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How to Calculate the Size of an Air Conditioner for a Server Room

John Walker

A server room houses computer servers, which generate substantial amounts of heat. Determining the size of air conditioning necessary for a server room is a little more complicated than evaluating the amount of cooling needed for a standard room or house. The process requires calculating the amount of wattage used by the equipment in addition to other factors in the room. Converting the measurements you obtain to tonnage, the measurement used to size an air conditioning (AC) unit, is simple math.

Server rooms can be cooled by split-systems, window units or portable AC units.
  1. Determine the room's initial BTU needs. Measure the width and length of the room, and then multiply the two measurements to get the room's square footage. Multiply the square footage by 337 to determine the room's initial BTU needs.

  2. Determine the total BTUs for all the equipment used in the room. Begin by calculating the wattage of all the equipment. A simple watt-hour meter can be plugged into the wall at each connection to measure each device accurately, or you can contact the device's manufacturer. The manufacturer will have a data sheet on the device that will tell the maximum and minimum wattage it uses. Multiply the wattage by 3.5 to find the total BTUs for the devices.

  3. Figure the room windows' impact. Calculate the area of each window, which is window length multiplied by window height. Multiply the area of south-facing windows by 870 and north-facing windows by 165. Add the totals. Multiply the resulting total by 1.5 if you do not have blinds or curtains over the windows. Skip this step if the room has no windows.

  4. Determine the tonnage needs for the room. Add together your calculations for the room's initial BTU needs, the total BTUs for all the equipment used in the room and the windows' impact. Divide the result by 12,000 to find the room's tonnage needs. Air conditioners are rated by the tons necessary to cool a room; amounts are rounded to the next highest 5/10ths of a ton. For example, if your calculation results in 2.8 tons, round the figure to 3 tons. If the calculation results in 4.3 tons, round up to 4.5 tons.