TECHNICAL FIELD

The present invention generally relates to a device for supplying preconditioned air to an aircraft on the ground.

BACKGROUND ART

During the time an aircraft is parked on the ground, the on board air conditioning system is generally turned off, whereas the high density of passen- gers, the interior lighting, the large number of windows, and the heavily insulated fuselage all contribute to raising the temperature of the cabin to uncomfortable levels. Therefore, preconditioned air is conventionally supplied to the aircraft directly into the cabin ventilation system. This may be done by connecting the aircraft either to a remote air conditioning unit, or to a portable air conditioning unit, which is towed close to the aircraft.

When connecting the aircraft to a remote ground-based air conditioning unit, a long hose is used to deliver the preconditioned air to the aircraft. Such a hose may be about 300 mm in diameter and 20 to 30 m in length. The hose is connected at one end to a connector provided on the exterior of the fuselage and communicating with the cabin ventilation system. At its other end, the hose is connected to a preconditioned air outlet of an independent air conditioning unit or of the airport air conditioning system, the preconditioned air outlet being situated about the airport terminal building, e.g. about a boarding gate. Unfortunately, the large dimensions of the hose involves large pressure drops and temperature variations. Furthermore, handling and storage of the hose when not in use is difficult.

The use of portable air conditioning units, as e.g. described in US 5,031 ,690, that are towed close to the aircraft eliminates the problems

associated with long hoses, since a short hose is then employed. In such a portable air conditioning unit, the cooling function is generally provided by a conventional vapour cycle refrigerant system, wherein the refrigerant compressor is driven by a diesel engine. Ambient air is sucked into the air conditioning unit and caused to flow through the evaporator of the refrigerant system so as to extract heat from this air. A blower is employed to supply the cool, preconditioned air to the aircraft at the desired flow conditions. A disadvantage of such air conditioning units is their relatively complex conception, since they include a refrigerant system and a diesel engine to operate the refrigerant system. Consequently, these units are relatively heavy and need to be either skid or truck mounted. In addition, exhaust gases from the diesel engine may be sucked into the air conditioning unit, which results in unpleasant odours for the passengers. Another disadvantage of such air conditioning units is that conventional vapour cycle refrigerant systems operate with CFCs, which are known for their harmful effect on the environment.

WO 2004/024561 discloses a simple and environmentally friendly device for supplying preconditioned air to an aircraft on the ground. Contrary to the conventional systems, this device does not use a vapour refrigerant system but operates on the "air cycle" principle: when a gas expands adiabatically from a given temperature, its final temperature at the new pressure is much lower. In the device, compressed air is thus expanded to obtain cool expanded air, which is then mixed with ambient air to elaborate preconditioned air at the desired temperature. As described in WO 2004/024561 , the compressed air which is expanded in the device is not produced therein, but is supplied to the device from a remote location (e.g. the airport building) by means of one or more compressed air hoses. Furthermore, in order to increase the amount of cool air, ambient air may be locally compressed in the device, the locally compressed ambient air being then also introduced in the expander. In such a case, the expander (e.g. of the rotary screw type) can be coupled to the ambient air compressor for driving the latter, thereby taking advantage of the work in the expander. For ease of use, the device features a rolling support, that allows the

device to be readily moved on the parking area by a ground technician. Furthermore, the device comprises one or more rotatable reels for winding and unwinding the compressed air hose.

Such a device has proved very satisfactory in practice, as it has a rela- tively light weight, can be easily moved and used by ground technicians, and operates on an environmentally friendly principle. However, it has been observed that under certain conditions where ambient air contains a relatively high amount of humidity, the operation of the device may be perturbed due to icing. US 2004/0074253 discloses a portable air conditioning unit comprising a rolling support on which are mounted an auxiliary power unit (APU) and an air conditioning module. Ambient air is compressed in a compressor of the APU and the resulting compressed air is supplied to the air conditioning module, where it is cooled in a first heat exchanger by ambient air. The cooled com- pressed air is then successively led to a second heat exchanger, a centrifugal moisture separator and a turbine, where it expands and cools. The expanded cool air is finally passed through the second heat exchanger (to cool the compressed air arriving from the first heat exchanger) before being delivered to the aircraft. This device works on the air cycle principle, which avoids the use of CFCs and other harmful gases; unfortunately, it still requires an APU for its operation.

