Cabin exhaust air assisted aircraft air conditioning system with a pneumatically driven ambient air compressor

Abstract

Aircraft air conditioning (10) with: - an ambient air line (12) through which ambient air can flow, which is connected to a mixer (14) of the aircraft air conditioning system (10) in order to supply ambient air to the mixer (14), - a cabin exhaust air duct (88) which can be connected to an aircraft cabin (16) and through which cabin exhaust air can flow, - a bleed air line (73) through which bleed air, which is bleeded by an engine (74) or an auxiliary engine, can flow, - an ambient air compressor (58) arranged in the ambient air line (12) for compressing the ambient air flowing through the ambient air line (12), - a refrigeration machine (17) comprising a refrigerant circuit (18) through which a refrigerant can flow and a refrigerant compressor (20) arranged in the refrigerant circuit (18), wherein the refrigerant circuit (18) is thermally coupled to the ambient air line (12) in order to transfer heat from the ambient air flowing through the ambient air line (12) to the refrigerant circulating in the refrigerant circuit (18) before the ambient air is fed into the mixer (14), - a turbine (60) coupled to the ambient air compressor (58) and adapted to drive the ambient air compressor (58), and - a control device (46) which is designed to control the operation of the aircraft air conditioning system (10) in such a way that, in a first operating state of the aircraft air conditioning system (10), ambient air from the ambient air line (12) is supplied to the turbine (60) and, in a second operating state of the aircraft air conditioning system (10), a mixture of bleed air from the bleed air line (73) and cabin exhaust air from the cabin exhaust air line (88) is supplied to the turbine (60), and that, after flowing through the turbine (60), turbine exhaust air flowing through a turbine exhaust air line (78) is guided into the mixer (14) of the aircraft air conditioning system (10) in the first operating state of the aircraft air conditioning system (10) and is discharged into an aircraft environment (15) in the second operating state of the aircraft air conditioning system (10).

Description

The invention relates to an aircraft air conditioning system and a method for operating an aircraft air conditioning system.An aircraft air conditioning system serves for setting and maintaining a desired pressure, a desired temperature and a desired air humidity in an aircraft cabin. In addition, the aircraft air conditioning system supplies sufficient fresh air into the aircraft cabin in order to ensure that a prescribed minimum proportion of fresh air is present in the aircraft cabin. EP 2 735 510 A1 and US 2014 / 0 144 163 A1 disclose an aircraft air conditioning system in which a refrigerating machine operated with a two-phase refrigerant is used to cool ambient air compressed by a multistage compressor. The refrigerating machine comprises a refrigerant circuit in which a compressor, a condenser, an expansion valve and an evaporator through which ambient air to be cooled flows are arranged. Bleed air taken from an engine or an auxiliary engine of the aircraft is used for driving the compressor of the refrigerating machine and for driving the multistage compressor for compressing the ambient air.EP 2 821 346 A1 relates to an aircraft air conditioning system having a cooling machine for cooling ambient air. In addition to ambient air, bleed air is supplied to the aircraft air conditioning system via a bleed air line, which bleed air is conducted via a bleed air turbine after flowing through a precooler, a cooler, a condenser and a water separator and before being supplied into a mixing chamber. The power take-off air turbine drives an ambient air compressor. The ambient air cooled by the refrigerating machine is conducted via an ambient air discharge line branch into a high-pressure region of a bleed air discharge line upstream of the turbine when the pressure of the ambient air exceeds a predetermined threshold value. In contrast, the ambient air cooled by the refrigerating machine is conducted via an ambient air discharge line branch into a low-pressure region of the bleed air discharge line downstream of the turbine when the pressure of the ambient air is lower than the predetermined threshold value. The mixture of ambient air and bleed air flowing through the bleed air discharge line downstream of the turbine is mixed with recirculation air from a recirculation air line in the mixing chamber.DE 27 15 090 A1 describes an aircraft air conditioning system in which bleed air taken from an aircraft engine is cooled by means of a heat exchanger arrangement arranged in a pipeline for drawing in fresh ambient air. After flowing through a first heat exchanger of the heat exchanger arrangement, the bleed air is supplied either to a turbine or to a compressor as a function of pressure. A recirculation line connected to an aircraft cabin is connectable to the compressor via a valve. Compressed air exiting the compressor is directed through a second heat exchanger of the heat exchanger arrangement and then fed to the turbine.US 2016 / 0 083 100 A1 discloses an aircraft air conditioning system comprising an ambient air supply line, the first end of which is connected to an ambient air inlet and the second end of which is connected to a mixer of the aircraft air conditioning system. A first compressor is disposed in the ambient air supply line and compresses the ambient air flowing through the ambient air supply line. A bleed turbine is driven by bleed flowing through a bleed supply line and is connected to the first compressor to drive it.The object of the invention is to provide an aircraft air conditioning system which enables energy-efficient air conditioning of an aircraft cabin. Furthermore, the object of the invention is to specify a method for operating an aircraft air conditioning system of this type.This object is achieved by an aircraft air conditioning system having the features of claim 1 and a method for operating an aircraft air conditioning system having the features of claim 12.An aircraft air conditioning system comprises an ambient air line through which ambient air can flow, which is connected to a mixer of the aircraft air conditioning system in order to supply ambient air taken from an aircraft environment to the mixer. The supply of ambient air into the ambient air line may be controlled by a valve arranged in the ambient air line. The mixer connected to the ambient air line can be a premixer or a main mixer of the aircraft air conditioning system, to which, in addition to the ambient air from the ambient air line, recirculation air discharged via a recirculation air line from an aircraft cabin to be air-conditioned by means of the aircraft air conditioning system can be supplied. In the mixer, the ambient air from the ambient air line is mixed with the recirculation air discharged from the aircraft cabin. The mixed air generated in the mixer is finally used for air conditioning the aircraft cabin.A cabin waste air line can be connected to the aircraft cabin to be air-conditioned by means of the aircraft air conditioning system and-just like the recirculation air line-cabin waste air discharged from the aircraft cabin can flow through it. Furthermore, the aircraft air conditioning system comprises a bleed air line through which bleed air can flow. The bleed air flowing through the bleed air line can be tapped from an engine or an auxiliary engine of an aircraft equipped with the aircraft air conditioning system. To control the flow of bleed air into the bleed air line, a corresponding control valve can be arranged in the bleed air line. The