Reduce Data Center Cooling Costs Through Perforated Raised Floor Tiles

By Author: Stam Bett
Total Articles: 452
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In the days of enterprise servers, the objective was keeping the entire data center cool with a uniform temperature of 55 degrees F. Of course, the cooling model has changed dramatically and now the aim is to cool individual pieces of equipment with little worry for ambient temperatures. With energy costs on the rise, many data centers are today concerned with reducing cooling costs through cost-effective measures.

A study by the Uptime Institute of 19 large computer rooms found that most facilities have an issue with hot spots and, for many reasons, data centers continue to throw AC at the problem, which usually doesn't work. One data center, for example, had 25% of its servers running hot yet had 10 times the necessary cooling capacity. Considering each computer room air conditioner removed can save about $10,000 every year, it's easy to see the importance of efficiency and ensuring cooled air actually reaches the equipment.

The Placement of Data Center Floor Tiles
Many involved in data center operations simply do not understand the science behind the placement of perforated raised floor tiles, and the ...
... percentage of perforation that should be used. Many times, individuals will reply that a specific decision was made for the placement of a tile because "the area felt warm."

Modeling can show the impact of not managing bypass airflow, which usually includes cable openings in raised floor systems where underflow air is leaking through. One study, for example, found that perforated raised floor tile airflow is boosted by 66% simply by sealing the cabling openings.

To maintain constant operating temperature, servers need cool air equivalent to the amount of power they consume, and the front of the equipment, where it draws in cool air, needs a specific amount of air. The 2x2 foot tile right in front of a server rack should be the only source of the rack's cooling needs, and any airflow coming from the tile should be drawn into the rack.

The Amount of Perforated Tiles
A major question to ask is what size perforations the data center floor tiles should have. Ideally, this should be the number necessary to ensure the equipment temperature is maintained while limiting any wasted capacity. You'll need to first determine peak power consumption, which should be listed on the placard on the equipment. The real amount the equipment draws is generally 25-60% of what is listed, depending on whether equipment runs constantly or during specific times. Start by using 45-50% of the rated power.

Once you determine total expected power draw of all components in a rack, you'll know the total expected power needs. You can then convert this into cooling needs. Total rack power consumption in kilowatts must be multiplied by 154 to give the total airflow in CFM necessary to maintain a proper temperature.

The raised floor tile perforation, or perforation percentage, will depend on a number of factors, which is why airflow modeling is essential. There isn't an easy way to determine the airflow output of a tile. If the airflow is low, the servers will run hot. If the airflow is high, money and energy is wasted.

In some cases, the result of the modeling will show there isn't adequate CFM to be delivered through a raised floor tile. In this case, you may need to turn to alternative cooling techniques, including water cooling, to remove up to 70kW of heat from a single cabinet.

Using this information and understanding the relationship between raised floor systems, perforated tiles and airflow modeling can allow data center managers to quickly find about 15% in power savings by mitigating bypass airflow, followed by a redesign of the raised floor layout by strategically placing perforated data center floor tiles.

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