Cool Roof Impact on Building Energy Need: The Role of Thermal Insulation with Varying Climate Conditions

Piselli Piselli,Cotana Cotana,Gracia Gracia,Pisello Pisello,Cabeza Cabeza,Saffari Saffari

doi:10.3390/en12173354

Piselli Piselli, Cotana Cotana + Show 4 more

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https://doi.org/10.3390/en12173354

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Abstract

Cool roof effectiveness in improving building thermal-energy performance is affected by different variables. In particular, roof insulation level and climate conditions are key parameters influencing cool roofs benefits and whole building energy performance. This work aims at assessing the role of cool roof in the optimum roof configuration, i.e., combination of solar reflectance capability and thermal insulation level, in terms of building energy performance in different climate conditions worldwide. To this aim, coupled dynamic thermal-energy simulation and optimization analysis is carried out. In detail, multi-dimensional optimization of combined building roof thermal insulation and solar reflectance is developed to minimize building annual energy consumption for heating–cooling. Results highlight how a high reflectance roof minimizes annual energy need for a small standard office building in the majority of considered climates. Moreover, building energy performance is more sensitive to roof solar reflectance than thermal insulation level, except for the coldest conditions. Therefore, for the selected building, the optimum roof typology presents high solar reflectance capability (0.8) and no/low insulation level (0.00–0.03 m), except for extremely hot or cold climate zones. Accordingly, this research shows how the classic approach of super-insulated buildings should be reframed for the office case toward truly environmentally friendly buildings.

Highlights

Nowadays, buildings are responsible for a large part of total energy use and greenhouse gases emissions worldwide [1]
Building upon the existing literature and previous contributions [32,33,34], the purpose of this study was to assess the effectiveness of designing consistent thermal insulation level and roof solar reflectance capability in terms of annual energy savings of the heating ventilation and air conditioning (HVAC)
The first step of analysis was the one-dimensional optimization of roof solar reflectance in the Moscow (Russia) and Tampere (Finland), which were heating dominated climates

Summary

Introduction

Buildings are responsible for a large part of total energy use and greenhouse gases emissions worldwide [1]. The construction sector has one of the highest potentials for the improvement of sustainable development and global energy efficiency [2]. High-performing building envelopes are needed to meet energy efficient buildings [4]. Taking this into consideration, cool roof technology is a widely acknowledged strategy for building thermal-energy performance improvement, by acting mainly on energy requirement for cooling [5,6] and urban heat island (UHI). Phenomenon mitigation [7,8] Given their high solar reflectance and thermal emissivity properties, compared to conventional construction materials, cool materials are capable of decreasing the heat released to the outdoor urban environment and to the indoor ambient air [9]

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