Daylight Technologies

Systems and controls for harnessing daylight

Good daylighting design provides useful illumination while minimizing heat gain and glare. Adequate daylighting reduces dependence on artificial light and is thus key to NZEBs. Appropriate use of windows, skylights, clerestories, and other apertures in the building provide means to harvest daylight. Modern technology even integrates daylighting systems with electric lighting to optimize lighting energy use. In this webinar, Sekhar Nori, an award-winning daylighing solutions expert, discusses various technologies and controls for harvesting daylight.

Skylights are prominently used in warehouses and similar typologies to provide illumination to large spaces. A low skylight-to-floor ratio (SFR) of around 1% is considered adequate in India, as compared to 5% for locations at higher latitudes. Beyond that results in heat gain.

Multi-glazed skylights are double glazed and triple glazed solutions for the skylights with improved heat and glare reduction. Lightpipes can be used for both top or side lighting to deliver diffused sunlight into dark corners and even basements. Lightpipes capture sunlight using a light collector exposed to sunlight and transport it through a highly reflective pipe. The lightpipe’s diameter determines the intensity of the diffused light delivered. Sekhar highlights the efficiency of his flagship product where the maximum run of the light pipes is as high as 15 meters.

Next, we learn about light shelves, horizontal surfaces that can reflect daylight deep into building interiors. The system of lightshelves of Skyshade blocks about 70-80% of the direct sunlight and reflects the remaining 20-30% of the sunlight into the room. This provides enough lighting for the room and also reduces the glare and heat transmission in the room.

Modern hybrid systems even integrate with the Building Management System (BMS). Since daylight flux doesn’t remain constant through the day, BMS integration facilitates the lighting requirement from electrical lights for the building. These systems may monitor only daylit area (Open loop systems) or areas that use both daylighting and electrical lighting systems (Closed loop systems).

Moving on in the webinar, Sekhar also offers insights into several projects that have successfully deployed daylighting systems, including new constructions and retrofits. For example, the Secunderabad Railway Station was retrofit with wall-mounted daylighting systems. Infact, the Indian Railways is planning to convert several of its other buildings to daylit spaces. The Rae Bareli Modern coach factory is the largest project in Asia to use daylighting systems. The Chennai International Airport under construction will use sun-tracking daylighting systems completely integrated with the electric lighting system.

The expected energy savings from these hybrid systems is about 40-50% for buildings operating 24 hours and it rises to around 70-80% for 10-12 hours of building operation. But, are these systems economically viable? In the webinar, we learn that typical projects can expect a payback period of around 2 years as compared to using fully LED systems. The payback period will be still lower if we take into consideration cooling load reduction. Considering the energy savings, from lighting and cooling loads, and the economics, the use of daylight technologies becoming a norm in retrofit and new projects makes sense.

This webinar was conducted on 4th August, 2019.