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

This article presents an analytical approach to estimate the background component of diffuse irradiance on vertical 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 the façades of orthogonal buildings using defined here vertical and horizontal anisotropic sky view factors. The cases of infinitely long urban canyons and infinitely high vertical walls also are studied. The resulting equations include an isotropic part and an anisotropic correction. At last the article describes the fundamental relations between anisotropic sky view factors, which form base of anisotropic factor algebra.

► Estimation of background diffuse irradiance under orthogonally obstructed sky. ► Anisotropic factors of four sky sectors to points on vertical surfaces. ► Average anisotropic factors of four sky sectors to vertical surfaces. ► The resulting equations include an isotropic part and an anisotropic correction. ► The base of anisotropic factor algebra is formulated.