AU2022203520A1 - Air mixing plenum, system and method - Google Patents

Abstract

An air mixing plenum comprising a first inlet for receiving air from a first source, a second inlet for receiving air from a second source, a venturi chamber having an outlet therein. Air from the first source and air from the second source are received through the first inlet and the second inlet and are directed toward the outlet in the venturi chamber thereby generating a venturi effect and the air from the first source and the air from the second source are mixed. 6/10 100 110 Filtered Fresh Air (from Atmosphere) Recirc atd r 108 122 118 112 120/ 106/ Combined Air (To Cabin HVAC) Venturi Effect and Vortex Action maintain the optimum mixture balance at the required pressure FIG. 9

Description

6/10

100 110 Filtered Fresh Air (from Atmosphere)

Recirc atd r

108 122 118

112

120/ 106/ Combined Air (To Cabin HVAC) Venturi Effect and Vortex Action maintain the optimum mixture balance at the required pressure

FIG. 9

AIR MIXING PLENUM, SYSTEM AND METHOD TECHNICAL FIELD

[1] The present invention relates to an air mixing plenum for cabin air

pressurisation and filtration in fixed and mobile plant, and a system and method for

pressuring and filtering air for a cabin.

BACKGROUND

[2] Any references to methods, apparatus or documents of the prior art are not to

be taken as constituting any evidence or admission that they formed, or form part of

the common general knowledge.

[3] Air filters are generally used to supply clean air to the cabin of fixed and

mobile plant used for industrial purposes, such as mining, drilling, construction,

farming, shipping and others throughout the world. The operators and occupants of

such plant would otherwise be exposed to hazardous dust and particles, which have

been known to cause serious diseases including for example silicosis, asbestosis

and other known diseases.

[4] There are other reasons why filtered air must be supplied to such plant and

equipment. Firstly, dust and particulate matter can interfere with the correct

operation of equipment and components inside the cabin, including for example

electronic equipment, computers and air conditioning systems. Secondly, many

countries have workplace laws and codes that set out requirements for standards

that apply to industrial air filtration systems used in fixed and mobile plant. One such

international standard is ISO 23875: Mining air quality. The practices outlined in the standard to protect personnel inside operator enclosures include: (a) exclusion of harmful respirable particulate exposure from both recirculation and external (fresh) air supply, (b) maintaining safe levels of carbon dioxide (Co2) - excess causes premature fatigue, lack of concentration, micro sleeps, acidosis, etc, (c) routine performance testing of air quality control systems throughout the lifecycle of the cabin to maintain compliance, including testing cab pressure, C02 concentration, fresh and recirculation filtration effectiveness at machine service intervals.

[5] Such air filtration systems generally consist of separate air pre-clean and

filtration units where (a) one unit is used to pre-clean and filter external air, and (b) a

second unit is used to filter and re-circulate internal air from the cabin. Separate units

for external and re-circulated air are required to provide ventilation, to ensure C02

does not build up beyond maximum allowable levels, and to maximise efficiency of

internal systems including heating, ventilation and air-conditioning (HVAC) systems.

[6] Separate pre-clean and / or filtration units have inherent drawbacks and

inefficiencies as follows: (a) the filtration units have to be mounted separately with

often separate ducting into and out of the cabin, which sometimes is difficult to do

due to space constraints, (b) each separate pre-clean and filtration unit and

recirculation unit requires separate dispersed oil particulate testing to EN1822

(HEPA filter classification) (DOP Testing), (c) the optimum balance between external

fresh pre-cleaned and filtered air and re-circulated filtered air to provide optimal

cabin pressurisation of 20-200 Pascals and C02 offset for 1-4 occupants or multiple

occupants is difficult to achieve, and (d) rapid filtration of re-circulation air is difficult

to achieve.

SUMMARY OF INVENTION

[7] In an aspect, the invention provides an air mixing plenum comprising:

a first inlet for receiving air from a first source;

a second inlet for receiving air from a second source; and

a venturi chamber having an outlet therein, wherein air from the first source and

air from the second source received through the first inlet and the second inlet are

directed toward the outlet in the venturi chamber thereby generating a venturi effect

and the air from the atmosphere and the recirculated air from the cabin are mixed.

