Evaluation of energy and lighting in schools considering solar protections

Abstract

The implementation of the solar protections laid out in the regulations and certification systems decreases cooling demands, although it has an uncontrolled and even unforeseen effect on daylighting. Achieving a balance between both requirements is a challenge for facade design, energy behavior, and lighting performance since restricting solar radiation contributions decreases daylight's contribution. This research aims to define a methodology that allows, in the early design stage, the evaluation of solar protection solutions that consider the optimal performance of daylight using annual dynamic indicators while maintaining adequate energy-saving levels. For this purpose, cooling energy consumption and dynamic indicators have been considered as the primary indicators, namely Spatial daylight autonomy (sDA), Annual Sunlight Exposure (ASE), and useful daylight illuminance (UDI) with variations of the Modified Solar Factor (MSF). Thermal and light performance assessments were made using energy modeling for two types of solar protection. The case study is a school classroom located in the city of Talca, in central Chile, considering window-to-wall ratios (WWR) of 40 %, 50 %, and 60 %. The premise's thermal and light behavior were obtained with both types of solar protection. The sDA and UDI results allowed making an approximation of optimal solutions, however, the ASE values in all cases, were classified as unsuitable for classroom use. The analysis suggests that better limit values for both requirements are obtained by organizing the results by WWR instead of by the MSF that each solution identifies. This methodology compared solar protection options at an early design stage, reaching recommended light performance levels and energy savings of 70 % or more, for the two types of solar protection. It is concluded that to achieve minimum acceptable daylighting levels, in balance with cooling energy consumption, it is necessary to consider annual dynamic assessments with sDA and UDI as relevant indicators.