This paper presents initial values of global and diffuse luminous efficacy at Saint-Pierre (Reunion Island). Firstly, data used were measured for a period of 6 months, from February to June 2008. During this period, all defined day-types have been studied (clear, cloudy and intermediate). Generally, the meteorological database of Reunion does not contain information for illuminance values. On the other hand, the local meteorological center has a 60-years-old database for solar irradiance (W.m -2 ). So it is important to determine Luminous Efficacy in order to find illuminance from solar irradiance (or luminance from solar radiance). The measured data were analyzed, and empirical constant models were developed and presented in this paper in order to determine luminous efficacy under different sky conditions. A comparison between these empirical constants (models) and existing models has been made. The method used to define sky conditions (overcast, intermediate and clear) and day-types characterization as well as classification will be presented in this work.
KeywordsGlobal and diffuse luminous efficacy, different sky conditions, solar irradiance, solar illuminance Another reason that prompts us to study these luminous efficacy values is that simulation software for buildings needs specific climatic data, particularly on outdoor illuminance.Hence, luminous efficacy models introduced in the software enables illuminance values simulation using solar irradiance databases.Firstly, empirical (or experimental) constant luminous efficacy (global and diffuse models) for this location (at 21°19'S, 55°28'E) is introduced. Materials, methods and experimental procedures are then presented. Results obtained confirm the accuracy of models.This work was done for a PhD thesis 1 and results obtained are used in CODYRUN 2 simulation software for predicted illuminance values in Reunion Island.
Literature reviewThe luminous efficacy of daylight (in lm/W) is defined as the ratio of daylight illuminance to solar irradiance. With the availability of the measured horizontal and/or vertical solar data, luminous efficacy for horizontal and/or vertical surfaces can be determined respectively. This gives building designers an indication of the relationship between daylight illuminance and solar irradiance. The bibliography is restricted to horizontal luminous efficacy cases only.
Many models exist in the scientific literature for determining indoor daylighting values. They are classified in three categories: numerical, simplified and empirical models. Nevertheless, each of these categories of models are not convenient for every application. Indeed, the numerical model requires high calculation time;conditions of use of the simplified models are limited, and experimental models need not only important financial resources but also a perfect control of experimental devices (e.g. scale model), as well as climatic characteristics of the location (e.g. in situ experiment).In this article, a new model based on a combination of multiple simplified models is established. The objective is to improve this category of model. The originality of our paper relies on the coupling of several simplified models of indoor daylighting calculations. The accuracy of the simulation code, introduced into CODYRUN software to simulate correctly indoor illuminance, is then verified.Besides, the software consists of a numerical building simulation code, developed in the Physics and Mathematical Engineering Laboratory for Energy and Environment (P.I.M.E.N.T) at the University of Reunion.Initially dedicated to the thermal, airflow and hydrous phenomena in the buildings, the software has been completed for the calculation of indoor daylighting. New models and algorithms -which rely on a semidetailed approach -will be presented in this paper.In order to validate the accuracy of the integrated models, many test cases have been considered as analytical, inter-software comparisons and experimental comparisons. In order to prove the accuracy of the new model -which can properly simulate the illuminance -a confrontation between the results obtained from the software (developed in this research paper) and the major made at a given place is described in details. A new statistical indicator to appreciate the margins of errors -named RSD (Reliability of Software Degrees) -is also be defined.
2The objective is not only to develop an efficient research tool to improve visual comfort and reduce energy consumption, but also to transfer the knowledge through these decision-making aids tools to praticians and decision makers.
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