[8] Preferably, the air mixing plenum further comprises a first chamber in direct

connection to the first inlet and a second chamber in direct connection to the second

outlet.

[9] Preferably, the air mixing plenum further comprises a volute member located

in at least one of the first and the second chambers.

[10] Preferably, the air mixing plenum further comprises a main body connected to

the tapered portion. Preferably, the first inlet and the second inlet are formed in the

main body.

[11] Preferably, the volute member for guiding air toward the outlet, wherein the

volute member abuts or is adjacent to a wall separating the first chamber from the

second chamber.

[12] Preferably, the venturi chamber is a tapered chamber or funnelled chamber.

[13] Preferably, the air mixing plenum further comprises a conduit between the first

inlet and the venturi chamber, wherein the conduit comprises a first end having a first

opening and a second end having a second opening. Preferably, the first end of the

conduit is connected to the first inlet.

[14] Preferably, a diameter of the second opening is less than a diameter of the

outlet.

[15] Preferably, the second end terminates at the outlet and wherein the second

opening is within or surrounded by the outlet.

[16] Preferably, the second end terminates at the outlet and wherein the second

opening is within the venturi chamber.

[17] Preferably the main body is polygonal or prismatic or cylindrical.

[18] Preferably, the main body is of a substantially constant diameter along a

longitudinal axis.

[19] Preferably, the venturi chamber is frustoconical.

[20] In another aspect, the invention provides an air pressurisation and filtration

system comprising:

a first air filtration unit connected to the first inlet, wherein the first air filtration

unit draws or receives air from the atmosphere;

a second air filtration unit connected to the second inlet, wherein the second

air filtration unit draws or receives recirculated air from a cabin;

an air mixing plenum comprising:

a first inlet for receiving air from the first filtration unit;

a second inlet for receiving air from the second filtration unit; and

a venturi chamber having an outlet therein, wherein air from the first filtration unit

and air from the second filtration unit received through the first inlet and the second

inlet are directed toward the outlet in the venturi chamber thereby generating a

venturi effect and the air from the atmosphere and the recirculated air from the cabin

are mixed.

[21] Preferably, the outlet is connected to an interior of the cabin.

[22] In another aspect, the invention provides a method of pressurising and

filtering air for a cabin, the method including the steps of: receiving air from an atmosphere surrounding the cabin through a first inlet of a plenum; receiving recirculated air from the cabin through a second inlet of the plenum; wherein the air from the atmosphere and the recirculated air from the cabin are directed toward the outlet in a venturi chamber of the plenum thereby generating a venturi effect and the air from the atmosphere and the recirculated air from the cabin are mixed.

BRIEF DESCRIPTION OF THE DRAWINGS

[23] Preferred features, embodiments and variations of the invention may be

discerned from the following Detailed Description which provides sufficient

information for those skilled in the art to perform the invention. The Detailed

Description is not to be regarded as limiting the scope of the preceding Summary of

the Invention in any way. The Detailed Description will make reference to a number

of drawings as follows:

Figure 1 is an exploded view of some of the components of part of an air

mixing plenum;

Figure 2 is an expanded view of the components of an air mixing plenum;

Figure 3 is a schematic view of the inside left hand components of an air

mixing plenum showing the circular component through which incoming air is

rotated;

Figure 4 is a schematic showing the outer components of an air mixing

plenum showing the air intake and mountings for an external filter unit;

Figure 5 is a schematic showing the inner right hand components of an air

mixing plenum showing the volute member through which incoming air is rotated;

Figure 6 is a plan view of the air mixing plenum according to the present

invention;

Figures 7-10 illustrate an embodiment of an air mixing plenum according to

the present invention;

Figures 11 and 12 illustrate another embodiment of an air mixing plenum;

Figure 13 illustrates yet another embodiment of air mixing plenum; and

Figures 14 and 15 illustrate an air mixing plenum attached to a cabin for air

pressurisation and filtration.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[24] Embodiments of the disclosure relate to a system for combining external pre

cleaned and filtered air and re-circulated filtered air to achieve 20-200 Pascal

pressurisation in the cabin and C02 offset for single or multiple occupants.

