Duct damper de-icing

[PoorRod]

A low temperature test facility I'm working on has a cold air system which delivers air into the test chamber at -50 degrees F. There are two air handlers so that one can be working while the other is being de-iced. Motorized dampers are used in the duct to isolate the air handlers, however, the dampers also ice up, and need to be de-iced before they can operate. The existing dampers are currently de-iced by hand, and a hands off method is needed. The dampers are approximately 40" x 60", and multi blade. Anyone have any suggestions for how to do this? The dampers can be replaced, if needed. I'm considering electric heat tape along the edges of the blades. Steam is also available on site. Any other ideas appreciated.

 

[imok2]

We use hair driers to deice many situations in refrigeration systems

 

[friartuck]

Why not fit a recirculation duct with dampers. Have this go to recirc once every 15mins or so. Switch on the heat and de-ice. Once done, open the dampers and let it run as normal. Cycle between one AHU and the other.

The recirc duct can go from the AHU outlet to the return/intake.



Friar Tuck of Sherwood

 

[ChasBean1]

I was thinking about an electric snow melt coil, but I'm not sure about this application. Heat trace is the best idea I can think of. Only concern is wiring to the location you mention, and ability of the wires to flex with damper movement and not hinder motion...

 

[PoorRod]

friartuck, the problem I'm having now is that the AHU discharge damper is what isolates the AHU from the test chamber. Hot air is then used to de-ice the AHU coils, but my problem is that the dampers ice up and are inoperable prior to starting the de-icing. I can't be dumping hot air into the chamber trying to de-ice the discharge damper. But you've given me an idea. I could install a heating duct that blows hot air across the damper and a return air duct on the opposite side, such that the hot air is drawn back to the de-icing heater, rather than into the test chamber. However, I think that electrical heaters on the damper blades, connected with flexible conduit, would be the easier option. Thanks for the replies.

 

[imok2]

Performance shall be designed for tight shutoff and tested in accordance with AMCA Standard 500. Leakage for a damper with seals shall not exceed 4 cfm per square foot at a 2.5-inch pressure differential. The damper must be rated to operate over a temperature range of -50 to 250°F (-46 to 121°C).
If this is of interest go here:

http://cgproducts.johnsoncontrols.com/CAT_PDF/1900208.pdf