Pressure relief for refrigeration system

Abstract

The present invention relates to a refrigeration system, such as one that can be used, for example, as an air conditioning system or to supply freezers in a supermarket. More specifically, it concerns the refrigerant flow in such a refrigeration system and a pressure relief system for the refrigerant.In particular, it concerns a refrigeration system (10) which extends in an interior region and an exterior region and which carries a refrigerant, wherein the refrigerant is under pressure in regions of the refrigeration system (10) and wherein at least one pressure relief valve (32, 34, 36, 38) is provided in the interior region, through which refrigerant can escape for pressure relief, and wherein a blow-off line (42, 44, 46, 48, 50) is provided which can receive refrigerant discharged from the pressure relief valve (32, 34, 36, 38) and leads from the interior region to the exterior region, characterized in that a refrigerant outlet and a pressure-controlled closing device (52) for the refrigerant outlet are provided in the exterior region on this blow-off line (42, 44, 46, 48, 50).

Description

Field of the invention

[0001] The present invention relates to a refrigeration system, such as one that can be used, for example, as an air conditioning system or to supply freezers in a supermarket. More specifically, it concerns the refrigerant flow in such a refrigeration system and a pressure relief system for the refrigerant. Background of the invention

[0002] US patent application 2012 / 0216558 A1 discloses a compact air conditioner that can be mounted close to a wall. The air conditioner has inlets and outlets that can be routed directly through openings in the wall.

[0003] Since this is a simple, compact device, pressure relief valves are not provided, at least not in large numbers, so that no more complex questions arise for the discharge of a refrigerant from such pressure relief devices.

[0004] German Patent Application DE 10 2007 043 162 A1 discloses an air conditioning system that is said to allow refrigerant transfer. Using an overflow valve, refrigerant can be drained from the high-pressure side of the system into a container on the low-pressure side. This prevents refrigerant loss.

[0005] This interesting approach is also not suitable for systems where refrigerant must be released under high pressure or where a large number of pressure relief valves must be arranged sensibly.

[0006] The present invention aims to provide an improved refrigeration system that is also suitable for cooling large rooms and units. The system is particularly suitable for operation with carbon dioxide as a refrigerant and also allows for safe pressure relief for this refrigerant.

[0007] This object is achieved by a refrigeration system according to claim 1. Advantageous further developments are specified in the subclaims. Further description

[0008] The present invention relates to a refrigeration system. This should generally be understood to mean a system that can absorb or release heat energy. Such systems typically operate with a refrigerant. By changing the pressure and / or temperature of the refrigerant, heat can be absorbed from the environment or released to the environment. The system is referred to herein as a refrigeration system because it is generally used primarily to cool an interior space or a unit housed there. It could therefore also be referred to as an air conditioning system. However, such systems are generally also suitable for heating a room. The term refrigeration system is therefore not intended to be limiting. It is even possible for such systems to be used primarily to heat rooms. They are then frequently referred to as heat pumps.

[0009] An air conditioning system uses a refrigerant circuit to control the temperature in an interior space. Its basic components are the refrigerant, an evaporator, and a condenser. Warm air is drawn from an interior space to be cooled and cooled. The refrigerant is evaporated in the evaporator. The refrigerant, now in gaseous form, is transported from the interior to an exterior space. There, it is compressed by a condenser (also called a condenser), returning it to a liquid state and releasing the absorbed heat.

[0010] It is typical for an air conditioning system or a refrigeration system in general, and also part of the present invention, that the refrigeration system extends into an indoor and an outdoor area. The refrigeration system should also contain a refrigerant. This refrigerant is pressurized, at least in certain areas of the refrigeration system.

[0011] There are several common refrigerants, typically hydrocarbons, often with one, two, or three carbon atoms. One common refrigerant is chlorodifluoromethane, typically referred to by refrigeration experts as R-22. Due to its poor environmental properties, it is rarely used these days. Common refrigerants are hydrofluorocarbons, such as R-410A or R-1234yf. R-404A, a zeotropic mixture of hydrocarbons, is also frequently used for cold storage. More environmentally friendly and increasingly widespread refrigerants are carbon dioxide (R-744) and propane (R-290).

[0012] Pressure relief valves are usually provided on refrigeration systems. During normal operation, no refrigerant should escape through the pressure relief valve, but these valves serve an important function as safety devices in case excessive pressures arise during abnormal operation. The pressure relief valves can be individually adjusted to the system and the refrigerant, so that pressure is reduced from a predetermined or selectable pressure. For this purpose, refrigerant is released through the valve, so that less refrigerant flows in the area connected to the valve.

