Some things to consider.
RH% rises dramatically when the air is cooled provided the absolute humidity remains unchanged. This chart will show you what I mean.
Air that is at 80.6 degrees at 50% RH (relative humidity) or 11.34 grams of H2O per KG of air
That same air cools to 69.8 degrees and now it's almost 75% RH.
Also, when ducting cool air through a warmer, humid area you will get condensation on the exposed cool surfaces of the ventilation system that you won't want dripping on plants or lights.
If the air outside can't help with cooling and has high absolute humidity then we can't really use it to vent our grow. In this case we must condition a "lung room" that the grow area can draw cooled / dehumidified air from. This air could be vented back into the lung room and recirculated, provided the air conditioning and or dehumidification can keep up. The air could also be vented outside. If you run a really sealed up, recirculating system then you need to make sure there is a supply of CO2. Either an occasional exchange of fresh air into the lung room or supplemental CO2 in either tank form or a CO2 generator running on natural gas or propane.
I hope all that helps you in your journey.