The Different Types of Air Distribution for IT Environments

Overview

In the taxonomy, supply and return can each be flooded, targeted or contained. Targeted means a mechanism (duct, perforated tile, in-row cooler) directs air within 3 meters (10 feet) of IT intake and exhaust; contained means complete enclosure with no mixing. For each combination the paper gives typical applications, relative efficiency, the share of hot exhaust captured and an indicative maximum rack density.

The figures form a clear staircase. Flooded supply with flooded return cools up to 3 kW per rack and suits small LAN rooms under 40 kW. Flooded supply with targeted return reaches 6 kW and captures 40-70% of exhaust; targeted/targeted reaches 8 kW and 60-80%. Any combination with contained return (or contained supply) is rated to 30 kW, and contained return captures 70-100% of hot exhaust.

The recommendations rest on market reality: traditional raised-floor flooded-return systems reliably cool only 5-6 kW per rack by design, while typical racks draw 3-5 kW and some exceed 30 kW. New builds are advised to use a hard floor with contained return, and row-based targeted-supply hard-floor implementations are recommended below 1 MW. Containing one air stream is judged enough; containing both is advised only for harsh environments.

Key points

1. Targeted means a mechanism (duct, perforated tile, in-row cooler) directs air within 3 meters (10 feet) of IT intake and exhaust; contained means full enclosure with no mixing.
2. Flooded supply/flooded return cools up to 3 kW per rack and suits small LAN rooms under 40 kW.
3. Flooded supply/targeted return reaches 6 kW and captures 40-70% of exhaust; targeted/targeted reaches 8 kW and 60-80%.
4. Any combination with contained return (or contained supply) is rated up to 30 kW; contained return captures 70-100% of exhaust.
5. Traditional raised-floor flooded-return systems reliably cool only 5-6 kW per rack; typical racks are 3-5 kW and some exceed 30 kW.
6. Row-based targeted-supply hard-floor implementations are recommended for data centres below 1 MW.
7. Contained supply or return is generally used for 5-15 kW racks; containing both streams is not recommended outside harsh environments.

Using it in design

• Model each white-space zone with supplyMode and returnMode enums (flooded, targeted, contained).
• Compare the zone's maximum rack kW with the ceiling for its combination (3/6/6/8/30 kW) and warn when exceeded; warn when both supply and return are contained without a harsh-environment flag.
• Default new builds to hard floor plus contained return, and suggest row-based cooling for halls under 1 MW.
• Offer a 3x3 picker in the UI that shows capture ratio and density limit for each cell.

Who should read it

Mechanical designers and decision makers choosing the air distribution architecture for a new hall.

Related standards

• ASHRAE TC 9.9 Thermal Guidelines

Publication details

Authors

Neil Rasmussen

Publisher

Schneider Electric

Year

2020

Document number

WP 55

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