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Appendix A A COMPUTER MODEL FOR ASSESSING AIRLINER CABIN AIR QUALITY Full understanding of cabin air quality requires, among other things, the monitoring of various pollutant concentrations. That is difficult and costly, because so many different pollutants require different monitoring devices and protocols. It would not be cost-effective to study all possible pollutants, although similarities in the sources and sinks of some pollutants would eliminate the necessity of monitoring all of them, and some pollutants are likely to be present in such low concentrations as to be unmeasurable and unimportant with respect to health or welfare. The prohibitive cost of an extensive monitoring program suggests that we look for a different approach to assessing cabin air quality. A model of cabin air quality could serve adequately as an investigative tool. An accurate, validated model could be used to pinpoint potential problems and to study the sensitivity of pollutant concentrations to various control measures. The costs associated with control methods can be estimated with a separate model. With the results of modeling pointing the way, the attack on the problem could be more focused. CONCEPTUAL DEVELOPMENT The model must account for the important aspects of cabin air quality. It must be flexible enough to be used for various types of pollutants with different source profiles, temporal patterns, and health implications. It must be accessible to persons unfamiliar with mathematical or computer modeling. In fact, the details of the model need not be known to the user; only the outcome need be analyzed. 22S
226 The question to be answered is simply stated: Given a few external characteristics, estimate the concentration of a pollutant in the cabin. Several physical characteristics are available to the modeler. Aircraft volumes and air-movement systems are well defined. Ventilation of the cabin is an energy-using process, the engineering designs are well optimized, and data are available. Information on air recirculation and filtering is also available, as is information on the source strengths of some of the pollutants, such as carbon dioxide and water vapor from humans, tobacco smoke, and ozone. Less is known about others, such as volatile organic compounds emitted from materials, insecticides, or cleaning agents. Other input data for the model are not readily available. These include information on air-mass movements between compartments in the cabin, rates of loss of reactive chemicals, and chemical deposition rates. These qualities can be estimated, but an effective model must include the ability to perform sensitivity analyses for them. Ideally, it should be possible to perform sensitivity analyses as the need arises for all quantities on which little information is available or for which design specifications are not met. Once the potential input data are known, selection of a model type can begin. The most appropriate type of model for this application should be based on the general mass-balance approach. All mechanisms for production and loss of the pollutant are accounted for properly, and the change in concentration per unit time is the difference between the two: dC/dt = P - LO, where C = concentration of pollutant, t = time, P = rate of production of pollutant, and L = rate of loss of pollutant. At equilibrium, dC/dt = 0--production rate equals loss rate. Solving for the concentration gives: C = P/L. (1) (2) ,i
