Our project is an office building with 300 regular occupants. One zone/occupancy category of the building is a multi-purpose room. This room is rarely used - only if there are gatherings or occasions. Also, adjacent rooms are cafeteria, fitness room, game room (rooms that occupants are considered transients). And the people that will occupy those spaces will be the same regular occupants of the building, and will definitely not occupy all those spaces simultaneously. How do we account for the population diversity on the required calculation to verify compliance given that for a whole month operation, this space only used twice or thrice and only for three to four hours?
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Andrew Mitchell, P.E.
PrincipalMitchell Gulledge Engineering, Inc.
LEEDuser Expert
126 thumbs up
December 18, 2012 - 5:48 pm
Mary Ann, I think you bring up an excellent point that illustrates the difference between the design ventilation flow required to be available as calculated by ASHRAE 62.1 and how to design a ventilation system to maximize energy efficiency. In short, the ventilation system must be designed such that it can deliver the ASHRAE recommended ventilation when the building is at its peak. The diversity of the building occupants allows you to take credit for the fact that, although the sum room occupants may be one number, the actual building occupants will probably never be that high.
The example I use with other engineers in my office is that if you had a simple office building with 10 offices and a 10 person conference room where no outside visitors were coming in, the diversity would be 50%. You must still calculate each room at maximum occupancy so you will end up with a total occupant number of 20. Since it's only designed to have 10 people 10/20=50%. The other rule that I use when doing a LEED calculation is that I always make sure the number of occupants after diversity is within 10% of the FTE for the project.
As for, the design element, you must make available the full ventilation flow. However, the full flow does not always need to be delivered. That is why we are allowed to utilize demand controlled ventilation in order to turn down the OA and save energy. Let me know if that helps or if you have a more specific question. Thanks.