# Patent

## Title
Refrigeration circuit and method for operating a refrigeration circuit

## Abstract

The invention relates to a refrigeration circuit having a mono- or multi-component refrigerant circulating therein, said refrigeration circuit comprising, in the direction of flow, a condenser, a collecting container, a relief device connected upstream of an evaporator, an evaporator and a compressor unit with single-stage compression.

    
    
        According to the invention, there is an intermediate relief device (a) arranged between the condenser (1) and the collecting container (3).
        Furthermore, there is disclosed a method of operating a refrigeration device in which pressure relief of the refrigerant to an (intermediate) pressure of 5 to 40 bar is effected in the intermediate relief device (a) arranged between the condenser (1) and the collecting container (3).

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This is the 35 USC 371 National Phase of International Application PCT/EP2005/008255, filed Jul. 29, 2005.
BACKGROUND OF THE INVENTION
The invention relates to a refrigeration circuit having a mono- or multi-component refrigerant circulating therein, said circuit comprising, in the direction of flow, a condenser, a collecting container, a relief device connected upstream of an evaporator, an evaporator and a compressor unit with single-stage compression.
Furthermore, the invention relates to a method of operating a refrigeration circuit.
The term “condenser” is to be understood to comprise both condensers and gas coolers.
Refrigeration circuits of the type concerned are well known. They are realized, for example, in refrigerating plants, so-called composite refrigerating plants, as used in supermarkets. In general, composite refrigerating plants feed there a multiplicity of cold consumers, such as cold storages, refrigerating and deep-freezing furniture. To this end, a mono- or multi-component refrigerant or refrigerant mixture circulates in the same.
A refrigeration circuit or refrigerating plant according to the prior art, realizing such a refrigeration circuit, shall be elucidated in more detail by way of the example illustrated in FIG. 1.
The mono- or single component refrigerant circulating in the refrigeration circuit is condensed in a condenser or gas cooler A—in the following briefly referred to as condenser only—which as a rule is arranged outside of a supermarket, e.g. on the roof thereof, by exchange of heat, preferably with respect to outside air.
The liquid refrigerant from the condenser A is supplied via a line B to a (refrigerant) collector C. Within a refrigeration circuit it is necessary at all times that sufficient refrigerant is present so that also in case of maximum refrigeration requirements the condensers of all cold consumers can be filled. However, due to the fact that in case of lower refrigeration requirements, some condensers are filled only partially or even are completely empty, the surplus of refrigerant during these times has to be collected in the collector C provided therefor.
From the collector C, the refrigerant passes via liquid line D to the cold consumers of the so-called normal refrigeration circuit. In this regard, the consumers F and F′ depicted in FIG. 1 stand for an arbitrary number of consumers of the normal refrigeration circuit. Each of the afore-mentioned cold consumers has an expansion valve E and E′, respectively, connected upstream thereof, in which pressure relief of the refrigerant flowing into the cold consumer or the evaporator(s) of the cold consumer takes place. The thus pressure-relieved refrigerant is evaporated in the evaporators of the cold consumers F and F′ and thereby refrigerates the corresponding refrigeration furniture and storage rooms.
The refrigerant evaporated in the cold consumers F and F′ of the normal refrigeration circuit then is fed via suction line G to compressor unit H and is compressed therein to the desired pressure between 10 and 25 bar. As a rule, the compressor unit H is of single-stage design only and has a plurality of compressors connected in parallel.
The refrigerant compressed in the compressor unit H then is fed via pressure line I to the afore-mentioned condenser A.
Via a second liquid line D′, refrigerant is fed from collector C to condensing means K and is evaporated therein, exchanging heat with the refrigerant of the deep-freeze circuit still to be elucidated, before it is supplied via line G′ to compressor unit H.
