REFRIGERATION CIRCUIT

Description

OBJECT OF THE INVENTION

The present invention is related to the field of refrigeration circuits, more particularly, to refrigeration circuits using CO₂ as refrigerant (R-744).

An object of the present invention is to provide a R-744 refrigerant circuit able to reduce the power consumption by increasing the energy efficiency.

BACKGROUND OF THE INVENTION

At present, there are different improvements introduced to the circuits with R-744 to increase their efficiency, which are mainly aimed to increase the efficiency of the facility in climates with high ambient temperatures.

The main problem in refrigeration circuits using R-744 is the high reduction in efficiency at medium-high ambient temperatures. This efficiency reduction is mainly despite to high power consumption of the medium-temperature compression rack (MTC).

A solution proposed consists of introducing in a circuit several ejectors (Multi-Ejector racks, MEJ). This circuit compresses part of the refrigerant of medium-temperature services to intermediate pressure (liquid receiver pressure). To do that, the multi-ejector uses R-744 with high pressure as motive flow, which reduces its pressure through a nozzle below the medium-temperature services pressure and, consequently, increases its velocity. Thus, the motive flow suctions part of the refrigerant of the medium-temperature services and is compressed to intermediate pressure. This circuit is used with different types of ejectors, the most used is the high-pressure multi-ejector.

The use of high-pressure multi-ejector reduces the refrigerant in the medium-temperature compression rack and consequently its power consumption. Additionally, the medium-temperature compression rack compresses part of the medium-temperature services refrigerant without a mechanical compressor taking the potential energy of the motive flow.

Nevertheless, this circuit needs an additional compression denoted as parallel compression rack to compress the refrigerant in vapor state generated by the multi-ejector. The vapor quality in the liquid receiver is higher and the capacity requirements in parallel compression rack is greater than the circuits without ejectors, having a similar cooling load.

The temperature at suction port of the medium-temperature compression rack is higher than the circuits without ejectors and, in consequence, the discharge temperature too, producing temperatures greater than 140° C. for ambient temperatures above 35° C.

The main problem of the high-pressure multi-ejector racks is that they do not operate efficiently for ambient temperatures below 30° C. in R-744 circuits. Also, the cost of using high-pressure multi-ejector racks is high. In addition, it has problems with the high oil transfer rate at the parallel compression rack due to the reduced superheat in suction port. Also, the suction pressure of the parallel compression rack is fixed by a liquid receiver, storing the refrigerant, and this compressor rack does not work at its optimal operating point (maximum compressor efficiency).

A lot of solutions have been proposed to improve the efficiency of a refrigeration circuit using R-744 at medium-high ambient temperatures. Nevertheless, few improvements are used at the present time. The most used improvements to R-744 circuits are the parallel compression, mechanical subcooling and ejectors, but these circuits have several limitations. Therefore, a circuit with lower limitations using R-744 for increasing the efficiency of the refrigeration process at medium-high ambient temperatures is needed.

As an example, document EP3872418 refers to a refrigerant circuit for increasing energy efficiency comprising a tank, storing liquid and vapor R-744; a first R-744 liquid line, connecting the tank to a medium-temperature line, and comprising a medium-temperature expansion valve connected to a medium-temperature evaporator connected to a suction line, which connects with a medium-temperature compressor; a low-temperature line, connected to the first R-744 liquid line, and comprising a low-temperature expansion valve connected to a low-temperature evaporator connected to a low-temperature compressor connected to the suction line; an adiabatic gas-cooler, connected to the medium-temperature compressor; a first back-pressure valve, connected to the tank and to a first heat exchanger, connected to the adiabatic gas-cooler; and a R-744 vapor line, connecting the tank with the first heat exchanger and with the suction line.

SUMMARY

The present invention is directed to a R-744 refrigerant circuit able to increase the efficiency of the refrigeration process, thus, reducing the power consumption in a large variety of locations having different ambient conditions and increasing the operation temperature range.

