Control Damper Leakage

[WTCM]

Hello Everyone,
I am currently working on a project which utilizes two air handling units. One is for the main building and the other is a dedicated unit for a lab space. If the lab AHU were to go down the main building unit ramps up and opens a control damper in a crossover duct to feed the lab space. The system works great, the only problem is that during normal operation we are seeing 1500 CFM (around 23%) loss down 50 LF of duct from the air handler. We have done extensive duct sealing and the only potential source of leakage left is the control damper in the crossover duct (the lab AHU is at a greater static pressure than the main building AHU). Does anyone know how well a control damper seals when it is fully closed? Is there a better alternative than a control damper?
Thanks Guys

 

[rmw]

Not very well. I assume that this is a louver damper. In heavy duty industrial dampers louvres can be built with blade tip seals and side jam seals and the leakage can be reduced to manageable levels but if you have to have zero or near zero leakage, you are going to have to get a different type damper.

rmw

 

[stanlsimon]

If you can get the manufacturer, make and model of the damper along with the static pressure drop across the damper, you may be able to calculate what the air flow rate should be. However some of the damper manufacturers have been lax about having dampers tested by third parties. (Like AMCA.)

Another problem might be the lack of operator motor torque required to fully shut the damper. Also there can be slop in the linkages, loose brackets, control problems etc. that prevent full closure. Do you have pneumatic or electrical operators?

 

[rogzog]

Is this new construction or an older existing system?

If it is a new construction, check what type of damper was specified and then verify that that is indeed the type installed. In a system isolation situation it should be a low leakage type damper with blade seals and rated for the appropiate static pressure that it will need to contain.

Also check the damper for damage. Bent blades, torn or missing seals or debris stuck in the damper can impair it's function. If an access door was not installed in the ductwork to acess the damper, it isn't much of a job to cut a hole and install one to look at the damper.

 

[WTCM]

Thanks for the help guys,

It is a louvered damper which is electrically operated. All the duct work is new and we have cut an access door to check the damper for any visible problems (we didn't see any).

I will have to check with our Sheetmetal contractor to see what was actually installed but the plans call for a motorized isolation damper to be installed at the cross over duct. From what you guys have said it sounds like they either installed the wrong damper or the one that was installed was not designed to prevent leakage (low leakage damper).

Looks like I have some more research to do.

Thanks again