Outside Air Dampers Icing Up
Outside Air Dampers Icing Up
(OP)
An owner has asked me to look at an existing condition in a very cold weather climate facility. The main mechanical room is located on the outside wall of the building to facilitate economizer operation. The outside air louvers and outside air dampers are located on one of the mechanical room's exterior wall. The entire mechanical room acts as a mixing plenum for return air and outside air. Note the return air (conditioned air) is humidified in winter to ~40% RH. You can picture what happens. When the humidified air touches the outside air dampers the water condenses on the dampers. It then drips down towards the bottom of the dampers and then ices up on both the lower portion of the dampers and on the floor of the mechanical room. The ice is up to two inches thick in spots and obviously hinders the dampers operation. Are there "heated" dampers or similar for cold weather applications. Any other ideas for dealing with this situation are greatly appreciated. Thanks.





RE: Outside Air Dampers Icing Up
RE: Outside Air Dampers Icing Up
RE: Outside Air Dampers Icing Up
RE: Outside Air Dampers Icing Up
the two air streams (possibly with ducting)
reduce the outside air volume,lower the
space %RH, or lower the return %RH prior to air
entering the Mechanical room.
Another idea is to position a unit heater
to discharge directly toward the OA damper
and place a condensate pan under the damper.
Using the mechanical room as a mix box is
RE: Outside Air Dampers Icing Up
I also like the idea of building a duct doghouse (extend ductwork from the OA damper bank inward into the plenum). An approx ~4 or more foot structure could minimize venturi effect of drawing moist air against the dampers via OA intake velocity. It could also offer a location for placement of a flow station if desired.
RE: Outside Air Dampers Icing Up
International Standard ISO 3966, Measurement of fluid flow in closed conduits - Velocity area method using Pitot static tubes (1977)3, defines the currently accepted method for traversing ducts. The Standard recommends a minimum of 25 points be measured in rectangular ducts. The ISO Standard has also been adopted as the basis of ANSI/ASHRAE Standard 1111.
But get this!!!Tests conducted at the U.S. Army Corps of Engineers’ Construction Engineering Research Laboratory (UACERL) evaluating sensor density of traverses and various airflow measuring devices, concluded that low sensor density (air) probes (3 sensors in a 22" x 40" duct) resulted in the same accuracy as a 35 point traverse measurement .
Any comments?
RE: Outside Air Dampers Icing Up