Grilles and diffusers are flexible devices that can be put almost anywhere to maximise airflows. Now the pressure’s on to be more energy efficient they are really coming into their own as Joe Wieckowski, general manager of Colman Moducel explains.
INVESTING in a well-designed ac system is a move in the right direction but to reap the real benefits of energy efficiency, costs savings and aesthetics, the overall design needs to embrace ancillary products such as grilles and diffusers to introduce air into a space.

Once regarded as peripheral devices, grilles and diffusers are now attracting the attention they deserve. They are very flexible devices and can be sited almost anywhere and it is no wonder they are widely used for internal applications, delivering fresh air for a building’s occupants.



Grilles are manufactured in a myriad of shapes, sizes and materials. They provide an economical means for distributing air in a building and are placed within floors, walls, ceilings and even doors to enable the air to pass through to other rooms. They are are ideal for office environments; when walls are moved, grilles in the ceilings or floors can be relocated to meet requirements. Even when altering ceiling layouts, extending the ductwork if necessary and re-siting the grilles is relatively simple.

Unlike door-mounted grilles, the majority of applications require ductwork along with dampers and plenum boxes to act as an equalising chamber and the grille itself to transfer the air. Grilles deliver air for a wide range of applications from small rooms to large exhibition halls and auditoriums. In addition to their functionality, aesthetics is often a key concern, hence the vast array of designs, materials and colours used.

The majority of grilles are bought off-the-shelf. Aluminium, steel and plastic are the most common materials and frequently powder-coated to achieve the desired finish. Prestigious projects warrant a customised approach and use brass or even wood for a higher quality and exclusive finish.



Designs are numerous, but most tend be rectangular or square with perforated patterns or swirl type designs. Circular grilles are very fashionable for ceilings as are floor grilles, which can make use of the existing raised floors, both are often backlit for greater effect.

Displacement ventilation

Another very effective method of moving air around a building is displacement ventilation. This relies on using the natural buoyancy (thermal convection) of warm air to deliver improved ventilation and comfort. Fresh filtered air is introduced at low velocity and low levels at a temperature between 3-6°C below the desired room temperature. The cooler supply air displaces the warmer room air, creating a zone of cool fresh air at the occupied level.

Any heat in the room generated from a person, lighting, machinery and/or equipment will generate a buoyant thermal plume, which will rise to ceiling level where it is extracted. Any contaminants produced by activities in the area will be transported upwards and out of the space. Simple but very effective.



Displacement ventilation offers many benefits and addresses environmental concerns by creating opportunities for using fresh-air based ‘free-cooling’ for a large proportion of the year.

Displacement ventilation systems are most suitable for environments that have high ventilation requirements. These are preferably where contaminants are warmer and/or lighter than the surrounding air, where the supply air is cooler than the ambient air and where the room heights are more than 3m.

In addition to industrial environments, applications include offices, classrooms, airports, atria, retail, food service areas, concert halls and lecture theatres. In many cases the reduced air volume requirements provided by displacement systems means that the costs in such environments would compare very favourably with a mixing system. A key feature of displacement ventilation systems is that supply air entry and extraction can be very discreet and aesthetically compatible with the architectural design of the building and any critical noise level requirements.

Terminal products include wall, floor or in special cases ceiling mounted units to high volume panels designed for high air flow rates in industrial premises to fully adjustable panels for areas with low supply air temperature.

Circular, half-round and quarter-round panels can be used innovatively. For example decorative panels doubling as a support beneath tables in airport lounges, integrated wall panels in corridors and in stair applications with air supplied through floor plenums between each tread.

The wise selection of air distribution systems can ultimately determine the overall effectiveness of an air conditioning system. There are no other hvac products that are as versatile, can lend themselves to such a wide choice of materials, shapes, colours, designs, and can be used in any building project.

Colman Moducel

01732 866066