WO2021105804A1

WO2021105804A1 - Methods and systems for regulating the temperature in a compartment of a vehicle

Info

Publication number: WO2021105804A1
Application number: PCT/IB2020/060457
Authority: WO
Inventors: Nicholas WYLLIE
Original assignee: Wyllie Nicholas
Priority date: 2019-11-29
Filing date: 2020-11-06
Publication date: 2021-06-03
Also published as: GB2589375B; GB2589375A8; GB2589375A; GB201917433D0

Abstract

A vehicle 34 comprises a temperature regulating system 30 for regulating the temperature in a compartment 32 of the vehicle, wherein the system comprises: a duct 36 for receiving a first airflow B when the vehicle is propelled and conveying the airflow to the compartment; a thermoelectric module 40 having a first side 42 located in the duct and a second side 44 external to the duct located in a second airflow A; and a controller 48 for controlling the thermoelectric module to draw heat from or dissipate heat to the first airflow and correspondingly to dissipate heat to or draw heat from the second airflow.

Description

METHODS AND SYSTEMS FOR REGULATING THE TEMPERATURE IN A

COMPARTMENT OF A VEHICLE

Field of the Invention

The invention relates to methods and systems for regulating the temperature in a compartment of a vehicle.

Background to the Invention

Vehicles for transporting people and/or objects are well known. Most traditional vehicles that are powered by a combustion engine comprise a cooling system that circulates a coolant such as water for cooling the engine, and heat from the cooling system is extracted to warm occupants in a vehicle cabin. Air conditioning systems comprise air conditioning pumps and a refrigerant that exchanges heat with air conveyed to a vehicle cabin.

Hybrid and electric vehicles adopt a variety of different systems but typically use one of an electric radiator, or a resistance wire, for heating and an air conditioning pump and refrigerant for cooling.

It is desirable to provide an improved heating and cooling solution for vehicles.

Summary of the Invention

The invention provides a vehicle comprising a temperature regulating system as specified in claim 1 and a temperature regulating system in or for a vehicle as specified in claim 17.

Brief Description of the Drawings

In order that the invention may be well understood, some examples thereof, which are given by way of example only, will now be described with reference to the drawings in which:

Figure l is a schematic representation of a vehicle comprising a temperature regulating system; Figure 2 is a schematic representation of a temperature regulating system;

Figure 3 is a schematic representation of another temperature regulating system;

Figure 4 is a schematic representation of yet another temperature regulating system; Figure 5a is a view along an axis of a further temperature regulating system;

Figure 5b is a section taken through the axis of the temperature regulating system shown in Figure 5a;

Figure 6 is a schematic representation of ducting arrangements of a temperature regulating system; and

Figure 7 is a schematic representation of a thermoelectric module of a temperature regulating system.

Detailed Description

Vehicles transport people or objects, and include automotive land vehicles such as cars, trucks and buses; railed vehicles such as trains and trams; watercraft such as ships and boats; and aircraft such as airplanes, including jets, rockets and helicopters.

Propulsion is typically provided by a motor that may be an internal combustion engine that combusts a fuel such as petrol or diesel, or an electric motor associated with a source of electrical power, such as a battery. Hydrogen powered vehicles are also known, including vehicles that have an engine that burns hydrogen in an internal combustion engine and vehicles in which hydrogen is reacted with oxygen in one or more fuel cells to run at least one electric motor. In other examples, vehicles may be propelled by natural forces such as wind in the case of sailing boats, or by magnetism or electromagnetism such as in maglev trains. In other examples, a vehicle may be arranged for connection to a means of propulsion as is the case with a trailer connected to a truck or railway carriage connected to a locomotive.

The source of energy in the case of an internal combustion engine is a fuel, such as petrol or diesel stored in an onboard tank. For an electric vehicle the source is typically an onboard battery. Trains or trams on the other hand may be connected to an overhead power supply and therefore have an electrical connector which when connected provides a source of energy. Vehicles may comprise an enclosed or partially enclosed compartment for transporting people or objects. It is often desirable to control or regulate the temperature in the compartment for the comfort of occupants. If the ambient temperature is cold the compartment may require heating and conversely if the ambient temperature is hot the compartment may require cooling. In the case of objects such as perishable goods a container compartment may require cooling to improve condition on delivery.

