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NC-2009 IEQp1:Minimum IAQ Performance

OA calculation

Hi, I just received the feedback from reviewer. We have AHU to supply 100% OA to the space and FCUs for secondary recirculation. Reviewer said: "The design system primary supply air flow volume (Vps) don't match the supply air flow of AHU in equipment schedule. + Calculation must be performed at the worst-case condition when VAV system is at minimum flow." I'm try to figure out where is the error in my calc. I'm checking Vdzd, Ds, Vpz, Vps. For example, Vdzd = 1,400 (OA /SA by AHU) + 10,000 (recirculated by FCU) = 11,400 cfm. How can I adjust (Ds). I had set Ds = 100% beforehand. I think that had made supply airflow by AHU was much larger than that in equipment schedule. And I just check that Vdzd * Ds = Vpz (supply airflow by AHU) = 1,400 cfm. So is it correct that I adjust Ds = 1,400/11,400 = 12%

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Tue, 06/16/2015 - 16:09

I think the error is in "Vdzd". You should enter here the total air supplied by all the FCU located in the space. This number must match that showed in the mechanical schedule. You shouldn't add OA, since it is already mixed in the FCU. "Ds" is ok in 100%. You can lower this percentage in case you now that all spaces cannot be fully occupied at the same time, for instance: workers can be either at the cafeteria or at their workstation, but they cannot be at both places at the same time (as long as string theory is not proven right).

Fri, 07/17/2015 - 02:55

Hi Gustavo, Thank you very much for your advice, I checked the VRP on Leedonline form, so Vps of AHU in LEEDonline form = summary of "Vdzd" which is total air supplied by all FCU according to you. So Vps in the form is not SA of AHU in equipment schedule, but it is the total supplied air of All FCUs related to this AHU. Do you think the reviewer made a mistake when asking me to match Vps in calculation and SA of AHUs in equipment schedule?

Fri, 07/17/2015 - 18:08

Hi Hieu, In my first message you asked about "Ds" and I wrongly told you the definition for other concept: "D" Diversity. Sorry about that". "Ds" is defined in the calculator's first tab. In some cases SA can match and Vps but I think that your best option is to contact the review team and ask them for some advise. They will be happy to assist you.

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