New ASHRAE guidelines challenge efficiency drive

Overview

D. Bizo's 2021 article in the Uptime Institute Journal explains what changed in the 5th edition of the ASHRAE Thermal Guidelines and how this affects data centre operations. The Thermal Guidelines were first released in 2004 and the 5th edition appeared in 2021. The article discusses how the changes can influence both operating set points and service level agreements (SLAs), and its title hints that the new rules sit in tension with efficiency goals.

The most visible change concerns humidity. The recommended upper relative humidity limit rises from 60% to 70%, but only where concentrations of corrosive gases are low. Otherwise relative humidity should be kept under 50%. Humidity flexibility is thereby tied to evidence about the contamination state of the environment. Contamination is measured with reactivity coupons. The guideline gives limits of 200 angstrom per month for silver and 300 angstrom per month for copper. These limits rest on experiments carried out with Syracuse University between 2015 and 2018, which showed that chlorine and H2S accelerate copper corrosion at higher humidity. The edition also introduces a new high-density class.

The article's practical message is that seeking energy savings by raising humidity now requires site air-quality data. Facilities that do not run coupon tests, or whose results fall outside the limits, must stay with the 50% ceiling. Set point and SLA decisions therefore have to be made together with contamination monitoring. The article addresses only these headline changes rather than the full content of the edition.

Key points

1. Recommended RH extends from 60% to 70% only with low corrosive gas concentrations; otherwise keep RH under 50%.
2. Reactivity coupon limits: silver 200 angstrom/month, copper 300 angstrom/month.
3. The basis is 2015-2018 experiments with Syracuse University: chlorine and H2S accelerate copper corrosion at higher humidity.
4. Thermal Guidelines were first released in 2004; the 5th edition was published in 2021.
5. The 5th edition includes a new high-density class.
6. The changes affect set points and SLAs.
7. Related standards: ASHRAE Thermal Guidelines 5th ed. and ANSI/ISA-71.04.

Using it in design

• Tie the humidity control setting to the contamination class: allow the 70% RH upper limit only when coupon test results are entered and within limits.
• Keep the RH upper limit at 50% when no coupon result exists or limits are exceeded.
• Define the silver and copper coupon values (200 and 300 angstrom per month) as thresholds in the contamination check.
• In set point and SLA recommendations, treat the 5th edition's high-density class as a separate option.

Who should read it

Data centre mechanical designers and operations engineers who set cooling set points, humidity control and SLA terms.

Related standards

• ASHRAE Thermal Guidelines 5th ed.
• ANSI/ISA-71.04

Publication details

Authors

D. Bizo

Publisher

Uptime Institute Journal (Uptime Institute)

Year

2021

Document language

English

Source type

Industry body

Access

Free to read

Licence

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

Citation