JP2009186033A - Two-stage compression refrigeration system - Google Patents

Abstract

In a two-stage compression refrigeration apparatus, a refrigerant circulation amount is stably controlled in accordance with an operation state.
A two-stage compression refrigeration apparatus (1) includes a two-stage compressor (21), a condenser (22), a high-stage expansion valve (23), and a gas-liquid separation from a gas-liquid two-phase refrigerant. The refrigerant circuit (20), in which the economizer (24), the low-stage side expansion valve (25), and the evaporator (26) that guide the refrigerant gas to the middle of the two-stage compressor (21) are sequentially connected by refrigerant piping It has. The high-stage side expansion valve (23) is composed of a temperature-sensitive automatic expansion valve (29) whose pressure reduction amount is adjusted so that the refrigerant superheat degree on the suction side of the two-stage compressor (21) becomes a predetermined value. The low stage side expansion valve (25) is constituted by a float expansion valve (25) whose pressure reduction amount is adjusted so that the liquid level height of the refrigerant liquid in the economizer (24) becomes a predetermined value.
[Selection] Figure 1

Description

  The present invention relates to a two-stage compression refrigeration apparatus.

  Conventionally, a two-stage compression refrigeration system has been used for applications such as air conditioning in buildings and cooling and air conditioning of large facilities in a factory (see, for example, Patent Documents 1, 2, and 3). The two-stage compression refrigeration apparatus described in Patent Literatures 1, 2, and 3 includes a two-stage compressor in which a high-pressure side compression mechanism and a low-pressure side compression mechanism are arranged in series, a condenser, and a high-stage side expansion valve. And a refrigerant circuit in which a low-stage expansion valve and an evaporator are sequentially connected. In the two-stage compression refrigeration apparatus, in order to prevent a reduction in compressor efficiency, the gas-liquid two-phase refrigerant is separated into a gas and a liquid between the high stage side expansion valve and the low stage side expansion valve, An economizer (intermediate cooler) that guides the refrigerant liquid to the evaporator side and guides the refrigerant gas to the middle of the two-stage compressor is provided.

In Patent Documents 1, 2, and 3, an orifice, an electric valve, and a float valve are used as the high stage side expansion valve and the low stage side expansion valve, respectively.
JP-A-6-323654 JP-A-11-344265 Japanese Patent Laid-Open No. 10-132395

  However, when an orifice is used as in Patent Document 1, even if the heat load of the evaporator (temperature change of cold water) or the inlet / outlet temperature of the two-stage compressor changes, the amount of pressure reduction can be adjusted according to the operating state. Therefore, the refrigerant circulation amount cannot be controlled, and there is a possibility that the refrigerant liquid in the evaporator may return to the liquid that is sucked into the compressor. Therefore, there has been a problem that a means for adjusting the refrigerant circulation amount must be provided separately in accordance with the heat load of the evaporator.

  Further, when the motor-operated valve is used as in Patent Document 2, it is possible to adjust the refrigerant circulation amount in accordance with the operation state, but there is a problem that the control becomes complicated and the cost is high. In addition, the control of the high-stage side expansion valve and the control of the low-stage side expansion valve may interfere with each other, resulting in a hunting phenomenon in which the control amounts vibrate above and below the target value, and the refrigerant circulation amount may not be adjusted appropriately. was there.

  In addition, when a float valve is used as in Patent Document 3, the liquid level of the liquid refrigerant in the container provided with the float valve is only controlled to a constant level, and similarly to the case where an orifice is used, the heat of the evaporator. There is a problem that the amount of decompression cannot be adjusted according to changes in the load, the inlet / outlet temperature of the two-stage compressor, and the like, and the amount of refrigerant circulation cannot be controlled in accordance with the operating state.

  The present invention has been made in view of the above points, and an object of the present invention is to stably control the refrigerant circulation amount according to the operation state in the two-stage compression refrigeration apparatus.

  The present invention provides a two-stage compressor (21), a condenser (22), a high-stage side expansion valve (23), and refrigerant gas separated from a gas-liquid two-phase refrigerant into the two-stage compressor (21 ), A two-stage compression refrigeration system comprising a refrigerant circuit (20) in which an economizer (24), a low-stage expansion valve (25), and an evaporator (26) are sequentially connected by refrigerant piping. The high stage side expansion valve (23) is a valve whose pressure reduction amount is adjusted so that the refrigerant superheat degree on the suction side of the two stage compressor (21) becomes a predetermined value, and the low stage side The expansion valve (25) is a valve whose pressure reduction amount is adjusted so that the liquid level of the refrigerant liquid in the economizer (24) becomes a predetermined value.

