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  1. #1
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    Commercial Kitchen Ventilation Inquiry

    I'm employed by a local school district as an equipment service technician. I've been here 8 years. One of my kitchens, which was built in 1999, has several exhaust hoods for various pieces of commercial kitchen equipment such as a natural gas fryer, gas convection ovens, gas atmospheric steamers, a gas pizza oven, etc.

    When I first started working here, one of my first projects was to go through all the exhaust hoods, make-up air units and roof ventilators to see what was working and what wasn't. To my surprise, a lot of the make-up air units on the roof had been disabled. Some roof ventilators going to some of the exhaust hoods were disabled, too. So, scratching my head and before I put a lot of time, effort and money into the equipment to make it operable, I talked to the manager about why certain exhaust hoods and make-up air units weren't being used. She told me that, because of the way the exhaust hoods were designed, whenever they ran the make-up air units, unconditioned outside air was being pumped into the work areas, which was often hot and damp air. We are along the Texas Gulf Coast, so we get those kind of hot and damp conditions a lot. I asked her to show me what she meant.

    So, she took me to the exhaust hood for the hamburger line and she turned it on. When I put my hand up inside the hood, there was good exhaust ventilation. When I put my hand on the outside front of the hood, where there are SS perforated panels, hot and damp air was being blown right down on the area around a prep table and directly on the heated merchandisers on the serving line. Right then, I knew why they didn't want to use this exhaust hood.

    So, my question is this. Why would they design a ventilation system where the make-up air is unconditioned? Are a lot of commercial kitchen ventilation systems designed this way? I'll be the first to admit that I am not a commercial kitchen ventilation expert, but to me, it just doesn't make any sense to be pumping in unconditioned air into a conditioned space, especially when it is blowing directly on the kitchen staff and on the serving line. Just so you know, they don't use the exhaust hoods over the convection ovens or steamers because there are food prep tables in those areas and the make-up air blows directly on those areas. FWIW, I do understand a little about how a building is air balanced and what that means as far as the HVAC in general, but again, I am definitely not an expert in that area.

    Thanks for any help you can give!
    With your chrome heart shining in the sun, long may you run.

  2. #2
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    > Why would they design a ventilation system where the make-up air is unconditioned?

    Because the makeup air is going right back out the exhuast fan. Cooling that air is very costly.

    > Are a lot of commercial kitchen ventilation systems designed this way?

    I'd guess maybe 75 percent. Up in New England they have to heat the makup air in better places.

    >it just doesn't make any sense to be pumping in unconditioned air into a conditioned space,

    In reality, when set up properly, it, along with a small amount of room conditioned air will go right back out the exhuast, not into the room per se.

    > especially when it is blowing directly [on the kitchen staff and] on the serving line

    I'd bet that the original line blueprint doesn't show a serving line that close to the hood.

    > they don't use the exhaust hoods over the convection ovens or steamers because there are food prep tables in those areas and...

    Oh dear lawd. Everybody have continious headaches? Ever performed a carbon monoxide test in that area? You really, really must have the exhuast hoods running over combustion equipment. It the law for a good reason. If you must, disable the makeup air fans and let the (now running) exhuast fans pull through the HVAC economizers.

  3. #3
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    Quote Originally Posted by BadBozo2315 View Post
    > Why would they design a ventilation system where the make-up air is unconditioned?

    Because the makeup air is going right back out the exhuast fan. Cooling that air is very costly.

    > Are a lot of commercial kitchen ventilation systems designed this way?

    I'd guess maybe 75 percent. Up in New England they have to heat the makup air in better places.

    >it just doesn't make any sense to be pumping in unconditioned air into a conditioned space,

    In reality, when set up properly, it, along with a small amount of room conditioned air will go right back out the exhuast, not into the room per se.

    > especially when it is blowing directly [on the kitchen staff and] on the serving line

    I'd bet that the original line blueprint doesn't show a serving line that close to the hood.

    > they don't use the exhaust hoods over the convection ovens or steamers because there are food prep tables in those areas and...

