Performance of roof materials high SRI, low SRI, and green roof in California climate zone 8 Los Angeles, California.

摘要

As cities expand, dark and inanimate surfaces cover more area; therefore, more solar energy is absorbed within the cities' area and the temperature goes up. The heat island effect elevates temperature particularly during the summer. Studies demonstrate that materials that reflect a large fraction of solar radiation and green roofs are two ways to decrease this effect.;Cool roof materials decrease the demand of energy during summer due to the fact that they bounce back the sun's radiation into space instead of transferring it to the building below. The amount of heat that reflects or is absorbed by the surface is measured by two characteristics, solar reflectance (rho) and absorptance (alpha.) The amount reradiated is characterized by thermal emittance (epsilon.);In order to compare the performance of roof materials, four test cells have been constructed. The author first compared (Round One Tests) the performance of four systems: a black roof without insulation, a cool roof without insulation, a conventional insulated black roof, and an insulated roof that is covered with cool roofing material. The test cells were made in climate zone 8 during June and July 2010.;Temperatures were measured inside, outside and above the roof. The inside temperature shows the effect of different material and insulation on the performance of building envelope. The outside measurement provides data to understand the Urban Heat Island effect that is caused by dark areas in the city. The roof assemblies of the cells are: (1) Black painted roof without insulation (2) Black painted roof with R-13 insulation (3) White Roof Coating (Solar Reflectance =0.84, Thermal Emittance=0.91) without insulation (4) White Roof Coating (Solar Reflectance =0.84, Thermal Emittance=0.91) with R-13 insulation;After September, the insulation was changed to R-30 for the insulated test cells in order to quantify the impact of insulation by comparing the inside and outside temperature for different insulation levels (Round Two Tests.);At the end of October, the black roof without insulation was replaced with a green roof (Round Three Tests.) The thermal mass of green roofs protects the building from getting cold during the winter as well as insulating the building during summer. Measurement inside and outside temperature and humidity of this test cells provide the data to compare the performance of mass as well as other aspect related to green roof with black and white roof. Evapotranspiration will reduce overheating, as well.;The measurement and analysis of indoor and outdoor temperature data will indicate the results. This paper aims to determine the effect of the insulation, color, and thermal mass on the performance of the roof in climate zone 8, Los Angeles.