In the absence of ground reflected radiation measured data, an average albedo value of 0.2, which describes the reflective properties of the bare ground is generally used. The variation of albedo based on different foreground surfaces and under different atmospheric conditions is an area which is under research. This paper presents an experimental investigation of albedos of different foreground materials that can be used for photovoltaic (PV) applications. Overcast skies are predominant in northerly locations and will have a high frequency of low solar altitudes, and thus ground reflection is an important contributor towards total solar energy gain. The foreground surfaces include common materials: Grass, sand, and cement slabs, and some non-conventional materials: White pebbles, white boards, white tiles, and aluminium foil. The impact of factors, such as ageing, solar elevation, rain, and cloud cover (sky conditions) is analysed to determine the changes in albedos of these materials. Each material was observed to have individual performance characteristics under these factors. It was found that the non-conventional materials were least prone to weather-related changes and have higher albedo values as compared to the conventional materials, and also have good potential to replace the conventional materials for any given PV application.

Radiation heat transfer has very many applications within the building services sector. CIBSE Guide A provides the physics background and the relevant mathematical functions for radiant energy exchanges between surfaces of different configurations in chapters 2 and 5. AQ1 The aim of this article is to present procedures for inter-surface radiant energy exchange that range from the most simple (macro-) to most general formulations that are based on a micromesh, finite-element approach. The justification for such detailed procedures and their applicability within the modern building energy simulation software is also covered.

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Radiation heat transfer has very many applications in building physics. In such studies, one has to deal with radiant energy exchanges between surfaces of different orientation and aspects. Two principal cases that may be cited here are exchanges between (i) surfaces that share a common edge and are at an angle to each other, and (ii) surfaces that are parallel to each other. Examples that may be cited here are walls of buildings and also ceiling and floor areas. In a previous work, the authors presented a generalised, numerical-oriented solution for analysing radiant exchange that belongs to case (i) cited above. In the present article, a generalised treatment for case (ii) is presented. A software tool is also provided for analysing the radiant exchange for surfaces that are parallel to each other and have uniform or non-uniform reflectivity, incident irradiation and/or emission. As a demonstration of the applicability of the present work, calculation of incident reflected irradiation on the walls of urban street canyons with varied orientation and non-uniform reflectivity is presented. Finally, the application of the presently developed tools for enhancing building design has been highlighted.