TECHNOLOGY VENTILATION
location, prevailing weather conditions (in particular wind direction) and the location and exposure of the louvres. These should then be balanced with the required air flow, the maximum acceptable pressure drop, the degree and depth of acceptable water penetration and, finally, the building’s exterior design, which can dictate where louvres can be placed. By considering these factors, designs can
help to improve building energy efficiency. Conversely, poor specification can lead to rainwater ingress, not enough ventilation, wasted energy and poor performance.
Construction Specialties A4080 system Standard drainable louvres give good air flow and some rain defence but do not perform so well with wind-driven rain
Construction Specialties RSH-5700 This type of louvre is used when high levels of ventilation and maximum protection from the rain are needed
As louvre design has changed in response to demand for better water protection, performance characteristics have also changed
turbulence with areas of low and high pressure. As the turbulence gives water droplets greater momentum, the droplets are thrown out into areas of low pressure and drain away. To get the best possible results from a louvre system, it is crucial that it is correctly specified.
Specifying louvres Specifying a louvre is always a compromise between airflow and water ingress. Traditionally, louvres are specified based on free area (typically 50%), calculated by measuring the clear distance between the blades and multiplying it by the width of the louvre panel (or height, if the blades are arranged vertically). Clearly, free area is dictated by the size of the
louvre. Industry commonly uses a 1m by 1m louvre when quoting free area but, in reality, louvres are never precisely this size. In fact, the smaller the louvre, the lower the proportion of free area, as it is affected by the space taken up by the head, cill, jambs or mullions, which stay the same size. Free area is affected by other factors, such as additional structural support, or if bird screens or insect meshes are fitted. Finally, and perhaps most importantly, free
area alone does not take into account how the air flows through a louvre, with too high a resistance to air flow not enough air will pass through, which can cause a rapid temperature rise inside a building, in turn causing problems with plant. As louvre design has changed in response
to demand for better water protection, performance characteristics have also changed. As a result, engineers and architects should consider a number of factors, including site
44 CIBSE Journal May 2013
The aesthetics of louvre design As louvres are an integral part of the building envelope, aesthetics are an important part of the specification process. Louvres come in a wide range of designs
and colours to suit any application. A louvre system that uses hidden mullions gives clean, architectural lines because the support system is behind the blades, making the mullions almost invisible. Mullions can be spaced about every 1 to 2m and blades are typically 3 to 4m long, dictated by transport restrictions and the weight of the blades. Hidden mullion systems are used to provide screening and protection to buildings with multiple openings. Louvres with visible mullions, on the other
hand, can be used as a design feature, to line up with curtain wall panels or windows. Again spaced every 1 to 2m, visible mullions bring additional benefits, as they are designed to be part of the drainage system. Most performance louvres can be shaped.
However, it is important to realise that performance can be reduced, particularly if horizontal louvres are being used on circular shapes, as the drainage characteristics of their complex blade profiles can be affected. Many louvres can be shaped on plan to give curves or the impression of a curve.
In summary Louvres can play an important role in improving energy efficiency of buildings. However, design has responded to demand for better rain protection and more efficient ventilation. As a result, performance characteristics have also changed and traditional methods of louvre selection purely on free area are no longer valid. Assessment of contributing factors is needed to ensure louvre systems supply a balance between ventilation, water protection, efficiency and aesthetics. CJ
l SIMON HUNTER is product manager of louvres at Construction Specialties
www.cibsejournal.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64