According to a first aspect, the refrigeration circuit of the invention comprises at least one first compressor, a first gas-cooler, a first heat exchanger, a first pressure reduction valve, a medium temperature heat exchanger, a medium temperature expansion valve and a liquid receiver for storing the R-744, which is in a mixed physical state, thus, storing a liquid R-744 and a vapor R-744.

The liquid R-744 is extracted from the liquid receiver by means of an outlet liquid line that is split in a first liquid line and a second liquid line.

The second liquid line is directed to a first heat exchanger after passing through a first expansion valve.

The first liquid line is directed to the first heat exchanger and then to a medium temperature heat exchanger after passing through a medium temperature expansion valve to return to the second liquid line downstream the first expansion valve so that the mixture enters the first heat exchanger to exchange heat with the refrigerant in the first liquid line and then flow to the at least one first compressor through a suction line.

The outlet of the at least one compressor is connected through a discharge line to the inlet of the first gas-cooler, and the outlet of the first gas-cooler is connected to a gas-cooler outlet line which is directed to the liquid receiver after passing through a first pressure reduction valve.

According to a second aspect of the invention, the refrigeration circuit may also comprise an outlet vapor line connected to the liquid receiver and a third heat exchanger.

The outlet vapor line comprises a second pressure reduction valve and is directed to the suction line at the outlet of the first heat exchanger.

The third heat exchanger is located in the suction line, between the first heat exchanger after mixing with the outlet vapor line and the at least one first compressor. The refrigerant in the suction line exchanges heat with the refrigerant flowing through the gas-cooler outlet line upstream the first pressure reduction valve and the refrigerant flowing through the suction line.

According to a third aspect, the refrigeration circuit may also comprise a first motorised multi way valve (27) located in the suction line (59) either at the inlet or at the outlet of the third heat exchanger (13), and a first pipe (75) connected to the first motorised multi way valve (27) and bypassing the third heat exchanger, creating a ring so that the refrigerant flows from the first heat exchanger mixed with the refrigerant from the outlet vapor line to the at least one first compressor either through the third heat exchanger, along the suction line, directly through the first pipe, bypassing the third heat exchanger, or as a mixture through both ways.

According to a fourth aspect, the refrigeration circuit may also comprise a second compressor connected to the at least one first compressor in parallel to the common discharge line, a second heat exchanger that exchanges heat between the refrigerant leaving the first gas-cooler and the refrigerant flowing through a first fluid line that branches from the gas-cooler outlet line, either at the inlet or at the outlet of the third heat exchanger, depressurized by a third expansion valve, and a second pipe that connects the inlet of the second compressor with the first fluid line leaving the second heat exchanger.

According to a fifth aspect, the refrigeration circuit may also comprise a first vapor line with a first motorised valve, connecting the outlet vapor line to the first fluid line at the inlet of the second heat exchanger.

According to a sixth aspect, the refrigeration circuit may also comprise a cooling line that connects the first liquid line at the inlet of the first heat exchanger with the first vapor line, and further comprises a cooling coil located within the liquid receiver and a fourth expansion valve.

According to a seventh aspect, the refrigeration circuit may also comprise a second motorised multi way valve located in the discharge line that is connected to the inlet of a fourth heat exchanger through a first branch. The outlet of the fourth heat exchanger is connected to the inlet of the first gas-cooler.

According to an eighth aspect, the refrigeration circuit may also comprise a third motorised multi way valve, located in the discharge line, that is connected to the outlet gas-cooler line through a second branch, bypassing the first gas-cooler.

According to a ninth aspect, the refrigeration circuit may also comprise a first check valve, located in the gas-cooler outlet line upstream the connection to the second branch, a third branch, comprising a third motorised valve that connects the inlet to the first gas-cooler with the outlet vapor line, and a fourth branch comprising a second expansion valve and a second check valve that connects the first liquid line with the gas-cooler outlet line upstream the first check valve.

The circuit may present several alternative configurations.

