Abstract
The accuracy and speed of the daylighting analysis developed for use in EnergyPlus is better than its predecessors. In EnergyPlus, the detailed method uses the Split-flux algorithm whereas the DElight method uses the Radiosity algorithm. Many existing studies have addressed the two methods, either individually or compared with other daylight analysis methods like Ray tracing but still there is lack of detailed comparative study of these two methods. Our previous studies show that the Split-flux method overestimates the illuminance, especially for the areas away from the window. The Radiosity method has the advantage of accurately predicting this illuminance because of how it deals with the diffuse light. For this study, the EnergyPlus model, which has been calibrated using data measured in a real building in previous studies, has also been used. The calibrated model has a south oriented window only. This model is then used to analyze the interior illuminance inside the room for north, west and east orientation of the window by rotating the model and by changing the wall reflectance of the model with south oriented window. Direct and diffuse component of the illuminance as well as the algorithms have been compared for a detailed analysis.
Highlights
Tsangrassoulis et al [11] developed the stand-alone model to predict the daylight performance and validated the model against the experimental data and the simulation results obtained from radiosity and ray-tracing methods
In EnergyPlus, either the Split-flux or Radiosity method can be used for calculation of interior illuminance
Daylight factor is calculated by dividing the interior illuminance by exterior horizontal illuminance
Summary
The window area ratio in buildings is increasing. glass curtain walls are becoming more and more commonplace. Versage et al [8] compared the Split-flux and Ray-tracing algorithms and found that Split-flux method provided illuminance higher than actual as the distance from windows was increased. Tsangrassoulis et al [11] developed the stand-alone model to predict the daylight performance and validated the model against the experimental data and the simulation results obtained from radiosity and ray-tracing methods. In EnergyPlus, either the Split-flux or Radiosity method can be used for calculation of interior illuminance. DOE-2.1E to EnergyPlus, sky type was increased from two to four and calculation of daylight factors was increased from twenty to hourly sun-path sun positions several times a year This increased the accuracy of the program but, as Versage et al found, this method provided higher illuminance values than actual [8]. The algorithms are compared to understand the final result from the two methods
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