OBJECT OF THE INVENTION

The object of the present invention is to provide an improved, environmentally friendly device for supplying preconditioned air to an aircraft on the ground, which is not susceptible to icing problems. This is achieved by a device as claimed in claim 1.

GENERAL DESCRIPTION OF THE INVENTION

The present device for supplying preconditioned air to an aircraft on the

ground comprises at least one compressed air inlet for supplying the device with primary compressed air and expander means downstream of the compressed air inlet for allowing compressed air to expand and cool. At least one ambient air compressor is provided for locally compressing ambient air, at least a part of the locally compressed ambient air being guided to the expander means to expand and cool. The device further comprises means for delivering preconditioned air to an aircraft on the ground, wherein the preconditioned air is elaborated from expanded cool air.

According to the invention, the at least part of the locally compressed am- bient air to be used in the expander means is, before its introduction in the expander means, passed through moisture separation means comprising a heat-exchanger to condense water vapour contained in the locally compressed ambient air. It is to be appreciated that at least a proportion of the expanded cool air is used as a coolant in the heat exchanger. The present invention thus uses the so-called "air cycle" for producing preconditioned air. The primary compressed air, which will normally form the main air source for the elaboration of preconditioned air, is advantageously delivered to the aircraft from a remote location (i.e. not produced in the device itself) and enters the device via the compressed air inlet(s). This eliminates the need — in the device itself — for a compressor and engine to drive the compressor. Consequently, the present device is lighter and of simpler conception than conventional portable air conditioning devices, such as e.g. that of US 5,031 ,690 or US 2004/0074253. This also means that the present device can be designed as a self-contained air-conditioner of light weight and reduced dimensions that can be easily manipulated on the parking area.

It is to be noted that in the device of the invention, locally compressed air is introduced in the expander means to increase the output flow available for the aircraft. This locally compressed air to be used in the expander means is first passed through a heat-exchanger to condense water vapour contained therein that could cause icing problems. The condensed water is then advanta-

geously withdrawn from the compressed ambient air flow path by appropriate means. In the heat exchanger, the cooling of the locally compressed air is carried out with expanded cool air from the expander means, so that no additional cooling medium or circuit is required to provide a coolant for the heat exchanger.

Further advantageous aspects of the present device are that (1 ) the working fluid is air, which is free, safe and non toxic; (2) the need for environmentally damaging refrigerant such as CFC, HCFC and the like is eliminated; and (3) air cycle equipment is extremely reliable, thereby reducing maintenance costs.

The moisture separation means preferably comprise water drainage means for withdrawing condensed water from the air flow circuit. Such water drainage means may be integrated in the heat exchanger, or arranged in the ducting leading from the heat exchanger to the expander means. A variety of water drainage means may be employed, however a condensation valve integrated in the heat exchanger is preferably used. Such a condensation valve may be of the electric or mechanical type with a capacity level sensor..

The moisture separation means preferably further comprise a radiator upstream of the heat exchanger to achieve a pre-cooling of the part of locally compressed ambient air to be introduced in the expander means.

If desired, appropriate water extraction devices known in the art, such as e.g. a regenerative dryer, may be further provided upstream of the expander means to extract moisture from the flow of locally compressed ambient air to the expander means. It is to be noted that the relatively cool condensed and separated water- collected from the heat exchanger and/or other appropriate water extraction device — can advantageously be used for further cooling purposes in the device. For example, it may be used to further cool the compressed ambient air exiting the heat-exchanger on its way to the expander means. This allows to further decrease the temperature of the expanded air and increases the

efficiency of the device. Another possibility is to use this cool separated water to cool the compressor heads and increase the efficiency (or the tolerance) of the ambient air compressors. Thirdly, the cool separated water may be sprayed onto the outer surface of the heat-exchanger in order to increase its cooling efficiency.