A functional component of a vehicle, such as a motor or battery, may be located in its own compartment. The component may have an operating temperature range which should not be exceeded for prolonged periods and may therefore require cooling or heating to allow them to operate within a specified temperature range.

Figure 1 shows in simplified form a vehicle, which in this example is an electric vehicle 10. The vehicle comprises a compartment 12 for transporting occupants and/or objects, and electric components 14, 16, 18 housed in compartments or housings 20, 22, 24.

The electric components include a source of electrical energy 14, such as a battery, a controller 16, and a motor assembly 18. The controller 16 may comprise a digital processing system and the motor assembly 18 may comprise an electric motor and inverter arranged to receive electrical energy from the source of electrical energy 14 for propelling the vehicle 10 in accordance with an output from the controller 16. The compartment 12 may include seats for people or storage systems for storing objects for transportation.

The compartment 12 typically requires temperature regulation for the comfort of the occupants or to control the thermal environment in which objects are stored for transportation for example by cooling perishable foods. A vehicle cabin may be partially open having a sunroof or convertible roof and the compartment may have a plurality of different zones in which the temperature is controlled to provide different temperature environments according to user demand. The vehicle components in compartments 20, 22, 24 typically have a thermal operating range outside which performance deteriorates or fails. Therefore, these compartments may be thermally regulated to provide the correct operating environment for the components they house. A temperature regulating system 25 exchanges heat energy with ambient air 26 received when the vehicle is propelled and conveys temperature regulating airflows 27 to compartments in the vehicle for cooling or heating.

Figure 2 shows a system 30 for regulating the temperature in a compartment 32 of a vehicle 34. When the vehicle 34 is propelled the motion generates an airflow, over and around the vehicle and through openings or vents in the vehicle that are arranged to an airflow. A duct 36 is arranged to receive an airflow B though an opening or vent 38 and convey the airflow to the compartment 32 for regulating the temperature in the compartment. A second airflow A forms a thermal reservoir from or to which heat can be drawn or dissipated.

A thermoelectric module 40 is associated with a source of electrical energy 46 and comprises a first side 42 in the duct 36 for location in, or exposure to, airflow B. In this example the source of electrical energy 46 is an onboard battery of the vehicle. However, in other examples the source of electrical energy may be provided by an electrical connector connectable to a power supply.

A second side 44 of the thermoelectric module 40 is disposed externally of the duct 36 for location in airflow A. A controller 48 is operably connected with the source of electrical energy 46 and the thermoelectric module 40 for controlling an electrical potential between the first side 42 and the second side 44 to cause heat to be drawn from one of airflow B and airflow A and dissipated to the other one of the airflows as shown by double-headed arrows to provide an airflow condition for cooling or heating the compartment 32 dependent on a temperature required in the compartment.

Preferably, a thermal sensor 50 for sensing a temperature in the compartment 32 is operably connected to the controller 48 to output a temperature signal to the controller. The controller 48 may control the supply of a heating or cooling airflow to the compartment 32 dependent on whether the value of the received signal from the temperature sensor 50 indicates the temperature is higher or lower than a required temperature in the compartment 32. In this illustrated arrangement the potential difference between the first and second side 42, 44 is reversible to cause heat to be transferred either from or to airflow B as required. In other examples the thermoelectric module 40 may by operable to transfer heat in only one direction relative to airflow B. This latter simplified arrangement may be appropriate if only one of heating or cooling is required. In this regard, it may be required that a vehicle component requires cooling to compensate for waste heat energy, but does not require heating.

In further examples, there may be a duct for heating and a duct for cooling. In this case, two thermoelectric modules are associated with respective ducts. One module would draw heat from the airflow in the associated duct and the other module would dissipate heat to the airflow in the associated duct. One or two reservoir airflows A may be provided to which, or from which, heat can be transferred.

In still further examples, a plurality of ducts may be provided for heating and cooling different zones within a single compartment, so that differential temperatures can be established between the zones e.g. between a driver zone, front-passenger zone and rear passenger zone or zones. An arrangement comprising a multiplicity of heating and cooling ducts is described in greater detail with reference to Figures 4, 5 and 6.

