Air Conditioning Flashcards
What is the air con system
INTRODUCTION The air conditioning system consists of a flow control system, the air conditioning units (the packs), a temperature control system, a distribution system, an avionics cooling system, an optional humidifier and a cabin pressure control system. The air conditioning system uses hot pressurized bleed air from the engines (temperature and pressure regulated by the bleed system), the auxiliary power unit or an external air source to provide a controlled atmosphere in the aircraft for flight crew and passenger comfort.
The air conditioning system is a dual system (two packs), each controlled automatically during all phases of operation by two air conditioning system controllers. The packs may also be controlled manually, if there is an automatic mode failure or controller failure. The packs provide cold air, which is then blended with hot air to regulate the temperatures individually to the flight deck and cabin. Individual temperature selections and system operation is controlled from the air conditioning panel on the cockpit overhead panel.
How much air is re circulated
Around 50 percent
How many outflow valves
2 , 1 at front and 1 at rear
The outflow valve at the front also receives avionics cooling air
What does ram air switch do
Used to provide ambient air to ventilate cockpit and cabin in event of pack failure
Recirc switch to isolate in case of smoke
What is AUX PRESS switch
Used to control alternate air source through the trim air system for cabin pressurisation
What are pack control switch settings
NORM- automatic
LO-low flow mode
HIGH-high flow mode
MAN-flow control valve is driven fully open
What do trim air valves do
Add hot air to raise the pack output temp which is usually around 10 degrees
Where does ram air valve supply
R/h side after pack
What happens when emerg de pressurisation button is pressed
The cabin de pressurises to 14500 ft then will maintain that setting
When is cabin rate indicator displayed
When MAN is selected
What happens with pack operation
INTRODUCTION
Figures A1, A2 and A3 The two flow control systems consist of a pack inlet temperature sensor, a bleed filter, an ozone converter, a flow sensor venturi, pack inlet flow sensor, pack inlet pressure sensor and a flow control valve. The flow control system features help in maintaining a healthy cabin environment and provide improved comfort for passengers and crew. The flow control system takes bleed air from the engine, the APU, or a ground air source. The flow control system filters and controls the air to operate the air conditioning units. Pack inlet temperature sensors measure the temperature of the hot air entering the flow control system. Bleed filters separate and remove dust or dirt particles from the air entering the air conditioning system by centrifugal action. The ozone converters through catalytic effect change ozone molecules (03) contained in the air from the pneumatic system into oxygen molecules (02). The flow sensor venturis contain pack inlet pressure sensor and pack inlet flow sensor transducers to measure the mass flow of the air to the air conditioning system. The flow control valves, controlled by the air conditioning system controllers (ACSCs) regulate mass flow of air to the air conditioning units. The ACSCs use the flow control system sensors along with other operational data (control panel selections and digital data from other computers) to make these flow control calculations.
What are air con components
COMPONENTS
The filtering and flow control system consists of the following components: • Air conditioning panel • Pack inlet temperature sensors • Bleed filters • Mechanical interfaces and coupling • Ozone converters • Flow sensor venturis • Pack inlet pressure sensors • Pack inlet flow sensors • Flow control valves • Air conditioning system controllers
What does air con panel do
Figure A3 FILTERING AND FLOW CONTROL SYSTEM addition to these inputs, pack flow is also modified according to control laws within the ACS controllers. The manual position is used for manual pack temperature control. Pack Inlet Temperature Sensors Figures A2 and A4 The pack inlet temperature sensors (PITSs) measure the temperature upstream of the cooling pack. The temperature signals are sent to the air conditioning system controllers through the electrical connector of each sensor. The sensors are installed in the aft equipment compartment upstream of the bleed filters. The PITS provides a dual air temperature measurement to its associated ACSC. Bleed Filters Figures A2 and A4 Controls are provided on the air conditioning panel for the following flow control functions: •L/R PACK P BAs • PACK CONTROL selector L/R PACK PBAs The L/R PACK PBAs control the flow control valves (FCVs) which in turn control the flow of bleed air into the ACUs. These PBAs are normally on, thus enabling pack operation to start immediately upon the supply of bleed air. An integral white OFF legend, when illuminated, indicates the pack has been manually selected OFF. The amber FAIL legend indicates that the pack has experienced a failure that has shut off the flow control valve. PACK CONTROL Selector The PACK CONTROL selector provides three flow control modes: low, normal and high flow. In addition to these inputs, pack flow is also modified according to control laws within the ACS controllers. The manual position is used for manual pack temperature control.
