Make up air or no make up air...that is the question.

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cosmo64
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2013/10/13 20:13:05 (permalink)

Make up air or no make up air...that is the question.

I'm about to pull the trigger on a 4' exhaust fan from Jeans and don't know enough about make up air to make an informed decision. First of all my HD doesn't require it. My menu will consist of all beef gormet hot dogs, pulled pork & paninis. Thanks in advance for your expert opinions. FYI the trailer is 6' x 12' and 7' high.
post edited by cosmo64 - 2013/10/13 20:17:18
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    fishscale28
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    Re:Make up air or no make up air...that is the question. 2013/10/13 22:51:18 (permalink)
    IF you want any chance of having any kind of AC in your truck/trailer you need some sort of makeup air.  I just used two of the ceiling mount RV fans spaced evenly in front of my 8' hood and it works perfectly.  Just the right amount of negative pressure.  If you don't care about AC and will always have a window/door open then you'll be fine.  Otherwise you need to provide some air for to makeup for whatever your hood is sucking out
     
     
    #2
    edwmax
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    Re:Make up air or no make up air...that is the question. 2013/10/14 07:12:12 (permalink)
    Depends on how you ventilate the trailer.   ... Air out at the hood equals air in from the door & windows (aka: makeup air).   What is the exhaust volume of the hood fan?  ... Hood fan volumes are usually too big for trailers making AC near impossible or at best very costly.
    #3
    fishscale28
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    Re:Make up air or no make up air...that is the question. 2013/10/14 11:14:52 (permalink)
    I matched the two roof top fans I have to just a hair under the CFMs of my hood fans.  I was then able to put ample AC in my truck and it works quite well.  It's a little warm towards the door (furthest away from air handler) but it's still very doable.  And its South Florida too...makeup air is key if you want AC
    #4
    edwmax
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    Re:Make up air or no make up air...that is the question. 2013/10/14 15:12:14 (permalink)
    Nice, but you still haven't told us what the system is.   A hood with a makeup sir system or a standard hood and separates roof fans blowing into the trailer.   .... Unless your hood is built with a makeup air system which recirculates the air 'under the hood', then you are not doing anything but blowing cooled air out the hood and windows.    How big is your AC and what is the CFM of the hood exhaust?
    #5
    cosmo64
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    Re:Make up air or no make up air...that is the question. 2013/10/14 20:39:21 (permalink)
    Thanks for the replies. The exhaust hood will have 1200 cfm, the rooftop a/c is 13500 btu advent with claimed 15000 btu output.
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    fishscale28
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    Re:Make up air or no make up air...that is the question. 2013/10/14 23:40:56 (permalink)
    So I would get two roof top fans and space them evenly in front of the hood-providing your makeup air.  It's not built in makeup air like a traditional restaurant hood but it will supply the air your hood is sucking out.  Then, and only then, will you be able to keep any of the cooling BTU's in the truck.  Otherwise your hood is sucking out everything your AC is putting out via whatever window/door you have open.   All you're looking to do is replace the air your hood sucks out.  Once that is balanced you'll be able to have AC and keep most of it in the truck.  Otherwise its a lost cause.  Trust me-I have adequate AC in my truck and I can run a shift without sweating like a bad girl in church...and I see other trucks who are miserably hot.  
    #7
    cosmo64
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    Re:Make up air or no make up air...that is the question. 2013/10/15 13:28:28 (permalink)
    THANKS FISH. I'M NOT YELLING. MY MOBILE BROWSER WON'T ALLOW LOWER CASE TODAY FOR SOME REASON.
    #8
    edwmax
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    Re:Make up air or no make up air...that is the question. 2013/10/15 16:01:50 (permalink)
    fishscale28

    So I would get two roof top fans and space them evenly in front of the hood-providing your makeup air.  It's not built in makeup air like a traditional restaurant hood but it will supply the air your hood is sucking out.    ...

     
    But the trick here is the roof top fans (one will do) needs to be ducted to the front of the hood and exhausted by a vent abt 3" wide and the full length of the hood; and directing the airflow down & towards the back of the hood.   This forms an 'air curtain' at the front of the hood and is the way hoods with makeup air are designed.  It is the 'air curtain' that helps to keep the cold air in the kitchen.  Just down blast roof fans will not do this.    ... Use smoke or tissue to see the air flow ...
     