227 Note that the ratio 1/L is a measure of the lifetime of the exponential approach to equilibrium. Small rates of loss imply a slow approach to equilibrium;,large rates of loss suggest that equilibrium will be established rapidly and will prevail. Figure A-1 is a schematic of a single component of a multibox model of an aircraft. The model consists of essentially separate boxes, each containing its own , production and loss mechanisms. Production mechanisms include pollutant presence in circulating air (Ri) and local source (Si). Potential production mechanisms from reactive chemistry can be added, although they are probably unimportant. Loss mechanisms include leakage (Li), main recirculating flow (Fi), and first-order losses from deposition or other processes (Ki). An assumed local equilibrium is established in each. A ' degree of communication is established between adjacent boxes only because of the presence of small forward and backward airflow terms (fi and bi). These terms act an additional loss mechanisms for the box in question, whereas terms from adjacent boxes act as production mechanisms. Rj - 1 bj Lj hi/ l Vi, Sit, Kj FIGURE A-1 Schematic of single component of multibox model of aircraft cabin air quality. text for explanation of symbols. i+1
228 The cabin itself is coupled to another system within the aircraft, the air cleaning system. Figure A-2 is a schematic of the aircraft as a whole. Note that the cabin can be considered to be a single compartment (box 0), with polluted air leaving the cabin (F) and entering the air cleaning system. There a portion of the polluted air (E) is exhausted, and the remainder is filtered, mixed with ambient makeup air (m), and returned to the cabin (R) as the supply air. Conservation of mass requires that F ~ L ~ E = m + R. where L is the amount leaked from the cabin to the atmosphere. More complicated systems require more complicated analysis. If all pollutants are generated in one place, but other placer are of interest, more boxes are needed to describe the system. As the system becomes more ~/ 1 Box OBo ( 1 30x 2 TRo~ {R1 R21 l 1 R ~ 1 m E F3 _ L3 _ 41 V3, S 3,K 3 b3 Box 3 -l R3 FIGURE A-2 Schematic of aircraft with air cleaning system. See text for explanation of symbols. F
229 complex, more information is needed for the model. Data on exchange of air from one box to another must be obtained. Analysis of the results also becomes more complex. Figure A-3 illustrates the detailed physical model schematically. In thin case, four of the detailed boxes are coupled within the cabin. Note that no forward flow (fi) is allowed out of the foremost compartment, nor is any backward flow (bi) allowed out of the rearmost compartment. This physical model is very general. Each compartment can have any volume (Vi) deemed appropriate. Preferential flow can be effected by manipulating the relative magnitudes Of fi and bit Differential source strengths can also be implemented. Additionally, control strategies and their economic impacts can be investigated. R 1 ~ Cabin _ ~ Box O ~ Air Cleaning System 80,`1 6 E m k Restriction: F + L + E = m + R . . !~ F FIGURE A-3 Schematic of coupled components for multibox model of aircraft cabin air quality. See text for explanation of symbols.
230 MATHEMATICAL DEVELOPMENT The determination of the concentrations in each of the compartments in the model described above requires the simultaneous solution of coupled, first-order linear differential equations obtained from Equation 1. At equilibrium, the solution is easily cast into the form of a matrix equation. Because of the nature of the physical model--i.e., interaction of adjacent boxes only--the mathematical form in tractable. Solutions can be obtained quickly and accurately for a large number of interacting boxes. To describe the system, start with an expansion of Equation 1 for the ith box. dt V, + Vj + Vj - Vj (me + /. + b. + Fj) + Ki The restrictions on fi and hi apply. At equilibrium, all dCi/dt vanish, and the matrix equation becomes (for a four-compartment case): Vo (I + fo + Fo) + Ko _ To o o (3) o -vl v~(~1 +f1 +F1)+ K1 -A cO cl c2 - v, v, (L3 ~ f3 + F3) ~ K3 1 Cs o o - ~2 V2 (L2 + f2 + F2) + K2 - ~2 o = Vo (5° + ROCr) (S1 + R1 Cr) V3 (S2 + RACY) Ve, (S3 + R3Cr) (4) where Cr represents the concentration of pollutant in the recirculated air. This system has a tridiagonal form and can be solved efficiently with LU factorization. The coupled cabin and air cleaning system is solved first, with an explicit solution of the two-by-two form.
