Moisture content of cool air at supply air diffuser in room! 1

[Hasni2]

Is it true that the moisture content of the air when it enters the conditioned room via supply air diffuser would be around 90%. I have designed the room at 50% RH but am bit confused after one of my college insiste that when cool air leaves the cooling coil of the AHU, it has 100% moisture content and by the time it reaches the room after travelling through the length of the duct, moisture content would remain around 90%. Something hard for me to agree. Please share your experience. Thanks

 

[sprinkler1000]

There will be no condensation if the design setting is 75 ºF 50% RH. Anyhow the supply duct should be insulated no matter what.

 

[Hasni2]

Must say this thread has been a source of great info for me and gave me a chance to revise psychrometrics. Just little curious to know about adding humidifiers on the supply air way, if someone could clarify the moist air properties on its route from cooling coils upto the room with moisture being added on the way !!

 

[Zesti]

Hasni2,

"Just little curious to know about adding humidifiers on the supply air way, if someone could clarify the moist air properties on its route from cooling coils upto the room with moisture being added on the way !!"

When the air after the cooling coil is at 90-95% RH, you can not add a lot more moisture to it.
You could get it up to 100%, but why would you want to do this??

If the requirements for the room state that a higher RH is needed in the room at roomtemperature, then this can only be achieved by releasing moisture in the room, not in the supply air.

Be sure to know the difference between "absolute moisture content" and "relative humidity".
And use the psychrometrics chart to see how temperature influences RH.

In my experience, mistakes are often made when RH requirements are specified.
And a lot of people fail to realize what is needed (equipment and energy) to fullfill RH requirements.