first straight portion 110a and the second straight portion 110b, which are provided in the same first hole set 115. The second folded portion 110d is provided on the other side (+X side) in the X direction relative to the fin module 80. The second folded portion 110d connects the other end in the X direction of the second straight portion 110b provided in one first hole set 115 and the first straight portion 110a provided in another first hole set 115 located, for example, above the first first hole set 115.

[0051] The third folded portion 111c is provided on one side in the X direction relative to the fin module 80. The third folded portion 111c connects the X-side ends of the third straight portion 111a provided in one second hole set 116 and the fourth straight portion 111b provided in another second hole set 116 located, for example, below the first second hole set 116. In the illustrated example, the third folded portion 111c wraps around the outside of the first folded portion 110c. The fourth folded portion 111d is provided on the other side in the X direction relative to the fin module 80. The fourth folded portion 111d connects the other ends in the X direction of the third straight portion 111a and the fourth straight portion 111b, which are provided in the same second hole set 116. In the illustrated example, the second folded portion 110c wraps around the outside of the fourth folded portion 111d.

[0052] Brine (antifreeze) used for defrosting the evaporator 21 flows through the warm brine channel 82. In this embodiment, the brine used is a material with a freezing point lower than the triple point of carbon dioxide, such as an HCFO-based brine.

[0053] The warm brine channel 82 is a tubular material (heat transfer tube) having an outer diameter that can be pressed into the warm brine hole 105. That is, the outer diameter of the warm brine channel 82 is equivalent to the diameter D2 of the warm brine hole 105 and smaller than the outer diameter of each coil 110, 111. The warm brine channel 82 penetrates the warm brine holes 105 facing each other in the X direction between adjacent fins 90, and extends upward in a meandering manner in the X direction by being folded back on both sides in the X direction relative to the fin module 80. Specifically, the warm brine channel 82 comprises a straight section 82a, a folded section 82b on one side, and a folded section 82c on the other side.

[0054] The straight section 82a is assembled in contact with the inner periphery of the warm brine hole 105 by press-fitting it into the warm brine hole 105 or the like. The straight section 82a is provided between adjacent fins 90 so as to penetrate the warm brine holes 105 that are opposite each other in the X direction. The one-sided folded portion 82b is provided on one side in the X direction relative to the fin module 80. The one-sided folded portion 82b connects the one-sided ends in the X direction of one straight portion 82a and a straight portion 82a located above the first straight portion 82a. In the illustrated example, the one-sided folded portion 82b is provided so as to straddle the second hole set 116 in the vertical direction. The other-side folded portion 82c is provided on the other side in the X direction relative to the fin module 80. The one-side folded portion 82c connects the other end in the X direction of one straight portion 82a and a straight portion 82a located, for example, below the first straight portion 82a. In the illustrated example, the other-side folded portion 82c is provided so as to straddle the first hole set 115 in the vertical direction.

[0055] Figure 4 is a configuration diagram showing the evaporator 21 and the gas-liquid separator 22. In Figure 4, the gas-liquid separator 22 is shown in cross-section. As shown in Figure 4, the evaporator 21 of this embodiment is positioned within a height range that includes at least a first height T1 and a second height T2 set lower than the first height T1. The first height T1 is the height from the lower end Ta of the refrigerant flow path 81, and is the height at which the liquid phase refrigerant sufficiently fills the refrigerant flow path 81 in the evaporator 21. In this embodiment, the first height T1 is set to, for example, 80% of the total vertical dimension of the refrigerant flow path 81 (dimension from the lower end Ta to the upper end Tb) from the lower end Ta of the refrigerant flow path 81.

[0056] In this case, it is preferable that the first height T1 be 90% or less, in that a predetermined amount of liquid-phase refrigerant can be filled into the refrigerant flow path 81 (in that it is possible to suppress the flow of more than a predetermined amount of liquid-phase refrigerant into the gas-liquid separator 22 and the return of the liquid-phase refrigerant to the compressor).

[0057] The second height T2 is the height from the lower end Ta of the refrigerant flow path 81, and is the height (lower limit height) at which the evaporator 21 is filled with the liquid phase refrigerant necessary to perform the predetermined cooling. In this embodiment, the second height T2 is set to, for example, 70% of the overall vertical dimension of the refrigerant flow path 81 from the lower end Ta of the refrigerant flow path 81. In this case, it is preferable that the second height T2 be 60% or more in order to secure the effective area of ​​the refrigerant flow path 81. However, the first height T1 and the second height T2 can be changed as appropriate.

