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 Message Boards » » Psychrometrics question Page [1]  
Wickerman
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I am trying to create a table with Dew Point on one axis, Dry Bulb Temperature on the other axis and the corresponding enthalpies inside. Does anybody know of a way to do this? Or does anybody know if such a table exists?

3/2/2011 10:07:09 PM

S
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I'm confused; isn't what you're describing the standard psychometric chart itself?

3/2/2011 10:55:58 PM

Wickerman
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I am trying to create a table in excel, which can be easily referred using formulas

3/2/2011 11:22:34 PM

CalledToArms
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Are you just looking for something will be quickly calculate the other psych points given two inputs?

http://www.trane.com/Commercial/Uploads/Exe/1250/SetUp.exe

3/3/2011 1:23:12 PM

Wickerman
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I want a whole table

Dbt 32 33 34 35 36....
Dp
32 Corresponding enthalpies inside
33
34
35
36
.
.
.

3/3/2011 2:44:41 PM

darkone
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This is trivially easy to do. What exactly do you need help with?

3/3/2011 2:58:04 PM

Wickerman
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What formulad would I use for this? I want to create this in excel..

3/3/2011 3:58:07 PM

CalledToArms
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Why do you need a table specifically as opposed to the interactive psyh chart I linked you to?

Also if you really need, there are Psych add-ons out there such as: http://www.linric.com/pfdown.htm

And I'm sure if you scour some forums via google people have written all the psych calculations into VB formulas. I have several of them written out in VB but not exactly what you are looking for.

3/3/2011 5:10:07 PM

Wickerman
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Because in an interactive psych chart I would have to look up a value every time I needed an entahlpy value corresponding to a DBT and Dew Point. I wan to automate this process, I currently have a spreadsheet that calculates savings achieved by the installation of an economizer. It has about 100 rows with Dry bulb and Dew Point values. So I would have to use the interactive psych chart about 100 times. A look-up table would make things a lot easier.

3/3/2011 5:26:06 PM

rbrthwrd
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just google excel psychrometric charts and download one of them

[Edited on March 3, 2011 at 9:17 PM. Reason : i have one i just downloaded]

3/3/2011 9:16:31 PM

Wickerman
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^ does it let you choose dew point and another parameter or does it calculate it for you based on other parameters?

3/3/2011 9:28:49 PM

rbrthwrd
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i don't have the file with me, but it would probably do what you want. i found lots of excel sheets and excel add-ins though, so just take a look and someone has probably already done this.

i think i downloaded mine from an HVAC message board

3/3/2011 10:21:30 PM

sglazier
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if you download one you could copy it into another tab and then do a vlookup or dget formula to reference the other property

3/5/2011 9:09:30 PM

Wickerman
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^ that is what I plan to do.. I still have not been able to create this table

3/6/2011 1:19:49 AM

rbrthwrd
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you could make your own function:
http://www.ageng.ndsu.nodak.edu/envr/PsycEqns.htm

or try these that someone has already written:
http://www.hvacware.net/engrproj.html

3/6/2011 8:05:54 PM

Shadowrunner
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I was really confused trying to figure out what the hell this thread had to do with psychometrics.

3/7/2011 4:38:23 PM

k289g
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I easily created the table in Excel using the ASHRAE LibHuAirProp_IP Add-In for EXCEL

I can send Wickerman the file as an email attachment if still needed. Its range is 32 to 80 FDP and 32 to 100 FDB. Could not find a way to attach it to this reply so if still needed send me an email to k289g@bellsouth.net

5/4/2011 6:52:18 PM

kevmcd86
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i have exactly what you need if you still need it...just let me know and i can scan it and send it

Wet bulb from 35-85F with enthalpies. exactly what you need to calculate total btuh for heating & cooling

cooling total btuh = 4.5 x CFM x (enthalpy entering - enthalpy leaving)
heating total btuh = 1.08 x CFM x (enthalpy leaving - enthalpy entering)

5/5/2011 3:21:42 PM

Wickerman
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^^ Email sent, ^ can you please email me what you got at get2vivek@hotmail.com. Thanks a lot!

5/5/2011 11:45:16 PM

CalledToArms
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^^I think you mean 1.08*CFM*deltaT not deltaH for the heating/sensible portion Kevin.

[Edited on May 15, 2011 at 12:34 PM. Reason : ]

5/15/2011 12:25:38 PM

Wickerman
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k289g is the man! he got me exactly what I needed. \thread

5/15/2011 3:00:37 PM

kevmcd86
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^^oops good catch!!!

6/17/2011 8:35:15 AM

CalledToArms
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And don't forget that the 1.08 and 4.5 are valid for the assumption that the density of the air is 0.075lbm/ft3. Not a big deal unless you are dealing with high altitudes etc. but worth keeping in mind.

6/18/2011 5:04:49 PM

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