**1. Introduction**

314 Solar Radiation

Yamauchi, J. (1927). The Light Flux Distribution of a System of Inter-reflecting Surfaces. *Researches of the Electro-technical Laboratory*. No. 190.Tokyo. (In Japanese). Yamauchi, J. (1929). The Amount of Flux Incident to Rectangular Floor through Rectangular Windows. *Researches of the Electro-technical Laboratory*. No. 250.Tokyo. Yamauchi, J. (1932). Theory of Field of Illumination. *Researches of the Electro-technical* 

*Laboratory*. Tokyo. No. 339.

Control of solar radiation, by passive solar tools is an important part of building design. External shading device, which is the part of passive solar systems, is an artificial environmental variable or element to control interior solar radiation on the base of desirable orientation of window. Solar heat gain, particularly via fenestration, typically dominates cooling performance (Olgyay, 1957).

The proper application of energy efficient shading devices in new buildings have the technical potential to save 50-70% of total perimeter zone energy use. Therefore, even if only 25-50% of potential could be captured, the economical benefit due to decrease in the size of HVAC plant and the energy consumption make them competitive, with large spin-off benefit on the visual comfort (Data, 2001). Moreover, overshading of the windows reduces daylighting, which results in increasing energy use for artificial lighting or internal heat gains (Littlefair, 1998). In that case, this can be possible with determination of optimum dimension and shape in the shading device design. However, evaluation of many needed variables, such as dimensions of window, solar geometry and climate data in design of shading devices needs a period of long time and include complex process (Szokolay, 1980). This situation makes the designer to pay insufficient attention to the external shading device applications (Ralegaonkar, 2005). In addition, like eaves overhangs, terrace and beams horizontal building elements which are not designed as an external shading device but their shape on the face as an extension of functional or structural devices, shade to transparent surfaces and this shading can negatively influence the thermal performance of the building (Yezioro, 2009). For this aspect, external shading device's shape and dimension should be evaluated carefully at design of the building especially in the Mediterranean climate zone in which solar heat gain is effective.

In shading device design methods, the trigonometric connection between angle of altitude and azimuth of the sun with dimension of window and shading device are taken basic criteria. However, design criteria of shading device is classified in four basic groups as given below (Olgyay, 1957).

<sup>\*</sup> Corresponding Author

**A. Solar geometry data:** The formulations and ground plane angle of the sun's yearly motion.

**B. Shape and dimension alternatives of window and shading device:** The formulations of determining the geometry of window and shading devices.

**C. Geographical location and climate data:** Climate data and the required comfort data obtained based on the climate data.

**D. Function and usage:** The shading device's material, detail and usage.

As mentioned above, the most important point in the shading device design is to show the dependence of shading device performance on the base of sun's one-year motion. Thereby, calculating the shading device design parameters with traditional methods requires comparison of various drawings and equations on the base of sun's one-year motion. Computerized design with simulation programming, in offering various numerical and graphical alternatives, is help to the designer by shortening the design period. In this article, computerized simulation program of solar tool is used to analyze shading devices in dimension and shape (Marsh, 2003).
