Public release date: 31-Jul-2009
Contact: Lerdlekha Tanachaikhan
Inderscience Publishers
A new approach to windows that could let in more light and cut indoor lighting needs by up to 99% in buildings in Tropical regions without losing the cooling effect of shades. Details are reported in the International Journal of Engineering Systems Modelling and Simulation this month.
Lerdlekha Tanachaikhan and colleagues in the School of Environment, Resources and Development, at the Asian Institute of Technology in Pathumtani, Thailand, explain that electric lighting is typically responsible for 25 to 40% of total electricity consumption in air-conditioned buildings. These figures could be reduced significantly they say if daylighting were used instead.
In Tropical regions, however, daylighting leads to a significant rise in temperature, which has to be countered by air-conditioning if the occupants are to remain cool and comfortable. This in turn consumes about 80% of the total electricity consumption for the building.
Earlier studies on daylighting in buildings indicate that window designs and positioning are as diverse as buildings themselves and none currently provides a satisfactory answer to saving on the lighting bills without pumping up the air-conditioning.
The team has developed a formula for tropical sky climate conditions that allows them to assess different window configurations for daylighting. The formula takes into account glass type, solar and visible light transmittance and reflectance, shading coefficient and the heat insulation value, U.
The formula shows that for a city, such as Bangkok, the potential for daylighting is high and could cut daytime electric lighting requirements significantly. The team suggests that for more than 95% of the occupancy period of a typical office building, daylight alone would suffice for lighting with the appropriate window configuration.
This saving would not be reduced significantly even with the use of vertical fins for east-facing windows and horizontal canopies for south-facing windows to reduce heating effects. Daylighting and shading effects can be optimized by following their formula and choosing appropriate windows size and positioning as well as other parameters, such as glazing transmittance.
Not just the tropics. Here in the Atlanta area, offices with windows, such as mine, don't need artificial lighting for much of the day.
2 comments:
Daylighting with skylights is the most effective way to daylight a building. However, you need a low rise building to start with. If you utilize up to the optimum 5% effective skylight to floor ratio in a building with high visible light transmission and 100% diffusion units, you will maximize the amount of hours a day / year you can shut your lights off. ASHRAE and the U.S. Department of Energy have studied and verified that this DOES NOT increase heat gain to the building, but the opposite. It will actually reduce A/C tonnage needs in a building if you shut the lights off with controls.
For more information, visit our blog at http://www.daylightingsaves.com or visit http://www.sunoptics.com to see what the worlds largest daylighting users specify for their high performance daylighting needs.
Thank you very much for this info.
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