A typical commercial kitchen has a large makeup air unit that provides air to a hood over the cooking surfaces, several exhaust fans, and (in our case) a large central cooling-only 0% OA AHU that provides cool air to the space.
I am puzzling over how to shoehorn this situation into the 62MZcalc spreadsheet.
Let's say I have 100% OA supply air at the hood of 1700 CFM, exhaust air at the hood of 2100 CFM. You can do the math and see 400 CFM of this exhaust air comes from "somewhere else" (Transfer air?). I am not sure how one handles transfer air in the 62MZcalc spreadsheet. Some fraction of the 1700 CFM hood supply air ends up in the kitchen, most of it gets swept up with the exhaust. 100% OA supply air is delivered at essentially room temperature, but right near the exhaust, so 100% Ez would not be appropriate.
What would you use for Ez zone air distribution effectivess? Would Supply air be "1700 CFM 100% outside air" in this case?
Would it be appropriate to use an Ez of 0.5, for "supply air near exhaust", counting the kitchen hood supply as the fresh air?
Aaron Dahlstrom
In Posse, LLC4 thumbs up
October 28, 2014 - 6:40 am
Lawrence -
I've puzzled over the same thing before.
First, if the zones served are entirely commercial kitchen zones, my reading of ASHRAE 62.1 indicates the zones are only required to be exhausted, not supplied with outdoor air. I believe compliance with ASHRAE 62.1 is through satisfying the required amount of exhaust air (and making up the air per section 5), not by supplying a specific amount of outdoor air.
If there are non-commercial kitchen zones in the space (eg a managers office, active occupiable storage, etc), these would require their own source of outdoor air.
A second point - we have seen issues shoehorning 100% OA systems into the 62MZ calculator. The calculator is generally for systems that have some recirculated air; if the systems are 100% OA, then they may be documented either in the Appendices of the LEED EQp1 template (generally at the bottom, if the "100% OA" checkbox is selected) or in a custom spreadsheet. While it may seem counter-intuitive, in some cases we've seen the required amount of outdoor air increase when zones were first documented in the 62MZ calculator and then moved to a 100% OA calculator later. I believe this is because the MZ calculator uses equations that do not treat zone air distribution effectiveness in the same way as it is treated in the 100% OA system equations from 62.1.
Lawrence Lile
Chief EngineerLile Engineering, LLC
76 thumbs up
October 29, 2014 - 1:27 pm
Thanks, Aaron. I can find an entry for kitchens in Table 6-4 requiring exhaust, no entry for commercial kitchens (and other items from 6-4) in Table 6-1 requiring fresh air. It makes sense that exhaust would be the only requirement, but I haven't found a paragraph in the standard that just comes right out and says this. Maybe a sharper eye than mine can find it?
The closest I can find is paragraph 6.2.8 "... exhaust makeup air can be any combination of outdoor air, transfer air or recirculated air."
Aaron Dahlstrom
In Posse, LLC4 thumbs up
October 29, 2014 - 5:09 pm
Yeah - I doubt the standard will have conclusive language that indicates "this and such space type does not require ventilation" - seems like it will be up to our interpretations of what the standard does say.
If you're looking at the 2007 version of the standard, I've relied on the language in section 5.10.2 to find the requirement that there be enough makeup provided to offset the exhaust, under certain conditions - "for a building, the design minimum outdoor air intake shall be greater than the design maximum exhaust airflow when the mechanical air-conditioning systems are dehumidifying."