What is a Make-up Air Unit?

Make-up air (MUA) systems perform their stated task.  They bring in fresh air to ‘make-up’ for air that has been removed from a building, or add extra air required for a specific purpose.  The MUA equipment tempers this air and delivers it at a desired condition and volume to suit the requirement.

Examples where make-up air may be required:

  • Kitchens using exhaust hoods

  • Manufacturing applications exhausting air such as paint booths

  • Building pressurization

MUA units are typically situated on roof spaces and direct the supply air down into duct work, although many configurations are available to suit the application.

Make-up Air Units

MUA units can employ various methods for heating and cooling the supplied air.  Hydronic, electric and gas are most common for heating, and evaporative and DX coils may be used for cooling.  Use of one method over another is usually dependent on application and location.

Gas-fired heating is one of the more popular methods for heat in Canada and this can further be broken down into two-types of units, direct and indirect-fired.  Direct-fired units push the outside air over a burner with no barrier between air and flame.  While this creates a very efficient heating method (close to 100%) it does push the products of combustion into the supply airstream.  This is not always ideal depending on the application.   An indirect-fired unit employs a heat exchanger to keep the supply air and combustion process separate and the products of combustion are exhausted to the atmosphere.  This results in a much cleaner supply air more suited to applications that demand it, such as residences and restaurants.

The first rule of any technology used in a business is that automation applied to an efficient operation will magnify the efficiency. The second is that automation applied to an inefficient operation will magnify the inefficiency.

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