A systems modeling approach to the analysis of daylight dimming systems

The determination of daylight dimming system performance is a complex analysis issue. To investigate the performance of such a system, a detailed computer analysis model (DayDim) was developed. This computer model considers the directional response of photosensors and application of the Perez daylight model into daylighting system performance analysis, which provides the capability to utilize actual weather data as input. The system performance can be analyzed by determining the photosensor response due to changing levels of both electric lighting and daylighting. Dimming algorithms can then be applied to determine an appropriate electric lighting level as is done in the lighting system controller. For daylighting analysis in this computer model, both the CIE standard daylight model and the Perez daylight model were used. The results from three typical sky types (CIE) were compared to those from the most sophisticated daylight model (Perez) now available.; To investigate the performance of a daylight dimming system, parameters such as control algorithms (photosensor orientation), seasonal changes, and sky types were considered. The correlation between daylight illuminance at a workplane point directly below the photosensor {dollar}(Esb{lcub}D{rcub}){dollar} and the photosensor signal {dollar}(Ssb{lcub}D{rcub}){dollar} was used as a measure of system performance. The ratios of {dollar}Esb{lcub}D{rcub}/Ssb{lcub}D{rcub}{dollar} across the year depend on sky conditions, season, and photosensor orientation. The ratio of {dollar}Esb{lcub}D{rcub}/Ssb{lcub}D{rcub}{dollar} is an important factor affecting system performance so that choosing the appropriate calibration time and a proper location of the photosensor are critical in order to reduce the difference among different sky types and seasons. Different ratios of {dollar}Esb{lcub}D{rcub}/Ssb{lcub}D{rcub}{dollar} produce variations from the target workplane design level for different sky types through different seasons.; In addition, a large office space employing an open-loop proportional control daylight dimming system was monitored. The workplane illuminance and lighting power consumption were monitored in order to quantify system performance and saved lighting energy from a daylight dimming system. The results showed that a daylight dimming system is a good way of reducing lighting energy throughout the year, and the lighting controller should be improved to account for the dynamic nature of the sky.