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Knowledge Series : Slot Diffusers

Linear Slot Diffusers, commonly known as Slot Diffusers, have been in use for a long time. This article discusses the various design and functional aspects of this efficient diffuser. Although Slot diffusers may be used on the side wall, they are mostly used in the ceilings with down throws. There are several aspect of this diffuser which should be considered, namely

  • Width of Slot : 20mm or 25mm
  • Number of Slots : 1 to 8 slots are generally available
  • Length of the Diffuser
  • With or Without Hit/Miss Damper
  • With or Without the VARIABLE Air Pattern Controller (Air Pattern Controller may be eliminated in Return air diffusers)*
  • Diffuser Plenum (Insulated or non-insulated)
  • Frame Style (Normal or Tegular)

The Slot Width is typically considered for the Volume of Air. 25mm Slots deliver more air than the 20mm Slots. Similarly the number of slots and the overall Length determines the Air Quantity being moved into the Space.
The Hit and Miss Damper is a pair of sliding black sheet metal component, which have elliptical cutouts and they are placed in such a manner than it can control/shut off the volume of air being passed through each slot. This volume control is obtained by sliding the damper using the sliding pin provided. This is field adjustable.
The most significant and dynamic part of the Diffuser is the Air Pattern Controller. This device is essentially a pair of black extruded aluminum extrusions which are in the shape of an “Eyelash”. This “Eyelash blade” runs throughout the Length of each slot of the diffuser. When used in ceiling applications, these pattern controller gives a lot of flexibility to the HVAC contractor and designer to manipulate the air pattern in the desired direction.

The diagram represents a 3 slot diffuser. Each slot if configured (field adjusted) to send the air in a specific direction. This is obtained my moving the air pattern controllers, using the fingers of your hand. In the left slot, you will notice that the left air pattern controller is lifted up and the right one is down. This will create a negative pressure pocket beneath the left pattern controller and which will pull the supply air towards the left, hence the air from this slot will move left as it exits that slot. On the right most slot, the opposite is done with the pattern controller, hence the air will move to the Right. In the centre the pattern controllers are both down, in this case the air will move straight down. Using the pattern controllers, the HVAC contractor can choose to throw the air downwards from all slots, all left, all right, or a mixture of all three. This versatile feature allows the architects and interior designers to place the diffuser in a corner or the perimeter and still be able to diffuse the air in the space. This feature is not available in a square diffuser which has fixed aperture as well as a fixed air pattern.

In many cases, a matching return air diffuser is also required in the same space as a supply air slot diffuser. In Return air diffusers, the Air pattern controller as well as the hit and miss damper may be completely eliminated making the diffuser much more economical.

Caryaire manufactures two frame styles in the Slot diffuser, One is the flat flange, and the other is a Tegular Flange which is especially suited for Armstrong Tech-zone tegular ceilings having 24mm or 15mm ceiling “Tee”.



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