The refrigerant of the deep-freezing circuit liquefied in condensing means K is supplied via line L to the collector M of the deep-freeze circuit. From the latter, the refrigerant is passed via line L to consumer P—which stands for an arbitrary number of consumers—having a relief device O connected upstream thereof, and is evaporated therein. Via suction line Q, the evaporated refrigerant is fed to the single-stage or multi-stage compressor unit R and is compressed in the same to a pressure between 25 and 40 bar and thereafter is supplied to the afore-mentioned condensing means K via pressure line S.
The refrigerant used in the normal refrigeration circuit is e.g. R 404A, whereas carbon dioxide is utilized for the deep-freeze circuit.
The compressor units H and R shown in FIG. 1, the collectors C and M as well as the condensing means K as a rule are disposed in a separate machine room. However, about 80 to 90 percent of the entire line network are arranged in the sales rooms, storage rooms or other rooms of a supermarket that are accessible to staff members and customers. As long as this line network does not make use of pressures of more than 35 to 40 bar, this is acceptable to the supermarket operator both under psychological aspects and for reasons of costs.
SUMMARY OF THE INVENTION
Presently, there are changes being made, operating also the afore-mentioned normal refrigeration circuit with the refrigerant CO2.
The sensible use of the natural refrigerant CO2 in commercial refrigeration systems so far fails to be successful on the one hand due to the insufficient energetic efficiency of the simple, single-stage cycle process in case of high (external) air temperatures. On the other hand, due to the material properties of CO2 there are high operating pressures—of up to 100 bar and above—necessary, which enormously aggravate the production of corresponding refrigeration circuits and refrigerating plants, respectively, for reasons of economy. Therefore, the refrigerant CO2 so far is commercially employed in cascade systems for deep-freezing only—as illustrated in exemplary manner by way of FIG. 1—, as the operating pressures realized there are not in excess of the usual maximum pressure level of 40 bar.
Due to the afore-mentioned higher pressures or pressure level, the tubing network of the refrigeration circuit has to be designed for these pressures or this pressure level. However, the materials required therefor are by far more expensive than those that can be utilized for the pressure levels realized so far. In addition thereto, it is very difficult to convey the idea of such comparatively high pressure levels to the operators of the plants as well.
Another problem exists in particular in using CO2 as refrigerant in that, in particular with correspondingly higher outer temperatures, transcritical operation of the refrigeration circuit becomes necessary. High external air temperatures have the result that comparatively high amounts of throttling vapour occur at the entry to the evaporator. The effective volumetric refrigerating power of the circulating refrigerant is reduced thereby, while however both the suction and the liquid lines as well as the evaporators need to have correspondingly larger dimensions in order to keep the pressure losses as low as possible.
It is the object of the present invention to indicate a refrigeration circuit as set out at the beginning as well as a method of operating a refrigeration circuit, in which the disadvantages mentioned are avoided.
To meet this object, there is suggested a refrigeration circuit which distinguishes itself in that an intermediate relief device is arranged between the condenser and the collecting container.
As regards the method, the underlying object is met in that pressure relief of the refrigerant to an (intermediate) pressure of 5 to 40 bar is effected in the intermediate relief device arranged between condenser and collecting container.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a prior art refrigerating plant.
FIG. 2 is a schematic view of a refrigerating plant according to the present disclosure.
FIG. 3 is a schematic view of a second refrigerating plant according to the present disclosure.
FIG. 4 is a partial schematic view of a third refrigerating plant according to the present disclosure.



