Cold Aisle or Hot Aisle Containment - Is one better than the other?

with power densities increasing in both Cloud and other HPC data centers there is a need to maximize the efficiency of the cooling systems for two purposes. The first is to provide the additional cooling capacity required in these facilities. The second is to minimize the power consumption of both the electrical delivery system and the cooling system. The cost of power is another driving force in this effort.One major factor of controlling the efficiency of the cooling system is to eliminate Bypass Airflow and Recirculation. A major contributor to eliminating Recirculation is to isolate the hot and cold airflows within the computer room. This is done with aisle containment, creating a physical barrier between the two airflows. These barriers eliminate recirculation of hot air into the Cold Aisle. With this accomplished the cooling task is reduced to providing the servers with just the correct amount of cold air to dissipate the heat generated by the computer equipment. Controlling this task will be touched upon in this paper.The primary purpose of the paper is to examine which configuration to employ, Hot or Cold Aisle containment, in the data centers where In-Room Cooling Units are used. There is no RIGHT answer. The decision depends on the size of the facility, the amount of equipment in the facility that requires high density cooling, the cooling system available or planned to be installed. Is it an economizer cooling system or a traditional central refrigeration cooling system? In addition, the localized cooling systems, e.g. In-Row Cooling units or Rear Door Heat Exchangers are also introduced in the end of the paper.The plusses and minuses will be explored.