[0013] Since not all refrigerants are environmentally friendly or harmless to health, the release of refrigerant can be problematic, especially indoors. Therefore, the invention provides for the discharge of refrigerant through a vent line, and in particular, for the discharge from the indoor area to the outdoor area.

[0014] Within the scope of the present invention, it is proposed that such a blow-off line is connected to a refrigerant outlet in the external area and that a pressure-controlled closing device for the refrigerant outlet is provided there.

[0015] The provision of such a blow-off line generally allows for the safe operation of refrigeration systems, as it allows the refrigerant to be removed from the interior. Even if the refrigerant is chemically non-toxic or problematic, the very low temperature of the refrigerant, the high pressure, or a temporary release of large quantities of refrigerant could cause damage, perhaps even personal injury, indoors.

[0016] However, these clear advantages of a blow-off line leading to the outside are accompanied by several disadvantages. First, a sufficient number of blow-off lines must be provided. This requires considerable effort, especially if multiple pressure relief valves are installed in a refrigeration system. In addition to the costs, the design of a system can be challenging if the space available in a particular area is limited.

[0017] Furthermore, the refrigerant outlet located outside means the system is open to the outside. Contamination can therefore potentially enter through the refrigerant outlet. Depending on the location and type of system, contamination may also be caused by natural contamination, such as leaves, organic particles, or even insects.

[0018] These problems are avoided or reduced within the scope of the present invention by a suitable closing device. However, such a closing device must allow for the safe discharge of even large quantities of refrigerant. In particular, it must be considered that very cold refrigerant, such as completely or partially solid refrigerant, such as icy refrigerant, must be safely discharged.

[0019] Within the scope of the present invention, it was recognized that a pressure-controlled closing device is very advantageous. The closing device is intended to open in response to a pressure build-up in the blow-off line (by pressure build-up we generally mean a force build-up). If such pressure is not present, the closing device remains closed. The mechanical design of the closing device can be used to define a threshold pressure (or a threshold force) above which the closing device opens. It can be particularly expedient if the closing device is at least partially controlled by gravity. The always and reliably present gravity can then be used by appropriate mechanical precautions to hold the closing device in the closed position. The closing device could, for example, comprise a closing flap.This closing flap can be oriented so that gravity pushes it into the closed position.

[0020] Alternatively or additionally, weights can be provided. Alternatively or additionally, a spring force or other elastic force can also be provided to hold the closing device in the closed position. The closed position is thus essentially the pressureless position, which is abandoned when the pressure in the relief line rises above a threshold value.

[0021] It is particularly advantageous if the entire cross-section of the blow-off line can be opened (in the case of a round line, the entire diameter). For this purpose, it is advantageous to provide the closing device at the end of a blow-off line or outlet line. The closing device can form an end piece for such a line, i.e. be connected to the end of the line and form the last component of a line path. A transition for the flow between the line and the closing device that is free of projections and recesses (and thus grooves and edges or smooth) is advantageous. Any closing flap or other closing device can then be positioned completely outside the blow-off line in the open position. If, for example, a shut-off valve, perhaps as a rotary valve, is provided in the line run, the valve will generally reduce the available line diameter even in the open position.

[0022] A refrigeration system that has a large number of pressure relief valves is particularly useful. A large number here means two or more. It is useful if the large number of pressure relief valves are connected to the blow-off line outside. A large number of supply lines can be used for this purpose. It is conceivable for all pressure relief valves to be connected to their own blow-off line leading outside. These blow-off lines can be connected there. However, it is generally not a problem if refrigerant released from different pressure relief valves mixes. It can therefore be useful to keep the blow-off lines assigned to a valve as short as possible.

[0023] It is advisable to design at least sections of the blow-off lines to be flexible. For example, a flexible hose material can be used, such as one made of plastic. Such a hose material can be suitably covered. In a spatially confined situation, it is difficult to integrate a large number of blow-off lines into a system. A flexible material allows for better-adapted line routing. Furthermore, a flexible material can facilitate the mechanical decoupling of vibrating components of the refrigeration system. Such components are motor-driven components, in particular the compressors. It is also advisable to connect a flexible line section to a fixed line section.For example, flexible pipe sections could connect the pressure relief valves to the central outlet pipe, whereby the central outlet pipe can be rigid, for example made of a solid pipe.

[0024] It is therefore advantageous to route a central outlet line to the locking device. It is advisable to provide this central outlet line in the interior. The central outlet line can thus extend from the interior to the exterior.

