EP2637882A1

EP2637882A1 - Air conditioning system for a cabin of a vehicle

Info

Publication number: EP2637882A1
Application number: EP10798603.6A
Authority: EP
Inventors: Frédéric LAUDET
Original assignee: Renault Trucks SAS
Current assignee: Volvo Truck Corp
Priority date: 2010-11-10
Filing date: 2010-11-10
Publication date: 2013-09-18
Also published as: JP5716157B2; WO2012063095A1; JP2013541466A

Abstract

The air conditioning system (1) comprises: a refrigerant circuit (3) carrying a refrigerant in a loop successively through a compressor (4), a condenser (5), an expander (8) and an evaporator (9) capable of cooling an air flow (10) directed towards the cabin (2), characterized in that it further comprises: a collector (12) for collecting the condensation fluids which appears on the evaporator (9) in use and a collecting pipe (13) for carrying said condensation fluids towards a heat exchanger, the heat exchanger being designed to allow a thermal contact between said condensation fluids and the refrigerant so that the refrigerant can be cooled by the condensation fluids, said condensation fluids being thereby heated a return pipe (14) capable of carrying at least part of said heated condensation fluids to the cabin (2) for humidifying said cabin (2).

Description

AIR CONDITIONING SYSTEM FOR A CABIN OF A VEHICLE

Field of the invention The present invention relates to an air conditioning system for a cabin of a vehicle, for example an industrial vehicle.

Technological background An air conditioning system has been a standard feature in vehicles for many years.

Such a system typically comprises a refrigerant circuit carrying a refrigerant in a loop. Conventionally, the refrigerant in gaseous phase is compressed into a high pressure gas in a compressor which is driven by the vehicle engine or by a dedicated motor. At the output of the compressor, the refrigerant is hot due to the compression. The refrigerant is then carried towards a condenser, which may be located in the front of the vehicle or at any other location where it may be contacted by a flow of ambient air, and in which the refrigerant is cooled down and condensed into a liquid, while remaining at a high pressure. The condenser is essentially a heat exchanger between the refrigerant, at high pressure, and the ambient air. In order to improve the condenser efficiency, a condenser fan driven by the vehicle engine or driven by a separate electric motor is generally arranged close to the condenser. The refrigerant in liquid phase, but at high pressure, is then expanded in an expander where its temperature drops dramatically, and it is then carried towards an evaporator where it is evaporated into a gas before entering the compressor again. The evaporation of the refrigerant in the evaporator is used to cool an air flow directed towards the cabin, in order to lower the cabin temperature. The evaporator is essentially a heat exchanger between the refrigerant, at low pressure, and the air which is to be blown inside the cabin. Of course, various types of air conditioning systems are based on this principle, but the various elements can vary from one embodiment to another. For example, the expander may be a mere calibrated orifice fluid passage or can be a thermal expansion valve. In the former case, the system may further comprise an accumulator between the evaporator and the compressor, and in the latter case, the system may further comprise a receiver dryer between the condenser and the expander.

In some operating conditions, such a conventional air conditioning system can have a poor efficiency or can require too much power to provide the expected cooling effect. This can happen when the outside temperature is high or when the vehicle is moving at low speed, for example in a city.

One solution to improve the system efficiency is to operate the system with recycled air. In other words, the air flow which is cooled at the evaporator and directed towards the cabin is not outside air but air coming from the cabin. Because recycled air is not as warm as outside air, less energy is required to reach the target temperature in the cabin. This results in lower fuel consumption, quicker reaching of the temperature target and better comfort for the driver in terms of temperature.

However, one consequence of this disposition is that the humidity in the cabin progressively drops, because one effect of the evaporator is to dehydrate the air it cools, and because no or few outside air is brought. As a result, the humidity in the cabin can be very low, which is not desirable as it can be uncomfortable for the driver, especially if he/she wears contact lenses.

It therefore appears that, from several standpoints, there is room for improvement in air conditioning system for vehicles.

