Historical Survey of Daylighting Calculations Methods and Their Use in Energy Performance Simulations

This paper traces the historical development of different daylighting calculation methods. Over the years there have been several developments in daylighting calculation methods. The last two decades have seen a number of new ideas and approaches in daylight calculation procedures. Recently, selected methods have been incorporated into the building energy performance simulation tools. This paper reviews selected tools in terms of their calculation of daylighting use in buildings with an emphasis on the daylighting algorithms these tools use. INTRODUCTION The scientific study of daylighting in the buildings is fairly recent; its inception started with measurements of the outdoor illumination in 1895 [1]. The measurements were mainly performed with illumination photometers. Many types of photometers were invented by different scientists [2], one of the earliest photometer which was used for daylight measurements was the photometer devised by Trotter A.P. [1]. The prime concern in daylighting research of buildings is assessment of its performance. Many methods, performance indictors, systems and tools were developed to asses the daylighting performance. Initial methods were mainly graphical in nature, such as Waldarm diagrams, Pliejel‘s pepper-pot diagrams, Building Research Establishment (BRE) daylight protractors and [5] Graphic Daylight Design Method (GDDM) method etc [9]. Later researchers tried to develop some empirical methods to calculate daylight performance in buildings. Some of these methods made their way into tools such as hand held calculator and later incorporated into more sophisticated computer tools which can perform daylighting analysis. Simultaneously many indicators were also developed such as; Daylight Factor (DF) [1] which is still used to represent the daylighting performance and more recently the Daylight Autonomy (DA) as well as the Useful Daylight Illuminance (UDI) [24]. Recently, Efforts were made to find out the impact of daylighting on the electric consumption in building and also its impact on the building‘s thermal performance. Some of these methods were incorporated into building energy performance tools such as DOE-21.e [6, 8], Energy Plus 1 , and eQuest 2 , to calculate the energy impact of different daylighting strategies in buildings. In addition to these tools were developed which are purely for daylighting analysis such as RADIANCE [19] and DAYSIM [22, 23]. Figure.1 provides a flowchart of the chronological development of the daylighting calculations used in the DOE 2.1e, DAYSIM, eQuest, and Energy Plus programs. SKY MODELS Daylighting in the building is the direct result of the amount of light coming from the sun and sky. The luminance distribution of the sky makes a tremendous impact on the amount of light entering the interiors of the building. The first studies on the sky luminance were performed in the cities of Chicago and Washington in United States by Kimball et al. [10]. They did extensive measurements of sky luminance over a period of three years from 1921-23 and proposed two sky models overcast (1923) and clear sky (1929). In 1929 Pokrowski, proposed a new formula to calculate the luminance distribution of a clear cloudless sky taking Rayleigh scattering into consideration [5]. In 1942 Moon and Spencer proposed an empirical formula for representing the luminance distribution of average overcast sky [5]. In 1951 McDermott and Gordon-Smith proposed a formula to calculate the luminance distribution of fully overcast sky [5]. Later in 1955 The International Commission on Illumination (CIE) adopted the Moon-Spencer formula as the standard for computing the overcast sky luminance distribution [5]. 1 http://apps1.eere.energy.gov/buildings/energyplus. 2 http://www.doe2.com/equest/ ESL-IC-09-11-07 Proceedings of the Ninth International Conference for Enhanced Building Operations, Austin, Texas, November 17 19, 2009