The typical moisture load from ventilation air calculations is based on what?

• A. The difference in humidity between indoor and outdoor air.
• B. Indoor air temperature alone.
• C. Outdoor ventilation rate only.
• D. Occupant density.

Answer: (A)

Moisture load from ventilation is driven by the moisture content the incoming air brings into the space. Specifically, it depends on the difference in humidity (humidity ratio) between outdoor air and indoor air. If the outdoor air is more humid than the indoor air, bringing that air in adds moisture to the space; if it’s drier, it can remove moisture. This humidity difference, multiplied by how much ventilation air is supplied, sets the latent moisture load.

That's why the best answer is the difference in humidity between indoor and outdoor air. Indoor air temperature alone doesn’t tell you how much moisture it contains. Outdoor ventilation rate matters for how much air is exchanged, but without the moisture content comparison, you can’t determine the latent load. Occupant density relates to internal moisture generation, not the moisture carried by the incoming ventilation air.