Summary

It is an object of the present invention to provide an improved air conditioning system for a cabin of a vehicle which can overcome the drawbacks encountered in conventional air conditioning systems.

Another object of the present invention is to provide an air conditioning system which has a high efficiency while also being comfortable for the driver, or more generally for the cabin occupants.

According to the invention such an air conditioning system for a cabin of a vehicle comprises:

- a refrigerant circuit carrying a refrigerant in a loop successively through a condenser and an evaporator capable of cooling an air flow directed towards the cabin;

- a collector for collecting condensation fluids which appear at the evaporator in use and a collecting pipe for carrying said condensation fluids towards a heat exchanger, the heat exchanger being designed to allow a thermal contact between said condensation fluids and the refrigerant so that the refrigerant can be cooled by the condensation fluids, said condensation fluids being thereby heated;

- a return pipe capable of carrying at least part of said heated condensation fluids to the cabin for humidifying said cabin.

The heat exchanger can be a dedicated heat exchanger located in the air-conditioning circuit at any point where the refrigerant is hot, i.e. preferably downstream of the compressor and upstream of the expander.

Nevertheless, according to the two embodiments which will be described in more details hereinafter, the heat exchanger is integrated with the condenser. Thus, in such a case, the invention provides a three-fluid heat exchanger forming the condenser with the refrigerant as a first fluid, ambient air as a second fluid, and condensation fluids from the evaporator as a third fluid. In other words, the refrigerant is cooled in the condenser under the action of two sources of cold: the ambient air and the condensation fluids, the heating of which contributes to the cooling of the refrigerant.

With this arrangement, the efficiency of the air conditioning system is greatly improved. Therefore, the system can provide enough cooled air in the cabin even during hot days or when the vehicle is moving at low speeds. The invention makes it possible to achieve this effect without requiring the condenser fan to rotate during long periods, and therefore contributes to reduce the fuel consumption. Moreover, by improving the system efficiency, the invention also makes it possible to reach more quickly the target temperature inside the cabin.

Another advantage of the invention is that the condensation fluids are canalized, and that this minimizes the amount of water being rejected on the ground, which can generate rust on the parts of the vehicle on which said water streams, and marks on the ground. Furthermore, the invention makes use of the condensation fluids which would otherwise be lost, knowing that the volume of water which is condensed per hour can be quite high, especially in hot and humid countries.

Moreover, the condensation fluids, once heated in the heat exchanger, is sent to the cabin, preferably in the form of water vapor and or heated humidified air, rather than being sent to the atmosphere. This helps keeping the humidity in the cabin at a comfortable level, in particular but not exclusively when the air conditioning system is operated with recycled air from the cabin.

An important aspect of the invention lies in that, with the condensation fluids being used to cool the condenser, it is possible to improve the condenser efficiency for a given size, or, alternatively, to reduce the condenser size for given efficiency, or to combine both effects, which cannot be achieved by prior art systems. The use of a smaller condenser in the front of the vehicle can be advantageous in some vehicles.

The invention provides an air conditioning system which will be capable of producing enough cooling efficiency even with refrigerants conforming to future regulations, which may be less effective.

The invention also concerns a vehicle having a cabin and such an air conditioning system.

These and other features and advantages will become apparent upon reading the following description in view of the drawings attached hereto representing, as non-limiting examples, embodiments of an air conditioning system according to the invention.

Brief description of the drawings

The following detailed description of several embodiments of the invention is better understood when read in conjunction with the appended drawings, it being however understood that the invention is not limited to the specific embodiments disclosed.

