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Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
1
Douglas S Walkinshaw, PhD., P.E.
Passenger aircraft ventilation system design challenges and
solutions
April 2005
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
2
Passenger Aircraft Ventilation System Design Challenges
Figure 1. A passenger aircraft ventilation system must cope with higher occupancy densities, a wider range of occupant ages, health conditions and activities, more unusual ventilation air contaminants, lower ventilation air moisture content and more severe fire safety challenges than any other public space ventilation system.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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Current ventilation norms
Building offices – 7 persons/10,000 ft3, Aircraft cabins – 230 persons/10,000 ft3
Building offices – > 18 L/s/person filtered low outdoor air VOCsAircraft cabins – > 3.75 L/s/p unfiltered bleed air VOCs, ozone
Building offices – 50 L/s/person (100 CFM/p)Aircraft cabins – 7.5-10 L/s/person (15-20 CFM/p)
Building offices – Fleecy chairs, carpets with low trafficAircraft cabins – Fleecy chairs, carpets with high traffic
Building offices – 20-65%Aircraft cabins – 5-25%
Building offices – copier, humanAircraft cabins – human, combustion, anti-corrosion treatment
Building offices – escape in minutesAircraft cabins – escape often not possible
Building offices – air pressure = 0.9 to 1 atm; BLOC = 95-100%Aircraft cabins – air pressure = 0.75 atm, BLOC = 85-90%
Occupant contagion
Indoor/outdoor air exchange rate
Air flow rate (outdoor + recirculation air)
Dust and allergens
Relative humidity
Volatile organic compounds
Fire, biological/chemical agent release
Blood oxygen content (BLOC)
Buildings: - 20F to +110FAircraft : - 55F to +110FOutdoor temperature environment
Table 1. Current ventilation norms: aircraft passenger cabins versus buildings
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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Six ventilation design challenges addressed in this presentation
Table 2. Aircraft ventilation design challenges and a set of solutions
Challenge # Aircraft Ventilation Challenge
1 Unusually contaminated ventilation air.
2 Exposure to occupant-generated pathogens and VOCs.
3 Limited biological/chemical agent release, fire fighting and smoke control capability
4 Low occupied space humidity and fuselage condensation.
5 Fuselage offgasing on the ground.
6Passenger cabin thermal discomfort due to warm fuselage on the ground on sunny days, and cold fuselage during cruising flight.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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ENGINE BLEED AIR CONTAMINATION SOURCESa. Ingestion of other aircraft engine fume exhaustb. Bearing oil leaksc. Deicer ingestiond. Oil coated ventilation ducts which sorb and later
desorb these contaminants
AIRCRAFT VENTILATION DESIGN CHALLENGE #1Contaminated ventilation (engine bleed) air
Table 3. Aircraft ventilation air contaminants
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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Figure 2. Volatile organic compound chromatogram for bleed air during flight, TVOC = 270 ug/m3. The dominant branched alkanes are typically associated with fuels and solvents. Their origin could have been the oil coating the ducts acting as a sorbent of, for example, earlier ingested engine exhaust fumes.
AIRCRAFT VENTILATION DESIGN CHALLENGE #1Contaminated ventilation (engine bleed) air
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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Bleed air study by
Fox
Bleed air study by Nagda
AM SD
Ethanol 36.0 118.7 0.0 0.0Acetone 9.7 18.7 3.0 2.7Acetaldehyde 8.8 15.6 1.0 1.2Toluene 5.5 8.6 3.8 5.9Propionaldehyde 4.0 7.4 0.8 1.3Methylene chloride 1.6 6.7 1.8 2.5m/p-Xylene 3.4 5.6 0.5 0.5o-Xylene 1.6 3.9 0.0 0.0Tetrachloroethylene 1.5 2.2 0.0 0.0Benzene 0.0 0.0 1.0 1.0
Compound name
Aircraft ventilation air ug/m3 (ref 2,3)
Air outside office buildings, ug/m3 (ref 1)
AIRCRAFT VENTILATION DESIGN CHALLENGE #1Contaminated ventilation (engine bleed) air
Table 3. Some volatile organic compound concentrations found in cabin ventilation air versus averages for the same VOCs in the air found outside office buildings.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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a. Aircraft ventilation and air circulation per person rates are lower than in any other public indoor environment.
b. High aircraft cabin occupancy density creates peak occupant generated pathogen and VOC exposures sooner than in any other public indoor environment.
c. Ceiling supply air diffusers are remote from perimeter seats, exacerbating the pathogen and VOC exposure loads in near the cabin liner.
AIRCRAFT VENTILATION DESIGN CHALLENGE #2Occupant-generated pathogen & volatile organic compounds (VOCs)
Table 4. Reasons for high occupant generated pathogens and VOCs in commercial aircraft passenger cabins.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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AIRCRAFT VENTILATION DESIGN CHALLENGE #2Occupant-generated pathogen & volatile organic compounds (VOCs)
Table 5. Three dominant volatile organic compounds found in aircraft cabin air versus their concentration averages in some office buildings.
