Do grey infrastructures always elevate urban temperature? No, utilizing grey infrastructures to mitigate urban heat island effects

Abstract

Urban heat island (UHI) has various adverse impacts on energy consumption, air quality, outdoor thermal comfort and health conditions. Compared with green and blue infrastructures, grey infrastructures (GREIs) have been less-commonly accepted since conventional materials are one of the causes enhancing solar radiation absorption and blocking soil latent heat release. This traditional concept can be changed with the adoption of innovative materials with the characteristics of high solar reflection and low heat release. However, using such GREIs comes with a large challenge in practice since some details (e.g. definition, application approaches) have not been fully understood. This paper, therefore, aims to characterize these details in aspects of definition and classification, cooling techniques, cooling control variables and application approaches, and then propose a framework to guide GREIs’ applications. Results show that albedo change, heat storage and heat harvesting are predominated cooling techniques of GREIs. Cooling performance of GREIs can be significantly influenced by various variables including color, thickness, construction materials and melting temperature. It is also found that there are more options for applying GREIs on roofs than pavements and walls. All these findings can support the proper selection and application of GREIs, thereby counterbalancing UHI effects.