Using Test Results to Select Louvres

Free open area size has long been used when selecting louvres. The way it works is simple. When comparing louvres, the assumption is a larger free open area results in a decrease in pressure drop. In other words, the bigger the hole for air to get through, the more air will get through. Simple.

The problem is it’s too simple. Louvres with a free open area of 48% can have a lower pressure drop (and let in more air) than alternative louvres with a free open area of 60%. This presents a risk when selecting louvres and doing so based on the free open area alone might end up costing you.

Why the assumption?

Maybe the assumption comes from opening a window. It would make sense to say a sash window opened to 50% allows for 50% of the air to flow in when fully open. Extrapolating this to louvres is easy enough and it’s a simple concept for everyone to understand.

But let’s say a casement window has the same free open area to the sash window. The amount of air coming in would be dependent on the direction of airflow, as that casement window might be blocking some air from getting in. So there are complications.

The complications

For a start, there’s the shape of the louvres, something which every calculation method used to calculate the open area fails to factor in. Two louvre profiles might have the exact same free open area of 50% but if one is streamlined and the other isn’t, there’ll be a significant difference in the amount of air which makes it through.

So, shape and design has a profound impact. Think of it this way — you could take a 1m by 1m sheet of aluminium and pierce it with thousands of little pin pricks until it had an effective open rate of 50%. Then take a second aluminium sheet and cut a single big hole that covers 50%. Which one will have a lower pressure drop?

The next complication comes from insect screens and louvres (with insect screens) ordered with a 50% open area have a higher pressure drop than the louvres with a 35% open area.

It doesn’t end there either. Two stage louvres are great for advanced weather protection but will almost always have a higher pressure drop. The air simply has greater resistance and a more difficult path to entry (or exit).

How to select the right louvres

The way to avoid all of the above is to dispense with the notion that the free open area is an indicator of the pressure drop or the performance of a louvre. We’d advise seeking information on the louvre based on test results from testing against BS/EN:13030 or AS/NZS 4740:2000. This standard sets out the guidelines for testing and classification of all weather and performance louvres. Louvres are subjected to 75mm/hour of water at a velocity of 13 m/s. The louvre is then given a three part classification based on; effectiveness, discharge loss coefficient and wind loading. Importantly, it’s only these test results that will provide the information needed to show compliance with H1 Energy Verification Method H1/VM3.

In conclusion, using the free open area as a method for determining pressure drop is wrong. As is using the free open area for assessing the overall performance of a louvre. You need to look at real test results to be sure of meeting the building code.

If you would like assistance with ventilation louvre selection, sizing or compliance demonstration, please feel free to reach out at [email protected] or (09) 973 3616.

VL-100S Twin Weatherstop Ventilation Louvre

Ventüer

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The Ventüer VL-100S aluminium louvre system is a single bank double weather stop ventilation louvre.

Designed for use as an air intake or exhaust louvre in situations where exposure to moderate levels of wind and rain are expected, and where some water carry over is acceptable
Good airflow characteristics, resulting in high ventilation rates
Ideal for natural ventilation of carpark buildings, plant rooms and basements where some water ingress will not damage interior linings or equipment
Constructed from extruded aluminium and suitable for salt-spray zones and other corrosive environments when powdercoated appropriately
Compatible with all common structure and cladding types, including precast concrete, metal cladding, fibre cement sheet and unitised curtainwall systems
Ancillaries such as bird mesh, insect mesh, dust filters, mechanical dampers and plenums can be supplied fitted to the rear face

When sized correctly, the VL-100S louvre system complies with the requirements for natural ventilation of buildings under the New Zealand Building Code clause G4
When installed in accordance with Ventüer technical literature, shop drawings and site-specific engineering the VL-100S louvre system complies with the requirements for structure under the New Zealand Building Code clause B1
When installed in accordance with Ventüer technical literature and shop drawings the VL-100S louvre system complies with the requirements around external moisture as outline in New Zealand Building Code clause E2

VL-55S Slimline Ventilation Louvre

Ventüer

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The Ventüer VL-55S aluminium louvre system is a slim single bank ventilation louvre ideal for small grilles, exhaust vents, louvred doors and mechanical screening.