[25] Figures 1 and 2 shows a first embodiment of an air mixing plenum 8 in an

exploded and assembled view, respectively. The air mixing plenum include bottom

mounting brackets 1 to allow the air mixing plenum to be mounted to a cabin (not

shown). Side mounting brackets 2 attachable to a rear panel 9 to allow an external

filter or pre-cleaning unit to be attached to the body of the air mixing plenum.

[26] The air mixing plenum 8 includes a first chamber in direct connection to a first

inlet and a second chamber in direct connection to a second inlet.

[27] The air mixing plenum 8 also includes a volute member 6 located in each of

the first and the second chamber.

[28] The front right outer housing forms a venturi chamber 3 for directing air. The

outer casing is made of metal and forms the body 4 of the air mixing plenum. The left

hand panel 5 forms the left side of the air mixing plenum 8 and the left panel of the

venturi chamber 3.

[29] The volute member 6 (formed according to an approximately logarithmic

curve) forms an air guide made of metal and provides a path that incoming air must

follow toward the venturi chamber 3 and outlet 7. The left hand side of the air mixing

plenum 8 is a mirror of the right hand side. Thus, the right hand side of the air mixing

plenum includes a second volute member (not shown). The volute member 6 for

guiding air toward the outlet abuts a wall separating the first chamber from the

second chamber.

[30] The air mixing plenum 8 combines pre-cleaned and filtered air from an

external environment of a cabin and re-circulated filtered air taken from the cabin.

The air from the external environment is pre-cleaned and filtered under pressure by

an external unit that can be bolted to the air mixing plenum 8. The pre-cleaned and

filtered, pressurised air is fed into the air mixing plenum 8 and directed to a circular

chamber 7a and then further directed to the forward venturi chamber 3 therefore

generating a venturi effect and speeding up and thus the output pressure being

adjustable according to the design of the circular chamber 7a and the venturi

chamber 3.

[31] In use, the air from the cabin is filtered under pressure by an external unit that

can be attached and connected to the air mixing plenum 8. The filtered pressurised

air is fed into the air mixing plenum 8 and directed to a circular chamber 7a and then further directed to the forward venturi chamber 3 therefore generating a venturi effect and speeding up and thus the output pressure being adjustable according to the design of the circular chamber 7a and the venturi chamber 3. The combination of the pre-cleaned and filtered air from the external environment of the cabin and the re circulated filtered air taken from the cabin is directed from the venturi chamber outlet

7 through return ducting into the cabin HVAC system. The pressure of the combined

airstream entering the cabin is monitored by an in-cabin pressure sensor. Optimum

in cabin pressure of up to 200 Pascals and C02 offset for a single to multiple

persons is achieved by the circular chamber 7a and the venturi chamber 3. The

resulting balanced air flow is described as a super venturi vortex effect.

[32] Figure 3 shows detail of the interior of the chamber 5a with volute member 7

having a varying radius 7a.

[33] Figure 4 shows an external left elevation of the air mixing plenum 8 showing

an air inlet and mounting brackets for the external air filter unit or pre-cleaner. The

right external elevation is identical.

[34] Figure 5 shows detail of volute member 6 and inlet 12.

[35] Figure 6 shows a top view of the exterior of the air mixing plenum 8.

[36] Figure 7 illustrates an embodiment of an air mixing plenum 100 for receiving

air from two sources, mixing the air and distributing the air into a cabin (either directly

or via the HVAC system connected to the cabin). The air mixing plenum 100 includes

a first inlet 102 for receiving air from a first source, a second inlet 104 for receiving

air from a second source, and a venturi chamber 106 having an outlet 108 therein.

Examples of the first source and the second source of air can be seen in Figures 14

and 15.

[37] The air mixing plenum 100 includes a single venturi chamber 106 that

receives air from the first and second sources, which will be detailed below.

[38] The air mixing plenum 100 includes a main body 110 connected to the venturi

chamber 104 which comprises a tapered chamber or funnelled chamber that is

substantially frustoconical. Together, the main body 110 and the venturi chamber

104 form an internal chamber.

