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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8445
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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what problems may I encounter not using a pant leg transition

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what problems may I encounter not using a pant leg transition and using a plenum

R G : Hi, I am R. G., sorry you're having trouble today, I will do my best to assist you in resolving you're issue.
R G : is this a residential air handler installation?

no this is a commercial 20 ton unit a carrier 50 BV020-64 we are in confined space I don't think I can make this fit.

Welcome to Just Answer!

Tell us please if it for a return or exhaust system, or a supply air system.... for a supply air there can be more issues than for a return or exhaust system... the way the rest of the system is configured from ends of the each branch makes a difference as well.

Customer: replied 4 years ago.

it is a supply duct, vav system, with variable speed fan

Hello again, if the pant leg splits air flow evenly on the two legs evenly ....and each leg has approximately the same air flow with a VAV box down stream of the split... you should have no problems created on that basis.

Same if you use a plenum if the branches of each leg are lateral. (90 degrees to the plenum)

If the VAV box is upstream of the pant leg split or plenum you can have problems if there are not balancing dampers at the registers or in each leg. even then, if one of the legs feed an outside zone along the window areas, and the other leg feeds an inside zone.. you can have a lot of problems as the seasons change and the load on the glass reverses from a heat load to a cooling load.

The VAV should be in each leg in that case, not upstream of the split.

There are many *other issues with VAV systems of all sorts due to bad design, or problems if load is greatly reduced in a zone and air flow drops ...and you end up with air 'falling' out of the registers creating cold spots or hot spots in zone... but those do not stem from these pant leg, or plenum type constructions alone.





Tell me what problems you are having with the system, and a bit about its history and the size of the overall system.

We can go from there as long as you rate this answer from me *positively.
.. I will hold this question open for a much larger discussion on these VAV systems engineering issues..


Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8445
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
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