Slimline single bank louvre designed for small grilles and louvred doors where exposure to moderate levels of wind and rain are expected, and where some water carry over is acceptable
Slim blade profile enables the construction of small louvre grilles and door inserts
High resistance to vandalism and damage thanks to sturdy construction
Constructed from extruded aluminium and suitable for salt-spray zones and other corrosive environments when powdercoated appropriately
Compatible with all common structure and cladding types, including precast concrete, metal cladding, fibre cement sheet and unitised curtainwall systems
Ancillaries such as bird mesh, insect mesh, dust filters, mechanical dampers and plenums can be supplied fitted to the rear face

When sized correctly, the VL-55S louvre system complies with the requirements for natural ventilation of buildings under the New Zealand Building Code clause G4
When installed in accordance with Ventüer technical literature, shop drawings and site-specific engineering the VL-55S louvre system complies with the requirements for structure under the New Zealand Building Code clause B1
When installed in accordance with Ventüer technical literature and shop drawings the VL-55S louvre system complies with the requirements around external moisture as outline in New Zealand Building Code clause E2

VL-2SD Double Bank Drainable Ventilation Louvre

Ventüer

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Best in its class, the Ventüer VL-2SD is a high performing two-stage weather louvre that provides optimum rain defence.

Best in its class, the Ventüer VL-2SD is a high performing two-stage weather louvre that provides optimum rain defence
High resistance to wind driven rain, suitable for high wind zones and exposed locations
Self-draining via rear blade profiles and concealed mullions, suitable for tall louvre panels
No size limitations. Panels can be modulised and assembled on site to and dimension, with the clip-fixed front blade profile providing a continuous appearance
The extruded aluminium louvre blades are supported on a two-piece pressure equalised mullion system, and bordered by a 150mm frame that ejects captured water to the front of the panel
Like the VL-3SD triple bank system, it can be combined with the VL-50CM louvre system to provide cost savings in inactive (blanked off) areas, and can also be fitted with bird mesh, insect mesh or dust filters
Available in a wide range of standard powdercoat colours, the VL-2SD is manufactured to order and can be fabricated in a wide range of sizes
Independently tested and certified to BS/EN:13030

When sized correctly, the VL-2SD louvre system complies with the requirements for natural ventilation of buildings under the New Zealand Building Code clause G4
When installed in accordance with Ventüer technical literature, shop drawings and site-specific engineering the VL-2SD louvre system complies with the requirements for structure under the New Zealand Building Code clause B1
When installed in accordance with Ventüer technical literature and shop drawings the VL-2SD louvre system complies with the requirements around external moisture as outline in New Zealand Building Code clause E2

VL-3SD Triple Bank Drainable Ventilation Louvre

Ventüer

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The Ventüer VL-3SD louvre system is a high performing three-stage weather louvre that provides ultimate protection from wind driven rain.

Designed for use as an air intake or exhaust louvre in situations where exposure to high levels of wind and rain are expected, and where water carry over is required to be minimal
Also suitable for use as a natural ventilation device providing passive air flow to internal spaces
Self-draining via rear blade profiles and concealed mullions, suitable for tall louvre panels
No size limitations. Panels can be modulised and assembled on site to and dimension, with the clip-fixed front blade profile providing a continuous appearance
Constructed from extruded aluminium and suitable for salt-spray zones and other corrosive environments when powdercoated appropriately
Compatible with all common structure and cladding types, including precast concrete, metal cladding, fibre cement sheet and unitised curtainwall systems
Ancillaries such as bird mesh, insect mesh, dust filters, mechanical dampers and plenums can be supplied fitted to the rear face

When sized correctly, the VL-3SD louvre system complies with the requirements for natural ventilation of buildings under the New Zealand Building Code clause G4
When installed in accordance with Ventüer technical literature, shop drawings and site-specific engineering the VL-3SD louvre system complies with the requirements for structure under the New Zealand Building Code clause B1
When installed in accordance with Ventüer technical literature and shop drawings the VL-3SD louvre system complies with the requirements around external moisture as outline in New Zealand Building Code clause E2

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