Some HVAC thoughts from me for a change vs. building envelope chatter:

Reading your postings above, you want high quality filtration along with modulation ability for your HVAC. Seems chilled water might be a good selection for that, as you can set up one or two air handlers with high MERV or HEPA filters, and as long as all of your ducts are within conditioned space, run the blower continuously to get constant filtration of the air. Modulate chilled water flow so your coil is always cool to cold during cooling season, so it can control space temp and dehumidifiy. You won't have the potential freeze-up problems using chilled water vs. DX, and you won't have a wet coil dumping moisture into the space when the compressor cycles off, since you would still flow chilled water through the coil during the compressor off-cycle. The amount of chilled water itself can be modulated to control zone temp, as long as the coil stays cold enough to dehumidify. Fresh air can be ducted into the return side of your AHUs.