#VALUE! error

**Phillip Maddi** · 07-12-2013, 06:16 PM

Hello All,

I am writing a code to get wet bulb temperature from dry bulb and relative humidity, but when I run my UDF, I am getting a #VALUE! error. I can't figure what parameters I should be setting to the correct data type as the are all numerical values. Any help is much appreciated.

'-------------------------------------------------------------------------------
'Calculate wet bulb temp given dry bulb temp and relative humidity
'
Function psychro_WBT(DBT, RH)
'
DBT = Dry_Bulb_°F
DBR = DBT + 459.67
c8 = -10440.397
c9 = -11.29465
c10 = -0.027022355
C11 = 0.00001289036
C12 = -2.4780681E-09
C13 = 6.5459673

Pws = Exp(c8 / DBR + c9 + c10 * DBR + C11 * DBR ^ 2 + C12 * DBR ^ 3 + C13 * Log(DBR))
Ws = 0.621945 * Pws / (14.7 - Pws)
Wact = RH * Pws

Do
WBT = DBR
Wnew = ((1093 - 0.556 * WBT) * Ws - 0.24 * (DBR - WBT)) / (1093 + 0.444 * DBR - WBT)
End
WBT = WBT - 0.1
Diff = (Wact - Wnew) / ((Wnew + Wact) / 2)
Loop Until Diff < 0.01

psychro_WBT = WBT

End Function

**stnkynts** · 07-12-2013, 06:48 PM

What is the purpose of this line?

DBT = Dry_Bulb_°F

You should also seriously consider declaring your variables

**Phillip Maddi** · 07-12-2013, 06:51 PM

Thanks that is a useless line. To declare variable is it just designating them with Dim BLAH As DataType?

**stnkynts** · 07-14-2013, 05:20 PM

Why do you have "End" in your loop? That will stop everything after that. The loop is flawed. Not sure what you are actually trying to do.

**Richard Buttrey** · 07-14-2013, 05:51 PM

....and why do you need a UDF? Is an approximation which doesn't require an iterative approach an option in which case you could use standard Excel functions, in some intermediate helper columns if necessary?

Explain the formula that links WBT to DBT and relative humidity in narrative form if necessary and maybe we can assist further.

**Phillip Maddi** · 07-15-2013, 12:28 PM

Thank you everyone for your help.

The End was to end the do command just because I thought I needed it. Overall, the UDF is to take the thousands of DBT and RH data points, and get other values from the psychrometric chart to perform further calculations. Because we do several of these analyses a week, it would be convenient to have a function to get the desired values.

Thanks again, and here is my current code:

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**AtulSwamy** · 01-29-2014, 10:54 AM

Phillip Maddi,
I am new for coding in VBA, and I came across your feed. I tried using you above mentioned code and was not able to get the right answer as the iteration stops right after 1st step. Please let me know if you had done something different which I was not able to catch.

Thanks,
Atul

**stnkynts** · 01-29-2014, 11:33 AM

Good morning Atul. Please do not ressurect a 6 month old post. If you have a question please start a new thread as it is more likely to get an answer that way.