The Importance of Mutual Understanding Between IT and Facilities - Part 2: Specifying A1, A2, A3, or A4 Servers

Overview

Published on the Upsite Technologies blog in 2025, Ian Seaton's post is the second part of a series on mutual understanding between IT and facilities. Its central argument is that the ASHRAE class of the servers IT buys can affect mechanical efficiency more than the choice of cooling equipment. It is an expert opinion piece and is freely readable.

The author reviews allowable ranges by class. Most servers sold are Class A2; A4 is mainly ruggedized equipment and carries a significant price premium. For reliability analysis he uses the X-factor method with a Chicago example: in the Chicago air-side economizer case, server reliability improved by about 1% compared with a constant 68 F baseline. He recommends translating percentages into counts: a 0.5% failure rate on 1,000 servers is about 5 failures, and a 5% increase adds roughly one failure per 1,000 servers over four years.

The post lists cities where Class A2 or A3 servers can be cooled year-round without refrigerant-based cooling. For Class A2, year-round free cooling is possible in, for example, Albuquerque, Boston, Chicago, Denver, Frankfurt, Phoenix and San Jose; A3 adds Austin, Dubai, Las Vegas and Sydney. Free cooling may cover roughly 80-90% of the year depending on bin data and can back up chillers to reduce redundant plant.

The author weighs the higher procurement cost of A3 servers against the chiller plant avoided, and notes that free cooling can add a layer of redundancy behind the mechanical plant. The limit of the post is that it is a blog article and the results depend on the chosen cities and hourly temperature data. The related document is ASHRAE Thermal Guidelines.

Key points

1. Most servers sold are Class A2; A4 is mainly ruggedized equipment with a significant price premium.
2. Chicago air-side economizer case: server reliability improved about 1% versus a constant 68 F baseline.
3. Translate percentages to counts: a 0.5% failure rate on 1,000 servers is about 5 failures; a 5% increase adds roughly one failure per 1,000 servers over four years.
4. Class A2 allows year-round free cooling in e.g. Albuquerque, Boston, Chicago, Denver, Frankfurt, Phoenix, San Jose; A3 adds Austin, Dubai, Las Vegas, Sydney.
5. Free cooling may cover roughly 80-90% of the year depending on bin data, and can back up chillers to reduce redundant plant.
6. Server ASHRAE class can affect mechanical efficiency more than the choice of cooling equipment.
7. The higher A3 procurement cost is weighed against chiller-plant avoidance.

Using it in design

• Expose server ASHRAE class as a project-level design input that drives economizer hours, chiller sizing and redundancy credit.
• Provide a per-site check of whether year-round compressor-free operation is possible for the selected class.
• Show the extra A3 procurement cost alongside the chiller plant avoided.
• Evaluate free cooling separately as a redundancy layer behind the mechanical plant.

Who should read it

IT managers, facility engineers and designers who make server procurement class and mechanical design decisions together.

Related standards

• ASHRAE Thermal Guidelines for Data Processing Environments

Publication details

Authors

Ian Seaton

Publisher

Upsite Technologies blog

Year

2025

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation