2021 Equipment Thermal Guidelines for Data Processing Environments - ASHRAE TC 9.9 Reference Card

Overview

This document is a free reference card reproducing Tables 2.1 and 2.2 of ASHRAE TC 9.9's Thermal Guidelines 5th edition (revised and expanded). It gathers the air-cooling envelopes for classes A1 to A4, B and C, plus the new H1 class for high-density servers, in one place. Notes on altitude derating, rate of change and humidity are included on the card.

The recommended range for A1-A4 is 18 to 27 C dry bulb, with dew point from -9 C to 15 C and up to 70% relative humidity (or 50% if corrosive pollutants are present). Allowable dry bulb is 15-32 C for A1, 10-35 C for A2, 5-40 C for A3 and 5-45 C for A4. The new H1 class has a recommended range of 18-22 C and an allowable range of 15-25 C.

The notes matter for design. Above 900 m the maximum allowable dry bulb is derated by 1 C per 300 m for A1/A2 (A3 per 175 m, A4 per 125 m, H1 per 500 m). Temperature change must not exceed 20 C in an hour or 5 C in any 15 minutes (tape 5 C/h). 70% rh is acceptable only if silver and copper coupons show corrosion below 200 and 300 angstrom per month respectively; otherwise keep rh at or below 50%. Limits: the card does not replace the full book and covers only air-cooling envelopes. Detailed rationale and other tables require the full publication.

Key points

1. Recommended range for A1-A4: 18-27 C dry bulb, -9 C to 15 C dew point and up to 70% rh (50% if corrosive pollutants).
2. Allowable dry bulb: A1 15-32 C, A2 10-35 C, A3 5-40 C, A4 5-45 C.
3. New class H1 for high-density servers: recommended 18-22 C, allowable 15-25 C.
4. Altitude derating above 900 m: 1 C per 300 m for A1/A2; A3 175 m, A4 125 m, H1 500 m.
5. Temperature change limit: 20 C in an hour and no more than 5 C in any 15 minutes (tape 5 C/h).
6. 70% rh only if silver/copper coupons show under 200/300 angstrom per month; otherwise 50% or less.

Using it in design

• Store class limits (A1-A4, B, C, H1) as data, with altitude derating functions and the coupon-dependent rh upper limit, in the rule engine.
• Check CRAH supply and return set points against the selected class.
• Calculate economizer hours against the envelope of the selected class.
• For sites above 900 m, derate the maximum allowable temperature by altitude.
• Ask for site coupon measurements before fixing the humidity upper limit.

Who should read it

Data center cooling designers, operations engineers and decision makers selecting an equipment thermal class.

Related standards

• ASHRAE Thermal Guidelines 5th ed.
• ANSI/ASHRAE Standard 90.4

Publication details

Authors

ASHRAE TC 9.9

Publisher

ASHRAE

Year

2021

Document number

TC 9.9 Reference Card

Document language

English

Source type

Standard

Access

Free to read

Licence

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

Citation