DETAILED DESCRIPTION
The refrigeration circuit according to the invention, the inventive method of operating a refrigeration circuit as well as further developments thereof will be elucidated in more detail hereinafter by way of the embodiments shown in FIGS. 2 to 4.
In this context, FIG. 2 illustrates a composite refrigeration plant in which a possible embodiment of the refrigeration circuit according to the invention is realized. In the following, a method shall be described in which halogenated fluorohydrocarbon(s), fluorohydrocarbon(s) or CO2 may be used as refrigerants.
The refrigerant that is compressed in compressor unit 6 to a pressure between 10 and 120 bar is fed via pressure line 7 to condenser or gas cooler 1 and is condensed or cooled in the same by way of external air. Via lines 2, 2′ and 2′′, the refrigerant is passed to refrigerant collector 3; however, according to the invention, the refrigerant now is pressure-relieved in intermediate relief device a to an intermediate pressure of 5 to 40 bar. This intermediate pressure relief provides for the advantage that the downstream tubing network as well as the collector 3 need to be designed for a lower pressure level only.
The pressure to which the refrigerant is relieved in said intermediate relief device a preferably is selected such that it is still underneath the lowest condensing or liquefying pressure to be expected.
In accordance with an advantageous development of the refrigeration circuit according to the invention, pressure line 7 is connected or adapted to be connected to collecting container 3, preferably to the gas space of the same. This connection between pressure line 7 and collecting container 3 may be effected e.g. via a connecting line 17 having a relief valve h disposed therein.
According to an advantageous development of the refrigeration circuit of the invention, pressure line 7 is connected or connectable to the line or line sections 2 and 2′, 2′′, respectively, connecting the condenser 1 and the collecting container 3. This connection between pressure line 7 and line 2 or 2′, 2′′, respectively, may be effected e.g. via the connecting line 18 shown in broken outline and having a valve i arranged therein.
According to an advantageous development of the refrigeration circuit of the invention, the collecting container 3, preferably the gas space thereof, is connected or connectable to the input of the compressor unit 6.
This connection between collecting container 3 and input of the compressor unit 6 may be established, for example, via a connecting line 12 which, as shown in FIG. 2, opens into suction line 11.
Via the relief valve e provided in line 12 as well as the relief valve h provided in line 17 or the valve i provided in line 18, the intermediate pressure chosen now may be kept constant for all operating conditions. However, it is also possible to provide for regulation such that a constant differential value with respect to the suction pressure is present. The effect achieved thereby is that the amount of throttling vapour at the evaporators is comparatively low, which has the result that the dimensioning of the liquid and suction lines may be correspondingly smaller. This holds also for the condensate line, as it is now no longer necessary that gaseous constituent parts flow back to the condenser 1 via the same. Thus, another effect achieved by the invention is that the required refrigerant filling amount may be reduced by up to approx. 30 percent.
Refrigerant is withdrawn from collector 3 via suction line 4 and is supplied to the refrigerant consumers and to the heat exchangers E2 and E3 of the same, respectively. Connected upstream thereof, there is a relief valve b and c, respectively, in which relief of the refrigerant flowing into the cold consumers takes place. The refrigerant evaporated in the cold consumers E2 and E3 subsequently is again fed via suction line 5 to compressor unit 6 or is sucked from the evaporators E2 and E3 via said suction line 5.
Part of the refrigerant withdrawn from collector 3 via line 4 is fed via line 8 to one or more deep-freeze consumers—illustrated in the form of heat exchanger E4—which also has a relief valve d connected upstream thereof. This partial refrigerant flow, after evaporation in the heat exchanger or cold consumer E4, is fed via suction line 9 to compressor unit 10 and compressed in the same to the input pressure of the compressor unit 6. The thus compressed partial refrigerant flow then is fed via line 11 to the input side of compressor unit 6.
As a further development of the invention, it is suggested that—as illustrated in FIG. 2—the collecting container 3 may have a heat transfer means E1 connected upstream thereof.
The heat transfer means E1 preferably is connected or connectable on the input side to the output of condenser 1.
As shown in FIG. 2, a partial flow of the condensed or cooled refrigerant can be withdrawn via a line 13, having a relief valve f arranged therein, from the condenser or gas cooler 1 and line 2, respectively, and can be evaporated in heat transfer means E1 by way of the refrigerant to be cooled which is fed to heat transfer means E1 via line 2′. The evaporated partial refrigerant flow then is fed via line 14 to a compressor 6′ which is associated with the compressor unit 6 described hereinbefore and which preferably performs sucking-on at a higher pressure level; in the same, the evaporated partial refrigerant flow then is compressed to the desired final pressure of compressor unit 6.