    Oh dear lawd. Everybody have continious headaches? Ever performed a carbon monoxide test in that area? You really, really must have the exhuast hoods running over combustion equipment. It the law for a good reason. If you must, disable the makeup air fans and let the (now running) exhuast fans pull through the HVAC economizers.
    I understand how the make-up air is supposed to work, but in this case, that air is not being directly affected by the exhaust hood. It is blowing out and away from the hood and, though some of the air is being pulled back into the exhaust hood, I would venture to guess that 75% of the air is not being directly pulled back into the hood. When it's 90-95 degrees outside, and adding in the humidity, it is extremely "nasty" air and I can't blame the staff for not wanting to work under those conditions. In some of my other kitchens, the make-up air is deposited within the hoods where it is being exhausted through the hood. But, in this case it is not. Regarding conditioned make-up air being costly, so is pulling out conditioned air through the exhaust fans, running the make-up air units or not.

    The original blueprints show the kitchen equipment and the serving lines exactly where they are located today. Nothing was or has been altered from the original drawings. In the prep area of the kitchen, where the ovens, steamers and other equipment are located, the prep tables are adjacent to the equipment so the food can be removed and prepared the moment it is removed from the equipment. Again, this area was designed that way, as are all the other kitchens in the school district. The problem kitchen is not unique to other kitchens in this school district or is it unique to other commercial kitchens I have seen.

    As far as disabling the make-up air units and only running the exhaust fans, that is being done over other equipment, but the exhaust fans do not pull through HVAC economizers. There is ample fresh air being pumped into the kitchen. It has its own outside air handling unit (OAHU) and it's own air handing units (AHUs) for cooling and heat, so I am perfectly satisfied that CO is not a problem. Not to mention, there are other exhaust fans running that prevent CO from being an issue.

    I am convinced that these exhaust hoods manufactured by Gaylord were either not designed properly for this application or they were not set up correctly when they were installed. I am waiting on a phone call from the manufacturer to see if they can provide some guidance.
    With your chrome heart shining in the sun, long may you run.

  4. #4
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    Here's a really good document on kitchen exhaust/keep makeup air design.

    exhaust design.pdf

    Sent from my Moto Z (2) using Tapatalk

  5. #5
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    Quote Originally Posted by shellkamp View Post
    Here's a really good document on kitchen exhaust/keep makeup air design.

    exhaust design.pdf

    Sent from my Moto Z (2) using Tapatalk
    I read this years ago, but had forgotten that I had and that there are, indeed, tempered makeup air units. Thanks for the information. This is the most important information, at least for this particular situation:

    Tempered or Untempered?

    Air that is heated or conditioned before it is brought in from the outdoors is called tempered air. If the goal is to make the kitchen comfortable, then utilize tempered air. If the goal is low cost, then use untempered air. Both tempered and untempered can be introduced, however, selecting the proper supply types will affect comfort and economic efficiency. Once this decision has been made a type of make-up air system can be selected, but always keep two things in mind. When tempering the air, use a source that will distribute the air throughout the kitchen to increase employee comfort. When using untempered air, use a source that will keep the air near the hood so it can be exhausted quickly without mixing in the space causing discomfort and increased heating/cooling loads. Make-up air temperature should not vary more then 10o F from the air in the space. However, this limit can be exceeded if the make-up air does not decrease the comfort of the occupied space or is part of an air conditioning system.
    So, apparently, the decision makers at the time decided it didn't matter if untempered make-up air was causing discomfort to the kitchen staff.
    With your chrome heart shining in the sun, long may you run.

  6. #6
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    Most restaurants don't really care if the cooking staff are uncomfortable. That's just part of the game of being in a busy kitchen. I would say around my area maybe 10% of the make up air units that I see have air conditioning. Of course I am in Minnesota and not Texas, so that might have something to do with it, but it does occasionally get hot and humid here in the summer time too.

    Also, I mostly deal with busy restaurants, which is probably a much different environment than the lunch lady land that you live in.

    If you can get approved for the funding to upgrade or replace your equipment with stuff that works better and is air conditioned, then go for it. Good luck.
    If at First You Don't Succeed, Skydiving Is Not for You.

  7. #7
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    Quote Originally Posted by ammoniadog View Post
    Most restaurants don't really care if the cooking staff are uncomfortable. That's just part of the game of being in a busy kitchen. I would say around my area maybe 10% of the make up air units that I see have air conditioning. Of course I am in Minnesota and not Texas, so that might have something to do with it, but it does occasionally get hot and humid here in the summer time too.

    Also, I mostly deal with busy restaurants, which is probably a much different environment than the lunch lady land that you live in.

    If you can get approved for the funding to upgrade or replace your equipment with stuff that works better and is air conditioned, then go for it. Good luck.
    Not that I do a lot of restaurants; but I've seen exactly 1 conditioned makeup air unit in the wild.

    Large package units to cool the kitchen areas? Sure. But regular-old 92 degree, 1000 percent outdoor air is coming in to replace the exhaust.

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  8. #8
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    Yeah, I get that restaurants aren't particularly concerned that the kitchen staff are uncomfortable because, let's face it, the turnover is high in restaurants, so why should the owners care if the kitchen staff are uncomfortable? On top of that, cooks and chefs are used to this environment if they've been in the business for any length of time. Also, I get that they're not going to spend money on equipment and utility bills for an area of the building that customers couldn't care less about as long as their food is good. I'm sure, besides labor costs, that the utility bill is one of the highest expenses of owning a restaurant. On the other hand, I've done work in commercial fast food establishments where the kitchens aren't completely separated from the dining area and I can tell you that the kitchens in these establishments are as comfortable as the dining area. So, I don't believe uncomfortable commercial kitchens are necessarily the norm, but that's just a guess on my part.

    One of the factors contributing to the situation I'm facing is that I have to deal with the HVAC people in the Maintenance Department of the school district. The kitchen manager is constantly putting in work orders about the heat in the serving line area. FYI, the kitchen area and the serving line area are two separate areas. Actually, the kitchen area where most of the equipment is located is not the problem. It's the serving line area, particularly the fryer station and the pizza station where each has its own exhaust hood and make-up air. And, of course, all serving lines have hot wells, so the steamed heat coming off the hot wells contributes substantially to the conditions. Then, when you have a fryer and a pizza oven five feet behind where you're serving, you're getting heat from front and back.

    I tried getting the Maintenance Department to locate that AHU's temperature sensor for the serving area to an area that more accurately senses the temperature in the space, but they claim the problem is from the ventilation system, which falls on my shoulders. I'm a one man show, so I don't have the firepower to go up against the Maintenance Department and, quite frankly, they couldn't care less about the kitchens. It's like we're the red-headed step child in the school district. Before I open up a can of worms by going to my boss, who will then go to her boss (which is also the Director of the Maintenance Department's boss), I want to make sure I have all my ducks in a row. That's why I'm trying to find out how I can get this ventilation system where it needs to before I get drawn into a battle between my boss and the maintenance department, which I know is coming sooner rather than later.
    With your chrome heart shining in the sun, long may you run.

  9. #9
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    Is the make up outside the hood near the ceiling tiles ?

  10. #10
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    Quote Originally Posted by VTP99 View Post
    Is the make up outside the hood near the ceiling tiles ?
    The hoods sort of resemble this hood, except not quite as long. There's one over the fryer on one serving line and one over the pizza oven on another serving line, so they're each probably 12-15 feet long. The perforated panels on the face of the hood is where the make-up air exits. As you can guess, the air coming out doesn't exactly blow straight down, so it's not like a curtain of air. The air is more diffused and blows out at an angle away from the hood. The tables in front of the appliances are about where the serving lines are located, so imagine you're standing there with your back to the hood and there's 90+ degree, high humidity air blowing on your head and you have 6 to 8 hot wells in front of you, not to mention the radiant heat coming from each appliance.

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    With your chrome heart shining in the sun, long may you run.

  11. #11
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    Just because a kitchen design meets the requirements of the air movement codes doesn't mean the design is good. Not running the MAU'S doesn't mean the unconditioned air is no longer entering the building it just means it is entering from another source or most likely multiple sources. You are going to pay to condition it no matter where it comes in. Proper quantities of make-up air, properly located and directed make-up air diffusers many times diminishes how uncomfortable unconditioned make-up air is. The kitchen system should be tested and balanced by a certified TAB contractor before trying to take corrective action of any kind. Let them know the problems experienced and ask for suggestions.
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  12. #12
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    I've seen a lot of hoods but I have never seen one that looks like that. How is the air supplied into that ? Multiple ducts from the top ?

  13. #13
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    The vertical panels are the make-up panels. They are big to cut down the velocity. With proper supply and exhaust the results are usually acceptable.
    No man can be both ignorant and free.
    Thomas Jefferson

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