231 OPERATING PROCEDURES The cabin air quality simulation model Cabinair is designed to be user-friendly and self-documenting. The operator specifies whole aircraft parameters as listed in Table A-1. Any of these parameters can be changed through commands. It is important, however, that consistency checks be made to ensure mass balance, etc. A warning is displayed when, for example, total flow in exceeds total flow out. Table A-1 lists a standard set of parameters programed as default values. These are appropriate for an L-1011 with four compartments and tobacco smoke as the pollutant of interest. TABLE A-1 Parameters for Whole Aircraft with L-1011 Four-Zone Parameterization Parameter Volume Recirculation Leak rate Net flow rate Deposition Source rate Exhaust flow Makeup flow Outdoor concentration Number of boxes Value 450.0 m3 150.0 m3/min 10.0 m3/min 140.0 m3/min 0.0033/min 83.3300 mg/min 140.0 m3/min 150.0 m3/min 0.01000 mg/m3 SIMULATING AIRLINER AIR QUALITY The Cabinair model was used to simulate the steady- state concentrations of environmental tobacco smoke, carbon dioxide, and water vapor in multiple zones of three aircraft: B-727-200, B-767-20O9 and MD-80. Flow parameters were developed from the technical ventilation specifications of the aircraft. Figures A-4, A-5, and A-6 show the outside-air supply, recirculation, and controlled and uncontrolled leakage for these three aircraft. The B-727-200 (Figure A-4) has a straightforward once-through ventilation system. The ECUs deliver 240 cfm, 350 cfm, and 2,235 cfm to the cockpit, first- class section, and coach sections respectively. The
232 112 Exhaust from Lavatories and Galley / Cockpit 130 Exhaust from Lavatories and Galley First Class ~ Cargo Bay I/ I.; ~,/; ~ I 240 F 1 350 F 350 Avionics Cooling {Exhaust) 2,2 35 F 1 050 Leakage 883 Exhaust 300 Cargo Heat (Exhaust) FIGURE A-4 B-727-200 cabin airflow distribution, cfm. All outside air. F. outside air. Uniform supply in cabin. Exhaust uniform at floor level. Leakage assumed uniform at 1,050 cfm. Arrows show direction of airflow. Based on information from Boeing (personal communication, 1985) and Lorengo and Porter.3 outside air delivered to the passenger sections (first class and coach) is assumed to be delivered uniformly over the entire length of the cabin. Air is discharged through both controlled and uncontrolled vents. The aft exhaust valve is used to control pressure and discharges 883 cfm. Avionics, cargo, lavatory, and galley vents (forward and aft) discharge a total of 892 cfm. There is leakage of 1,050 cfm. The B-767-200 (Figure A-5) has a more complex ventilation system. The 2,388 cfm from the ECUs is mixed with 2,388 cfm of filtered recirculation air from the forward cabin and delivered to the cockpit and to the overhead air vents in the cabin. The overboard discharge manifold draws air from lavatories, galleys, and the aft avionics compartments, which then mixes with floor-level cabin exhaust and is discharged overboard. The MD-80 ventilation system (Figure A-6) is different from either of the other two. The cockpit is supplied only with outside air. Recirculation air is drawn from along the floor of both first-class and coach sections of the passenger cabin and is mixed with outside air. This mixed air is then delivered to the first-class and coach sections -
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235 With these data and standard configuration diagrams available from Trans World Airlines (Figures A-7, A-8, and A-9), a volume-weighted partitioning of the flows was made. The volume of a given zone was assumed to be directly proportional to the linear dimension of the zone as a fraction of the total length of the aircraft. Generally, after the initial partitioning, flow imbalances remained. These imbalances were eliminated by allowing forward or backward flow to or from adjacent zones to compensate for an excess or deficiency of air movement. Flows were thus balanced to within approximately 1 m3/min over the entire aircraft. The source strengths used in the simulations were as follows. For respirable particles, cigarette smoke is the prima An source. An active smoker produces / COCkDit \ Closet - ~ 1 - CD 2- m ~ 3- 12@ 0~ 4- m m Closet- ~ cm 6-pita ~E|FI 7_ I, 1 i 1 mutt 8 - ! ' ! 