Fan-powered VAV's with a ducted return

[psu104]

Looking to put up a small office building. We are looking at fan-powered VAV's (parallel type) and the tenant is requesting a ducted return.

Question... since fan-powered VAV's grab plenum air for reheat.... will this work with a ducted return? Our plenum depth will be in the range of 6-8'. I've seen this work well in plenum returns but never with a ducted return system.

[psu104]

sorry..i guess a bit more detail would help...

I generally see fan-powered VAV's in a plenum return where the VAV's grab "tempered" plenum air (70F or so) in the heating mode before going through the coil. In lieu of VAV's without fans where the boxes heat 100% of the non-tempered air from the supply duct (55F or so).

the ducted return would grab air direct from the office space via return grilles and be ducted directly back to the RTU.

I'm a bit worried about pressure issues since the fan-powered VAV's are still grabbing plenum air even though the main RTU has a ducted return.

[beenthere]

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[genduct]

So they should work BUT why the ducted return in the first place?

[psu104]

So they should work BUT why the ducted return in the first place?

good question.... we have a very large plenum in this building 6-7' and the user is concerned about keeping the air-stream clean. They also have a corp policy about only using ducted returns though we are working verifying this.