There is a HVAC tech who seems otherwise very good, tells me that a fresh air inlet duct would allow a lot of humidity into the house. I live in S.Texas and the climate is indeed hot and humid. The FA duct I imagine, would be probably 5-inch flex from the AC return plenum, to a pickup point under the eaves on the north side of the house. There would be a filter, a damper and I would expect airflow to be under 100 CFM when the AC is running full speed (possibly 2-stage system).
The counter argument that I have heard is: the extra humidity load will be less than you think, in most houses. That there *already* is a sizable infiltration and that is worse because of being unfiltered, untreated air. The argument says that having a FA inlet increases the pressure inside the house (or at least makes it suck less) and there will be a reduction in infiltration.
Certainly the FA inlet provides at least one pass thru the AC system to dehumidify. And it will be filtered whereas the infiltration air won't. Is there a common sense way to measure what's going on? Possibly to estimate the additional humidity load on the AC system?
And last, is there any literature which attempts to give answers? Something from Lstiburek would be ideal, or Florida's FSEC maybe.
Thanks very much -- Pstu