    cosmo64

    Thanks for the replies. The exhaust hood will have 1200 cfm, the rooftop a/c is 13500 btu advent with claimed 15000 btu output.
         ... This is an air change of 2 1/2 X's the air volume of the trailer per min.  You are completely changing the air in the trailer every 24 seconds.   There is no way the AC can keep up at 350 to 400 cfm (15000 btu AC).  At best the AC can do is to blow on the work area. Then of course you will feel cool.     For a 4 ft hood, the size of this trailer, I think you could get by with an exhaust fan at about 300 or 400 cfm.   ... A simple way to check the hood exhaust is with a tissue at the front of the hood and just above the cook top/grill (??).  If the tissue pulls to the rear (gently or slightly) then the exhaust is enough.  Heat, vapor, and gases is being pulled out by the hood.
    post edited by edwmax - 2013/10/15 19:59:46
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    RodBangkok
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    Re:Make up air or no make up air...that is the question. 2013/10/15 19:46:53 (permalink)
    edwmax describes one method of directing makeup air, I'll offer another that works also.  Duct the makeup air down to the bottom and if possible in the center of the appliances to be vented.  Terminate this duct below the appliance fume exit.  Such that the makeup air helps carry the fumes and heat upward into the vent.  Play with some smoke as suggested above to adjust the A/C or ventilation air such that it does not get vented directly into the hood area.  Also it is vital that the size of all fans is calculated accurately, not just estimated with fan sizes off the shelf.  The general idea is to try and keep the makeup air easily accessible to the hood while isolating the room conditioning air from the hood.
    #10
    edwmax
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    Re:Make up air or no make up air...that is the question. 2013/10/15 19:58:12 (permalink)
    Thanks Rod I haven't thought of that.   ... Another thing I would do  is to extend the chimneys of the frier & range (may be some flat grills) up to the bottom of the hood.   This would reduce the need for air flow to pull that heat & exhaust gases out.
    #11
    fishscale28
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    Re:Make up air or no make up air...that is the question. 2013/10/16 00:24:53 (permalink)
    Yes you're all right...but also overthinking it.  The best, most balanced make up airs have perfectly aligned plenums that provide just the amount air to supply just shy of what the hoods are pulling out.  You should never feel makeup air-it should be-as you say-a curtain that provides an invisible but definitive flow of air over the front (or from the bottom of the hood/appliances) so that anything under the hood is contained and pulled out.  Has to be the right amount of negative pressure though.
     
    Should you get a hood with well designed makeup plenums?  Sure!  Find one that fits in a food truck that allows for wall and ceiling clearance and allows you to THEN have another makeup fan (which is huge-just as big as the fan you'll use for your exhaust) and the required ducting.  Not going to happen....
     
    Next best option is to provide fans, evenly spaced, in/on your roof.  Is it perfect?  No...but does it work?  Yes!  Will one work?  YES!  CFM wise...the reality of the spacing is the issue...where plenums come into play...they can take one fan and evenly distribute the suction...which if your 4'10" and don't need clearance than you're ok with building some ducts.   Otherwise-grab two fans and place them evenly in front of your hood...it works.
     
    I think its awesome that you're getting some info here...I actually inquired before/during my build and got very little info that led me in any direction...Luckily I've been apart of 7 separate restaurant build outs and have learned alot from hood/exhaust companies and had a great friend from Captive Air work with me on what I was doing to make the best of what we could do.  And what I have works.  Is it perfect?  No not really...but how many professional kitchens have you been in where its been perfect?
     
    And edwmax-with all due respect-yes it does work (having the fans placed evenly with the tissue test).  I've even done the smoke plug tests required by Captive Air and while not perfect its certainly workable and within respectable tolerances.
     
    When I say you should have two fans with downblow I'm not saying it should be full blast fans there just to be there.  The whole idea is to provide your exhaust the air it is pulling out.  Which two well spaced fans in front of the hood will do.  All day long.
     
    And just for my curiosity-since I didn't get a good idea when I inquired a few months ago-how do you guys do makeup air?  How did you build it into your trucks/trailers?  How is it working for you?  Are you using AC?  Is it keeping up?
     
    Just curious....thanks!!!!
     
     
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    RodBangkok
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    Re:Make up air or no make up air...that is the question. 2013/10/16 03:01:51 (permalink)
    Below is a link to a very good technical document on optimizing make up air.  I've referenced it here I think in the past, but for the sake of providing info in this thread I'll include it again.  The article shows different ways of designing a system and offers some analytical data on their efficiency.  Pay particular to attention to the designs that use a short circuit all in one hood, these are just a waste of good money and I'm even surprised that they are offered by reputable companies.  But I'll let the article speak for itself, hope its of use to others that reference this thread.  As with many things there's more than one way to skin a cat, and a lot of ways to skin this one, but at least hopefully by reading this thread people will realize make up air is something that must be considered and calculated correctly or you can waste a lot of money on heating and or A/C in your environment.
    http://www.fishnick.com/v...ign_Guide_2_031504.pdf
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    edwmax
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    Re:Make up air or no make up air...that is the question. 2013/10/16 04:23:09 (permalink)
    Your doing what you want and apparently satisfied with it.  So why did you start this thread if you didn't want the input from other members here?     ... As I said above the hood exhaust is too big and the AC is over-sized.    The 13000/15000 BTU AC is capable of cooling up to 900 sqf.  Your trailer is only 76 sqf.  
     
    The roof top fans are blowing directly down on who ever is working in front of the hood.   So if the fans system works as you say, this person is not feeling any cooling from the AC.  This air is drawn out by the hood exhaust per your description.  If he does feel the AC cool air, then my point has been proven.    ... If he doesn't feel the AC cool air, then cooling is from high volume outside cool air flow and the AC is a waste.
     
    In BM kitchens hoods with makeup air are hard to design and maintain.   Many hoods don't work as claimed by the installer.   But hoods that seem best effective work with approximately 75% makeup air.  Higher makeup quantities are greatly effected by close proximity of HVAC vents, doors/windows, or equipment.   ... Where Codes now require fresh outside makeup into the HVAC system, higher makeup efficiency of the kitchen hood makeup is not necessary. The kitchen hood can be used as an exhaust for the portion of air being replace by the HVAC makeup system.   ... The point of a kitchen makeup air hood system is to save money by reducing the cost of cooling air drawn in from the outside and the size of AC required.   A BM commercial kitchen will add a load of 5 ton to 10 tons extra cooling ($600 to $1500 per month) to the building AC load.  
     
    So a 15000 BTU AC (900/76 sqf; abt 3 to 5 Xs oversize) will cost you about $6 per day to run.  I don't see where you've achieved any savings; but done the same many other trailer/truck vendors; ...  just put in an oversize AC blowing on the work area.
     
    Good luck with your trailer & project ...
    post edited by edwmax - 2013/10/16 04:27:50
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    cosmo64
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    Re:Make up air or no make up air...that is the question. 2013/10/16 17:59:01 (permalink)
    Thank you all again for your knowledgeable input. I spoke with a tech at JEANS Restaraunt Supply yesterday. He said that based on my equipment & menu, no make up air will be necessary with a downgrade to a 200 cfm fan. He said reducing fan speed to lowest setting & only using the exhaust fan for a few seconds when needed will negate the need. He said if I add any additional equipment, I will need to go back to a higher capacity fan & make up air
    post edited by cosmo64 - 2013/10/16 18:02:33
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    edwmax
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    Re:Make up air or no make up air...that is the question. 2013/10/16 18:46:42 (permalink)
    cosmo64

    Thank you all again for your knowledgeable input. I spoke with a tech at JEANS Restaraunt Supply yesterday. He said that based on my equipment & menu, no make up air will be necessary with a downgrade to a 200 cfm fan. He said reducing fan speed to lowest setting & only using the exhaust fan for a few seconds when needed will negate the need. He said if I add any additional equipment, I will need to go back to a higher capacity fan & make up air

     
    YES!  ... vindicated and verified ... ...   A Three speed exhaust fan (200, 400, & 600 cfm) may work the best. Just switch to a high speed if there is any smoke buildup in the trailer.
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    fishscale28
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    Re:Make up air or no make up air...that is the question. 2013/10/16 23:34:37 (permalink)
    I'd still love to see what you seasoned guys have for makeup air in your setups.  Just merely from curiosity.  I was desperately interested in getting some info a few months ago and didn't have anyone show any real time setups they were currently using.  We can go over plans, theories and ideas all day long but I would still love to see what you guys are sporting.
     
    I've been in professional kitchen all my life.  Never ever will you have AC on the line that is adequate enough to be called "a cool line."  But there are well designed hoods that contain the heat, pull the smoke and balance the air being pulled out and taken in.  Even Captive Air and all the other clowns have all these fancy formulas etc., and they sound great on paper (or on a forum) but the reality is much different than reality.  
     
    My hood sucks 1400 CFM.  My makeup air fans-although not as fancy as a plenum setup as I would have liked-provide between 600-1400 CFM.  It works.  And I don't need a door or window open to keep things flowing.  And my AC still works.  Its just as good, if not better, than the majority of the kitchens I've spent many years in
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    fishscale28
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    Re:Make up air or no make up air...that is the question. 2013/10/20 03:10:56 (permalink)
    Still would love to see everyone's makeup air solutions..............
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    edwmax
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    Re:Make up air or no make up air...that is the question. 2013/10/20 06:10:50 (permalink)
    Most vendors here don't do make air systems.  They use the hood to exhaust the heat of the trailer and to draw fresh air thought the windows or doors.   ... There are several threads on this topic.   Use the search button above to find them.
    post edited by edwmax - 2013/10/20 18:35:23
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    fishscale28
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    Re:Make up air or no make up air...that is the question. 2013/10/20 16:20:35 (permalink)
    I actually did quite a bit of searching on it before and during my build and there may have been some threads, but not much definitive info. I just saw you're input and mastery of the ideas and theories about the subject and was just curious what YOUR setup was. But thanks though
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    gonzojuice
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    Re:Make up air or no make up air...that is the question. 2013/10/23 09:40:18 (permalink)
    Most of the trucks and trailers in Austin don't have a make up air system. This is why they all claim that their AC systems weren't worth putting in. The hood just pulls all of the air through any available cracks and crevices or open windows and doors. This pulls all of the AC out. I have one buddy that was telling me that in the winter his employee that works the window is bundled up big time since the cold air rushes through the window past her every time she opens it.
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    fishscale28
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    Re:Make up air or no make up air...that is the question. 2013/10/24 11:14:24 (permalink)
    I get that...I do.  I know most trucks don't worry with it.  Same down here.  BUT, with the opinions and matter-of-fact info offered here I thought it would be great to see what the poster's personal setups were.  I was just curious that's all.
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    BulahLerry
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    Re:Make up air or no make up air...that is the question. 2014/02/20 01:59:58 (permalink)
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