What are the benefits of using Fan-Powered VAV boxes?
What are the benefits of using Fan-Powered VAV boxes?
(OP)
As opposed to not wasting all the money on all the boxes, and just cycling the return/supply fan on and off?
THANKS!
THANKS!





RE: What are the benefits of using Fan-Powered VAV boxes?
RE: What are the benefits of using Fan-Powered VAV boxes?
The primary DOAS air is then sized for both the cooling load and the minimum ventilation air so the VAV part of the box modulates the cool primary supply air to meet the load while the fan-powered recirc air provides reheat capability. During unoccupied mode, the main AHU is off and the fan-powered box cycles on/off on a call for heating primarily at nights and weekends.
Most of my experience is with re-heat only fan-powered systems, being in a northern climate. Others on this board who design these for southern hot'n'humid climates may have more to say on this.
RE: What are the benefits of using Fan-Powered VAV boxes?
RE: What are the benefits of using Fan-Powered VAV boxes?
Discharge air temperature must not exceed about 90°F so discharge heated air can mix with cool room air without stratification.
The system cost less than wall to wall enclosure finned tube radiation system.
RE: What are the benefits of using Fan-Powered VAV boxes?
RE: What are the benefits of using Fan-Powered VAV boxes?
You now have the added benefit of not needing as much reheat since, as lilliput1 said, you are reheating the relatively warmer plenum air. Which means smaller heating coil requirements. (75 F to 90 F vs 55 F to 90 F) There is a payback both in first cost (smaller coils, smaller gauge wire or smaller hot water pipe and boiler), and energy usage when heating during occupied times.
When you look at unoccupied times you don't have to run a 20, 30, or possibly 50 HP fan motor to heat one exterior zone that needs heat and can just run the VAV box's 1/4 HP motor and recirculate the air in that one zone.
Those are the reasons I would "waste" the money on the boxes .
RE: What are the benefits of using Fan-Powered VAV boxes?
I always figured heat from lights that warm up a plenum ceiling space could get sent back down to the space with them, probably an advantage in heating up North.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: What are the benefits of using Fan-Powered VAV boxes?