Ki-Se Kim, Eun-Chul Kang, and Euy-Joon Lee, Korea Institute of Energy Research (KIER), 71-2 Jang-Dong Yusong-Gu, Daejeon 305-343, South Korea

M. Masaood Hashmi and I. A.Qazi, Pakistan Council of Renewable Energy Technologies (PCRET), Plot No. 25, Sector H-9, Islamabad, Pakistan

Energy saving objectives and improvements of visual comfort in buildings have led to a growing need for a better daylighting system. Visual comfort includes sufficient illumination of the room in general, and the working area in particular, without colour distortion and with the absence of contrast and glare etc. Today, however, with the growing demand for improved illumination quality and with people becoming more aware of the fact that natural resources are finite and that the balance of the global climate is threatened, daylighting principles of traditional architecture are being revitalized.

It is obvious that if daylight is used to offset lighting energy requirements over a larger floor area, additional energy savings can be obtained (Beltran L. O. et al.). As a result, in the past decade a variety of systems have been developed to improve the usage of daylight in office buildings. Scattering systems like windows filled with granular aerogels (Dengler J. and Wittwer V., 1994), light diffusing films (Beck A. et al.) or specular reflecting lamellae and light guiding systems integrated between double pane windows (Koster H., 1989), are some examples. Prismatic layers excluding direct sunlight, via total internal reflection, have also become available. In the following the newly developed daylighting system with prismatic solar hybrid collector (PSHC) panel is described.

The main objective of using the PSHC system is 1) to control the transmitted sunlight by reflecting, refracting, or diffracting its rays onto the ceiling, 2) to obtain the maximum penetration of sunlight for a wide range of solar altitudes, 3) to improve and increase the uniformity of glare-free daylight distribution at all distances in the building under variable sun and sky conditions and 4) to produce better thermal conditions inside the building by transferring the incident solar radiations through the individual glass sheets and prisms (by convection and longwave IR-radiation).

The experimental data is used to assess the performance of the test room equipped with a prismatic glazing panel integrated to the top window of south — facing wall of the room and to evaluate the performance of this PSHC system in terms of thermal and visual comfort. Tests of this study are carried out for twin rooms of same dimensions, one with PSHC window and the other with normal window. The former is called the target room while the later is labeled as the reference room. The thermal and day lighting performance results are presented and discussed, along with recommendations for further research and development.