BSEE AUTOMATIC SHADING
Daylight is a fantasc resource, but it has to be controlled. Sam Woodward, Customer Educaon Leader, Europe and Africa at Lutron Electronics, explains how automated shading makes this possible.
don’t forget the other major benefit of daylight: it’s free. In homes, workplaces and commercial buildings of all kinds, architects and designers are going out of their way to bring daylight indoors. Buildings research body BRE says: “access to natural light is a vital part of a healthy environment”, while building services engineering body CIBSE advises: “Daylight is the only freely available light source and yet all too often it is overlooked. Well controlled daylight can provide a space with the best possible lighting effect, superb colour rendering, superior user comfort and with zero cost or CO2 emissions.” The key words there are “well controlled daylight”. People love daylight – but only when it suits them. They don’t like it when it’s too bright, creates uncomfortable glare, or makes the room too hot.
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It’s hardly surprising that sunlight is difficult to control: it’s the most powerful light source we have, but it’s constantly moving and changing, is significantly affected by unpredictable weather patterns, and it doesn’t come with a switch.
Managing this isn’t easy. Light levels outdoors vary between 1,000 lux on a cloudy day to more than 100,000 lux in bright sunshine, whereas the European standard for workplace lighting (EN12464-1) recommends just 300 to 500 lux indoors for most tasks. The location and orientation of a building has a significant impact on the sunlight it will receive, and every building’s needs are different. Daylight integration has to be carefully planned to take advantage of all its benefits, while avoiding excess glare, unwanted silhouetting and shadows, and mitigating heat gain and privacy issues. Integrated, automated shading control solutions ensure you get the benefits of daylight indoors without the downsides.
uChoosing blinds that balance performance and aesthecs is essenal.
Why choose shades?
Automated interior solar blinds can minimise glare from the sun, reduce
atural light makes us feel good, and our bodies and minds react well to it. If that all sounds too touchy-feely, then
solar heat gain and save energy used for air conditioning and artificial lighting.
Other options include exterior louvres and electrochromic glass, but these have significant disadvantages. Louvres create sharp lines of bright sunlight, while electrochromic glass can be slow to respond to light, can struggle to reduce the sun’s glare, and can affect the colour of light indoors. These options are usually fixed and permanent, making them very difficult to change once a building is completed and occupied. Shades help avoid these problems, and they can also be added to buildings post-occupancy. Blinds also do a great job of preserving views to the outdoors, which has a positive effect on the atmosphere in a building, giving people a sense of place and a connection to nature, and allowing the eyes to relax by focusing on things in the distance.
Getting the most out of shades
Good shading design requires a number of decisions to be made, including consideration of the size, number and location of windows, the overall layout of the space, and the type of glass used.
To achieve an optimal design, engineers need to decide how to prioritise daylight access, glare control, views, and heat gain. For instance, minimising glare may be important in an area where important technical tasks are being performed, but less important in a reception area, where designers may choose to prioritise clearer views of the outdoors. It’s important to be able to quantify light levels, glare and heat gain. Heat gain is measured using the solar heat gain coefficient (G-value), and there are various metrics for measuring glare, including the widely used unified glare rating (Tv, APSH).
Shading produces the best results when control is automated, using continual calculation of the sun’s position in the sky, combined with sensor readings at each window position to measure actual local light levels, to communicate that information across the systems controls, and to adjust the height of shades accordingly.
Shades move into precise positions throughout the day to protect the occupants from glare and solar gain, while letting light in where that’s desirable. As part of a dynamic, responsive system, shades on windows facing different directions will react differently as the sun moves around a building.
A combined system can integrate control of shades with electric lighting, making control easier (and can even integrate with control of other building services too).
Automated shading systems have been found to unlock significant efficiencies. A study by Lutron and Purdue University in the US found energy savings of 65% were possible from automated shade control compared to manual control.1 There is a lot for buildings engineers to consider when specifying shading.
18 BUILDING SERVICES & ENVIRONMENTAL ENGINEER MAY 2018
Adversing: 01622 699116 Editorial: 01354 461430
DAYLIGHT CONTROL WITH SHADES Making the most of a free light source
Harnessing daylight’s wonderful natural resource helps save energy and improve work environments, maximising comfort and therefore productivity too. Good quality shading delivers in spades.
Choosing the right shade fabric
Selection of blind fabric that appropriately balances performance and aesthetics is essential. Different fabric properties affect how much light and heat gets through, and how clearly people inside can see out. The colour and opacity of the fabric, and the pattern of the wave all have an impact – and there can be significant performance differences between fabrics of the same colour. Unfortunately, there can be considerable variances in a shade fabric from the quoted specification. When selecting fabrics to meet specific glare or solar gain targets then it’s important to select specification- grade fabrics like those that conform to Lutron’s THEIA Performance Specification2
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The THEIA specification sets out tolerances for visible light transmittance (+/-1% of total or +/-20% x Tv) and openness (+/-0.75%), ensuring that glare and solar gain don’t wreak havoc with performance and comfort.
The key metrics for blind fabric are:
u Visible light transmittance (Tv): The total amount of visible light that gets through the shade, either directly or diffusely. u Openness: The percentage of light hitting the shade, which gets through directly– determined by the size, shape and number of the openings in the weave. u Solar reflectance (Rs): The percentage of solar energy that the fabric reflects away.
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The locaon and orientaon of a building has a significant impact on the sunlight it will receive, and every building’s needs are dierent. Daylight integraon has to be carefully planned to take advantage of all its benefits, while avoiding excess glare, unwanted silhoueng and shadows, and migang heat gain and privacy issues.
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References: 1
Lutron - Energy Savings:
http://performanceshadingadvisor.com/ LutronResourcesStaging/pdf/
energySavings.pdf 2
Lutron – Fabric Properties and Building Performance:
http://performanceshadingadvisor.com/ pdfs/THEIA_whitepaper_201504_Rev1.0.pdf
VISIT OUR WEBSITE:
www.bsee.co.uk
uDaylight integraon has to be planned to take advantage of all its beneflts.
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