  In the present invention, the refrigerant superheat degree on the suction side of the two-stage compressor (21) is controlled to be constant by the high stage side expansion valve (23), while the economizer (24) in the economizer (24) is controlled by the low stage side expansion valve (25). The liquid level of the refrigerant liquid is controlled so that the gas and liquid are reliably separated. Accordingly, the liquid level height of the evaporator (26) and the liquid level of the condenser (22) are controlled by the high stage side expansion valve (23), while the economizer is controlled by the low stage side expansion valve (25). The liquid level in (24) will be controlled.

  Specifically, the high stage side expansion valve (23) controls the refrigerant superheating degree on the suction side of the two stage compressor (21) to be constant regardless of changes in the operating state. The liquid level changes accordingly. For example, when the capacity is large, heat exchange is performed between the refrigerant and the cold water even in the original gas phase region by forming. Therefore, the liquid level in the evaporator (26) becomes low. On the other hand, since the flow rate of the refrigerant after evaporation increases, the time for heat exchange between the evaporated refrigerant and cold water is shortened. Thus, in order to obtain a certain degree of superheat, the amount of heat exchange must be increased, and the high stage side expansion valve (23) lowers the liquid level in the evaporator (26) by increasing the amount of decompression. To control. In addition, since most of the refrigerant other than the amount stored in the evaporator (26) is stored in the condenser (22), the liquid level of the evaporator (26) is increased by the high stage side expansion valve (23) as described above. When the height is determined, the liquid level of the condenser (22) is also controlled. Therefore, the high-stage expansion valve (23) has a function of controlling the refrigerant superheat degree on the suction side of the two-stage compressor (21) to be constant, so that the liquid in the evaporator (26) and the condenser (22) A function for controlling the surface is also provided.

  On the other hand, the low stage side expansion valve (25) has a function of controlling the liquid level height in the economizer (24) according to the refrigerant circulation amount.

  In a second aspect based on the first aspect, the high-stage expansion valve (23) is provided with a temperature sensing cylinder (29c) for sensing the refrigerant temperature on the suction side of the two-stage compressor (21). This is a warm automatic expansion valve (29).

  In the second invention, the temperature-sensitive automatic expansion valve (29) is used as a valve capable of adjusting the amount of pressure reduction so that the refrigerant superheating degree on the suction side of the two-stage compressor (21) becomes a predetermined value. The high stage expansion valve (23) capable of controlling the superheat degree of the refrigerant on the suction side of the two-stage compressor (21) is easily configured. Further, since the temperature-sensitive automatic expansion valve (29) is relatively inexpensive, the refrigerant superheating degree on the suction side of the two-stage compressor (21) can be adjusted at a low cost.

  In a third aspect based on the first aspect, the high stage expansion valve (23) is an electric expansion valve (30), and the superheat degree on the suction side of the two-stage compressor (21) is a predetermined value. Thus, a control device (27) for controlling the opening degree of the electric expansion valve (30) is further provided.

  In the third aspect of the invention, the electric expansion in which the opening degree is controlled by the control device (27) as a valve whose pressure reduction amount can be adjusted so that the refrigerant superheat degree on the suction side of the two-stage compressor (21) becomes a predetermined value. Since the valve (30) is used, the refrigerant superheat degree on the suction side of the two-stage compressor (21) can be kept more accurately and constant. Moreover, according to the electric expansion valve (30) controlled by the control device (27), since the response is quick, it is possible to cope with a sudden change in the operating state.

  According to a fourth invention, in any one of the first to third inventions, the low stage side expansion valve (25) includes a float (25b) provided in the economizer (24), and the economizer (24 Float expansion valve (25) having a valve body (25a) attached to a liquid outlet (24b) for leading out the liquid refrigerant in the inside and having an opening degree adjusted according to the height position of the float (25b) It is.

