Which statement best describes stratification in an air handler unit's mixed air plenum?

Which statement best describes stratification in an air handler unit's mixed air plenum?

• A. Always desirable
• B. Sometimes desirable
• C. Not applicable
• D. Never desirable

Answer: (D)

In the mixed air plenum of an air handler, you want the outdoor air and return air to blend into one uniform stream before it goes to the coil and supply duct. Stratification means the air becomes layered by temperature, with warmer air at the top and cooler air at the bottom, due to incomplete mixing. This uneven mixture means the coil sees different conditions at different heights, which leads to inconsistent cooling or heating, poorer humidity control, and reduced overall efficiency. Because the purpose of the mixed air plenum is to provide a single, homogeneous air path for treatment, stratification undermines that goal. That’s why stratification in the mixed air plenum is never desirable.

In the mixed air plenum of an air handler, you want the outdoor air and return air to blend into one uniform stream before it goes to the coil and supply duct. Stratification means the air becomes layered by temperature, with warmer air at the top and cooler air at the bottom, due to incomplete mixing. This uneven mixture means the coil sees different conditions at different heights, which leads to inconsistent cooling or heating, poorer humidity control, and reduced overall efficiency. Because the purpose of the mixed air plenum is to provide a single, homogeneous air path for treatment, stratification undermines that goal. That’s why stratification in the mixed air plenum is never desirable.