aircraft air conditioning system further comprises an ambient air compressor arranged in the ambient air line for compressing the ambient air flowing through the ambient air line.A refrigerating machine of the aircraft air-conditioning system comprises a refrigerant circuit through which a refrigerant can flow and a refrigerant compressor arranged in the refrigerant circuit. The refrigerant circuit is preferably thermally coupled to the ambient air line via a heat exchanger, which is designed, for example, in the form of an evaporator, in order to transfer heat from the ambient air flowing through the ambient air line to the refrigerant circulating in the refrigerant circuit before the ambient air is supplied to the mixer. In the aircraft air conditioning system, an air conditioning process consequently takes place, in which the ambient air is firstly compressed by the ambient air compressor and is subsequently cooled to a desired temperature by the transfer of heat to the refrigerant circulating in the refrigerant circuit of the refrigerating machine. By means of a corresponding pre-compression of the ambient air in the ambient air compressor, the efficiency of this air conditioning process can be controlled as required.The aircraft air conditioning system is further equipped with a turbine coupled to the ambient air compressor and configured to drive the ambient air compressor. A control device of the aircraft air conditioning system is configured to control the operation of the aircraft air conditioning system in such a way that ambient air from the ambient air line is supplied to the turbine in a first operating state of the aircraft air conditioning system and a mixture of bleed air from the bleed air line and cabin bleed air from the cabin bleed air line is supplied to the turbine in a second operating state of the aircraft air conditioning system. In the first operating state of the aircraft air conditioning system, the pressure of the pre-compressed ambient air is thus used to drive the turbine, as a result of which a portion of the energy used by the compression of the ambient air can be recovered.In the second operating state of the aircraft air conditioning system, on the other hand, the pressure of the exhaust air discharged from an aircraft cabin, which exceeds the ambient pressure outside the aircraft from a specific flight altitude during flight operation of an aircraft equipped with the aircraft air conditioning system, is used for energy recovery. The energy recovered from the pre-compressed ambient air or the cabin waste air is used to drive the ambient air compressor. This allows the bleed air requirement of the air conditioning system to be reduced. The engine or auxiliary engine providing the bleed air can accordingly be operated particularly energy-efficiently.The control device is preferably configured to control the operation of the aircraft air conditioning system in such a way that ambient air from the ambient air line is supplied to the turbine in ground operation of an aircraft equipped with the aircraft air conditioning system and a mixture of bleed air from the bleed air line and cabin bleed air from the cabin bleed air line is supplied to the turbine in flight operation of the aircraft equipped with the aircraft air conditioning system. During ground operation of the aircraft equipped with the aircraft air conditioning system, the ambient air is preferably compressed, when flowing through the ambient air compressor, to a pressure above the setpoint cabin pressure, which allows dehumidification of the ambient air and subsequent use of the ambient air for driving the turbine. The cooling of the ambient air is then effected both by the transfer of heat to the refrigerant circuit of the refrigerating machine and by the expansion of the ambient air in the turbine.In the flight mode of the aircraft equipped with the aircraft air conditioning system, on the other hand, the pressure of the exhaust air discharged from the aircraft cabin exceeds the ambient pressure outside the aircraft from a specific flight altitude (approximately 6000 m). As a result, in flight operation of the aircraft equipped with the aircraft air conditioning system, in particular from a flight altitude of 6000 m, in addition to bleed air, the cabin bleed air discharged from the aircraft cabin via the cabin bleed line can also be used to drive the turbine. As a result, energy recovery potentials can be optimally utilized both in ground operation and in flight operation of the aircraft.The turbine is preferably arranged in a turbine inlet line connected to an inlet of the turbine. In particular, the turbine can be arranged downstream of a water separator and / or downstream of a reheater in the turbine inlet air line. The term "downstream" here refers to the direction of flow of the ambient air through the turbine inlet air line in the first operating state of the aircraft air conditioning system. When flowing through the water separator, the ambient air to be supplied to the turbine in the first operating state of the aircraft air conditioning system can be dehumidified to such an extent that it is ensured that not too much moisture is supplied to the mixer and consequently to the aircraft cabin to be air-conditioned.The reheater arranged in the turbine inlet air line serves in particular to heat the ambient air flowing through the turbine inlet air line in the first operating state of the aircraft air conditioning system before it is supplied into the turbine and in particular establishes a thermal coupling between the turbine inlet air line and a section of the ambient air line situated downstream of the ambient air compressor. As used herein, the term "downstream" refers to the direction of flow of ambient air through the ambient air conduit. As a result, the reheater brings the warm ambient air flowing through the ambient air line into thermal contact with the ambient air flowing through the turbine inlet air line after being compressed in the ambient air compressor before being supplied into the turbine. Water drops remaining in the ambient air stream can be vaporized in the reheater to protect the turbine from damage from drop impact or cavitation. Further, the reheater increases the output of the turbine.In a preferred embodiment of the aircraft air conditioning system, the ambient air line opens into the turbine inlet air line, in particular upstream of the water separator. This arrangement ensures that ambient air flowing through the ambient air line is dehumidified in the water separator before being fed into the turbine. The bleed air line, on the other hand, preferably opens into the turbine feed air line downstream of the reheater. The air under pressure flowing through the bleed line is drier and therefore does not have to be conducted through the water separator.The cabin exhaust line can open into the exhaust line upstream of a mouth point of the exhaust line into the turbine intake line. Such a configuration makes it possible for the cabin waste air flowing through the cabin waste air line to mix with the waste air flowing through the waste air line before it is fed into the turbine. The cabin waste air is also drier than the ambient air flowing through the turbine inlet air line in the first operating state of the aircraft air conditioning system, so that dehumidifying the cabin waste air can likewise be dispensed with.The aircraft air conditioning system preferably further comprises an ambient air bypass line connectable to the ambient air line. The ambient air bypass line may be configured to direct ambient air flowing through the ambient air line past the turbine into the mixer. For example, the ambient air bypass line can be connectable to the