Every discharge path through a series fan-powered VAV terminal passes through the local fan.
In the series arrangement shown here, central primary air mixes with ceiling-plenum return air upstream of the local fan, and all terminal discharge passes through that fan. A parallel fan-powered terminal puts the local fan on a separate branch; its airflow path and control sequence are different and are not represented here.
Follow the airflow through the equipment.
Primary inlet
Conditioned primary air enters from the central system through the terminal control section.
Plenum return
The local fan draws recirculated room air from the ceiling plenum into the series terminal.
Upstream mixing
Primary and plenum-return air combine before they reach the local fan inlet.
Series fan and supply
All mixed discharge passes through the terminal fan, then through the downstream duct and diffuser.
What the fan is responsible for
- Move the complete mixed supply airflow through the series terminal and downstream distribution.
- Operate across the allowed primary-air range and heating or cooling sequence.
- Meet occupied-space sound and control requirements inside a compact enclosure.
Why the route matters
- Treating total supply as outdoor air can overstate ventilation.
- Applying this series path to a parallel terminal misstates when and where the local fan moves air.
- A fan selected at free air may miss its duty once filters, coils, casing and duct are included.
Define these inputs before choosing a fan
A LONGWELL route to evaluate: DD direct-drive commercial centrifugal blowers
LONGWELL DD direct-drive commercial centrifugal blower materials are associated with tube and VAV terminal applications at family level. Evaluate a candidate from the series terminal's total supply airflow, installed resistance, casing orientation, sound and control sequence, then validate the assembled terminal across its full primary-air range.
Verify the complete equipment, not the fan in isolation
Confirm the terminal is series type, then define both airflows.
Send the series terminal layout, primary and total supply ranges, installed resistance, casing orientation, sound criteria and sequence so a DD blower family can be reviewed.