[0058] <Gas-liquid separator 22> The gas-liquid separator 22 includes a housing 120, an inlet passage 121, a gas discharge passage 122, a liquid discharge opening 123, an oil discharge opening 124, a baffle plate 125, a first liquid level sensor 126, and a second liquid level sensor 127. The housing 120 is a container for separating the gaseous-liquid two-phase refrigerant and lubricating oil that have passed through the evaporator 21. That is, the housing 120 stores two layers of liquid, with the liquid phase refrigerant separated from the gaseous-liquid two-phase refrigerant as the lower layer and the lubricating oil as the upper layer. The housing 120 is positioned adjacent to the evaporator 21 in the horizontal direction. The housing 120 is positioned within a range that includes at least a first height T1 and a second height T2 in the vertical direction. In this embodiment, the housing 120 is positioned so as to straddle the first height T1 and the second height T2 in the vertical direction.

[0059] The housing 120 comprises a cylindrical portion 120a, a bottom wall 120b, and a top wall 120c. The cylindrical portion 120a is formed as a cylinder with its vertical direction as the axial direction. The bottom wall 120b closes the lower end opening of the cylindrical portion 120a. The bottom wall 120b is located between the lower end Ta of the refrigerant flow path 81 and the second height T2. The top wall 120c closes the upper end opening of the cylindrical portion 120a. The top wall 120c is located above the upper end Tb of the refrigerant flow path 81. However, the top wall 120c may be located below the upper end Tb of the refrigerant flow path 81, as long as it is located above at least the first height T1.

[0060] The inflow channel 121 constitutes the downstream end of the gas-liquid two-phase line 32. In other words, the inflow channel 121 is part of the refrigerant main channel 25. In cross-sectional view, the inflow channel 121 is formed in a downward L-shape. The inflow channel 121 comprises an inflow penetration portion 121a, a hanging portion 121b, and a closing portion 121c.

[0061] The inlet penetration 121a penetrates the upper end of the cylindrical portion 120a. Specifically, the inlet penetration 121a extends along the upper end Tb of the refrigerant flow path 81. However, the inlet penetration 121a only needs to be provided in the portion of the cylindrical portion 120a that is located above the first height T1. The tip of the inlet penetration 121a is located on the axis O of the housing 120.

[0062] The hanging portion 121b extends downward along axis O from the tip of the inlet penetration portion 121a within the housing 120. The lower end of the hanging portion 121b is located below the second height T2. In the illustrated example, the lower end of the hanging portion 121b reaches the lower end of the cylindrical portion 120a. Multiple inlets 129 are formed at the lower part of the hanging portion 121b, connecting the inside and outside of the hanging portion 121b. The inlets 129 allow the gas-liquid two-phase refrigerant flowing through the inlet channel 121 to flow into the housing 120. Multiple inlets 129 are arranged at intervals in the vertical direction and in the circumferential direction of the hanging portion 121b.

[0063] In this embodiment, at least a portion of the hanging portion 121b is immersed in the liquid phase refrigerant stored in the housing 120. That is, at least some of the inlets 129 formed in the hanging portion 121b open into the liquid phase refrigerant stored in the housing 120. In the illustrated example, the uppermost inlet 129 is located below the first height T1. The lowermost inlet 129 is located below the second height T2. However, it is sufficient that any of the multiple inlets 129 are located below the first height T1.

[0064] The occluding portion 121c closes the lower end opening of the hanging portion 121b. Therefore, the inflow channel 121 does not open in a position facing the bottom wall 120b. The occluding portion 121c is positioned away from the bottom wall 120b and faces the liquid discharge opening 123.

[0065] The gas discharge passage 122 constitutes the upstream end of the first gas return line 35. In other words, the gas discharge passage 122 is part of the refrigerant main passage 25. In cross-sectional view, the gas discharge passage 122 is formed in an L-shape. The gas discharge passage 122 comprises a discharge penetration portion 122a and an upright portion 122b.

[0066] The discharge penetration 122a penetrates the cylindrical portion 120a at a position opposite the inlet penetration 121a. The tip of the discharge penetration 122a is located inside the housing 120. The upright portion 122b extends upward from the tip of the discharge penetration portion 122a. The upper end opening of the upright portion 122b opens upward above the inflow passage 121. That is, the upper end opening of the upright portion 122b opens above the upper end Tb of the refrigerant passage 81. The gaseous refrigerant present in the housing 120 flows into the gas discharge passage 122 through the upper end opening of the upright portion 122b. The opening position of the gas discharge passage 122 can be changed as appropriate, as long as it is above the first height T1. In this case, it is preferable that the opening position of the gas discharge passage 122 is above the first height T1 and above the baffle plate 125.

