Properly Deployed Airflow Management Devices

Description

All airflow management strategies strive to either maximize cooling by supplying cooling (“supply”) air directly to equipment, or by eliminating the mixing and recirculation of hot equipment exhaust air.

A long–term monitoring study of 19 data centers by the Uptime Institute concluded that only 60% of the cool air being pumped into the data center was cooling equipment. It also found that 10% of the data centers had hot spots.²² (Data center hot spots refer to server input air conditions that are either too hot or too dry, according to the American Society of Heating, Refrigerating and Air–Conditioning Engineers (ASHRAE) TC 9.9 guidelines.)

Sound airflow management strategies are becoming even more important as data centers accommodate modern high–density server racks, which demand 20 kW to 30 kW of power per rack versus 2 kW per rack just a few years ago—and generate ten or more times the amount of heat per square foot.

• Diffusers should be positioned to deliver cool air directly to the IT equipment. At a minimum, diffusers should not be placed such that they direct air at rack or equipment heat exhausts.
• Blanking panels are fundamental to efficient airflow control in server racks. On the front of server racks, unused rack spaces (open areas) are covered with blanking plates so that air passes through the equipment rather than around it. Blanking panels decrease server inlet air temperatures as well as increase the temperature of air returning to the CRAC, both of which improve operational efficiency. (See Figure 7 and 8 below.) BNY Mellon, an ENERGY STAR certified data center, employed blanking panels as part of their energy efficiency upgrades.
• Structured cabling systems can eliminate disorderly and excess cables that might constrain exhaust airflow from rack–mounted equipment. In addition, cutting cables and power cords to the correct length will provide more room for air to flow away from the back of the rack. (See Figures 9 and 10 below.)
• Eliminating sub–floor obstructions can improve efficiency. Many data centers use the sub–floor plenum for more than just airflow. Cabling, for instance, can impede proper air circulation, and taking fixed obstructions into account can yield a more efficient floor tile arrangement.
• Floor grommets (see Figure 11) improve cooling efficiency by sealing areas where cables enter and exit plenums (such as a raised floor). Less leakage helps direct more cold air to the equipment that needs cooling.
• Vented tiles are incorrectly located or sized in many data centers. Due to the complexity of airflow behavior, the correct configurations are not readily obvious. A professional air flow assessment can help identify ways to improve cooling efficiency.

Savings and Costs

• Adding a single 12" blanking panel to the middle of a server rack can yield 1% to 2% energy savings.²⁴
• Blanking panels cost approximately $4 to $12 per 1U panel.²⁵ Assuming 10 U of empty space per rack, the costs will be $40 to $120 per rack.²⁶
• Labor costs will vary, depending on the type of blanking panel. Installing 1000 U of blanking panels required more than 80 hours of labor, according to one study.²⁷
• Floor grommets cost roughly $50 to $100 each, depending on the size and function.
• The Green Grid recently completed a  comprehensive analysis (PDF, 2 KB)  of return on investment and power usage effectiveness for data center efficiency upgrades. Payback for adding baffles and blanking panels, repositioning temperature/humidity sensors, and adjusting temperature setpoints was 29 months on capital costs alone.
• Google’s Green Data Centers: Network POP Case Study (PDF, 4 KB) examines a small data center’s efforts at efficiency with optimized air vent tiles, temperature and humidity adjustments, cold aisle containment, and CRAC air return extensions that had an ROI of less than one year.

Considerations

• Due to the complexity of airflow in data centers, the proper use of airflow management devices such as diffusers, blanking panels, structured cabling, floor grommets, and vented tiles is not always obvious. A professional air flow assessment can help identify ways to improve cooling efficiency in data centers by better deploying these devices. A professional assessment should include examination of:
  • The amount of airflow in relation to the hottest server racks,
  • The size of under–floor supply plenums,
  • Pressure in under–floor supply plenums,
  • The size of return plenums or ceiling height, and
  • Location and size of vented tiles (e.g., not located in the hot aisle).