1 ~ ~ , a_ TV ~ 10- ~ 1; 1 1;; ! 11- mu! 1 I,; 12, ~ ~ ! 1 1 1 i ' :~ ~ 1 i ! [ ! ~ ' 5- 1 i i 1 [ 1 i 1 6- [~1 C:: 7~1lii ~1 8 -I 1 1 1 1 1 1 1 1 19- ~ 1 1 i 1 20- ~ i i to 2 1 -|Trl 23- ~t ~ 1;; 24- =2 ~ I 25- ~1 1 i 26- 1~ 1 1 ' 1 GalleY- ~ r t Lavatory Galley Galley -27 ~ -28 Gstiev~ i I I ~29 Auxiliary ~I ! I 1 1~30 Service Bar ~: Lavat ~ - Zone Rows Seats Crew Flight Deck First Class Lavatory and Galley First Class Non-Smoking First Class Smoking Coach Non Smoking Coach Transition Coach Smoking Coach Lavatory and Galley 13 8 1 4 4 519 81 2 20 21 12 22-30 41 1 FIGURE A-7 Standard B-727-200 interior arrangement. Numbers of rows allotted for smoking can be increased or reduced according to demand for non- smoking seats. Figure reprinted with permission from Trans World Airlines. 4
236 rpapirable particles at approximately 3 mg/min. On the average ? a smoker smokes 2 cigarettes/in and takes 10 min/clgareete, thus smoking one-third of the time. The scenarios investigated include an average state in which one-third of the smokers are smoking or every smoker is smoking at one-third the maximal rate. At a maximum, all smokers are smoking simultaneously. For carbon dioxide, a source strength of 0.5 L/min per person is used (a source strength of 0.5 L/min per person is used to approximate the proportions of active crewmembers and sedentary passengers). 2 ASHRAE user 0.3 L/min.l The figure of 0.5 L/min is equivalent to 760 mg/min per person. A sedentary person, such as a passenger, A / Cockpit \ Lavatory tall 6- 7- 8- 9_ 1 0- 1 1 _ 12 _ / Galley Lavato rv s ,, . , I ,, ...._ m ~ m ~ Em, m m , , , m m m m m Ill Em, m m m m m LL] m 18-t 19 - ~1 20- m t111 m 21- m ~ m 22- m cm m m m: m 27 - m 1 1 1 1 m 23- m mm m 33_ m mm m 335- m An, m Lavatory- Em,, [E Closet Movie Screen - 1 _ Movie Screen ~ 6 - 7 -8 _ 9 -10 -11 ~12 1 4^ Closet Lavatory Movie Screen - 18 -19 -20 -21 -22 -23 -24 -25 As_ -26 -27 -28 -29 -30 -3 1 -32 -33 -34 _35 -36 Lavatory Galley 37' Galley ~ Galley \~L Galley Zone Rows Seats Crew Flight Deck First Class Lavatory and Galley First Class Non-Smoking First Class Smoking Business Non-Smoking Business Smoking Business Lavatory and Galley Coach Non-Smoking Coach Transition Coach Smoking Coach Lavatory and Galley 1-2 12 3 6 6-10 30 ~ 1-14 16 18-27 28-29 30-37 67 18 48 l 1 1 FIGURE A-8 Standard B-767-200 interior arrangement. Numbers of rows allotted for smoking can be increased or reduced according to demand for nonsmoking seats. Figure reprinted with permission from Trans World Airlines.4
237 produces water vapor at 700 mg/min, whereas an active person, such as a crew member, produces 2,000 mg/min. Ambient concentrations of particles, carbon dioxide, and water are 0.010 ~g/m3, 330 ppm, and 1.5 g/kg of air, respectively. Changing these values (by filtration) will alter the results only slightly for respirable particles, but might have larger effects for carbon dioxide and water vapor. Data in Tables A-1 through A-3 are for aircraft in the standard configuration, including normal recirculation and full occupancy with all packs running. Table A-4 presents data on the MD-80 aircraft, assuming, for comparative purposes, no recirculation. Table A-5 presents data on the B-767-200 aircraft with no recirculation, and Table A-6 presents data on the B-767-200 aircraft, assuming standard operating conditions, but only 60% occupancy. L L - Galley Navahos ~ r Closets 3 ~ 1- 1~ ~1 23_ m m Zone Rows Seats Crew _ _ Flight Deck - - 2 6- m cat First Class Lavatory and Galley - - - . ~ ~ First Class Non-Smoking 1-2 8 1 3 _ ~ First Class Smoking 3 4 9 ~ Cow Coach Non-Smoking 5-22 85 2 To G ~ ~ 1 Coach Transition 23 24 10 ', Q 1 . - ! Coach Smoking 25 33 35 1 72 m ~ cO h Lavatory and Galley ,4 Q ~ ~ I ac 15 ~ If '6 ~ ~ 77 m Hi 18_ m ^9 ~ f i ! I 20 m all 21 am CD' 22- m AD 23- m coal 24- C t~T1 _ '~ m in 26- m cod FIGURE A-9 Standard MD-80 28- m G 29 interior arrangement. Numbers Ga''ev ~ ~ 30 of rows allotted for smoking Ga''ev ~ C3 32 can be increased or reduced '-Kiev- ~ ~ 33 according to demand for non LavaTorV - _ _ - Lavatory ~=i smoking seats. Figure reprinted with permission from tlB Trans World Airlines.4