Figure 1 is a schematic representation of an air conditioning system according to the invention;

Figure 2 is a schematic representation of the air conditioning system of Figure 1 , showing more specifically the circuit of condensation water and of water vapor;

Figures 3 and 4 schematically show a condenser of the prior art;

Figures 5 and 6 show conduits to be used in a first embodiment of a condenser of an air conditioning system according to the invention;

Figures 7 and 8 are detailed views, respectively in cross section and in perspective, of a condenser according to said first embodiment;

Figure 9 is a schematic cross section of a part of a condenser according to a second embodiment of the invention. Detailed description of the invention

As this is illustrated in Figures 1 and 2, an air conditioning system 1 for a cabin 2 of a vehicle first comprises a refrigerant circuit 3 which carries a refrigerant in a loop.

In the refrigerant circuit 3, the refrigerant, as a low pressure gas, enters a compressor 4 driven by the vehicle engine or by a dedicated motor. After the compressor 4, the high pressure and high temperature gaseous refrigerant is directed towards a condenser 5 which may located in the front of the vehicle, and in which the refrigerant is condensed into a high pressure liquid. A fan 6 driven by the vehicle engine or by a separate motor may be provided close to the condenser 5 in order to improve its efficiency. In this embodiment, the refrigerant flows towards a receiver dryer 7 and then flows through an expander 8, which is here embodied as a thermal expansion valve. A pressure sensor could be provided in the circuit between the receiver dryer 7 and the expander 8. In the expander, the high pressure liquid is expanded, so that its pressure is lowered, thereby considerably reducing its temperature. The low pressure refrigerant then enters an evaporator 9 where it is evaporated into a low pressure gas. Said gaseous refrigerant then flows back towards the compressor 4.

At the evaporator 9, the evaporation of the refrigerant is used to cool an air flow 10 which is conveyed towards the cabin 2 for example with the help of a blower. Conversely, the air flows heats the refrigerant, thereby promoting its evaporation.

The air conditioning system 1 according to the invention further comprises a collector 12 for collecting the condensation fluids which may appear on the evaporator 9 in use, and a collecting pipe 13 for carrying said condensation fluids towards a heat exchanger, which, in both embodiments which will be described, is integrated with the condenser 5. The condensation fluids primarily comprises water which is condensed on the evaporator because the air which comes into contact with the evaporator is cooled and thereby loses part of its ability to carry water vapor. Said collecting pipe 13 can also carry cold air. Presence of air may derive from the fact the collecting pipe 13 originates near the evaporator, where air may be slightly pressurized due to the blower of the air conditioning system. The collecting pipe 13 can include a water tank 18 which is capable of receiving water from the evaporator 9. In the illustrated embodiment, the water tank 18 is located upstream from the condenser 5, and an overflow duct 190 is provided from said water tank 18 towards a downstream point of the collecting pipe 13.

In the condenser 5, the refrigerant is cooled both by ambient air and by said condensation fluids. The condensation fluids are thereby heated by the refrigerant at the condenser. Due to this heating, at least part of the condensation water may be transformed into water vapor. This water vapor will eventually mix with air carried by the collecting pipe so as to form heated humidified air. The condensation fluids heated at the condenser 5 are then carried by a return pipe 14 to the cabin 2, in order to humidify the cabin 2. At the output of the condenser, the condensation fluids may therefore contain water vapor and/or humidified air, and/or possibly some residual water.

Referring now more particularly to Figure 2, the cabin 2 includes at least one air duct 15 comprising openings 16 by which air can enter the cabin 2. The air duct is preferably part of a cabin ventilating circuit comprising several ducts, each with several openings, so as to distribute ventilating air selectively towards the feet of the passengers, towards the body and head of the passengers, or towards the windshield or other window surfaces. An air conditioner 17 coupled to the evaporator 9 is provided inside the cabin 2 or in an engine compartment to send cooled air into said air duct 15.

The return pipe preferably delivers at least part of the heated condensation fluids to the duct 15. In the duct, these heated condensation fluids will mix with incoming air to the cabin. The return pipe can deliver the heated fluids to the duct so that they are distributed amongst all openings 16. Preferably though, the heated fluids are not distributed to those openings directed towards the windshield or other windows, but rather to those openings directed towards the upper part of the body of the passengers. Preferably only the gaseous part of the heated condensation fluids is delivered to the cabin, while possible residual water is preferably discarded either to the outside of the vehicle, or to the tank 18. Nevertheless, residual heated condensation water may also be nebulized to be introduced in the cabin.