In a first configuration, the refrigeration circuit may additionally comprise:

• • a second fluid line, with a second motorised valve, which connects the gas-cooler outlet line at the outlet of the third heat exchanger with the liquid receiver,
  • a pressure increaser device located at the outlet of the second compressor,
  • a fourth fluid line that connects the second pipe to the pressure increaser device, and
  • a pressure exchanger configured to exchange pressure between the refrigerant flowing through the second fluid line and the refrigerant flowing through the fourth fluid line.

In a second configuration, the refrigeration circuit may additionally comprise:

• • a second fluid line, with a second motorised valve, which connects the gas-cooler outlet line at the outlet of the third heat exchanger with the liquid receiver,
  • a fifth fluid line connecting the second pipe with the first gas-cooler outlet line and comprising a second gas-cooler and a pump, and
  • a pressure exchanger configured to exchange pressure between the refrigerant flowing through the second fluid line and the fifth fluid line,

In a third configuration, the refrigeration circuit may additionally comprise:

• • a second fluid line, with a second motorised valve, which connects the gas-cooler outlet line at the outlet of the third heat exchanger with the liquid receiver,
  • a sixth fluid line connecting the second pipe with the first gas-cooler outlet line,
  • a pressure exchanger configured to exchange pressure between the refrigerant flowing through the second fluid line and the sixth fluid line. In this case, the first gas-cooler comprises an additional circuit where the sixth fluid line is connected downstream the pressure exchanger, and
  • a pump located at the outlet of the additional circuit and in the sixth fluid line.

These three configurations may also comprise:

• • a third compressor connected to the first and second compressors in parallel to the common discharge line,
  • a fourth motorised multi-way valve located on the second pipe feeding the second compressor that also connects with the inlet of the first and second compressors, and
  • a fifth motorised multi-way valve located in the sixth fluid line and also connected to a third fluid line that splits from either the outlet of one of the first compressors (1) or the outlet of the third compressor (3) upstream a third check valve (9″),

With this configuration, the refrigerant flowing through the second pipe can be switched between the inlet of the second compressor and the inlet of the rest of compressors.

According to a tenth aspect of the invention, the refrigeration circuit may also comprise a low temperature liquid line connecting the first liquid line with the suction line, the low temperature liquid line comprising a low temperature expansion valve, a low temperature heat exchanger, a low temperature compressor, and a desuperheater.

According to an eleventh aspect of the invention, the refrigeration circuit may be configured so that the low temperature liquid line, at the outlet of the low temperature heat exchanger, is connected to the first heat exchanger upstream the low temperature compressor. In this situation, the first heat exchanger is configured to exchange heat between the refrigerant in the low temperature liquid line and the refrigerant flowing through the first liquid line.

According to a twelfth aspect of the invention, the refrigeration circuit may also comprise:

• • a seventh motorised multi-way valve (88) disposed downstream the low temperature heat exchanger and
  • a seventh fluid line that connects the seventh motorised multi-way valve with the inlet of the low temperature compressor.

In this situation, the refrigerant may either flow to the first heat exchanger or directly flow the low temperature compressor, bypassing the first heat exchanger. The seventh motorised multi-way valve is configured to be controlled based on the superheat in the suction of the low temperature compressor.

According to a thirteenth aspect, the refrigeration circuit may also comprise a sixth motorised multi way valve located at the outlet of the desuperheater.

In this case, the refrigerant flowing from the desuperheater may be switched either to the suction line at the inlet of the at least one first compressor or to the sixth fluid line at the inlet of the pressure exchanger.

DESCRIPTION OF THE DRAWINGS

To complement the description being made and in order to aid towards a better understanding of the characteristics of the invention, in accordance with a preferred example of practical embodiment thereof, a set of drawings is attached as an integral part of said description wherein, with illustrative and non-limiting character, the following has been represented:

FIG. 1.—Shows a schematic view of another refrigerant circuit known in the state of the art comprising a liquid receiver with an outlet liquid line that is directed to a heat exchanger to flow, after mixing with an outlet vapor line also connected to the liquid receiver, to a compressor and a gas-cooler to return to the liquid receiver.

FIG. 2.—Shows a schematic view of a pressure-enthalpy diagram of the circuit shown in FIG. 1 in a transcritical operation mode, wherein the vertical axis represents the pressure and the horizontal axis represents the enthalpy.

FIG. 3.—Shows a schematic view of a refrigerant circuit known in the state of the art where, additionally to the circuit of FIG. 1, comprises a second liquid line, parallel to the first one, comprising an additional heat exchanger connected to a compressor and a desuperheater.

FIG. 4.—Shows a schematic view of a pressure-enthalpy diagram of the circuit shown in FIG. 3 in a transcritical operation mode, wherein the vertical axis represents the pressure and the horizontal axis represents the enthalpy.

FIG. 5.—Shows a schematic view of a first embodiment of the refrigerant circuit of the invention.

FIG. 6.—Shows a schematic view of a second embodiment of the refrigerant circuit of the invention.

FIG. 7.—Shows a schematic view of a third embodiment of the refrigerant circuit of the invention.

FIG. 8.—Shows a schematic view of a pressure-enthalpy diagram of the circuit shown in FIG. 7 in a transcritical operation mode, wherein the vertical axis represents the pressure and the horizontal axis represents the enthalpy.

FIG. 9.—Shows a schematic view of a fourth embodiment of the refrigerant circuit of the invention.

FIG. 10.—Shows a schematic view of a pressure-enthalpy diagram of the circuit shown in FIG. 9 in a transcritical operation mode, wherein the vertical axis represents the pressure and the horizontal axis represents the enthalpy.

FIG. 11.—Shows a schematic view of a fifth embodiment of the refrigerant circuit of the invention.

FIG. 12.—Shows a schematic view of a sixth embodiment of the refrigerant circuit of the invention with a cooling line comprising a cooling coil.

FIG. 13.—Shows a schematic view of a seventh embodiment of the refrigerant circuit of the invention.

FIG. 14.—Shows a schematic view of an eighth embodiment of the refrigerant circuit of the invention.

FIG. 15.—Shows a schematic view of a ninth embodiment of the refrigerant circuit of the invention.

FIG. 16.—Shows a schematic view of a tenth embodiment of the refrigerant circuit of the invention.

FIG. 17.—Shows a schematic view of an eleventh embodiment of the refrigerant circuit of the invention.

FIG. 18.—Shows a schematic view of a twelfth embodiment of the refrigerant circuit of the invention.

FIG. 19.—Shows a schematic view of a thirteenth embodiment of the refrigerant circuit of the invention.

FIG. 20.—Shows a schematic view of a fourteenth embodiment of the refrigerant circuit of the invention with

FIG. 21.—Shows a schematic view of a fifteenth embodiment of the refrigerant circuit of the invention with

FIG. 22.—Shows a schematic view of a sixteenth embodiment of the refrigerant circuit of the invention with

FIG. 23.—Shows a schematic view of a seventeenth embodiment of the refrigerant circuit of the invention with

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention is directed to a refrigerant circuit with the capacity to increase the energy efficiency, particularly, when operating in changing-temperature environments in order to reduce the overall power consumption.

Further advantages of the refrigerant circuit are described in relation to the figures, which represent particular embodiments of the invention non-limiting the scope of the invention defined by the claims.

FIG. 5 shows a first embodiment of the refrigerant circuit of the present invention.

It comprises a liquid receiver (17) connected to an outlet liquid line (80), in order to provide the circuit with liquid, and to an inlet line to receive liquid from the circuit.

The outlet liquid line (80) is split in a first liquid line (81) and a second liquid line (82) that comprises a first expansion valve (28).

The first liquid line (81) is directed to a first heat exchanger (18) and then to a medium temperature heat exchanger (20) after passing through a medium temperature expansion valve (19) which is then returned to the second liquid line (82) downstream the first expansion valve (28).

The second liquid line (82) is directed to the first heat exchanger (18) after passing through the first expansion valve (28) and mix with the refrigerant of the first liquid line (81) leaving the medium temperature heat exchanger (20) to exchange heat with the refrigerant of the first liquid line (81). The outlet of the first heat exchanger (18) is connected to the inlet of at least one first compressor (1) through a suction line (59).

