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Need calculation formula used for fresh air

nytech28 Member Posts: 67

I have around 1700 SF of commercial space that needs hvac system that's required to have fresh air to be mixed with the hvac system , the G.C wants to install 2- 3 ton ducted units , I need to know what's the formula used in the hvac industry to determine the required CFM of fresh air for the premise I also need to consider the units are heatpumps & mixing fresh can that affect supply air temp ? , any suggestion would help. trying to save time to get info on all this.


  • Jamie Hall
    Jamie Hall Member Posts: 23,447
    The fresh air requirements are specified in air changes per hour, and vary with the use and occupancy of the space. You need the volume of the space and the required air changes per hour, and then you can get cfm from that.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • bburd
    bburd Member Posts: 923
    ASHRAE 62.1, ventilation for acceptable indoor air quality, specifies a minimum volume of fresh air per person in the space.

    EBEBRATT-Ed Member Posts: 15,631
    As both the above posts said this is a code issue depending on the occupancy and use of the space.

    If manufacturing you have to account for fumes sometimes in schools they generally go by the Co2 in the air.

    It varies widely, not one size fits all.

    The old rule of thumb was 10% OA but that can be an energy hog and should not be used as a general rule.
  • nytech28
    nytech28 Member Posts: 67
    got it probably need mechanical engineer to take survey.