Occupancy Doubt

For the EBOM rating system, you are supposed to use "the maximum number of people expected to occupy the zone during typical usage." Here's what the LEED Tips for EBOM 2009 says: "Remember that all values of occupancy used to define minimum outside airflow requirements must be based on the maximum occupancy expected during normal facility operation and not on design occupancy, minimum occupancy, or unusual or emergency conditions. According to the Reduced Occupancy Guidance for LEED for Existing Buildings, the default values for occupancy listed in ASHRAE standard 62.1-2007 should be used only for completely vacant spaces." This means that you should consider "normal" building usage and use an occupancy value that would be considered maximum during actual "normal" or "typical" conditions. That's not an average, but it's also not the absolute peak that might occur during an extraordinary circumstance. If this occupancy level causes an issue for you, you could look at averaging techniques from Section 6.2.6.2 of ASHRAE 62.1-2007. The reference guide does say you can use those averaging techniques if the expected number of occupants fluctuates. That probably wouldn't help much though, as that kind of averaging makes more difference for spaces like lobbies with high ceilings and peak occupancies that may last only 15 minutes, than for a classroom with a normal height ceiling where the peak occupancy is closer to an hour or so. The time "T" over which you can average the occupancy is obtained from the equation, T=3v/Vbz, where T=averaging time in minutes v=volume of the zone in cubic feet Vbz=the breathing zone outdoor airflow calculated for the typical maximum people OA rate plus the area OA rate For example, for a 900 square foot classroom with a 9 foot high ceiling and a typical maximum of 30 occupants: v = 900 sf x 9 ft = 8,100 cubic feet Vbz = (10 cfm/person x 30 people) + (0.12 cfm/sf x 900 sf) = 408 T = 3v/Vbz = 60 minutes (which does you no good if typical classes are 1 hour or longer) For EBOM, you should be basing your calculations on a performance period that occurs over a time period during which the building is occupied. This means that you or the building owner or tenant should be able to observe the classrooms during actual usage to determine what the "typical" maximum occupancies are.