What is the mixed air temperature for a system with 20% outdoor air, an outdoor temperature of 90°F and a return air temperature of 80°F?

To find the mixed air temperature in a system with a specific percentage of outdoor air, you can use the formula for calculating the weighted average of the temperatures based on the proportions of outdoor air and return air.

In this case:

• The outdoor air temperature is 90°F.

• The return air temperature is 80°F.

• The system has 20% outdoor air and 80% return air.

Using the formula for the mixed air temperature:

[

\text{Mixed Air Temperature} = ( \text{Outdoor Air Percentage} \times \text{Outdoor Air Temperature} ) + ( \text{Return Air Percentage} \times \text{Return Air Temperature} )

]

Substituting the values:

[

\text{Mixed Air Temperature} = (0.20 \times 90°F) + (0.80 \times 80°F)

]

Calculating the components:

• For outdoor air: ( 0.20 \times 90°F = 18°F )

• For return air: ( 0.80 \times 80°F = 64°F )

Adding these results gives:

[

\text{Mixed Air Temperature} = 18°F + 64°F =