ambient air line in the region of a point of opening of the ambient air line into the turbine inlet air line, so that the ambient air flowing through the ambient air line can be selectively conducted either into the turbine inlet air line or the ambient air bypass line.In principle, the aircraft air conditioning system can comprise only one ambient air compressor. In a preferred embodiment of the aircraft air conditioning system, however, the ambient air compression takes place in two stages, so that a further ambient air compressor is connected upstream of the ambient air compressor. The further ambient air compressor may be coupled to a further turbine driving the further ambient air compressor. To drive the further turbine, bleed air flowing through the bleed line is preferably supplied to the further turbine. The operation of the further turbine is preferably controlled by the control device of the aircraft air conditioning system in such a way that the bleed air flowing through the bleed air line is expanded to the cabin pressure level when flowing through the further turbine in the second operating state of the aircraft air conditioning system, i.e. in flight operation of an aircraft equipped with the aircraft air conditioning system. As a result, the bleed air can be mixed optimally with the cabin exhaust air from the cabin exhaust line before it is supplied into the turbine.In flight operation, in particular in cruise operation, of an aircraft equipped with the aircraft air conditioning system, dehumidifying the ambient air which is very dry at the cruise altitude of the aircraft prior to its supply into the aircraft cabin is not necessary. Accordingly, the water separator, the reheater and the turbine may be bypassed and ambient air from the ambient air line may be directed directly into the mixer of the aircraft air conditioning system. The cooling of the ambient air is then effected exclusively by the transfer of heat to the refrigerant circuit of the refrigerating machine.In a preferred embodiment, the aircraft air conditioning system further comprises a first regulating valve arrangement for controlling the supply of ambient air from the ambient air line into the turbine inlet air line or the ambient air bypass line. The first control valve arrangement may comprise a control valve arranged in the turbine inlet air line and a control valve arranged in the bypass ambient air line. Alternatively, however, the first control valve arrangement can also be designed in the form of a 3-way valve arrangement which is arranged in the region of a connection point of the ambient air line to the turbine inlet air line and the ambient air bypass line. The control device is preferably configured to control the operation of the first control valve arrangement such that the ambient air flowing through the ambient air line is conducted into the turbine inlet air line in the first operating state of the aircraft air conditioning system and into the ambient air bypass line in the second operating state of the aircraft air conditioning system.The aircraft aircraft aircraft installation preferably further comprises a turbine exhaust line connected to an outlet of the turbine. The turbine exhaust line may have a first turbine exhaust line branch and a second turbine exhaust line branch. Preferably, the turbine exhaust line branches downstream of the turbine into the first turbine exhaust line branch and the second turbine exhaust line branch. As used herein, the term "downstream" refers to the direction of flow of the turbine exhaust exiting the outlet of the turbine through the turbine exhaust duct. The first turbine exhaust line branch is preferably connected to the mixer of the aircraft air conditioning system and can in particular open directly into the mixer.The second turbine exhaust line branch, on the other hand, can be connected to the aircraft environment, so that turbine exhaust air can be discharged into the aircraft environment via the second turbine exhaust line branch. For example, the second turbine exhaust air line branch can open into a ram air channel. A condenser of the refrigerating machine and / or at least one precooler can be arranged in the ram air duct, for example. The turbine exhaust air conducted into the ram air duct can be used for cooling the condenser and / or the at least one precooler. This can reduce the ram air requirement of the aircraft air conditioning system and consequently the aerodynamic resistance caused by the supply of ram air into the aircraft air conditioning system. This enables a reduction in the fuel consumption of the aircraft.The aircraft air conditioning system preferably further comprises a second control valve arrangement for controlling the supply of turbine waste air into the first turbine waste air line branch and the second turbine waste air line branch, respectively. The second control valve arrangement may comprise a control valve arranged in the first turbine exhaust line branch and a control valve arranged in the second turbine exhaust line branch. Alternatively, however, the second control valve arrangement can also be designed in the form of a 3-way valve arrangement which is arranged in the region of a branching point of the turbine exhaust line into the first turbine exhaust line branch and the second turbine exhaust line branch in the turbine exhaust line.The control device is configured to control the operation of the aircraft air conditioning system and in particular the operation of the second control valve arrangement such that the turbine exhaust air flowing through the turbine exhaust air line is conducted in the first operating state of the aircraft air conditioning system, for example, via the first turbine exhaust air line branch into the mixer of the aircraft air conditioning system and is discharged in the second operating state of the aircraft air conditioning system, for example, via the second turbine exhaust air line branch into the aircraft environment. Accordingly, it is ensured that the ambient air used in the first operating state of the aircraft air conditioning system for driving the turbine can be conducted, after its expansion in the turbine, into the mixer and from there into the aircraft cabin. The mixture of bleed air and cabin bleed air used for driving the turbine in the second operating state of the aircraft air conditioning system, on the other hand, is preferably discharged into the aircraft environment after its expansion in the turbine.In a preferred embodiment, the aircraft air conditioning system further comprises a bleed air bypass line which can be connected to the bleed air line. The bleed air bypass line is preferably configured to direct bleed air flowing through the bleed air line past the turbine. By way of the bleed air bypass line, bleed air can thus be conducted past the turbine, for example after flowing through a further turbine which serves for driving a further ambient air compressor connected upstream of the ambient air compressor. The bleed air bypass line may be connected to the aircraft environment via the second turbine bleed air line branch.The aircraft air conditioning system may comprise a third control valve arrangement. The control device is preferably configured to control the operation of the third control valve arrangement such that the bleed air flowing through the bleed air line is conducted into the aircraft environment via the bleed air bypass line in the first operating state of the aircraft air conditioning system, in which the turbine is driven by ambient air. In the second operating state of the aircraft air conditioning system, on the other hand, the control device preferably controls the operation of the third control valve arrangement