It will appear to those skilled in the art that in the device of the invention there will normally be three different air flows: (1 ) expanded cold air as exiting from the expander means, (2) warmer expanded cold air having served as coolant in the heat exchanger and (3) hot compressed ambient air as produced by the ambient air compressor. These three airflows may be used to elaborate the preconditioned air to be delivered to the aircraft. Accordingly, the device of the invention advantageously comprises a mixing chamber which may be fed with one, two or all three of these airflows. Valve means may be provided on one or more of the ducting delivering these air flows to allow a controlled mixing.

Preferably, means are provided for controlling the proportion of expanded cool air through the heat exchanger in function of the temperature of the compressed ambient air exiting the heat exchanger.

In a preferred embodiment, compressed ambient air that is not used in the expander means is directed to the mixing chamber via a conduit with regulation valve. This valve is then controlled to deliver the desired amount of compressed ambient air to the mixing chamber.

The expander means may comprise one or more turbine expander, rotary screw expander or displacement expander, or combinations thereof. However, rotary screw expanders are preferred for their high volumetric capacity.

The use of turbine or rotary screw expanders also allows to take advantage of the work produced by the expansion by coupling these expanders to the ambient air compressors, preferably through adapted gearboxes. This avoids the need for additional driving means for the ambient air compressors. The means for delivering the preconditioned air to the aircraft on the

ground preferably comprise a flexible delivery hose having a first end in communication with the mixing chamber and an opposite, second end to be connected to the aircraft.

In order to allow the device to be readily transported to one or more air- crafts, it advantageously comprises a rolling structure with rotatable wheels.

As already mentioned, the primary compressed air may preferably be delivered to the device by compressed air hoses. Such compressed air hoses may be of substantial length (which could be dozens of meters). Therefore, to facilitate the work of the ground technicians, the device is advantageously provided with one rotatable reel per compressed air hose for winding and unwinding the latter. The rotatable reel(s) may be coupled to an electric, hydraulic or pneumatic motor to facilitate the operation thereof.

Of course, the device shall preferably comprise control means to regulate the different air flows to the mixing chamber and to control the expansion and the ambient compression.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will now be described, by way of example, with reference to the accompanying drawing (Fig.1 ), which is a diagram of a preferred embodiment of a device for supplying preconditioned air to an aircraft on the ground in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig.1 is a diagram illustrating the operating principle of a preferred embodiment of a device 10 for supplying preconditioned air to an aircraft on the ground. This device 10 operates on the air-cycle principle: compressed air is expanded in the device 10 to provide cool air, which is then used for elaborating a preconditioned air flow to be delivered to an aircraft. It is to be noted that a main part of the compressed air that is expanded in the device 10 is not produced therein, but delivered thereto from a remote location by means of

compressed air hoses. The primary compressed air is normally produced in this remote location, e.g. the airport building or another facility, which forms a remote ground based compressed air supply unit.

Turning now to Fig.1 , the expander means in the present device 10 com- prise two expanders 12 and 12', preferably of the rotary screw type, which are each supplied with primary compressed air entering the device 10 via respective compressed air inlets 14 and 14'. As already indicated, this primary compressed air is supplied to the device 10 from a remote location via compressed air hoses (not shown). The primary compressed air is thus led to the rotary screw expanders 12 and 12', where it expands to lower temperature and pressure, thereby providing expanded cool air at the expander outlets. As explained below, this expanded cool air will then serve for cooling the aircraft cabin to which the device 10 is connected.

Reference signs 16 and 16' indicate a pair of ambient air compressors downstream of a pair of ambient air inlets 18 and 18', preferably provided with filters (not shown). These ambient air compressors 16 and 16', also preferably of the rotary screw type, are advantageously coupled to the expanders 12 and 12' via adapted gear boxes 20 and 20'. The ambient air compressors are thus driven by the rotary screw expanders 12 and 12', so that no additional equip- ment is needed for driving the ambient air compressors 16 and 16'. The locally compressed ambient air exiting the ambient air compressors 16 and 16' is at a pressure higher than the inlet pressure and at a relatively hot temperature. In order to increase the cool airflow available for the aircraft, a certain proportion of the compressed ambient air is introduced into the expanders 12 and 12'. As can be seen on Fig.1 , the outlet of the first ambient air compressor 16 is connected to a first conduit 22, which is also in communication with the outlet of the second compressor 16'. This first conduit then divides into a second conduit 24 equipped with a regulating valve 25 and a third conduit 26 that guides at least a proportion of the locally compressed ambient air to the expanders 12 and 12'. During its flow in the third conduit 26, the locally com-

