Hi, I am performing cooling load calculations for a general hospital.in one zone I rerquire 100% freshy air for TB clinics and other ares, like , clean utility, pharmacy,waiting and corridor to have normal 15% freash air. I sit possible to literally achieve this through one AHU.Thanks

No sir, you can not perform two(2) different AHU functions at the same time. For a hundred percent Fresh Air one, the equip should dedicated for that purpose only, because we are talking of 2 different environmental conditions that can not be establish by a single equipment.

With all due respect to r2g2rbm2004, I beg to disagree on his comment. You can always design an AHU as you needed. All you have to do is calculate enough fresh air intake to the AHU to handle your 100% fresh air zone (which in turn will be exhausted through exhaust fans) add the 15% fresh air for another zone and recirculate about 42% of your supply air. From there, add your heat load inside and calculate your AHU capacity. The ideal equipment for this set up though is a chilled water AHU.