As an alternative to the afore-mentioned (additional) compressor 6′, it is also possible to make use of multi-cylinder compressors and to then deliver the amount of throttling vapour to be sucked off, to one or several cylinders of each compressor at a higher pressure level.
By way of the heat transfer means E1, the refrigerant flow to be pressure-relieved in the intermediate relief device a preferably is cooled to such an extent that the amount of throttling vapour of the pressure-relieved refrigerant is minimized.
As an alternative or in addition thereto, the amounts of throttling vapour arising in collector 3 may also be sucked off at a higher pressure level via line 12 as well as line 15 shown in broken outline by means of compressor 6′.
FIG. 3 illustrates an embodiment of the refrigeration circuit according to the invention and of the inventive method of operating a refrigeration circuit in which the refrigerant withdrawn from collecting container 3 via line 4 is subjected to sub-cooling in heat exchanger E5.
In this context, sub-cooling—in accordance with an advantageous development of the invention—takes place in heat exchange with the flash gas withdrawn from collecting container 3 via line 12.
Liquid lines, such as e.g. line 4 shown in FIGS. 2 and 3, having a temperature level below ambient temperature are subject to heat radiation. The result of the latter is that the refrigerant flowing within the liquid line is partially evaporated, thus causing undesirable amounts of vapour to be formed. In order to prevent this, refrigerants so far are sub-cooled either by expansion of a partial flow of the refrigerant and subsequent evaporation or by an internal thermal transfer with respect to a suction gas flow which is thereby superheated.
In the refrigeration circuit according to the invention or the method according to the invention, the temperature distance between suction and liquid line and the refrigerant circulating therein, respectively, possibly may be too small for realizing an internal thermal transfer for the required sub-cooling of the refrigerant flowing in the liquid line.
Thus, it is suggested according to a further development of the invention—as already pointed out—that the refrigerant withdrawn from collecting container 3 via line 4 be sub-cooled in heat exchanger or sub-cooler E5 with respect to the flash gas from collecting container 3 via line 12, which is pressure-relieved or flash-relieved in valve e. After passage through the heat exchanger or sub-cooler E5, the pressure-relieved refrigerant that is superheated in heat exchanger E5 is fed via line sections 12′ and 11 to the input of compressor unit 6. Due to superheating of the flash gas flow withdrawn from collecting container 3 via line 12, sufficient sub-cooling of the refrigerant flowing in line 4 is achieved in said line 4; such sub-cooling of the refrigerant enhances the regulating operation of the relief or injection valves b, c and d connected upstream of the evaporators E2, E3 and E4.
Liquid droplets that are not deposited from the collecting container 3 via line 12 due to too small dimensioning and/or excessive filling of the collecting container 3, and are carried along in the flash gas, will be evaporated at the latest in the heat exchanger/sub-cooler E5. The process described thus provides the additional advantage that the operational safety of the compressors or the compressor unit 6 is enhanced due to safe superheating of the flash gas flow.
FIG. 4 illustrates an additional development of the refrigeration circuit and the method of operating a refrigeration circuit according to the invention. For the sake of better visibility,
FIG. 4 shows only sections of the refrigerant circuit according to the invention as shown in FIGS. 2 and 3.
As a further development of the inventive method of operating a refrigeration circuit, it suggested that at least a partial flow of the flash gas withdrawn from the collecting container is subject to overheating at least temporarily at least with respect to a partial flow of the compressed refrigerant.
FIG. 4 illustrates a possible development of the method according to the invention, in which a partial flow of the flash gas withdrawn from collecting container 3 via line 12 is at least temporarily supplied to a heat exchanger E6 via line 16 and is superheated in the same with respect to the refrigerant compressed in compressor unit 6.
In the process illustrated in FIG. 4, the flash gas flow to be superheated is superheated in heat exchanger E6 with respect to the entirety of the refrigerant flow compressed in compressor unit 6, which is fed via line 7 to the condenser or cooler that is not shown in FIG. 4.
Upon passage through the heat exchanger/superheater E6, the flash gas flow is fed via line 16′ to the input of compressor 6′ of compressor unit 6.
The process illustrated in FIG. 4 reliably ensures that liquid shares contained in the flash gas are evaporated without any doubt, which results in enhanced safety for the compressors or the compressor unit 6.