Referring to Figure 2, a fan 52 may be provided for increasing or generating the airflow B. The fan 52 may have any suitable arrangement for inducing airflow, such as an impeller driven on an axial shaft. The fan 52 generates an airflow and may be arranged for circulating cooled or heated air in the compartment 32 when the vehicle is stationary or increasing the airflow if the vehicle is propelled at velocities that are insufficient to generate a required airflow. The fan 52 may be connected to receive electrical energy from the source of electrical energy 46 and controlled by the controller 48.

In one arrangement, the fan 52 may be used to generate electrical energy for storage by the source of electrical energy 46 or for application to the thermoelectric module 40. For example, if the vehicle is propelled at a velocity that generates more airflow than is required, a portion of that fluid flow energy (kinetic energy) can be removed and converted to electrical energy, using the fan and a generator. The generator is configured to receiving kinetic energy and convert the received kinetic energy into electrical energy, typically by induction. This arrangement allows energy to be recovered when a vehicle is in motion for subsequent use for temperature control when the vehicle is stationary or moving slowly. Alternatively, energy generation and temperature regulation may be implemented simultaneously. The controller 48 may include suitable electrical components for converting the electrical energy received from the fan-generator for storage in the source of electrical energy 46. Alternatively, the fan-generator may be configured to output electrical energy conditioned for storage by the source of electrical energy.

Figure 3 shows another vehicle 60 that is provided with a temperature regulating system 61. The temperature regulating system 61 comprises a second duct 62 for conveying the second airflow described above in relation to Figure 2. Components shown in Figure 3 that are the same as, or similar to, components shown in Figure 2 are given the same reference numerals and are not described again in detail.

The second duct 62 has a fluid inlet or vent 64 and a fluid outlet or vent 66. Air is drawn into the inlet 64 by motion of the vehicle or by a fan 68 and exchanges thermal energy with the second side 44 of the thermoelectric module 40 located in the second duct 62. The air that is heated or cooled by the heat exchange is conveyed along the second duct 62 and exhausted through the outlet 66.

In this example there are respective fans 52, 68 associated with the respective airflows A, B, but there may be a just single fan for generating both airflows A and B, and there may be a single opening or inlet vent in place of openings 38, 64.

The duct 62 acts as a reservoir for exchanged heat energy and may be arranged to receive ambient air from atmosphere external to the vehicle and exhaust to atmosphere. The temperature of the ambient air is not increased or decreased to any significant extent and therefore acts as a constant temperature reservoir. The duct 62 may alternatively be arranged for conveying airflow to or from another compartment of the vehicle. For example, if compartment 1 in Figure 3 is a cabin for occupants that requires heating in winter airflow B is heated and consequently airflow A is cooled. The cooled airflow may be conveyed to a compartment (not shown) of the vehicle that requires cooling, such as a motor compartment. Figure 4 shows another vehicle 70 that is provided a plurality of compartments 32, 74 and a temperature regulating system 71 that comprises respective compartment ducts 36, 76 for conveying regulating airflows B, C to the compartments. Components shown in Figure 4 that are the same as, or similar to, components shown in Figures 2 and 3 are given the same reference numerals and are not described again in detail.

Thermoelectric modules 40, 78 associated with respective compartment ducts 36, 76. Each thermoelectric module 40, 78 has a first side 44, 80 in the respective compartment duct 36, 76 for location in the regulating airflow B, C and a second side 42, 82 external to the compartment ducts 36, 76 for location in the reservoir airflow A. In another example, the second sides 42, 82 may be located in a compartment duct that acts as a reservoir for exchanged heat and leads to another compartment (not shown), or there may be more than one ambient air reservoir duct.

The controller 48 is operably connected to the thermoelectric modules 40, 78 to control the electrical potentials between the first sides 44, 80 and the respective second sides 42, 82 to cause heat to be drawn from or dissipated to the reservoir airflow(s) for cooling or heating the compartments 32, 74 dependent on the temperatures required in the compartments. As shown in this example, the controller 48 is connected to respective temperature sensors 50 associated with the compartments 32, 74 for controlling the respective temperatures dependent on the sensed temperatures in the compartments.

A fan 84 generates airflow C when required or recovers energy from airflow C. Alternatively, a single fan may be used in place of the fans 52, 68, 84.

