ASHRAE Standard 90.4-2022 governs energy efficiency of data centers and is referenced by Title 24 Part 6 §140.9 (CA) and IECC §C407 (AZ/NV). PUE design ceiling varies by climate zone: ZN-3 coastal CA 1.61 design / 1.84 annualized; ZN-2B Phoenix and Las Vegas 1.40 design / 1.61 annualized — desert climates have tighter limits because economizer hours are fewer. Required: airside economizers above ~10kW per rack density when climate supports, hot-aisle / cold-aisle containment, variable-speed fans, on-site PV per Title 24 (CA only).