Preferably, the air conditioning system 1 can further comprise a humidity sensor 19 located in the vehicle cabin 2 and means coupled to said humidity sensor 19 and capable of regulating the flow of heated condensation fluids depending on the measured humidity. Said means can include an electronic controller 20 coupled to said sensor 19 and to a first valve 21 located on the collecting pipe 13 between the water tank 18 and the condenser 5, and a second valve 22 located on the return pipe 14 between the condenser 5 and the air duct 15. As shown in this example, the second valve 22 can be a three way valve for directing the heated condensation fluids either to the air duct 15, and/or to the atmosphere, if no humidification of the cabin air is necessary. Alternatively, the sensor 19 can be a temperature and humidity sensor.

The flow of condensation fluids in the collecting pipe, in the heat exchanger, and in the return pipe may result from the slight overpressure at the evaporator, from gravity, and/or through the provision of a pump located for example in the collecting and/or return pipes.

Two embodiments of condensers which can be used in an air conditioning system according to the invention will now be described.

In an implementation of the invention, the condenser 5 has a general structure similar to the conventional condenser illustrated in Figures 3 and 4 with additional or alternative features which will be described subsequently.

Thus, the condenser 5 can have a substantially parallelepiped shape. It includes a refrigerant inlet 25 and a refrigerant outlet 26 which can be located close to a same vertical edge 27 of the condenser 5, the outlet 26 being preferably arranged above the inlet 25.

The condenser 5 can comprise a plurality of parallel conduits 29 from the refrigerant inlet 25 to the refrigerant outlet 26, said conduits 29 extending between the vertical edges 27, 28 of the condenser 5. In order to improve the condenser efficiency, fins 30 can be provided between adjacent conduits 29.

Furthermore, a side chamber may be located on each side of the conduits, preferably close to the corresponding vertical edge 27, 28. Thus, a first side chamber 31 is located close to the vertical edge 27 of the inlet 25 and outlet 26, and a second side chamber 32 is located close to the other vertical edge 28. The chambers 31 , 32 are in fluid communication with the conduits 29.

The conduits 29 can be arranged in successive series of parallel conduits from the refrigerant inlet 25 to the refrigerant outlet 26. In the illustrated embodiment, the condenser 5 comprises three successive series of conduits 29, i.e. a first series 33 at the top part of the condenser 5, a second series 34 at the intermediate part of the condenser 5, and a third series 35 at the bottom part of the condenser 5. For example, the first series 33 can comprise nine conduits 29, the second series 34 can comprise seven conduits 29, and the third series 35 can comprise six conduits 29. Of course, these numbers are purely indicative.

In the conduits 29 of a given series, the refrigerant flows in the same direction, whereas it flows in opposite directions in the conduits 29 of one series and in the conduits 29 of the subsequent series. The first chamber 31 comprises a partition wall 36 located substantially at the level of the border 37 between the first series 33 and the second series 34, and the second chamber 32 comprises a partition wall 38 located substantially at the level of the border 39 between the second series 34 and the third series 35.

In the example depicted in Figures 3 and 4, the gaseous refrigerant flow enters the first side chamber 31 of the condenser 5 by the inlet 25, up to the partition wall 36, and is divided into subflows each carried by a conduit 29 of the first series 33. The refrigerant then enters the second side chamber 32, up to the partition wall 38, and flows through the conduits 29 of the second series 34, in the opposite direction, towards the first side chamber 31 . Finally, the refrigerant flows through the conduits 29 of the third series 35, towards the second side chamber 32. The refrigerant is collected by a return pipe 40 which extends substantially vertically along the second side chamber 32 and then substantially horizontally towards the outlet 26.