The controller 48 shown in Figures 2 to 4 may be configured to cause the source of electrical energy 46 to apply a positive electrical potential from the first side to the second side of the or each thermoelectric module or from the second side to the first side dependent on a requirement for compartment heating or cooling. Suitable electronic components are provided to permit electrical switching between the source of electrical energy 46 and thermoelectric modules 40, 78. In other examples, particularly in cases in which a compartment may only ever require one of cooling or heating, switching may not be required. A motor compartment for example may only suffer from overheating and not from excessively cold temperatures.

The thermoelectric module or modules may be configured to recover energy when there is a temperature differential between airflows. Instead of applying an electrical potential between the first and second sides of a thermoelectric module as has been described above, a temperature differential between the first and second sides causes an electrical potential to be generated, which may be recovered. Suitable electronic components may be provided to cause this electrical potential to be transferred to the source of electrical energy 46 or made available for application to other thermoelectric modules.

Figures 5a and 5b show an example of a temperature regulating system 100 similar to the system 71 shown in Figure 4, having three airflows A, B, C. The temperature regulating system 100 comprises a duct 102 having a generally circular cross-section supported by a duct support or housing 104. In this example the duct 102 is divided into three sectors. A half-disc shaped duct sector 106 conveys reservoir airflow A. Two quadrant-shaped duct sectors 108, 110 convey regulating airflows B, C. The duct 102 is divided by partitions 107, 109, which separate the respective airflows A, B, C. The partitions 107, 109 may be insulated to reduce transfer of heat energy between the airflows A, B, C. Three duct sectors are provided in this example. However, in other examples a duct may be divided into any number of sectors, or sub-ducts, as required.

Figure 5a shows three thermoelectric modules for exchanging heat between the sectors. A thermoelectric module 112 exchanges heat between airflow A and airflow B. A thermoelectric module 114 exchanges heat between airflow A and airflow C. A thermoelectric module 116 exchanges heat between airflow B and airflow C.

A fan 118 is supported on an axial shaft 120 for rotation by a motor to generate, or enhance, the airflows A, B, C when required, or to recover kinetic energy from airflows generated by vehicle motion for supplying electrical energy to the thermoelectric modules or for storage for later use. The thermoelectric modules 112, 114 are controlled to regulate the temperature of the airflows B, C so that they are cooler or hotter than airflow A. The provision of thermoelectric module 116 allows heat to be exchanged between the regulating airflows, which in this example are airflows B, C.

Figure 6 shows a ducting system arranged to convey thermally regulated airflows 120, 122, 124 to any one of a plurality of different compartments. In this example an airflow A is drawn from atmosphere into a system 126 for thermal regulation and exhausted to atmosphere. A flow control system 128 comprises a plurality of switches or other suitable control elements operably connected to a controller 48 for controlling the flow air to any selected one of the plurality of compartments. Preferably, both the flow route and volumetric flow rate are controlled for regulating the temperature in the compartments. The flow control system 128 may comprise any combination of, for example, switches, vents, apertures, and flaps or other flow control devices for directing a required thermally regulated volumetric flow to any one or more of the compartments. One or more components of the flow control system 128 may be manually controlled rather than controlled by the controller 48. For example, an occupant of a vehicle cabin may set a temperature of 20° C by manual operation of a user interface in the cabin. A thermostat located to sense temperature in the cabin senses a temperature of 18°C and outputs a corresponding signal to the controller 48. The controller 48 controls the flow control system 128 to direct warmed airflow to the cabin for increasing the temperature. The volumetric flow rate to the cabin is preferably also controlled initially by increasing it in order to decrease the time taken to achieve the required temperature and then decreasing the flow rate to maintain temperature. In another example, a component of the vehicle may have a rated thermal operating range of 5° C to 50° C. If the operating range exceeds the upper limit, a sensor of the component, or a separate sensor disposed in the compartment housing the component outputs a signal to the controller 48. The controller 48 controls the flow control system 128 to direct a cooled airflow to the compartment housing the component for decreasing the temperature. The volumetric flow rate to the compartment may, for example, be controlled to provide a maximum rate so that the component is cooled quickly to reduce any possible damage.

An example of a thermoelectric module that may be used as any of the thermoelectric modules 40, 78, 112, 114, 116 described above is shown in Figure 7. The thermoelectric module shown in Figure 7 has arbitrarily assigned the reference numeral 114. The thermoelectric module 114 comprises at least one thermally conducting plate 132 that defines the first side of the module and at least one thermally conducting plate 134 that defines the second side of the module. The or each thermally conducting plate 132, 134 may be a metallic plate that may, for example, be made of aluminium or an aluminium alloy. In some examples, instead of a metallic plate, a plate made of some other thermally conducting material, for example a ceramic, may be used.

