Commercial Kitchen Make up air Fan

[RareBugTX]

Hello guys.
My office designed a kitchen expansion where a new 12x4 type II hood was installed. It included a thru roof Exhaust fan and a Make up air unit. City came back with a few revisions. They want us to show air balance on schedule. I consulted with a mechanical engr and proposed to show a diagram where MUAF is suplying the actual hood (inside). To me this does not make sense. I have always shown supply diffuser in the vicinity of the hood and it has been approved and built. Could you provide your feedback?

Ps. Curious guys asking what is an SE dealing with a Kitchen exhaust systems. Please refrain. I dont have the answer. Hahah :0)

 

[Drazen]

there is special type of hood which receives much of air directly into hood, employing induction effect and therefore saving energy for ca 70% make-up air for the fact that you don't need to supply all make-up air via space, but only portion of air which satisfy ventilation requirements (which are almost always much lower than exhaust make-up requirements).

 

[317069]

Does the code in your area need you to provide a schedule air balance, if not then it seems a new guy in the city want to show himself in front of his boss,(look boss, I catch him)
You can either put a schedule on your drawing and save your time, or send him a letter asking about the code reference he is using, city job is to make sure that your work conforms to the code, not to evaluate your design or arrange your drawings.

 

[chicopee]

Your push-pull ventilation system is a terrific system and I wish more restaurants would install them. I would ask the inspector for a copy of the regulation concerning hood and exhaust fan system on which he(she) is basing their request for an air balance schedule. Note the letterhead to make sure that it bears the city's name and that document is signed. No signature and no letterhead may invalidate the inspector's request.

 

[willard3]

Why are you paying an HVAC guy if you don't want his advice?

 

[chicopee]

For an air balance schedule, it is no big deal with your push-pull system. Provide the drawing with its fan specifications, duct specifications, CFM specifications and test results of CFM's at both inlet and outlet above cooking appliances. You may also need to show the automatic fire extinguishing system specs if such system is in the plan. If the ME that you consulted is a PE better yet.

 

[dbill74]

An air balance schedule is easy enough to put together. Simply list all sources of outside air and exhaust air, sum them and show the difference. It's not worth fighting the official over; it'd be worth asking for the requirement for future reference.

It sounds as though a registered mechanical P.E. did not design the system, so city is simply trying to verify the new expansion hasn't thrown off the building's overall balance and more importantly relative pressurization to the outdoors.
It's been awhile since I've designed or worked with a kitchen hood that includes exhaust and make-up air, but I seem to recall the exhaust air being greater than the make-up air (~10%). The reason for this would be to ensure that hood is always exhausting grease laden air instead of pushing that air into the kitchen (bad for people's heatlh). This becomes important to the overall building's pressure (balance) because if the hood exhaust is greater than all other sources of outside air, the building will go 'negative'. This is bad because 1) exterior doors can become "heavy" and hard to open (possibly hindering building egress if the doors swing outward); 2) a positively pressurized building keeps mold causing humidity out. Note that too much positive pressure can be bad too causing unwanted stress on the structure (think balloon), outward swinging exterior doors may not close or whistle.