Abstract

Integration of daylighting into buildings using motorized interior shades is challenging. If it is done properly, reduction of energy for artificial lighting and eventually building cooling demand can be achieved, while providing an improved visual and thermal office environment, beneficial for the occupants' health and performance. If it is poorly done, it can lead to increased cooling demand due to overheating, thermal discomfort and glare problems. In this study, the daylighting and thermal performance of "bottom-up" shades was presented. The bottom-up is a motorized roller shade that operates in reverse of a conventional roller shade (opens from top to bottom), so as to cover the bottom part of the window, providing privacy to the occupants, while allowing daylight to enter from the top section. A daylighting simulation model, validated with experimental results, was developed in order to establish correlations between the shade position, outdoor illuminance and work plane illuminance for different outdoor conditions as well as to allow a sensitivity analysis of the impact of shade optical properties on the results. Moreover, the model was used to compare "bottom-up" shades with conventional roller shades. The results showed that the Daylight Autonomy (DA) for the bottom-up is 8%-58% higher than the DA for a conventional roller shade, with a difference of 46% at the back part of the room, away from the façade, where the use of artificial lighting is usually more needed, proving the advantage of bottom-up shade versus conventional roller shades, by allowing the natural light to enter from the top section of the façade deep into the room. Thermal experiments were conducted to examine the possible advantages of the use of a bottom-up shade's "sealed" cavity, showing increase of the effective thermal resistance of the fenestration, compared with no shades and with conventional roller shades. Finally, a methodology is proposed for the development of a control algorithm for a bottom-up shade, applicable for any location and orientation.