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Advanced Energy Efficient Building Envelope Systems

Moncef Krarti
Moncef Krarti
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ASME Press
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Light colored roofs, known as cool roofs, have gained popularity as a strategy to reduce cooling energy use for both residential and commercial buildings. While static cool roofs (SCRs) with constant optical properties are effective in reducing cooling thermal loads, they can increase energy use due to heating. A solution to avoiding significant heating energy penalties is the adoption of dynamic cool roofs (DCRs) with variable reflective coatings. This chapter explores the potential energy savings of DCRs with seasonally variable reflective surfaces for various building prototypes when compared a static cool roofs. The analysis demonstrates that any additional energy savings from DCRs depend largely on the climate, insulation level, reflectance of the roof, and to a lesser extent on the building thermal mass. This chapter shows that older buildings, with low insulation levels, in colder climates are the best target for retrofit using DCRs. Specifically, reported results, discussed throughout the chapter, show that when a variable reflective costing is applied to low insulation buildings, source energy savings can be achieved and range from 4.33 to 19.44 MJ/m2 (i.e., 1.6 to 4.9%) for residential units and from 1.17 to 18.00 MJ/m2 (i.e., 0.3 to 3.9%) for offices. Based on an economic analysis, it is found that the break-even cost for a variable reflectance coating system with a 22-year life span ranges from 0.80 to 4.84 $/m2 for residential buildings, and from 0.86 to 4.92 $/m2 for commercial buildings.

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