[39] Air from the first source and air from the second source are received through

the first inlet 102 and the second inlet 104, respectively, into the main body 110 and

are directed toward the outlet 108 in the venturi chamber 106 thereby generating a

venturi effect and the air from the first source and the air from the second source are

mixed.

[40] The first inlet 102 and the second inlet 104 are formed in the main body 110

which is substantially prismatic but may also be cylindrical or polygonal. The main

body 110 is of a substantially constant diameter along a longitudinal axis.

[41] The air mixing plenum 100 includes a conduit 112 between the first inlet 102

and the venturi chamber 106, wherein the conduit 112 has a first end 114 having a

first opening 116 and a second end 118 having a second opening 120 where the first

end 114 of the conduit 112 is connected to the first inlet 102.

[42] As can be seen in Figures 7 to 9, a diameter of the second opening 118 of the

conduit 112 is less than a diameter of the outlet 108 in the venturi chamber 106. This

allows air entering the chamber through the second inlet 104 to exit the chamber via

the outlet 108.

[43] The second end 118 terminates adjacent the outlet 108 such that the second

opening 118 is within the venturi chamber 106. In some alternative embodiments,

the second end of the conduit terminates at the outlet such that the second opening is within or surrounded by the outlet. That is, the opening of the second end of the conduit is aligned with the outlet.

[44] In the view shown in Figure 9, a vane 122 can be seen located in the outlet

108.

[45] With reference to Figure 9, generalised path lines of air flow through the air

mixing plenum 100 are shown. Filtered air is introduced to the internal chamber of

the air mixing plenum 100 from a recirculation unit via the second inlet 104 (a

recirculation inlet spigot). Filtered fresh air is introduced to the conduit 112 of the air

mixing plenum 100 via the first inlet 102 (a fresh air inlet spigot) from the fresh air

unit.

[46] Turning to Figure 10, movement of the air through the air mixing plenum 100

can be seen.

[47] After a short time, equilibrium of flow and pressure in the internal chamber is

reached and recirculation air being displaced from the internal chamber at a constant

rate of volume per time via the outlet 108 (a combined air outlet spigot) necessarily

undergoes acceleration due to the changing cross section in the transition zone in

the venturi chamber 106. The subsequent increase in velocity results in a localized

lowering of pressure at the outlet 108, relative to the air in the main body 110. Fresh

air is introduced to the flow stream in this low pressure zone near the outlet 108 via

the conduit 112 and is thereby assisted by the pressure differential, resulting in a

higher overall achievable pressure in a given system and hence the ability to

overcome resistance to flow and cab leakage inherent to the system design.

[48] When flow and pressure in the cab reach equilibrium, by definition, fresh air

introduction is equal to leakage from the system. The ability to introduce more fresh

air as required by a system not only enables pressurisation of the system, but also, the displacement of expired air, which has a higher concentration of carbon dioxide, and has been associated with operator drowsiness and impaired cognitive ability, leading to accidents. Directional vanes in the outlet 108 can be used to impart spin on the airflow, improving the flow profile by maintaining lamination in the downstream flow thereby reducing turbulence.

[49] Another embodiment of an air mixing plenum 200 is shown in Figures 11 and

12.

[50] Figure 11 shows the air mixing plenum 200 includes a first inlet 202 for

receiving air from a first source, a second inlet 204 for receiving air from a second

source, and a venturi chamber 206 having an outlet 208 therein.

[51] The air mixing plenum 200 includes a main body 210 connected to the venturi

chamber 204 which comprises a tapered chamber or funnelled chamber that is

substantially frustoconical. Together, the main body 210 and the venturi chamber

204 form an internal chamber.

[52] Air from the first source and air from the second source are received through

the first inlet 202 and the second inlet 204, respectively, into the main body 210 and

are directed toward the outlet 208 in the venturi chamber 206 thereby generating a

venturi effect and the air from the first source and the air from the second source are

mixed.

[53] The first inlet 202 and the second inlet 204 are formed in the main body 210

which is substantially cylindrical. The main body 210 is of a substantially constant

diameter along a longitudinal axis.

