The joint influence of albedo and insulation on roof performance: An observational study

Abstract

This article focuses on understanding the temperature and heat flux fields in building roofs, and how they are modulated by the interacting influences of albedo and insulation at annual, seasonal and diurnal scales. High precision heat flux plates and thermocouples were installed over multiple rooftops of varying insulation thickness and albedo in the Northeastern United States to monitor the temperature and the heat flux into and out of the roof structures for a whole year. Our analysis shows that while membrane reflectivity (albedo) plays a dominant role in reducing the heat conducted inward through the roof structures during the warmer months, insulation thickness becomes the main roof attribute in preventing heat loss from the buildings during colder months. On a diurnal scale, the thermal state of the white roof structures fluctuated little compared to black roof structures; membrane temperature over white roofs ranged between 10°C and 45°C during summer months compared to black membranes that ranged between 10°C and 80°C. Insulation thickness, apart from reducing the heat conducted through the roof structure, also delayed the transfer of heat, owing to the thermal inertia of the insulation layer. This has important implications for determining the peak heating and cooling times.

The joint influence of albedo and insulation on roof performance: A modeling study

“…One of our unambiguous conclusions from an associated experimental study [2] was that white roofs were highly effective in reducing the cooling loads during the summer months, while insulation thickness (R-value) was the main determinant of roof energy efficiency during winter periods. But the observational study was not well suited for exploring the optimum (in term of financial cost) combination of albedo and R-value for a given geographical location.…”

“…Similar to warmer months, this difference is significantly reduced for insulation thickness greater than 18 cm (R8.4). As we also point out in the associated experimental study [2], this discrepancy between summer time benefits and winter time penalties of cool roofs, despite the fact that the Northeastern US has about 5 times more heating degree days than cooling degree days, is related to the negligible impact of albedo during peak heating periods (which occur during nighttime and in the winter when the insolation periods are short), as opposed to its prominent role during peak cooling periods (occurring in the afternoon and in the summer when the insolation periods are long).…”

“…at the interface between the insulation foam and roof frame. The complete details of the measurements and schematics of the installed sensors are provided in Ramamurthy et al [2].…”

“…The aim is to identify the optimal combination of albedo and insulation that would minimize total cost (material and operating energy costs) for roofs in the region, but the research methodologies used here (though clearly not the conclusions) can obviously be applied to any other site anywhere in the world. The observational part of the study [2], as well as previous research in the same region [4], suggest that the albedo expected to yield the highest energy efficiency would be a high one, corresponding to a white roof. The simulations we conduct here will aid in corroborating these conclusions, and the expansion of the parameter space (albedo and insulation) will allow us to explore/identify the optimal roof design.…”

Timber Chips as the Insulation Material for Energy Saving in Prefabricated Offices

“…There is evidence to suggest that in a hot climate such as in Riyadh, Saudi Arabia, the surface temperature with roof insulation will be 4.5˝C cooler than that of roofs without insulation [4]. Roof insulation could reduce the heat conducted through the roof structure, and delay the transfer of heat [5]. The optimized insulation material and insulation location for flat roofs exposed to sunshine to reduce heat gain were analyzed in a recent study [6].…”