Multi-objective optimization of classrooms’ daylight performance and energy use in U.S. Climate Zones

Early design decisions have a considerable influence on energy use and occupants’ comfort in buildings. Balancing these two design aspects is extremely important in educational buildings where comfort conditions affect students' health and learning ability. Recent studies have shown a high sensitivity of adolescents and children towards lighting environment, proving the ability of better lighting conditions to improve students’ performance and general health. Admitting more daylight into classrooms can achieve the objectives of regulating students' circadian rhythms due to the proper amount, spectrum, and duration of daylight compared to electric light while minimizing energy use. This study uses multi-objective optimization to find the optimal classroom design in the cold, mixed-humid, hot-humid, and hot-dry climate zones of the U.S. The optimization objectives include minimizing energy use and maximizing the horizontal (desk-plane) and vertical (corneal or eye-plane) daylighting levels. Department of Energy (DOE) primary school building is used as a reference model. Results have shown that rectangular-south-oriented classrooms have the least energy use, while rectangular-north-oriented classrooms provide the highest and most uniform daylighting levels at the desk plane through the entire classroom and at least to the middle of the classroom at the eye-plane. Shallow classrooms with northeast- and southeast windows provide maximum daylighting levels at the eye-plane in the depth of the classroom. The classroom design with the best overall performance in all objectives has a rectangular plan and a northeast-oriented window. All optimal solutions have 3–5% higher window-to-wall ratio (WWR), higher window head height, and 5–8% less energy use than the reference classroom.