shading device, windows performance, energy demand, thermal comfort, visual comfort
Solar radiation plays a significant role in reducing building energy consumption for air-conditioning and lighting and affects thermal and visual comfort conditions. Additionally, for the occupants of confined spaces, daylight strongly affects not only the human performance but also the general well-being, both from a psychological and physiological point of view. On the other hand, large windows on building façades may facilitate the entry of daylight and solar heat gains, increasing the risks of overheating or visual discomfort. In these cases, the proper use and control of shading devices is mandatory to prevent glare and direct solar radiation on the occupants, even while affecting the energy performance. The best balance between those contrasting requisites has to be defined by comparing the behavior of different combinations of glazing systems and shading devices, while considering the specific application context. In the assessment, different metrics are needed to analyze both comfort and energy aspects. In this paper, the effects of external and internal roller shades, both on thermal and visual comfort and on overall building energy demand, have been considered for the climatic conditions of Rome. An open-space office with windows distributed on a single façade or on opposite façades, and directed towards 2 orientations (South or South/North and East or East/West) has been simulated. The window area and the glazing system have been changed in order to evaluate the shading performance in several office configurations. The thermal comfort indoor conditions have been controlled by fixing adequate operative temperature set points. Shades with three different levels of solar and light transmission coefficients have been chosen for the comparison. To fulfill occupant visual comfort, the shades are controlled based on two set points: on a limit glare index of 22 DGI and on the maximum total solar radiation incident on the windows - 150 W m-2. An illuminance level of 500 lux during the hours of occupation is guaranteed by dimmable artificial lighting. Concerning the energy performance, the office primary energy demand for heating, cooling and lighting have been calculated. The assessment of the long-term comfort conditions has been conducted on a seasonal basis, taking into account both the thermal and visual comfort conditions. Regarding thermal comfort, the Discomfort Time weighted by the Predicted Percent of Dissatisfied (WDTPPD) and the radiant temperature asymmetry have been calculated in 9 points in the office including also the effect of the diffuse and beam solar radiation directly reaching the occupants. The visual comfort has been assessed through three climate-based metrics: the Spatial Daylight Autonomy (sDA), which describes the annual sufficiency of ambient daylight levels, the Annual Sunlight Exposure (ASE), which describes the annual potential risk of visual discomfort in interior work environments and the Daylight Glare Probability (DGP), which is the percentage of disturbed people. The dynamic simulation has been conducted in EnergyPlus 8, while the visual aspects have been analyzed with DaySim and equivalent lighting simulation codes.