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How natural light can reduce energy use and improve the passenger experience

We only have to look at the seating choices of people in any building to know that as human beings we enjoy natural light. Go into any restaurant or open plan office and you'll see people naturally locating themselves near the windows.

 

We know we want to be near natural light and have views to outside, however in the last century the use of artificial electric light has allowed us to build ever larger and deep-plan buildings for reasons of space efficiency and economies of scale.  This has left building occupants more remote from daylight and driven up running costs and energy demands as a result. Lighting in many airports is now the largest sole energy demand of the terminal, beating both heating and cooling on an annual basis.

Resetting the body-clock

In the airport environment, access to daylight is particularly important. Passengers arriving from distant time-zones will be able to reduce the effects of jet-lag by quickly exposing themselves to daylight in their new destination. This will allow the circadian rhythms, or internal body-clock, of the traveller to become more quickly synchronised with the new destination. The effect can be improved further by adjusting the colour temperature of artificial lighting in deep-plan or reduced daylight environments (e.g. security and immigration areas) to mimic the outside lighting conditions.  These subtle changes between blue/white light during the day and warmer tones in the evening mimic the external environment. This changing condition will also help airport staff working shift patterns remain alert in the working environment when they are not able to directly access natural light.

Helping people find their way

Architectural design rightly places a huge emphasis on creating amazing spaces with light, whether this is dramatic statements to emphasise scale and volume, or more subtle measures to create a sense of calm or tranquillity. In the airport environment, lighting of the internal structure and surfaces can be an important factor for passenger orientation and wayfinding by giving a greater understanding of the building logic and organisation.  It is important that the artificial lighting and daylight have a common approach to maintain a consistent lighting level of these key building features.

Pushing the boundaries

As designers, we also focus on the amenity value of light to enable building users to enjoy a space, or allow workers to perform tasks in visual comfort. Of course, all of these functions must be completed in the most low-energy way possible.  Developments in recent years such as LED fittings and daylight linked dimming control have become common place in the design of just about every type of building. Airports give us the opportunity to push the envelope harder and develop schemes to both enhance passenger experience and reduce our demand for electricity, ultimately reducing our carbon emissions.

Too much of a good thing?

When designing airport spaces, we consider optimising daylight alongside other key elements like passenger thermal comfort, building heating and cooling demand and the potentially negative impacts of excessive daylight, such as glare.  The challenge here is to achieve ample levels of daylight without allowing in too much solar heat, thereby causing a rise in annual cooling demand. We also need to promote daylight penetration from lower winter sun angles to provide free heating. 

Only by creating a full picture of the ‘Building Physics’ of a space can we understand the comfort and energy effectiveness in operation. The design of integrated, high-performance spaces requires assessment of these elements in parallel. 

The analysis of daylight must also consider the potential for glare from both horizontal and vertical sources.  In an airport, high level roof lights can be a source of ‘veiling reflections’ on both computer screens and display boards.  Clearly, these risks need to be removed to ensure the effective operation of the airport for both passengers and staff. Our analysis includes review of these aspects to assist in the positioning of screens and boards, as well as the use of shading devices to eliminate unwanted glare at a full range of sun angles.

Botanical benefits

An increasing challenge to be incorporated into the daylight design of airport spaces is the desire for internal landscaping and inclusion of vegetation. Like exposure to daylight, human well-being is improved through access to a green environment. Stress reduction, improvements to air and acoustic quality and a sense of connection to the local external environment are all achieved through expressive botanical design.  The daylight design therefore needs to achieve high natural light levels as needed to support photosynthesis for plant maintenance and health.  

The key challenge this brings the design is how to achieve these demanding light levels without driving up the cooling demand of the space through solar heat gain.  Our analysis of these approaches will include the use of ‘climate based daylight modelling’ methods to determine the amount of time areas spend at the higher illuminance levels which are adequate for plant growth, but not sustained for long periods of time where impact on cooling demand will be significant.

Assessing the daylight requirements for an airport environment is a complex process. Through a range of analysis methods we’re able to optimise daylight for energy use and human comfort.  These approaches help promote the health and well-being of passengers and also reduce the running cost of an airport.

By David Williams, Technical Director  Building Physics, WSP

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