In the shown embodiments, the refrigerant is cooled and condensed in the condenser 5 both by means of ambient air and by means of the condensation fluids. In the conduits 29 of the first series 33, the refrigerant is mostly gaseous, while in the conduits 29 of the third series 35, the refrigerant is mostly liquid.

Figures 5 to 8 relate to a first embodiment of a condenser 5 for an air conditioning system according to the invention.

According to this embodiment, at least one of the conduits 29 comprises an inner fluid passage 41 in which the condensation fluids can flow and an outer fluid passage 42, substantially coaxial with the inner fluid passage 41 , and in which the refrigerant can flow. The inner and outer fluid passages are separated by a continuous wall of the material of which the conduits 29 are made, for example a metal such as aluminium. The inner and outer fluid passages are therefore fluid tight with respect one to the other. Air circulates around the outer surface of the conduit.

So that conduits 29 can be made easily, for example in a single piece by extrusion, the outer fluid passage 42 can be formed of a plurality of separate holes 43 which extend axially, and which are arranged substantially all around the inner fluid passage 41 . The conduits 29 can have a substantially circular cross section (figure 5) or a flattened cross section (figure 6).

Preferably, at least the conduits 29 of the last series - here the third series 35 - are made with an inner fluid passage 41 and an outer fluid passage 42, typically according to figures 5 or 6. Indeed, since the refrigerant flowing in the conduits 29 of the third series 35 is mostly liquid, there is a better heat transfer coefficient between the refrigerant and the condensation fluids, which helps improving the condenser efficiency.

As illustrated in figures 7 and 8, the conduits 29 can be made so that the inner fluid passage 41 extends at each ends axially further than the outer fluid passages 42, 43. The conduits are connected to the side chambers so that the outer fluid passages 42, 43 are in fluid connection with the corresponding side chamber. On the other hand, the inner fluid passage 41 extends all the way through the side chamber and out of the side chamber, with no fluid communication between the inner fluid passage and the corresponding side chamber. The inner fluid passage 41 of one conduit 29 is connected at one end by a connecting tube 44 which can be substantially C-shaped, and which is located outside the corresponding side chamber 31 , 32, to the corresponding end of the inner fluid passage of one of the adjacent conduits 29. At its opposite end (not shown), the inner fluid passage 41 of the same conduit 29 is connected by another connecting tube 44, to the corresponding end of the inner fluid passage of the other one of the adjacent conduits 29. Therefore, the inner fluid passages of the adjacent conduits form a serpentine path along the series of conduits, with the condensate fluids flowing in one direction in a conduit 29, and flowing in the opposite direction in the adjacent conduit. As a consequence, the condensation fluids follow a serpentine path between the side chambers 31 , 32.

This first embodiment of a condenser 5 is very efficient since it ensures a thermal transfer between the refrigerant and the condensation fluids along the whole length of the conduits 29. According to a second embodiment, illustrated in figure 9, the condenser 5 can further comprise an additional conduit 45 in which the condensation fluids can flow, said additional conduit 45 being located in at least one side chamber 31 , 32.

The additional conduit 45 can have a U shape extending along the whole height of the side chamber 31 , 32. It is preferably also equipped with an overflow duct 46. In the illustrated embodiment, there is provided a cap 47 at the upper end of the corresponding side chamber 31 , 32, and fins 48 designed to improve the heat transfer between the condensation fluids flowing in the conduit 45 and the refrigerant flowing in the conduits 29.

A significant advantage of this second embodiment is that it is makes it possible to improve the condenser efficiency without requiring costly modifications of said condenser structure.

Of course, the features of the first and second embodiments can be combined in a same condenser 5 to further improve its efficiency.

Thanks to the invention, the humidity in the cabin is regulated by the introduction of heated condensation fluids, so that no undesirable feeling of moisture is felt by the passengers. The heat necessary for the process is "free", inasmuch it is heat which would otherwise be dissipated to the ambient air, and it in fact contributes to a better efficiency of the air conditioning unit so that the benefit of this heat transfer is twofold.