  In the fourth aspect of the invention, since the float expansion valve (25) is used as a valve whose pressure reduction amount can be adjusted so that the level of the refrigerant liquid in the economizer (24) becomes a predetermined value, the economizer (24) A low-stage expansion valve (25) capable of controlling the liquid level of the refrigerant liquid inside is easily configured. Moreover, since the float expansion valve (25) is relatively inexpensive, the liquid level control of the refrigerant liquid in the economizer (24) can be performed at a low cost.

  As described above, according to the present invention, the high-stage side expansion valve (23) can control the refrigerant superheating degree on the suction side of the two-stage compressor (21) to be constant regardless of changes in the operating state. it can. Thereby, since the refrigerant circulation amount in the refrigerant circuit (20) is suitably controlled according to the operating state, for example, the liquid to the two-stage compressor (21) due to the increase in the liquid refrigerant in the evaporator (26) Return and the like can be prevented.

  Further, according to the present invention, the liquid level of the liquid refrigerant in the economizer (24) can be controlled by the low stage side expansion valve (25). Thereby, the liquid return to the middle of the two-stage compressor (21) due to the increase of the liquid refrigerant in the economizer (24) can be prevented.

  Furthermore, in the present invention, the high stage expansion valve (23) has a function of controlling the refrigerant superheat degree on the suction side of the two-stage compressor (21) to be constant, so that the evaporator (26) and the condenser ( The low-stage expansion valve (25) has the function of controlling the liquid level in the economizer (24) to reliably separate the gas and liquid, while also having the function of controlling the liquid level of 22) . As described above, according to the present invention, the functions required of the high-stage side expansion valve (23) and the low-stage side expansion valve (25) are completely different from each other. You can change the subject. Therefore, it is possible to avoid mutual interference between the controls. Therefore, it is possible to prevent the hunting phenomenon caused by the mutual interference of the controls, and to stably control each other.

  Further, according to the second aspect of the invention, the temperature-sensitive automatic expansion valve (29) is used as a valve whose pressure reduction amount can be adjusted so that the refrigerant superheat degree on the suction side of the two-stage compressor (21) becomes a predetermined value. Thus, the high stage expansion valve (23) capable of controlling the refrigerant superheating degree on the suction side of the two-stage compressor (21) can be easily configured. Further, since the temperature-sensitive automatic expansion valve (29) is relatively inexpensive, the refrigerant superheat degree control on the suction side of the two-stage compressor (21) can be performed at a low cost.

  Further, according to the third invention, the opening degree is controlled by the control device (27) as a valve whose pressure reduction amount can be adjusted so that the refrigerant superheating degree on the suction side of the two-stage compressor (21) becomes a predetermined value. By using the electric expansion valve (30), the refrigerant superheat degree on the suction side of the two-stage compressor (21) can be kept more accurately and constant. Further, according to the control device (27) and the electric expansion valve (30), since the response is quick, it is possible to cope with a sudden change in the operating state.

  Further, according to the fourth aspect of the invention, by using the float expansion valve (25) as a valve capable of adjusting the amount of pressure reduction so that the liquid level height of the refrigerant liquid in the economizer (24) becomes a predetermined value, the economizer The low stage expansion valve (25) capable of controlling the liquid level of the refrigerant liquid in (24) can be easily configured. Moreover, since the float expansion valve (25) is relatively inexpensive, the liquid level control of the refrigerant liquid in the economizer (24) can be performed at a low cost.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, a two-stage turbo chiller (1) including the two-stage turbo compressor (21) shown in FIG. 1 is employed as the two-stage compression refrigeration apparatus according to the present invention.

  FIG. 1 is a piping system diagram schematically showing the configuration of a two-stage turbo chiller (1) according to an embodiment of the present invention. As shown in FIG. 1, the two-stage turbo refrigerator (1) includes a two-stage turbo compressor (21), a condenser (22), a high-stage side expansion valve (23), and a low-stage side expansion valve ( 25) and an evaporator (26) are provided with a refrigerant circuit (20) for performing a vapor compression refrigeration cycle in which the refrigerant pipes are sequentially connected by a refrigerant pipe. An economizer (24) according to the present invention is provided between the high stage side expansion valve (23) and the low stage side expansion valve (25) of the refrigerant circuit (20).

