Is Make up Air required in a kitchen

[emalsyd]

A local boys & girls club is installing a small kitchen area. They are adding a 6 burner stovetop and a 4'x4' hood above. Exhaust is 1125 cfm. Is a MUA unit required or can they take in transfer air from the adjoining 4000sq ft activities room. The activities room is served by a rooftop unit which is bringing in enough outside air to handle the fresh air requirements in the activities room.

From what they are saying, the kitchen will be used sporadically.

 

[ME27272727]

It's good practice and usually code required to provide makeup air for kitchen hoods. 2015 IMC section 505.2 requires makeup air on systems greater than 400 CFM.

 

[dbill74]

It is permissible to rely on air from the activities room as make-up for the kitchen hood.

What you need to be wary of is the overall building pressurization. You will need to review all source of outside air and exhaust air; you may need to adjust the control strategies of the other systems in the building.

The simplest, easiest strategy though is to provide a make-up air fan for the hood. Provided the make-up air is introduced at the face of the hood, anything more than a filter usually isn't required as it will be pulled right into the hood before it has the chance to mix with the rest of the air in the kitchen.

 

[SAK9]

Dbill74

Is this valid when outside air temperature is at extremes like 1C or 45C?

The kitchen hood has to draw 100% of the air over the cook tops to contain odors and extract suspended grease particles in the air.This means that the replacement air needs to come in at about or slightly above cook top level.The replacement air will be brushing past the cook.So should not the replacement air be at or about room temperature?If the replacement air is too cold it is quite likely that the cooking vapors can condense at the hood filter and fall back onto the cook top.

 

[dbill74]

SAK9,
Note that I said "usually". It would depend on the specific application and the percentage of MUA you are using. For a large commercial kitchen in locations where you experience those extremes for long periods, tempering the MUA would make sense. Consider also when those temperatures occur and will the hood be in operation during those times.

Most of my experience with kitchen hoods is for smaller hoods for something like Applebee's, or Chile's in southeast USA. For these applications where the MUA has been about 80% hood exhaust, we've gotten by without tempering the MUA. Going on memory, I'd say average hood exhaust was in the 2,000-4,000 CFM range.

I would consider it good practice to have MUA not more than 80-85% hood EA. This ensures that air flow around the hood is into the hood and as the MUA mixes with room air, also it will be tempered some, so you won't blast the cook with 1°C or 45°C air. Consider also some model hoods have MUA on the outside of the curtain while others have it on the inside.

If you're worried about the cook's comfort, you can reduce the amount of MUA and increase the amount of room temperature that is mixing with MUA to make the cook more comfortable. Just remember doing this will require more OA entering the building through AHUs and DOAS units which will need to be of larger capacities. As engineers, it is our job to find the right balance between economics and performance.

With regards to your concern about steam condensing and falling back to the cooking surface, I'm having a hard time seeing that happen. First, the cook top(s) is gong to be heating the MUA. Second, the hood itself is going to pulling steam vapor out as well. If you or anyone else has actually experienced "rain" under a hood, I would love to hear about.