The safest and most professional route is to buy the official PDF from the ASHRAE Bookstore (www.ashrae.org). As of 2025, the current version is ASHRAE 90.4-2022 (with possible addenda). Cost is typically $99–$150 for members, $150–$200 for non-members.
Many data centers require N+1 or 2N cooling redundancy. Redundant pumps and chillers add parasitic load. Solution: Use the "partial load" compliance path allowed in Section 7 of the standard, which accounts for part-load efficiencies. ashrae 90.4 pdf
If you work for a large engineering firm or a data center operator, check your internal document management system. Many firms purchase site licenses for ASHRAE standards. The safest and most professional route is to
Many jurisdictions (including parts of the US and international regions) have adopted ASHRAE 90.4 by reference. If you are a code official, your jurisdiction may provide access. Check with: Many data centers require N+1 or 2N cooling redundancy