The outlet of the at least one compressor (1) is connected through a discharge line (41) to the inlet of a first gas-cooler (7), and the outlet of the first gas-cooler (7) is connected to a gas-cooler outlet line (50) which is directed to the inlet line of the liquid receiver (17) after passing through a first pressure reduction valve (14).

In this embodiment, the first heat exchanger (18) introduces a superheat in the suction line (59) to operate with low superheating in the medium temperature heat exchanger (20) and with higher evaporation temperature to reduce the energy consumption in the at least one first compressor (1). Additionally, a subcooling in the first liquid line (81) is introduced in order to reduce the flash-gas in the expansion valves of the medium temperature expansion valve (19), increasing the cooling capacity of the first compressors (1). With the first expansion valve (28), the superheat in the suction line (59) of the first compressors (1) is controlled.

FIG. 6 shows an amendment to the circuit shown in FIG. 5 where an outlet vapor line (90) and a third heat exchanger (13) have been introduced.

The outlet vapor line (90) comprises a second pressure reduction valve (16) and connects the liquid receiver (17) with the suction line (59) at the outlet of the first heat exchanger (18), where the suction line (59), before heading to the at least one first compressor (1), is directed to a third heat exchanger (13) to exchange heat with the refrigerant flowing through the gas-cooler outlet line (50) upstream the first pressure reduction valve (14).

The third heat exchanger (13) introduces an additional superheat in the suction line (59) to operate with very low superheating in the medium temperature heat exchanger (20) and with higher evaporation temperature than the circuit of FIG. 5 to reduce more the energy consumption. Additionally, a subcooling is introduced in the gas-cooler outlet line (50) to reduce the flash-gas in the liquid receiver (17) and the flash-gas to the first compressors (1) by the outlet vapor line (90) together with a second pressure reduction valve (16). With this modification the cooling capacity of the first compressors (1) is increased more and the energy consumption is also reduced.

FIG. 7 includes, additionally to the circuit of FIG. 6, a first pipe (75) that is connected to the suction line (59) and bypasses the third heat exchanger (13), so that a ring is created. Additionally, a first motorised multi-wat valve (27) is connected to both the first pipe (75) and the suction line (59) either upstream the third heat exchanger (13), as represented in FIG. 7, or also downstream.

With this embodiment, the refrigerant flowing from the outlet of the first heat exchanger (18) after mixing with the refrigerant from the outlet vapor line (90) is directed to the at least one first compressor (1) either through the third heat exchanger (13), through the first pipe (75), or as a mixture through both elements (75, 13).

The first motorised multi-way valve (27) controls both the high and the low superheat in the suction line (59) to ensure a controlled superheat value in the suction of the at least one first compressor (1).

FIG. 9 shows an amendment to the circuit in FIG. 7 which additionally includes a second heat exchanger (10) and a first fluid line (51) that splits from the gas-cooler outlet line (50).

The second heat exchanger (10) is located between the first gas-cooler (7) and the third heat exchanger (13).

The second heat exchanger (10) exchanges heat between the refrigerant leaving the first gas-cooler (7), which is then directed to the third heat exchanger (13), and the refrigerant flowing through the first fluid line (51) after passing through a third expansion valve (12).

However, although FIG. 9 represents this split at the outlet of the second heat exchanger (10), it may be as well at the inlet.

In any of both cases, a second pipe (65) connects the first fluid line (51) at the outlet of the second heat exchanger (10) with the inlet of a second compressor (2). The outlet of the second compressor (2) is connected to the discharge line (41), working in parallel with the at least one compressor (1).

This embodiment introduces a great additional subcooling in the gas-cooler outlet line (50), using a second compressor (2) working at a suction pressure higher than the liquid receiver (17), with higher operating efficiency due to their lower compression ratio and increasing their mass flow capacity. These elements reduce the flash-gas in the liquid receiver (17) and the flash-gas to the first compressors (1). Additionally, the cooling capacity of the first compressors (1) is increased. This embodiment may be applicable to any one of the circuits of FIGS. 5 to 7.

