Solar shading system based on daylight directing glass lamellas

The overheating problems in office buildings must be solved with efficient solar shadings in order to reduce the energy demand for cooling and ventilation. At the same time the solar shading should not reduce the daylight level in the building on overcast days because it would result in a lower visual comfort level and increased energy consumption for lighting. The paper describes a new type of solar shading system based on variable lamellas made of solar control glass with high reflectance coating which reduces the solar gain on sunny days and at the same time is able to redirect some of the daylight further into the back of the room where it is needed on overcast days. Daylight simulations performed in IESve/Radiance show that the maximum effect of redirecting the daylight on overcast days is obtained with a slat angle of 30° with the reflective coating upwards. On sunny days when the solar gain must be reduced the lamellas are turned into vertical position acting as an extra layer of solar control glass that reduces the solar energy gain but still allows a good view out. Measurements of the daylight performance were carried out on a full scale model of the solar shading system in SBi's Daylight Laboratory. The results show that the new shading system under overcast conditions reduces the daylight factor, DF, close to the façade while the DF is unchanged or even higher in the back of the office. Under sunny sky conditions the daylight level as well as the heat load is reduced in the office. Compared to traditional solar shading systems with less transparent lamellas the new solar shading system yields a higher DF improving the distribution and exploitation of daylight in the office and furthermore it gives a less obstructed view out. Daylight simulations in IESve/Radiance on a model similar to SBi's Daylight Laboratory with the glass lamellas installed was evaluated and compared with the measurements and it was found that IESve/Radiance may be used to evaluate the daylight performance of glass lamellas systems in most situations. In order to evaluate the effect on indoor temperatures and energy consumption the new solar shading system was mounted in DTU's Passys test cell in front of a traditional glass façade. The measurements and calculations show that the solar shading system with the lamellas in vertical position reduces the solar gain significantly resulting in an improved indoor thermal climate and a reduction in the energy demand for cooling and ventilation.Presenters: name: Jacob Birck Laustsen affiliation: (Technical University of Denmark, BYG.DTU) email: jbl@byg.dtu.d