## Claims

1. A refrigeration circuit having a refrigerant circulating therein, said refrigeration circuit enabling a transcritical operation, said refrigeration circuit comprising, in the direction of flow: a condenser/gascooler (1); a collecting container (3); a relief device (b, c); an evaporator (E2, E3); and a compressor unit (6) compressing the refrigerant to a pressure between 10 and 120 bar, wherein: an intermediate relief device (a) is arranged between the condenser (1) and the collecting container (3), the intermediate relief device relieving downstream pressure to an intermediate pressure of 5-40 bar; a gas space of the collecting container (3) is connected or connectable (11, 12) to an input of the compressor unit (6); a relief valve (e) is in a connection line (11, 12) between the gas space of the collecting container (3) and the input of the compressor unit (6); a line (2) from the condenser/gascooler (1) divides into a first line section (2′) and into a second line section (13); in the second line section (13) a relief valve is arranged; the refrigerant in the second line section (13) is evaporated in the heat transfer means (E1) against the refrigerant in the first line section (2′); a pressure line (7) is connected or connectable to a line (2, 2′, 2′′) connecting the condenser/gascooler (1) and the collecting container (3); and a line (18) having a valve (i) provided therein connects a first line section (2′) after the heat transfer means (E1) with the pressure line (7) after the compressor unit (6).

2. The refrigeration circuit according to claim 1, wherein the refrigerant comprises CO2.

3. The refrigeration circuit according to claim 1, characterized in that a heat transfer means (E1) is connected upstream of the collecting container (3).

4. The refrigeration circuit according to claim 3, characterized in that the heat transfer means (E1) is connected or connectable (2, 13) on an input side to an output of the condenser/gascooler (1).

5. The refrigeration circuit according to claim 1, wherein the second line section (13, 14) after the heat transfer means (E1) is connected or connectable to an input of a compressor (6′) of the compressor unit (6).

6. The refrigeration circuit according to claim 1, wherein the gas space of the collecting container (3) is connected or connectable to an input of a compressor (6′) of the compressor unit (6).

7. The refrigeration circuit according to claim 1, wherein a pressure line (7) is connected or connectable directly to the collecting container (3).

8. The refrigeration circuit according to claim 1, wherein a relief valve (h) is in a line (17) connecting the pressure line (7) to the collecting container (3).

9. The refrigeration circuit according to claim 1, wherein a heat exchanger/subcooler (E5) is arranged between the collecting container (3) and the relief device (c, b, d).

10. The refrigeration circuit according to claim 9, wherein the heat exchanger/subcooler (E5) is connected or connectable (12) on an input side to the gas space of the collecting container (3).

11. The refrigeration circuit according to claim 9, wherein the liquid refrigerant is subcooled in the heat exchanger/subcooler (E5) with respect to the flash gas from the collecting container (3) which has been relieved by the valve (e).

12. The refrigeration circuit according to claim 1, wherein the refrigerant withdrawn from the collecting container (3) is fed via a line (8) to one or more deepfreeze consumers (E4) having a relief valve (d) connected upstream thereof.

13. The refrigeration circuit according to claim 1, wherein a second compressor unit (10) is provided which is supplied via a suction line (9) with refrigerant evaporated in a deep-freeze consumer (E4), wherein the refrigerant compressed in the compressor unit (10) is fed via a suction line (11) to the compressor unit (6).

14. Method for transcritical operation of the refrigeration circuit according claim 1, wherein:
the pressure relief of the refrigerant to an intermediate pressure of 5 to 40 bar is effected in the intermediate relief device (a) arranged between the condenser/gascooler (1) and the collecting container (3); and
the intermediate pressure is kept constant by means of the relief valve (e) in the connection line (11, 12) between the gas space of the collecting container (3) and the input of the compressor unit (6).

15. The method according to claim 14, characterized in that the refrigerant (2) is subjected to additional cooling (E1) prior to intermediate pressure-relief (a) of the same.

16. The method according to claim 15, characterized in that cooling (E1) of the refrigerant (2) is effected with respect to a partial flow of the refrigerant (13).

17. The method according to claim 14, characterized in that the refrigerant (4) withdrawn from the collecting container (3) is subjected to subcooling (E5).

