[slaine]

I have a question around correctly simulating the air with different densities. It would make sense to me that dry air at the same atmospheric pressure would have a lower density than humid at the same atmospheric pressure. What densities should I use for example for 50% humidity vs. 80% humidity for a HVAC supply case?

[LuckyTran]

Use Dalton's law of partial pressures. Your wet density is:


or


Obviously there is two or more steps not shown to convert relative humidity into the partial pressure.


As mentioned already, since the molecular weight of water (2 hydrogens and 1 oxygen) is less than the other molecular compounds (N-2, O-2, and CO2 are all heavier than 1-Oxygen), the density of wet air is less than dry air. If not for this property, the sky would rain fire instead of rain; and it did, many eons ago.

[slaine]

Originally Posted by LuckyTran

Use Dalton's law of partial pressures. Your wet density is:


or


Obviously there is two or more steps not shown to convert relative humidity into the partial pressure.


As mentioned already, since the molecular weight of water (2 hydrogens and 1 oxygen) is less than the other molecular compounds (N-2, O-2, and CO2 are all heavier than 1-Oxygen), the density of wet air is less than dry air. If not for this property, the sky would rain fire instead of rain; and it did, many eons ago.

Many thanks for this.