Air Density Corrections 2

[Matador]

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

Thanks in advance.

 

[rb1957]

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

 

[Matador]

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

 

[Gearhead]

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

 

[IRstuff]

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

 

[Matador]

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.

 

[IRstuff]

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

 

[Matador]

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.

 

[IRstuff]

And again, it reads like you're asking for a density-altitude equation.

TTFN

 

[katmar]

Matador,

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

http://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

 

[MintJulep]

Google for psychrometric excel

lots of hits.

 

[Matador]

Thank you Katmar, this is exactly what I needed.