[wreckless192]

Hi,
Hope you can help me with this problem. I have an application where I need to determine the dew point temp. the parameters are as follows:
- the ambient outside air is between -40F to 122F
- the ambient humidity is 190.4 gr/lb
- the ambient pressure is 10.1 to 14.7 psia
- the temperature inside the duct is between 30F to 112F

I'm trying to find out at what temperature will condensation form on the outside on the duct. If you can tell me how to determine this (given the humidity in gr/lb) that would be greatly appreciated. I've searched different sites and calculators, but they all have the humidity units in (%).

Thanks Wreckless192
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[NorthernHeat]

That is because gr/lb can be the same at 70 degrees as it is at 80 degreen but the %RH is quite different.

The more saturated the air is at any given temperature is actuall what determines dew point.

Even atmospheric pressure will change the air density and the formula for finding the saturation point of air.

I'm not sure of the formula but it must be something along this line if it helps you search more online. The wieght of dry are at a specific pressure and temperature (probably needs to be found on an engineering chart, or a quite lengthy formula) plus the wait of the water will give you the total density then another long formula or pschometric chart will convert it to RH