Using Floor Tiles with Increased Perforation

Servers and other racked equipment are more than capable of cooling themselves with onboard fans. This equipment has a three part set of cooling specifications requiring the data center to supply.

- The first is air temperature typically between 65˚F and 80˚F.
- 30%-60% relative humidity (some experts prefer the higher air density that 60% RH has to offer however, there is a higher energy consumption associated with the production of humidity).
- CFM: 1 kW equals 120CFM to maintain a 20˚F delta through the device.

The percentage of perforation of the floor tile in conjunction with the sub-floor air pressure will dictate the amount of air that can flow through it. Increasing the percentage of perforation can increase the amount of air that the tile can flow, so why not replace all of the perforated floor tiles with 56% perforated grates? The answer; the sub-floor pressure may drop to the point where air delivery in sections of the data centers will depreciate greatly.

In the model below the top pane uses a single 56% perforated tile. The flow is increased through the 56% perforated tiles relatively. In the lower pane all of the perforated tiles are 56% perforated. The air flow varies greatly due to a drop in sub-floor pressure.

The key here is moderation. Place the higher perforated tiled in front of the higher density enclosures which require them. As mentioned above, 120cfm of air will maintain a 20˚F delta for a 1kW load. How can you tell if you are doing it right?

1. Measure the electrical load of the enclosure you are trying to cool. This can be done by multiplying the current reading on the power strip meters by the voltage of the power in the strips. Example: 22amps x 208volts= 4,576watts or 4.576kW.

2. Now multiply the 4.567kW by 120cfm = 548cfm of air required

3. Now you will need to use a tool called a “Flow Hood Balometer”. This flow hood has a 2’x2’ square box that fits over the 2’x2’ perforated floor tile. Inside the flow hood box is a meter that measures the amount of air flowing through it. These flow hood may be able to be rented from your local rental facility otherwise they rage from $800-$3000 new.

4. Adjust the percentage of perforation to match the airflow requirement as closely as possible. Some perforated floor tiles have an adjustable baffle that you can use to change the airflow of the tile.

5. Let the tile sit for about 20-30 minutes and return to take temperature readings at the front top, middle, and bottom of the cabinet. If any of the temperatures exceed 80˚F you may have to increase the cfm of air flow through the tile. You may also need to correct some in-efficiencies discussed further in this document.

6. Another option is to have a data center professional conduct a Computational Fluid Dynamic (CFD) study on your data center which can provide all of this information.