Thermal and energy performance of green roof and cool roof: A comparison study in Shanghai area

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.

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Effects of Extensive Green Roofs on Energy Performance of School Buildings in Four North American Climates

Water ◽

10.3390/w12010006 ◽

2019 ◽

Vol 12 (1) ◽

pp. 6 ◽

Cited By ~ 3

Author(s):

Milad Mahmoodzadeh ◽

Phalguni Mukhopadhyaya ◽

Caterina Valeo

Keyword(s):

Leaf Area Index ◽

Leaf Area ◽

Plant Height ◽

Green Roof ◽

Green Roofs ◽

Energy Performance ◽

Design Parameters ◽

Soil Thickness ◽

Area Index ◽

Roof Design

A comprehensive parametric analysis was conducted to evaluate the influence of the green roof design parameters on the thermal or energy performance of a secondary school building in four distinctively different climate zones in North America (i.e., Toronto, ON, Canada; Vancouver, BC, Canada; Las Vegas, NV, USA and Miami, FL, USA). Soil moisture content, soil thermal properties, leaf area index, plant height, leaf albedo, thermal insulation thickness and soil thickness were used as design variables. Optimal parameters of green roofs were found to be functionally related to meteorological conditions in each city. In terms of energy savings, the results showed that the light-weight substrate had better thermal performance for the uninsulated green roof. Additionally, the recommended soil thickness and leaf area index for all four cities were 15 cm and 5 respectively. The optimal plant height for the cooling dominated climates is 30 cm and for the heating dominated cities is 10 cm. The plant albedo had the least impact on the energy consumption while it was effective in mitigating the heat island effect. Finally, unlike the cooling load, which was largely influenced by the substrate and vegetation, the heating load was considerably affected by the thermal insulation instead of green roof design parameters.

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A hygrothermal green roof model to simulate moisture and energy performance of building components

Energy and Buildings ◽

10.1016/j.enbuild.2017.04.001 ◽

2017 ◽

Vol 145 ◽

pp. 79-91 ◽

Cited By ~ 15

Author(s):

D. Zirkelbach ◽

S.-R. Mehra ◽

K.-P. Sedlbauer ◽

H.-M. Künzel ◽

B. Stöckl

Keyword(s):

Green Roof ◽

Energy Performance ◽

Building Components

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Roof–envelope ratio impact on green roof energy performance

Urban Ecosystems ◽

10.1007/s11252-008-0053-z ◽

2008 ◽

Vol 11 (4) ◽

pp. 399-408 ◽

Cited By ~ 26

Author(s):

Ryan Martens ◽

Brad Bass ◽

Susana Saiz Alcazar

Keyword(s):

Green Roof ◽

Energy Performance

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A Conceptual Review of the Potential of Cool Roofs as an Effective Passive Solar Technique: Elaboration of Benefits and Drawbacks

Frontiers in Energy Research ◽

10.3389/fenrg.2021.738182 ◽

2021 ◽

Vol 9 ◽

Author(s):

Babak Ashtari ◽

Mansour Yeganeh ◽

Mohammadreza Bemanian ◽

Bahareh Vojdani Fakhr

Keyword(s):

Clean Energy ◽

Building Energy ◽

Energy Performance ◽

Cool Roof ◽

Indoor Thermal Comfort ◽

Pros And Cons ◽

Passive Solar ◽

Number Of Publications ◽

Roof Design ◽

Cool Roofs

Cool roofs, as feasible and efficient passive solar technique that reduces building energy requirements for cooling and improves indoor thermal comfort conditions, have received considerable attention in recent years and as a result, a number of concepts, methods, and experiences have been developed during the related research. Although some studies have been conducted on this subject in the form of review articles, taking into consideration the large number of publications, there is still a call for some review papers dealing with the potential of cool roofs and providing a thorough report on their energy performance and a detailed summary of their pros and cons on the basis of the relevant studies. On this account, this study contributes a systematic review of the issued paper in Scopus and Web of Science regarding the cool roof technologies to recognize the advantages and challenges of cool roofs in practice and its future trends. In addition, detailed summary of advantages and drawbacks of this passive solar measure has been developed, as itemized factors corresponded to the codified references. A total of 90 published reports were analyzed, declaring that a cool roof is an efficient approach for generating clean energy on the building scale. This article induces an overall view of the advantages and restrictions of the cool roof throughout the world. Conclusions give a valuable reference for improving the cool roof design for their more widespread use in the building industry.

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Probabilistic prediction of green roof energy performance under parameter uncertainty

Energy ◽

10.1016/j.energy.2014.09.043 ◽

2014 ◽

Vol 77 ◽

pp. 667-674 ◽

Cited By ~ 18

Author(s):

Min (Max) Liu

Keyword(s):

Parameter Uncertainty ◽

Green Roof ◽

Energy Performance ◽

Probabilistic Prediction

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

Energies ◽

10.3390/en13082030 ◽

2020 ◽

Vol 13 (8) ◽

pp. 2030

Author(s):

Mansoureh Gholami ◽

Alberto Barbaresi ◽

Patrizia Tassinari ◽

Marco Bovo ◽

Daniele Torreggiani

Keyword(s):

Thermal Performance ◽

Mediterranean Climate ◽

Green Roof ◽

Green Roofs ◽

Energy Performance ◽

Building Envelope ◽

Considerable Proportion ◽

Urban Context ◽

Cooling Period ◽

The Impact

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.

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