One of the most common complaints of data center owners and operators is needing extra cooling capacity because an existing system won't maintain an acceptable temperature. The truth is, this issue isn't usually caused by insufficient capacity but rather poor airflow management. Improving the design of a computer raised floor will not only reduce the amount of air that needs to be supplied to the equipment, it will use less energy and improve temperature distribution across cabinets.
To improve air flow, air flow waste must be minimized and all air flow supplied must produce effective cooling. The bane of raised floor systems is known as bypass air flow, which is cold supply air that doesn't cool the IT load productively. It simply passes around the equipment, mixes with warm air in the room and then returns to the air-handling unit (AHU).
Many times, the obvious solution appears to be using colder supply air, but this does not actually change the proportion of air that bypasses, and servers will still get recirculation air. It's common for computer raised floor owners to then conclude their are hot spots, so insufficient cooling is the problem. The AHU supply air temperature can be further lowered, which will maintain the recirculated air at low enough temperatures, but it's incredibly wasteful.
Another approach many turn to is adding more air, which is also disastrous. It's possible that this can eventually supply cold air to the tops of cabinets, but the cost will be tremendous. Fortunately, adopting good air flow management strategies can mitigate by both bypass and recirculation air flow.
1. Create hot and cold aisles
This is the primary step toward stopping a mixed thermal environment through separating cold and hot air streams with careful arrangement of cabinets in parallel rows with the inlet sides of servers facing each other across the aisle. By closing gaps between adjacent cabinets in each lineup, bypass and recirculation air flow can be further reduced.
2. Blanking panel installation in open slots
Bypass and recirculation air flow can also happen inside cabinets, so you cannot effectively cool the equipment in the cabinet without preventing these internal paths. Installing horizontal and vertical blanking panels can reduce air flow. Remember, though, that blanking panels are often removed and not replaced again during the installation and removal of equipment in the cabinet, so equipment should be installed from the bottom up with no gaps between servers to minimize recirculation in the cabinet.
3. Install perforated data center floor tiles in cold aisles
Installing perforated data center floor tiles anywhere but cold aisles can increase bypass air flow, and there is no reason to install these raised floor tiles in a hot aisle except as a maintenance tile, which is carried to where work must be performed so an employee can work in the hot environment in somewhat comfort. These maintenance raised floor tiles should not remain in the hot aisle permanently.
4. Seal gaps between raised floor systems and walls and columns
While sealing the gaps between raised floor systems and walls may seem obvious, it's surprising how often it's neglected. These gaps can be quickly noticed along walls, but bypass air flow can also be found where column walls have not been finished above the ceiling or below the floor. Energy efficient self-forming foam conforms to any area where it is inserted, blocking cold air from escaping into open spaces. This is an excellent solution to sealing gaps between the floor system and walls or columns.
5. Use appropriate raised floor tiles
All too often, computer raised floor owners try to fix hot spots or air shortage problems by installing a high-capacity grate near the hot spot. A grate will usually allow 3x more air to pass through than a perforated raised floor tile, and, while installing these grates near a hot spot may seem to fix the issue, it can actually worsen it. When these grates are installed in raised floor systems dominated by perforated tiles, and the under-floor space has a fixed pressure, the output of the grate will blow air off the top of the aisle, allowing the cabinet to capture very little.
Begin by determining the width of cold aisles early in the plan, as this width will determine the amount of cooling that needs to be delivered to the aisle. If perforated computer floor tiles will be used, all of the cold aisles sharing the under-floor plenum should be supplied with perforated tiles. If the space will have a higher load, grates can be used in all cold aisles with the same under-floor plenum.
6. Manage placement of perforated raised floor tiles
Finally, determine the load and place the appropriate number of perforated data center floor tiles OR grates to cool the load. Installing too few tiles will cause recirculation, while placing too many increases bypass. If you must choose between a small amount of recirculation or bypass, the bypass is preferable.
