Raised Floors vs Hard Floors for Data Center Applications

Overview

The paper lists the raised floor's four original functions: cold-air plenum, data and power cable path, signal reference grid and piping route. It argues that most of these no longer need a raised floor. Early data centres under 2 kW per cabinet could work with a 0.5 m floor; at 5-10 kW per cabinet an air-distribution floor needs 1 m or more with no underfloor obstructions. A floor used only for underfloor water piping needs a depth of 0.4 m or less.

The drawbacks come with numbers. At a 1:12 maximum slope a 1 m floor needs a 12 m ramp; each ramp consumes about 15 m2, so the usual two ramps take 30 m2, which can equal more than 10 IT cabinets. Typical racks can reach 1000 kg, and full load capability needs every tile in place. In a high-density room (over 6 kW average per rack), removing tiles disrupts airflow. Cost is about $215 per square metre, excluding cabling and seismic engineering. Kobe 1995 meant about 5 weeks (50,000 minutes) of downtime, against 5 minutes per year for 5-nines, 10,000 times worse than the design value.

Hard-floor cooling options are rear-door heat exchangers, row-based coolers with hot-aisle containment, ceiling-return plenums and ducted hot-aisle containment to a central plant. Raised floors remain appropriate mainly as shallow piping spaces for chilled-water distribution, or for low-density spaces with unknown row layouts such as caged colocation.

In the colocation case, a 1 m raised floor can support about 5 kW per rack on average (actual colo is typically 3-4 kW per cabinet). Rooms under 50 cabinets strongly favour hard floors. Cold-aisle containment suits raised floors and hot-aisle containment suits hard floors.

Key points

1. Under 2 kW per cabinet a 0.5 m floor worked; at 5-10 kW an air-distribution floor needs 1 m or more with no underfloor obstructions.
2. A piping-only raised floor needs a depth of 0.4 m or less.
3. A 1:12 ramp for a 1 m floor is 12 m long; each ramp takes about 15 m2, 30 m2 for two, equal to more than 10 IT cabinets.
4. In high-density rooms (above 6 kW average per rack) tile removal disrupts airflow; with an airflow floor, cables should not run underfloor.
5. Typical racks can reach 1000 kg; full floor load capability requires all tiles in place.
6. Raised floor costs about $215 per square metre, excluding cabling and seismic engineering.
7. Kobe 1995: about 5 weeks (50,000 minutes) of downtime versus 5 minutes per year for 5-nines.
8. In caged colocation a 1 m floor supports about 5 kW per rack average (actual 3-4 kW); rooms under 50 cabinets favour hard floors.

Using it in design

• Give each data hall a floor-system parameter: raised air plenum, raised piping only, or hard floor.
• Warn when a raised air plenum has average density above 5 kW and depth under 1.0 m; when density exceeds 6 kW per rack and power or data cables run underfloor, suggest overhead busway or trays.
• Reserve about 15 m2 per ramp (length = 12 x floor height) at each egress and deduct it from white space.
• Default to cold-aisle containment for raised floors and hot-aisle containment for hard floors, and let a seismic-zone input warn about raised floors without engineered bracing.

Who should read it

Designers choosing a data hall floor system and decision makers weighing its cost.

Related standards

• FIPS PUB 94

Publication details

Authors

Neil Rasmussen

Publisher

Schneider Electric

Year

2014

Document number

WP 19

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