You might think that setting up one of these boxes would be very simular to the parallel box, but in fact they are very different. The biggest difference is the fan inside will always run. When the space is calling for full cooling the primary damper opens to its design flow and the fan gets all of its airflow from the main air handler. The design cfm of both the fan and the primary air must be the same. Too much primary air will dump out the back of the box. When there is not enough primary airflow the fan will draw in return air mixing it with primary air and cause the discharge temperature to by high. When the space temperature is satisfied the primary air damper goes to its minimum design and the fan then draws in return air from the back of the box to allow for a constant flow into the space. Here are the steps in setting up the balance of this box:
- Run the box into full cooling mode.
- Adjust the fan speed to get design total grille volumes.
- Balance outlets to design.
- If inlet duct is straight and long enough then do a pitot tube traverse to get design primary airflow. If unable to do a traverse then take velocity readings at the filter to maintain a neutral pressure.
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