Cabin air low GM
Cabin air high GM AM SD
Ethanol 324.0 1,116.0 81.1 82.3
Toluene 6.6 68.0 11.0 7.5
Acetone 40.8 58.9 26.3 8.9
Aircraft cabin air, ug/m3 (ref 2,3)
Office buildings, ug/m3 (ref 1)Compound
name
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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0
0.05
0.1
0.15
0.2
0.25
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Time after occupancy, hours
Rela
tive b
ioeff
luen
t (g
ases,
pat
co
ncen
trati
on
s
V= 5CFM/p SLE,occupancy=230 p/10,000ft3V= 5CFM/p SLE,occupancy=25 p/10,000ft3V= 5 CFM/SLE,occupancy = 7p/10,000ft3
Equilibrium concentrationFor all ODs
Office OD
School OD
Aircraft cabin OD
Figure 3. The impact of occupancy density on occupant-generated pathogen and VOC exposures. Aircraft ODs are higher and movement more limited than in any other common publicspace, creating higher occupant-generated VOC and pathogen exposures in aircraft cabins than in any other public space.
AIRCRAFT VENTILATION DESIGN CHALLENGE #2Occupant-generated pathogen & volatile organic compounds (VOCs)
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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a. Fire in the cavity behind the liner currently cannot be extinguished using Halon as phosgene will be produced which could enter the cabin and kill the occupants.
b. Smoke in the cavity behind the liner can enter into the cabin.
c. Smoke, biological and chemical agents released in the occupied space currently can only be exhausted at the floor in most aircraft. This is inefficient as convection currents tend to move these agents in the opposite direction.
AIRCRAFT VENTILATION DESIGN CHALLENGE #3Limited firefighting, smoke, biological and chemical agent control
capability
Table 6. Problems with current emergency air contaminant removal measures in aircraft passenger cabins.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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The generally accepted minimum relative humidity for comfort is 20% to 65%. The optimal relative humidity range for health is 40-50%. Typically neither of these ranges are met in aircraft for two reasons:
a. The low moisture content of the ventilation air creates aircraft occupied space humidities of 10% or lower, during international flights. Such low occupied space humidity can cause respiratory and eye discomfort. For some with respiratory problems, it can result in acute health problems.
b. Aircraft occupied spaces generally are not humidified. This is because humid cabin air passes through openings in the occupied space liner onto the cold fuselage behind. Here the moisture condenses creating a number of problems. These include added dead weight, deterioration of the insulation, wiring and fuselage, microbial growth and drips through the liner onto the occupants and furnishings below.
AIRCRAFT VENTILATION DESIGN CHALLENGE #4Occupied space humidity and fuselage condensation
Table 7. Fuselage condensation – the reason why aircraft passenger occupied spaces are not humidified
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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Stack Pressure = Air density *(Ti-To) * H/2
Figure 4. STACK PRESSURES create air circulation flows between the occupied space and the fuselage cavity behind the liner. This air circulation deposits occupied space air humidity as condensate on the cold fuselage. Stack pressures are created by the thermal gradient between the occupied space and the outdoor air, which can exceed 70 Celsius degrees during cruise.
AIRCRAFT VENTILATION DESIGN CHALLENGE #4Occupied space humidity and fuselage condensation
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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AIRCRAFT VENTILATION DESIGN CHALLENGE #5Fuselage offgasing
Figure 5. Volatile organic compound chromatogram for fuselage (envelope) VOCs at take-off, TVOC = 22,000 ug/m3. VOCs primarily originated with anti-corrosion treatment oil. These VOC concentrations are highest before take-off with the fuselage heated in a summer sun. Other fuselage VOC sources include wet insulation and microbial growth.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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0
100
200
300
400
500
600
ug/m3
World indoornorm
Canadaindoor norm
Gasper Envelope
Figure 6. Envelope and gasper microbial volatile organic compounds (MVOCs). Samples taken while on the runway. MVOCs were higher than indoor air norms in the fuselage envelope behind the occupied space liner, and lower in the gasper bleed air. The MVOC primary origin in the envelope likely was the insulation.
AIRCRAFT VENTILATION DESIGN CHALLENGE #5Fuselage offgasing and microbial growth
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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AIRCRAFT VENTILATION DESIGN CHALLENGE #6Thermal discomfort
a. On the ground, during boarding and prior to take-off, aircraft occupied spaces can be uncomfortably warm. In part this is because the aluminum skin and cavity behind the liner heat rapidly in the sun to temperatures well in excess of 100F. The forced air circulation cannot keep up with this thermal load.
b. In the air during cruise, the cavity behind the liner cools under external temperatures in excess of –50 F, reaching its cold soak condition in about an hour. This can make for cool occupied spaces, particularly under low occupancies and during sleeping periods on international flights.
Table 8. Occupied space thermal discomfort is caused in part by high fuselage external thermal loads.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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A ventilation technology used in industrial environments
ECHO Air*
is being developed for aircraft to address these six ventilation design challenges.
