A lot of hyperscale data centers, often built for ai, are built cheaply so there is no CRAC air conditioner nor any other air conditioners using refrigerant (direct expansion air conditioners) nor air or water cooled chillers. As air enters the building, it passes though electrostatic filters to remove dust, then through evaporative coolers which spray water to cool the air and then directly into the cold aisles in the data hall. Then The hot aisles are vented directly to the atmosphere through the roof. The server fans are very loud and can be heard outside.