By providing a specific condenser as a three-fluid heat exchanger having an improved efficiency, the invention makes it possible to quickly regulate the working of the compressor 4 and of the fan 6. This results in a decrease in the fuel consumption due to the operation of the compressor 4 and of the fan 6.

In order to further improve the efficiency of the air conditioning system 1 , the process according to the invention comprises coupling the flow of condensation fluids in the condenser with the starting of the fan, when required.

Of course, the invention is not restricted to the embodiment described above by way of non-limiting example, but on the contrary it encompasses all embodiments thereof.

Claims

1. An air conditioning system for a cabin (2) of a vehicle, comprising a refrigerant circuit (3) carrying a refrigerant in a loop successively through a compressor (4), a condenser (5), an expander (8) and an evaporator (9) capable of cooling an air flow (10) directed towards the cabin (2), characterized in that it further comprises:

a collector (12) for collecting the condensation fluids which appear at the evaporator (9) in use and a collecting pipe (13) for carrying said condensation fluids towards a heat exchanger (5), the heat exchanger (5) being designed to allow a thermal contact between said condensation fluids and the refrigerant so that the refrigerant can be cooled by the condensation fluids, said condensation fluids being thereby heated

a return pipe (14) capable of carrying at least part of said heated condensation fluids to the cabin (2) for humidifying said cabin (2).

2. The air conditioning system according to claim 1 , characterized in that the heat exchanger is integrated with the condenser (5).

3. The air conditioning system according to claim 2, characterized in that t the condenser (5) which comprises a plurality of parallel conduits (29), around which ambient air can circulate,, at least one of said conduits (29) comprising an inner fluid passage (41) in which the condensation fluids can flow and an outer fluid passage (42), substantially coaxial with the inner fluid passage (41), the refrigerant flowing in said outer fluid passages (41 , 42).

4. The air conditioning system according to claim 3, characterized in that the outer fluid passage (42) is formed of a plurality of holes (43) which extend axially substantially all around the inner fluid passage (41), and in which the refrigerant can flow.

5. The air conditioning system according to claim 3 or claim 4, characterized in that the conduits (29) have a substantially circular cross section or a flattened cross section.

6. The air conditioning system according to any one of claims 3 to

5, characterized in that it comprises successive series (33, 34, 35) of parallel conduits (29) around which ambient air can circulate, the refrigerant flowing in the same direction in the conduits (29) of a given series, and flowing in opposite directions in the conduits (29) of one series and in the conduits (29) of the subsequent series, at least the conduits (29) of the last series (35) each comprising an inner fluid passage (41 ) in which the condensation fluids can flow and an outer fluid passage (42), substantially coaxial with the inner fluid passage (41 ), the refrigerant flowing in said inner fluid passage (41 , 42).

7. The air conditioning system according to any one of claims 2 to

6, characterized in that the condenser (5) comprises a plurality of parallel conduits (29) from the refrigerant inlet (25) to the refrigerant outlet (26), and a side chamber (31 , 32) located on each side of the conduits (29), wherein the refrigerant can flow from one conduit to a subsequent conduit, the condenser (5) further comprising an additional conduit (45) in which the condensation fluids can flow, said additional conduit (45) being located in at least one side chamber (31 , 32).

8. The air conditioning system according to any one of claims 1 to

6, characterized in that the collecting pipe (13) includes a water tank (18) capable of receiving water from the evaporator (9).

9. The air conditioning system according to any one of claims 1 to 8, characterized in that it further comprises a humidity sensor (19) located in the vehicle cabin (2) and means (20, 21 , 22) coupled to said humidity sensor (19) and capable of regulating the flow of heated condensation fluids depending on the measured humidity.

10. A vehicle having a cabin (2), characterized in that it comprises conditioning system (1 ) according to any one of the preceding claims.