Methodology for determining fenestration ranges for daylight and energy efficiency in Estonia

Daylight is of interest in architecture for two reasons: On one hand it is appreciated and requested to make the interiors of buildings pleasant and comfortable and to save energy for electric lighting and heating. On the other hand excessive direct solar exposure can cause occupant discomfort and harm the energy efficiency of buildings causing overheating during the warm season. In Estonia, a daylight ordinance establishes the minimum average Daylight Factor for residential buildings and an energy efficiency ordinance sets the maximum acceptable degree hours of overheating. The two requirements are potentially conflicting. The recent architectural trend in Estonia is to use very large windows in residential building design. Even in the Estonian heating dominated climate this causes overheating issues that lead to the previously mentioned regulations. This paper explores the relationship of opening ratios, daylighting and overheating potential analyzing 7812 design variants taking into account room, windows and external wall sizes, presence of shading or balconies and different types of ventilation. It is shown that the overheating potential can be contained and both requirements can be satisfied only using measures such as shading and ventilation.