Strong influence of convective heat transfer efficiency on the cooling benefits of green roof irrigation

Wang, Linying; Huang, Maoyi; Li, Dan

doi:10.1088/1748-9326/ac18ea

Title: Strong influence of convective heat transfer efficiency on the cooling benefits of green roof irrigation

Journal Article · 09 August 2021 · Environmental Research Letters

DOI: https://doi.org/10.1088/1748-9326/ac18ea · OSTI ID:1835467

; Huang, Maoyi;

Abstract By enhancing evapotranspiration (ET), green roofs provide cooling benefits for the urban environment and are recognized as a promising heat mitigation strategy. The evaporative cooling effects of green roofs strongly depend on the soil moisture conditions and thus irrigation may be needed to sustain the cooling benefits. It has been shown that the magnitude of cooling benefits offered by green roof irrigation varies spatially, but its controlling factors remain elusive. In this study, we combine a surface energy balance (SEB) model with global simulations generated by an improved Earth System Model to illustrate the key factors controlling the cooling benefits of green roof irrigation. We employ a simple irrigation scheme, which is only active when there is no ice in soil layers and when the soil moisture is below field capacity. As a result, most of the irrigation water leaves the green roof system via ET. We find that the magnitude and also the spatial variability of the cooling benefits of green roof irrigation are controlled by the irrigation amount, and a surface energy redistribution factor that encodes the efficiencies of different SEB components in transferring heat. Further analysis indicates that the enhancement of latent heat flux due to irrigation is largely balanced by the reduction of sensible heat flux on green roofs. Therefore, the amount of irrigation needed per unit decrease of green roof surface temperature is mainly controlled by the convective heat transfer efficiency. A lower convective heat transfer efficiency (e.g. under a lower wind speed) helps reduce the amount of irrigation needed per unit decrease of green roof surface temperature. This study highlights the importance of SEB in constraining the cooling benefits of green roof irrigation and provides valuable guidance for urban planners and policy makers in terms of heat mitigation and sustainable water management.

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Sponsoring Organization:: USDOE

OSTI ID:: 1835467

Journal Information:: Environmental Research Letters, Journal Name: Environmental Research Letters Journal Issue: 8 Vol. 16; ISSN 1748-9326

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: United Kingdom

Language:: English

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