Citation: Fabbri, K.; Antonini, E.; Marchi, L. Sun-Shading Sails in Courtyards: An Italian Case Study with RayMan. Sustainability 2023, 15, 13033. https://doi.org/10.3390/su151713033 Academic Editor: Giouli Mihalakakou Received: 18 July 2023 Revised: 15 August 2023 Accepted: 28 August 2023 Published: 29 August 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sustainability Article Sun-Shading Sails in Courtyards: An Italian Case Study with RayMan Kristian Fabbri , Ernesto Antonini * and Lia Marchi Department of Architecture, University of Bologna, 40136 Bologna, Italy; kristian.fabbri@unibo.it (K.F.); lia.marchi3@unibo.it (L.M.) * Correspondence: ernesto.antonini@unibo.it Abstract: Forecasts of a drastic increase in temperatures in the coming decades are driving the adop- tion of design strategies and solutions to improve the livability of urban environments. Increasing attention is being paid to the thermal comfort of open spaces by both designers and researchers. Nature-based solutions and man-made devices to improve the comfort of outdoor spaces during summer are spreading, but effective, easy simulation and design support tools for this purpose are still lacking, as most of the available software such as ENVI-met or RayMan cannot model such devices. As Physiological Equivalent Temperature (PET) is one of the most relevant and comprehen- sive indicators of Outdoor Thermal Comfort (OTC), this study aims to investigate PET variations of different artificial shading systems and propose a simplified methodology for assessing them through analytical simulations with RayMan software. When modeling the shading elements, the trick adopted for this purpose is to associate different cloud densities with the shading provided by the screens, thus overcoming a gap that affects the software. The procedure is digitally tested in a covered courtyard case study in Bologna (Italy). Diverse options proposed by the designers for textile screening materials have been compared, showing that these reduce by at least 1 ◦ C the PET-gauged thermal stress. Beyond specific results, the main outcome of this study is the procedure developed to simulate sun-shading sail effects on OTC by means of RayMan, which can support designers in planning effective solutions for open space livability in summertime. Keywords: heat stress; PET; RayMan; courtyard; sun-shading sail 1. Introduction Due to climate change effects, scientists forecast an increase in global temperature of at least +1.5 ◦ C by 2050 in the lowest emission scenario [1]. In Europe (EU), this will result in at least a +1.6 ◦ C Annual Mean Temperature and +1.9 ◦ C Max Temperature of the warmest month in 2050, with respect to the reference period 1985–2014 [2]. Under all future climate change scenarios for EU, the number of hot days, as well as the intensity (i.e., duration +63%) and frequency of heatwaves (+19%), are expected to increase. Consequently, rising mean temperatures will intensify heat stress in cities, particularly in the Mediterranean region and Eastern Europe. Outdoor thermal comfort in urban environments will be increasingly affected with significant implications on livability in cities and citizens’ wellbeing [3]. Therefore, the protection of urban areas from global warming will be one of the key challenges of the next decades that policy makers and designers should address as soon and effectively as possible [4,5]. In this regard, a consistent and growing body of literature is focusing on the evaluation of Outdoor Thermal Comfort (OTC) in diverse outdoor spaces, from public pathways and squares [6–9], to parks [10] and building courtyards [11–15]. These are all, in fact, collective or public spaces intended for relations among citizens, where good OTC levels are essential to encourage or even allow people to use outdoor facilities [16]. Sustainability 2023, 15, 13033. https://doi.org/10.3390/su151713033 https://www.mdpi.com/journal/sustainability