EP1895246B3 - Refrigeration circuit and method for operating a refrigeration circuit - Google Patents

Abstract

Refrigerant is circulated in a predetermined flow direction comprised of a heat-rejecting heat exchanger (4), intermediate throttle valve (6), receiver (8), evaporator throttle valves (10), evaporator (14), compressor (20) and flash gas tapping line (26). The flash gas tapping line is connected to the receiver and to the compressor. An independent claim is also included for a refrigeration circuit operating method.

Description

The invention relates to a refrigeration cycle in which a one- or multi-component refrigerant circulates, comprising in the flow direction a condenser, a collecting container, an expansion device upstream of an evaporator, an evaporator and a single-stage compressing compressor unit.
Furthermore, the invention relates to a method for operating a refrigeration cycle.
The term "liquefier" should be understood to mean both liquefier and gas cooler.
Generic refrigeration cycles are well known. They are for example in refrigeration systems, so-called composite refrigeration systems, such as those used in supermarkets, implemented. Composite refrigeration systems generally supply a variety of refrigerants, such as Kühlräüme, refrigerators and freezers. For this purpose circulates in them a one- or multi-component refrigerant or refrigerant mixture.
A counting of the prior art refrigeration cycle or a refrigeration system in which such a refrigeration cycle is realized, is based on the in the FIG. 1 illustrated embodiment explained in more detail.
The circulating in the Kältekreislaüf one- or multi-component refrigerant is in a condenser or gas cooler A - hereinafter referred to only as a condenser - which is usually outside the supermarket, for example, on the roof, arranged by heat exchange, preferably condensed against outside air.
The liquid refrigerant from the condenser A is fed via line B to a (refrigerant) collector C. Within a refrigeration cycle always so much refrigerant must be present that even with maximum cooling demand, the evaporator of all refrigeration consumers can be filled. However, with lower cooling requirements individual evaporators are only partially filled or even completely empty, the excess refrigerant must be collected during these times in the designated collector C.

From the collector C, the refrigerant passes through the liquid line D to the cold consumers of the so-called normal cooling circuit. Here are the in the FIG. 1 represented consumers F and F 'for any number of consumers of the normal refrigeration cycle. Each of the aforementioned refrigeration consumers is preceded by an expansion valve E or E ', in which the refrigerant flowing into the refrigeration appliance or the evaporator or the evaporator of the refrigeration consumer is expanded. The so-relaxed refrigerant is evaporated in the evaporators of the refrigerant consumers F and F 'and thus cools the corresponding refrigeration cabinets and rooms.

The vaporized in the Kälteverbrauchem F and F 'of the normal cooling circuit refrigerant is then fed via the suction line G of the compressor unit H and compressed in this to the desired pressure between 10 and 25 bar usually the compressor unit H is formed only one stage and has a plurality of parallel connected compressor on.

The compressed in the compressor unit H refrigerant is then fed via the pressure line I in turn to the aforementioned condenser A.

Via a second liquid line D 'is the condenser C refrigerant supplied to the condenser K and evaporated in this heat exchange with the refrigerant of the still to be explained Tiefkühlkreislaufes before it is fed via the line G' of the compressor unit H.

The liquefied in the condenser K refrigerant of Tiefkühlkreislaufes is supplied via line L to the collector M of the freezing circuit From this is via the line N, the refrigerant to the consumer P - this is for any number of consumers - which is preceded by a relaxation device O, respectively and evaporated in this. Via the suction line Q, the vaporized refrigerant is fed to the single-stage or multi-stage compressor unit R, in this pressure compressed between 25 and 40 bar and then fed via the pressure line S to the aforementioned capacitor K.

As a refrigerant of the normal refrigeration cycle, for example, R 404A is used, while for the freezing cycle carbon dioxide is used.

The in the FIG. 1 shown compressor units H and R, the collector C and M and the capacitor K are usually arranged in a separate machine room. However, about 80 to 90% of the entire pipeline network is located in the sales rooms, the storage areas or other areas of a supermarket accessible to employees and customers. As long as this line network operates at pressures of no more than 35 to 40 bar, this is acceptable to the supermarket operators both from a psychological point of view and for cost reasons.

Currently, it is going to operate even the above-described normal cooling circuit with the refrigerant CO ₂ .

The sensible use of the natural refrigerant CO ₂ in commercial refrigeration fails on the one hand because of the insufficient energetic efficiency of the simple, single-stage cycle at high (outside) air temperatures. On the other hand, owing to the material properties of CO _2, high working pressures - up to 100 bar and above - are required, which make it extremely difficult to manufacture corresponding refrigeration circuits or refrigerating plates for economic reasons. Commercially, the refrigerant CO _{2 is} therefore so far only used in cascade systems in the freezing - as exemplified by the FIG. 1 is explained - since the working pressures realized there do not exceed the usual, maximum pressure of 40 bar.

