An environmental air conditioning system for providing conditioned air to a conditioned air space, comprising: a first module comprising: a turbofan engine or an auxiliary power unit; a first heat exchanger having a heat rejection side with an inlet and an outlet, with the inlet in fluid communication with compressed air bled from the turbofan engine or the APU; a first turbine having an inlet and an outlet, the inlet in fluid communication with the outlet of the heat rejection side of the first heat exchanger; a first water collector having an inlet in fluid communication with an outlet of the first turbine, a water outlet, and an air outlet; a first airflow path having an inlet and an outlet, with the inlet in fluid communication with an air source, and with a heat absorption side of the first heat exchanger disposed in the airflow path; a first module auxiliary fan that promotes airflow along the first airflow path; and a power transfer path that transfers power from the first turbine to the first module auxiliary fan; and a second module comprising: a mixing manifold having a first inlet in fluid communication with a flow of conditioned air from the conditioned air space, a second inlet in fluid communication with the air outlet of the first water collector, and an outlet; and characterized by further comprising a second turbine having an inlet in controllable fluid communication with either or both of the conditioned air space and the air outlet of the first water collector; a second heat exchanger having a heat rejection side with an inlet and an outlet, with the heat rejection side inlet in fluid communication with the mixing manifold outlet, and a heat absorption side with an inlet and an outlet, with the heat absorption side inlet in fluid communication with the second turbine outlet; and a second module fan that promotes airflow along a second airflow path from the mixing manifold past the heat rejection side of the second heat exchanger to the conditioned air space; a power transfer path that transfers power from the second turbine to the second module fan. a turbofan engine or an auxiliary power unit; a first heat exchanger having a heat rejection side with an inlet and an outlet, with the inlet in fluid communication with compressed air bled from the turbofan engine or the APU; a first turbine having an inlet and an outlet, the inlet in fluid communication with the outlet of the heat rejection side of the first heat exchanger; a first water collector having an inlet in fluid communication with an outlet of the first turbine, a water outlet, and an air outlet; a first airflow path having an inlet and an outlet, with the inlet in fluid communication with an air source, and with a heat absorption side of the first heat exchanger disposed in the airflow path; a first module auxiliary fan that promotes airflow along the first airflow path; and a power transfer path that transfers power from the first turbine to the first module auxiliary fan; and a mixing manifold having a first inlet in fluid communication with a flow of conditioned air from the conditioned air space, a second inlet in fluid communication with the air outlet of the first water collector, and an outlet; and characterized by further comprising a second turbine having an inlet in controllable fluid communication with either or both of the conditioned air space and the air outlet of the first water collector; a second heat exchanger having a heat rejection side with an inlet and an outlet, with the heat rejection side inlet in fluid communication with the mixing manifold outlet, and a heat absorption side with an inlet and an outlet, with the heat absorption side inlet in fluid communication with the second turbine outlet; and a second module fan that promotes airflow along a second airflow path from the mixing manifold past the heat rejection side of the second heat exchanger to the conditioned air space; a power transfer path that transfers power from the second turbine to the second module fan.