Abstract: There is disclosed an environmental control system for thermally conditioning air within an enclosed space comprising: a refrigerant circuit having a compressor, an indoor heat exchanger, an expansion device, and an outdoor heat exchanger. The system further comprises an intake flowpath for directing an intake flow of fresh air to the enclosed space, wherein a heat-transfer section of the indoor heat exchanger is located within the intake flowpath to thermally condition the intake flow of fresh air before entering the enclosed space. The system further comprises an exhaust flowpath for directing an exhaust flow of thermally conditioned air to an external environment. A recovery heat exchanger is provided to transfer thermal energy between the exhaust flow and the intake flow at a location within the intake flowpath that is upstream of the heat-transfer section of the indoor heat exchanger.