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How to Cope with Heat in your Data Center

We frequently receive inquiries from people experiencing cooling problems in their data centers. Some have real challenges, often related to blade technology or other high density applications, which cannot be solved without moving to a more suitable environment, but most of your cooling problems can be addressed through less drastic means. Some are quite simple, inexpensive, and easy to implement.

While every data center is different, many of the cooling problems we find can be addressed using the following measures. They are listed in order of their ease in implementing: start with the first ones and work your way down the list until you have the problem under control. (Most, but not all of these tips apply to data centers with raised floors. Correcting problems when there is no raised floor is more dependent on a variety of factors that are difficult to predict without more information.)

  1. Remove solid doors from your network cabinets. Almost all computer equipment is designed with a front to rear airflow system, using integral fans to cool the internal components. If the cool air can’t get to the front of the server or out of the rear of the cabinet, the equipment will be starved for air. If you need doors for security, use perforated doors that allow air to pass.
  2. Install blank-off panels in any empty rack spaces between servers, and along the sides of the cabinets (inside) to prevent air recirculation within the rack. Even after solid doors have been removed or replaced with perforated doors, you may still have recirculation occurring above, below, or around the servers. Air takes the path of least resistance, and the perforated doors can provide more resistance than the open space around the equipment. Server and cabinet manufacturers sell panels for this purpose, or they may be fabricated from suitable materials by the enterprising person with available time.
  3. Seal cable cutouts in the raised floor tiles – including those directly below cabinets. Large openings allow large volumes of air to pass, with a corresponding drop in static pressure in the vicinity of the opening. Nearby perforated tiles will experience a drop in airflow. Below-floor air distribution systems are most effective when the pressure below the floor is as uniform as possible. Uncontrolled cable openings work against this goal. There are several products on the market for just this purpose, including special pillows, brush type inserts and foam-based inserts.
  4. Look closely at the location of perforated tiles or grilles relative to where they are needed: along the front of server cabinets. It is not uncommon for us to see rogue air outlets or perforated tiles merrily dumping air in areas with no cooling load whatsoever. Put the cool air where you and your servers need it: along the front of the cabinets (i.e. the famous cold aisle). But be careful to avoid placing air outlets too close to the air handler discharge: the high velocity jet of air in close proximity to the A/C unit discharge can cause a “venturi” effect that actually sucks air from the room into the raised floor plenum through what you believed were air outlets. Usually, by the time the air has traveled about 6 feet radially from the A/C unit it has spread out and slowed down enough to prevent this problem. The actual distance varies, depending on the specific configuration of your room (i.e. size of A/C unit, raised floor depth, and proximity of the A/C unit to other units and walls).
  5. Make sure the total number of perforated tiles or air outlets installed is consistent with the capacity of your air handling systems. For every 3 tons of air conditioning capacity, you should have approximately 2 perforated tiles. The ratio that works for your data center will vary depending on the specific characteristics of your air conditioning equipment and perforated tiles, but it gives you a clue as to whether you are close or way off track. You aren’t way off track if your ratio is anywhere from 1 ton per tile, or even 3 tons per tile. NOTE: Beware the temptation to add more perforated tiles in hopes of increasing airflow. Unless you have significantly fewer tiles than you need to match the airflow capacity of your air conditioning equipment, you will end up reducing the airflow to the rest of your computer equipment. If you believe you have an air imbalance, we advise that you avoid the rules of thumb offered in the “popular data center press” and hire an experienced data center HVAC engineer (that would be Reliable Resources) to work with.
  6. Remove unnecessary power and communications cables from under the raised floor, and especially from areas directly below perforated tiles or floor grilles. The shallower the raised floor, the more likely it is that excess cabling will be a problem.
  7. If possible, install an overhead conveyance system for all new communications cabling and migrate existing underfloor cable to the overhead conveyance. This will free up space below the raised floor for airflow – but make sure you are not creating a new problem with the solution. If you don’t have a raised floor pay attention: Overhead conveyance in a data center with a low ceiling height can introduce airflow obstructions in the return air path to the A/C units that could increase recirculation of warm air at the top of your server cabinets. Coordinate the evaluation of underfloor and overhead airflow paths to arrive at the most rational solution.
  8. Relocate hot racks (or high density servers) to a different part of the computer room where there are fewer servers. Leave plenty of room around the hot racks so that the inherent thermal mass of the surrounding air can even out the temperature. Make sure you install perforated tiles or grilles at these locations (but see Tip #5 above).
  9. If you have a row of cabinets directly in front of and parallel to an A/C unit, the rear of the cabinets (the hot air discharge side) should face the A/C unit. Otherwise the hot air will have to circulate back over the top of the cabinets on its way to the A/C unit inlet, and may be drawn back into the topmost servers.
  10. Try to avoid installing servers in the very top of your cabinets. Warm air from the hot aisle is more likely to re-circulate over the tops of the cabinets if you have servers occupying the top spots. The more space you can leave at the top, the better.
  11. The same concept described in Tip #10 applies to the end cabinets in each aisle – warm air also recirculates around the ends. If you have some equipment that is less heat sensitive, concentrate it in these end cabinets.

If you have any questions about how to cope with heat within your specific data center configuration call Reliable Resources at 612-279-0411 or contact us via email.