*USA patent 6,491,254 B1Patents pending in Canada, Germany, France, Spain, Sweden & United Kingdom
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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Six Aircraft Ventilation Design Challenges & The ECHO Air Solution
Table 9. Aircraft occupied space ventilation challenges problems and ECHO Air measures
Challenge # Aircraft Ventilation Challenge ECHO Air Solution
1 Unusually contaminated ventilation air.Pass bleed air through cavity behind liner to filter particles and sorb VOCs before entering the occupied space as cleaned ventilation air.
2 Exposure to occupant-generated pathogens and VOCs.
Improve ventilation effectiveness by supplying ventilation air through the liner as well as via ceiling diffusers.
3 Limited biological/chemical agent release, fire fighting and smoke control capability
Exhaust smoke from the occupied space through the liner and from there directly to the outdoors, keeping the liner at negative pressure relative to the occupied space. If there is a fire behind the liner, inject Halon into this cavity while keeping this
4 Low occupied space humidity and fuselage condensation.
Pressure the cavity behind the liner to prevent humid cabin air entry to the fuselage.
5 Fuselage offgasing on the ground. Exhaust and depressurize the cavity behind the liner during runway taxi and ascent.
6Passenger cabin thermal discomfort due to warm fuselage on the ground on sunny days, and cold fuselage during cruising flight.
Cool and heat the cavity behind the liner as required using appropriately tempered bleed air.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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Occupied space liner and the fuselage envelope
The ‘envelope’ is the section between the cabin liner and the plane aluminum skin.
Figure 7. Currently air movement in the aircraft envelope is uncontrolled. This uncontrolled movement creates fire hazard, air quality and moisture problems. The cabin envelope is located between the cabin liner and the aircraft aluminum skin. It contains the structural frame, insulation wiring and ducts.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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• The envelope is pressurized relative to the occupied space by offsetting stack pressures which would otherwise force occupied space air into the envelope. This pressurization is achieved byinjecting engine bleed air or another dry air source, at a measured rate and temperature, assisted where required by flow blockers and liner sealing reducing injection rate requirements. This injected air subsequently enters the occupied space through liner leakage.
• Pressure difference barrier required across the liner: >1 Pa at all locations at all times. (1 Pa = 0.004 in. w.g.; 1 Pa= 0.00015 psi)
ECHO Air Aircraft Ventilation System
“envelope air pressurization mode”
Table 10. ECHO Air envelope pressurization relative to the occupied space during normal cruising flight.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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Bleed air supply to envelope is filtered, pressurizes and conditions the envelope and then it enters cabin.
ECHO Air Aircraft Ventilation System
“envelope air pressurization mode”
Envelope flow blockers reduce stack pressures and airflow requirements.
Figure 8. ECHO Air envelope pressurization relative to the occupied space during normal cruising flight.
Drawing courtesy of Air Data Inc., Canada.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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ECHO Air Aircraft Ventilation System
“envelope air depressurization mode”
• The envelope is depressurized relative to the occupied space by offsetting stack pressures which would otherwise force envelope air into the occupied space. This depressurization is achieved by exhausting air from the cavity at a measured rate, assisted where required by flow blockers which reduce stack pressures, and liner sealing reducing exhaust flow requirements.
Table 11. ECHO Air envelope depressurization relative to the occupied space during taxi, ascent and emergency situations
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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Envelope depressurization traps envelope contaminants & draws in cabin air contaminants
Direct envelope exhaust eliminates envelope air cont-aminants
Envelope tubes inject fire suppressant
Envelope smoke sensors identify and locate an envelope fire
Envelope flow blockers limit envelope fire spread.
ECHO Air Aircraft Ventilation System
“envelope air depressurization mode”
Figure 9. ECHO Air envelope depressurization relative to the occupied space during taxi, ascent and emergency situations.
Drawing courtesy of Air Data Inc., Canada.
Copyright Indoor Air Technologies Inc. Canada & USA 1-800-558-5892
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ECHO Air Ventilation Advantages Over Current Aircraft Ventilation Designs
Envelope Pressurization Mode
a. Filters engine bleed air particles and sorbs gases before this air enters the occupied space as ventilation air, reducing and eliminating associated health and comfort risks.
b. Improves ventilation effectiveness through better occupied space air circulation, reducing VOC and pathogen exposure.
c. Prevents humidity condensation behind the liner and the associated fuselage structural and insulation damage while allowing occupied space relative humidity to be safely increased to comfortable and healthy levels.
d. Improves occupant thermal comfort through cabin liner radiant heating and cooling.
Envelope Depressurization Mode
a. Quickly vents smoke from electrical fires behind the cabin liner without allowing its entry into the occupied space, preventing potential injuries and death.
b. Enables the safe use of Halon to suppress fires behind the cabin liner.
c. Accelerates the clearing of bioterrorism agents and of smoke, preventing potential injuries, illness and death.
d. Removes humidity and volatile organic compounds from the cavity behind the liner during taxi and take-off before they can freeze in the envelope or enter the occupied space.
Table 12. ECHO Air ventilation advantages over current aircraft ventilation system designs