I am working my way through ACCA's latest manual LLH (Low Load Homes). The postulate of continuous fan increases indoor humidity in the cooling season arises in Section 8. This principle has been shouted from the roof tops of many building science venues for years. And up until this point, I have embraced that Kool-Aid with the masses.
The subject matter is discussed in an Allison Bailes article found here from 2012. https://www.energyvanguard.com/blog/76674/This-Thermostat-Setting-Can-Cost-You-Money-and-Make-You-Sick
Apparently, I am a slow learner. Because, as I think about the physics, it isn't intuitive to me. Perhaps someone can clarify it, possibly Dr Bailes.
Assume a heat pump air handler with duct system that is entirely in the conditioned space. Cooling is energized. Coil gets cold and falls below dew point of the return inlet air. Humidity in the air changes from vapor to liquid. Condensation flows down the fins of the coil into the drain pan and hopefully is drained out of the unit to the exterior. Compressor shuts off, leaving X amount of liquid water on the coil.
This is where I stumble. If the blower shuts off with the compressor, the condensation resident on the coil just sits there and eventually evaporates or dries to the ambient air in the air handler. And since the duct work is connected to the conditioned space (technically just another unspecified room of the house), that evaporated moisture eventually becomes part of the air in the living space. Hence it will elevate the indoor RH.
Second scenario is the blower runs continuously, which does have a lot of desirable benefits. The air dries the coil quicker. Consequently, you might see a spike in the indoor humidity levels.
But in the end, I don't see the difference. One introduces additional humidity over time. The other in less time.
One possible difference is the unit energizes before the coil gets completely dry. That would tend to imply the coil stay predominately wet and there is a consistent reservoir of condensation that simply stays put much like a hydrophilic buffer. Even if this is so, it needs to stop to inhibit microbiological and biofilm production.
Any comments to straighten me out????