Starting Construction

[DeeDubya]

Moisture laden air (higher RH) is lighter than dry air. That's right.
Yep, fortunately it has changed my plans for the intake/supply arrangement for the humidifier and I have avoided a major fuck-up. I was planning to pull air into the bypass humidifier from down low and discharge it high hoping for a better RH balance within the humidor. Not so. I need to pull mid to upper level air into the humidifier and blow it downward. Here's why...

Effect of water vapor
The addition of water vapor to air (making the air humid) reduces the density of the air, which may at first appear contrary to logic.

This occurs because the molecular mass of water (18) is less than the molecular mass of air (around 29). For any gas, at a given temperature and pressure, the number of molecules present is constant for a particular volume. So when water molecules (vapor) are introduced to the air, the number of air molecules must reduce by the same number in a given volume, without the pressure or temperature increasing. Hence the mass per unit volume of the gas (its density) decreases.

The density of humid air may be calculated as a mixture of ideal gases. In this case, the partial pressure of water vapor is known as the vapor pressure. Using this method, error in the density calculation is less than 0.2% in the range of −10 °C to 50 °C. The density of humid air is found by:

[1]
Where:

Density of the humid air (kg/m³)
pd = Partial pressure of dry air (Pa)
Rd = Specific gas constant for dry air, 287.05 J/(kg·K)
T = Temperature (K)
pv = Pressure of water vapor (Pa)
Rv = Specific gas constant for water vapor, 461.495 J/(kg·K)
The vapor pressure of water may be calculated from the saturation vapor pressure and relative humidity. It is found by:


Where:

pv = Vapor pressure of water
Relative humidity
psat = Saturation vapor pressure
The saturation vapor pressure of water at any given temperature is the vapor pressure when relative humidity is 100%. A simplification of the regression [1] used to find this, can be formulated as:


IMPORTANT:

This will give a result in mbar (millibar), 1 mbar = 0.001 bar = 0.1 kPa = 100 Pa
pd is found considering partial pressure, resulting in:

Where p simply notes the absolute pressure in the observed system.

Well Slap me Naked.