Light shelf geometry for daylight and lighting energy saving in small medium enterprise open office plan in Malaysia

Abstract

Open office plan are common due to their space efficiency. However, daylight, a cardinal design element which has a rendering that best matches the human eye with its attendant physiological, psychological, task performance improvement and the energy conservation merits are not enjoyed in most open office plans. This is due to the use of large unilateral side-lighting which results in excessive and low illumination at the work plane in area close to window and at the back of the office room respectively. This illuminance contrast causes visual discomfort, a situation which makes office tenants avoid available daylight with blind and depend on electric lighting. Light shelf (LS) is one of the daylighting systems which have been studied in the past, however, these research were done mostly in the temperate climate which is different from the tropical climate. Besides, there is a scarcity of the research on energy saving implication of daylighting with LS in the tropics, and as such, the thrust of this research is to study the daylighting performance of LS and its attendant lighting energy saving for open office plan in tropical climate. External LS of 0.6 m and 0.9 m depth placed at different angles with the clerestory window were combined with internal LS of 0.6 m depth at different tilt angles from the clerestory. Additionally, internal LS of 0.6 m depth was introduced at a distance of 0.6 m and 1.05 m from the internal LS to test the effect of additional shelves. Sixty-seven (67) LS test cases were studied using simulation with the application of Integrated Environmental Solution Virtual Environment. The result proved that LS cases improved the daylighting quantity by reducing excessive illumination at the area near the window opening of a unilateral side-lighting office and increasing it at the back where the illuminance level was low. LS was able to improve work plane illuminance (WPI) distribution across the whole room compared to the base case with the range of 65.22 % to 80.00 %. It also improved WPI distribution between the adjacent points in the room with the range of 17.06 % to 25.00 % and saved energy for electric lighting ranging from 11.70 % to 15.97 %. This study therefore, concluded that the depth and angle of the LS affect its efficiency. Hence, the finding of this study encourages the use of LS in the open office plan with unilateral side-lighting by recommending optimum LS geometries based on different orientations.