[0025] The term "outlet line" is used here essentially interchangeably with the term "blow-off line." The outlet line is typically a section of the blow-off line or a separate line component that runs at least partially outside. Typically, several blow-off lines are routed from different pressure relief valves to one outlet line. A closing device according to the invention can be provided on several outlet lines; however, it is usually sufficient to provide one closing device for more than one blow-off line or even for all blow-off lines (then usually at the end of a central outlet line), since the closing device then operates reliably.

[0026] It is advisable to connect pressure relief valves at different temperatures and / or different pressures together to the central outlet line.

[0027] It is quite useful if pressure relief of more than 10 bar can take place at individual pressure relief valves.

[0028] It is possible that an iso-enthalpic expansion takes place at at least one pressure relief valve of the refrigeration system. Within the scope of the invention, it is also possible that an expansion takes place into the fixed region of the pressure-enthalpy curve.

[0029] During the described expansions, especially at very low temperatures, the state of the coolant can change. In particular, the coolant can transform into a solid state. It is especially critical that cold solid particles are vented to the outside, because even with a non-toxic refrigerant, the release of cold solid particles can cause damage indoors. Carbon dioxide, in particular, poses a risk of suffocation because it can displace oxygen, so special caution is required when using this refrigerant.

[0030] These particles also pose a particular problem for the closure device. Such particles can clog the closure device. This can lead to malfunctions, particularly when multiple pressure relief valves are connected to a central outlet line. Frozen coolant can clog the closure device, preventing liquid coolant from being released. This can also affect liquid coolant from other pressure relief valves. This can pose a safety risk. This can be avoided by using a pressure-controlled closure device, particularly a pressure-controlled closure device with a large diameter.

[0031] The present invention is particularly suitable for refrigeration systems in which a first temperature and a first pressure prevail at a first pressure relief valve and a second pressure and a second temperature prevail at a second pressure relief valve and in which the first pressure is different from the second pressure and / or the first temperature is different from the second temperature

[0032] The present invention is therefore also well suited for refrigeration systems in which an isoenthalpic expansion of the refrigerant through at least one aggregate state takes place at at least one pressure relief valve and in which an expansion of the refrigerant takes place at a pressure relief valve in such a way that the refrigerant assumes a solid aggregate state

[0033] The present invention is particularly suitable for refrigeration systems that use carbon dioxide as a refrigerant. Carbon dioxide readily forms dry ice in a temperature range typical for refrigeration systems. This dry ice can clog a closing device. However, the closing device according to the invention is not blocked at all or only slightly by dry ice, thus allowing particularly safe operation of the refrigeration system.

[0034] Further features, as well as advantages of the invention, will become apparent from the following drawings and the accompanying description. In the figures and the accompanying descriptions, features of the invention are described in combination. However, these features may also be encompassed by an inventive subject matter in other combinations. Each disclosed feature is therefore also to be considered as disclosed in technically expedient combinations with other features. Some of the figures are slightly simplified and schematic. Fig. 1 shows a schematic view of an exemplary refrigeration system according to the present invention. Fig. 2 shows a typical enthalpy and pressure diagram for a refrigeration system according to the present invention. Possible pressure relief situations are illustrated in the diagram.

[0035] Fig. 1shows a schematic overview of a refrigeration system 10 according to the invention. This comprises a gas cooler 12, which is typically provided in the outer region of the refrigeration system. From the gas cooler, refrigerant flows to the high-pressure valve 14 (the lines for the refrigerant are not designated in more detail here). The refrigerant flows on into the medium-pressure vessel 16. There, liquid and gaseous refrigerant are separated from one another. Gaseous refrigerant is at least partially discharged via the medium-pressure valve 18. From the medium-pressure vessel, refrigerant is passed on to the injection valve 20. From there, it is passed on to the normal cooling evaporator 22. Cooling takes place in this area; normal cooling should describe cooling to a first temperature range, for example, this can be a temperature range of around +8°C, as is used in refrigerators.

[0036] Additional refrigerant is supplied from the medium-pressure vessel 16 via the injection valve 24 to the deep-freeze evaporator 26. Cooling in the area of ​​the deep-freeze evaporator 26 can be used, for example, to cool freezers, thus having a target temperature range of approximately -20°C.

[0037] Refrigerant is supplied from the low-temperature evaporator 26 to the low-temperature compressor 28. This partially compresses the refrigerant before it is supplied to the medium-temperature compressor 30. The medium-temperature compressor also receives refrigerant discharged from the medium-temperature evaporator 22.

[0038] Furthermore, on the low-pressure side of the medium-temperature refrigeration compressor 30, refrigerant is taken up by the medium-pressure valve 18.

[0039] Refrigerant is then returned to the gas cooler 12 on the pressure side of the medium temperature compressor 30.