[0067] The liquid discharge opening 123 constitutes the upstream end of the liquid return line 36. The liquid discharge opening 123 penetrates the bottom wall 120b in the vertical direction. The upper end opening of the liquid discharge opening 123 opens upward at the lower end inside the housing 120. That is, the upper end opening of the liquid discharge opening 123 opens in a portion located below the second height T2. Liquid phase refrigerant from the refrigerant present inside the housing 120 flows into the liquid discharge opening 123 due to its own gravity (head difference between the gas-liquid separator 22 and the inlet portion of the refrigerant flow path 81).

[0068] The oil discharge opening 124 constitutes the upstream end of the oil recovery line 40. The oil discharge opening 124 is provided by penetrating the portion of the cylindrical section 120a that is located below the portion connected to the inflow passage 121. The oil discharge opening 124 is located in the vertical center of the cylindrical section 120a. Specifically, the oil discharge opening 124 opens into the housing 120 at a position of first height T1. In other words, the oil discharge opening 124 opens into the housing 120 at a portion located above the uppermost inlet 129 among the multiple inlets 129. Lubricating oil that remains as the supernatant of the liquid phase refrigerant inside the housing 120 flows into the oil discharge opening 124. The lubricating oil that flows into the oil discharge opening 124 flows into the oil separator 23 due to its own weight (head difference between the gas-liquid separator 22 and the oil separator 23). Furthermore, the oil discharge opening 124 only needs to be formed at a position higher than the second height T2.

[0069] The baffle plate 125 has the function of preventing liquid-phase refrigerant flowing into the housing 120 through the inlet 129 from reaching the gas discharge passage 122. In this embodiment, a plurality of baffle plates 125 are provided at vertically spaced intervals at the upper end of the hanging portion 121b (the portion located above the inlet 129). The gas discharge passage 122 described above opens above the baffle plates 125 within the housing 120. Each baffle plate 125 is formed in a skirt shape (conical shape) with an outer diameter that gradually increases towards the bottom. The baffle plates 125 are attached to the hanging portion 121b so as to partition the inside of the housing 120 in the vertical direction.

[0070] The baffle plate 125 has multiple through holes (not shown) that penetrate it vertically. Each through hole connects the space below and above the baffle plate 125 within the housing 120. The through holes in each baffle plate 125 are spaced apart so that they do not overlap each other in a plan view.

[0071] The first liquid level sensor 126 detects that the liquid level (liquid phase refrigerant and lubricating oil) inside the housing 120 is at a first height T1. The second liquid level sensor 127 detects that the liquid level inside the housing 120 is at the second height T2. Each liquid level sensor 126, 127 may be a contact type (float type, electrode type, etc.) or a non-contact type (ultrasonic type, etc.).

[0072] <Defrosting device 12> As shown in Figure 1, the defrosting device 12 circulates brine between itself and the evaporator 21 during defrosting of the evaporator 21. In other words, the refrigeration system 1 of this embodiment can be switched between a cooling mode, in which the inside of the refrigerated warehouse 10 is cooled via the evaporator 21 by the operation of the refrigeration device 11, and a defrosting mode, in which frost accumulated on the evaporator 21 (fin module 80, etc.) is removed when the refrigeration device 11 is stopped. The defrosting mode is performed periodically, for example, after the refrigeration device 11 has been driven in cooling mode for a predetermined time. However, the switch from cooling mode to defrosting mode may be performed manually or based on changes in the internal temperature during cooling mode.

[0073] The defrosting device 12 is connected to the evaporator 21 via a brine supply line 140 and a brine return line 141. Brine, adjusted to a desired temperature by the defrosting device 12, flows through the brine supply line 140 toward the evaporator 21. In this embodiment, so-called warm brine, adjusted to a temperature higher than the refrigerant temperature (for example, around 25°C), can be supplied. The upstream end of the brine supply line 140 is connected to the defrosting device 12. The downstream end of the brine supply line 140 is connected to the lower end (upstream end) of the warm brine flow path 82 via an inlet header (not shown).

[0074] The brine return line 141 carries the brine used for defrosting in the evaporator 21 toward the defrosting device 12. The upstream end of the brine return line 141 is connected to the upper end (downstream end) of the warm brine flow path 82 via an outlet header (not shown). The downstream end of the brine return line 141 is connected to the defrosting device 12.

[0075] <Control Unit 13> The control unit 13 shown in Figure 1 comprehensively controls the operation of the refrigeration system 1. The control unit 13 is realized by a hardware processor such as a CPU executing a computer program (software) stored in a memory unit. The control unit 13 controls the flow of refrigerant and lubricating oil by switching the opening and closing of the oil recovery valve 51, oil return valve 52, and gas return valve 53 according to the operating mode of the refrigeration system 1. In addition, the control unit 13 controls the liquid level of the evaporator 21 (refrigerant flow path 81) by adjusting the opening degree of the expansion valve 31 and the output of the refrigeration unit 20 based on the liquid level of the gas-liquid separator 22 detected by the liquid level sensors 126 and 127.

