Search

• Development of two PAR models under all sky conditions. • Use of the CIE standard sky taxonomy for classification of all sky conditions. • Ten meteorological indices studied for PAR modelling. • ANN and MLR models yield equivalent results after previous feature selection. In this study, ten-minute meteorological data-sets recorded at Burgos, Spain, are used to develop models of Photosynthetic Active Radiation (P A R) following two different procedures: multilinear regression and Artificial Neural Networks. Ten Meteorological Indices (MIs) are chosen as inputs to the models: clearness index (k t), diffuse fraction (k d), direct fraction (k b), Perez's clear sky index (ɛ), brightness index (Δ), cloud cover (C C), air temperature (T), pressure (P), solar azimuth cosine (c o s Z), and horizontal global irradiation (R a G H). The experimental data are clustered according to the sky conditions, following the CIE standard sky classification. A previous feature selection procedure established the most adequate MIs for modelling P A R in clear, partial and overcast sky conditions. R a G H was the common MI used by all models and for all sky conditions. Additional variables were also included: the geometrical parameter, c o s Z , and three variables related to the sky conditions, k t , ε , and Δ. Both modelling methods, multilinear regression and ANN, yielded very high determination coefficients (R 2) with very close results in the models for each of the different sky conditions. Slight improvements can be observed in the ANN models. The results underline the equivalence of multilinear regression models and ANN models of PAR following previous feature selection procedures. [ABSTRACT FROM AUTHOR]

Abstract Daylighting is recognized as an important and useful strategy in the design of energy efficient buildings. Daylight is still the best source of light for good colour rendering and visual comfort. In this study, a new model of global luminous efficacy over a horizontal surface is proposed. A comparative study of eighteen classic models is presented, to obtain global horizontal illuminance, using both, the original formulation and new formulae with local adaptations, in order to determine the most suitable models for the conditions in Burgos (Spain). With this aim in mind, the selected models consisted of six models developed for all sky conditions, five models for clear sky conditions, three for partly cloudy sky and four for modelling overcast sky conditions. These eighteen models were also compared with the proposed model using experimental global illuminance measurements for different sky conditions. It was shown that the proposed model behaved in a better way than most of the classic models selected from the literature; both for all sky conditions and for particular sky conditions (clear, partly cloudy and overcast). The proposed model was therefore generally applicable, with no need to employ a different model for each particular sky condition. Highlights • A new model of global luminous efficacy over a horizontal surface is proposed. • A comparative study of eighteen classic luminous efficacy models is presented. • The proposed model behaves in a better way than most of the classic models analysed. • Global illuminance in all sky and in particular sky conditions can be determined. [ABSTRACT FROM AUTHOR]