FIG. 11 includes, additionally to the circuit of FIG. 9, a first vapor line (62) that comprises a first motorised valve (15) and connects the outlet vapor line (90) at the outlet of the liquid receiver (17) with the first fluid line (51) at the inlet of the second heat exchanger (10), downstream the third expansion valve (12).

This embodiment allows the second compressor (2) to work in parallel with the first compressors (1) if it is necessary to suction the flash-gas from the liquid receiver (17) or to work as an emergency unit to reduce the pressure of the liquid receiver (17) when the installation is stopped. This embodiment may be applicable to the circuit comprising the outlet vapor line (90) provided with the second heat exchanger (10), the first fluid line (51) provided with the third expansion valve (12), the compressor (2), and the second pressure reduction valve (16).

FIG. 12 includes, additionally to the circuit of FIG. 11, a cooling line (43) that connects the first liquid line (81) at the inlet of the first heat exchanger (18) with the first vapor line (62) downstream the first motorised valve (15), at the inlet of the second heat exchanger (10) after passing through a fourth expansion valve (29) and also through a cooling coil (91) located within the liquid receiver (17).

This embodiment allows the second compressor (2) to work as an emergency unit to reduce the pressure of the liquid receiver (17) when the installation is stopped. By cooling refrigerant accumulated in the liquid receiver (17) with the depressurized refrigerant flowing in the cooling coil (91), the pressure in the liquid receiver (17) can be reduced.

As represented in FIG. 13, the circuit includes, additionally to the circuit of FIG. 12, a second motorised multi way valve (4) located in the discharge line (41) that is also connected to a first branch (42) connecting to the inlet of a fourth heat exchanger (5) which outlet is connected to the inlet of the first gas-cooler.

In this situation, the refrigerant leaving the compressors (1, 2) may be directed either to the first gas-cooler (7), bypassing the fourth heat exchanger (5), or to the fourth heat exchanger (5) and then to the first gas-cooler (7).

This embodiment allows to use the heat generated in the discharge line (41) for several applications using the heat exchanger (5) as tap water, climate control or heat recovery. Also, this embodiment may be applicable to any one of the circuits of FIGS. 5, 6, 7, 9, 11, and 12.

FIG. 14 includes, additionally to the circuit of FIG. 13, a third motorised multi way valve (6) located at the inlet of the first gas-cooler (7) that is also connected to a second branch (66) that connects with the outlet gas-cooler line (50), bypassing the first gas-cooler (7).

This embodiment allows to by-pass the first gas-cooler (7) in order to generate more temperature upstream the first pressure reduction valve (14) increasing the operation of the compressors (1, 2) to generate additional heat for use in several applications using the fourth heat exchanger (5) as tap water, climate control or heat recovery in the discharge line (41).

FIG. 15 includes additionally to the circuit of FIG. 14:

• • a first check valve (9) located in the gas-cooler outlet line (50) upstream the connection to the second branch (66), so that the refrigerant passing through the second branch (66) is not allowed to flow back into the gas-cooler (7),
  • a third branch (71), comprising a third motorised valve (45), connecting the inlet to the first gas-cooler (7) downstream the third motorised multi way valve (6), to the outlet vapor line (90), downstream the second pressure reduction valve (16), and
  • a fourth branch (83), comprising a second expansion valve (11) and a second check valve (9′), connecting the first liquid line (81) downstream the first heat exchanger (18) with the gas-cooler outlet line (50) upstream the first check valve (9), so that the refrigerant leaving the first gas-cooler (7) cannot flow into the fourth branch (83).

This embodiment allows to generate additional heat in the discharge line (41) for low cooling demand in the medium temperature heat exchanger (20). It generates and additional cooling load for the first compressors (1) when it is necessary to generate an additional heat recovery in the fourth heat exchanger (5).