Due to the above-mentioned higher pressures or pressure, the pipe network of the refrigeration cycle must be designed for these pressures or pressure. However, the materials required for this are far more expensive than those that can be used in the previously implemented printing layers. In addition, such, comparatively high. However, pressure systems are also very difficult to convey to plant operators.

Another problem is especially when using CO ₂ as a refrigerant in that at high ambient temperatures, a supercritical operation of the refrigeration cycle is required. High outside air temperatures mean that comparatively high throttle steam emissions occur at the evaporator inlet. This reduces the effective volumetric cooling capacity of the circulating refrigerant, however, both suction and liquid lines and the evaporators must be sized accordingly larger to keep the pressure losses as low as possible.

From the EP 0 431 797 A2 For example, a refrigeration system is known that includes a condenser for releasing heat into the environment, a refrigerant tank receiving refrigerant and allowing a mixture of the gas-phase and liquid-phase refrigerant, the liquid-phase refrigerant collecting in the lower portion of the container, means for refrigerating from the outlet side of the condenser to the tank, at least a first compressor that passes the refrigerant through the condenser, at least one evaporator operating in a low temperature environment, at least one second compressor that draws refrigerant through the low temperature evaporator, and a heat exchange line the lower portion of the container, which is normally immersed in liquid refrigerant, wherein the outlet of the second compressor is connected to the inlet end of the heat exchange line.

From the JP 61 064526 a cooling device for a motor vehicle is known. The refrigerant is sucked into the inner part of a first compression chamber, which is the ninth cylinder of a compressor consisting of ten cylinders, from a suction port for cooling, and the refrigerant is sucked into a chamber having an inclined plate from an intake port, with a higher pressure than the refrigerant sucked into the inner part of the second compressor, which is a first cylinder, from a suction port to the refrigerant flow into the inner parts of the first and second compressors by the differences in pressure when a piston reached a connection hole. As a result, the pressure for the refrigerant within the two compressors is raised before being compressed by a compressor, and the same amount of refrigerant suction can be obtained by a more compact compressor.

From the US-A-5,103,650 is a refrigeration system with a variety of evaporators known. In this system, three pairs of expansion valves and evaporators are connected in series, and there are also three compressors connected in series.

Out SCHIESARO P ET AL: "Development Of A Two Stage CO2 Supermarket System", IIR Conference. New Technologies at Commercial Refrigeration, XX, XX, July 22, 2002 (2002-07-22), pages 1-10, XP001169091 For example, a refrigeration cycle is known which comprises a two-stage compressor on the high pressure side, an internal heat exchanger between the gas withdrawn at low pressure by the high pressure compressor and the gas expelled from the gas cooler, and a receiver having carbon dioxide in the liquid / gaseous state , From the collecting tank, a pump pumps the liquid CO ₂ to the normal cooling refrigeration consumer, from where it flows back to the collecting tank. In addition, the liquid CO ₂ passes from the sump via a thermostatic valve to the direct expansion evaporator of a refrigerated refrigeration consumer, and after evaporation therein, the CO ₂ is withdrawn by a low pressure compressor, vaporized and returned to the sump in the gaseous state where the gas is deprived and then withdrawn through the two-stage high-pressure compressor at the same pressure level, without a valve being arranged in the line leading from the collecting container to the two-stage high-pressure compressor.

The JP 1 318860 A shows a refrigeration cycle with a compressor having a normal refrigerant compressor section 4 and a freezer compressor section 3, with a sump 8, with a normal refrigerant evaporator 12 and a cryogenic evaporator 10. Liquid refrigerant is from the bottom of the sump 8 via a line 8a to the normal cooling evaporator 12 and a separate line, in which a pressure reducer 9 is arranged, fed to a deep-freeze evaporator 10. From the deep-freeze evaporator 10, the refrigerant evaporated there then reaches the deep-freeze compressor section 3, and the refrigerant evaporated in the normal-temperature evaporator 12 enters the normal-length refrigerant compressor section 4. Gaseous refrigerant passes from the upper section of the sump 8 to the normal-low-pressure section 4 at the same pressure level in this line, a valve is provided.

Object of the present invention is to provide a generic refrigeration cycle and a method for operating a refrigeration cycle, which avoids the disadvantages mentioned.

This object is achieved by the refrigeration cycle according to claim 1 and a method for operating a refrigeration cycle according to claim 11.

