Mass balance in humidification analysis helps ensure which of the following?

• A. The moisture gained by the air equals the moisture removed by the air, accounting for stored moisture.
• B. The air temperature never changes.
• C. The outdoor humidity is irrelevant.
• D. The humidity setpoint is never exceeded.

Answer: (A)

Mass balance in humidification analysis is about conserving moisture in the space. The idea is that the moisture entering the space (via supply air and any indoor sources) must be matched by the moisture leaving the space (via exhaust and return air) plus any change in stored moisture in the space (in walls, furnishings, and other materials). In steady operation with no net storage, the moisture gained by the air equals the moisture removed by the air. This principle underpins how we assess and control humidity, ensuring the latent load and ventilation exchanges are balanced.

Outdoor humidity and temperature effects matter because outdoor air brings in water vapor, affecting how much must be added or removed. The goal isn’t that temperature or setpoints are guaranteed never to be exceeded by the mass balance alone; rather, the mass balance ensures moisture flows are accounted for, including any storage changes, so humidity control can be properly managed.