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How to Calculate Airflow for Parallel Fans

Air flow for parallel fan banks is an additive calculation if the fans are sized identically. The air flow is a volumetric measure of the amount of cubic feet of air flowing through a duct or open channel each minute. Each fan has the capability of discharging a variable and maximum volume of air. This is important when calculating how quickly the air in a building can be exchanged per hour. The number of air exchanges per hour is used for enclosed work areas containing noxious gases or vapors.

Things You'll Need

Pen
Paper
Calculator

Instructions

- 1
  Determine the volumetric space of a building or work space. For instance, assume a large production area is 75 feet by 125 feet by 25 feet tall. The volume of the space is 234,375 cubic feet (75 x 125 x 25).
- 2
  Determine the minimum number of air exchanges per hour required for a noxious production process. For example, assume that the air must be exchanged at least two times every hour. This is a total required volume of 468,750 cubic feet per hour, or 7,813 cubic feet per minute.
- 3
  Determine the maximum operating capacity of fresh air fan. This is found in the manufacturer̵7;s literature but, for this example, can be assumed to be 2,000 cubic feet per minute.
- 4
  Determine the maximum number of fans required and the volume of air flow from a bank of parallel fans. This can be done by dividing the required air exchange flow rate by the fan̵7;s capacity. This is 7,813/2,000, or 3.9 fans. Therefore, four fans will be required and will have a total air flow capacity of 8,000 cubic feet per minute.

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