In the refrigeration cycle, an intermediate expansion device is arranged between the condenser and the collecting container.

On the process side takes place in the intermediate between the condenser and the collecting intermediate relaxation device, a relaxation of the refrigerant to an (intermediate) pressure of 5 to 40 bar.

The inventive refrigeration cycle, the inventive method for operating a refrigeration cycle and other embodiments thereof are described below with reference to in the FIGS. 2 to 4 shown embodiments explained in more detail.

This shows the FIG. 2 its composite refrigeration system in which a possible embodiment of the refrigeration cycle according to the invention is realized. In the following, a procedure is described in which as a refrigerant HFC (s), HFC (s) or CO ₂ can be used.

The compressed in the compressor unit 6 to a pressure between 10 and 120 bar refrigerant is fed via the pressure line 7 to the condenser or gas cooler 1 and condensed in this against external flow or deprived. The refrigerant is supplied to the refrigerant collector 3 via the lines 2, 2 'and 2 ", but according to the invention it is expanded in the intermediate expansion device a to an intermediate pressure of 5 to 40 bar and the collector 3 must be designed only to a lower pressure.

The pressure to which the refrigerant is expanded in the mentioned intermediate relaxation device a, is hereby preferably selected so that it is still below the lowest expected condensing pressure.

According to an advantageous embodiment of the refrigeration cycle according to the invention, the pressure line 7 with the sump 3. preferably with the gas space, connected or connectable. This connection between the pressure line 7 and the collecting container 3 can take place, for example, via a connecting line 17, in which an expansion valve h is arranged.

According to an advantageous embodiment of the refrigeration cycle according to the invention, the pressure line 7 is connected or connectable to the line or line sections 2 or 2 ', 2 "connecting the liquefier 1 and the collecting container 3. This connection between the pressure line 7 and the line 2 or 2 ', 2 ", for example, via the dashed lines shown connecting line 18, in which a valve j is arranged, take place.

According to an advantageous embodiment of the refrigeration cycle according to the invention the collecting container 3, preferably the gas space, connected to the input of the compressor unit 6 or connectable.

This connection between the collecting container 3 and the input of the compressor unit 6 can, for example, via a connecting line 12, as in the FIG. 2 shown, in the suction line 11 opens, done.

About the provided in the line 12 expansion valve e and provided in the line 17 expansion valve h or das.in the line 18 provided valve j, the selected intermediate pressure can now be kept constant for all operating conditions. However, it is also possible a scheme such that a constant difference value to the suction pressure exists. This ensures that the throttle steam fraction at the evaporators is comparatively small, with the result that the liquid and suction lines can be dimensioned correspondingly smaller. This also applies to the condensate line, since now no gaseous components have to flow through them back into the condenser 1. By means of the invention, it is thus also achieved that the required amount of refrigerant charge can be reduced by up to approximately 30%.

Via the suction line 4 refrigerant is withdrawn from the collector 3 and the refrigerant consumers or their heat exchangers E2 and E3 supplied. This is preceded by a respective expansion valve b and c, in which the refrigerant flowing into the refrigeration consumer is expanded. The refrigerant evaporated in the refrigeration consumers E2 and E3 is then fed back to the compressor unit 6 via the suction line 5 or sucked out of the evaporators E2 and E3 by the latter.

A portion of the withdrawn from the collector 3 via line 4 refrigerant is fed via line 8 one or more frozen consumers - represented by the heat exchanger E4-, which is also preceded by a relaxation valve d supplied. After the evaporation in the heat exchanger or cold consumer E4, this partial refrigerant flow is fed to the compressor unit 10 via the suction line 9 and compressed thereinto to the inlet pressure of the compressor unit 6. The refrigerant partial stream thus compressed is then fed via line 11 to the inlet side of the compressor unit 6.

The invention further, it is proposed that -as in the FIG. 2 represented in the collecting container 3, a heat exchanger E1 can be connected upstream.

Here, the heat exchanger E1 is preferably connected on the input side to the output of the condenser 1 or connectable.

Like in the FIG. 2 shown, can now via line 13, in which an expansion valve f is provided, a partial stream of the liquefy or desing refrigerant from the condenser or gas cooler 1 and the line 2 and withdrawn in the heat exchanger E1 against the to be rehied, the heat exchanger E1 via line 2 'supplied refrigerant to be evaporated. The vaporized refrigerant partial stream is then fed via line 14 to a compressor 6 ', which is associated with the above-described compressor unit 6 and which preferably sucks at a higher pressure level, and in this compressed to the desired final pressure of the compressor unit 6.

