ASHRAE Standard 90.1 — full title "Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings" — is the national energy standard for commercial buildings. It governs the building envelope, HVAC systems, economizers, controls, service water heating, power, and lighting, and for more than three decades it has been the technical basis for U.S. commercial energy codes. When a jurisdiction adopts a commercial energy code, it is usually adopting some edition of 90.1.
The current published edition is 90.1-2022, ANSI-approved in May 2023. The U.S. Department of Energy estimates it cuts building energy cost by more than 15% versus 90.1-2019 and more than 48% versus the 2004 edition — the cumulative effect of tighter envelope, control, and equipment requirements over successive cycles.
For a commercial owner this is why a new rooftop or chiller project carries requirements a home replacement never does: minimum equipment efficiency, mandatory economizers on larger units, demand-control ventilation, and digital controls all trace back to 90.1 (or the IECC, which mirrors it). Which edition applies depends on what your city or state has adopted, so a competent commercial contractor will know the locally enforced version and design the job to pass plan review against it — not just install a unit and hope it clears inspection.