  The two-stage turbo compressor (21) includes a low stage impeller (21a) and a high stage impeller (21b). The low stage impeller (21a) and the high stage impeller (21b) are connected in series. The two-stage turbo compressor (21) is provided with a suction capacity control mechanism (21c) for controlling the suction capacity and a discharge capacity control mechanism (21d) for controlling the discharge capacity. The low-pressure (PL) refrigerant sucked into the lower stage is compressed to the intermediate pressure (PM) by the lower stage impeller (21a) and sucked into the higher stage. The refrigerant sucked into the high stage is compressed by the high stage impeller (21b) to become a high-pressure (PH) gas refrigerant.

  The condenser (22) is a so-called shell-and-tube condenser including a shell (cylindrical copper) and a plurality of cooling pipes arranged in the shell. A high-pressure (PL) refrigerant gas compressed in the two-stage turbo compressor (21) is introduced into the shell, and the refrigerant gas is cooled by cooling water flowing in the cooling pipe. As a result, the refrigerant gas condenses outside the cooling pipe and becomes liquid and accumulates at the bottom of the shell.

  The high-stage expansion valve (23) is connected to the valve body (29a) and the valve body (29a) via a capillary tube (29b), and the refrigerant temperature on the suction side of the two-stage turbo compressor (21) is adjusted. Equipped with a temperature sensing cylinder (29c) for sensing and a thin tube (29d) connected to the low pressure side piping on the outlet side of the evaporator (26), and the refrigerant superheat degree on the suction side of the two-stage turbo compressor (21) is constant An external pressure equalizing type temperature-sensitive expansion valve is controlled. The liquid refrigerant and the gas refrigerant condensed in the condenser (22) are reduced to an intermediate pressure (PL) by the high stage side expansion valve (23) and introduced into the economizer (24). The decompression amount of the high stage expansion valve (23) is adjusted according to the temperature and pressure on the outlet side of the evaporator (26). Thereby, the refrigerant circulation amount is controlled so that the refrigerant superheat degree on the suction side of the two-stage turbo compressor (21) becomes constant.

  The economizer (24) is connected to a gas pipe (28) connected in the middle of the two-stage turbo compressor (21). The economizer (24) connects the inlet for introducing the refrigerant from the condenser (22), the liquid outlet (24b) for guiding the liquid refrigerant inside the evaporator (26), and the gas pipe (28). A tank (24a) in which a gas outlet is formed. Then, in the tank (24a) of the economizer (24), the gas-liquid two-phase refrigerant is gas-liquid separated. The gas refrigerant after gas-liquid separation is led to the middle of the two-stage turbo compressor (21) through the gas pipe (28), while the liquid refrigerant is led to the evaporator (26) side.

  The low stage side expansion valve (25) is constituted by a float type float expansion valve (25) and is built in the economizer (24). Specifically, it is attached to a liquid outlet (24b) formed in the tank (24a) of the economizer (24). The float expansion valve (25) includes a valve body (25a) attached to a liquid outlet (24b) formed in a tank of the economizer (24) and a float (25b) attached to the valve body (25a). It is configured. The float expansion valve (25) is configured such that the float (25b) moves up and down according to the liquid level height of the liquid refrigerant in the economizer (24), thereby adjusting the pressure reduction amount. Specifically, when the liquid level rises, the opening of the valve body (25a) increases and the pressure reduction amount decreases, while when the liquid level decreases, the opening of the valve body (25a) decreases and the pressure reduction amount increases. It is configured to let you. With such a configuration, the liquid refrigerant separated by the economizer (24) is decompressed by the float expansion valve (25) when it flows out toward the evaporator (26).

  The evaporator (26) is constituted by a full liquid evaporator, and in this embodiment, is constituted by a so-called shell and tube type evaporator. The evaporator (26) is supplied with the liquid refrigerant that has been gas-liquid separated by the economizer (24), decompressed by the float expansion valve (25). A heat transfer tube is arranged in the shell, and water as an object to be cooled flows in the heat transfer tube. The liquid refrigerant supplied into the shell absorbs heat from the water in the heat transfer tube, evaporates, and is converted into a gas that is led to the suction side of the two-stage turbo compressor (21).

