There are two different types of fan powered boxes; parallel and series. In this tutorial we are going to talk about the parallel box. This type of box is a very simple design and easy to set up. The primary air or cooling flow is set up just like a single duct vav. The basic concept is to open the primary air damper and turn off fan and heat when in cooling mode. In heating mode primary air damper drives closed or to a minimum and the fan and heat come on. The airflow being supplied comes from the return air above the ceiling. This air is said to be filtered by the main air handler however some box manufactures have a filter before airflow enters the fan. One important thing to remember when setting up the primary airflow is to make sure that the fan is not running. When setting up the fan cfm the primary air damper should drive closed or to a low percentage. The fan speed should then be adjusted by either a speed controller or by a box discharge damper depending on the manufacture. Heater volts, amps, and temperatures should also be taken.
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