The or each thermally conducting plate 132, 134 may be contoured to increase its surface area (over and above the surface area of a planar surface) so that more of its surface is available for contact with airflow. This increased surface area improves heat exchange with the airflow, whether by cooling or heating the airflow. In the example shown in Figure 7, the plates 132, 134 comprise heat exchange formations in the form of a plurality of fins 138 extending generally perpendicularly from the body of the plate. In other examples the formations may comprise a grid, mesh or diffuser which projects into the duct. Alternatively, the formations may extend about an inner surface of the duct to contact the airflow through 360°.

In the example shown in Figure 7, the thermoelectric module 114 comprises at least one Peltier module 136 disposed intermediate the first and second plates 132, 134 to transfer heat energy between the sides of the thermoelectric module defined by the plates. The Peltier module 136 is disposed in a partition 107 intermediate the two sides of the thermoelectric module.

The Peltier module 136 may be connected to the plates 132, 134 with a heat conducting paste or the like applied to the respective interfaces between the Peltier module 136 and the plates to ensure a good thermal bond for efficient transfer of heat from between opposite sides of the thermoelectric module.

In operation, the controller 48 and source of electrical energy 46 define a control and power supply unit arranged to distribute electric power to the Peltier modules 136. A control and power supply unit may comprise any suitable form of electric charge storage device and may include another vehicle storage device, for example the main vehicle battery. The electric charge storage device may comprise a battery or supercapacitor. It is to be understood that although the controller is described and shown herein as one unit, this is not essential and it may be made up of separate circuits, components or sub-assemblies that are suitably connected as required.

In some examples, the controller may be configured to switch the thermoelectric modules between a heating and cooling mode in which the Peltier modules are supplied with electricity to cause them to move heat energy towards one side and a generating mode in which the supply of electricity is interrupted so that the temperature gradient across the Peltier modules may cause the generation of an electric current. This functionality may be used to provide a control strategy in which the Peltier modules are switched between the two modes in order to balance temperature regulation with energy generation.

A thermoelectric module may comprise a single Peltier module 136 or a plurality of connected Peltier modules. The stacking of the Peltier modules to provide enhanced performance is known to those skilled in the art and so will not be described in detail herein.

For some examples, the thermoelectric modules and/or fan(s) may be powered by electricity generated by one or more solar panels.

In the illustrated example, both sides of the thermoelectric module or modules are disposed within the vehicle and exposed to respective airflows channelled within the vehicle. This is not to be taken as limiting as in some examples, a side of a thermoelectric module may be disposed externally of a vehicle or in an opening defined in an exterior surface of a vehicle.

Thus, there is disclosed a vehicle with a thermoelectric module configured to modify the thermal condition of a first airflow that may be admitted to a compartment or space of a vehicle, by at least one of adding heat to said airflow and removing heat from said airflow. The thermoelectric module may be arranged to transfer heat from said first airflow to a second airflow, which second airflow may be exhausted to atmosphere or directed to another compartment or space of the vehicle. Additionally, or alternatively, the thermoelectric module may transfer heat from the second airflow to the first airflow. Suitable flow control devices may be provided to control at least one of the first and second airflow in terms of opening and closing a duct or throttling the airflow through a duct. One or more fans may be used to augment at least one of the first and second airflows when the motion of the vehicle is insufficient to generate an adequate airflow or to generate at least one of the airflows when the vehicle is stationary. The fan may be a part of, or connected with, an electricity generating device to convert kinetic energy of the fan into electrical energy that may be used directly in the vehicle or stored in a battery, capacitor or the like for later use. The thermoelectric module may be selectively disconnected from its power supply and a temperature differential across the module may be used to generate electrical energy that may be used directly in the vehicle or stored in a battery, capacitor or the like for later use.