[0040] This results in a typical refrigeration circuit of a refrigeration system 10. The refrigeration system 10 can also be designed in a different way, for example, as a refrigeration system with only one evaporator. As explained, the refrigeration system can also be used for other purposes, for example, as a heat pump.

[0041] A series of pressure relief valves is provided for the safe operation of the refrigeration system shown. In particular, pressure relief valve 32 is provided on the medium-pressure vessel 16. Furthermore, pressure relief valve 34 is provided in the low-temperature refrigeration area. Pressure relief valve 36 is provided in the medium-temperature refrigeration area. Pressure relief valve 38 is provided on the pressure side of compressor 30.

[0042] Each of these pressure relief valves is connected to its own blow-off line. These form a pressure relief network 40. These blow-off lines can be very short in individual cases. Blow-off line 42 is provided for valve 32, blow-off line 44 for valve 34, blow-off line 46 for valve 36, and blow-off line 48 for valve 38. These blow-off lines are combined into a common line. This central blow-off line or outlet line 50 can be routed from the interior to the exterior. It can also run exclusively outdoors. The closing device 52 is connected to the individual blow-off lines and thus to the pressure relief valves via this outlet line 50.

[0043] Fig. 2shows a phase diagram for a refrigerant such as can be used in a refrigeration system according to the present invention. The refrigerant, whose phase diagram is shown in the form of a pressure-enthalpy diagram, is carbon dioxide or—in refrigeration terms—R744.

[0044] In the diagram, the pressure P in bar is plotted on the vertical axis, and the enthalpy value H in kilojoules per kilogram is plotted on the horizontal axis. Enthalpy describes the energetic system state of the refrigerant enclosed in the refrigeration system. Heat input into the system leads to an increase in enthalpy, and heat output from the system leads to a decrease in enthalpy.

[0045] Diagram 60 shows lines of constant temperature, so-called isotherms 62. In the center of the diagram is a dividing line that roughly describes a hill. This dividing line is formed by the boiling point line 64 and the dew point line 66.

[0046] To the left of the boiling point line 64, i.e. in a range of lower enthalpy values, the refrigerant is in the liquid phase, for example in the range 68. To the right of the boiling point line 66, i.e. in a range of high enthalpy values, the refrigerant is in the gaseous phase, for example in the range 70.

[0047] Within the region 72 enclosed by the boiling point curve 64 and the dew point curve 66, i.e., almost the entire area within the hill, the refrigerant exists partly in the liquid and partly in the gaseous phase. This region is therefore also referred to as the two-phase region 72.

[0048] At the lower edge of the two-phase region 72 is region 74, which includes a region of relatively low pressures down to approximately 5 bar. In this region, carbon dioxide forms dry ice. This region is of particular relevance to the present invention, as dry ice can obstruct or clog inappropriately designed pressure relief devices.

[0049] The diagram shows some typical refrigerant state transitions. Since pressure reduction occurs without the addition or removal of heat energy during pressure release, isenthalpic transitions, i.e., transitions along vertical lines, are to be expected.

[0050] These are used for pressure relief at various valves in the Fig. 1This is to be expected from the system shown in the example. Line 76 describes a first pressure relief transition. During this transition, the refrigerant changes from a pressure of approximately 40 bar to a pressureless state. The pressureless state is understood to be atmospheric pressure, i.e., approximately 1 bar.

[0051] Such a pressure relief transition could occur at the pressure relief valve 32 of the medium-pressure vessel. During normal operation, the refrigerant would be present there in gaseous or wet vapor form. A significant pressure reduction would result in a transition to a more liquid phase. Upon complete pressure relief down to 1 bar, the line moves into the dry ice region 74. With this pressure relief at valve 32, dry ice formation would be expected.

[0052] Line 78 represents a second pressure relief transition. Such a pressure relief transition would be typical for pressure relief valve 36 in the normal cooling area. Along this line, similar coolant phases would be expected as along line 76, and dry ice formation would again be likely.

[0053] Line 80 represents a third pressure relief transition. Such a pressure relief transition could occur at the pressure relief valve 34 for the deep freeze. During this pressure relief, the coolant would be predominantly in gaseous form.

[0054] In typical systems, a pressure relief transition also occurs starting from very high pressures; one such transition is shown here as an example of a fourth pressure relief transition 82. It describes the conditions at the pressure relief valve 38 on the pressure side of the compressor. Here, a large pressure range is traversed, with pressure relief taking place over almost 100 bar. Given the position of the transition line 82 in region 70 of the gaseous phase of the coolant, no dry ice or liquid coolant is to be expected here. However, due to the need to relieve pressure quickly and strongly starting from a high pressure, this pressure relief must be able to proceed unhindered by disruptive liquid or even solid phase components.

