Abstract
It is quite difficult to find studies regarding area-wide data from UAV (Unmanned Aerial Vehicle) remote sensing in evaluating the energy saving performance of a cool roof. Acknowledging these constraints, we investigated whether LRV (Light Reflectance Value) signatures derived from UAV imagery could be used effectively as an indicator of area-wide heating and cooling load that distinctively appears according to rooftop color. The case study provides some quantitative tangible evidence for two distinct colors: A whitish color roof appears near the edge of the highest LRV (91.36) and with a low temperature (rooftop surface temperature: (38.03 °C), while a blackish color roof shows the lowest LRV (18.14) with a very high temperature (65.03 °C) where solar radiation is extensively absorbed. A strong negative association (Pearson correlation coefficient, r = −0.76) was observed between the LRV and surface temperature, implying that a higher LRV (e.g., a white color) plays a decisive role in lowering the surface temperature. This research can be used as a valuable reference introducing LRV in evaluating the thermal performance of rooftop color as rooftops satisfying the requirement of a cool roof (reflecting 75% or more of incoming solar energy) are identified based on area-wide objective evidence from UAV imagery.
Highlights
The roof design is a decisive factor in conserving the energy of the building because the roof surface is directly exposed to solar radiation and is a pathway to transfer ambient solar heat inside the building
This research can be used as a valuable reference introducing light reflectance value (LRV) in evaluating the thermal performance of rooftop color as rooftops satisfying the requirement of a cool roof are identified based on area-wide objective evidence from Unmanned aerial vehicles (UAVs) imagery
This study demonstrated the potential of LRV signatures in evaluating cool roofing performance according to rooftop color by quantitatively classifying surface reflectivity from UAV imagery
Summary
The roof design is a decisive factor in conserving the energy of the building because the roof surface is directly exposed to solar radiation and is a pathway to transfer ambient solar heat inside the building. Among the researches related to the roof designs in conserving the energy, roof gardens (green roof) and cool roof accounts about 50% of articles registered in the Web of Science database until 2018 [10]. It means that rooftop greening and cool roof are attracting attention from many researchers all over the world as the roofing designs requiring an in-depth study to mitigate the heating/cooling loads by handling heat conduction into the buildings. A cool roof can be installed in any building without any difficulty and has advantages of low initial investment and maintenance cost
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