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Overview of pre-conditioned air unit working principle and types

Views: 0     Author: Site Editor     Publish Time: 2022-07-11      Origin: Site

As we all know, all aircrafts must have fresh air sent into the cabin to maintain a comfortable environment in the cabin whether they are flying in the air, waiting to fly at the airport or staying overnight on the tarmac.

What is an pre-conditioned air unit?

Pre-conditioned air unit is a brand-new type of air-conditioning unit that is placed outside of civil aviation aircraft and uses long air supply ducts and aircraft-specific connectors to supply air to the cabin through the external air-conditioning interface at the lower part of the aircraft fuselage and the complex air supply ducts inside the fuselage wind special air conditioner.

Pre-conditioned air unit working principle

The aircraft ground air conditioning unit adopts all-electric drive, direct evaporative refrigeration cycle technology, which can ventilate, cool, dehumidify and heat the aircraft, and has the function of air filtration. Provides a comfortable air-conditioned environment for overnight stays and ground maintenance.

1. Refrigeration system

The use of multi-stage direct evaporative refrigeration is beneficial to meet the requirements of large enthalpy difference and low temperature air supply of the unit. When the ambient temperature changes greatly, the multi-stage refrigeration system can ensure the low supply air temperature requirement.pca hose company -Julong

2. Air supply system

(1) Refrigeration air supply

After the ambient air passes through the filter, it enters the primary evaporator for pre-cooling, and then enters the blower. After passing through the blower, it enters the secondary evaporator and the tertiary evaporator, and is further cooled. After the air is cooled, it is sent into the aircraft cabin at higher pressure and lower temperature.

(2) Heating and air supply.

After the ambient air passes through the filter, it enters the primary heater for heating, and then enters the blower. After passing through the blower, it enters the secondary heater and is further heated. After the air is heated, it is sent into the aircraft cabin with higher pressure and higher temperature.

(3) Control system.

According to the different needs of various types of civil aircraft produced by Boeing and Airbus, the control system of the ground air-conditioning unit of the aircraft must meet the requirements of variable air volume and variable air pressure; when the ambient temperature changes, choose cooling, air supply or heating Requirements for the use of different operating modes. Therefore, the electrical control system of the aircraft ground air conditioning unit must adopt a highly reliable programmable PLC control system to ensure the automatic, efficient, reliable and economical operation of the unit.

Pre-conditioned air unit characteristics

1. Adopt imported fully enclosed scroll refrigeration compressor. It has the advantages of high efficiency, low noise, small vibration, reliable operation and long life. Aircraft Ground Air Conditioning Unit

2. The main refrigeration components are all made by domestic and foreign famous brand professional manufacturers, with superior performance and reliable operation.

3. The air-cooled evaporator and condenser are high-efficiency copper tube sleeve aluminum fins, which are manufactured by heat exchanger processing equipment imported from the United States. They have the characteristics of compact structure, small volume, light weight and high heat exchange efficiency.

4. The high-pressure centrifugal blower and axial-flow condensing fan from famous domestic and foreign professional manufacturers are used, which have the characteristics of low noise, high pressure head, large air volume and high efficiency.

5. The computer control system of the unit automatically loads and unloads according to the load change to adjust the output of the cooling capacity of the unit, so that the cooling capacity can be accurately matched with the actual cooling and heating load, so that the working compressor always maintains the highest efficiency state, high efficiency and energy saving.

6. The defrosting method of the unit adopts the hot gas bypass method, which avoids the impact of the frequent start and stop of the compressor on the system, thereby ensuring the stable operation of the system.

Pre-conditioned air unit classification

According to the installation method, aircraft ground air conditioning units can be divided into bridge-mounted, floor-mounted and mobile. The most widely used is the bridge hanging type. The ground air conditioning unit of the bridge-mounted aircraft is divided into the rear exhaust type and the downward exhaust type.

The rearward exhaust type aircraft ground air-conditioning unit can prevent the backflow of hot air from the apron and improve the heat exchange efficiency of the condenser because the exhaust direction of the condenser is parallel to the direction of the apron. However, because the cooling fan is far away from the end of the condenser, the The wind speed is low and the wind speed at the near end is high, and the uneven wind speed of the condenser causes the uneven temperature field, which leads to the reduction of heat exchange efficiency.

The ground air-conditioning unit of the downward-exhausting aircraft is very close to the apron due to the low cabin door of the aircraft when connecting the Boeing 737 series aircraft because the exhaust direction of the condenser is perpendicular to the direction of the apron, and the hot air is easy to flow back, which affects the condensation. However, due to the low height of the aircraft ground air conditioning unit, the close distance between the cooling fan and the end of the condenser, the wind speed on the face of the condenser is relatively uniform, and the heat exchange efficiency of the condenser is high.

The structure design of the rearward exhaust type and the downward exhaust type aircraft ground air conditioning unit has its own advantages and disadvantages. Which structure type should be selected must be based on the actual situation of the airport, in order to improve the heat exchange efficiency of the unit, and the safe, reliable and economical operation is the final design target.



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