Cabin exhaust air assisted aircraft air conditioning system with an electrically 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 (74) which can be connected to an aircraft cabin (16) and through which cabin exhaust air 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 (86) 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 is supplied from the ambient air line (12) to the turbine (86) and, in a second operating state of the aircraft air conditioning system (10), cabin exhaust air is supplied from the cabin exhaust air line (74), wherein the turbine (86) is arranged downstream of a reheater (82) in a turbine supply air line (78) connected to an inlet of the turbine (86), and wherein the cabin exhaust air line (74) opens into the turbine supply air line (78) upstream of the reheater (82).

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.DE 10 2015 207 436 A1 relates to an aircraft air conditioning system having a cooling machine for cooling ambient air. A turbine driving an ambient air compressor is flushed by ambient air directed through a fourth portion of an ambient air duct. Ambient air cooled by the refrigerating machine is supplied to a mixer and there mixed with recirculation air from a recirculation air line.US 2003 / 0 051 500 A1 describes an aircraft air conditioning system in which ambient air supplied via a ram air duct is successively conducted through a first compressor, a first heat exchanger, a second compressor, a second heat exchanger, a reheater, a first turbine, a condenser and a second turbine and finally supplied to a mixer. Only ram air is supplied to the first turbine driving the first compressor during ground operation and at a low flight height of an aircraft equipped with the aircraft air conditioning system. In the flight mode of the aircraft at a high flight altitude, on the other hand, cabin waste air is supplied to the first turbine. This allows utilization of the energy contained in the cabin waste air under elevated pressure.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 15 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 9.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 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 cabin waste air from the cabin waste 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. As a result, the energy consumption of a compressor drive, which is designed, for example, in the form of an electric motor, can be reduced.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 cabin waste air from the cabin waste air line is supplied 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, the turbine can be driven during flight operation of the aircraft equipped with the aircraft air conditioning system, in particular starting from a flight altitude of 6000 m, by the cabin waste air discharged from the aircraft cabin via the cabin waste air line. As a result, energy recovery potentials can be optimally utilized both in ground operation and in flight operation of the aircraft.The turbine is disposed in a turbine inlet duct connected to an inlet of the turbine. In particular, the turbine can be arranged downstream of a water separator. According to the invention, the turbine is arranged downstream of a reheater in the turbine inlet air line. The term "downstream" here refers to the flow direction of the ambient air (in the first operating state of the aircraft air conditioning system) or of the cabin waste air (in the second operating state of the aircraft air conditioning system) through the turbine inlet air line. 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) or cabin waste air (in the second operating state of the aircraft air conditioning system) before it is fed 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, after compression thereof in the ambient air compressor, into thermal contact with the ambient air flowing through the turbine inlet air line or cabin waste air before supply thereof into the turbine. Water drops remaining in the ambient air stream or the cabin exhaust air stream can be evaporated in the reheater in order to protect the turbine from damage due to drop strike 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. In contrast, according to the invention, the cabin waste air line opens into the turbine feed air line upstream of the reheater. This arrangement ensures that ambient air flowing through the ambient air line is dehumidified in the water separator before being fed into the turbine. In contrast, cabin waste air flowing through the cabin waste air line is drier and therefore does not have to be conducted through the water separator.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 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 a 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 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 preferably configured to control the operation of the second control valve arrangement such that the turbine exhaust air flowing through the turbine exhaust air line is conducted via the first turbine exhaust air line branch into the mixer of the aircraft air conditioning system in the first operating state of the aircraft air conditioning system and is discharged into the aircraft environment via the second turbine exhaust air line branch in the second operating state of the aircraft air conditioning system. 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. In the second operating state of the aircraft air conditioning system, cabin waste air used for driving the turbine, on the other hand, is preferably discharged into the aircraft environment after its expansion in the turbine.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, in a first operating state of the aircraft air conditioning system, ambient air is supplied from the ambient air line to a turbine which is coupled to the ambient air compressor and is configured to drive the ambient air compressor, and, in a second operating state of the aircraft air conditioning system, cabin waste air is supplied from a cabin waste air line which can be connected to an aircraft cabin.Preferably, the operation of the aircraft air conditioning system is controlled 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 cabin waste air from the cabin waste air line is supplied in flight operation of the aircraft equipped with the aircraft air conditioning system.