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[EnergyPlus_Support] Re: zone air humidity ratio

The radiant system can only combat sensible load. 

The total load from people is very roughly 50% latent 50% sensible (depending on humidity, temperature and room airflow velocity, these percentages change).

As the radiant system typically requires less air change, the small supply air volume must be dryer to combat the same latent part of the load.

The in room air velocities decrease for the radiant system, but this is not calculated by energy plus. the in room air velocities are fixed user inputs. Increased air velocities will also effect to dry out the skin more and I think also is in the calculation determining how much moisture the person puts into the room.

The air may "feel" dryer for a air only system, but this is due to in room air velocities.

A good reference for this is ASHRAE standard 55, which shows different graphs that demonstrate the effect of velocity, temp and humidity on comfort.



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