Calculating Wet-Bulb Temp 1

[Herman2]

I am upgrading some cooling tower controls and would like to monitor sump temperature as compared to ambient wet-bulb temperature. My weather station reads dry-bulb and relative humidity.

I'm willing to assume constant barometric pressure. Does anyone have a nice set of expressions I can use to calculate wet-buld temperature from the measured values?

My ASHRAE book has a set that requires iteration / trial and error. Has anyone done some curve-fitting or the like?

Thanks.

 

[imok2]

Herman2
this should work for you!

http://www.connel.net/freeware/airduct.shtml

docendo discimus

 

[Herman2]

I appreciate the really fast response from [imok2], And my question was answered. But I need an expression I can load into a PLC. This freeware will be great for checking things out.

Thanks...

 

[billspen]

How about this?

a1 b1 a2 b2
0.724582967 0.81706445 0.112208011 0.17578135

twb=(a1*tdb^b1)*rh^(a2*tdb^b2)
29.91 bar press
temp db 55 to 95, rh 30 to 100

 

[billspen]

If you can't raise numbers to powers in the PLC here is another solution, not as accurate but should be accurate enought for what you are doing.

a1 b1 a2 b2
0.004043651 -0.039353174 0.612121032 3.207748018

twb=(a1*tdb+b1)*rh+(a2*tdb+b2)

same range as equation posted previous to this