Mixed Air Formula Example 2
Formula to use if you only know Outdoor Air Temp, Return Air Temp, and Return Air Percent required:
Note: To Use Temperatures there needs to be a minimum of 10°F between Outside air and Return Air or it is not going to work very well.
Mixed Air Temp=OAT - ((OAT-RAT) x RA%)
For Example:
Outside Air temp = 90°F
Return Air Temp = 70°F
Return Air intake = 80%
Step 1: Mixed Air Temp=90°F - ((90°F-70°F) x .8%)
Step 2: Mixed Air Temp=90°F - (20°F x .8%)
Step 3: Mixed Air Temp=90°F - 16°F
Step 4: Mixed Air Temp=74°
If you know the Enthalpies, you can use a similar formula but plug in Enthalpies.
Mixed Air Enthalpy={(RA Enthalpy-RA%)+ (OA Enthalpy x OA%)} x 100