[0076] <Operation method of refrigeration system 1> Next, the operation method of the refrigeration system 1 described above will be explained. The following explanation will describe the operation in cooling mode, defrost mode, and oil recovery mode, respectively.

[0077] <Cooling Mode> As shown in Figure 1, in cooling mode, the control unit 13 opens the oil recovery valve 51 and the gas return valve 53, and closes the oil return valve 52. That is, in cooling mode, the inside of the gas-liquid separator 22 and the inside of the oil separator 23 are in communication through the oil recovery line 40, and the first gas return line 35 and the inside of the oil separator 23 are in communication through the second gas return line 43. On the other hand, in cooling mode, the communication between the first gas return line 35 and the inside of the oil separator 23 via the oil return line 42 is blocked. When the refrigeration system 11 is operated in this state, the liquid phase refrigerant discharged from the refrigeration unit 20 is supplied directly into the evaporator 21 (refrigerant flow path 81) through the supply line 30. The refrigerant flowing into the refrigerant flow path 81 flows upward while meandering in the X direction. The liquid phase refrigerant flowing into the refrigerant flow path 81 then exchanges heat with the air inside the chamber passing between adjacent fins 90 via the fins 90, etc. In other words, the evaporator 21 cools the area around it by absorbing heat of vaporization from the surroundings as the refrigerant in the refrigerant flow path 81 vaporizes. As a result, the air inside the storage area is cooled, and the inside of the refrigerated storage area 10 is maintained at the desired temperature.

[0078] The refrigerant, after heat exchange with the air inside the chamber, becomes a gas-liquid two-phase system and is discharged from the evaporator 21 into the gas-liquid two-phase line 32, before flowing into the gas-liquid separator 22. Specifically, the refrigerant flowing through the gas-liquid two-phase line 32 passes through the inflow channel 121 and then flows into the gas-liquid separator 22 (housing 120) through the inlet 129. Of the refrigerant that has flowed into the gas-liquid separator 22, the gas phase refrigerant flows into the gas discharge channel 122 through the upper end opening of the upright section 122b and is discharged from the gas-liquid separator 22. The gas phase refrigerant that has flowed into the gas discharge channel 122 flows through the first gas return line 35 and is returned to the refrigeration unit 20. The gas phase refrigerant returned to the refrigeration unit 20 is converted back into liquid phase refrigerant in the refrigeration unit 20 and then supplied to the evaporator 21.

[0079] On the other hand, of the refrigerant that flows into the gas-liquid separator 22, the liquid phase refrigerant is stored in the housing 120. In the refrigeration system 1 of this embodiment, the evaporator 21 and the gas-liquid separator 22 are arranged within a height range including the first height T1 and the second height T2. Furthermore, the evaporator 21 and the gas-liquid separator 22 are constantly in communication with each other through the gas-liquid two-phase line 32 and the liquid return line 36. That is, in cooling mode, the inside of the evaporator 21 (inside the refrigerant flow path 81) and the inside of the gas-liquid separator 22 (inside the housing 120) are maintained at the same pressure. In this case, the liquid phase refrigerant stored in the gas-liquid separator 22 is returned to the evaporator 21 due to the head difference between the gas-liquid separator 22 and the inlet portion of the refrigerant flow path 81. Specifically, the liquid phase refrigerant stored in the gas-liquid separator 22 flows into the liquid discharge opening 123 through the upper end opening of the liquid discharge opening 123. Subsequently, the liquid phase refrigerant is returned to the downstream side of the expansion valve 31 in the supply line 30 via the liquid return line 36. The liquid phase refrigerant returned to the supply line 30 merges with the liquid phase refrigerant supplied from the refrigeration unit 20 and is then returned to the evaporator 21.

[0080] In this embodiment of the refrigeration system 1, the inside of the evaporator 21 (inside the refrigerant flow path 81) and the inside of the gas-liquid separator 22 (inside the housing 120) are maintained at the same pressure. Therefore, the liquid level of the liquid phase refrigerant in the refrigerant flow path 81 is equal to the liquid level of the liquid phase refrigerant in the housing 120. In other words, the liquid level in the refrigerant flow path 81 can be determined based on the liquid level in the housing 120. In this embodiment, the liquid level in the refrigerant flow path 81 is adjusted by controlling the opening degree of the expansion valve 31 based on the liquid level in the housing 120.

