Daylighting Modeling – What You Need to Know
By Tim Metcalfe
Hear the word ‘daylighting’ and many people think just that – simply using the light of the day within a building by strategically placing a couple windows or a skylight. But as architects know, daylighting is quite possibly one of the most important aspects of the building envelope, both in terms of energy efficiency and occupant comfort. Many quantitative studies over the years have repeatedly confirmed daylighting’s benefits of higher productivity through improved environments in educational and commercial settings.
Daylight modeling displays the relationship between a building and the environment that surrounds it. It is a way to easily validate design changes to clients by visually and quantitatively presenting the benefits of the proposed design changes. Costly design changes can be avoided later in the construction process by implementing and testing changes during the design process.
Daylighting not only improves the performance of its occupants but also improves a building’s performance. And few components of a building hold as much potential as the building envelope – and as many challenges – for contributing to the sustainability of a building. How can architects design with daylighting more effectively, eliminating costly factors such as solar heat gain and glare? Advancing technologies offer answers in materials and approaches that contribute unprecedented energy efficiency and economy with a building-integrated approach.
Daylight modeling can be used to ensure criteria and conditions are being met within a space for LEED credit. Attendees will gain a comprehensive understating of the benefits and best uses for different daylight analysis methods, such as base radiance, daylight autonomy, volumetrics and 3D grid analysis.
As architects search for ways to incorporate more daylighting for greater sustainability, they are finding advancing technologies that enable them to incorporate a whole-building design with respect to daylighting. These technologies include translucent glazings that diffuse light as they add thermal value, insulating aerogels that double the glazing’s thermal values, spectrally selective coatings that reduce heat loads while collecting and transferring solar heat, transparent photovoltaic modules that deliver 3x concentration with no tracking systems and co-functional LED-based systems that transform translucent luminosity into true illumination. Such technologies can create skylights and walls that perform multiple functions, creating enhanced sustainability and contributing to LEED certification.
These advances revolve around today’s high-performance polycarbonate glazing technology, which brings building owners and occupants the benefits of diffuse daylighting without the burdens of solar heat gain and glare. Results are lower heating, cooling and lighting costs plus improved interior comfort for greater productivity, often at initial costs one-third to one-half less than traditional systems, along with exceptional life-cycle savings.
Energy Efficiency – Multiwall polycarbonates typically range from 6mm to 40 mm 7 layers thick, for example, which achieves U-value down to 0.19, R-value up to 5.26 and diffuse light transmission up to 68%. Add translucent aerogel insulation to this and the U-value can go to 0.10, R-value to 10, light transmission to 33%. Double-glazed systems can increase both thermal values and security. A new transparent, spectrally selective low-E coating applied to the interior cells can reject infrared rays by 40% - 95%, UV rays to 99%, solar energy from 40% - 85%, while maintaining light transmission from 25% - 65%, for significant savings in HVAC equipment and operation. This coating enhances U-values and also reflects heat back into buildings without allowing it to escape. Emerging technology in building-integrated photovoltaics (BIPV) is meshing translucent polycarbonates with transparent solar modules to achieve lower-cost systems that generate electricity and provide daylighting with minimal heat gain; the first of these is expected to reach the market by mid-2010.
Light Transmission – Diffuse daylighting with translucent polycarbonates in skylights, curtain walls and clerestories eliminates the distracting, uncomfortable glare and hot spots that result from direct daylight. That’s critical when there’s a computer on every desk or a classroom where every inch of usable space counts. Translucent polycarbonates allow a wide range of visible light transmission, depending on the tint and thickness chosen. Typical ranges are 80% to 60%, spreading user-friendly daylight evenly throughout a space and projecting it 30% deeper into the space. Translucent interior walls and partitions too can continue the flow of diffuse natural light while maintaining privacy.
Design and Engineering Flexibility – Gaining energy efficiency doesn’t mean sacrificing design and engineering flexibility. Shatterproof, multiwall polycarbonates are 200 times stronger than glass at only 1/6th the weight, enabling designs with wider spans and lighter supports. Cold forming for curves and accents is easy. Colors, textures and structural capacities encompass a wide range, and sheets run from standard 4’x8’ up to 29’ long with options up to 48’ long. Custom systems can incorporate glass sections for visibility and ventilation in prime systems for new construction, full replacement for retrofit or overglazing without removal of existing windows and skylights.
Architectural Aesthetics – With today’s polycarbonates, high performance is complemented by colors with architectural appeal, ranging from blues and greens to the metallic sheen of silver, plus textures that range from satin matte to hammered crystal. One of the most appealing advantages is the illumination possibility with this translucent material. Translucent walls can integrate dynamic color-changing backlighting and cavity lighting engineered with custom low-voltage LED light grids that add dramatic design effects for both interior and exterior applications, creating a co-functional luminous element that’s also a true primary illumination source.
Incorporating daylighting technologies from the very onset of building construction or renovation can decrease expenses both during the design phase and once the building is complete. This is an important quality of building design in today’s architecture market.