[54] The air mixing plenum 200 includes a conduit 212 between the first inlet 202

and the venturi chamber 206, wherein the conduit 212 has a first end 214 having a first opening 216 and a second end 218 having a second opening 220 where the first end 214 of the conduit 212 is connected to the first inlet 202.

[55] As can be seen in Figure 11, a diameter of the second opening 218 of the

conduit 212 is less than a diameter of the outlet 208 in the venturi chamber 206. This

allows air entering the chamber through the second inlet 204 to exit the chamber via

the outlet 208.

[56] The second end 218 terminates adjacent the outlet 208 such that the second

opening 218 is within the venturi chamber 206. In some alternative embodiments,

the second end of the conduit terminates at the outlet such that the second opening

is within or surrounded by the outlet. That is, the opening of the second end of the

conduit is aligned with the outlet.

[57] Figure 13 illustrates an embodiment of an air mixing plenum 300. The air

mixing plenum 300 includes a first inlet 302 for receiving air from a first source, a

second inlet 304 for receiving air from a second source, and a venturi chamber 306

having an outlet 208 therein.

[58] The air mixing plenum 300 includes a main body 310 connected to the venturi

chamber 304 which comprises a tapered chamber or funnelled chamber that is

substantially frustoconical. Together, the main body 310 and the venturi chamber

304 form an internal chamber.

[59] Air from the first source and air from the second source are received through

the first inlet 302 and the second inlet 304, respectively, into the main body 310 and

are directed toward the outlet 308 in the venturi chamber 306 thereby generating a

venturi effect and the air from the first source and the air from the second source are

mixed.

[60] The first inlet 302 and the second inlet 304 are formed in the main body 310

which is substantially rectangular. The main body 310 is of a substantially constant

diameter along a longitudinal axis.

[61] The air mixing plenum 300 includes a conduit 312 between the first inlet 302

and the venturi chamber 306, wherein the conduit 312 has a first end 314 having a

first opening 316 and a second end 318 having a second opening 320 where the first

end 314 of the conduit 312 is connected to the first inlet 302.

[62] A diameter of the second opening 318 of the conduit 312 is less than a

diameter of the outlet 308 in the venturi chamber 306. This allows air entering the

chamber through the second inlet 304 to exit the chamber via the outlet 308.

[63] The second end 318 terminates adjacent the outlet 308 such that the second

opening 318 is within the venturi chamber 306. In some alternative embodiments,

the second end of the conduit terminates at the outlet such that the second opening

is within or surrounded by the outlet. That is, the opening of the second end of the

conduit is aligned with the outlet.

[64] Figures 14 and 15 show an air pressurisation and filtration system 400 having

an air mixing plenum 402 as described herein.

[65] The air mixing plenum 402 is mounted to the roof of a cabin 408. A cabin

includes any type of cabin, including an operator inside a cabin, a cabin without an

operator, a large cabin or a small cabin, in an environment that may be dusty or

contain other pollutants. The cabin 408 typically has a sealed interior and an exterior,

and the ducting from and to the air mixing plenum 402 penetrates the cabin 408.

[66] The system 400 also includes a first air filtration unit 404 connected to the first

inlet of the air mixing plenum 402 and a second air filtration unit 406 connected to

the second inlet of the air mixing plenum 402. In use, the first air filtration unit 404 draws or receives air from the atmosphere and the second air filtration unit 406 draws or receives recirculated air from a cabin 408. Air from the first filtration unit

404 and air from the second filtration unit 406 received through the first inlet and the

second inlet are directed toward the outlet in the venturi chamber of the air mixing

plenum 402 thereby generating a venturi effect and the air from the atmosphere and

the recirculated air from the cabin 408 are mixed. Effectively, the external and

internal air are combined in the air mixing plenum 402 and fed back into the cabin

408 to remove contaminants and maintain pressure in the cabin 408 which can leak

from the cabin 408 over time.

[67] The outlet is connected to an interior of the cabin 408 to deliver and disperse

the combined air from the air mixing plenum 402.

