Guide to aircraft air conditioning system functions

Aircraft air conditioning system functions

Almost all of the air circulating in the aircraft comes from the aircraft air conditioning system, which is a major part of the aircraft cabin environmental control system. The cabin environmental control system provides the following three functions: cabin pressurization, temperature regulation, and equipment cooling.

Aircraft cabin environment control system includes air conditioning system, pressurization control system, equipment cooling system and distribution system. Modern jet airliners generally fly in the lower part of the stratosphere, and even the altitude of short-range regional flight routes is above 5,000 meters above sea level, but we rarely feel hypoxia or uncomfortable because of the low air pressure when flying. The role of cabin pressurization.

Aircraft air conditioning provides a large amount of conditioned fresh air to the cabin, which pressurizes and regulates the entire cabin (including the cockpit, passenger cabin, cargo compartment, onboard equipment compartment), so that the actual aircraft cabin altitude is maintained at the altitude Below 2500 meters or even the height of sea level, most people will not feel strange at this height in the natural environment. The functions of aircraft air conditioners to adjust the cabin ambient temperature and equipment cooling are similar, both to ensure the requirements of personnel and equipment for the living or working environment.

Aircraft air conditioning boosting function

Under normal conditions, the air conditioner of the Boeing 737-300 aircraft will deliver about 38 cubic meters of completely fresh air-conditioned air into the cabin every minute. Let's make an assumption, note that we are making a maximum assumption here. Assuming that the average lung capacity of a person is at most 4,000 milliliters, the Boeing 737-300 passenger aircraft can carry a maximum of 149 passengers in the economy class layout, plus the maximum number of aircrews of 11 people, and each person takes a deep breath per second. Then it is easy to calculate that everyone needs 38 cubic meters per minute, and the air conditioning supply of the aircraft fully meets the demand. The actual situation is much better than the above calculation, because an adult normally breathes about 0.01 cubic meters of air per minute, and 160 people only need about 1.6 cubic meters per minute, and the normal air supply per minute of the 737-300 aircraft air conditioner is the same as that of the passengers. nearly 24 times as much. The air-conditioning air supply energy of other models is much larger than that of the Boeing 737-300, and some can even reach 80 times the demand of all passengers. These gases not only ensure the normal breathing of the occupants, but also ensure that the pressure in the cabin is stable and appropriate. But you can imagine that the air is always supplied to the cabin, and if there is no outlet, the fuselage will blow up like a balloon. Therefore, there is also an air outlet on the aircraft cabin, called an outflow valve, which is specially used for deflation. The adjustment of the cabin pressure and the adjustment of the ventilation rate are all completed by this outflow valve, which is directly controlled by the cabin pressure controller. In order to make the passengers feel comfortable throughout the flight, when the plane is still on the runway before takeoff, the cabin pressure controller will close all the outflow valves to generate a little positive pressure for the entire cabin. At this time, the cabin pressure is higher than the external natural environment. It should be higher than 0.1 PSI, so that passengers will not feel the uncomfortable feeling of "pressing their ears" when the attitude of the plane changes abruptly when the plane lifts its head off the ground. Cabin pressure decreases as the aircraft climbs, but is always higher than outside air pressure. When the aircraft is cruising, the pressure of the aircraft cabin is 7.45-8 PSI higher than the outside world, that is to say, the actual "pressure altitude" in the aircraft cabin is much lower than the outside environment, which is why many passengers use the air pressure on their watches. The altimeter only indicates about one kilometer to measure the altitude of the aircraft. The fundamental reason why this altitude is much lower than the flight altitude declared by the crew is that you are measuring the pressure and altitude in the cabin. When the plane descends, cabin pressure also increases. After the plane lands, the cabin pressure controller will output a 0.15PSI bias signal, the purpose of which is to make the cabin pressure lower than the current pressure at the airport. In order to meet this "requirement", the cabin pressure controller will open all the outflow valves and "try" to let the air in the cabin light, of course, this is impossible. But doing so can keep the cabin pressure consistent with the outside world, and the flight attendant will not open the door due to the pressure difference or the sudden pressure relief will occur when the cabin door is opened and closed. We refer to the series of changes in cabin pressure as the flight altitude changes as the cabin pressure regime. If the outflow valve is blocked due to some kind of failure, it may cause the pressure of the aircraft cabin to be excessively higher than the external pressure or lower than the external pressure. Maintain the pressure difference balance between the cabin and the natural environment. There are two positive pressure relief valves and one negative pressure relief valve on the Boeing 737-300. When the positive pressure relief valve opens when the cabin pressure is higher than the outside pressure of 8.5PSI, the negative pressure relief valve is opened when the outside pressure is higher than the cabin pressure by 1PSI. open to balance the internal and external pressures.

Of course, because the energy source of the aircraft air conditioner mainly comes from the compressed air of the air source main pipe, and in normal flight, the compressed air of the air source main pipe comes from the bleed air of the engine. In order to reduce the burden on the engine and save fuel, the pressurized gas in the cabin of the aircraft is sometimes not completely discharged out of the plane, but will also be recycled and reused. At this time, a recirculation fan is introduced. This recirculation fan can collect a part of the air in the cabin, pass through a high-precision air filter, and send it into the mixing main pipe again, and then flow from the air conditioning outlet through the distribution main pipe. come out. Modern commercial airliners are equipped with "High Efficiency Particulate Filtration" (HEPA). The system consists of three parts: primary air filter, high-efficiency air filter and charcoal air filter. This filter element system works very efficiently. After the air is filtered, 99.97% of bacterial and viral particles are removed. Research data shows that HEPA air filters can remove more than 99.97% of particles with a diameter of 0.003 microns in the air. The size of bacteria is generally above 1 micron, while the size of viruses is about 0.003 to 0.5 microns, and viruses rarely exist as monomers, usually in droplets or other virus clusters (with a size of 0.01 microns to 0.2 microns). time) appears in the air. When the recirculated air is mixed with the outside air provided by the air conditioning components in the mixing main pipe, the sterilization and disinfection effect of the ozone remaining in the outside air can eliminate the viruses and bacteria that may still survive in the recirculated air. Therefore, the air that finally enters the cabin can be said to be very clean and odor-free. If you do smell a peculiar smell from the air conditioner, it means there is an oil leak in the aircraft engine or air conditioner assembly, which must be repaired. In this way, the cleanliness of the cabin air of the aircraft has reached the same quality as the air supplied by the hospital operating room, which undoubtedly plays a key and positive role in curbing the spread of influenza. These filters are frequently replaced to ensure efficient and safe operation of the air conditioning system. Every time I do this kind of work, I must wear a disposable full-body conjoined protective suit in strict accordance with the requirements of the maintenance manual, with all-encompassing goggles, high-efficiency filter masks and rubber sealing gloves. The removed air filter must be in the first place. Time to put it in a sealable plastic bag and send it to a specialized manufacturer for disposal. After cleaning and sterilizing the entire recirculation system, a new air filter is replaced, and personal protective equipment such as protective clothing also needs to be sealed and scrapped. Of course, in addition to this, the entire cabin will be ventilated and disinfected every time the plane passes by, ensuring the safety of passengers.