Enthalpy control in humidification tends to prioritize which air stream?

• A. It favors air streams with lower enthalpy, even if they are warmer.
• B. It favors higher enthalpy air streams.
• C. It has no effect on humidity control.
• D. It completely eliminates the need for ventilation.

Answer: (A)

When humidification is controlled by enthalpy, the goal is to bring the air to a target total heat content (enthalpy) efficiently. Adding moisture increases enthalpy mainly through latent heat, with less impact on the sensible temperature. Therefore it’s most effective to treat the air stream that already has lower enthalpy (drier air), even if that stream happens to be warmer. Humidifying this drier, lower-enthalpy air raises its enthalpy toward the setpoint using moisture addition rather than large sensible heating or cooling, which saves energy and gives better humidity control. Targeting a higher-enthalpy stream would be less efficient, since adding moisture to already higher-energy air yields smaller changes in humidity ratio and can push conditions away from the desired balance. Ventilation requirements are a separate consideration and aren’t determined by this control principle.