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Variable Speed Drives on Makeup Air Handlers

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  rev. 2008-11-25        

Existing Conditions

Ventilation to xxx is supplied by constant volume make-up air fan system xxx.  There is a constant air flow regardless of occupancy and actual ventilation requirements in the space.

Retrofit Conditions

We recommend installing a variable frequency drive (VFD) and inverter duty motor on the make-up air fan.  The fan speed will modulate to maintain adequate ventilation rates.  The low fan speed would be set at the drive to ensure adequate flow at all times to prevent burnout of the furnace heat exchanger or freezing of the direct expansion cooling coil.>

Further Benefits



Application Details

Allow for rebalancing of the distribution system if average airflow is significantly reduced.

Issues and Concerns






There are two parts to the savings calculations:

1.Thermal savings  based on changes in air flow as well as the source and efficiency of heating and/or cooling.
2.Fan savings based on standard Variable Frequency Drive calculations.

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