pressed ambient air is preferably first passed through a radiator 28, to reduce the temperature of the compressed ambient air. Downstream of the radiator 28, the compressed air is passed through a heat-exchanger, generally indicated 30, in order to further cool the compressed ambient air and condense moisture contained therein. It is to be appreciated that cool expanded air from the expanders 12 and 12' is used as coolant in this heat-exchanger 30. Indeed, a fourth conduit 32 which is connected to the outlet of the first expander 12 and is also in communication with the outlet of the second expander 12' splits into a fifth conduit 34 with a regulating valve 36 and a sixth conduit 38 carrying a certain part of the cool expanded air flowing out of the expanders 12 and 12' to the heat-exchanger 30.

In the present embodiment, the heat-exchanger 30 is of simple design and consists of a chamber 40 serially mounted in the conduit 38 so that the expanded cold air flows trough the chamber 40. The third conduit 26 which carries the compressed ambient air to be introduced in the expanders 12 and 12' traverses this chamber 40 so as to bring the locally compressed air in heat exchange relation ship with the expanded cool air. As the compressed ambient air flows in the third conduit 26 through chamber 20, heat is removed from the hot compressed air by the expanded cold air, and water vapour contained in the compressed ambient air condenses. For increased heat exchange surface, the third conduit 26 has a serpentine shape in the chamber 30. In order to remove the condensed water from the flow of compressed ambient air to the expanders 12, 12', the condensed water is preferably drained from the heat exchanger 30. This is preferably done by means of a condensation valve (not shown) integrated in the heat exchanger 30. The condensation valve may be of the mechanical or electronic type with a capacity level sensor, so that it can automatically perform the drainage when the condensed water level exceeds a predetermined threshold (or at predetermined time intervals). Instead of this preferred simple design of heat exchanger 30 and condensation valve, it is clear that a variety of other designs that will allow bringing the compressed ambient air in heat exchange relationship with the expanded cool air can be

used.

Due to the drying of the air in conduit 26 by means of the heat exchanger 30, the humidity of the air reaching the expanders 12 and 12' is very low. The temperature fall of the air during the expansion will therefore not cause any icing problem that could perturb operation of the device 10 or even damage the latter. It is to be appreciated that the use of expanded cool air as coolant in the heat exchanger 30 is a simple and efficient way to cool the locally compressed ambient air.

It is to be noted that the relatively cool condensed and separated water (that may have a temperature about 5 ⁰ C) — extracted from the heat exchanger

30 and/or other appropriate water extraction device — can advantageously be re-employed for further cooling in the device 10. For example, it may be used to further cool the compressed ambient air exiting the heat-exchanger 30 on its way to the expander 12, 12'. This allows to further decrease the temperature of the cool expanded air and increases the efficiency of the device 10. Another possibility is to use this cool separated water to cool the compressor heads and increase the efficiency (or the tolerance) of the ambient air compressors 16 and

16'. Thirdly, the cool separated water may be sprayed on the outer surface (i.e. external surface of chamber 40) of the heat-exchanger 30 in order to increase its overall cooling efficiency.

Regarding now more specifically the elaboration of the preconditioned air flow, it will appear that in the present embodiment, three different air flows are available: expanded cool air as delivered by the expanders 12 and 12' is carried in fifth conduit 34, warmer expanded air used as coolant and exiting the heat exchanger 30 is carried by sixth conduit 38 downstream of the heat exchanger 30, and the hot locally compressed air in the second conduit 24. In order to take advantage of these different air flows, the fifth, sixth and second conduit 34, 38 and 24 respectively, open into a mixing chamber 42, preferably taking the form of a conduit of larger cross-section than the other conduits. The preconditioned air elaborated in the mixing chamber is then delivered to the

aircraft by means of a flexible delivery hose 44 having a first end 46 in communication with the mixing chamber 42 and an opposite second end 48 for connection to a preconditioned air inlet port of an aircraft.

