Makeup Air Units

A Makeup Air Unit (MAU, or sometimes MUA) brings in 100% outdoor air. There is no return air. No mixing. Whatever temperature and humidity exists outside is what you start with.

That distinction matters. A standard AHU blends outdoor air with return air from the building, which means the mixed air temperature stays relatively moderate: even on a -10°F winter day, return air at 70°F brings the mix up considerably before the coils even touch it. A MAU has no such help. On that same day, the heating coil sees -10°F air directly and must bring it up to a deliverable temperature before it enters the space.

Where do you find MAUs? Anywhere a large exhaust demand creates a negative pressure that must be compensated:

• ·Commercial kitchens, hood exhaust removes large volumes of air continuously
• ·Hospital operating rooms and lab spaces, pressurization and contamination control require 100% OA
• ·Parking garages, CO exhaust strategies require makeup air
• ·Large industrial spaces, process exhaust, welding booths, spray booths

The control challenge is straightforward to state and tricky to execute: you must condition outdoor air to a comfortable, code-compliant delivery temperature under all outdoor conditions, while protecting the equipment from freezing and the space from overcooling or overheating.