[0081] Specifically, based on the detection result from the first liquid level sensor 126, the control unit 13 determines that the liquid level in the housing 120 has reached a first height T1, and reduces the opening of the expansion valve 31 and lowers the output of the refrigeration unit 20 (low output mode). In low output mode, the control unit 13 determines that the evaporator 21 is filled with a sufficient amount of liquid-phase refrigerant and reduces the amount of liquid-phase refrigerant supplied to the evaporator 21. On the other hand, based on the detection result from the second liquid level sensor 127, if the control unit 13 determines that the liquid level in the housing 120 is less than the first height T1 and has reached the second height T2, it increases the opening of the expansion valve 31 and increases the output of the refrigeration unit 20 (high output mode). In high output mode, if the control unit 13 determines that there is a risk of insufficient liquid phase refrigerant necessary for normal operation in the evaporator 21, it increases the amount of liquid phase refrigerant supplied to the evaporator 21. In low output mode, the opening of the expansion valve 31 may be set to 0.

[0082] In this way, the control unit 13 adjusts the opening degree of the expansion valve 31 and the output of the refrigeration unit 20 based on the detection results from the liquid level sensors 126 and 127, thereby maintaining the liquid level of the gas-liquid separator 22 between the first height T1 and the second height T2. As a result, the liquid level of the liquid phase refrigerant filling the evaporator 21 is maintained within the desired range (the range between the first height T1 and the second height T2). By maintaining the liquid level of the gas-liquid separator 22 between the first height T1 and the second height T2, during the cooling mode, at least some of the inlets 129 formed in the hanging portion 121b open into the liquid phase refrigerant stored in the housing 120.

[0083] Furthermore, lubricating oil is retained in the gas-liquid separator 22 as the supernatant of the liquid phase refrigerant. In other words, two layers of liquid are stored in the gas-liquid separator 22, with the refrigerant in the lower layer and the oil in the upper layer. In this case, since the oil separator 23 is located below the connection point (oil discharge opening 124) to the oil recovery line 40 of the gas-liquid separator 22, when the oil in the upper layer reaches the same height as the oil discharge opening 124, it is discharged from the gas-liquid separator 22 through the oil discharge opening 124. In cooling mode, since the oil recovery valve 51 is open, the oil discharged from the gas-liquid separator 22 flows towards the oil separator 23 through the oil recovery line 40 due to the head difference between the gas-liquid separator 22 and the oil separator 23. As a result, the lubricating oil contained in the refrigerant is stored in the oil separator 23.

[0084] Furthermore, the lubricating oil flowing into the oil separator 23 may contain refrigerant (mainly liquid-phase refrigerant) that has flowed from the gas-liquid separator 22 along with the lubricating oil. Heaters 55 are provided in the oil separator 23 and the oil return line 42, and the liquid-phase refrigerant contained in the oil separator 23 is heated by the heaters 55 and vaporized before being discharged from the oil separator 23 through the second gas return line 43. The gaseous refrigerant that flows into the second gas return line 43 merges with the gaseous refrigerant discharged from the gas-liquid separator 22 in the first gas return line 35 and is then returned to the refrigeration unit 20.

[0085] <Defrost Mode> In defrost mode, the defrosting device 12 is operated with the refrigeration unit 20 stopped. In defrost mode, brine adjusted to the desired temperature by the defrosting device 12 passes through the evaporator 21, warming the evaporator 21 and removing frost that has accumulated on it. Specifically, the brine flowing through the brine supply line 140 flows into the upstream end of the warm brine flow path 82 via the inlet header. The brine that flows into the warm brine flow path 82 flows upward while meandering in the X direction. The heat from the brine flowing through the warm brine flow path 82 warms the warm brine flow path 82 and the fins 90, etc. This melts the frost that has accumulated on the warm brine flow path 82 and the fins 90, etc. The water generated from the melted frost falls through the gaps between adjacent fins 90. This removes frost from the evaporator 21. In addition, the defrost mode is performed with the oil recovery valve 51 and gas return valve 53 open and the oil return valve 52 closed, similar to the cooling mode.

[0086] In this embodiment, the row of holes for the warm brine 93 is arranged between the rows of holes for the refrigerant 91 and 92 that constitute the refrigerant hole set 94, so that the warm brine channel 82 and the refrigerant channel 81 are located in close proximity. Therefore, the heat of the brine flowing through the warm brine channel 82 is also transferred to the refrigerant channels 81 which are located on both sides of the warm brine channel 82 in the Y direction. Consequently, the refrigerant flowing through the refrigerant channel 81 is efficiently heated by the brine. In this case, for example, the latent heat of condensation when the liquid phase refrigerant flowing through the refrigerant channel 81 evaporates and then condenses again can heat the refrigerant channel 81 and the fins 90. This makes it possible to melt frost that has accumulated on parts located around the refrigerant channel 81 by utilizing the latent heat of condensation of the refrigerant. As a result, it is easier to achieve the desired defrosting performance while keeping the brine temperature relatively low. Therefore, it is possible to suppress the evaporation of moisture present around the refrigerant channel 81 by the heat of the brine and suppress frost formation in locations other than the evaporator 21. The defrost mode may be terminated after the defrost device 12 has been operating for a predetermined time, or it may be terminated when the refrigerant pressure in the refrigerant flow path 81 is detected and rises to a predetermined pressure.

