Unlike 90.1, which mandates economizers in many climates, 90.4 takes a more nuanced approach. It defines (based on ASHRAE Standard 169) and provides tables of allowed mechanical system types. For example:
ASHRAE 90.4 is considered a "sister standard" or companion to the more general . ASHRAE Releases Revised Version of Data Center Standard
When you open the , you will find two primary compliance paths:
ASHRAE Standard 90.4, , establishes the minimum energy efficiency requirements for the design, construction, and operation of data center facilities . Unlike Standard 90.1, which is for general commercial buildings, 90.4 is specifically tailored to the unique, high-density load requirements of data centers . Core Compliance Framework ashrae 90.4 pdf
| Feature | ASHRAE 90.1 | ASHRAE 90.4 | | :--- | :--- | :--- | | | All commercial buildings (offices, malls, hospitals) | Data centers only | | Metric | Energy Cost Budget (ECB) or Energy Use Intensity (EUI) | Mechanical Load Component (MLC) & Electrical Loss Component (ELC) | | Cooling Focus | Compression refrigeration efficiency (EER, COP) | Economizer usage, partial load performance, and free-cooling hours | | Power | Minimal (lighting, plug loads) | UPS efficiency, transformer losses, and power distribution chain | | Compliance | Prescriptive or performance (simulation) | Component-based (ELC/MLC) or simulation (Annex A) |
The heart of ASHRAE 90.4 is the , defined as the annual mechanical energy consumption (cooling, fans, pumps, humidification) divided by the annual IT equipment energy consumption. This yields a dimensionless number. For example, an MLC of 0.30 means that cooling and air movement use 30% of the IT energy.
Yes. LEED v4 and v4.1 credit EA Preeq-2 (Minimum Energy Performance) accepts 90.4 for data centers. You must provide calculation sheets showing MLC/ELC compliance. Unlike 90
The allowable MLC varies by climate zone. Data centers in Phoenix, AZ (hot climate) have a higher (more lenient) MLC than those in Seattle, WA (mild climate) because cooling requires more energy in hot environments.
Published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), Standard 90.4 establishes the for the design, construction, and operation of data centers. It applies to facilities with a conditioned floor space power density greater than 20 W/ft² and IT equipment loads exceeding 10 kW . Key focuses include:
Building codes (e.g., IECC, California Title 24) have begun incorporating 90.4 by reference. As of 2025, many U.S. states and international jurisdictions require 90.4 for new data centers over a certain size (e.g., 50 kW IT load or 500 ft²). ASHRAE Releases Revised Version of Data Center Standard
ASHRAE Standard 90.4 is a landmark achievement in data center energy regulation. By shifting from prescriptive rules to a performance-based Mechanical Load Component metric, it recognizes that data centers are not ordinary buildings. The standard gives engineers the freedom to innovate—using airside economizers, liquid cooling, or thermal storage—while holding them accountable to an energy budget. As digital infrastructure expands and AI drives power densities upward, 90.4 provides a flexible, rigorous framework that balances efficiency with the non-negotiable need for reliability. For any engineer, owner, or operator designing a modern data center, understanding and applying ASHRAE 90.4 is no longer optional—it is essential.
A common mistake is assuming Standard 90.4 covers everything. The PDF explicitly excludes: