Louvres make the grade

In the education sector, getting ventilation right and ensuring a healthy and comfortable environment has never been more important. Andy Moul of Construction Specialties looks at key factors which need to be taken into consideration when specifying external louvres as part of a building’s ventilation solution

Ventilation design is a balancing act between delivering a high quality of air and thermal comfort, while maintaining energy efficiency standards and noise control. Ease of maintenance and long term operational costs of running the system add to the complexity.

Published in 2018, a revised Building Bulletin 101 (BB101) – ‘Guidelines on ventilation, thermal comfort and indoor air quality in schools’ – places an emphasis on ventilation strategies in educational facilities. Although not a legal requirement in itself, BB101 is referenced in Approved Documents Part F (‘means of ventilation’) and L2A (‘conservation of fuel and power’) of the Building Regulations and sets out detailed guidelines for ventilation rates in different building areas, delivering improved air quality and achieving adaptive thermal comfort. Since the document also stipulates a requirement for a controllable and draught-free air supply, it means that windows, which have traditionally been used to provide fresh air to a room, should no longer be seen as a sole method of ventilation.

BB101 looks in detail at different ventilation strategies, from natural, through hybrid or mixed mode, to mechanical ventilation and sets out performance standards for all of them.

As a means of providing airflow into a building, external louvre systems have an important part to play in ventilation strategies, and their performance characteristics need to be taken into consideration alongside aesthetic requirements.

Louvre specification
There are three main types of louvre systems available, offering different performance characteristics. Designed to be simple and economical, screening louvres utilise a flat blade profile to provide airflow into a building and some rain defence. These are typically used at the top of buildings to hide unsightly HVAC systems, or perhaps in car parks to allow for ventilation of exhaust fumes.

Ventilation louvres are chosen when airflow is a key consideration. They may provide adequate rain defence in light rain, but their performance generally falls short in wind-driven rain conditions.

When potential rain penetration is an issue, specifiers should consider rain defence louvres with integral water collection and drainage. These systems are designed to stop wind-driven rain entering a building, while allowing efficient passage of air. This is achieved through either a complex single-blade profile extrusion to give a slim louvre depth or a deeper, multi-bank system.

Louvre performance
Traditionally, louvres were specified based on a simplistic, physical ‘free area’, which simply relates to the gaps between the blades in the louvre design that facilitate airflow, but this does not quantify airflow efficiency. Therefore, specifiers should be placing more importance on the ‘design pressure drop’ and aerodynamic airflow efficiency. This is a true indicator of a louvre’s performance, which ensures mechanical equipment has the required airflow to optimise function.

When it comes to the selection of a rain defence louvre system, third-party test data should be examined to ensure a project’s functional requirements will be met. The BS EN 13030:2001 standard is used for evaluating a louvre’s effectiveness against rain penetration as well as its airflow characteristics, and enables specifiers to directly compare the performance of the different weather louvre systems available.

All performance considerations such as required airflow, the maximum acceptable pressure drop, and the degree and depth of acceptable water penetration should therefore be balanced with the building’s envelope design – hence the need for a ‘form and function’ approach.

Other specification factors
A site’s location and the position of louvres on a building is another important consideration in louvre selection, as exposure to prevailing weather conditions – in particular wind direction – will affect the amount of potential wind-driven rain penetration. In addition, BB101 recommends that ventilation intakes are positioned away from the direct impact of air pollutant sources, such as parking areas, loading bays or busy roads, while exhaust locations should be chosen or designed to minimise re-entry of exhaust air into the building.

Louvres are available in a wide range of designs, finishes and colours to suit any application. A louvre system that uses hidden mullions, for example, gives continuous, architectural lines because the support system is behind the blades, making the mullions almost invisible. Louvres with visible mullions, on the other hand, can be used as a design feature to line up with joints between exterior wall panels or with windows. These systems are typically supplied in a prefabricated modular form and are available in designs offering horizontal or vertical blade configurations.

Other design options include models utilising varying blade depths for added interest, or hidden behind decorative features such as perforated panels – which can also act as bird screens. Specification should always be supported with performance test data, as such features can potentially increase a louvre’s resistance to airflow.

Desired looks
Architectural louvre systems provide creative freedom to specifiers without sacrificing airflow performance.

An excellent way to address air quality and ventilation challenges in schools and colleges, louvres can improve a building’s energy efficiency, lowering power consumption and thus reducing carbon emissions. They can also have a positive, creative impact on a building’s exterior design.

Andy Moul is technical manager at Construction Specialties