FIG. 16 includes additionally to the circuit of FIG. 15:

• • a second fluid line (93), with a second motorised valve (22), that connects the gas-cooler outlet line (50) at the outlet of the third heat exchanger (13) with the liquid receiver (17),
  • a pressure increaser device (95) located at the outlet of the second compressor (2),
  • a fourth fluid line (94) that connects the second pipe (65) to the pressure increaser device (95),
  • a pressure exchanger (21) configured to exchange pressure between the refrigerant flowing through the second fluid line (93) and the refrigerant flowing through the fourth fluid line (94).

This embodiment allows to use the pressure reduction from the gas-cooler outlet line (50) to the liquid receiver (17) in order to increase the pressure of the refrigerant in the other part of the installation using a pressure exchanger (21) with no need of an additional compressor. Additionally, there is a pressure increaser device (95) from the fourth fluid line (94) to the discharge line (41). This embodiment may be applicable to any one of the circuits of FIGS. 9, 11, 12, 13, 14 and 15.

FIG. 17 is an alternative embodiment to the circuit represented in FIG. 16 wherein the second pipe (65), instead of being connected to the outlet of the second compressor (2), is connected to the first gas-cooler outlet line (50) and additionally comprises a second gas-cooler (8) and a pump (38).

In this way, this embodiment of the refrigeration circuit comprises, additionally to the circuit of FIG. 15:

• • a second fluid line (93), with a second motorised valve (22), that connects the gas-cooler outlet line (50) at the outlet of the third heat exchanger (13) with the liquid receiver (17),
  • a fifth fluid line (67) connecting the second pipe (65) with the first gas-cooler outlet line (50) and comprising a second gas-cooler (8) and a pump (38),
  • a pressure exchanger (21) configured to exchange pressure between the refrigerant flowing through the second fluid line (93) and the fifth fluid line (67)

This embodiment allows to use the pressure reduction from the gas-cooler outlet line (50) to the liquid receiver (17) to increase the pressure of the refrigerant in the other part of the installation with no need of additional compressors. In this way, the compressor (2) does not need to increase the pressure in the fifth fluid line (67) to the discharge line and it can work independent than the compressor (2) operation. The second gas-cooler (8) has the advantage regarding the one used in the circuit shown in FIG. 18 that the pressure exchanger (21) can be used independently in the main installation. This embodiment may be applicable to any one of the circuits of FIGS. 9, 11, 12, 13, 14 and 15.

FIG. 18 is a second alternative embodiment to that represented in FIGS. 16 and 17. In this case, additionally to the features included in FIG. 15, the circuit includes:

• • a second fluid line (93), with a second motorised valve (22), that connects the gas-cooler outlet line (50) at the outlet of the third heat exchanger (13) with the liquid receiver (17),
  • a sixth fluid line (68) connecting the second pipe (65) with the first gas-cooler outlet line (50),
  • a pressure exchanger (21) configured to exchange pressure between the refrigerant flowing through the fifth fluid line (93) and the sixth fluid line (68), and wherein the first gas-cooler (7) comprises an additional circuit where the sixth fluid line (68) is connected downstream the pressure exchanger (21), and
  • a pump (38) located at the outlet of the additional circuit and in the sixth fluid line (68).

The difference of this circuit with the circuit of FIG. 17 is that, instead of using the second gas-cooler (8), the first gas-cooler (7) is used with an additional circuit. This embodiment may be applicable to any one of the circuits of FIGS. 9, 11, 12, 13, 14 and 15. In this embodiment, since a part of the first gas-cooler (7) can be used as instead of the second gas cooler, the product can be designed compactly. Also, it is possible to reduce the cost of the product.

FIG. 19 is an alternative embodiment to the circuit represented in FIG. 18 that additionally comprises:

• • a third compressor (3) connected to the rest of compressors (1, 2) in parallel and also to the common discharge line (41),
  • a fourth motorised multi-way valve (31) located on the second pipe (65) feeding the second compressor (2) that also connects with the inlet of the rest of the compressors (1, 3), and
  • a fifth motorised multi-way valve (30) located in the fourth fluid line (94) and also connected to a third fluid line (92) that splits from the outlet of the third compressor (3) upstream a third check valve (9″), so that the refrigerant flowing through the fifth tubing (65) can be switched between the inlet of the third compressor (3) and the inlet of the rest of compressors (1, 2).

