realistic CFM on a food trailer

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THE WILD DOG
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2011/12/07 21:17:59 (permalink)

realistic CFM on a food trailer

what is an ideal CFM for a concession truck hood exhaust fan ? I know 1500 and beyond is pretty much overkill.. I can't remember what I was told, I think it was somewhere around 800cfm as a minimum... Can anyone shed some light on that for me... THanks
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    Dr of BBQ
    Filet Mignon
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    Re:realistic CFM on a food trailer 2011/12/07 23:43:26 (permalink)
    It depends on the equipment (BTUs) and then I'd look at the square footage of your rig if your going to try and keep it cool in the summer time by running the exhaust fan. I know some of the exhaust fan / hood companies have charts online. How is your build going?
    #2
    THE WILD DOG
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    Re:realistic CFM on a food trailer 2011/12/08 08:05:09 (permalink)
    thanks DR. The build is coming along well. Just have to finish the plumbing and the gas lines and fig out a way to mount the LP and a few odds and ends and we will be ready to roll. Lost 15 days of work due to a nasty bacteria infection in my lower leg but almost 100% again. Having an issue finding gas struts for my window and looks like i might have to go with automotive mounts for that. I'll be posting pics soon.
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    edwmax
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    Re:realistic CFM on a food trailer 2011/12/08 08:09:08 (permalink)
    Below is what I posted in another thread.  ... But a more simple test and to regulate the fan speed is to use a tissue to see if the air is being drawn towards the fan/hood.    Hold the tissue along the outer edge of the equipment and watch the free end.   The minimum fan CFM that draws the tissue inward shows a positive indication that heat & gases are being exhausted.    ... A variable speed hood fan would be good to have.       ... However, check your local code if you have to meet them.
     
    The size you gave for the trailer is 7ft X 18ft & assuming 8ft ceiling ht, the trailer volume is 1008 cft.     ... The exhaust for vent hoods are usually based on a 'rule of thumb' of 100 to 300 cfm per foot length of hood; with 200 cfm being for medium heat kitchen commercial equipment.   ... Another 'rule of thumb' is to exhaust 100 cfm of air per every 10,000 BTU of heat. You haven't gave BTU size of your Equipment      ... You have a small size trailer compared to a commercial kitchen; ... the difference being other air currents that effect the air flow of the hood which would or should not exist in your trailer.    So I think you only need to use an exhaust rate of 100 cfm per ft. of hood.    .... a 7ft hood @ 100 cfm => 700 exhaust air.  Cross check this calculation with the Total BTU size of the cooking equipment.   ... At this rate the trailer will completely change air every 1 3/4 minutes.   ... Since the AC will not cool this amount of air, keep the window open (or door) so the air flow will cool you while working.   

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    THE WILD DOG
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    Re:realistic CFM on a food trailer 2011/12/08 08:36:20 (permalink)
    my griddle has
  • Two "U" Burner, 25,000 BTU/Hr. Each
  • Two Manual High-Low Controls
  • Propane is 45,000 BTU/Hr. the length of the inside portion of the truck is about 17ft of work space.
    I found a fan and mount for $169. has 3 variable speeds that range from
    CFM HIGH 1,520 CFM MEDIUM 1,400 CFM LOW 1,250
     
     
    http://www.globalindustri...st-fan-shutter-mounted
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    edwmax
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    Re:realistic CFM on a food trailer 2011/12/08 09:10:07 (permalink)
    will that fan fit to your hood plenum?      The hood design has allot to do with minimum CFM flow required for it to operate properly;  
    • hood length,
    • height of front above floor (6'-4 min ???),
    • height above equipment (48" max ???),
    • how far the sides extend down (helps direct the air flow to be from the front of the equipment & thus minimize required CFM)
    • would makeup air be used/needed in the hood???   I don't think this to be a issue in trucks or trailers unless all the windows & doors are to be closed while the hood is operating.    ... air exhausted must be replaced with fresh air.
     
    post edited by edwmax - 2011/12/08 09:12:21
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    THE WILD DOG
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    Re:realistic CFM on a food trailer 2011/12/08 10:27:08 (permalink)
    my hood is 4ft x 3ft
    my height from floor is about 6'5-ish give or take
    height above equip is about 36-48 ( eyeballed from memory) but no more than
    it's a low profile hood, the back sides are about 1' and the front about 2-3"
    no make up air necessary, have vents and window
    #7
    THE WILD DOG
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    Re:realistic CFM on a food trailer 2011/12/08 10:47:18 (permalink)



     
    #8
    edwmax
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    Re:realistic CFM on a food trailer 2011/12/08 16:55:23 (permalink)
    From the dimension you give, the vertical height of the back of the hood is about 12". Deducting about 2" (more or less ?) from the bottom for the grease rail & to clear inside edge of the filters leaves 10" to install a fan.   The fan opening needs to be framed with an angle to match as required for the fan.    .... I don't see a fan larger than 8" can fit into the plenum, may be smaller.     The fan you linked to is 14" diameter.   The only way for that fan can work is to mount to the side of the hood with a larger plenum box connected by a duct (8" diam) to the end of the hood.   ... Assuming wall mounted fan & shutter since that is the type linked to.
     
    From the length of the hood, I think you only need 400 to 800 CFM of exhaust air.  ... You stated the 45,000 BTU/per hr for the propane; then  45000/10000 X100 CFM = 450 CFM   ???
    post edited by edwmax - 2011/12/08 16:59:22
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