convert cfm for square footage?

bmetbmet Solar Expert Posts: 630 ✭✭
I'm looking for an estimate on how long it would take to change the air in my shop. It's 10' x 10' X 6' with a Hay Barn roof. attachment.php?attachmentid=1892&stc=1&d=1307920284

My Power Pack sits for days without being used, so there's some potential. I've installed two 12VDC fans that are the perfect fits for the vents. Rated @ 75CFM & 350mA each, they're powered off of my SunSaver's LVD. attachment.php?attachmentid=1893&stc=1&d=1307920284

They're mounted in 2.5" thick medium-density foam board. Together they use 650mA of Current, so my PV is not being strained while maintaining the battery. I could probably add one or two more of these 12VDC fans without too much trouble,but would like to know how long it is taking to exchange the air. Is there a simplified way to convert cfm to the square footage of a building? Thank you.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: covert cfm for square footage?

    10' by 10' by 6' is 600 cubic feet. 75 cfm will change the air in eight minutes.
    More or less - depending on how "flow-through" the air path is.
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: covert cfm for square footage?

    Thanks for the quick response, Cariboocoot. The floor plan lists it as 832 sq. feet. What I wasn't sure of, is whether they meant that as the whole interior volume, or just the amount of space for storage (there is 4' x 10' of loft in there as well).
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: covert cfm for square footage?

    No telling how manufacturers come up with their numbers. Spin of the wheel perhaps. 10' by 10' is 100 square feet, not 832 square feet. 4' by 10' is another 40 square feet. The numbers don't add up any which way. :confused:

    But multiplying the exterior or maximum interior dimensions gives you a close number on cubic capacity.

    The tricky bit is that the 75 cfm fan may not actually move 75 cfm if there's any restriction on the outlet or intake.
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: covert cfm for square footage?

    The picture doesn't make it clear. The hay barn roof starts at 6'. Is the rest of the manufacturer's data the 'height' above the loft, or is it the entire gabled space?
    I try not to obstruct any of the floor-level vents, but intentionally placed my battery in front of one.

    Thank you for the estimate.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: covert cfm for square footage?

    Square feet is a flat surface - like a floor or a wall. Cubic feet is the entire volume inside.

    So a 10'x10' floor would be 100 sq' (square feet). Times 6' high would be 600 cu' (cubic feet).

    To the start of the barn roof. So add what...say another 10'x10'x3', which would be 300 cu'. for the part above where the barn roof starts.

    Totals out at roughly 900 cu'. if the roof was square, but since it slopes, it'll be less.

    So I'm thinking the manufacturer's specs probably say 832 cubic feet for the entire inside volume, but you're reading it as 832 square feet.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: convert cfm for square footage?

    in any case be sure to not let it run too long as it would deplete your battery.
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: convert cfm for square footage?

    Thank you DWH, Cariboocoot, and Niel. I believe 3 of these fans will be my safe limit, drawing a total of 1.2 Amps. So far, with record temps all
    Week being at 100 degrees or more, my battery has kept its float at 13.8VDC while exchanging the air. It just gets too hot and humid for stagnant storage, and if I am not using my power pack that often the PV seems able to do two things at once. Take care.
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