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An automated daylighting control system

© 2019 EPFL

© 2019 EPFL

Dr. Yujie Wu successfully defended his thesis on Friday, May 3rd.
He outlined the concept of an independent, decentralized system with a built-in photometric device to automatically manage the blinds position in buildings. A new step towards the Energy Transition 2050 and living and/or working spaces with low carbon emission.

Sufficient daylight exposure contributes to occupants' well-being, productivity and health in buildings. However, excessive sunlight ingress induces discomfort glare and increases the cooling load during the warm season. The performance of manual shading systems is limited by the users’ low interaction frequency. Since sky conditions are dynamic, frequent blinds adjustments are necessary, but these are impractical for users to manage.

Various shading automation systems have been proposed to foster the utilization of daylight in buildings, the performance of which is limited by a number of factors, including insufficient glare protection, disturbing movement of slats, privacy issues, and commissioning difficulty. In this doctoral thesis, an integrated daylighting control system is suggested and demonstrated to regulate daylight in buildings. Based on real-time lighting computations based on the monitored luminance distribution of the sky and landscape, the proposed system is fully decentralized. First, an embedded photometric device (EPD) was designed and validated, showing improved accuracy in daylighting simulations compared to using standard sky models. The EPD is composed of an image sensor and a microprocessor. After calibration, the spectral response of the imaging system is close to the photopic eye sensitivity function V(lamba) achieving a 8.9% spectral correction error. The luminance detection range spans from 1.2 x 102 to 3.8 x 109 cd/m2, covering extremes of both the shadowing landscape and the sun orb luminance. The EPD monitors the luminance distribution of the sky vault and the ground fraction.

Based on the generated luminance map, the EPD is able to perform on-board lighting computing. The performance of work-plane illuminance (WPI) simulation was cross validated with a lux-meter array in a daylighting test module under different sky conditions, achieving a mismatch below 10%. Secondly, since the bidirectional distribution function (BTDF) commonly used in daylighting simulation involves bulky data, a compression scheme based on planar wavelet transforms was investigated; its generic error and influence on daylighting simulation were studied at various compression ratios. Results showed that both WPI and daylight glare probability (DGP) are relatively immune to a BTDF compression ratio below 100.

Thirdly, an automated Venetian blind was designed which integrates the EPD both as a photometric sensing unit and a controller based on real-time lighting simulations. The EPD determines an optimal shading position according to the simulation results, to offer sufficient WPI, mitigate excessive solar heat gain (SHG), temper discomfort glare, and maximize outwards view. 'In-situ' experiments demonstrated that the automated Venetian blinds were able to regulate WPI in an efficient way. The expected reduction of cooling loads due to SHG was estimated to 47% compared to the absence of shading protection during the warm season. It was also demonstrated to mitigate discomfort glare timely, including veiling glare from surroundings. A subjective study conducted with 34 human subjects showed satisfaction with regulated daylight provision, glare mitigation, and quietness of the slats movement.

Finally, the EPD was used to control tint states of a split-pane electrochromic (EC) window to secure occupants' visual satisfaction. Experimental results in a full-scale testbed showed that the WPI was maintained within the required range under clear skies during 83% of the time, and the DGP during 95% of the time; under partly cloudy skies, the WPI was maintained within the range during 62% to 68% of the time and for the DGP during 85% to 94% of the time offering an optimal visual comfort.

Funding

This research was funded by the Swiss Innovation Agency Innosuisse through the Swiss Competence Center for Energy Research "Future Energy Efficient Buildings and Districts" (SCCER FEEB&D).

References

Wu Yujie, Prof. Jean-Louis Scartezzini, Dr. Jérôme Kämpf, chef de groupe "Energy Informatics Group"Institut de recherche IDIAP (dirs) Automated Daylighting Control System based on Sky Luminance Monitoring and Lighting Computing. EPFL Thesis N°9498, 2019.


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