Air Conditioning Flashcards
Overview 1
The air-conditioning system supplies conditioned air to the cockpit and cabin through three distribution air ducts.
An environmental control unit (ECU) provides cold air to an overhead duct. Warm bleed air is mixed with the cold air from the ECU for temperature-controlled air supplied through the floor and sidewalk ducts.
Overview 2
Temperature is controlled from the temperature control panel in the cockpit or remote control panel in the cabin.
The temperature control panel has the option for automatic or manual temperature control.
What provides the environmental and pressurization air?
Environmental and pressurization air is provided by hot bleed air from the engines or APU.
Can a single engine maintain aircraft environmental and pressurization requirements?
Yes in most operating conditions.
Engine bleed air
High pressure (HP) or low pressure (LP) bleed air is extracted from the engine. The HO valve is controlled automatically by printed circuit board (PCB) logic whenever the L-R ENG BLD AIR selectors are in the NORM position. Valve operation is dependent on various factors, such as throttle position, aircraft altitude, squat switch position, and anti-ice operation. A check valve in the ductwork prevents HP air from entering the LP section of the compressor.
APU bleed air
APU bleed air can be used when the engines are running or shut down. During normal operations, the APU supplies all the bleed air on the ground and in the air up to approximately 20 000 feet. At that altitude, engine bleed air pressure becomes greater than APU bleed air pressure and supplies all the air for the air conditioning system. Reverse flow of bleed air into the engine ducts or APU ducts is prevented by a check valve within the ductwork.
Air-cycle machine (ACM).
Bleed air from the engine(s) or the APU is used to power the ACU. Air passing through the ACM compressor and turbine sections causes the impeller to turn. The main components of the ACM includes the fan, the compressor, and the turbine.
Bleed air coming from the primary heat exchanger is compressed and heated by the compressor prior to entering the secondary heat exchanger. After the air is cooled, it enters the turbine section where it is rapidly expanded, driving the turbine and reducing the tempreture of the air.
A single shaft connecting the turbine and compressor also drives a fan. The fan pulls ambient air through the ACM inlet and across the heat exchangers. Air is exhausted through a vent on the right side of the fuselage.
Heat exchangers.
The primary and secondary heat exchangers use cool ram air to aid in the cooling process of the hot bleed air as it passes through the ACM. The primary heat exchanger cools the incoming bleed air from the engine pylon precoolers prior to entering the compressor. The secondary heat exchanger reduces the temperature of the air coming from the compressor prior to entering the turbine.
CKPT TEMP SEL/ CABIN TEMP SEL: provides for manual or automatic control of temperature for the cockpit or cabin.
AUTO - provides automatic temperature control. Rotating the knob to the HOT or COLD position allows the sensors to maintain a comfortable cabin or cockpit temperature.
CKPT TEMP SEL/ CABIN TEMP SEL: provides for manual or automatic control of temperature for the cockpit or cabin.
MANUAL- in this position, the knob is spring loaded to the neutral (6 o’ clock) position. Rotating the knob toward the HOT or COLD position drives the temperature control valves open or closed. Digital temperature selection is disabled in the MANUAL position.
DISPLAY SELECTOR
CKPT or CAB - displays the temperature as measured by the respective zone sensor.
DISPLAY SELECTOR
SEL - displays selected cockpit or cabin temperature with the CKPT and CABIN TEMP SEL knobs in the AUTO position.
DISPLAY SELECTOR
SUPPLY - displays the temperature in the respective cockpit or cabin supply duct. Allows the crew to view the temperature of the air as it passes through the underfloor ducts.
CABIN TEMP CONTROL
The passenger in seat 6 can be given control of the cabin temperature with this button. Selecting CABIN gives control of the automatic temperature selection to the VIP panel in the cabin.
RECIRC AIR: A cabin recirculating fan increases air movement through the floor and sidewalk outlets. A check valve prevents a reverse flow of air from the floor and sidewalks into the overhead supply. A series of piccolo tubes in the overhead ducting allows an escape path for air if all outlets are closed. The fan is controlled with a CABIN NORM/hi button on the PRESSURIZATION control panel.
Two cockpit recirculation fans increase air flow from the left and right cockpit ducts. One fan is behind the pilot seat and one is behind the copilot seat. Fan speed is controlled by CKPT NORM/OFF button on the PRESSURIZATION PANEL.
