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2 Environmental Control Systems on Commercial Passenger Aircraft
Pages 39-63

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From page 39...
... The conditioned air is then delivered to the cabin and cockpit to maintain a comfortable environment. DESCRIPTION OF ENVIRONMENTAL CONTROL SYSTEMS COMPRESSED-AIR SOURCES On the ground, compressed air for the ECS can be obtained from an auxiliary power unit (APU)
From page 40...
... The use of separate compressors increases weight, decreases reliability, and imposer additional maintenance requirements. For ground air-conditioning, high-temperature compressed air can be supplied to the cabin through the ECU from an onboard APU or from a portable ground cart.
From page 41...
... To prevent freezing of the water separator, ACM discharge temperatures must be limited to about 35°F. Recent developments have led to the use of high-pressure water separators that condense and remove moisture from the bleed air before it expands in the turbine.
From page 42...
... FIGURE 2-1 Operation of aircraft environmental control unit in cruise conditions at 3S,OOO ft.
From page 43...
... is determined by cabin areas, rather than by number of passengers -- outside air will not be distributed strictly on a Der-nas~en~er hack ~ First-class and business sections of the cabin might have 2-3 times an high a ventilation rate per occupant as the economy section. O ~ Because of the larger solar and electronic cooling loads in the cockpit, ventilation per flight crew member might be 10 times as high as that in the cabin, or even higher.
From page 44...
... The air is then exhausted overboard through outflow valves controlled to maintain the desired cabin pressure. Figure 2-2 illustrates typical passenger cabin airflow patterns.
From page 45...
... RECIRCULATION SYSTEMS Recirculation systems have been used on the early Convair 880 and 990, B-707, DC-8, Lockheed Electra, and many other older aircraft that used vapor-cycle cooling systems. The use of air recirculation systems in modern aircraft has recently increased with the advent of higher engine bypass ratios, higher jet-fuel costs, the design of "stretched" versions of production aircraft, and the development of advanced ECUs that use highpressure water separators.
From page 46...
... Turbine bypass and heat-exchanger airflow valves are typically used to establish the ECU discharge temperature and a zone reheating system to establish supply temperatures for each zone. Where discharge air from the ECUs is mixed in a plenum, the ECU discharge temperature is controlled to meet the demands of the zone that requires the coldest air, and a reheating system is used to add hot bleed air to the other zones, which need less cooling or more heating.
From page 47...
... during descent.1 2 The crew can select higher or lower rates of change, but the controls are normally set at the recommended value, which is usually identified by an index mark on the pressure control panel.
From page 48...
... Normal conditions include full passenger load, operation of all ECUs at rated flow, and steady-state cruise. Airlines may increase the passenger capacity above what is shown in Table 2-1, and that would reduce passenger ventilation rates.
From page 49...
... A NASA-sponsored study in 19801° showed that about 62,000 gal of fuel, or about 1% of the annual total, could be saved per year per DC-10 if the flight crew reduced the ventilation flow from 18 cfm to 8 cfm per passenger. The combined effect on passenger ventilation rate of reducing ventilating air flow and variations in seating density is shown in Table 2-1.
From page 50...
... Therefore, although passenger demand follows a normal distribution, the flight load-factor distribution is a truncated normal curve, as shown in Figure 2-4. The Boeing Commercial Airplane Company studied the relationship between average passenger load factor and unaccommodated demand (the percentage of passengers who cannot be accommodated at their desired departure times)
From page 51...
... A ventilation distribution was then calculated by the Committee on the basis of the load factors in Figure 2-S, the ventilation rate of each major aircraft model, and the percentage of seat-hours flown by that model (Table 2-3~. These ventilation distributions (Figures 2-6 and 2-7)
From page 52...
... Based on data from U.S. FAAl9 and ATA.3 TABLE 2-3 Seat-Hours Flown and Ventilation Rates, by Aircraft Typea Proportion of Total Seat-Hoursb Aircraft Flown Annuallv.
From page 53...
... 1 985 22.6 1 0.4 20.9 10.1 10 OUTSI DE Al R cfm/passenger 30 40 50-50+ FIGURE 2-6 Ventilation rate distribution, minimal flow, for mayor U.S.
From page 54...
... At high outside-air ventilation rates, passenger well-being is increased with respect to carbon monoxide and carbon dioxide, contamination due to smoking, and odor. Increasing total cabin airflow (with either outside or recirculated air)
From page 55...
... 4 Thus, even at the lowest ventilation rates on aircraft, there is no significant reduction in the percentage of oxygen in the cabin. Contamination with carbon dioxide varies inversely with ventilation rate, because carbon dioxide production by passengers is nearly constant.
From page 56...
... Data from Halfpenny and Starrett.6 0 10 20 30 40 50 60 70 80 V E NT I LAT I O N R ATE, of m/smoker FIGURE 2-8 Relationship of ventilation rate to acceptability by smokers and nonsmokers of tobacco smoke odor/irritation.
From page 57...
... The contamination at various ventilation rates encountered in airplane smoking sections and the average contamination in the cabin when air in smoking and nonsmoking sections is fully mixed are also shown in Figure 2-8. Contamination in the form of tars can affect aircraft systems where cabin air is used for cooling.
From page 58...
... , cabin relative humidity varies inversely with ventilation rate (see Figure 2_9~.12 40 30 o I 20 UJ Cl LU CC 10 o \` 65 F \ \ Air/ 70 F - ~75-F Cabin Temp iO OUTSIDE AIR, cfm/passenger 20 25 30 FIGURE 2-9 Relation of relative humidity and outsideair ventilation rate. Equivalent cabin altitude, 6,500 ft.
From page 59...
... Residual cabin ozone concentration is a function of the outside concentration, the design of the air distribution system, the use of catalysts or adsorbers, and the total airflow. Each airplane has a characteristic cabin ozone retention factor, which is the ratio of the ozone concentration in the cabin to the ozone concentration in outside air after it has passed through the ECU.
From page 60...
... The weight penalty for basic ECS equipment should not be charged to the design ventilation air flow, because the equipment is normally sized to meet design cooling requirements, which are based on hot-day conditions at sea level. However, if the ventilation rate were increased above the flow required for cooling as designed, then the weight penalty of the added ECS equipment (large ducts, valves, heat exchangers, etc.)
From page 61...
... The Significance of Airline Passenger Load factors. Washington, D.C.: Air Transport Association of America, 1980.
From page 62...
... Federal Aviation Administration Technical Center, 1985. (draft)
From page 63...
... W Tobacco smoke dilution recommendations for comfortable ventilation.


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