Residential kitchens - continuous exhaust

[WinniPEng]

Hello,
I'm working on a design for a multi-storey apartment building. Each suite's kitchen will have a residential-style range hood over the stove-top, each one containing a washable grease filter, and the hood will recirculate the air back into the kitchen. ASHRAE requires that each kitchen have some exhaust to outdoors, and this will be met with a vertical exhaust plenum for each 'stack' of suites from floor to floor, with an exhaust branch duct on each floor that will draw 25 cfm from every kitchen. The top of the plenum will terminate with an exhaust fan on the roof, which will operate continuously. My question is: does each of these 25 cfm exhaust grilles need to have a grease filter installed on it, if the range hood already has one? (Note, I realize it makes sense to have it from a practical point of view, but I need to know if code requires it. Location of the project is in Manitoba, Canada)
Thanks!

 

[Drazen]

You appear to need very specific answer, so my generalisation may not satisfy you.

None of grease filters that I know can provide anything similar to ideal filtering, morever they show different results with different fan speeds (face velocity is mostly crucial for good separation), so code would hardly prescribe what is not controllable.

There can be code requirement for mandatory approachability for regular cleaning.

25 cfm seems to me as very large quantity for continious exhaust, especially when the fact is that kitchen is not used continiously, that will "kill" your energy efficiency, especially in (assumable) cold Canada.

Recirculating kitchen hoods are worst thing in HVAC industry I know about, and I allways ask for written client's instruction to specify them, enraged users are common related to them.

 

[GMcD]

Here's an idea. Read the Manitoba Provincial Building Code and see what it says. If it is silent or vague, check with the local Building Inspector to see what they normally find acceptable. Typically you need the constant air exhaust to ventilate the suites - both the National Building Code of Canada, as well as the Provincial Building Codes will require dedicated suite ventilation to maintain a minimum air change rate (typically from 0.33 to 0.5 ACH).

Your central exhaust fan on the roof wouldn't necessarily need any grease filter, since the exhaust air will be so diluted, and the amount of aerosol grease will be minimal. While the recirculating range hoods may be acceptable to Code, it's best practice to duct the range exhaust out of the suite/building for odour control.

 

[IRstuff]

Frankly, exhausting ANY amount of the flow back into the kitchen is a horrid idea. It dumps oil back into the kitchen, leaving a messy residue on all the walls and floors, and completely defeats the concept of exhausting the cooking smells

TTFN

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[WinniPEng]

Thank you for the quick responses to the question.
For further clarification: there is a section of the building code (Part 9) that deals exclusively with housing and small commercial buildings. This section contains a requirement for a grease filter on any exhaust intake that is within 3 meters of a stove-top. Since this project is larger, this section is not applicable and so this provision need not be followed (in my mind). However, the authourity having jurisdiction will sometimes enforce a "good engineering practice" clause (as they should) that is applicable in all cases. My concern is that they could use the fact that the 3 m restirction is noted in Part 9, and conclude that this constitutes "good engineering practice" and apply this requirement to every suite in the building in question.

Notwithstanding the above, I seemed to recall reading in some other code or standard that this restirction was four feet, rather than 3 meters. I just can't recall which code or standard this was. Does anyone else recall reading this somewhere?

As for the recriculating hoods, the consensus seems to be that they do more harm than good. The code does not require a hood over the stove-top - would I be better to delete the hood altogether, and just leave the continuous 25 cfm exhaust intake (located at ceiling level, close to the stove, and furnished with a grease filter)?

 

[Drazen]

If you have enough room for vertical exhaust plenem, can you use that space to design separate exhasut stacks for each kitchen hood, that is best solution overally in my opinion?!

Individual stack should not be smaller than 5".