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
Dylan Connelly
Mechanical EngineerIntegral Group
LEEDuser Expert
472 thumbs up
July 21, 2013 - 12:56 pm
Esteban,
It sounds like you have a system that provides outside air into a ceiling plenum. That type of outside delivery system is no longer satisfactory in the codes I deal with. You have to either directly duct outside air to each FCU or duct to within 5 feet of the FCU's return air intake. The reason is that the FCUs closest to the outside air supply will take the most of the outside air and the FCUs furthest away will get the most diluted outside air.
However, since this is CI. You could probably be grandfathered in by going with option 2. You don't comply with the ASHRAE standards, but the outside air system can still provide at least 10 CFM/person of outside into the ceiling plenum.