Dual Duct VAV boxes - Inlet Pressure

Sparky Bill

I am working on a project and the contractor installed Trane Dual-duct VAV boxes. The hot side inlets are pinned 100% open regardless to what is happening in the space. The manufacturer's literature calls for a maximum inlet static pressure of 0.75"w.c. I suspect the inlet static pressure is greater than 1.0"w.c.



I have read cutsheet data from other dual duct models and other manufacturers. Most call for a maximum inlet pressure of 1.5"w.c.



From my experience with single duct VAVs the usual issues involve the minimum required inlet pressure but not exceeding the maximum.



Does anybody have any dual-duct experience to draw upon?

RJ_4

vav

Are they DDC boxes or pneumatic.   minumum static is critical, If you want vairiable air volume your boxes will need velocity controls, do they have a hot duct and cold duct run to them,  need a little more info.

Sparky Bill

Dual Duct VAV boxes - Inlet Pressure

There are DDC controls. The primary inlet (cold side) is varaible volume with an air flow sensor. The discharge duct (mixed air) is constant volume with an air flow sensor. The secondary inlet (hot side) is variable volume and modulates to meet the total air flow (Discharge) set point (no air flow sensor).

Secondary (Hot Side) air flow = Total (Mixed) air ACTUAL flow  - Primary (Cold) air ACTUAL flow.

The engineer has not provided a traditional dual duct box design. Functional testing has proven the Total (Mixed) air flow to be deficient. Additionally the secondary air flow damper is 100% open regardless of the primary air damper postion.

The inlet static appears to be in excess of 1" w.c. Low inlet static pressure does not appear to be an issue (as you identified as "critical"). The product shop drawings do indicate a "maximum inlet static pressure" of 0.75"w.c.

Sparky Bill

Dual Duct VAV boxes - Inlet Pressure

There are DDC controls. The primary inlet (cold side) is varaible volume with an air flow sensor. The discharge duct (mixed air) is constant volume with an air flow sensor. The secondary inlet (hot side) is variable volume and modulates to meet the total air flow (Discharge) set point (no air flow sensor).

Secondary (Hot Side) air flow = Total (Mixed) air ACTUAL flow  - Primary (Cold) air ACTUAL flow.

The engineer has not provided a traditional dual duct box design. Functional testing has proven the Total (Mixed) air flow to be deficient. Additionally the secondary air flow damper is 100% open regardless of the primary air damper postion.

The inlet static appears to be in excess of 1" w.c. Low inlet static pressure does not appear to be an issue (as you identified as "critical"). The product shop drawings do indicate a "maximum inlet static pressure" of 0.75"w.c.

RJ_4

vav

Contact your local Trane rep. ask for  literature and request a I.O.M. (manual)  also on yahoo look up   HVAC units-Varitrane dual duct boxes.   you will need some training on this one.   may need  Rover/comm 4 software and Rover tool