Calculating Target Delta T w/ Manufacturers’ Data

This tip was a COMMENT on the sensible heat ratio tip left by Jim Bergmann. As usual, Jim makes a great point; once you get the “sensible” capacity for a piece of equipment at a set of conditions, you can easily calculate a true target delta T.

Another interesting thing you can do is use this information to determine the approximate target temperature split under any load condition. There are some additional footnotes on that chart, likely saying the return air conditions are at 80 degrees at each of the respective wet-bulb temperatures.

To do so, find the sensible capacity at any set of conditions. For example, at 95 degrees outdoor air and 1400 CFM, the sensible capacity is:

At 72 wb 25,010 BTUH

At 67 wb 31,730 BTUH

At 63 wb 37,360 BTUH

At 57 wb 37,930 BTUH

Using the sensible heat formula, BTUH = 1.08 x CFM x Delta T

Delta T = BTUH /(1.08 x CFM)


Delta T = 25, 010/(1.08 x 1400)

or 16.6°

Delta T = 31,370/(1.08 x 1400)

or 20.74°

Delta T = 37,360/(1.08 x 1400)

or 24.70°

Delta T = 37,930/(1.08 x 1400)

or 25.08°

So, you can see that the target temperature split also has a lot to do with the return air and outdoor air conditions, and it has a lot of variation

—Jim Bergmann w/ MeasureQuick

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