By means of the heat exchanger E1, the refrigerant stream to be expanded in the intermediate expansion device a is preferably cooled to such an extent that the throttled vapor portion of the expanded refrigerant is minimized.

Alternatively or additionally, the resulting in the collector 3 throttle steam fractions can be sucked off via the line 12 and the dashed line 15 by means of the compressor 6 'at a higher pressure level.

In the FIG. 3 1 shows an embodiment of the refrigeration cycle according to the invention or of the method according to the invention for operating a refrigeration cycle, in which the refrigerant drawn off from the collecting container 3 via the line 4 is subjected to supercooling in the heat exchanger E5

In this case, the subcooling takes place - in accordance with an advantageous embodiment of the invention - in heat exchange with the withdrawn from the reservoir 3 via line flash gas.

Liquid lines, such as those in the Figures 2 and 3 shown line 4, with a temperature level below the ambient temperature are exposed to heat radiation. This has the consequence that the refrigerant flowing inside the liquid line partially evaporates, thus resulting in the formation of undesirable vapor contents. To prevent this, refrigerant so far either by an expansion of a partial flow of the refrigerant and subsequent evaporation or by an internal heat transfer to a suction gas stream, which is thereby overheated, undercooled

In the refrigeration cycle according to the invention or the procedure according to the invention, the temperature interval between the suction and liquid line or the circulating refrigerant therein may be too low to realize an internal heat transfer for the required supercooling of the refrigerant flowing in the liquid line.

Further developing the invention therefore, as already mentioned, proposes to subcool the refrigerant drawn off from the collecting container 3 via line 4 in the heat exchanger or subcooler E5 against the flash gas expanded from the collecting container 3 via line 12 and in the valve e. After passing through the heat exchanger or subcooler E5, the expanded refrigerant which has been overheated in the heat exchanger E5 is fed via the line sections 12 'and 11 to the inlet of the compressor unit 6. Due to the overheating of the withdrawn from the reservoir 3 via line 12 Flashgasstromes a sufficient subcooling of the refrigerant flowing in it is achieved in the liquid line 4; This subcooling of the refrigerant improves the regular operation of the expansion or Enspritzventile b, c and d, which are upstream of the evaporators E2, E3 and E4.

Liquid droplets which are not separated from the collecting container 3 via line 12 due to a too small dimensioning and / or overfilling of the collecting container 3 and carried along with the flash gas, are evaporated at the latest in the heat exchanger / subcooler E5. The procedure described thus has the additional advantage that the reliability of the compressor or compressor unit 6 is increased due to a safe overheating of the flash gas stream.

The FIG. 4 shows a further, Augestaltung the refrigeration cycle of the invention or the inventive method for operating a Käftekrelslaufes. For the sake of clarity is in the FIG. 4 only a part of the in the FIG. 2 and 3 illustrated refrigeration circuit according to the invention shown

The method according to the invention for operating a refrigeration cycle further develops that at least a partial flow of the flash gas withdrawn from the collecting container is at least temporarily overheated against at least a partial flow of the compressed refrigerant.

The FIG. 4 shows a possible embodiment of the method according to the invention, in which at least temporarily a partial flow of the withdrawn from the reservoir 3 via line 12 flash gas via line 16 to a heat exchanger E6 and superheated in this against the compressed in the compressor unit 6 refrigerant.

When in the FIG. 4 As shown, the Flashgasstrom to be overheated in the heat exchanger E6 against the entire, compressed in the compressor unit 6 refrigerant flow via line 7 in the FIG. 4 not shown condenser or desuperheater is supplied, superheated.

After passing through the heat exchanger / superheater E6, the flash gas stream is supplied via line 16 'to the inlet of the compressor 6' of the compressor unit 6.

The in the FIG. 4 The procedure described makes it possible to ensure that liquid components contained in the flash gas are unambiguously vaporized, resulting in increased safety for the compressor or compressor unit 6.

Claims (16)

