Louvre window systems

6 September 2013

It is estimated that 45 per cent of the UK's carbon dioxide emissions come from buildings, principally from space heating and cooling, water heating and lighting.

In an effort to demonstrate corporate social responsibility towards the environment, building owners are increasingly seeking to improve the environmental credentials
of both new and existing building stock.

A good way of improving energy performance is to ensure that a building's louvre system is as efficient as possible.

Louvres are window shutters with horizontal slats, which are angled to admit light and air, but to keep out rain, direct sunshine and noise.

Improving its efficiency means specifying the most appropriate louvres for a new building or replacing ageing louvres with new, high performing systems.

This is because, as well as allowing natural ventilation to a building, an efficient louvre system can improve air flow while protecting these openings against rain ingress. As a result, less power is needed to move the volumes of air required and, in the case of HVAC systems, improved energy efficiency can sometimes mean a smaller and less powerful system is required for space heating and cooling.

Louvre design is continually developing in response to demand for better water protection and, as a result, the latest systems are a long way from the simple screening louvres of the past.


Multi-use
Screening louvres are still suitable for locations where water penetration will not cause significant problems (such as screening of rooftop plant or in a multi-storey car park). They typically have simple blade shapes, which allow good air flow, but give limited defence against rain. Standard drainable blades, on the other hand, give good air flow and some rain defence, but do not perform as well with wind-driven rain. They are used when occasional ingress is not a major concern and where some drainage of cascading water is required.

Storm-resistant or performance louvres typically provide moderate -to-good air flow with excellent defence against wind-driven rain. They are used when high levels of ventilation and maximum protection from the rain is needed, for instance when sensitive equipment such as HVAC plant is behind the louvre.

The type of louvre system chosen will depend on the balance being struck between air flow and water ingress. All louvres restrict the passage of air. This resistance is called a 'pressure drop'. Too high a pressure drop and not enough air will be allowed through, which can cause a rapid temperature rise inside a building, in turn causing problems with generators and HVAC equipment.


Specification
Louvre specification needs to consider a number of factors, including site location, prevailing weather conditions (in particular wind direction) and the location and exposure of the louvres (which will dictate air flow rate and the amount of potential wind-driven rain).

These factors 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.

As louvres are an integral part of the building envelope, aesthetics are important, but it is essential performance is not compromised. Louvres come in a wide range of designs, colours and finishes to suit most buildings. They can be hidden behind features or perforated panels (which can also act as bird and insect screens), but this can obviously increase resistance to air flow. Additionally, most performance louvres can be shaped (for example to create curves) but this can impact on drainage capabilities.

A well-designed louvre will reduce the pressure drop, allowing a larger volume of air through and thus cutting the amount of fan power needed to deliver the required air flow. Conversely, poor specification can lead to rainwater ingress, not enough ventilation, wasted energy and poor performance, not only of the equipment being ventilated, but of the entire building.

Louvres are an excellent way of helping facilities managers meet ever-more demanding environmental legislation and client requirements for sustainable buildings, playing an important role in improving energy efficiency, lowering power consumption and reducing carbon emissions. However, to help improve a building's energy performance and get the best possible results from a louvre system, it is crucial that it is correctly specified.


Louvre specification
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).

Free area is dictated by the size of the louvre, with industry commonly using a 1m by 1m louvre when quoting free area. However louvres are never precisely this size. Free area is also affected by other factors, such as additional structural support, or if bird screens or insect
meshes are fitted.

There is a need to move away from specifying louvres purely on free area. A number of factors need to be considered, including site location, prevailing weather conditions (in particular wind direction) and the location and exposure of the louvres (which will dictate airflow rate and the amount of potential wind-driven rain).


Simon Hunter, product manager of louvres at Construction Specialties