Ventilation issues on cooling load calculations

[ADAG]

I am working on the design of a Constant volume, DX a/c system (cooling only)for a Government Office. For the cooling load calculation I am including a ventilation load of 15 CFM/person in occupied office areas. Now in this same building I also have a cafeteria room, to be used only by the office staff (around 20 people). If I now again include a ventilation load of 15 CFM/person for these same people when in the cafeteria, I will be doubling the required ventilation air and introducing double the air I actually need (and oversizing my equipment). If I don’t, I will run short on the supply air for the cafeteria. What is the criteria to follow? Perhaps the best would be to have an independent system for the cafeteria, but what if this is not possible?

Another issue on ventilation: Considering the local construction standards I know I will be having some infiltration, this however is hardly quantifiable. Should I reduce my system ventilation requirements (i.e. 15CFM/person to 10 CFM person) to compensate for the infiltration ventilation?

Thank you,

 

[williamsGA]

You need follow the ASHREA 62 guidelines. It is no longer as simple as 15 cfm/person. You will need to take into account the airflow percentage that is delivered to each space, and what portion of that is OA. Since it is a constant volume system this is an easy calculation. Also, ASHREA 62 now requires OA for space contaminates, this is a OA/sf number, and OA occupants.