Abstract
While it is well-known that cool roofs can efficiently reduce cooling demand in buildings, their overall energy performance in mixed and cold climates has been a topic of debate. This paper presents a comprehensive simulation study to evaluate the combined impact of roof reflectivity, insulation level, and construction type (adhered vs attached) on annual energy demand and energy costs in the United States, for different buildings and climate zones. EnergyPlus was used to model three building types (retail, office, and school buildings) for the 16 most climate-representative locations in the US using typical reflectivity and insulation values. The results show that (i) roof reflectivity is equally important to roof insulation in warm climates; (ii) for low-rise offices and schools, the benefits of reflective roofs vs dark-colored roofs are clear for all US climatic zones, with higher savings in warm climates; (iii) for big-box-retail buildings, reflective roofs perform better except for cold climate zones 7–8; (iv) dark-colored, mechanically attached roofs achieve slightly better performance than reflective roofs in mixed and cold climates. Decision makers should consider building type, climatic conditions, roof insulation levels, and durability performance, along with roof reflectivity, when assessing the overall potential benefits of cool roofs.
Highlights
In order to answer the questions about the benefits of cool roofs vs black roofs in different climatic zones, this paper presents a detailed modeling study that combines the effect of building characteristics and climatic conditions with the joint effect of roof reflectivity, insulation level, and attachment type
We show that the energy performance of cool roofs is related to roof insulation and depends on the building type in each climate
The results of this section show the effects of roof reflectivity and roof insulation for each location and building type for adhered roof construction
Summary
Cool and reflective roofs can decrease roof surface temperatures and building cooling load. They can contribute to reducing radiative heat flux to the atmosphere, which may potentially mitigate the urban heat island effect at a city scale [1,2,3,4]. The benefits of cool roofs in warm climates have not been questioned. Recent reports have expressed concerns about their overall energy impact in mixed and cold climates, where heating is a significant part of the building energy use, and dark roofs are considered more effective. A review on the overall efficiency of reflective roofs and questions about their applicability and effectiveness in specific climates are presented below
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