It is critical to differentiate between an ERV and a HRV (which this topic seems to be about). The former provides somewhere for excess moisture to go.

What %RH do you see in ERV ducts on a humid day?

An HRV can't cool the incoming air below it's dew-point practically speaking, and rare are the humidity events where the dew point is so dramatically higher than the conditioned space air that condensation can collect in the duct. Duct's are pretty crappy heat exchangers, after all.

Not saying that it can't happen, just that those events will be pretty rare in most US locations, at reasonable indoor temps. If you're air conditioning the place to 68F when the outdoor dew points are bumping on 80F, maybe you'd get some condensation going in the ducts, but where does that really happen? Even in swamps like Okeechobee FL outdoor dew points north of 75F are pretty short lived events, and most folks won't be setting the AC setpoint much lower than 75F.

If you are conditioning the interior (or more accurately, the air in the HRV ducts) to 75F in Orlando in August, you will have ~100% RH daily and weeks on end of > 80% humidity in the ducts. There I would worry about mold growing - if you used a HRV (which you shouldn't).

Posted By jonr on 24 Jun 2013 06:17 PM
If you are conditioning the interior (or more accurately, the air in the HRV ducts) to 75F in Orlando in August, you will have ~100% RH daily and weeks on end of > 80% humidity in the ducts. There I would worry about mold growing - if you used a HRV (which you shouldn't).

We do not have 100% humidity daily, the current humidity in Orlando is 58%, dew point is 74, It not going to be a whole lot different in August, I have been in Florida for 29 years, the humitity is high at night for short periods of time and during the day will burn off to about 55% by 10 AM and stay there for until about 8PM

As I said, "in the ducts" - not outside. My figures are based on 39 year averages (70-76F DP) from Weatherspark and are consistent with current conditions (74 DP). Your outdoor %RH values are irrelevant. But then so is HRV use in FL.