Gas turbine engine air cycle system

An air cycle system (100) for a gas turbine engine includes a compressor (62), a turbine (64) and a heat exchanger (66) fluidly connected between the compressor (62) and the turbine (64). A fluid source (92) communicates a fluid through the heat exchanger (66). The heat exchanger (66) exchanges heat between the fluid and an airflow communicated through the heat exchanger (66) from the compressor (62) to provide a conditioned airflow.