787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Air Systems -
Air Conditioning System
Description
Copyright © The Boeing Company. See title page for details.
D615Z003-TBC 2.20.3
Air Distribution
Recirculation fans assist the packs to maintain a constant ventilation rate through
the cabin. The fans draw cabin air through filters, then reintroduce the air into the
conditioned air distribution system.
The flight deck receives 100% conditioned outside air and the passenger cabin
receives a mix of outside air and recirculated air. Flight deck pressure is
maintained slightly higher than the passenger cabin pressure to prevent smoke
from entering the flight deck. Some recirculated air is supplied to the flight deck
if one pack is off and its associated lower recirculation fan is on.
Outside air flow is reduced during failure conditions and electrical load shed
conditions to protect the electrical power distribution system and to ensure that
sufficient electrical power is available to other critical airplane systems.
Cabin attendants can reduce outside airflow to the cabin based on the number of
airplane occupants. This reduction is limited to ensure that a minimum air flow is
always supplied to the cabin.
Air exhausted from the passenger cabin flows into the upper recirculation system
or to the lower deck, where it is either exhausted overboard through outflow
valves or drawn into the lower recirculation system. Air from the recirculation
fans is mixed with pack air before entering the distribution ducts.
The lower recirculation ducts contain liquid-to-air heat exchangers capable of
additional cabin cooling. Lower recirculation cooling reduces the power required
from the CACs. Lower recirculation cooling is provided by the Integrated Cooling
System (ICS) which is a common galley cooling system.
When upper and/or lower RECIRCULATION FAN switches are OFF, an EICAS
advisory message RECIRC FAN UPR and/or LWR OFF is displayed. Turning the
recirculation fans off does not increase the amount of fresh air to the passenger
cabin, but results in a decreased in airflow instead.
CAUTION: Recirculation fans must remain ON during hot weather
operations unless a non-normal checklist directs to select them
off.
A de-humidification system is located in the crown area of the passenger
compartment. The system operates automatically when electrical power is
available. It uses two zonal dryers (forward & aft) to remove moist air from the
crown area. Fans recirculate dry air back to the crown area while moist air is
exhausted below the cabin floor.
February 15, 2010
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