[0087] <Oil recovery mode> In this embodiment, the oil recovery mode is performed after the defrost mode ends and before the cooling mode starts. In the oil recovery mode, the refrigeration unit 20 is operated to supply liquid phase refrigerant to the evaporator 21, and the lubricating oil stored in the oil separator 23 is returned to the refrigeration unit 20.

[0088] In oil recovery mode, the control unit 13 opens the expansion valve 31 and the oil return valve 52, and closes the oil recovery valve 51 and the gas return valve 53. That is, in oil recovery mode, the first gas return line 35 and the inside of the oil separator 23 are in communication through the oil return line 42. On the other hand, in oil recovery mode, the communication between the inside of the gas-liquid separator 22 and the inside of the oil separator 23 through the oil recovery line 40 is blocked, and the communication between the first gas return line 35 and the inside of the oil separator 23 is blocked through the second gas return line 43. In this state, when the refrigeration system 11 is operated, the liquid phase refrigerant discharged from the refrigeration unit 20 is supplied to the evaporator 21 (refrigerant flow path 81) through the supply line 30, similar to the cooling mode.

[0089] Incidentally, when defrosting is performed using the defrost mode described above, the temperature of the refrigerant present in the refrigerant flow path 81 rises, causing the pressure in the refrigerant main flow path 25 and the oil separator 23 to increase. When the oil recovery mode is performed in this state, the refrigerant in the first gas return line 35 is drawn towards the refrigeration unit 20 (compressor), creating negative pressure in the first gas return line 35, including the connection point with the oil return line 42. Since the pressure in the oil separator 23 has increased due to the effect of the defrost mode, this differential pressure causes the lubricating oil present in the oil separator 23 to flow into the first gas return line 35 through the oil return line 42 during the oil recovery mode. Therefore, the gaseous refrigerant and lubricating oil present in the oil separator 23 are returned to the refrigeration unit 20 together with the gaseous refrigerant flowing through the first gas return line 35.

[0090] The operation time for the oil recovery mode may be a predetermined time based on a timer (not shown). The control unit 13 may also determine whether to switch from the defrost mode to the oil recovery mode based on the detection result of the temperature sensor 54 (temperature in the oil return line 42). That is, the control unit 13 may allow switching from the defrost mode to the oil recovery mode when the temperature in the oil return line 42 is higher than a predetermined temperature (for example, -50°C). If the temperature in the oil return line 42 is lower than the predetermined temperature, there is a possibility that liquid phase refrigerant is present in the oil return line 42. Therefore, by prohibiting switching to the oil recovery mode when the temperature in the oil return line 42 is lower than the predetermined temperature, it is possible to suppress the inflow of liquid phase refrigerant into the first gas return line 35 through the oil return line 42.

[0091] As described above, the refrigeration system 1 of this embodiment includes a liquid-filled evaporator 21 that has coils 110, 111 filled with liquid-phase refrigerant generated in the refrigeration unit 20 and is installed in the refrigerated warehouse 10 to cool the air inside the warehouse by exchanging heat between the air inside the warehouse and the refrigerant; a supply line 30 connected to the upstream ends of the coils 110, 111 and through which the refrigerant flowing into the evaporator 21 flows; an expansion valve 31 provided in the supply line 30; a gas-liquid two-phase line 32 connected to the downstream ends of the coils 110, 111 and through which the gas-liquid two-phase refrigerant flowing out of the evaporator 21 flows; a gas-liquid separator 22 connected to the gas-liquid two-phase line 32 and separating the refrigerant flowing out of the evaporator 21 into liquid and gas phases; and a liquid return line (liquid line) 36 connecting the lower end of the gas-liquid separator 22 and the portion of the supply line 30 located between the expansion valve 31 and the evaporator 21. In this configuration, the liquid-phase refrigerant flowing through the supply line 30 passes through the expansion valve 31 and is then supplied directly to the evaporator 21. This allows for a smoother supply of liquid-phase refrigerant to the evaporator 21 compared to the conventional configuration where liquid-phase refrigerant is supplied to the evaporator via a surge tank. In this case, even immediately after entering defrost mode, for example, liquid-phase refrigerant is supplied sequentially from the refrigeration unit 20, thus avoiding a refrigerant shortage in the evaporator 21 and allowing for a quick transition to normal cooling mode. Furthermore, since there is no need to enlarge the surge tank to ensure head difference, an increase in refrigerant volume and an increase in the size of the refrigeration system 1 can be suppressed. Furthermore, in this embodiment, since the gas-liquid separator 22 is connected to the evaporator 21 downstream of the evaporator 21 via the gas-liquid two-phase line 32, the gas-liquid separator 22 is supplied with a highly dehydrated gas-liquid two-phase refrigerant that has been used for heat exchange in the evaporator 21. Therefore, the gas-liquid separator 22 can easily separate the gas-liquid two-phase refrigerant into the gas phase refrigerant and the liquid phase refrigerant.