[0055] The devices provided within the scope of the present invention also enable the inclusion of a pressure relief valve in a system with several pressure relief valves, which, for example, causes a pressure drop of more than 100 bar.

[0056] It is therefore crucial that the entire discharge system, including the blow-off lines and the closing device, works reliably and allows rapid and safe pressure relief even if dry ice forms on all or just some of the connected pressure relief valves or if a different phase mixture of the refrigerant occurs.

[0057] It is precisely in this respect that the present invention proves to be useful. List of reference symbols 10 Refrigeration system 12 Gas cooler (outdoor unit) 14 High pressure valve 16 Medium-pressure vessels 18 Medium pressure valve 20 Injector 22 Medium temperature evaporator 24 Injector 26 freezer evaporator, 28 Freezer compressor 30 Medium temperature compressor 32 Pressure relief valve medium pressure vessel 34 Pressure relief valve for deep freezing 36 Pressure relief valve normal cooling 38 Pressure relief valve for medium temperature compressor (pressure side) 40 Pressure relief network 42 Blow-off line for valve 32, 44 Blow-off line for valve 34 46 Blow-off line for valve 38, 48 Blow-off line for valve 38 50 Outlet line 52 locking device 60 Pressure-enthalpy diagram 62 isotherm 64 boiling point 66 dew line 68 Liquid phase area 70 Gaseous phase region 72 Two-phase area 74 Area of ​​dry ice formation 78 First pressure relief transition, 78 Second pressure relief transition 80 Third pressure relief transition 82 Fourth pressure relief transition

Claims

1. Refrigeration system (10) which extends in an interior and an exterior area and which carries a refrigerant, wherein the refrigerant is under pressure in areas of the refrigeration system (10) and wherein at least one pressure relief valve (32, 34, 36, 38) is provided in the interior area through which refrigerant can escape for pressure relief, and wherein a blow-off line (42, 44, 46, 48, 50) is provided which can receive refrigerant released by the pressure relief valve (32, 34, 36, 38) and leads from the interior area to the exterior area, characterized in that a refrigerant outlet and a pressure-controlled closing device (52) for the refrigerant outlet are provided in the outer area of this blow-off line (42, 44, 46, 48, 50).

2. Refrigeration system (10) according to the preceding claim, which comprises at least two pressure relief valves (32, 34, 36, 38).

3. Refrigeration system (10) according to the preceding claim, in which a plurality of pressure relief valves (32, 34, 36, 38) are provided, in which furthermore each pressure relief valve is connected to a respective blow-off line and in which the blow-off lines are combined in a central outlet line (50).

4. Refrigeration system (10) according to one of the preceding claims, wherein at least a portion of the blow-off lines (42, 44, 46, 48, 50) is flexible.

5. Refrigeration system (10) according to claim 2, 3 or 4, in which a first temperature and a first pressure prevail at a first pressure relief valve and a second pressure and a second temperature prevail at a second pressure relief valve and in which the first pressure is different from the second pressure and / or the first temperature is different from the second temperature.

6. Refrigeration system (10) according to one of the preceding claims, wherein the closing device (52) is designed such that the opening of the entire cross-section of the blow-off line is possible.

7. Refrigeration system (10) according to one of the preceding claims, wherein the closing device (52) forms the end piece of a central outlet line (50).

8. Refrigeration system (10) according to one of the preceding claims, in which gravity is used as the adjusting force for the closing device.

9. Refrigeration system (10) according to one of the preceding claims, wherein the pressure-free position of the closing device is the closed position.

10. Refrigeration system (10) according to one of the preceding claims, wherein the closing device comprises a closing flap.

11. Refrigeration system (10) according to one of the preceding claims, in which a pressure relief of more than 10 bar takes place at at least one pressure relief valve (32, 34, 36, 38).

12. Refrigeration system (10) according to one of the preceding claims, wherein the pressure relief of the refrigerant leads to a temperature reduction of the refrigerant to negative temperatures.

13. Refrigeration system (10) according to one of the preceding claims, in which an isoenthalpic expansion of the refrigerant through at least one state of aggregation takes place at at least one pressure relief valve (32, 34, 36, 38).

14. Refrigeration system (10) according to one of the preceding claims, in which the refrigerant is expanded at at least one pressure relief valve (32, 34, 36, 38) in such a way that the refrigerant assumes a solid state of aggregation.

15. Refrigeration system (10) according to one of the preceding claims, wherein the refrigerant is carbon dioxide.

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