The elaboration of the preconditioned air to the desired temperature and pressure thus generally involves mixing the three airflows. A typical temperature value of preconditioned air to be delivered to an aircraft is -5 ⁰ C. The expanded cool air delivered by the expanders 12 and 12' may reach very cold temperatures, e.g. -5O ⁰ C and below. In the present embodiment, the expansion is preferably controlled to reach a temperature of in the range of -4O ⁰ C to -25 ⁰ C downstream of the expanders. As a result, the expanded cool air will normally be mixed with warmer air in the mixing chamber 42, i.e. with warmer expanded cool air having served as coolant in the heat exchanger 30 and/or with hot locally compressed ambient air. Preferably, the final temperature adjustment of the preconditioned air is done by providing an adapted amount of hot com- pressed ambient air through conduit 24, which can reach temperatures up to 200 ⁰ C as a result of compression. Therefore, a temperature sensor 50 is arranged in the mixing chamber 42 and the flow of hot compressed air is regulated in function of the desired output temperature via valve 25.

The temperature of the compressed ambient air exiting the heat ex- changer 30 is preferably adjusted by varying the amount of expanded cold air flowing through conduit 38 and thus through the heat exchanger 30 by means of regulation valve 36. The temperature of the compressed ambient air exiting the heat exchanger 30 is measured by a temperature sensor 52.

The elaboration of the preconditioned air flow is advantageously auto- matically done by an electronic control unit: having input means for an operator to set the desired output temperature and pressure; receiving temperature and pressure information from various sensors (such as sensors 50 and 52); and capable of controlling operating parameters in the device (e.g. the compressors and valves). Examples of operating values are given hereinafter. Primary compressed

air is supplied to the device 10 at a temperature of 10 to 4O ⁰ C and pressure of 7 to 10 bars. The ambient air is sucked in the device 10 through inlets 18 and 18' and compressed, providing hot compressed ambient air at a pressure of e.g. 4 bars and a temperature up to 200 ⁰ C. Downstream of the radiator 28, the hot compressed air reaches a temperature below 7O ⁰ C and a pressure of about 2-4 bars, still with a humidity comparable to that of the external ambient air. After the passage through the heat exchanger 30, the compressed ambient air has reached a temperature of e.g. about 15 ⁰ C above ambient and sufficient moisture has been removed in order to prevent icing problems. The expansion in the expanders is preferably carried out to obtain expanded cool air at a temperature of about -4O ⁰ C and a pressure that is determined in view of the desired delivery pressure to the aircraft and taking into account the pressure drop in the device 10 itself. For a final overpressure of e.g. 50 mbar a pressure of 1.2 bars has been set at the exit of the expanders. It is to be noted that in the present embodiment, the hot compressed ambient air is delivered to the mixing chamber at a pressure superior to the desired delivery pressure, and is thus also taken into account. Besides, one will note that when using screw expanders, the compressed ambient air may be introduced in the expanders at different position, and need not necessarily be mixed with the primary com- pressed air upstream of the expander inlet. Finally, the flow of hot compressed air in the mixing chamber 42 is controlled to reach the desired value of -5 ⁰ C for the preconditioned air.

Although not shown in the drawing, the present device 10 preferably takes the form of a self-contained vehicle with a rolling support comprising rotatably mounted wheels. This allows the ground technicians to easily transport the device 10 from one aircraft to another. Also, the device is preferably provided with rotatable reels for winding and unwinding the compressed air hoses (which may be several dozens of meters in length) used to carry the primary compressed air to device 10. The compressed air hoses are preferably wound on the reels in such a way that they can be unwound from the hose extremity that connects the remote ground-based compressed air unit wherein the primary

compressed air is produced (as is e.g. described in WO 2004/024561 ). This provides an important advantage since, when the device is not used and stored near the ground-based compressed air supply, the compressed air hoses are completely wound around their respective reels. When the device is moved towards an aircraft, the compressed air hoses are automatically unrolled from the reels and laid on the floor. This avoids extensive wear of the compressed air hoses due to abrasion since they are not dragged on the floor.

A flight of stairs may further be provided on the device 10 to permit the ground technician to more easily access preconditioned air ports in the fuse- lage.