Although it has not been represented, in this embodiment, the third fluid line (92) may as well split from the outlet of one of the first compressors (1) instead of the outlet of the third compressor (3).

This embodiment allows to use the pressure reduction from the gas-cooler outlet line (50) to the liquid receiver (17) to increase the pressure of the refrigerant in the other part of the installation. In this case, the suction line of the pressure exchanger (21) goes from the liquid receiver (17) or from the medium temperature heat exchanger (20) using an additional compressor (3).

FIG. 20 includes, additionally to the circuit of FIG. 13:

• • a low temperature expansion valve (25),
  • a low temperature heat exchanger (23),
  • a low temperature compressor (39), and
  • a desuperheater (37),
    located in a low temperature liquid line (84) connecting the first liquid line (81) with the suction line (59).

This embodiment allows to use the system for other evaporation temperatures.

The system will not work in this way, sucking flow from the medium temperature evaporators. This is because the pressure exchanger (21) needs to have more pressure in the inlet valve line (30) than in the outlet line (93) (receiver pressure), so a compressor is needed in order to increase the medium temperature evaporating pressure (about 28 bar) to a pressure of about 2 bar above the receiver pressure (about 42 bar).

This embodiment may be applicable to any one of the circuits of FIGS. 5, 6, 7, 9, 11, 12, 13, 14, 15, 16, 17, 18 and 19.

FIG. 21 includes, additionally to the circuit of FIG. 20, an amendment to the low temperature circuit wherein the outlet of the low temperature heat exchanger (23), instead of being directed directly to the low temperature compressor (39), is first directed to the first heat exchanger (18), which is configured to exchange heat with the refrigerant flowing through the first liquid line (81).

This embodiment allows to introduce a superheat in the low temperature liquid line (84) with the first heat exchanger (18) to operate with low superheating in the low temperature heat exchanger (23) and with higher evaporation temperature to reduce the energy consumption in the low temperature compressor (39). Additionally, it introduces a subcooling in the first liquid line (81) to reduce the flash-gas in both the medium and low temperature expansion valves (19, 25), increasing the cooling capacity of the first compressors (1) and the low temperature compressor (39). In this embodiment, a plate heat exchanger having three flow channels may be used as one of the samples of the first heat exchanger. By using this type of plate heat exchanger, a superheat can be introduced in two refrigerants at different temperatures with one heat exchanger, so the product can be designed compactly. Also, it is possible to reduce the cost of the product. This embodiment may be applicable to circuits to which the embodiment in FIG. 20 is applicable.

It must be noted that raising the evaporating temperature is possible and is a consequence of minimising superheat at the evaporator and it is the raising of the evaporating temperature that gives us the great improvement in the efficiency of the system.

FIG. 22 includes, additionally to the circuit of FIG. 21:

• • a seventh motorised multi-way valve (88) disposed downstream the low temperature heat exchanger (23) and
  • a seventh fluid line (89) that connects the seventh motorised multi-way valve (88) with the inlet of the low temperature compressor (39).

This configuration allows the possibility of the refrigerant to bypass the first heat exchanger (18).

Additionally, the seventh motorised multi-way valve (88) is configured to be controlled based on the superheat in the suction of the low temperature compressor (39), so that high superheating in the suction line may be prevented.

Additionally, to the circuit of FIG. 22, the circuit of FIG. 23 also includes a sixth motorised multi way valve (86) located at the outlet of the desuperheater (37).

The sixth motorised multi valve (86) is configured so that the refrigerant leaving the desuperheater (37) can be switched between the inlet of the first compressor (1), and the inlet of the pressure exchanger (21), through a third fluid line (87), on the side where the increase in pressure is caused by the refrigerant flowing through the fifth fluid line (93).