A Comparison of Energy and Thermal Performance of Rooftop Greenhouses and Green Roofs in Mediterranean Climate: A Hygrothermal Assessment in WUFI

Patrizia Tassinari,Daniele Torreggiani,Alberto Barbaresi,Marco Bovo,Mansoureh Gholami

doi:10.3390/en13082030

Abstract

In urban areas, a considerable proportion of energy demand is allocated to buildings. Since rooftops constitute one-fourth of all urban surfaces, an increasing amount of attention is paid to achieving the most efficient shapes and component designs compatible with every climate and urban context, for rooftops of varying sizes. In this study, three types of rooftop technologies, namely insulated, green roof, and rooftop greenhouse, are evaluated for energy and thermal performance using computer simulations. Water surface exposure, absorption, and intrusion are the three important factors in the calculation of hygrothermal models that impact energy consumption and building envelope performance; however, a few studies are specifically focused on providing realistic results in multi-dimensional hygrothermal models and the assessment of the impact of moisture in roofing solutions. This paper aims at evaluating the performance of three different roofing technologies through a two-dimensional hygrothermal simulation in software WUFI. To accomplish this, a precise localized microclimate model of a complex urban context on the scale of a neighborhood was employed to evaluate the cooling and heating loads of the buildings, the impact of the water content in the green roof on the thermal behavior of the roof surface, and the feasibility of designing a building with nearly zero cooling needs. A two-story building in the city center of Bologna, Italy is modelled. Simulation results have shown that during the cooling period, the performance of the designed rooftop greenhouse is the most effective by 50% reduction in cooling loads. Besides, the impact of moisture in green roofs has been detected as a negative factor for thermal and energy performance of the building in the Mediterranean climate. The results ultimately highlighted the capability of passively-designed rooftop greenhouses to create a building with nearly zero cooling needs.

Highlights

The energy consumption of urban buildings constitutes a considerable proportion of the world’s energy demands
A comparison was made between insulation, green roofs, and rooftop greenhouses to analyze energy performance and thermal behavior of buildings
The building was modelled in WUFI, using three scenarios: insulated, green roof, and a rooftop greenhouse

Summary

Introduction

The energy consumption of urban buildings constitutes a considerable proportion of the world’s energy demands. Examining innovative strategies to create climate-conscious designs and harnessing the potential of urban areas to reduce the energy demand of urban buildings through controlling solar heat gains are increasingly attracting attention [1]. Many European local governments are more and more interested in the implementation of these urban building strategies in order to make a net-zero energy vision achievable by 2020 [3]. Implementing these strategies is highly dependent on the construction and energy-saving systems but in general, the role of these roofs in saving energy varies; some of them just reduce heat transfer while others may impact the energy-saving rate through thermal inertia [4,5]. Green roofs have been studied from a wide variety of aspects such as water runoff mitigation [10], aesthetic, or social impacts [11]

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