Duct Problems

[apprentice3]

Today i had a water source heat pump feeding a classroom and 3 offices. It has a main trunk line with 8" taps coming off of it. There are a total of 7 taps on this unit. 4 for the classroom and 1 for each office. Well the problem i am having is the one diffuser nearest to the unit isn't putting out hardly any air. I pulled the duct off and inspected inside the duct. At this point in the duct, it is like there is a dead spot. The air is just turbulating around the opening. This duct tap comes off right after the flex connector. It is the first fed. The diffusers that come off further down the main get plenty of air. Why is this? What can i do to the ducting to fix this problem? The office with the problem has the stat. So it is causing no heat or cool to go into the room. So it either burns everyone out or freezes everyone out depending.

Thanks for the help!

[Gib's Son]

Too high of velocity, the air just blows on by. Add a scoop.

Oops, hope that aint DIY. If so a mod can remove and spank me.

[Lash]

How many people have messed with the downtream dampers to get more/less heat or cooling in their office?

A simple professional re-balance may help things. Either that or it may not have been properly balanced in the first place.

[dijit]

How far away is this duct from any changes in direction?
Is there a long section of straight duct before the tap or is it right after a change in direction?
Do you have shoe taps?

[apprentice3]

Too high of velocity, the air just blows on by. Add a scoop.

Oops, hope that aint DIY. If so a mod can remove and spank me.

Yea i was thinking that, but i just didn't know how much that would help. I haven't used them that much. I heard something from a sheet metal guy stating that the air is more even at the end of the trunk.

How many people have messed with the downtream dampers to get more/less heat or cooling in their office?

A simple professional re-balance may help things. Either that or it may not have been properly balanced in the first place.

Actually every damper is open all the way down the trunk line.

How far away is this duct from any changes in direction?
Is there a long section of straight duct before the tap or is it right after a change in direction?
Do you have shoe taps?

The main duct just comes straight off of the heat pump, goes into a flex connector, and is just a straight run all the way to the end cap. The duct doesn't change directions or switch sizes. The tap with the problem is right up next to the discharge of the unit. There is no long straight run before the taps.

Shoe taps? Are they taps with scoops?

[Gib's Son]

Might want to relocate the takeoff further down the duct where there is less turbulence and and the velocity has slowed, probably the easiest solution.

[AC5096]

Today i had a water source heat pump feeding a classroom and 3 offices. It has a main trunk line with 8" taps coming off of it. There are a total of 7 taps on this unit. 4 for the classroom and 1 for each office. Well the problem i am having is the one diffuser nearest to the unit isn't putting out hardly any air. I pulled the duct off and inspected inside the duct. At this point in the duct, it is like there is a dead spot. The air is just turbulating around the opening. This duct tap comes off right after the flex connector. It is the first fed. The diffusers that come off further down the main get plenty of air. Why is this? What can i do to the ducting to fix this problem? The office with the problem has the stat. So it is causing no heat or cool to go into the room. So it either burns everyone out or freezes everyone out depending.

Thanks for the help!

How long is the plenum?

Usually with that many take offs and a long plenum, it's best to reduce it. A scoop would help, but a new properly sized plenum would be the best solution.

[Williamsma]

Too high of velocity, the air just blows on by. Add a scoop.

Oops, hope that aint DIY. If so a mod can remove and spank me.

Yea i was thinking that, but i just didn't know how much that would help. I haven't used them that much. I heard something from a sheet metal guy stating that the air is more even at the end of the trunk.

How many people have messed with the downtream dampers to get more/less heat or cooling in their office?

A simple professional re-balance may help things. Either that or it may not have been properly balanced in the first place.

Actually every damper is open all the way down the trunk line.

How far away is this duct from any changes in direction?
Is there a long section of straight duct before the tap or is it right after a change in direction?
Do you have shoe taps?

The main duct just comes straight off of the heat pump, goes into a flex connector, and is just a straight run all the way to the end cap. The duct doesn't change directions or switch sizes. The tap with the problem is right up next to the discharge of the unit. There is no long straight run before the taps.

Shoe taps? Are they taps with scoops?

The rule of thumb I use is the first tap has to 3 times the diameter of the duct away from the discharge of the unit. So if the duct is 8" dia, then your first tap is set at 24" away from the unit. This also applies to change of directions.

[skibme]

Is there a transition in duct size anywhere along the main trunk?There should be after a few taps are taken off.This will add pressure to your outllet.

[genduct]

Might want to relocate the takeoff further down the duct where there is less turbulence and and the velocity has slowed, probably the easiest solution.

I'd be a little uncomfortable with a "scope" that might really disrupt the high velocity air stream coming off the unit as per your first thought

[second opinion]

+1

[Gib's Son]

I'd be a little uncomfortable with a "scope" that might really disrupt the high velocity air stream coming off the unit as per your first thought

I kinda missed the turbulence word first time around. That being said, I have seen it many times with high velocities that the air just rushes on by the first branch.

[synergy]

Sounds like you have no static pressure. Too many openings or too many air exits to allow for static pressure to build up and push the air out of the closest registors. Close down some of the dampers until you get static pressure in the trunk. I Should think you would need a 1/2 inch or so of pressure at 2/3 down the trunk run, on a unit that size.