Machine Shops

Machine Shop Ventilation is all about improving the air quality. When designing a ventilation system for a machine shop, you need to consider variables and goals. Most ventilation goals can be achieved through the use of  a combination of strategically positioned Exhaust Fans and or Supply Fans or Louvers and Shutters. Louvers and Shutters often have a velocity rating by the manufacturer. You want to take care not to exceed the velocity rating of a louver to ensure there is no water penetration at times when it is raining outside. The goal is to replace the inside stagnant air with fresh outside air. Variables can be size of the shop, equipment and installation costs, power supply, outside temperatures, contaminants in the air, employee location, sound levels etc.

First step and probably most important is the size of the shop. You need to know the volume of the shop measured in cubic feet because you are going to use that number to give you a general idea on how many Exhaust Fans and Intake Shutters or Louvers and what size is going to be needed to effectively ventilate the area. This can be calculated by taking the length in feet multiplied by the width in feet multiplied by the average ceiling height in feet. If there are any interior structures such as office space, subtract that from the total volume of the space. The resulting number should be the volume in cubic feet.

Second step is power and location. You need to look at the location and power source you have available in your shop and consider the best location for ventilation fans. Some shops only have 115 volt or 230 volt single phase power available while others have higher voltages such as 230 volt, 460 volt and even 575 volt (popular in Canada). Generally, once you get past 1 horsepower, three phase fans are less expensive and cheaper to operate while low voltage single phase fans are a good fit for smaller machine shops. A General Rule in Ventilation is that "Air Flow Follows the Path of Least Resistance" so when your moving fresh air from one location to another, typically you want the intake or fresh air source on one end of your building and the exhaust source on the opposite end ensuring that the flow of air covers the entire floor space. There are always exceptions to this rule. One is if you have equipment giving off heat or unwanted fumes. It may be an advantage to locate the exhaust fan directly above or behind the equipment to minimize the possibility of the heat or fumes generated by the machine or process escaping to other parts of your shop. You need to consider if you want to mount the fans on the wall or on the roof or if you want to utilize ducting.

Third step is air exchange rate and fan selection. A General Air Exhange Rate for a Machine Shop is somewhere between 3-6 minutes. This means after you turn the fans on, the inside shop air is replaced with clean and fresh outside air within 3 to 6 minutes as long the fans are running continuously. For example, a 50 Ft. Wide x 100 Ft. Long Shop with 18 Ft. average ceiling height is 50 Ft. x 100 Ft. x 18 Ft. = 90,000 Cubic Feet. If I want an air exchange rate every 5 minutes or 12 times an hour, I divide 90,000 Cu.Ft./5 Minutes = 18,000 Cubic Feet per Minute (CFM). I would need a total of 18,000 CFM to get the job done. Sometimes you can utilize just one fan but multiple fans may be better to make sure there is a uniform airflow across the entire building.

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