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.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 second electric motor 60. 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.In the ambient air line 12, a precooler 68 for precooling the ambient air compressed by the ambient air compressor 58 is 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.Downstream of the ambient air compressor 58 and upstream of the precooler 68, a trim air line 74 branches off from the ambient air line 12. The trim air flow through the trim air line 74 will be controlled by a trim air valve 76 disposed in the trim air line 74.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 third electric motor 72.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 a turbine 86. The turbine 86 is coupled to the ambient air compressor 58. In particular, the ambient air compressor 58 and the turbine 86 are arranged on a common shaft.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 84 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 and downstream 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.The aircraft air conditioning system 10 further comprises a cabin waste air line 74, 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-can be flown through by cabin waste air discharged from the aircraft cabin 16. The control of the cabin waste air flow through the cabin waste air line 74 is effected by means of a valve 76 arranged in the cabin waste air line 74, the cabin waste air line 74 opens into the turbine feed air line downstream of the water separator 80 with respect to the flow direction of the turbine feed air through the turbine feed air line 78.Furthermore, a reheater 82 is arranged in the turbine inlet air line 78 downstream of the opening of the cabin outlet air line 74 into the turbine inlet air line 78. The reheater 82, arranged downstream of the water separator 80 and upstream of the turbine 86 with respect to the direction of flow of the turbine inlet air through the turbine inlet air line 78, serves to heat the turbine inlet air flowing through the turbine inlet air line 78 before it is fed into the turbine 86 and establishes a thermal coupling between the turbine inlet 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 82, water drops remaining in the turbine inflow after flowing through the water separator 80 are evaporated to protect the turbine 86 from damage due to drop knocking or cavitation. Further, the reheater 82 increases the output of the turbine 86.The aircraft air conditioning system 10 further comprises an ambient air bypass line 90, which is configured to direct ambient air flowing through the ambient air line 12 past the turbine 86 into the mixer 14 as required. In the aircraft air conditioning system 10 shown in FIG. 1, the ambient air bypass line 90 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 79 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 90. With the aid of the first control valve arrangement 79, 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 90. The first control valve arrangement 79 comprises a control valve 88 arranged in the turbine inlet air line 78 and a control valve 92 arranged in the bypass ambient air line 90; alternatively, however, the first control valve arrangement 79 can also be designed in the form of a 3-way valve arrangement which can be 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 90. A check valve 91 arranged in the ambient air bypass line 90 prevents air from being able to flow back from the mixer 14 into the ambient air bypass line 90.Connected to an outlet of the turbine 86 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 86 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 86 through the turbine exhaust line 94. the first turbine exhaust 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 channel 52, where the turbine exhaust air conducted into the ram air channel 52 can be used to cool the condenser 24 of the refrigerating machine 17 and 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 96 for controlling the supply of turbine exhaust air into the first turbine exhaust air line branch 94 aand the second turbine exhaust air line branch 94 b, respectively. The second control valve arrangement 96 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. Alternatively, however, the second control valve assembly 96 may also include a control valve disposed in the first turbine exhaust line branch 94 aand a control valve disposed in the second turbine exhaust line branch 94 b.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 ambient air from the ambient air line 12 is supplied to the turbine 86 in a first operating state of the aircraft air conditioning system 10 and cabin waste air from the cabin waste air line 74 in a second operating state of the aircraft air conditioning system 10. 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 86. 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 can reduce the power consumption of the electric motor 60 driving the ambient air compressor 58.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 86 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 79 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. To do this, the control valve 88 located in the turbine inlet air line 78 is opened, while the control valve 92 located in the bypass ambient air line 90 is closed. The valve 76 disposed in the cabin exhaust line 74 is closed to inhibit the supply of cabin exhaust through the cabin exhaust line 74 into the turbine intake line 78.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 86. 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 86.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 96 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 96 to a position to clear the first turbine exhaust branch 94a while closing the second turbine exhaust branch 94b.