VAV Diffusers

[MechGuy22]

Im replacing a small fan coil unit in a existing building for a exterior zone. I was thinking about using PRICE vav diffusers for some zone control. Ive noticed that on their website they always seem to use a pressure control valve VAV terminal between the supply/return. Would it be possible to use their VAV diffusers along with a variable frequency drive that varies the fan speed based on the pressure in the duct system?

I appreciate any help, ive never used these VAV diffusers before.

 

[cdxx139]

Sounnds like an expensive solution. You caould also keep constant volume and dump the excess air in the plenum with a pressure relief damper, but the manufactutrer's rep would probably be the best source.

knowledge is power

 

[MechGuy22]

Ive heard some nightmare stories with pressure relief dampers and dumping excess air into the return.

 

[cdxx139]

Please share, Id love to hear them.

The only issue I can think of is if it origianlly wasnt a return plenum, and dumping air would make it a return plenum which casues code issues for electrical.

knowledge is power

 

[MechGuy22]

The entire system based based off of that damper which is sensitive to any type of change. They are better suited in a chilled water versus a DX. The basic complaint ive seen is that they just stop working after 4-5 months. A VFD is more energy efficient and allows for better control. I just havent seen it installed with a VAV diffuser system though.

 

[cdxx139]

I can't think of why your idea wouldnt work in theory. I suggest you confirm with the manufacturer. And if the fan coil is small enough, maybe an ECM motor is available instead of VFD? Might be cheaper and more energy efficient.

knowledge is power

 

[MechGuy22]

Thanks Cdxx, I will actually look into the ECM motor, sounds like it might work.

 

[KiwiMace]

My opinion is that VAV dampers are good for about one zone in a multi-zone system. e.g. Jobs where a constant speed rooftop unit is supplying a larger open plan space and an office. Locating the VAV damper in the office provides a little more comfort where the budget doesn't allow anything more tailored.

 

[317069]

you are dealing with one zone only, why did you think of VAV diffusers from the first?
VAV diffusers and VFD are part of VAV system but not whole system.
Please check attachment, it might give some information