Data center cooling problems can compromise availability and increase costs. The ideal data center cooling system requires an adaptable, highly-available, maintainable, manageable, and cost effective design.
When working to design an effective data center cooling system, there are a number of commonly deployed data center cooling techniques that should not be implemented. They are:
- Reducing the CRAC supply air temperature to compensate for hot spots
- Using cabinet and/or enclosures with either roof-mounted fans and/or under-cabinet floor cut-outs, without internal baffles
- Isolating high-density RLUs
Simply making the air colder will not solve a data center cooling problem. The root of the problem is either a lack of cold air volume to the equipment inlet or it is lack of sufficient hot return air removal from the outlet of the equipment. All things equal, any piece of equipment with internal fans will cool it self. Typically, equipment manufactures do not even specify an inlet temperature. They usually provide only a percentage of clear space the front and rear of the equipment must be maintained to ensure adequate convection.
CFD analysis conclusively proves that roof-mounted fans and under-cabinet air cut-outs will not sufficiently cool a cabinet unless air baffles are utilized to isolate the cold air and hot air sections. Without baffles, roof-mounted fan will draw not only the desired hot air in the rear, but also a volume of cold air from the front prior to being drawn in by the IT load. This serves only to cool the volume of hot air which we have previously established as a bad strategy. Similarly, providing a cut-out in the access floor directly beneath the cabinet will provide cold air to the inlet of the IT loads, however, it will also leak air into the hot aisle. Again, this only serves to cool the hot air.
While isolating high-density equipment isn’t always a bad idea, special considerations must be made. Isolating the hot air is in fact, a good idea. However, the problem is in achieving a sufficient volume of cold air from the raised floor. Even then, assuming enough perforated floor tiles are dedicated to provide a sufficient air volume, too much of the hot air re-circulates from the back of the equipment to the front air inlet and combines with the cold air.
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