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 86 is driven by the cabin waste air discharged from the aircraft cabin 16 via the cabin waste air line 74 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 cabin waste air from the cabin waste air line 74 is supplied to the turbine 86 during flight operation of the aircraft equipped with the aircraft air conditioning system 10. Accordingly, the valve 76 disposed in the cabin exhaust line 74 is opened to allow cabin exhaust to be supplied through the cabin exhaust line 74 into the turbine intake line 78.At the same time, the operation of the first control valve arrangement 79 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 90. To do this, the control valve 88 located in the turbine inlet air line 78 is closed, while the control valve 92 located in the bypass ambient air line 90 is opened. 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. Thus, the water separator 80, the reheater 82, and the turbine 86 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 96 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 cabin waste air used in the second operating state of the aircraft air conditioning system 10 for driving the turbine 86 is discharged into the aircraft environment after its expansion in the turbine 86.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 86 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 more than 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 feed ambient air to the mixer (14), - a cabin waste air line (74) which can be connected to an aircraft cabin (16) and through which cabin waste air 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), 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 supplied to the mixer (14), - a turbine (86) 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 ambient air is supplied from the ambient air line (12) to the turbine (86) in a first operating state of the aircraft air conditioning system (10) and cabin waste air is supplied from the cabin waste air line (74) in a second operating state of the aircraft air conditioning system (10), wherein the turbine (86) is arranged downstream of a reheater (82) in a turbine inlet air line (78) connected to an inlet of the turbine (86), and wherein the cabin outlet air line (74) opens into the turbine inlet air line (78) upstream of the reheater (82).Aircraft air conditioning system (10) according to claim 1, wherein the control device (46) is configured to control the operation of the aircraft air conditioning system (10) such that ambient air is supplied from the ambient air line (12) to the turbine (86) in ground operation of an aircraft equipped with the aircraft air conditioning system (10) and cabin waste air is supplied from the cabin waste air line (74) in flight operation of the aircraft equipped with the aircraft air conditioning system (10).Aircraft air conditioning system (10) according to Claim 1 or 2, wherein the turbine (86) is arranged in particular downstream of a water separator (80) in a turbine inlet air line (78) connected to an inlet of the turbine (86).Aircraft air-conditioning system (10) 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).Aircraft air conditioning system (10) according to one of Claims 1 to 4, which furthermore comprises an ambient air bypass line (90) 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 (86) into the mixer (14).Aircraft air conditioning system (10) according to Claim 5, which further comprises a first control valve arrangement (79), wherein the control device (46) is configured to control the operation of the first control valve arrangement (79) 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 (90) in the second operating state of the aircraft air conditioning system (10).The aircraft air conditioning system (10) according to any one of claims 1 to 6, further comprising a turbine exhaust line (94) connected to an outlet of the turbine (86), having a first turbine exhaust line branch (94a) and a second turbine exhaust line branch (94b), wherein the first turbine exhaust line branch (94a) is in particular connected to the mixer (14) of the aircraft air conditioning system (10) and wherein the second turbine exhaust line branch (94b) is in particular connected to an aircraft environment (15).Aircraft air conditioning system (10) according to claim 7, further comprising a second control valve arrangement (96), wherein the control device (46) is configured to control the operation of the second control valve arrangement (96) such that the turbine waste air flowing through the turbine waste air line (94) is conducted into the mixer (14) of the aircraft air conditioning system (10) via the 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 the second turbine waste air line branch (94b) 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 (86) 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 cabin waste air from a cabin waste air line (74) which can be connected to an aircraft cabin (16) in a second operating state of the aircraft air conditioning system (10), wherein the turbine (86) is arranged downstream of a reheater (82) in a turbine feed air line (78) which is connected to an inlet of the turbine (86) and wherein the cabin waste air line (74) opens into the turbine feed air line (78) upstream of the reheater (82).The method of claim 9, wherein the operation of the aircraft air conditioner (10) is controlled such that ambient air from the ambient air line (12) is supplied to the turbine (86) during ground operation of an aircraft equipped with the aircraft air conditioner (10) and cabin waste air from the cabin waste air line (74) during flight operation of the aircraft equipped with the aircraft air conditioner (10).Method according to Claim 9 or 10, wherein the operation of a first regulating valve arrangement (79) 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 (86) and in the second operating state of the aircraft air-conditioning system (10) through an ambient air bypass line (90) past the turbine (86) into the mixer (14).Method according to one of Claims 9 to 11, wherein the operation of a second regulating valve arrangement (96) is controlled such that turbine waste air flowing through a turbine waste air line (94) connected to an outlet of the turbine (86) 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 an aircraft environment (15) via a second turbine waste air line branch (94b) in the second operating state of the aircraft air conditioning system (10).

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