What are pack inlet temp sensors
Pack Inlet Temperature Sensors Figures A2 and A4
The pack inlet temperature sensors (PITSs) measure the temperature upstream of the cooling pack. The temperature signals are sent to the air conditioning system controllers through the electrical connector of each sensor. The sensors are installed in the aft equipment compartment upstream of the bleed filters. The PITS provides a dual air temperature measurement to its associated ACSC.
What are bleed filters
The hot bleed air from the bleed air supply system flows through a bleed filter, which separates dust by centrifugal action. Inside the stainless steel body of the bleed filters dust collects in a chamber. Suction is applied to a fitting on the filters through a tube that comes from the ram air outlet duct. The suction removes the dust collected in the chamber. The bleed filters are installed in the aft equipment compartment between the pack inlet temperature sensors and the ozone converters.
What is ozone converter
The ozone converters change the ozone in the bleed air into oxygen (by catalysis effect). This is to permit flight in high altitude conditions. The body has two flanges and two mounting brackets. The ozone converters are installed in the aft equipment compartment between the bleed filters and the flow sensor venturis. The component manufacturer must eventually restore the ozone converter. Fore more information, see the Time Limits/Maintenance Checks manual (TLMC).
What flow sensor and venturis are their
Flow Sensor Venturis
Figures A2 and A5 The flow sensor venturis measure the mass flow of the air upstream of each air conditioning system. The flow sensor venturis have a light alloy body with a venturi in the middle. There are two static pressure outlets on each flow sensor venturi, one for the pack inlet pressure sensor (PIPS) and one for the pack inlet flow sensor (PIFS). The flow sensor venturis are installed in the aft equipment compartment between the ozone converters and the flow control valves.
What are PACK INLET PRESS SENSORS
The pack inlet pressure sensors (PIPSs) measure the pressure upstream of the air conditioning units. The sensors have a static pressure inlet, which connects to the static pressure outlet on the flow sensor venturis. A pressure-sensitive mechanism in each sensor changes the pressure to an electrical signal. This signal is sent to the air conditioning system controller through an electrical connector. The sensors are installed in the aft equipment compartment between the bleed filters and the flow control valves.
What is PACK INLET FLOW SENSOR
Pack Inlet Flow Sensors
Figures A2 and A5 The pack inlet flow sensors (PIFSs) measure the difference in pressure between the two pressure outlets of each venturi. A pressure-sensitive mechanism changes the difference in pressure to an electrical signal. This signal is sent to the air conditioning system controller through its electrical connector. The sensors are installed in the aft equipment compartment between the bleed filters and the flow control valves.
What does flow control valve do
Flow Control Valves
Figure A6 The flow control valves (FCVs) are electrically controlled and pneumatically operated. The mass flow to the air conditioning units goes through the flow control valves. They isolate, if necessary, the air conditioning units from the pneumatic system. The valves automatically close when there is no bleed air. FILTERING AND FLOW CONTROL SYSTEM The pneumatic actuator controls the position of the valve. The actuator has a piston assembly and a spring, which closes the valve. A microswitch sends an electrical signal to the air conditioning system controller when the valve is fully closed. The regulator (pressure-regulating valve) supplies a constant pressure to the actuator. A torque motor adjusts the size of the vent opening for the pressure. The air conditioning system controller supplies current to the torque motor to control the position of the valve. An ON/OFF solenoid on the regulator fully releases the pressure when it is energized. This will cause the valve to close fully. In addition, the compressor pneumatic overheat (CPNOH) sensor bleeds off the FCV actuator chamber pressure to reduce the FCV opening in case of excessive ACU compressor discharge temperature. The flow control valves are installed in the aft equipment compartment between the flow sensor venturis and the air conditioning units. A device on the valve is provided to manually lock the valve in the closed position for dispatch purposes.
What happens with sensor failure
Gives default reading so can still control, to keep system in operation
Abnormal Operation LEGEND HIGH Flow (lb/min) NORM Flow (lb/min) LOW Flow (lb/min) G_21_00_041_Apr08 Pack Inlet Flow Sensor Failure In case of a PIFS failure (disagree, out of range, or sensor power supply off) detected by the ACSC, a calculation of the actual airflow through the flow sensor venturi cannot be made. In this case, the ACSC controls the FCV position, depending on the pack inlet pressure and the aircraft altitude.
