Hello everybody We are working on a CI 2009 Office project with dedicated Fan Coil Units for each space. The FCU are located above the ceiling (inside the plenum). FCU take the necessary air from the Plenum which works as a "Mixing Chamber" combining return and outside air. Since all the FCU per floor take the same ventilation air from the plenum: ¿could we treat it as a Multiple-Zone system by adding up FCU rated CFMs in order to calculate the minimum OA rate that should be provided to the plenum? or ¿shall we comply with 62.1-2007/5.2.2 (which basically would be covered taking the required OA rate (Voz) near each FCU using additional ductwork) and calculate Voz for each space independently (Single-Zone)? Thanks

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Julia Weatherby

President

Weatherby Design & Co. Engineers

LEEDuser Basic Member

67 thumbs up

Mon, 07/29/2013 - 22:21

It sounds like a multiple zone recirculating system to me. You may need to use some judgement as to how much of the air for each zone is "locally recirculated" versus being air that is approximately equivalent to the average return air condition. In practicality, there are often obstructions such as partitions or structural beams in the ceiling plenum that keep the outdoor air from fully mixing with all the return air in the plenum.

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