# Thread: Udarrell

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## Udarrell

Udarrell, I'm trying to figure out how to use the enthalpy chart to get total BTU. I have the Testo 610 , 550's and the Get-Cool software on a Palm. Whate are the numbers across the top?

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4. Originally Posted by 1manarmy
Udarrell, I'm trying to figure out how to use the enthalpy chart to get total BTU. I have the Testo 610, 550's and the Get-Cool software on a Palm. What are the numbers across the top?
The numbers across the top are merely the degree increments in tenths, using a digital thermometer the tenths of a particular degree are important.

Say you got 61.5-F wet bulb, reading across the top to .5 then down to 61 on you get an enthalpy of 27.50 Btu per lb of dry air.

Then you take the other wet bulb temp & subtract it form the other to get the enthalpy change.

Say it is 51-F wet bulb; that's 20.86; 27.50 - 20.86 is an enthalpy change of 6.64.

Example: If you had a 3-Ton A/C with an airflow of 1200-CFM * 4.5 (at sea level) is 5400 * 6.64 is 35,856-Btuh.
You also have to have an accurate method to get the operating CFM of the indoor blower!

3-Ton is of course, 36,000-Btuh which you seldom achieve & many 3-ton units are rated well under 36,000-Btuh; nor do they come even close to getting their Nominal Rating in the field - due to too many factors to list here, now...

It is easy & fast using your Testo WB instrument, which I don't have...it is also easy to make errors when transferring the numbers to the enthalpy chart numbers...Do it right.

It is accurate on my little Half Ton Window units.

This enthalpy chart is in my text book on page 364.

Good Luck...
Last edited by udarrell; 07-15-2012 at 08:57 PM. Reason: Chart is on page 364 in my text book...

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