Fermilab recently had to satisfy its chilled water demand while operating as efficiently as possible. Fermilab’s Cryomodule Test Facility utilizes two AAON outdoor air-cooled chiller / mechanical rooms with built-in free cooling modules to provide cooling for the test facility year-round. The systems are designed to provide 100% free cooling at an ambient temperature of 40 F and below. Partial free cooling is available between 40-70 F. Facility maintenance personnel use the integral vestibules that house compressors, controls and pumping systems.