  Next, the operation of the two-stage turbo chiller (1) will be described. First, when the operation is started, the low-stage and high-stage impellers (21a, 21b) of the two-stage turbo compressor (21) rotate, and the low-pressure (in the refrigerant circuit (20) ( PL) refrigerant is inhaled. At this time, the refrigerant capacity to be sucked is adjusted by the suction capacity control mechanism (21c). Then, the low-pressure (PL) refrigerant sucked into the lower stage is compressed to the intermediate pressure (PM) by the lower stage impeller (21a) and sucked into the higher stage. The refrigerant sucked into the high stage side is compressed by the high stage impeller (21b) to become a high-pressure (PH) gas refrigerant and discharged to the refrigerant circuit (20). At this time, the refrigerant capacity discharged by the discharge capacity control mechanism (21d) is adjusted.

  The high-pressure (PH) refrigerant discharged from the two-stage turbo compressor (21) to the refrigerant circuit (20) is cooled and condensed in the condenser (22). Then, the liquid refrigerant and the gas refrigerant condensed in the condenser (22) are reduced to an intermediate pressure (PL) by the high stage side expansion valve (23) and introduced into the economizer (24). The decompression amount of the high stage expansion valve (23) is adjusted according to the temperature and pressure on the outlet side of the evaporator (26). Thereby, the refrigerant circulation amount is controlled so that the refrigerant superheat degree on the suction side of the two-stage turbo compressor (21) becomes a predetermined value.

  In the tank (24a) of the economizer (24), the introduced gas-liquid two-phase refrigerant is gas-liquid separated. The gas refrigerant after gas-liquid separation is led to the middle of the two-stage turbo compressor (21) via the gas pipe (28), while the liquid refrigerant is led to the evaporator (26) side.

  The intermediate-pressure (PM) gas refrigerant introduced to the middle of the two-stage turbo compressor (21) is mixed with the intermediate pressure (PM) compressed on the low-pressure side of the two-stage turbo compressor (21). Inhaled to the side and compressed.

  On the other hand, when the liquid refrigerant guided to the evaporator (26) flows out from the liquid outlet part (24b) toward the evaporator (26), the float expansion valve (25) provided in the liquid outlet part (24b) The pressure is reduced to a low pressure (PL) by the pressure and supplied to the evaporator (26). The float expansion valve (25) is configured such that the float (25b) moves up and down in accordance with the liquid level of the liquid refrigerant in the economizer (24), thereby adjusting the pressure reduction amount. Specifically, when the liquid level rises, the opening of the valve body (25a) increases and the pressure reduction amount decreases, while when the liquid level decreases, the opening of the valve body (25a) decreases and the pressure reduction amount increases. It is configured to let you. With such a configuration, the liquid level of the refrigerant liquid in the economizer (24) is controlled to be a predetermined value by the float expansion valve (25).

  The low-pressure (PL) refrigerant thus depressurized by the float expansion valve (25) and supplied to the evaporator (26) absorbs heat from the water in the heat transfer pipe and evaporates to become a gas, which is a two-stage turbocharger. Guided to the suction side of the compressor (21). The gas refrigerant is sucked into the two-stage turbo compressor (21) and compressed.

-Effect of the embodiment-
As described above, in the present embodiment, the high stage side expansion valve (23) is constituted by a valve whose pressure reduction amount is adjusted so that the refrigerant superheat degree on the suction side of the two stage turbo compressor (21) becomes a predetermined value. ing. Therefore, the high-stage side expansion valve (23) can control the refrigerant superheat degree on the suction side of the two-stage turbo compressor (21) to be constant regardless of the change in the operating state. Thereby, since the refrigerant circulation amount in the refrigerant circuit (20) is suitably controlled according to the operating state, for example, to the two-stage turbo compressor (21) due to the increase of the liquid refrigerant in the evaporator (26) Liquid return and the like can be prevented.

  Moreover, in this embodiment, the low stage side expansion valve (25) is comprised by the valve by which the pressure reduction amount is adjusted so that the liquid level height of the refrigerant | coolant liquid in an economizer (24) may become predetermined value. Therefore, the liquid level of the liquid refrigerant in the economizer (24) can be controlled by the low stage side expansion valve (25). Thereby, liquid return to the middle of the two-stage turbo compressor (21) or gas bypass to the evaporator (26) due to an increase in the liquid refrigerant in the economizer (24) can be prevented.

  Furthermore, in the present embodiment, the liquid level height of the evaporator (26) and the liquid level height of the condenser (22) are controlled by the high stage side expansion valve (23), while the low stage side expansion valve (25). ), The liquid level in the economizer (24) is controlled.

