Aircraft air conditioning cooling components and ground air conditioning air sources

If the aircraft is on the ground, what will be the impact on the aircraft when the aircraft air conditioning cooling unit and the ground air conditioning air source are used at the same time?

Main components of cabin temperature control

Temperature sensor: The function of the temperature sensor is to sense the temperature of the controlled object (air in the cockpit or the pipe), and convert the temperature signal into electrical (resistance, potential), displacement, deformation and other signals, and input it into the controller, it is a signal feeling and conversion elements. The temperature sensors of the temperature control system mainly include the cabin temperature sensor, the cabin air supply pipeline limit temperature sensor and the air supply pipeline temperature sensor.

Temperature Controller: The cabin temperature controller is the command center for cabin temperature control. It accepts signals from the cabin temperature premonitor, cabin air supply pipe temperature premonitor, cabin air supply pipe limit temperature sensor and temperature selection signal, and sends out instructions to the temperature control valve after synthesis and amplification to control the opening of the temperature control valve.

Temperature control valve: The temperature control valve is used to control the air mixing ratio of the cold and hot circuits of the air conditioning system. There are two types of temperature control valves commonly used in modern civil aircrafts: double valve and single valve.

Basic principles of cabin temperature control

A certain flow of air from the flow control valve is divided into two paths through the temperature control valve: one path goes to the refrigeration system to cool it down, which is called "cold path", and the other path is called "hot path". The cold and hot air are mixed in the mixing chamber before entering the airtight cabin. Then enter the cabin through the cabin air distribution system. The temperature controller accepts the predetermined temperature and the actual temperature fed back by the cockpit, compares it, outputs a current proportional to the temperature deviation, controls the temperature control valve, and adjusts the flow of the cold and hot circuits, so as to control the temperature.

The basic principle of cabin temperature control is actually to control the mixing ratio of cold and hot air in the mixing header before entering the airtight cabin, and finally supply the cabin through the riser connected to the mixing header. If the aircraft is on the ground and the bleed air is turned on, the zone temperature controller calculates the temperature command of the cold air and sends this command information to the component controller, which then adjusts the temperature of the cold air leaving the air conditioning component. At the same time, the regional temperature controller also receives the command temperature from the cockpit crew and the actual temperature in the cockpit sensed by the cabin temperature sensor. The regional controller compares the actual temperature of the cabin with the command temperature selected by the crew to adjust the opening of the trim valve to control the flow of hot air in the trim valve, and finally complete the temperature adjustment.

From the basic principle of cabin temperature control, it can be known that in the case of using an air conditioner assembly for cabin temperature control, the zone temperature controller controls the flow of cold air at the outlet of the air conditioner assembly through the assembly controller. At the same time, the actual temperature of the cabin felt by the cabin temperature sensor and the commanded temperature of the cockpit crew are received to calculate the flow rate of the hot air of the trim valve, so as to control the cabin temperature. A portion of the conditioned air provided by the external air conditioning unit is not controlled and directed by any temperature sensor or any computer component within the aircraft air conditioning system mixing assembly. Then, after this part of the uncontrolled gas is mixed with the gas from the air source component, the temperature data in the mixing component may be inaccurate, so that the air conditioning cooling component cannot control the air temperature correctly.

If both ground air and onboard air conditioning are used to feed the system, and their one-way valves (blue and red) are both open normally, the aircraft seems to be getting 2.5x to 3x the fresh air. The flow of the two airflows in the pipeline may undergo complex changes, and the gas near the one-way valve may flow irregularly, causing the flap to not fully open or to vibrate, instead of opening and closing normally. The valve is more prone to fatigue and failure, which in turn affects the upstream and downstream systems; if the one-way valve of the ground air conditioning interface falls off, it will even affect the cabin pressurization.

   In short, if the aircraft air conditioning cooling component and the ground air conditioning air supply provide air supply to the mixing header at the same time, the aircraft air conditioning cooling component will not be able to control the air temperature, and it will also cause equipment damage.