Thermal VAV versus Powered VAV

[sridhar1312]

Can you please let me know the difference between the thermal diffuser and Powered VAV.
Where it more apt to use Thermally actuated diffuser and where powered VAV box.
Can Thermal diffuser can be used where there is no VFD/VSD on AHU fan Motor.

 

[BM4BRANES]

Are you refering to "thermofuser", vs a conventional vav box? Vav boxes are almost always found in buildings with other vav boxes and work reliably well. Thermofusers are used on small contant volume package units with trouble spots where the area of trouble differs from the area near the thermostat. At best, they stink and fall short of low expectations. Don't exceed applying to more than 1/10th of volume. I've removed more than installed by far due to misapplication. They should not be considered as a reasonable substitution for a conventional vav box.

 

[RossABQ]

My experience is similar to "BM4Branes" (clever!), but I have heard from other designers that problems with thermofusers arise when they are dropped into a system that was designed for VAV boxes, with no modifications. This can happen when a contractor is looking to shave costs.

 

[atlas06]

In addition, they do not allow reheat for spaces such as conference rooms, excess air goes into the plenum,conference rooms cannot get min outdoor air with such a product, due to no possibility for full flow with reheat.
the fan system operates as a CV system. It does not throttle at all.

Good only for spot temperature control and no more.

 

[sridhar1312]

Thanks for the inputs. please let me know for DX type equipment where there is no VFD on the air handler Thermofuser is more appropriate.Am I correct.

 

[btuhack]

Yup,wait... NO,...wait... what?