[0092] Furthermore, in the refrigeration system 1 of this embodiment, the lower end of the gas-liquid separator 22 is located above the upstream ends of the coils 110 and 111. This configuration allows for a more compact gas-liquid separator 22 and reduces the amount of refrigerant in the liquid phase stored within the gas-liquid separator 22, thereby suppressing the need for larger equipment and increased manufacturing costs. As a result, a compact and simple configuration ensures cooling performance with the evaporator 21, making it easy to maintain the refrigerated warehouse 10 at the desired temperature.

[0093] The refrigeration system 1 of this embodiment includes a first liquid level sensor 126 for detecting the liquid level of the liquid phase refrigerant stored in the gas-liquid separator 22, and a control unit 13 for controlling the opening degree of the expansion valve 31 based on the detection result of the first liquid level sensor 126. The evaporator 21 and the gas-liquid separator 22 are each arranged within a dimensional range that includes a first height T1 in the vertical direction, and the control unit 13 adjusts the opening degree of the expansion valve 31 based on the detection result of the first liquid level sensor 126 so that the liquid level in the gas-liquid separator 22 is maintained at the first height T1. With this configuration, since the evaporator 21 and the gas-liquid separator 22 are each positioned within a dimensional range that includes the first height T1, the liquid level of the liquid phase refrigerant stored in the evaporator 21 and the gas-liquid separator 22 is maintained at the same level. This allows the liquid level of the refrigerant in the evaporator 21 (coils 110, 111) to be controlled based on the liquid level of the refrigerant in the gas-liquid separator 22. Specifically, by adjusting the opening of the expansion valve 31 so that the liquid level in the gas-liquid separator 22 is maintained at the first height T1 based on the detection result of the first liquid level sensor 126, the liquid level in the evaporator 21 is maintained at the first height T1. This makes it possible to provide a smaller and lower-cost refrigeration system 1 compared to a configuration in which refrigerant is supplied to the evaporator 21 by a separate refrigerant pump or the like.

[0094] In the refrigeration system 1 of this embodiment, a second liquid level sensor 127 is provided in the gas-liquid separator 22 below the first liquid level sensor 126. The control unit 13 reduces the opening of the expansion valve 31 when it determines, based on the detection result of the first liquid level sensor 126, that the liquid level in the gas-liquid separator 22 is at a first height, and increases the opening of the expansion valve 31 when it determines, based on the detection result of the second liquid level sensor 127, that the liquid level in the gas-liquid separator 22 is at a second height T2, which is lower than the first height T1. With this configuration, the timing of adjusting the opening degree of the expansion valve 31 can be controlled with greater precision compared to when it is determined solely by the first height T1.

[0095] In the refrigeration system 1 of this embodiment, an oil recovery line 40 for discharging lubricating oil contained in the refrigerant within the gas-liquid separator 22 is connected to the portion of the gas-liquid separator 22 located at the same position as the first height T1 or below the first height T1, and an oil separator 23 for storing the oil flowing through the oil recovery line 40 is provided in the portion located below the first height T1. In this configuration, the gas-liquid separator 22 stores two layers of liquid: the refrigerant in the lower layer and the lubricating oil in the upper layer. In this case, when the lubricating oil in the upper layer reaches the same height as the connection point of the oil recovery line 40 (oil discharge opening 124), it is discharged from the gas-liquid separator 22 through the oil discharge opening 124. The lubricating oil discharged from the gas-liquid separator 22 is stored in the oil separator 23. In other words, lubricating oil can be removed from the evaporator 21 even while the refrigeration system 1 is in operation. As a result, the decrease in heat transfer efficiency due to lubricating oil can be suppressed, making it easier to maintain cooling efficiency.

[0096] In the refrigeration system 1 of this embodiment, the refrigerant is carbon dioxide. With this configuration, by using a so-called full-liquid evaporator 21, there is no need to consider the degree of superheating as with a dry evaporator. Therefore, when carbon dioxide is used as the refrigerant, it is easier to lower the supply temperature of the refrigerant to the evaporator 21. This makes it easier to maintain an extremely low temperature inside the refrigerated warehouse 10. Furthermore, using a natural refrigerant such as carbon dioxide is desirable from the perspective of the global environment, such as GWP (Global Warming Potential).

