Energy and Buildings 76 (2014) 199–210 Contents lists available at ScienceDirect Energy and Buildings j ourna l ho me page: www.elsevier.com/locate/enbuild Analysis of solar shading caused by building-integrated Vertical Heliostat Fields Aurelio González-Pardo, Almudena Rodríguez, José González-Aguilar, Manuel Romero ∗ IMDEA Energy Institute, Ramón de la Sagra 3, 28935 Móstoles, Spain a r t i c l e i n f o Article history: Received 12 August 2013 Received in revised form 7 December 2013 Accepted 9 February 2014 Available online 16 February 2014 Keywords: Heliostat Solar shading Daylighting Architectural integration Concentrating Solar Power a b s t r a c t The “Vertical Heliostat Field” (VHF) concept proposes a solution to integrate solar heliostat fields in urban communities with the aim of deploying modular Concentrating Solar Power systems nearby populated areas. Its distinctive feature resides in the use of special mirror layouts where heliostats should be dis- tributed on a vertical surface (i.e., a building fac ¸ ade). The VHF reflects radiation coming from the sun toward a common point where a solar receiver has been placed for power generation or other high temperature applications. This work presents the optical performance of the Vertical Heliostat Field as a shading system, study- ing the daylighting evolution inside the building as a function of VHF parameters (separation between heliostats, date, field zone, etc.), though always preserving the compatibility with the primary goal of achieving good performance and operational efficiencies as a solar thermal power plant comparable to a conventional central receiver system. Direct and diffuse components of solar radiation have been con- sidered separately. Results indicate that a field with reduced spacing between heliostats provides a good performance as an element for shading building fac ¸ ades. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Proper management of sunlight impinging onto a south fac ¸ ade is an important issue in the design of energy-efficient buildings. Sunny climates present an excess of solar gain that causes high energy consumption due to cooling needs. In cold climates, irradi- ance entering through the windows can contribute to passive solar heating. The use of shading devices enables controlling incoming sunrays, improving illumination comfort and decreasing the energy consumption. A variety of devices to control daylight in buildings may be found in the literature. Alzoubi et al. [1] studied the effect of vertical and horizontal louvers on the quality of daylighting in buildings and the associated energy saving by performing simulations of a typical small office ideally provided with a standard window size. Geom- etry, tilt angle and reflectance of venetian blinds were studied by Tzempelikos [2], analyzing the impact of these factors on interior lighting and direct light penetration. Breitenbach el al. [3] devel- oped a mathematical model to characterize double-glazing units Abbreviations: CSP, Concentrating Solar Power; DNI, Direct Normal Irradiance; NS, North–South; SR, spacing ratio; VHF, Vertical Heliostat Field. ∗ Corresponding author. Tel.: +34 917371120; fax: +34 917371140. E-mail address: manuel.romero@imdea.org (M. Romero). which incorporate venetian blinds, considering optical properties of the components and angle of rotation of the blind, solar screens, which consist of external perforated panels that are fixed in front of windows, have been proposed by Sherif et al. [4,5]. They analyzed the influence of perforation percentage of solar screens on daylight- ing performance in a typical room of a building in a desert location, identifying the minimum perforation percentage of screen open- ings that provides adequate illuminance level. Ceiling elements can contribute to the illumination comfort in a room, as it was shown by Freewan et al. [6]. They studied the impact of ceiling geometries on the performance of louvers by using performance indicators (the illuminance level and its distribution uniformity) to assess day- lighting performance. Shameri et al. [7] reviewed the main works related to double skin fac ¸ ade, which is a special type of building envelope, where a second skin, usually a transparent glazing, is placed in front of a regular building fac ¸ ade [8]. They highlighted the higher attention that is receiving this kind of facility in the lat- est years. Pérez et al. [9] presented a classification of green vertical systems for buildings, reviewing the mechanisms by which green fac ¸ ades can be used as passive energy saving systems (by means of shadowing, insulation evaporative cooling and barrier effect to the wind) and they also described the first results about the behav- ior of a double-skin green fac ¸ ade. Ottelé et al. [10] also studied green fac ¸ ades by comparing life cycle analysis for different greening systems to evaluate the optimal one. http://dx.doi.org/10.1016/j.enbuild.2014.02.009 0378-7788/© 2014 Elsevier B.V. All rights reserved.