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NC-2009 IEQp1:Minimum IAQ Performance

Minimum Indoor Air Quality Performance Calculation

My Project is Having one FAHU on roof which is supplying treated Fresh air to all AHU"s, which further supplying the mixture of outdoor air and Recirculated air to various zone via VAV (no reheating, no recirculating fan) unit and this air (-Extract) is returning back to same AHU after serving to room load, so what should be my zone secondary recirculation fraction and what would be my zone primary air flow whether it would be same as zone discharge air flow or I need to consider the primary air flow value as (0.3*Vdz) if my minimum VAV flow setpoint is 30%. In calculator Vpz is mentioned as lowest primary airflow value expected at the designed condition, What is mean by these?

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Fri, 07/07/2017 - 09:50

You should model each system separately. If the FAHU is only supplying air, it should not be modeled since it effectively is not different than just ducting to the outdoors. If you are not doing any induction or local recirculation other than the system that is receiving fresh air, your zone primary airflow fraction should be 1.0 (same as discharge flow rate).

Tue, 07/11/2017 - 13:40

I Appreciate your response and I agree that if there is no other secondary recirculation or Induction in the zone than Vdz i:e zone discharge air flow should be same as Vpz zone primary air flow which leads to Ep=1 and Er=0 for No Sec Recirculation. But in Leed v2009v4 Calculator at Zone Secondary Recirculation Fraction (Er) Table on the Instruction page it is mentioned that Er=1 only if "Systems with system level recirculation (eg: Dual Fan-Dual Duct systems with ducted return)" is it same as my system? where recirculation is only through AHU. In one of my project, I got a comment from Usgbc where I considered Primary air flow fraction Ep=1 "For VAV system, It appears that the Calculations may not have been performed for the worst-case conditions.For this project, worst -case conditions are under minimal cooling load conditions when the VAV systems are at minimum flow" How to calculate this worst case in LEED v2009v4 Calculator? or shall I need to submit a separate calculation by mentioning the Fresh air supply in case of minimum VAV position and complying with ASHRAE Minimum "Area Fresh Air Requirement"

Wed, 07/12/2017 - 18:00

Hi Amal, Ep is calculated automatically after entering Vdz and Vpz. For systems with VAV boxes, you should enter the maximum airflow of the VAV box in the column Vdz. Vpz is for the minimum airflow of the box.

Thu, 07/13/2017 - 12:09

Thanks for Response Mr. Gustavo , But if I am using Vdz (Max Flow of VAV) and Vpz as (Minimum Flow of VAV) in LEED calculator this is generating a very low overall ventilation efficiency in the range of 0.17 t0 0.2 which resulting a very high fresh air demand around 4 times of Vbz (Breathing zone Air flow requirement) and also this contradicts with the response made by Mr. Andrew Mitchell above as "If you are not doing any induction or local recirculation other than the system that is receiving fresh air, your zone primary air-flow fraction should be 1.0 (same as discharge flow rate)". As per the LEED requirement, we need to supply minimum fresh air (0.06 cfm/sqft) to area in case of minimum VAV position and (0.06 cfm/sq.ft + 5cfm/occupancy) in case of VAV in Maximum position. But this checking criterion is not available in calculator if you study the calculator broadly.

Sun, 02/18/2018 - 07:30

hi Amal any luck with that ?
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Devendra Chaughule
Senior Manager - Sustainable Services
Surmount
LEEDuser Basic Member
29 thumbs up

Thu, 08/11/2022 - 02:26

Hi Amal, How u have addressed the above comment of the reviewer? 
Thanks Devendra C.
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Andrey Kuznetsov
ESG consultant, LEED AP BD+C
Self Employed
LEEDuser Basic Member
36 thumbs up

Sat, 04/29/2023 - 20:16

I suppose it was made via some coefficients that reduce/increase demand of fresh air. 

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