Grilles and Diffusers
A grille is a device for supplying or extracting air vertically without any deflection.
A diffuser normally has profiled blades to direct the air at an angle as it leaves the unit into the space, as shown below.
Grilles and Diffusers can be manufactured in:
q Mild steel
q Stainless steel
Finishes can be white, any colour, brushed or anodised aluminium, stainless steel or chrome.
Grilles and diffusers may be mounted in ceilings, floors, walls, doors and in ducts. Some are suitable for horizontal or vertical mounting while floors grilles tend to be especially strong to withstand foot traffic.
There are several types of grille and diffuser to choose from, as follows;
v Egg grate grille
v Bar grille
v Transfer grille
v Louvre bladed diffuser
v Straight bladed diffuser
v Linear slot diffuser
Less commonly used diffusers are as follows;
o Swirl diffuser
o Floor outlet diffuser
o Jet diffuser
o Punkah diffuser
o Barrel diffuser
o Perforated diffuser
o Plain face diffuser
The Egg Crate Grille is probably one of the simplest and cheapest grilles.
In some cases the plenum box above the grille is visible from the room below.
If air is to be removed by an extract ventilation system then a diffuser with profiled blades to direct the air is not necessary and an egg grate grille can be used.
The blades of this type of grille are shaped as a bar compared to a narrow blade.
The bar profile may be ‘T’ shaped to reduce ‘see through’ visibility.
Some linear bar grilles have adjustable blades or angled blades to reduce ‘see through’.
These are often used in doors and walls to provide ventilation but stop the spread of smoke and fire should it occur. An intumescent fire damper is incorporated in some Transfer grilles as a means of isolation in the event of a fire.
Louvre Bladed Diffuser
These are used to supply air at ceiling level.
The curved blades deflect air in one, two, three or four directions depending on where the diffuser is situated.
Diffusers may also be circular as shown below.
These are cheaper than Louvre Bladed Diffusers.
Some types have adjustable bladed as shown below.
These are used for an alternative air distribution pattern and for aesthetic reasons.
Air can be delivered around the perimeter of a room as opposed to point sources interposed in a ceiling space.
Linear slots can be used for return air as well as supply.
In many cases blanking plates are used to create ‘dummy’ slots so that a continuous linear effect is created.
One to four slot widths are common depending on how much air is to be delivered.
Some proprietary plenum boxes are quite tall are require a large ceiling void, to overcome this a special box can be manufactured to fit the available space.
Some Slot Diffusers have an adjustable air pattern so that the air distribution can match the room shape.
If sound insulation is required in an air conditioning system then a lined plenum box may provide sufficient sound attenuation.
There are some specialised grilles and diffusers as described below.
High turbulence occurs immediately within the proximity of the diffuser, which allows high air change rates to be successfully supplied into the room.
With careful selection swirl diffusers can handle up to 30 air changes per hour while still satisfying relevant comfort criteria.
There is an advantage in supplying cool air conditioned air at low level.
This can be achieved by floor outlets.
Floor diffusers are also useful in areas with raised floors so that ductwork can be accommodated under the floor.
Another area for floor outlets is under large areas of glass so that condensation and cold down draughts are eliminated.
Used in areas where the ceiling is high and large air velocities are needed to reach the occupied space.
The high volume and long throw of these diffusers makes them suitable for large halls
Some jet diffusers can be reversible and rotatable which allows the air jet to be adjusted for both pattern and deflection.
Used to give flexible air direction, sometimes in the back of seats so that occupants have control over flow and direction of air.
Perforated diffusers are suitable for installation in 600mm ceiling tiles.
The face plate may be pivoted down to gain access.
The diffusers are constructed from aluminium or stainless steel the flat face plates are perforated, this means that they are easily cleaned and are used in some kitchens.
Valves are used where the air flow needs to be regulated or throttled and are suitable for supply and exhaust applications.