Ductwork Switch from Constant Volume to VAV

[BronYrAur]

I am getting involved with a job in progress where a constant volume low pressure system is being converted to VAV. All of the system truck ductwork has already been replaced with the same size new ductwork (constructed for higher pressure).

The air handler will be repalced with a new one capable of VAV operation. Since the trunk ductwork has already been repalced with the same size as the existing, it is larger than I would normaly size for a VAV application. Does this hurt me? The AHU fan will be of sufficient size and will be VFD controlled. I just do not have a comfort level with oversized ductwork. That's obviously better than undersized, but will it cause me any concerns? I need to deliver 1.5" of static to the VAV boxes.

 

[willard3]

The only thing the larger ductwork will do is decrease fan operating costs and decrease self noise.

 

[Wareagl487]

No issues that I can imagine. The benefit of medium pressure systems is the decreased area of ductwork (smaller) required for plenums with limited space. As stated by Willard, the benefit is decreased noise transmission from the ductwork due to the lower velocities.

I think you are fine.

Andy W.

 

[RossABQ]

1.5" delivered to the VAV's seems unnecessarily high, offhand...but we have no details of the system.

 

[AbbyNormal]

if it was short of cooling, you can move more air now

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[BronYrAur]

Thanks all. It seemed logical enough, but I wanted to double-check.