For the first time, the standard includes specific exemptions for small telecom shelters (under 50 sq ft) and battery backup rooms, acknowledging their intermittent and low-density loads.
If you are looking for the "upd" (update), you are likely interested in the changes between the 2016, 2019, and 2022 versions.
| Myth | Fact | |------|------| | “ASHRAE 904 covers all buildings” | No – 90.4 is for data centers only. 90.1 covers other buildings. | | “The free PDF from 2016 is fine” | No – updates after 2019 changed economizer rules significantly. | | “90.4 is optional” | No – it is referenced by many state energy codes (Title 24, etc.). | | “UPD means a new 904 standard” | No – it means an updated version of 90.4. | ashrae 904 pdf upd
Post-2020 updates typically refine how the model handles variable-speed drives (VSDs) and equipment that cycles on/off frequently (like inverter heat pumps). Older line-load models often overestimated energy use for modern equipment.
In alignment with global Kigali Amendment targets (phasing down HFCs), newer updates to Standard 904 now require users to include the cost of future refrigerant replacement or decommissioning. Older PDFs ignore this, leading to artificially low LCC for high-GWP refrigerants. For the first time, the standard includes specific
First published in 2016, ASHRAE 90.4 differs fundamentally from its sibling Standard 90.1. While 90.1 applies to most commercial buildings, 90.4 is tailored specifically to data centers — recognizing their unique load profiles, redundancy requirements, and cooling challenges. Rather than prescribing prescriptive component efficiencies, 90.4 uses a power usage effectiveness (PUE) -based compliance path, allowing designers flexibility in exchange for measured performance.
The standard applies to:
Many engineers and students mistakenly write “ASHRAE 904” because:
Important: There is no ASHRAE 904. If a PDF claims to be “ASHRAE 904,” it is either a mislabeled 90.4 or a fake document. Important: There is no ASHRAE 904