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NC-2009 IEQp1:Minimum IAQ Performance

100% OA System or Multiple Zone Recirculating System?

Our project is an office building for 60 FTE. It has just one air handler which supplies 100% outdoor air to 2 big working spaces (1st floor & 2nd floor). Besides the main working space, each floor has 3 closed individual offices. Each of this offices have an exhaust fan pulling air outside the building and receiving fresh air that comes from the adjacent main working space through air vents. When going through Ashrae 62.1 , section 6, we are not sure if our project should be treated as "100% Outdoor Air System" (6.2.4) or "Multiple-Zone Recirculating System" (6.2.5). It seems to us that the definition of 6.2.5 "Multiple-Zone Recirculating System" stands for an air economizer, which is definitely not our case. Which system fits our project, 6.2.4 or 6.2.5? Thanks in advance for your help.

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Mon, 01/28/2013 - 20:22

Hi Gaston, you would most certainly use the 100% OA system if you have no return air. That being said, the enclosed offices cannot be ventilated with transfer air from another space. I have never heard of an office building with one pass air though. That sounds very inefficient. What type of climate zone is your project located in?

Mon, 01/28/2013 - 23:32

Thanks for your quick reply Andrew. Our climate zone is the Monterrey Bay Area, CA, which is a very mild climate. I have just realized that the offices will have operable windows, so now that I see, they will be naturally ventilated, I apologize for not telling you this before. The exhaust fan is intended for pulling out the hot air. Another question, the naturally ventilated offices don't have to be taken into consideration when calculating Vot right?

Tue, 01/29/2013 - 19:37

No, they do not. You will have to fill out the LEED template for both mechanically and naturally ventilated spaces.

Wed, 01/30/2013 - 05:12

Thanks Andrew. Let me ask you another question that comes to me when making the zoning division in the floor plans. I have 3 similar closed offices adjacent one to each other, all of them fully natural ventilated, can I consider the 3 of them as a whole Zone or shall I consider each office as a different Zone? And regarding hallways, corridors and circulations, are they considered as occupied spaces? shall they be included in calculations as independent zones? Thanks in advance for your help!

Fri, 02/01/2013 - 22:01

Each office should be input as a separate zone unless it has unobstructed permanent openings to other naturally ventilated areas. As for corridors, they are occupied and do require ventilation. I usually include them as independent zones since they have a different space type requirement from most other zones.

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