Estimation of background diffuse irradiance on orthogonal surfaces under partially obstructed anisotropic sky. Part II – Horizontal surfaces

This article presents a novel analytical approach to estimate the background component of diffuse irradiance on horizontal surfaces under partially obstructed anisotropic sky, when neighbor orthogonal vertical and horizontal surfaces hide parts of the sky dome. This helps to calculate the incident diffuse radiation onto horizontal roofs of orthogonal buildings using the defined here horizontal anisotropic sky view factors. The case of infinitely long urban canyon also is studied. The resulting equations include an isotropic part and an anisotropic correction. At last the article describes diffuse energy balance principles as a part of the base of anisotropic factor algebra. The article includes examples that demonstrate how new anisotropic view factors can be computed from a set of known factors with the help of anisotropic factor algebra.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights•A novel analytical approach to estimate the background diffuse irradiance under obstructed sky.•Anisotropic factors from the basic sky sectors to points of horizontal surfaces.•Average anisotropic factors of the basic sky sectors to horizontal surfaces.•The resulting equations include an isotropic part and an anisotropic correction.•Two balance principles are added to the base of the anisotropic factor algebra.