18. The method according to claim 17, characterized in that subcooling (E5) of the refrigerant (4) withdrawn from the collecting container (3) is effected with respect to the flash gas (12) withdrawn from the collecting container (3).

19. The method according to claim 14, characterized in that at least a partial flow of the flash gas (12) withdrawn from the collecting container (3) is superheated (E6, E7) at least temporarily with respect to the compressed refrigerant (7).

20. The method according to claim 14, characterized in that the quantity of the flash gas sucked off at the intermediate pressure level is regulated by valves (g, x, y, z).

21. The method according to claim 14, characterized in that the intermediate pressure is regulated to a constant difference from the suction pressure by means of at least one valve (e, h, j).

22. A method for operation of the refrigeration circuit according to claim 1, wherein:
the condenser/gascooler (1) operates at a condensing or liquefying pressure;
the pressure relief of the refrigerant to an intermediate pressure of beneath a lowest expected said condensing or liquefying pressure is effected in the intermediate relief device (a) arranged between the condenser/gascooler (1) and the collecting container (3); and
the intermediate pressure is kept constant by means of the relief valve (e) in the connection line (11, 12) between the gas space of the collecting container (3) and the input of the compressor unit (6).

23. The refrigeration circuit of claim 1 wherein:
the compressor unit (6) is a single-stage compressor unit;
a pressure line (7) carries compressor refrigerant from the compressor unit (6) to the condenser/gascooler (1); and
a flash gas sucked off from the gas space of the collecting container is superheated in a heat exchanger (E6) against compressed refrigerant in the pressure line (7).

24. The refrigeration circuit of claim 1 wherein:
a pressure line (7) releases compressed refrigerant from the compressor unit (6) to the condenser/gascooler (1);
the pressure line (7) is connected or connectable to the gas space of the collecting container (3) via a connecting line (17) having an additional relief valve (h) therein or the pressure line (7) is connected or connectable via connecting line (18) having an additional valve (j) therein to a line connecting the condenser/gascooler (1) to the intermediate relief device (a); and
the additional relief valve (e) and the additional relief valve (h; j) allow to keep the intermediate pressure constant for all operating conditions.

25. The refrigeration circuit of claim 1 wherein:
the compressor unit (6) is a single-stage compressor unit; and
the connection line (11, 12) joins a compressor suction line (5) at a position upstream of the compressor unit (6).

26. The refrigeration circuit of claim 1 wherein:
the compressor unit (6) is a single-stage compressor unit;
a heat exchanger/subcooler (E5) is between the collecting container (3) and the expansion device (B, C);
a subcooling of the refrigerant sucked off from the container (3) is affected in the heat exchanger/subcooler (E5) against the flash gas coming from the collecting container (3) over the connection line (11, 12); and
the flash gas is expanded by the expansion valve (E).

27. A refrigeration circuit having a refrigerant circulating therein, said refrigeration circuit enabling a transcritical operation, said refrigeration circuit comprising, in the direction of flow: a condenser/gascooler (1); a collecting container (3); a relief device (b, c); an evaporator (E2, E3); and a compressor unit (6), wherein: an intermediate relief device (a) is between the condenser (1) and the collecting container (3); the circuit further includes at least one freezing consumer (E4), a relief valve (d) upstream of the at least one freezing consumer, and a further compressor unit (10); in operation, refrigerant is sucked off from the collecting container (3), is led to the evaporators (E2, E3) and is led, after evaporation in the evaporators (E2, E3) to the compressor unit (6); a partial flow of refrigerant is led directly from the collecting container (3) to the relief valve (d), the at least one freezing consumer (E4) and then after evaporation in the at least one freezing consumer, to the further compressor unit (10); and in operation, the further compressor unit compresses the refrigerant partial flow to the input pressure of the compressor unit (6) to pass the partial flow to the input of the compressor unit (6); a heat transfer means (E6) is provided, in which a flash gas withdrawn from the collecting container (3) is superheated with respect to compressed refrigerant in a pressure line (7); the flashgas upon passage through the heat transfer means (E6) is fed via a line (16′) to an input of a compressor (6′) of the compressor unit (6); and at least one valve (g; x, y, z) is provided in the line (16, 16′).