Power and Cooling Guidelines for Deploying IT in Colocation Data Centers

Overview

The causes are fragmented leasing, many low-density racks that each take a PDU breaker position, cooling designed for around 4 kW per rack, and hot/cold air mixing. Low-density racks are typically fed by a single-phase 16-20 A circuit and draw under 2 kW, yet each takes a branch-circuit position and can strand transformer capacity. The DCD 2012 census average was 4.05 kW, with 58% of racks under 5 kW, 28% at 5-10 kW and 14% above 10 kW.

The paper argues that raising average rack density recovers the first three kinds of stranding (space, power, power distribution) while containment recovers cooling-distribution capacity. More than 50% air leakage (bypass) is routinely observed. Hot aisle containment is cited as saving 43% of annual cooling system energy cost versus cold aisle containment, about a 15% reduction in annualized PUE (from WP 135).

Recommended practices are overhead cabling, 750-800 mm wide racks rather than standard 600 mm for cable management, hot/cold aisle layout with containment and blanking, ducted or close-coupled cooling for high-density racks, and scalable UPS/PDU and DCIM capacity management. For tenants, a 3-phase rack PDU and circuit supporting a 10-15 kW peak with a mix of C13 and C19 receptacles is recommended.

Sample AUP rules in Table 1: draw below 80% of breaker capacity; hot/cold aisle layout; equipment above 6 kW/rack must use containment and/or chimney racks; blanking panels, sealed cutouts, overhead cabling and wide racks.

Key points

1. Low-density racks use single-phase 16-20 A feeds and draw under 2 kW but take a PDU branch-circuit position.
2. Most colocation is designed for about 4 kW/rack; DCD 2012 average 4.05 kW (58% of racks under 5 kW, 28% 5-10 kW, 14% above 10 kW).
3. More than 50% air leakage is routinely observed.
4. Hot aisle containment saves 43% of annual cooling energy cost versus cold aisle, about 15% of annualized PUE (WP 135).
5. Wide racks are 750-800 mm versus standard 600 mm.
6. Tenant rack feed: 3-phase PDU, 10-15 kW peak, C13 and C19 mix.
7. Example AUP: draw under 80% of breaker capacity; containment or chimney racks above 6 kW/rack.

Using it in design

• Warn when rack branch-circuit load exceeds 80% of breaker rating.
• Require containment or chimney/ducted racks when a rack exceeds a configurable threshold, defaulting to 6 kW.
• Flag rows not in hot/cold aisle orientation, tenant cages facing exhaust-to-intake, and under-floor cabling in supply plenums.
• Show the five stranding dimensions per room or cage (space, power, power distribution, cooling, cooling distribution) and highlight the binding one.

Who should read it

Colocation providers and engineers planning tenant IT deployments.

Related standards

• ASHRAE TC 9.9 Thermal Guidelines for Data Processing Environments
• EN 50600-2-3
• IEC 60320-1

Publication details

Authors

Paul Lin; Victor Avelar

Publisher

Schneider Electric

Year

2013

Document number

WP 173

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