Building Envelope Performance to Achievement of Energy-Efficient Buildings : a case study analysis in Ulil Albab Mosque Yogyakarta

The performance of the building envelope is one of the most important in energy-efficient buildings. As the outermost layer, the building envelope will be very decisive for heat transfer from outside to inside the building. The performance of the building envelope in heat transfer refers to as the Overall Thermal Transfer Value (OTTV). OTTV measures the average heat gain into the building through the building envelope. It is a measure widely adopted in many countries to improve the design of energy-efficient buildings. The OTTV value strongly influences the ratio of transparent openings on the building facade. The size of the transparent opening will affect the inclusion of natural lighting in the building. This study aims to see how closely the relationship between the OTTV value and the achievement of natural lighting in buildings according to standards. The values used as success standards are the GBCI and SNI parameters. This research expects to provide a reference for existing buildings to improve building performance, especially for energy efficiency. This study uses a simulation method with OTTV worksheets and DIAlux Evo calculations. The mosque chooses to be a case study because the mosque is a building that has a distinctive orientation. In this research, Ulil Albab mosque, Yogyakarta, for the case study. For the location of Yogyakarta, the Qibla direction is azimuth direction 294° 42′ 39.894″ (Northwest) from Yogyakarta, where the radiation factor value is the largest. The results of this study indicate that the OTTV value can follow the standard by lowering the percentage of WWR in a facade with a high radiation factor value. Still, a WWR that is too small can result in natural lighting being unable to enter the room. In this building, the most efficient thing to do is replace the transparent material with one with better thermal properties.