such that the bleed air flowing through the bleed air line is conducted into the turbine feed air line. The cabin exhaust line preferably opens downstream of the branch of the bleed air bypass line from the bleed air line into the bleed air line, wherein the term "downstream" here refers to the flow direction of the bleed air through the bleed air line.In a method for operating an aircraft air conditioning system, ambient air is conducted through an ambient air line which is connected to a mixer of the aircraft air conditioning system in order to supply ambient air to the mixer. The ambient air flowing through the ambient air line is compressed in an ambient air compressor arranged in the ambient air line. A refrigerating machine is provided which comprises a refrigerant circuit through which a refrigerant can flow and a refrigerant compressor arranged in the refrigerant circuit. The refrigerant circuit of the refrigerating machine is thermally coupled to the ambient air line in order to transfer heat from the ambient air flowing through the ambient air line to the refrigerant circulating in the refrigerant circuit before the ambient air is supplied into the mixer. The operation of the aircraft air conditioning system is controlled in such a way that a turbine, which is coupled to the ambient air compressor and is configured to drive the ambient air compressor, is supplied with ambient air from the ambient air line in a first operating state of the aircraft air conditioning system and a mixture of bleed air, which is tapped by an engine or an auxiliary engine, is supplied from a bleed air line and cabin bleed air from a cabin bleed air line which can be connected to an aircraft cabin in a second operating state of the aircraft air conditioning system.The operation of the aircraft air conditioning system is preferably controlled in such a way that, in ground operation of an aircraft equipped with the aircraft air conditioning system, ambient air from the ambient air line is supplied to the turbine and, in flight operation of the aircraft equipped with the aircraft air conditioning system, a mixture of bleed air from the bleed air line and cabin bleed air from the cabin bleed air line is supplied.The operation of a first control valve arrangement can be controlled such that the ambient air flowing through the ambient air line is conducted in the first operating state of the aircraft air conditioning system into a turbine inlet air line connected to an inlet of the turbine and in the second operating state of the aircraft air conditioning system through an ambient air bypass line past the turbine into the mixer.The operation of a second control valve arrangement can be controlled such that turbine exhaust air flowing through a turbine exhaust line connected to an outlet of the turbine is conducted into the mixer of the aircraft air conditioning system via a first turbine exhaust line branch in the first operating state of the aircraft air conditioning system and into an aircraft environment via a second turbine exhaust line branch in the second operating state of the aircraft air conditioning system.The operation of a third control valve arrangement can be controlled in such a way that the bleed air flowing through the bleed air line is conducted past the turbine into the aircraft environment via a bleed air bypass line in the first operating state of the aircraft air conditioning system and is conducted into the turbine feed air line in the second operating state of the aircraft air conditioning system.A preferred embodiment of the invention will now be explained in more detail with reference to the attached schematic drawing, which shows FIG. 1 shows an air conditioning system for air conditioning an aircraft cabin.An aircraft air conditioning system 10 illustrated in FIG. 1 comprises an ambient air line 12 through which ambient air can flow, which is connected to a mixer 14 of the aircraft air conditioning system 10 in order to supply the ambient air taken from an aircraft environment 15 to the mixer 14. The supply of ambient air into the ambient air line 12 is controlled by means of a valve 13 arranged in the ambient air line. In the mixer 14, the ambient air from the ambient air line 12 is mixed with recirculation air discharged from an aircraft cabin 16. The mixed air generated in the mixer 14 is finally used for air conditioning the aircraft cabin 16.The aircraft air conditioning system 10 is equipped with a refrigerating machine 17 which comprises a refrigerant circuit 18 through which a two-phase refrigerant, for example R134A (CH 2 F-CF 3), CO 2 or R-245fa (1,1,1,3,3-pentafluoropropane), flows, and a refrigerant compressor 20 arranged in the refrigerant circuit 18. The refrigerant compressor 20 is driven by a first electric motor 22. The refrigerant circuit 18 is thermally coupled to the ambient air line to transfer heat from the ambient air flowing through the ambient air line 12 to the refrigerant circulating in the refrigerant circuit 18 prior to supplying the ambient air to the mixer 14. In addition to the refrigerant compressor 20, a condenser 24, a refrigerant collector 26, an expansion valve 28, and an evaporator 30, which thermally couples the refrigerant circuit 18 to the ambient air line 12, are arranged in the refrigerant circuit 18.The refrigerant circuit 18 of the refrigerating machine 17 is further thermally coupled to a recirculation air line 32 through which recirculation air flows and connected to the mixer 14 of the aircraft air-conditioning system 10, in order to transfer heat from the recirculation air flowing through the recirculation air line 32 to the refrigerant flowing through the refrigerant circuit 18. The thermal coupling between the refrigerant circuit 18 and the recirculation air line 32 is realized by a further evaporator 34, which is arranged in a connecting line 36 branching off from the refrigerant collector 26 arranged in the refrigerant circuit 18. The flow of refrigerant through the connecting line 36 is controlled by a control valve 38 disposed in the connecting line 36. Further, in the connection line 36, a further expansion valve 40 is arranged upstream of the further evaporator 34 with respect to the flow direction of the refrigerant through the refrigerant circuit 18. By the further expansion valve 40, the pressure and temperature of the refrigerant flowing through the connection line 36 can be adjusted as desired before the refrigerant is introduced into the further evaporator 34.In the aircraft air conditioning system 10, the refrigerating machine 17 is thus used not only for cooling the ambient air flowing through the ambient air line 12 but also for cooling recirculation air discharged from the aircraft cabin to be air conditioned. The recirculation air can therefore be cooled to the same low temperature as the ambient air flowing through the ambient air line 12 before it is fed into the mixer 14 of the aircraft air conditioning system 10. Consequently, it is possible to dispense with cooling the ambient air to a temperature which is below a desired setpoint cabin inlet air temperature by heat transfer to the refrigerant circulating in the refrigerant circuit 18 of the refrigerating machine 17. Furthermore, operation of the refrigerating machine 17 with relatively high minimum refrigerant temperatures is made possible.An ambient air compressor 58 for compressing the ambient air flowing through the ambient air line 12 is arranged in the ambient air line 12. The speed controlled ambient air compressor 58 is driven by a turbine 60. In the embodiment of an aircraft air conditioning system 10 shown in FIG. 1, the ambient air compressor 58 and the turbine 60 are arranged on a common shaft 62. The ambient air