238 Generally, when air is recirculated, the concentrations of pollutants increase. As occupancy decreases, the concentrations of pollutants decrease. Although it is not exact, one can approximate both these phenomena as linear; i.e., 50% recirculation will result in doubling the pollutant concentrations, and 50X occupancy will halve the concentrations. TABLE A-2 Calculated Concentrations of Various Pollutants on Simulated B-727-200 Aircraft Relative Environmental Tobacco Humidity Smoke, m~/n~3CO2, (Water Zonea AverageMaximumC Dam Valor), TO Cockpit 0.0100.010 517 7.8 First-class lavatory and galley 0.0100.010 435 5.5 First-class nonsmoking 0.0100.010 919 8.7 First-class smoking 1.3023.886 1,178 10.8 Coach nonsmoking 0.0580.154 1,284 10.9 Coach transition 0.0180.034 1,373 11.6 Coach smoking 2.2436.708 1,367 11.6 Coach lavatory and galley 0.2990.876 484 4.4 Whole aircraftd 0.5601.661 1,139 10.1 Volume averagede 0.5701.691 1,154 10.1 Supply air 0.0100.010 330 3.7 e a Zones are examples of standard configuration zones; 100% occupancy assumed; no recirculation. Supply air concentration is ambient concentration. CO2 and water vapor concentrations assume temperature of 20°C. b One-third of cigarette smokers smoking at any time (2 cigarettes/in). c All cigarette smokers on plane smoking at same time. d Average concentration derived from arithmetic average of zonal concentrations. Derived from zonal concentrations weighted by volume.
239 TABLE A-3 Calculated Concentrations of Various Pollutants on Simulated B-767-200 Aircraft Zonea Environmental Tobacco Smoke, m~/m3 co2, Average MaximumC Relative Humidity (Water pom Vapor,, % Cockpit 0.297 0.872770 7.2 First-class lavatory and galley O.295 0.865770 6.7 First-class nonsmoking 0.293 0.8601,240 10.3 First-class smoking 1.196 3.5691,469 12.0 Business-class nonsmoking O.471 1.3951,535 11.5 Business-class smoking 1.998 5.9761,590 11.8 Business-class lavatory and galley 0.314 0.9231,140 8.2 Coach nonsmoking 0.293 0.8611,483 11.4 Coach transition 0.293 0.8611,773 13.7 Coach smoking 2.380 7.1221,662 12.8 Coach lavatory and galley 0.660 1.9611,610 6.6 Whole aircraftd O.798 2.3751,354 10.5 Volume averagede 0.827 2.4611,389 10.7 Supply air 0.300 0.881707 6.2 a Zones are examples of standard configuration zones; 100X occupancy assumed; 50% of return air recirculated. CO2 and water vapor concentrations assume temperature of 20°C. b One-third of cigarette smokers smoking at any time (2 cigarettes/in). C All cigarette smokers on plane smoking at same time. d Average concentration derived from arithmetic average of tonal concentrations. e Derived from zonal concentrations weighted by volume .
240 TABLE A-4 Calculated Concentrations of Various Pollutants on Simulated MD-80 Aircraft Relative Environmental Tobacco Humidity Smoke, ma/m3 C02, (Water Zonea Average MaximumC Dpm Vapor), % Cockpit 0.126 1.214 638 7.6 First-class lavatory and galley 0.125 0.784 599 6.3 First-class nonsmoking 0.125 0.577 965 9.2 First-class smoking 0.688 2.209 867 10.1 Coach nonsmoking 0.206 0.634 1,522 12.6 Coach transition 0.638 1.912 1,585 12.7 Coach smoking 2.237 6.710 1,452 11.9 Coach lavatory and galley 0.124 0.370 540 4.5 Whole aircraftd O.631 1.968 1,329 11.2 Volume averagede O.593 1.850 1,270 10.8 Supply air 0.127 0.380 519 5.1 a Zones are examples of standard configuration zones; 100X occupancy assumed; 21X of return air recirculated. CO2 and water vapor concentrations assume temperature of 20°C. b One-third of cigarette smokers smoking at any time (2 cigarettes/in). c All cigarette smokers on plane smoking at same time. d Average concentration derived from arithmetic average of zonal concentrations. e Derived from zonal concentrations weighted by volume.
