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The purpose of this paper is to determine the approximate window-to-wall ratio (WWR), window width-to-height ratio (WHR) and sill level for a room in Rasht–Gilan province and to present an optimal window in each of the WWR ranges providing the minimum energy consumption by integrating artificial lighting and thermal analyses, whilst maintaining internal comfort conditions using dynamic evaluation.

The process of modelling has four main steps: 1 – defining the building's features and requirements, 2 – validating input weather file data by on-site measurement, 3 – determining input parameters for the lighting and thermal analysis and 4 – clarifying variable parameters and fitness function for the optimization algorithm. Also, the survey study is performed in a daylit office room, in which 30 employees are employed to answer the questions in three different times of a day. In this process, the impact of daylight on their visual comfort is surveyed in 1,350 different illuminance levels which are manually recorded.

The range of useful daylight illuminance (UDI) values is determined as 200–1,000 lux. The optimum range of WWRs in the case study is 15%–25%. Also, due to the appropriate window height, electric lighting could be decreased by 40%.

Thermal and lighting performance in buildings is the relation of facade characteristics to environmental sustainability. Recent studies focussed on optimizing WWR and window characteristics considering thermal comfort and energy analyses. However, architects need freedom for designing façade and making decisions in their first sketches. Thus a guideline for optimum window conditions in each WWR is required. Also, considering occupants' behaviour in practical buildings, the visual comfort investigation is a gap in WWR optimization.