compressor 58 is controlled by a control device 46 of the aircraft air conditioning system 10 in such a way that it compresses the ambient air flowing through the ambient air line 12 to a pressure which is greater than the setpoint cabin pressure in the aircraft cabin 16 to be air-conditioned.A further ambient air compressor 64 is connected upstream of the ambient air compressor 58, i.e. the further ambient air compressor 64 is arranged in the ambient air line 12 upstream of the ambient air compressor 58 with respect to the flow direction of the ambient air through the ambient air line 12. The speed-controlled further ambient air compressor 64 is driven by a further turbine 66. In the embodiment of an aircraft air conditioning system 10 shown in FIG. 1, the further ambient air compressor 64 and the further turbine 66 are arranged on a common shaft 67.In the ambient air line 12, a precooler 68 for precooling the ambient air compressed by the ambient air compressor 58 is furthermore arranged downstream of the ambient air compressor 58. The term "downstream" here refers to the direction of flow of the ambient air through the ambient air line 12. The ram air flow through the ram air duct 52 is controlled by the control of inlet and outlet flaps 53 which are indicated only schematically in the drawing. In the precooler 68, the ambient air which has been heated by the compression in the ambient air compressor 58 is cooled back to a desired lower temperature. Downstream of the precooler 68, the ambient air line 12 is thermally coupled to the refrigerant circuit 18 via the evaporator 30 arranged in the refrigerant circuit 18 of the refrigerating machine 17.In addition to the precooler 68, the condenser 24 of the refrigerating machine 17 is also arranged in the ram air duct 52, wherein the condenser 24 is positioned upstream of the precooler 68 in the ram air duct 52 with respect to the flow direction of the ram air through the ram air duct 52. In order to ensure that ram air flows properly through the ram air duct 52 even during ground operation of an aircraft equipped with the aircraft air conditioning system 10, a blower 70 for conveying ram air through the ram air duct 52 is furthermore arranged in the ram air duct 52. The blower 70 is driven by a second electric motor 72.Furthermore, the aircraft air conditioning system 10 comprises a bleed air line 73 through which bleed air can flow. The bleed air flowing through the bleed air line 73 is tapped off from an engine 74 or an auxiliary engine of an aircraft equipped with the aircraft air conditioning system. To control the flow of bleed air into the bleed air line 73, a corresponding control valve 75 is provided in the bleed air line 73. The further turbine 66 is arranged in the bleed air line 73, so that the further turbine is driven by the bleed air flowing through the bleed air line 73.Upstream of the further turbine 66, a trim air line 76 branches off from the bleed air line 73, wherein the term "upstream" here refers to the flow direction of the bleed air through the bleed air line 73. The trim air flow through the trim air line 76 is controlled by a trim air valve 77 disposed in the trim air line 76 and an expansion valve 79.Downstream of the thermal coupling of the ambient air line 12 to the refrigerant circuit 18 of the refrigerating machine 17 by means of the evaporator 30, the ambient air line 12 opens into a turbine inlet air line 78, The turbine inlet air line 78 is connected to the inlet of the turbine 60. A water separator 80 is arranged in the turbine inlet air line 78. When flowing through the water separator 80, the ambient air conducted from the ambient air line 12 into the turbine inlet air line 78 is dehumidified to such an extent that it is ensured that not too much moisture is supplied to the aircraft cabin 16 to be conditioned. Water separated from the ambient air in the water separator 80 is conducted via a drainage line 82 into the ram air duct 52 and injected into the ram air duct 52 via water injection nozzles 87 which, with respect to the flow direction of the ram air through the ram air duct 52, are arranged upstream of the condenser 24 of the refrigerating machine 17 in the ram air duct 52. In this case, the water partly evaporates and cools the ram air flowing through the ram air duct 52.Furthermore, a reheater 81 is arranged in the turbine inlet air line 78 downstream of the opening of the cabin outlet air line 88 into the turbine inlet air line 78. The reheater 81 arranged downstream of the water separator 80 and upstream of the turbine 60, with respect to the direction of flow of the turbine inlet air through the turbine inlet air line 78, serves to heat the ambient air flowing through the turbine inlet air line 78 before it is supplied into the turbine 60 and establishes a thermal coupling between the ambient air flowing through the turbine inlet air line 78 downstream of the water separator 80 and the warm ambient air flowing through the ambient air line 12 downstream of the ambient air compressor 58. In the reheater 81, water drops remaining in the ambient air flow after flowing through the water separator 80 are evaporated to protect the turbine 60 from damage due to drop knocking or cavitation. Furthermore, the reheater 81 increases the power output of the turbine 60, and downstream of the reheater 81, i.e., immediately upstream of the turbine 60, the bleed line 73 opens into the turbine feed line 78.The aircraft air conditioning system 10 further comprises a cabin waste air line 88 which can be connected to the aircraft cabin 16 to be air-conditioned by means of the aircraft air conditioning system 10 and-like the recirculation air line 32-through which cabin waste air discharged from the aircraft cabin 16 can flow. The cabin waste air flow through the cabin waste air line 88 is controlled by means of a valve 90 arranged in the cabin waste air line 88, the cabin waste air line 88 opens, with respect to the flow direction of the bleed air through the bleed air line 73, downstream of the further turbine 66 and upstream of an opening point M of the bleed air line 73 into the turbine feed air line 78 into the bleed air line 73.An ambient air bypass line 92 of the aircraft air conditioning system 10 is configured to direct ambient air flowing through the ambient air line 12 past the turbine 60 into the mixer 14, as required. In the aircraft air conditioning system 10 shown in FIG. 1, the ambient air bypass line 92 is connected to the ambient air line 12 in the region of a point of opening P of the ambient air line 12 into the turbine inlet air line 78. A first control valve arrangement 93 serves to control the supply of ambient air from the ambient air line 12 into the turbine inlet air line 78 or the ambient air bypass line 92, respectively. With the aid of the first control valve arrangement 93, the ambient air flowing through the ambient air line 12 can thus be selectively conducted either into the turbine inlet air line 78 or the ambient air bypass line 92. The first control valve arrangement 93 is designed in the form of a 3-way valve arrangement which is arranged in the region of the connection point P of the ambient air line 12 to the turbine inlet air line 78 and the ambient air bypass line 92.Connected to an outlet of the turbine 60 is a turbine exhaust line 94. The turbine exhaust line 94 has a first turbine exhaust line branch 94 aand a second turbine exhaust line branch 94 b. Specifically, the turbine exhaust line 94 branches downstream of the turbine 60 into the first turbine exhaust line branch 94 aand the second turbine exhaust line branch 94 b. The term "downstream" here refers to the direction of flow of the turbine exhaust air exiting from the outlet of the turbine 60 