What does AIR CON CONTROLLER DO
Air Conditioning System Controllers
Figure A7 Two air conditioning system controllers (ACSCs) are the primary computing units in the environmental control system. The ACSCs control the cockpit and cabin temperature with the functions that follow: •Heating • Cooling • Ventilation • Pack operation The air conditioning system controllers (ACSCs) control the position of the flow control valve (FCV) by modulating the current to the FCV torque motor. The ACSC measures the mass flow through the flow sensor venturi, using the pack inlet pressure sensor (PIPS), pack inlet flow sensor (PIFS) and pack inlet temperature sensor (PITS). There are two air conditioning system controllers, one for each air conditioning unit. Each air conditioning system controller has two channels, A and B. Each air conditioning system controller only uses one channel a day, channel A on odd days and channel B on even days. Channel A and channel B each have their own 28-DC power supply. The channel that is active controls the power output and supplies the drive signals for the system components. The other channel works in parallel mode, but does not control outputs. This procedure of operation makes the ACSC more reliable. If a failure occurs, the remaining channel controls the system. The desired mass flow is determined by the ACSC. This demand depends on: • Cabin and aircraft altitude • Outside ambient temperature (for ground operations) • Pilot flow selection (low, normal or high flow) • Number of operating cooling packs
• Cabin temperature error Special logic and algorithms are implemented within the ACS controller for the following: • To ensure that the FCV does not open if bleed air supply pressure is lower than 15 psig (for automatic mode) • Normal flow is selected on ground for air cycle machine (ACM) quick starting • Normal flow is selected in flight for ACM quick starting • The flow rate is controlled in case of a high pressure gradient at the flow control inlet
Flow control automatic
Automatic Control Assuming that the cockpit control switches are in their normal position, the ON/OFF solenoid is deenergized and the FCV is enabled to open. This allows flow supply even in the event of electrical failure. The flow control system can be manually switched off by selecting the appropriate PACK PBA to the OFF position. The OFF legend will illuminate. Three different flow levels (LOW, NORM, HI) can be selected by the PACK CONTROL selector on the air conditioning panel.
Flow control ground
Flow Control – Ground Operation On the ground, according to the pilot selection, the flow demand determined by the ACSC is set to: • 40 lb/min in case of HIGH flow selection (PACK CONTROL selector) • 30 lb/min in case of NORM flow selection • 20 lb/min in case of LO flow selection In order to achieve the necessary cooling and heating performance, the normal flow is increased using the following laws: • The normal flow is increased by 1 lb/min/°C for outside ambient temperature (TAT provided to the ACSC by DAU) higher than +30°C or lower than 0°C • The normal flow is increased by 2 lb/min/°C for a zone temperature error greater than ±5°C • For all cases,
Flow control flight
Flow Control – Flight Operation The flow demand determined by the ACSC depends on the aircraft altitude and selection. • If NORM flow is selected, the flow demand decreases with aircraft altitude from 30 lb/min at sea level to 18 lb/min at 51,000 feet • If HIGH flow is selected, the flow demand decreases with aircraft altitude from 40 lb/min at sea level to 23 lb/min at 51,000 feet • If LOW flow is selected, the flow demand decreases with aircraft altitude from 20 lb/min at sea level to 18 lb/min at 51,000 feet In addition, in case of single-pack operation, the high flow demand is automatically selected by the ACSC. For aircraft altitudes above 15,000 feet, if the cabin altitude increases above 9000 feet, the ACSC increases the flow rate to prevent cabin depressurization. The flow demand is increased by 2 lb/min/1000 ft for cabin altitudes above 9000 feet.
What happens with overheat
Pack Inlet Overheat In case of a pack inlet temperature (as detected by the pack inlet temperature sensor (PITS)) higher than 260°C (500°F) for more than 30 seconds or higher than 280°C (536°F) for more than 10 seconds, the FCV is driven closed by the ACSC (maximum current supplied to the FCV torque motor). At the same time, the PACK FAIL caution message is displayed. Compressor Discharge Overheat For compressor discharge temperatures (as detected by the compressor discharge temperature sensor (CDTS)) between 220°C (428°F) and 250°C (482°F), the flow supplied to the cooling pack is reduced by the ACSC by increasing the current supplied to the FCV torque motor. The FCV closing command is applied by the ACSC (maximum current supplied to the FCV torque motor) when a compressor discharge temperature of 260°C (500°F) is reached for more than 1 second. At the same time, the PACK FAIL caution message is displayed. Pack Discharge Overheat The FCV closing command is applied by the ACSC when a pack discharge temperature of 95°C (203°F) (as detected by the pack discharge temperature sensor (PDTS)) is reached for more than 40 seconds. At the same time, the PACK FAIL caution message is displayed.
