Fixed Inlet Vanes 1

[Saturninus]

I have run across several supply and return fans where they fixed the inlet guide vanes. There are working terminal boxes, still, but the inlet vanes don't move.

They are fixed somewhat closed, most likely because if they were fixed wide open, this would overcool the zones. There is perimeter heat (no reheat in terminal boxes).

Here are my questions:

1. would it be wise to change out these inlet vanes and replace them with a VSD?
2. what is the effect of leaving these inlet vanes in the airstream? Are they cutting the fan motor power by pre-spinning the air? Or are they increasing the fan motor power by increasing the static pressure resistance that the fan has to overcome?
3. How would I model this?

In advance, I really appreciate any help.

 

[imok2]

They have in essence converted the system to a constant supply fan system for some reason, apparently they are not interested in energy savings. Of course this will work in a fashion but this is 80's technology. The state of the art today is VSD if your interested in energy savings.

 

[ChrisConley]

1. Well, I'd replace them with a VSD, but it depends on what your budget is. From an energy point of view VSD is much more efficient than inlet vanes.

2. The vanes are a pressure loss increasing fan power, and are costing energy. If the system is working as a constant volume system, why not remove the vanes and then rebalance the fans (new pulley's etc.). You'll end up with the same system, but less energy, and not a lot of cost.

3. Eh?

 

[simsd]

Let me start out by saying that inlet guide vanes are junk! Always have been and always will be.

The reason they are probably locked in place is that they start to seize over the years because maintenance is neglected.

As stated by the other responders, you essentially have a constant volume fan system blowing into the VAV boxes (Assuming the Terminal boxes are VAV). I would assume it's noisy when the boxes back down.

If there is variance in the air requirements then go for the VFD.

If not, then rebalance the fans.