Claims

1. A vehicle comprising a compartment and a temperature regulating system for regulating the temperature in the compartment, the system comprising: a compartment duct for receiving a first airflow that is caused by the motion of the vehicle relative to the external air and for conveying the first airflow to the compartment, a thermoelectric module associated with a source of electrical energy and having a first side in the duct for location in the first airflow and a second side located externally of the duct for exposure to a second airflow that is caused by the motion of the vehicle relative to the external air, and a controller for controlling an electrical potential between the first side and the second side to cause heat to be drawn from one of the first airflow and the second airflow and dissipated to the other one of the first airflow and the second airflow for cooling or heating the compartment dependent on a temperature required.

2. A vehicle as claimed in claim 1, further comprising a reservoir duct for conveying the second airflow, the second side of the thermoelectric module being located in the reservoir duct for heat exchange with the second airflow.

3. A vehicle as claimed in claim 1 or 2, comprising a plurality of said compartments, wherein the system comprises a plurality of compartment ducts for conveying respective first airflows to the compartments, and a thermoelectric modules associated with respective said compartment ducts, each thermoelectric module having a first side disposed in the respective compartment duct for exposure to the respective first airflow and a second side disposed externally of the duct for exposure to the second reservoir airflow or a different one of the first airflows, wherein the controller is arranged to control the electrical potentials between the first sides and the second sides of the thermoelectric modules to cause heat to be drawn from or dissipated to the first airflows for cooling or heating the compartments dependent on the temperatures required in the compartments.

4. A vehicle as claimed in any one of the preceding claims, wherein the controller is configured with the source of electrical energy and the or each thermoelectric module to apply a positive electrical potential from the first side to the second side of the or each thermoelectric module or from the second side to the first side dependent on a requirement for compartment heating or cooling.

5. A vehicle as claimed in claim 3 or 4, wherein at least one thermoelectric module is associated with two compartment ducts for exchanging heat energy between the respective first airflows conveyed by the respective compartment ducts.

6. A vehicle as claimed in claim 3, 4 or 5, comprising a ducting system comprising a plurality of said compartment ducts for conveying respective first airflows to the compartments and a flow control system operably connected to the controller for controlling the volumetric flow rate of said first airflows.

7. A vehicle as claimed in claim 6, wherein the flow control system comprises one or more of flow switches, vanes, apertures or flaps for controlling the first airflows conveyed to the compartments.

8. A vehicle as claimed in any one of the preceding claims, comprising at least one fan for increasing at least one first or second airflow when the vehicle is in motion generating at least one first or second airflow when the vehicle is stationary.

9. A vehicle as claimed in claim 8, further comprising a generator for generating electrical energy from kinetic energy of the or each fan caused by at least one first or second airflow when the vehicle is in motion for storage or supply to a thermoelectric module.

10. A vehicle as claimed in any one of the preceding claims, wherein a said thermoelectric module has a said first side comprising at least one thermally conducting plate and a said second side comprises at least one thermally conducting plate.

11. A vehicle as claimed in claim 10, wherein the or each thermally conducting plate is contoured.

12. A vehicle as claimed in any one of the preceding claims, wherein a said thermoelectric module comprises at least one Peltier module disposed intermediate said first and second sides to transfer heat energy between said sides.

13. A vehicle as claimed in claim 12, wherein said at least one Peltier module is disposed in a partition disposed intermediate said sides.

14. A vehicle as claimed in any one of the preceding claims, comprising a temperature sensor for outputting a temperature indicating signal to the controller and the controller is configured to control the temperature of said airflow conveyed to said compartment dependent on the temperature indicating signal.

15. A vehicle as claimed in any one of the preceding claims, comprising a motor for propelling the vehicle, said motor being an electric motor or a hybrid motor.

16. A vehicle as claimed in any one of the preceding claims that does not comprise a combustion engine.

17. In or for a vehicle, a temperature regulating system for regulating a temperature in a compartment of the vehicle, the temperature regulating system comprising: a compartment duct for receiving a first airflow that is caused by the motion of the vehicle relative to the external air and for conveying the first airflow to the compartment, a thermoelectric module associated with a source of electrical energy and having a first side in the duct for location in the first airflow and a second side disposed externally of the duct to be exposed to a second airflow that is caused by the motion of the vehicle relative to the external air, and a controller for controlling an electrical potential between the first side and the second side to cause heat to be drawn from one of the first airflow and the second airflow and dissipated to the other one of the first airflow and the second airflow for cooling or heating the compartment dependent on a temperature required.

18. A temperature regulating system as claimed in claim 17, further comprising at least one fan for increasing at least one first or second airflow.