through the turbine exhaust air line 94. the first turbine exhaust air line branch 94 aopens into the mixer 14 of the aircraft air conditioning system 10.The second turbine exhaust line branch 94 b, on the other hand, is connected to the aircraft environment 15, so that turbine exhaust air can be discharged into the aircraft environment 15 via the second turbine exhaust line branch 94 b. In the aircraft air conditioning system 10 shown in FIG. 1, the second turbine exhaust air line branch 94 bopens into the ram air duct 52, wherein the second turbine exhaust air line branch 94 bbranches before its opening into the ram air duct 52 into a first branch line 95 awhich opens into the ram air duct 52 upstream of the condenser 24 of the refrigerating machine 17 and a second branch line 95 bwhich opens into the ram air duct 52 downstream of the condenser 24 of the refrigerating machine 17 but upstream of the precooler 68. The terms "upstream" and "downstream" refer here to the direction of flow of ram air through the ram air duct 52; a valve 96 controls the turbine exhaust air flow through the first and second branch ducts 95 a, 95 bof the second turbine exhaust air duct branch 94 b. The turbine exhaust air conducted into the ram air duct 52 can be used for cooling the condenser 24 of the refrigerating machine 17 or the precooler 68. As a result, the ram air requirement of the aircraft air conditioning system 10 can be reduced.The aircraft air conditioning system 10 further comprises a second control valve arrangement 97 for controlling the supply of turbine waste air into the first turbine waste air line branch 94 aand the second turbine waste air line branch 94 b, respectively. The second control valve arrangement 97 is designed in the form of a 3-way valve arrangement which is arranged in the region of a branching point of the turbine exhaust air line 94 into the first turbine exhaust air line branch 94 aand the second turbine exhaust air line branch 94 bin the turbine exhaust air line 94.The aircraft air conditioning system 10 is furthermore equipped with a bleed air bypass line 98, which branches off from the bleed air line 73 downstream of the further turbine 66, with respect to the flow direction of the bleed air through the bleed air line 73. The bleed air flowing through the bleed air line 73 can be conducted past the turbine 60 via the bleed air bypass line 98 after flowing through the further turbine 66 for driving the further ambient air compressor 64 upstream of the ambient air compressor 58. The bleed air bypass line 98 opens into the second turbine bleed air line branch 94 band is thus connected to the aircraft environment 15 via the second turbine bleed air line branch 94 band the ram air channel 52.Finally, the aircraft air conditioning system 10 comprises a third control valve arrangement 99. With the aid of the third control valve arrangement 99, the bleed air flowing through the bleed air line 73 downstream of the further turbine 66 can be selectively conducted either into the turbine feed air line 78 or the bleed air bypass line 98. The third control valve arrangement 99 is designed in the form of a 3-way valve arrangement which is arranged in the region of the branch point A of the bleed air bypass line 98 from the bleed air line 73.The control device 46 of the aircraft air conditioning system 10 controls the operation of the aircraft air conditioning system 10 in such a way that, in a first operating state of the aircraft air conditioning system 10, ambient air is supplied from the ambient air line 12 and, in a second operating state of the aircraft air conditioning system 10, a mixture of bleed air from the bleed air line 73 and cabin bleed air from the cabin bleed air line 88 is supplied to the turbine 60. In the first operating state of the aircraft air conditioning system 10, the pressure of the pre-compressed ambient air is thus used to drive the turbine 60. In the second operating state of the aircraft air conditioning system 10, on the other hand, the pressure of the exhaust air discharged from an aircraft cabin, which exceeds the ambient pressure outside the aircraft from a specific flight altitude during flight operation of an aircraft equipped with the aircraft air conditioning system 10, is used for energy recovery. The energy recovered from the pre-compressed ambient air or the cabin waste air is used to drive the ambient air compressor 58. This allows the bleed air flow required to drive the ambient air compressor 58 to be reduced and, accordingly, the energy efficiency of the aircraft air conditioning system to be improved.In particular, the control device 46 controls the operation of the aircraft air conditioning system 10 in such a way that ambient air is supplied from the ambient air line 12 to the turbine 60 during ground operation of an aircraft equipped with the aircraft air conditioning system 10. For this purpose, the control device 46 controls the operation of the first regulating valve arrangement 93 in the ground operation of an aircraft equipped with the aircraft air conditioning system 10, i.e. in the first operating state of the aircraft air conditioning system 10, in such a way that the ambient air flowing through the ambient air line is conducted into the turbine inlet air line 78. This is accomplished by controlling the first 3-way control valve assembly 93 to a position to clear the turbine inlet air line 78 while closing the ambient air bypass line 92. The valve 90 disposed in the cabin exhaust line 88 is closed to inhibit the supply of cabin exhaust through the cabin exhaust line 88 into the PTU 73.Furthermore, the control device 46 controls the ambient air compressor 58 during ground operation of the aircraft equipped with the aircraft air conditioning system 10 in such a way that the ambient air is compressed, when flowing through the ambient air compressor 58, to a pressure which is above the setpoint cabin pressure and which enables dehumidification of the ambient air and subsequent use of the ambient air for driving the turbine 60. The cooling of the ambient air is then effected both by the transfer of heat to the refrigerant circuit 18 of the refrigerating machine 17 and by the expansion of the ambient air in the turbine 60.In addition, in ground operation of an aircraft equipped with the aircraft air conditioning system 10, i.e. in the first operating state of the aircraft air conditioning system 10, the operation of the second control valve arrangement 97 is controlled by the control device 46 in such a way that the turbine exhaust air flowing through the turbine exhaust air line 94 is conducted via the first turbine exhaust air line branch 94 ainto the mixer 14 of the aircraft air conditioning system 10 and is used for air conditioning the aircraft cabin 16. This is accomplished by controlling the second 3-way control valve assembly 97 to a position in which it releases the first turbine exhaust branch 94a while closing the second turbine exhaust branch 94b.Finally, in ground operation of an aircraft equipped with the aircraft air conditioning system 10, the third 3-way valve arrangement 99 is controlled into a position in which it releases the bleed air bypass line 98, while it closes a section of the bleed air line 73 which, in relation to the flow direction of the bleed air through the bleed air line 73, is situated downstream of the branch point A of the bleed air bypass line 98 from the bleed air line 73. Accordingly, in the first operating state of the aircraft air conditioning system 10, the bleed air, after flowing through the further turbine 66, is conducted via the bleed air bypass line 98 into the second turbine bleed air line branch 94 band is discharged via the ram air channel 52 into the