Indoor daylight illuminance: a comparison between experimentally determined varying CIE sky-type and a predefined CIE sky model
(2019) The International Conference on Future Cities-2019 — Location: Indian Institute of Technology, Roorkee, India
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- Abstract
- The output accuracy of the building performance simulation tools depends on the employed models. Most daylighting simulation tools evaluate the daylight performance in built-environment through illuminance based metrics, and refer the Perez all weather model or the CIE model. Sky-luminance distribution of the ambient sky impacts the indoor daylight distribution dynamically, based on sun-position and other outdoor and indoor scattering parameters. The approach of employing the generic sky-models throughout the year could result in lower accuracy prediction of indoor illuminance distribution. This study was conducted to identify the improvement in prediction accuracy for indoor illuminance distribution, by deploying measured sky-luminance distribution data, or closest sky-model as input as compared to using a pre-defined CIE sky-model for various time instances. Measurements from a previously reported sky-scanning device are used to identify closest sky-type which is used as a key input in simulating indoor daylight distribution. The indoor illuminance distribution is simulated for a sample space through algorithm scripted in Python (PY) and also with HoneyBee module in Rhino-Grasshopper (GH). The GH approach uses Radiance engine to perform daylight simulations for the space, and spatially discretized Indoor illuminance values are derived for uniform and varying sky type scenarios using both Python and Radiance approach. The temporal trend in illuminance levels between PY and GH outputs is similar for same sky type through various points of the day. For uniform and varying sky types, mean standard deviation in illuminance levels of 782.1 and 238.6 lux is respectively observed between PY and GH outputs. Owing to neglecting internal reflections in PY algorithm, much reduced illuminance levels are noted, as compared to GH outputs. It is inferred that identifiers for closest CIE sky-type for various time-points may improve simulation accuracy in daylight illuminance calculations.
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Maskarenj, M., & Kumar, M. N. V. S. (2019). Indoor daylight illuminance: a comparison between experimentally determined varying CIE sky-type and a predefined CIE sky model. The International Conference on Future Cities-2019. Published. The International Conference on Future Cities-2019, Indian Institute of Technology, Roorkee, India. https://hdl.handle.net/2078.5/104361 (Original work published 2019)