[68] Analysis of the air mixing plenums described herein and a comparative Y

piece style plenum produced the following results:

Plenum Max. Max. Outlet Max. Inlet Max Inlet Outlet Mass

Style System Velocity Velocity Velocity Flow Rate

Velocity (m/s) Recirculated Fresh Air (kg/s)

(m/s) Air (m/s) (m/s) (CFM)

Air Mixing 28.368 23.414 9.4408 5.8679 0.11621

Plenum 100 (207.9)

Air Mixing 26.419 22.477 9.9749 5.3603 0.11477

Plenum 200 (205.4)

Y-Piece 15.039 13.52 9.8483 2.4935 0.094486

(169.1)

[69] The results for air mixing plenum 100 and air mixing plenum 200 show

substantial gains in flow velocity and flow rate as the air is drawn into the system. It

is also seen that increases in pressure are obtained. The Inventor envisions that this

can be of benefit as it allows for the cabin to not require as much sealing to gain

positive pressure outcomes. Both venturi systems performed well in analysis with

marked gains over the Y-Piece plenum.

[70] Embodiments of the system described herein can include ducting, including

tubing and fittings, that convey air to and from the cabin and the plenum, and

filtration units that process the air. Advantageously, the use of the two air filtration

units provides an opportunity for contaminants that have been introduced to the cab,

typically when doors or windows have been opened, or on an occupants clothing, to

be filtered out. Both units typically include an electrically powered fan that imparts

impetus on the air, and a filter cartridge that removes particulate matter and/or

contaminants from the air, hence the system provides both pressurisation and

purification of air in the enclosed cabin, with the aim of maintaining cleanliness of the

cabin air and hence operator health, as well as reduced downtime of the machine for

cabin air conditioning (HVAC) service and the associated costs.

[71] A sensor in the cabin can be used to monitor the difference in pressure

between the air in the cab and the outside atmosphere, and this data is used to alert

the operator to variance from the set range as required. This alert may be indicative

of a malfunction of the system, excessive leakage of air from the cab if for example,

a door is left open, or the need to replace a filter due to loading. In a foreseeable

variation, the pressure data may be used to regulate fan speed or a vent valve to

prevent over-pressurisation which could otherwise lead to operator illness or equipment damage. The In-cabin monitor sensor senses the air pressure and CO2 in the cabin and informs the occupant of a low pressure state and CO 2 build up.

[72] Embodiments of the air mixing plenum and system described herein can be

used with heavy earthmoving equipment in the mining and construction industries. It

is envisioned that embodiments of the system can be used on mobile or static cabins

or operations rooms wherever air pressurisation and/or filtration may be of benefit.

[73] Advantageously, the embodiments of the air mixing plenum described herein

facilitate commixing of the fresh and recirculated air streams for introduction through

the HVAC intake register, maximizing the effectiveness of heating and cooling

functions. Furthermore, introduction of fresh and recirculated air through a common

duct minimises the requirement for structural modification of the cabin. Generally,

existing recirculation and fresh air registers can be utilized for air uptake with minor

modifications.

[74] Embodiments of the invention provide separate air pre-cleaner and filtration

units and re-circulation filter units which are attached to a single core plenum unit to

allow a single mounting on the plant cabin and a single ducting into and out of the

operator cabin. This results in a single unit where the output air of the air pre-cleaner

and filter unit is combined and mixed with the output air from the re-circulation filter

unit and directed through a single outlet from the core plenum unit into the cabin of

the plant. Rather than mounting two separate units with two ducting outlets to the

cabin, the core module allows for quicker and easier installation, thereby reducing

costs and physical footprint.

[75] Advantageously, the single core plenum unit with attached filter units can be

DOP Tested as a single unit and certification provided for compliance with ISO

23875.

[76] Further advantageously, embodiments of the single core plenum unit

optimises the balance between external pre-cleaned and filtered air and re-circulated

filtered air to achieve up to 200 Pascal pressurisation in the cabin and C02 offset for

four persons. This is achieved by optimum internal pathways (provided by the shape

and configuration) within the plenum to produce a mixing balance of the external pre

cleaned and filtered air and re-circulated filtered air that results in a mixed stream of

air produced through a combination of vortex and venturi effect.

