Next in our design sequence is the resultant determination of the best configuration or layout of those racks/cabinets. From a user standpoint, both the front and rear of the equipment need access. The front is typically accessed for user interface and monitoring of computer activity while rear access is required for running electrical power and connective computer cables. The most common approach for a layout, then, is to provide equipment in rows that create an aisle such that the fronts of the equipment face each other and allow a person to access and view equipment on the left and right side of the aisle. Similarly, the back sides of the equipment then face each other allowing a common cabling aisle to serve the two facing rows of racks or cabinets. Thus aisles alternate between accessing the front and rear of the vertically stacked equipment.

Other items such as wall mounted cabinets and cable runway need to be factored into the final layout and design of a computer room. Images courtesy of Chatsworth Products, Inc.

 

Supplementing this approach, it is also possible to use some smaller wall mounted cabinets around the perimeter of the room. These need to be assessed carefully for appropriate use, but in some cases they can provide compact, space saving storage for a wide variety of applications. Additionally, some thought needs to be given to the need for additional work or maneuvering space required by the owner/users, the  main distribution path of the cables, the monitoring and control equipment that may be required, and the normal entrance and egress requirements. Once all of the options for a layout are reviewed, a final decision can be made as to the optimum size and shape of the space or spaces needed to house it all.

Attention then needs to shift to the control of the cooling system for the room(s). As mentioned, a small single row rack system may be readily incorporated into the overall HVAC system of a larger building without much difficulty. However, a larger system with multiple rows of dense equipment requires closer analysis and collaboration.

The first thing to recognize is that the nature of the aisles with equipment facing each other creates aisles along the back where heat from that hardware is directed, usually by internal equipment fans. The fronts of the equipment are comparatively cooler since the heat is not blown in that direction. Hence, the reality of a typical data center room layout is that it is not only a series of alternating interface access and cabling access aisles, it is also a series of alternating hot aisles and cold aisles. Therein lies the essence of the cooling design problem—how to appropriately cool the equipment and the surrounding space in a fairly uniform manner that is efficient in both energy use and costs. 

Alternating hot and cold aisles in data centers prevents equipment exhaust air from blowing directly into the fronts of cabinets. Images courtesy of Chatsworth Products, Inc.