Aircraft, air conditioning, environmental control system, vapor-compression cycle, retrofit, bleed air
The environmental control system is an essential subsystem of an aircraft, which has to comply some vital tasks. These include the setting of the desired temperature, humidity and cabin pressure, as well as ensuring the fresh air or oxygen supply and air quality. The requirements must be achieved in very different ambient conditions. This refers to the environmental conditions in the flight and ground cases, and also to the different climate zones. In addition, the existing interfaces to the aircraft must be taken into account. State of the art in currently used commercial aircrafts is an environmental control system, which is based on the air cycle and is driven by bleed air from the engine. This technology allows only a significantly lower coefficient of performance for the given boundary conditions compared to a vapor-compression refrigeration system. Therefore the potential application of the vapor cycle in the aircraft air conditioning system is investigated in a research project with the cooperation partner Airbus. The new system has to be developed as a replacement of the existing air cycle system. In a detailed simulation model the thermodynamic state variables are calculated for every element and different operating cases. The calculation results are then used to investigate and size the main components, e.g. heat exchangers and turbomachinery. After the optimization of the system parameters and the individual components the new system is compared with the existing system. The benchmark shows a considerably decrease of bleed air mass flow for the reference cases on ground and in flight, both at hot ambient conditions.