Economizers in Tier Certified Data Centers (Keith Klesner)

Overview

Keith Klesner's 2016 Uptime Institute Journal article reviews economizer types: direct air, direct air plus evaporative, indirect evaporative, pumped-refrigerant dry coolers and water-side economizers. It explains how to apply them without breaking Tier III/IV objectives. Uptime consultants observed that roughly one-third of new data centre designs include an economizer function.

Citing The Green Grid's 2011 survey, the article notes that 49% of large data centres used economizers and 24% were considering them. Direct-air rooftop economizer units report PUE around 1.30-1.60 and consume very little water. Outside-air units for mission-critical spaces must be able to run 100% recirculation during pollution or wildfire smoke events.

Commercial rooftop units adapted for 24x7 use need adequate filtration, full recirculation capability and well-tested control sequences across every operating mode. A DX unit with an air-side economizer can go from no power to full cooling in 120 seconds or less, with four operating modes; a chilled-water unit with wetted media may have nine modes, all of which must be tested.

Worst-case design conditions, not typical weather, govern Tier compliance. Most commercial HVAC ratings are at 95 F (35 C), and designs must be checked against the site's worst-case conditions. As a limitation, this is a journal article and offers no detailed calculation. Copyright belongs to Uptime Institute.

Key points

1. Uptime consultants observed roughly one-third of new data centre designs include an economizer function.
2. The Green Grid 2011 survey: 49% of large data centres used economizers and 24% were considering them.
3. Direct-air rooftop economizer units report PUE around 1.30-1.60 and consume very little water.
4. Outside-air units for mission-critical spaces must run 100% recirculation during pollution or wildfire smoke events.
5. A DX unit with an air-side economizer can go from no power to full cooling in 120 s or less, with four operating modes.
6. A chilled-water unit with wetted media may have nine modes, all of which must be tested.
7. Most commercial HVAC ratings are at 35 C (95 F); designs must be checked against the site's worst-case conditions.

Using it in design

• Catalogue economizer units with operating modes, restart time and recirculation capability.
• For outside-air economizers, require filtration and a 100% recirculation mode.
• Check cooling capacity at the site's extreme design temperatures, not at the 35 C rating.
• Generate a commissioning test list covering every mode.

Who should read it

Mechanical designers selecting free cooling and economizers for Tier-targeted data centres.

Related standards

• ASHRAE 90.4
• Uptime Institute Tier Standard: Topology

Publication details

Authors

Keith Klesner

Publisher

Uptime Institute Journal

Year

2016

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