Relative Humidity

[moxiepilot]

I can't find my reference offhand, but what is the formula for calculating RH?

I thought it was something like:

RH = ((Temp / Dewpoint) * 100 ) + 100

Anyone?

 

[Minuteman]

This is the formula I use:

Its really a curve-fit to a more-complicated relationship that considers specific heats and partial pressures and yer mama, so it works only with "air" (and not any other gasses).

 

[moxiepilot]

you really threw my mama into this??!?

LOL

 

[AirborneMedic_ANGa10]

[Dewpoint/Temperature]*100= rh%

 

[Minuteman]

I don't know how accurate an approximation you need, but the relationship between temperature, dewpoint, and relative humidity is non-linear, so you can't really know the relative humidity with just the ratio.

That said, I tried a couple of fits to the fit and found you can get a pretty darn close using:

%RH =100*[ (Tdew + 273.15)/(Tamb + 273.15) ] + (Tdew-Tamb)

(all temperatures in °C, valid between -20°C to +40°C for a dewpoint spread of not more than 25°C )

 

[moxiepilot]

i didnt even think of it being non-linear, but now that you mention it it is obvious as to why...duh. thanks folks for the enlightenment and formulas.