×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Air Density Corrections2

## Air Density Corrections

(OP)
I'm looking for an Excel spreadsheet that gives me the air density at different temperatures and altitudes.

The project involves a cooling tower heat load and the temperature range is from 75F - 115F at an altitude of 1640 ft

### RE: Air Density Corrections

yahoo "standard atmosphere" ...
there a lots of tables you can copy, some refs may have equations ...

you'll probably need to remember high school chemistry to correct for your non-standard temperatures

good luck

### RE: Air Density Corrections

(OP)
I have not been able to find anything that doesn't require interpolation between the different values.

### RE: Air Density Corrections

NIST has tables or you could use something like TK Solve which has the values built in and links to Excel.

### RE: Air Density Corrections

Perhaps you need to look again.  There have been at least 3 different equations on the web for calculating the density altitude.  In fact, most of the tables on the web are based on one of the equations.

TTFN

### RE: Air Density Corrections

(OP)
Sorry but I don't want the density altitude.

I want to be able to vary the inlet and outlet air properties for a cooling tower without interpolating for every value I choose.

I don't need to know the density is the same as it would be at 4000 ft, then compare that to the outlet which could be equivalent to 8000 ft.

### RE: Air Density Corrections

Perhaps you need to clearly restate your problem, since your original question was:
"gives me the air density at different temperatures and altitudes,"

which sounds a lot like you wanted a density altitude equation.

TTFN

### RE: Air Density Corrections

(OP)
Sorry for not being clear.

Does anyone have a Excel spreadsheet or can you provide the formulas to determine the air densities at different temperatures and altitudes?

This is a cooling tower application and the altitude is 1640 ft. My calculations revolve around temperatures in the 75F - 125F range.

Any help will be greatly appreciated.

TTFN

### RE: Air Density Corrections

2

The effect of altitude on atmospheric pressure was discussed recently in the HVAC/R forum. See thread403-121661

Using the equation given there by quark (and confirmed by 25362) you can calculate that your atmospheric pressure at an altitude of 1620 ft (500m) will be 95.45 kPa abs.

Once you have the pressure you can plug it into the ideal gas equation (PV = nRT) and solve for density (= 1/V) as a function of temperature.  This gives
Density (kg/m3) = 332.46 / T
where T is temperature in Kelvin

This will be very easy to put into a spreadsheet. If you want to check your numbers there is a gas density calculator that is part of the gas mass to volume converter built into Uconeer. This is a free engineering units conversion program available from www.katmarsoftware.com

However, you must remeber that all these calculations are based on *dry* air. If you are doing calculations for a cooling tower your air will be wet, and the moisture content will be changing.

If you know the moisture content you could adjust the solution to the ideal gas law given above to take the varying molecular weight into account. Or let the spreadsheet do this for you.

Or you could just short-circuit the whole thing and download the free psychrometric calculator from
http://www.gpengineeringsoft.com/pages/pdtpsychrocalc.html

lots of hits.

### RE: Air Density Corrections

(OP)
Thank you Katmar, this is exactly what I needed.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!