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Negative air pressure in commercial kitchen

klarenbeek

Silver Member
Joined
Jan 28, 2010
Messages
217
Location
Sioux Falls, SD
Insufficient or no makeup air can cause a lot more problems than that. The hood system will pull from wherever it can get it, including out of the sewer system right through the traps. We had one restaurant built several years back where decades ago there was an old landfill. The makeup air unit was 3 phase and didn't get wired right so the blower spun backwards not supplying any makeup air. When they first started the hoods, the exhaust pulled methane right out of the ground. Fortunately it was discovered very quickly .
 

Bryant

Registered User
Joined
Dec 19, 2018
Messages
79
Location
Virginia
I am not an expert by any stretch and it is difficult at best to apply all of the systems within systems concerning the totality of mechanical systems without a basic practical engineering point of view IMHO. That being said, I think the mechanical code (chapter 4 & 5) really is about checking of minimum numbers as they apply to ventilation/exhaust air or perhaps better stated, ventilation & exhaust systems functionality, nothing to do with human comfort.
Human comfort in a kitchen really gets blown away by all the exchange rates that intermingle with the kitchen exhaust system(s) IMO.
From a conservation approach (IECC), the intent IMO, is to abandon the energy sucking circuit venting of commercial hoods which cause all kinds of imbalances to the positive or negative pressure differences by having equipment running 24/7 without direct control intervention. Remember positive or negative pressure is atmospheric pressure. In the case of hoods being slightly negative, the idea is to keep the air in the room, hence not smelling your steak cooking a 100 feet away from the kitchen, is an improper design. The opposite, positive pressure, think hospital room keeping unwanted air out.
Coming back to the logic of providing the make up air to the kitchen hood from other spaces (RTU's. HVAC, MAU's, etc.) is not a bad idea, slightly negative at the hood(s). The energy savings are enormous versa all of that human comfort air being sucked out by the exhaust with excessive negative pressure.
But it is always a challenge capturing the exact CFM's required (the total rate of ventilation air) when unknowns exist without confirmed compliance with the air barrier requirements for exfiltration/infiltration accounted for, hence the requirements to meet the leakage rates.
The reason for opining, is from a project I am reviewing with under floor supply plenums. OMAU's, RTU's & kitchen hoods and not accounting for types of exhaust fans. i.e. bathroom, IT closets & etc..
Speaking off numbers game. Does anyone know of a site that provides some free training on mechanical systems, that kind of explains the madness. The code and commentary only go so far in knowledge....
Thanks
Bryant
 

cda

Sawhorse 123
Joined
Oct 19, 2009
Messages
18,861
Location
Basement
I am not an expert by any stretch and it is difficult at best to apply all of the systems within systems concerning the totality of mechanical systems without a basic practical engineering point of view IMHO. That being said, I think the mechanical code (chapter 4 & 5) really is about checking of minimum numbers as they apply to ventilation/exhaust air or perhaps better stated, ventilation & exhaust systems functionality, nothing to do with human comfort.
Human comfort in a kitchen really gets blown away by all the exchange rates that intermingle with the kitchen exhaust system(s) IMO.
From a conservation approach (IECC), the intent IMO, is to abandon the energy sucking circuit venting of commercial hoods which cause all kinds of imbalances to the positive or negative pressure differences by having equipment running 24/7 without direct control intervention. Remember positive or negative pressure is atmospheric pressure. In the case of hoods being slightly negative, the idea is to keep the air in the room, hence not smelling your steak cooking a 100 feet away from the kitchen, is an improper design. The opposite, positive pressure, think hospital room keeping unwanted air out.
Coming back to the logic of providing the make up air to the kitchen hood from other spaces (RTU's. HVAC, MAU's, etc.) is not a bad idea, slightly negative at the hood(s). The energy savings are enormous versa all of that human comfort air being sucked out by the exhaust with excessive negative pressure.
But it is always a challenge capturing the exact CFM's required (the total rate of ventilation air) when unknowns exist without confirmed compliance with the air barrier requirements for exfiltration/infiltration accounted for, hence the requirements to meet the leakage rates.
The reason for opining, is from a project I am reviewing with under floor supply plenums. OMAU's, RTU's & kitchen hoods and not accounting for types of exhaust fans. i.e. bathroom, IT closets & etc..
Speaking off numbers game. Does anyone know of a site that provides some free training on mechanical systems, that kind of explains the madness. The code and commentary only go so far in knowledge....
Thanks
Bryant



you might look thru this site and see if you find a class, book or help


 

Sifu

Gold Member
Joined
Sep 3, 2011
Messages
1,378
Check with Captiveaire. While they may have a proprietary agenda, the do offer classes, usually in association with local code chapters or jurisdictions. And if you can get past the self-promotion, they are very good and informative classes.
 
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