[0097] (Other variations) While preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications are possible without departing from the spirit of the present invention. The present invention is not limited by the above description, but only by the appended claims. In the above-described embodiment, a configuration was described in which the opening degree of the expansion valve 31 is adjusted based on the liquid level of the liquid phase refrigerant in the gas-liquid separator 22 (inside the housing 120), but the configuration is not limited to this. In the above-described embodiment, a configuration was explained in which the opening degree of the expansion valve 31 is controlled based on the detection results of the first liquid level sensor 126 and the second liquid level sensor 127, but the configuration is not limited to this. A configuration in which the opening degree of the expansion valve 31 is controlled based only on the detection result of the first liquid level sensor 126 is also possible. Furthermore, in addition to the first liquid level sensor 126 and the second liquid level sensor 127, the opening degree of the expansion valve 31 may be controlled using one or more other liquid level sensors.

[0098] In the embodiment described above, a configuration was described in which an oil discharge opening 124 is provided in the gas-liquid separator 22, but the oil discharge opening 124 is not an essential component. In the above-described embodiment, a configuration was explained in which the lubricating oil flows from the gas-liquid separator 22 to the oil separator 23 by its own weight, but the configuration is not limited to this. The lubricating oil may be moved from the gas-liquid separator 22 to the oil separator 23 by means other than its own weight.

[0099] In the embodiment described above, a configuration was described in which defrosting is performed by brine flowing through a warm brine channel 82 assembled in the fin module 80, but the configuration is not limited to this. Defrosting may also be performed by using a separate heater or by spraying brine or water onto the fin module 80.

[0100] Furthermore, without departing from the spirit of the present invention, the components in the embodiments described above can be replaced with well-known components as appropriate, and the modifications described above can be combined as appropriate. [Explanation of symbols]

[0101] 1: Refrigeration system 10: Refrigerated warehouse 13: Control Unit 20: Refrigeration unit 21: Evaporator 22: Gas-liquid separator 23:Oil separator 30: Feed line 31: Expansion valve 32: Gas-liquid two-phase line 36: Liquid return line (liquid line) 40: Oil recovery line 110: First coil (coil) 111: Second coil (coil) 124:Oil drain opening 126: First liquid level sensor 127: Second liquid level sensor T1: First height T2: Second height

Claims

1. Refrigeration unit and A liquid-filled evaporator has a coil filled with liquid-phase refrigerant generated by the aforementioned refrigeration unit, is installed in a cold storage warehouse, and cools the air inside the warehouse by performing heat exchange between the air inside the warehouse and the refrigerant. A supply line is connected to the upstream end of the coil and through which the refrigerant flowing into the evaporator flows, An expansion valve provided in the aforementioned feed line, A gas-liquid two-phase line is connected to the downstream end of the coil, through which the gas-liquid two-phase refrigerant flowing out of the evaporator flows, A gas-liquid separator connected to the aforementioned gas-liquid two-phase line, which separates the refrigerant discharged from the evaporator into a liquid phase and a gas phase, The gas-liquid separator comprises a liquid line connecting the lower end of the gas-liquid separator to the portion of the supply line located between the expansion valve and the evaporator, A refrigeration system in which the lower end of the gas-liquid separator is located above the upstream end of the coil.

2. A first liquid level sensor is provided in the gas-liquid separator and detects the liquid level height of the refrigerant in the liquid phase stored in the gas-liquid separator, The system includes a control unit that controls the opening degree of the expansion valve based on the detection result of the first liquid level sensor, The evaporator and the gas-liquid separator are each arranged within a dimensional range that includes a first height in the vertical direction. The refrigeration system according to claim 1, wherein the control unit adjusts the opening degree of the expansion valve based on the detection result of the first liquid level sensor so that the liquid level in the gas-liquid separator is maintained at a first height.

3. A second liquid level sensor is provided below the first liquid level sensor in the gas-liquid separator. The refrigeration system according to claim 2, wherein the control unit reduces the opening of the expansion valve when it determines, based on the detection result of the first liquid level sensor, that the liquid level in the gas-liquid separator is at a first height, and increases the opening of the expansion valve when it determines, based on the detection result of the second liquid level sensor, that the liquid level in the gas-liquid separator is at a second height lower than the first height.

4. The refrigerant contains oil, which has a lower specific gravity than the refrigerant itself. In the portion of the gas-liquid separator located at the same height as the first height or below the first height, an oil recovery line is provided for discharging oil contained in the refrigerant within the gas-liquid separator. The refrigeration system according to claim 2 or 3, wherein an oil separator for storing oil flowing through the oil recovery line is provided in a portion located below the connection portion between the gas-liquid separator and the oil recovery line.

5. A refrigeration system according to any one of claims 1 to 3, wherein the refrigerant is carbon dioxide.

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