  Specifically, the high stage side expansion valve (23) controls the evaporator superheat degree on the suction side of the two-stage turbo compressor (21) to be constant regardless of changes in the operating state. The liquid level of the liquid crystal changes accordingly. For example, when the capacity is large, heat exchange is performed between the refrigerant and the cold water even in the original gas phase region by forming. Therefore, the liquid level in the evaporator (26) becomes low. On the other hand, since the flow rate of the refrigerant after evaporation increases, the time for heat exchange between the evaporated refrigerant and cold water is shortened. Thus, in order to obtain a certain degree of superheat, the amount of heat exchange must be increased, and the high stage side expansion valve (23) lowers the liquid level in the evaporator (26) by increasing the amount of decompression. To control. In addition, since most of the refrigerant other than the amount stored in the evaporator (26) is stored in the condenser (22), the liquid level of the evaporator (26) is increased by the high stage side expansion valve (23) as described above. When the height is determined, the liquid level of the condenser (22) is also controlled. Therefore, the high-stage expansion valve (23) has a function of controlling the refrigerant superheat degree on the suction side of the two-stage compressor (21) to be constant, so that the liquid in the evaporator (26) and the condenser (22) A function for controlling the surface is also provided.

  On the other hand, the low stage side expansion valve (25) has a function of controlling the liquid level in the economizer (24) to be constant.

  As described above, according to the present embodiment, the functions required of the high stage side expansion valve (23) and the low stage side expansion valve (25) are completely different from each other. The control object can be changed. Therefore, it is possible to avoid mutual interference between the controls. Therefore, it is possible to prevent the hunting phenomenon caused by the mutual interference of the controls, and to stably control each other.

  In this embodiment, the high-stage expansion valve (23) is a temperature-sensitive automatic expansion valve (29c) provided with a temperature-sensing cylinder (29c) that senses the refrigerant temperature on the suction side of the two-stage turbo compressor (21). 29). Therefore, the high stage expansion valve (23) capable of controlling the superheat degree of the refrigerant on the suction side of the two-stage turbo compressor (21) can be easily configured. Further, since the temperature-sensitive automatic expansion valve (29) is relatively inexpensive, the refrigerant superheat control on the suction side of the two-stage turbo compressor (21) can be performed at a low cost.

  In the present embodiment, the low-stage expansion valve (25) includes a float (25b) provided in the economizer (24) and a valve whose opening degree is adjusted according to the height position of the float (25b). A float expansion valve (25) having a body (25a). Therefore, the low stage side expansion valve (25) capable of controlling the liquid level of the refrigerant liquid in the economizer (24) can be easily configured. Moreover, since the float expansion valve (25) is relatively inexpensive, the liquid level control of the refrigerant liquid in the economizer (24) can be performed at a low cost.

<< Modification 1 >>
In the above embodiment, the temperature-sensitive automatic expansion valve (29) provided with the temperature-sensitive cylinder (29c) is used as the high-stage expansion valve (23). However, the high stage expansion valve (23) according to the present invention is not limited to this. Any valve may be used as long as the pressure reduction amount is adjusted so that the degree of refrigerant superheating on the suction side of the two-stage turbo compressor (21) becomes a predetermined value. The high stage side expansion valve (23) may be constituted by an electric expansion valve (30) as shown in FIG. 2, for example. The configuration will be described below.

  The high stage side expansion valve (23) is constituted by an electric expansion valve (30). Moreover, in this modification 1, the control apparatus (27) which controls the opening degree of an electric expansion valve (30) is provided, and the electric expansion valve (30) is connected to the control apparatus (27). Further, in the first modification, a suction temperature sensor (30a) for detecting the refrigerant temperature on the suction side of the two-stage turbo compressor (21) and a suction pressure sensor (30b) for detecting the refrigerant pressure on the suction side are provided. These sensors (30a, 30b) are connected to the control device (27).