[77] Even further advantageously, embodiments of the core plenum module allows

rapid filtration of re-circulation air within the cabin.

[78] In some embodiments, temperature regulated (preheated or precooled by the

HVAC system) and filtered air is mixed by the plenum with external ambient pre

cleaned and filtered air for the purpose of re-introduction to the operator space to

make HVAC operation more efficient and thermal comfort for the occupants of the

cabin quicker and better.

[79] In compliance with the statute, the invention has been described in language

more or less specific to structural or methodical features. The term "comprises" and

its variations, such as "comprising" and "comprised of' is used throughout in an

inclusive sense and not to the exclusion of any additional features.

[80] It is to be understood that the invention is not limited to specific features

shown or described since the means herein described comprises preferred forms of

putting the invention into effect.

[81] The invention is, therefore, claimed in any of its forms or modifications within

the proper scope of the appended claims appropriately interpreted by those skilled in

the art.

Claims (17)

1. An air mixing plenum comprising:

a first inlet for receiving air from a first source;

a second inlet for receiving air from a second source; and

a venturi chamber having an outlet therein, wherein air from the first source and

air from the second source received through the first inlet and the second inlet are

directed toward the outlet in the venturi chamber thereby generating a venturi effect,

and the air from the first source and the air from the second source are mixed.

2. The air mixing plenum of claim 1 further comprising a first chamber in direct

connection to the first inlet and a second chamber in direct connection to the second

inlet.

3. The air mixing plenum of claim 2 further comprising a volute member located

in at least one of the first and the second chambers.

4. The air mixing plenum of claim 2 or claim 3, wherein the venturi chamber

comprises a tapered chamber or funnelled chamber connected to a main body.

5. The air mixing plenum of claim 3, wherein the first inlet and the second inlet

are formed in the main body.

6. The air mixing plenum of claim 2, wherein the volute member for guiding air

toward the outlet, wherein the volute member abuts or is adjacent to a wall

separating the first chamber from the second chamber.

7. The air mixing plenum of any one of the preceding claims further comprising a

conduit between the first inlet and the venturi chamber, wherein the conduit

comprises a first end having a first opening and a second end having a second

opening.

8. The air mixing plenum of claim 8, wherein the first end of the conduit is

connected to the first inlet.

9. The air mixing plenum of claim 9, wherein a diameter of the second opening is

less than a diameter of the outlet.

10.The air mixing plenum of any one of claims 8 to 10, wherein the second end

terminates at the outlet and wherein the second opening is within or surrounded by

the outlet.

11.The air mixing plenum of any one of claims 8 to 10, wherein the second end

terminates at the outlet and wherein the second opening is within the venturi

chamber.

12.The air mixing plenum of claim 4, wherein the main body is polygonal or

prismatic or cylindrical.

13.The air mixing plenum of claim 4, wherein the main body is of a substantially

constant diameter along a longitudinal axis.

14.The air mixing plenum of any one of the preceding claims, wherein the venturi

chamber is frustoconical.

15.An air pressurisation and filtration system comprising:

a first air filtration unit, wherein the first air filtration unit draws or receives air

from the atmosphere;

a second air filtration unit, wherein the second air filtration unit draws or

receives recirculated air from a cabin;

an air mixing plenum comprising:

a first inlet connected to the first air filtration unit;

a second inlet connected to the second filtration unit; and a venturi chamber having an outlet therein, wherein air from the first filtration unit and air from the second filtration unit received through the first inlet and the second inlet are directed toward the outlet in the venturi chamber thereby generating a venturi effect and the air from the atmosphere and the recirculated air from the cabin are mixed.

16.The system of claim 16, wherein the outlet is connected to an interior of the

cabin.

17.A method of pressurising and filtering air for a cabin, the method including the

steps of:

receiving air from an atmosphere surrounding the cabin through a first inlet of an

air mixing plenum;

receiving recirculated air from the cabin through a second inlet of the air mixing

plenum;

wherein the air from the atmosphere and the recirculated air from the cabin are

directed toward the outlet in a venturi chamber of the air mixing plenum thereby

generating a venturi effect and the air from the atmosphere and the recirculated air

from the cabin are mixed.