aircraft environment 15.In the flight operation of the aircraft equipped with the aircraft air conditioning system 10, on the other hand, the pressure of the exhaust air discharged from the aircraft cabin exceeds the ambient pressure outside the aircraft from a specific flight altitude (approximately 6000 m). Therefore, the control device 46 controls the operation of the aircraft air conditioning system 10 in such a way that the turbine 60 is driven by a mixture of bleed air from the bleed air line 73 and cabin bleed air from the cabin bleed air line 88 during flight operation of the aircraft equipped with the aircraft air conditioning system 10, i.e. in the second operating state of the aircraft air conditioning system 10. For this purpose, the control device 46 controls the operation of the aircraft air conditioning system 10 in its second operating state in such a way that a mixture of bleed air from the bleed air line 73 and cabin bleed air from the cabin bleed air line 88 is supplied to the turbine 60 during flight operation of the aircraft equipped with the aircraft air conditioning system 10. Accordingly, the valve 90 disposed in the cabin exhaust line 88 is opened to allow cabin exhaust to be supplied through the cabin exhaust line 88 into the PTU 73.At the same time, the control device 46 controls the operation of the third regulating valve arrangement 99 in such a way that the bleed air flowing through the bleed air line 73 is conducted together with the cabin bleed air from the cabin bleed air line 88 into the turbine feed air line 78 in the second operating state of the aircraft air conditioning system 10. The operation of the first control valve arrangement 93, on the other hand, is controlled by the control device 46 in such a way that the ambient air flowing through the ambient air line 12 is conducted directly into the mixer 14 via the ambient air bypass line 92. This is accomplished by controlling the first 3-way control valve assembly 93 to a position closing the turbine inlet air line 78 while releasing the ambient air bypass line 92. In flight operation, in particular in cruise operation, of an aircraft equipped with the aircraft air conditioning system 10, dehumidifying the ambient air that is very dry at the cruise altitude of the aircraft is not necessary before it is fed into the aircraft cabin 16. Accordingly, the water separator 80, the reheater 81, and the turbine 60 may be bypassed and ambient air from the ambient air line 12 may be directed into the mixer 14 of the aircraft air conditioning system 10. The cooling of the ambient air is then effected exclusively by the transfer of heat to the refrigerant circuit 18 of the refrigerating machine 17.Finally, in the second operating state of the aircraft air conditioning system 10, i.e. in flight operation of an aircraft equipped with the aircraft air conditioning system 10, the control device 46 controls the operation of the second regulating valve arrangement 97 in such a way that the turbine exhaust air flowing through the turbine exhaust air line 94 is discharged into the aircraft environment via the second turbine exhaust air line branch 94 b. Accordingly, it is ensured that the mixture of bleed air and cabin exhaust air used for driving the turbine 60 in the second operating state of the aircraft air conditioning system 10 is discharged into the aircraft environment after its expansion in the turbine 60.Because the ambient air compressor 58 compresses the ambient air flowing through the ambient air line 12 to a pressure which is greater than the setpoint cabin pressure in the aircraft cabin 16 to be air-conditioned, the turbine 60 also makes it possible to implement a cold air process in which the ambient air flowing through the ambient air line 12 is firstly compressed and then expanded again and cooled in the process. Accordingly, in the aircraft air conditioning system 10, either exclusively the cold steam process running in the refrigeration system 17 (for example in flight operation of an aircraft equipped with the aircraft air conditioning system 10 at a flight altitude of 6000 m) or both the cold steam process and the cold air process (for example in ground operation of an aircraft equipped with the aircraft air conditioning system 10 or in flight operation of the aircraft up to a flight altitude of 6000 m) can be used for conditioning and cooling the ambient air flowing through the ambient air line 12.Finally, by switching off the refrigerating machine 17, operation of the aircraft air-conditioning system 10 is also possible using only the cold air process. This may be useful, for example, if the aircraft cabin 16 is to be heated by means of the aircraft air conditioning system 10. An operation of the aircraft air conditioning system 10 using only the cold air process is also possible as an emergency operation in the event of a failure of the refrigeration machine 17.

Claims

Aircraft air-conditioning system (10) having: - an ambient air line (12) through which ambient air can flow, which is connected to a mixer (14) of the aircraft air-conditioning system (10) in order to supply ambient air to the mixer (14), - a cabin exhaust air line (88) which can be connected to an aircraft cabin (16) and through which cabin exhaust air can flow, - a bleed air line (73) through which bleed air, which is drawn off by an engine (74) or an auxiliary engine, can flow, - an ambient air compressor (58), which is arranged in the ambient air line (12), for compressing the ambient air flowing through the ambient air line (12), - a refrigerating machine (17), which comprises a refrigerant circuit (18) through which a refrigerant can flow and a refrigerant compressor (20) arranged in the refrigerant circuit (18), the refrigerant circuit (18) being thermally coupled to the ambient air line (12), in order to transfer heat from the ambient air flowing through the ambient air line (12) to the refrigerant circulating in the refrigerant circuit (18) before the ambient air is supplied to the mixer (14), - a turbine (60) which is coupled to the ambient air compressor (58) and is configured to drive the ambient air compressor (58), and - a control device (46) which is configured to control the operation of the aircraft air conditioning system (10) such that, in a first operating state of the aircraft air conditioning system (10), ambient air is supplied to the turbine (60) from the ambient air line (12) and, in a second operating state of the aircraft air conditioning system (10), a mixture of bleed air from the bleed air line (73) and cabin bleed air from the cabin bleed air line (88), and in that a turbine exhaust air line (78), which flows through after flowing through the turbine (60), is conducted into the mixer (14) of the aircraft air conditioning system (10) in the first operating state of the aircraft air conditioning system (10) and is discharged into an aircraft environment (15) in the second operating state of the aircraft air conditioning system (10).Aircraft air conditioning system according to claim 1, wherein the control device (46) is configured to control the operation of the aircraft air conditioning system (10) such that in ground operation of an aircraft equipped with the aircraft air conditioning system (10), ambient air is supplied from the ambient air line (12) to the turbine (60) and in flight operation of the aircraft equipped with the aircraft air conditioning system (10), a mixture of bleed air from the bleed air line (73) and cabin bleed air from the cabin bleed air line (88) is supplied.Aircraft aircraft aircraft installation according to claim 1 or 2, wherein the turbine (60) is arranged in particular downstream of a water separator (80) and / or downstream of a reheater (81) in a turbine inlet air line (78) connected to an inlet of the turbine (60).Aircraft air-conditioning system according to Claim 3, wherein the ambient air line (12) opens into the turbine inlet air line (78), in particular upstream of the water separator (80), and / or wherein the outlet air line (73) opens into the turbine inlet air line (78), in particular downstream of the reheater (81).Aircraft air conditioning system according to Claim 3 or 4, wherein the cabin exhaust air line (88) opens into the turbine supply air line (78) in the exhaust air line (73) upstream of an opening point (M) of the exhaust air line (73).Aircraft air conditioning system according to one of Claims 1 to 5, which furthermore comprises an ambient air bypass line (92) which can be connected to the ambient air line (12) and is designed to conduct ambient air flowing through the ambient air line (12) past the turbine (60) into the mixer (14).Aircraft air conditioning system according to claim 6, further comprising a first control valve arrangement (93), wherein the control device (46) is configured to control the operation of the first control valve arrangement (93) such that the ambient air flowing through the ambient air line (12) is conducted into the turbine inlet air line (78) in the first operating state of the aircraft air conditioning system (10) and into the ambient air bypass line (92) in the second operating state of the aircraft air conditioning system (10).Aircraft aircraft aircraft installation according to one of Claims 1 to 7, which furthermore comprises a turbine exhaust line (94), which is connected to an outlet of the turbine (60) and has a first turbine exhaust line branch (94a) and a second turbine exhaust line branch (94b), wherein the first turbine exhaust line branch (94a) is connected in particular to the mixer (14) of the aircraft air conditioning system (10), and wherein the second turbine exhaust line branch (94b) is connected in particular to the aircraft environment (15).Aircraft air conditioning system according to claim 8, further comprising a second control valve arrangement (97), wherein the control device (46) is configured to control the operation of the second control valve arrangement (97) such that the turbine exhaust air flowing through the turbine exhaust air line (78) is conducted into the mixer (14) of the aircraft air conditioning system (10) via the first turbine exhaust air line branch (94a) in the first operating state of the aircraft air conditioning system (10) and into the aircraft environment (15) via the second turbine exhaust air line branch (94b) in the second operating state of the aircraft air conditioning system (10).Aircraft air conditioning system according to one of Claims 1 to 9, which furthermore comprises a bleed air bypass line (98) which can be connected to the bleed air line (73) and is designed to direct bleed air flowing through the bleed air line (73) past the turbine (60), wherein the bleed air bypass line (98) is connected to the aircraft environment (15) in particular via the second turbine bleed air line branch (94b).Aircraft air conditioning system according to claim 10, further comprising a third control valve arrangement (99), wherein the control device (46) is configured to control the operation of the third control valve arrangement (99) such that the bleed air flowing through the bleed air line (73) is conducted into the aircraft environment (15) via the bleed air bypass line (98) in the first operating state of the aircraft air conditioning system (10) and is conducted into the turbine feed air line (78) in the second operating state of the aircraft air conditioning system (10).Method for operating an aircraft air-conditioning system (10), having the steps of: - conducting ambient air through an ambient air line (12) which is connected to a mixer (14) of the aircraft air-conditioning system (10) in order to feed ambient air to the mixer (14), - compressing the ambient air flowing through the ambient air line (12) in an ambient air compressor (58) arranged in the ambient air line (12), - providing a refrigerating machine (17) which comprises a refrigerant circuit (18) through which a refrigerant can flow and a refrigerant compressor (20) arranged in the refrigerant circuit (18), - thermally coupling the refrigerant circuit (18) of the refrigerating machine (17) to the ambient air line (12) in order, before the ambient air is fed into the mixer (14), to transfer heat from the ambient air flowing through the ambient air line (12) to the refrigerant circulating in the refrigerant circuit (18), controlling the operation of the aircraft air conditioning system (10) in such a way that a turbine (60), which is coupled to the ambient air compressor (58) and is configured to drive the ambient air compressor (58), is supplied with ambient air from the ambient air line (12) in a first operating state of the aircraft air conditioning system (10) and a mixture of bleed air, which is drawn off by an engine (74) or an auxiliary engine, is supplied from a bleed air line (73) and cabin bleed air from a cabin bleed air line (88) which can be connected to an aircraft cabin (16) in a second operating state of the aircraft air conditioning system (10), and in that a turbine exhaust air line (78), which flows through after flowing through the turbine (60), is conducted into the mixer (14) of the aircraft air conditioning system (10) in the first operating state of the aircraft air conditioning system (10) and is discharged into an aircraft environment (15) in the second operating state of the aircraft air conditioning system (10).Method according to claim 12, wherein the operation of the aircraft air conditioning system (10) is controlled in such a way that in ground operation of an aircraft equipped with the aircraft air conditioning system (10), ambient air is supplied from the ambient air line (12) and in flight operation of the aircraft equipped with the aircraft air conditioning system (10), a mixture of bleed air from the bleed air line (73) and cabin bleed air from the cabin bleed air line (88) is supplied to the turbine (60).Method according to Claim 12 or 13, wherein the operation of a first regulating valve arrangement (93) is controlled such that the ambient air flowing through the ambient air line (12) is conducted in the first operating state of the aircraft air conditioning system (10) into a turbine inlet air line (78) connected to an inlet of the turbine (60) and in the second operating state of the aircraft air conditioning system (10) through an ambient air bypass line (92) past the turbine (60) into the mixer (14).Method according to one of Claims 12 to 14, wherein the operation of a second control valve arrangement (97) is controlled such that turbine waste air flowing through a turbine waste air line (94) connected to an outlet of the turbine (60) is conducted into the mixer (14) of the aircraft air conditioning system (10) via a first turbine waste air line branch (94a) in the first operating state of the aircraft air conditioning system (10) and into the aircraft environment (15) via a second turbine waste air line branch (94b) in the second operating state of the aircraft air conditioning system (10), and / or wherein the operation of a third control valve arrangement (99) is controlled such that, the bleed air flowing through the bleed air line (73) is conducted past the turbine (60) into the aircraft environment (15) in the first operating state of the aircraft air conditioning system (10) via a bleed air bypass line (98) and is conducted into the turbine feed air line (78) in the second operating state of the aircraft air conditioning system (10).

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