  With this configuration, the control device (27) derives the refrigerant superheat degree on the suction side of the two-stage turbo compressor (21) based on the detection signals of the suction temperature sensor (30a) and the suction pressure sensor (30b). At the same time, the opening degree of the electric expansion valve (30) is controlled so that the degree of refrigerant superheating on the suction side of the two-stage turbo compressor (21) becomes a predetermined value. Specifically, when the degree of refrigerant superheat on the suction side of the two-stage turbo compressor (21) is higher than a predetermined value, the degree of refrigerant circulation in the refrigerant circuit (20) is increased by increasing the opening of the electric expansion valve (30). Increase. On the other hand, when the refrigerant superheat degree on the suction side of the two-stage turbo compressor (21) is lower than a predetermined value, the opening degree of the electric expansion valve (30) is reduced to reduce the refrigerant circulation amount of the refrigerant circuit (20). .

  Also in the two-stage compression refrigeration apparatus according to the first modification, the same effect as in the above embodiment can be obtained. Further, by using the electric expansion valve (30) whose opening degree is controlled by the control device (27) as the high stage side expansion valve (23), the refrigerant superheat degree on the suction side of the two-stage turbo compressor (21) can be reduced. It can be kept more accurate and constant. Further, according to the control device (27) and the electric expansion valve (30), since the response is quick, it is possible to cope with a sudden change in the operating state.

  In the first modification, the refrigerant superheat degree on the suction side of the two-stage turbo compressor (21) is derived using the suction temperature sensor (30a) and the suction pressure sensor (30b). The means for deriving the refrigerant superheat degree on the suction side of the machine (21) is not limited to these, and for example, a discharge temperature sensor, a discharge pressure sensor, or the like may be used.

<< Other Embodiments >>
Although the two-stage turbo refrigerator (1) has been described in the above embodiment, the two-stage compression refrigeration apparatus according to the present invention is not limited to this. Instead of the centrifugal two-stage turbo compressor, for example, a refrigeration apparatus including a rotary type or scroll type two-stage compressor may be used.

  In addition, the above embodiment is an essentially preferable illustration, Comprising: It does not intend restrict | limiting the range of this invention, its application thing, or its use.

  As described above, the present invention is useful for a turbo refrigerator.

It is a piping system figure showing the composition of the turbo refrigerator concerning an embodiment. It is a piping system diagram which shows the structure of the turbo refrigerator based on the modification 1.

Explanation of symbols

1 Two-stage turbo refrigerator
20 Refrigerant circuit
21 Two-stage turbo compressor (two-stage compressor)
22 Condenser
23 High-stage expansion valve
24 Economizer
24a tank
24b Liquid outlet
25 Low stage expansion valve (float expansion valve)
25a Disc
25b float
26 Evaporator
27 Control device
28 Gas piping
29 Temperature-sensitive automatic expansion valve
29a Valve body
29b Capillary tube
29c Temperature sensing tube
29d capillary
30 Electric expansion valve
30a Suction temperature sensor
30b Suction pressure sensor

Claims (4)

Two-stage compressor (21), condenser (22), high-stage expansion valve (23), and refrigerant gas separated from the gas-liquid two-phase refrigerant are placed in the middle of the two-stage compressor (21). A two-stage compression refrigeration system comprising a refrigerant circuit (20) in which a leading economizer (24), a low-stage side expansion valve (25), and an evaporator (26) are sequentially connected by refrigerant piping,
The high-stage expansion valve (23) is a valve whose pressure reduction amount is adjusted so that the refrigerant superheat degree on the suction side of the two-stage compressor (21) becomes a predetermined value,
The low stage side expansion valve (25) is a valve whose pressure reduction amount is adjusted so that the liquid level of the refrigerant liquid in the economizer (24) becomes a predetermined value. Stage compression refrigeration equipment. In claim 1,
The high-stage expansion valve (23) is a temperature-sensitive automatic expansion valve (29) provided with a temperature-sensitive cylinder (29c) for sensing the refrigerant temperature on the suction side of the two-stage compressor (21). A two-stage compression refrigeration system characterized. In claim 1,
The high stage side expansion valve (23) is an electric expansion valve (30),
And further comprising a control device (27) for controlling the opening degree of the electric expansion valve (30) so that the refrigerant superheating degree on the suction side of the two-stage compressor (21) becomes a predetermined value. Stage compression refrigeration equipment. In any one of Claims 1-3,
The low-stage expansion valve (25) is attached to a float (25b) provided in the economizer (24) and a liquid outlet (24b) for leading out the liquid refrigerant in the economizer (24). A two-stage compression refrigeration apparatus comprising a float expansion valve (25) having a valve body (25a) whose opening degree is adjusted according to a height position of the float (25b).
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