Natural Ventilation Applicability

[ajthvac]

I am trying to determine if the (NYS) mechanical code restricts the use of natural ventilation to certain occupancies (i.e. residences).

I recently took over (inherited) the design of a college dormitory. Individual dorm rooms were being ventilated via natural means. No problem there. However, various common areas, such as the TV lounge, computer lab and fitness area were also being ventilated via natural means.

Per the (NYS) mechanical code if a room has windows with an operable area of 4% of the total floor area then natural ventilation may be used. However, no mention is made of occupant density.

My concern is that high occupancy rooms will not be properly ventilated, especially in the winter when windows stay shut.

Any thoughts on this matter will be greatly appreciated.

 

[ChasBean1]

I agree with you. For many engineering applications, codes offer the bare minimum. I think it would be safer to mechanically ventilate. I'd say do the 15 cfm per person (or 30 cfm per bedroom, whichever it was). I'm pretty sure you need to pick a design criteria and not ride the fence, e.g., 2% open windows and 8 cfm per person. That just means you don't meet either.

Some systems I've seen dump make-up air into corridors (think about reheat if you want to dehumidify in the summer - inner corridors don't have any heat load). The corridor make-up systems rely on undercut doors and toilet exhaust in rooms to draw make-up air through. That might be a fairly easy & safe design strategy. Good luck! -CB

 

[MarauderX]

Very true about the lack of ventilation during the winter. I'm not sure what systems you are installing, but it sounds like convectors or other 4-pipe system with no ducted ventilation.

We usually supply corridors and common rooms with separate systems, even a small VAV air system, for ventilation. Depending on the the client and the comfort level, you might want to operate the system at minimum during the cooling season and full open during the heating season. Size a small cooling coil to bring the ventilation air down to 75 degrees (not 55) for the summer, and a pre-heating coil to provide 70 (instead of ~80) in the winter. Put the whole system on one larger VAV for more 1st cost and energy savings and use the rest of the system to handle the heating & cooling loads seperately.

I suppose according to code you would be fine with the operable windows for natural ventilation, but it may be a question for the client/architect to answer.