If the outdoor air temperature is 90 degrees and the return air is 76 degrees, what is the mixed air temperature with 15% outdoor air introduced?

To find the mixed air temperature with 15% outdoor air introduced, it is helpful to apply the formula for mixed air temperature, which takes into account the proportions of outdoor air and return air temperatures. The mixed air temperature can be calculated as follows:

Mixed Air Temperature = (Fraction of Outdoor Air × Outdoor Air Temperature) + (Fraction of Return Air × Return Air Temperature)

In this scenario, the outdoor air temperature is 90 degrees and the return air is 76 degrees. The fraction of outdoor air is 15%, or 0.15, which implies that the fraction of return air is 85%, or 0.85.

Using the formula:

Mixed Air Temperature = (0.15 × 90) + (0.85 × 76)

Calculating each part:

• 0.15 × 90 = 13.5

• 0.85 × 76 = 64.6

Now, adding these together gives:

Mixed Air Temperature = 13.5 + 64.6 = 78.1 degrees

Thus, with the introduction of 15% outdoor air, the mixed air temperature is correctly calculated to be 78.1 degrees, making this the accurate answer.