US Patent 11912418 Aircraft cabin air conditioning system

An aircraft air conditioning system comprises intakes ram air from outside the aircraft, and uses a heat exchanger to pretreat (preheat or precool) some of the ram air. The system further includes a heat recovery unit that uses the cabin exhaust air to further heat the pretreated ram air, resulting in conditioned ram air. The system further includes an air conditioning pack unit to produce a first conditioned air stream from the conditioned ram air. The system further includes a mixing box to mix the first conditioned air stream with another subflow of ram air to produce a second conditioned air stream.