An environmental control system comprising: a primary heat exchanger comprising: a first hot section comprising: a first passage fluidically connected to a hot fluid source; a second hot section comprising: a second passage fluidically connected to the first passage; and a third hot section comprising: a third passage fluidically connected to the second passage; a heat exchanger outlet line fluidically connected to the third passage; a bypass line fluidically connecting both the first passage and the second passage with the heat exchanger outlet line; an air cycle machine further comprising: a compressor, wherein an inlet of the compressor is fluidically connected to the heat exchanger outlet line; a secondary heat exchanger fluidically connected to an outlet of the compressor; a first turbine; a second turbine, wherein the first and second turbines are fluidically connected to an outlet of the secondary heat exchanger, and wherein the first and second turbines are mechanically coupled to the compressor via a shaft (48a,48b); a first load cooling heat exchanger fluidically connected to the first turbine; and a second load cooling heat exchanger fluidically connected between the second turbine and a system outlet; a first valve, wherein the first valve fluidically connects the hot fluid source and the second passage when the first valve is open, and wherein the first valve fluidically connects the hot fluid source and the third passage when the first valve is open; a second valve in the bypass line; a third valve fluidically connected between the secondary heat exchanger and the second turbine; and a fourth valve fluidically connected between the first load cooling heat exchanger and the system outlet. a primary heat exchanger comprising: a first hot section comprising: a first passage fluidically connected to a hot fluid source; a second hot section comprising: a second passage fluidically connected to the first passage; and a third hot section comprising: a third passage fluidically connected to the second passage; a heat exchanger outlet line fluidically connected to the third passage; a bypass line fluidically connecting both the first passage and the second passage with the heat exchanger outlet line; a first hot section comprising: a first passage fluidically connected to a hot fluid source; a second hot section comprising: a second passage fluidically connected to the first passage; and a third hot section comprising: a third passage fluidically connected to the second passage; a heat exchanger outlet line fluidically connected to the third passage; a bypass line fluidically connecting both the first passage and the second passage with the heat exchanger outlet line; an air cycle machine further comprising: a compressor, wherein an inlet of the compressor is fluidically connected to the heat exchanger outlet line; a secondary heat exchanger fluidically connected to an outlet of the compressor; a first turbine; a second turbine, wherein the first and second turbines are fluidically connected to an outlet of the secondary heat exchanger, and wherein the first and second turbines are mechanically coupled to the compressor via a shaft (48a,48b); a first load cooling heat exchanger fluidically connected to the first turbine; and a second load cooling heat exchanger fluidically connected between the second turbine and a system outlet; a compressor, wherein an inlet of the compressor is fluidically connected to the heat exchanger outlet line; a secondary heat exchanger fluidically connected to an outlet of the compressor; a first turbine; a second turbine, wherein the first and second turbines are fluidically connected to an outlet of the secondary heat exchanger, and wherein the first and second turbines are mechanically coupled to the compressor via a shaft (48a,48b); a first load cooling heat exchanger fluidically connected to the first turbine; and a second load cooling heat exchanger fluidically connected between the second turbine and a system outlet; a first valve, wherein the first valve fluidically connects the hot fluid source and the second passage when the first valve is open, and wherein the first valve fluidically connects the hot fluid source and the third passage when the first valve is open; a second valve in the bypass line; a third valve fluidically connected between the secondary heat exchanger and the second turbine; and a fourth valve fluidically connected between the first load cooling heat exchanger and the system outlet.