When holes have been made in a wall, partition, door or duct to allow the passage of air to or from a ventilated space; grilles, registers (i.e. grilles fitted with adjustable dampers), and louvred panels are used to cover these holes. Apart from providing a neat and attractive finish to the installation, grilles and registers are used to give directional and volume control to the flow of air, and louvred panels fitted externally are designed to prevent the entry of rain.
Types of Grilles & Louvres
There are numerous types of designs of grille, such as expanded and extruded metal, pressed sheet steel in various patterns, pressed steel louvres, double or chevron louvres for light proof installations, fixed and adjustable louvres, and egg-crate patterns in anodised aluminium and plastics. They are made in a wide range of sizes and various finishes, and the final choice is usually ased on appearance, size and price, although the ability to allow ransfer and/or deflection of air is the prime objective.
Free Area
A very important factor to be taken into consideration when selecting these items for a particular duty, and this cannot be stressed to highly, is their FREE AREA. That is the open area of the grille through which are can pass freely, and this may be between 40% and 90% of the face area. When investigating complaints of unsatisfactory operation of an installation, we find that the majority of these are due to the grilles used in walls or ducting to allow the movement of air to or from the room, having insufficient free area for the purpose, and therefore causing too high a resistance to airflow. The free areas of grilles, and in some cases their resistance to airflow, will be found in manufacturers' catalogues.
A guide to some of the types of grilles available:
|
% free area of grille
|
Size of Grille (mm) to give approximate free area cm²
| | 325
| 500
| 650
| 1000
| 1300
| 1600
| | 90
| 200 × 200
| 250 × 250
| 300 × 250
| 350 × 350
| 400 × 400
| 450 × 400
| | 75
| 250 × 200
| 300 × 250
| 300 × 300
| 400 × 350
| 450 × 400
| 500 × 450
| | 65
| 250 × 200
| 300 × 250
| 350 × 300
| 400 × 400
| 450 × 450
| 500 × 500
| | 60
| 250 × 250
| 300 × 300
| 350 × 300
| 450 × 400
| 500 × 450
| 550 × 500
| | 55
| 250 × 250
| 350 × 300
| 350 × 350
| 450 × 350
| 500 × 500
| 550 × 550
| | 50
| 300 × 250
| 350 × 300
| 400 × 350
| 450 × 450
| 550 × 500
| 600 × 550
|
Approximate free areas of grille types:
Egg Crate up to 90%
Pressed steel up to 75%
Fixed Louvre 30-70%
Adjustable blade 45-65%
Double deflection up to 60%
Chevron louvre up to 65%
Weather louvre 40-55%
|