1. A refrigeration circuit, comprising, in the flow direction, a liquefier/gas cooler (1), an intermediate expansion device (a), a collecting container (3), an expansion device (b, c) upstream of an evaporator (E2, E3), an evaporator (E2, E3) and a compressor unit (6), wherein an additional compressor unit (10) and at least one deep-freezing consumer (E4) with an upstream expansion valve (d) are provided, wherein, during operation, refrigerant is drawn via a suction line (4) from the collecting container (3), expanded in the expansion device (b, c) and supplied to the evaporators (E2, E3), and, after evaporation in the evaporators (E2, E3), supplied via a suction line (5) to the compressor unit (6), and a partial refrigerant flow from the collecting container (3) is supplied via the suction line (4) and a line (8) branching off therefrom to the at least one deep-freezing consumer (E4), and, after the evaporation that has occurred therein, it is supplied to the additional compressor unit (10), wherein the refrigeration circuit enables a supercritical operation, wherein, during operation, the additional compressor unit (10) compresses the partial refrigerant flow to the inlet pressure of the compressor unit (6) and supplies it, via a suction line (11) leading in front of the compressor unit (6) into the suction line (5), to the inlet side of the compressor unit (6), and wherein the gas space of the collecting container (3) is connected or can be connected to the inlet of the compressor unit (6), and wherein, in the connecting line (11, 12), between the gas space of the collecting container (3) and the inlet of the compressor unit (6), an expansion valve (e) is provided.
2. The refrigeration circuit according to Claim 1, wherein a heat exchanger (E1) is located upstream of the collecting container (3).
3. The refrigeration circuit according to Claim 2, wherein the heat exchanger (E1) is connected or can be connected on the inlet side to the outlet of the liquefier (1).
4. The refrigeration circuit according to Claim 2 or 3, wherein the heat exchanger (E1) is connected or can be connected on the outlet side to the inlet of a compressor (6') of the compressor unit (6).
5. The refrigeration circuit according to any one of the preceding claims, wherein the gas space of the collecting container (3) is connected or can be connected to the inlet of the compressor unit (6).
6. The refrigeration circuit according to any one of the preceding claims, wherein the gas space of the collecting container (3) is connected or can be connected to the inlet of a compressor (6') of the compressor unit (6).
7. The refrigeration circuit according to any one of the preceding claims, wherein the pressure line (7) is connected or can be connected to the collecting container (3), preferably to the gas space thereof, or to the line (2, 2', 2") connecting the liquefier/gas cooler (1) and the collecting container (3).
8. The refrigeration circuit according to any one of the preceding claims, wherein, between the collecting container (3) and the expansion device (c, b, d) upstream of an evaporator, a heat exchanger/subcooler (E5) is arranged.
9. The refrigeration circuit according to any one of the preceding claims, wherein the heat exchanger/subcooler (E5) is connected or can be connected on the inlet side to the gas space of the collecting container (3).
10. Method for operating a refrigeration circuit according to any one of the preceding claims, comprising the following steps:

    expanding the refrigerant in the intermediate expansion device (a) arranged between the liquefier/gas cooler (1) and the collecting container (3) to an intermediate pressure of 5 to 40 bar,

    drawing refrigerant from the collecting container (3) and supplying same to the evaporators (E2, E3) via a suction line (4),

    expanding the refrigerant in expansion valves (b, c) upstream of the evaporators (E2, E3),

    evaporating the refrigerant in the evaporators (E2, E3) and supplying the evaporated refrigerant to the compressor unit (6) via a suction line (5),

    supplying a partial refrigerant flow from the collecting container (3) to the at least one deep-freezing consumer (E4) via the suction line (4) and a line (8) branching off therefrom,

    evaporating the partial refrigerant flow in the at least one deep-freezing consumer (E4),

    supplying the evaporated partial refrigerant flow to the additional compressor unit (10),

    wherein a supercritical operation is enabled,

    wherein the additional compressor unit (10) compresses the partial refrigerant flow to the inlet pressure of the compressor unit (6) and supplies it, via a suction line (11) leading in front of the compressor unit (6) into the suction line (5), to the inlet side of the compressor unit (6), and wherein the intermediate pressure is regulated to a constant value by means of an expansion valve (e) provided in the connecting line (11, 12) between the gas space of the collecting container (3) and the inlet of the compressor unit (6).
11. The method according to Claim 10, wherein the refrigerant (2) is cooled before the intermediate expansion (a) thereof.
12. The method according to Claim 11, wherein the cooling (E1) of the refrigerant (2) occurs against a partial flow of the refrigerant (13).
13. The method according to any one of Claims 10 to 12, wherein the refrigerant (4) drawn from the collecting container (3) is subcooled.
14. The method according to Claim 13, wherein the subcooling (E5) of the refrigerant (4) drawn from the collecting container (3) occurs against the flash gas (12) drawn from the collecting container (3).
15. The method according to any one of Claims 10 to 14, wherein at least one partial flow of the flash gas (12) drawn from the collecting container (3) is superheated at least temporarily against the compressed refrigerant (7).
16. The method according to any one of Claims 10 to 15, wherein the intermediate pressure is regulated by means of at least one valve (e, h, j) to a constant value and/or to a constant difference with respect to the suction pressure.

Images