241 TABLE A-5 Calculated Concentrations of Varions Pollutants on Simulated B-767-200 Aircraft with No Recirculation Relative Environmental Tobacco Humidity Smoke, ma/m3 CO2, (Water Zonea Average MaximumC Dam Vapor), X Cockpit 0.010 0.010 393 4.9 Firnt-class lavatory and galley O.010 0.010 393 4.6 First-class nonsmoking O.010 0.010 863 8.3 First-class smoking 0.914 2.721 1,091 10.1 Business-class nonsmoking 0.190 0.549 1,157 9.6 Busines~-class smoking 1.717 5.131 1,212 9.9 Business-class lavatory and galley 0.315 0.075 762 6.3 Coach nonsmoking 0.010 0.010 1,105 9.4 Coach transition 0;010 0.010 1,394 11.7 Coach smoking 2.097 6.271 1,283 10.8 Coach lavatory and galley 0.376 1.110 518 4.6 Whole aircraftd O.515 1.525 976 8.5 Volume averagede 0.544 1.611 1,011 8.7 Supply air 0.010 0.010 330 3.7 a Zones are examples of standard configuration zones; 100% occupancy assumed. CO2 and water vapor concentrations assume temperature of 20°C. b One-third of cigarette smokers smoking at any time (2 cigarettes/in). c All cigarette smokers on plane smoking at same time. d Average concentration derived from arithmetic average of zonal concentrations. e Derived from zonal concentrations weighted by volume.
242 TABLE A-6 Calculated Concentrations of Various Pollutants on Simulated B-767-200 Aircraft with 60% Occupancy and 50% Recirculation - ,Zonea Environmental Tobacco Smoke, m~/m3 co2, Average MaximumC Relative Humidity (Water plum Vapor), TO Cockpit 0.182 0.527 521 5.5 First-class lavatory and galley O.181 0.523 483 5.1 First-class nonsmoking O.180 0.520 681 7.2 First-class smoking 0.722 2.145 777 8.3 Business-class nonsmoking 0.287 0.841 747 7.9 Business-class smoking 1.203 3.589 760 8.1 Business-class lavatory and galley 0.192 0.558 563 6.0 Coach nonsmoking 0.180 0.520 747 7.9 Coach transition 0.180 0.520 877 9.3 Coach smoking 1.432 4.277 827 8.8 Coach lavatory and galley 0.400 1.180 473 5.0 Whole aircraftd 0.483 1.525 693 7.5 Volume averagede O.500 1.429 706 7.5 Supply air 0.184 0.533 474 5.0 a Zones are examples of standard configuration zones. CO2 and water vapor concentrations assume temperature of 20°C. b One-third of cigarette smokers smoking at any time (2 cigarettes/in). c All cigarette smokers on plane smoking at same time. d Average concentration derived from arithmetic average of zonal concentrations. e Derived from zonal concentrations weighted by volume.
243 REFERENCES 1. American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. ASHRAE Standard: Ventilation for Acceptable Air Quality. ASHRAE 62-1981. Atlanta, Gal: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., 1981. 2. Balvanz, J., S. C. Bowman, A. Fobelets, T. Lee, K. Papamichael, and R. Yoder. Examination of the Cabin Environment of Commercial Aircraft. Ames, Iowa: Iowa State University, 1982. 3. Lorengo, D. E., and A. Porter. Aircraft Ventilation Systems Study: Final Report. DTFA-03-84-CO-0084. Atlantic City, N.J.: U.S. Federal Aviation Administration Technical Center, 1985. (draft) 4. Trans World Airlines. TWA Aircraft Seating Guide. New York, N.Y.: Trans World Airlines, 1984.
