Psychometric Equation Question

[psugreen]

Is there an equation that could be plugged into an excel spreadsheet to calculate enthalpy at a known dry bulb and wet bulb temperature? Or is there a equation for total energy with known entering and leaving dry bulb/wet bulb air temperatures?

 

[MintJulep]

It's "psychrometric equation", which when entered into Google will return many hits, including downloadable Excel things.

 

[trashcanman]

Oh yeah. Look at pages 12-16, Chapter 6, 2005 ASHRAE HANDBOOK OF FUNDAMENTALS. There are your equations for everything you want. They can be put into a spreadsheet easily.

 

[UtilityLouie]

I use an Excel "plug-in" called @air...

It works great and gives you many other properties if needed.

 

[zuccus]

UtilityLouie,

Can you provide a link please, I couldn't find it with google.

Thanks

 

[imok2]

Enthalpy is calculated using Equation 32 from Chapter 6 of the 2001 ASHRAE Handbook of Fundamentals.



H = (0.24 x T) + [W x (1061 + 0.444 x T)]



Where:

H = enthalpy (Btu/lb)

T = dry-bulb temperature (°F)

W = specific humidity (lbwater / lbdry air)

 

[psugreen]

Thanks all for your help. The link for the @air program that UtilityLouie referred to is

http://www.techwareeng.com/prodAA.htm.

They have a 30 day trial version that I'm going to try out. Imok2, the equation I'm looking for is enthalpy when you have known dry bulb and wet bulb temps which is often the case when figuring the total energy for a cooling coil. Need the enthalpy so I can solve the equation (total energy = 4.5 * Airflow (CFM) * Delta h). Thanks again for the quick responses. This is a great message board.

 

[quark]

You can download a psychrometric spreadsheet from this website

http://www.hvacware.net/engrproj.html

Making your own spreadsheet is pretty easy if you refer to ASHRAE HOF equations, provided you know DBT and WBT. The real trouble is with DBT and RH.