Optimized cool roofs: Integrating albedo and thermal emittance with R-value

For cool roofs the combined effect of the three parameters that define heat gain and loss from a roof, namely solar albedo α, thermal emittance E, and sub-roof R-value, must be considered. An accurate contribution of night sky cooling, and hence humidity and total down-welling atmospheric radiation is needed. A systematic analysis of the contribution of a roof to average cooling load per day and to peak load reductions is presented for a temperate climate zone over 6 cooling months using an hour-by-hour analysis. Eighteen 3-parameter sets (α,E,R) demonstrate the over-riding importance of a high α, while sensitivity to R-value and E drops away as albedo rises. Up-front cost per unit reductions in peak demand or average energy use per day always rises strongly as R rises unless albedo is low. A moderate R∼1.63 is superior to high R unless a roof is dark, or winter heating demand is high. We indicate briefly why the roof typically does not present a dominant influence on average winter heating needs in most temperate zones, enhancing the benefits of cool roofs. © 2011 Elsevier B.V. All rights reserved

Carbon uptake by mature Amazon forests has mitigated Amazon nations' carbon emissions

BACKGROUND: Several independent lines of evidence suggest that Amazon forests have provided a significant carbon sink service, and also that the Amazon carbon sink in intact, mature forests may now be threatened as a result of different processes. There has however been no work done to quantify non-land-use-change forest carbon fluxes on a national basis within Amazonia, or to place these national fluxes and their possible changes in the context of the major anthropogenic carbon fluxes in the region. Here we present a first attempt to interpret results from ground-based monitoring of mature forest carbon fluxes in a biogeographically, politically, and temporally differentiated way. Specifically, using results from a large long-term network of forest plots, we estimate the Amazon biomass carbon balance over the last three decades for the different regions and nine nations of Amazonia, and evaluate the magnitude and trajectory of these differentiated balances in relation to major national anthropogenic carbon emissions. RESULTS: The sink of carbon into mature forests has been remarkably geographically ubiquitous across Amazonia, being substantial and persistent in each of the five biogeographic regions within Amazonia. Between 1980 and 2010, it has more than mitigated the fossil fuel emissions of every single national economy, except that of Venezuela. For most nations (Bolivia, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname) the sink has probably additionally mitigated all anthropogenic carbon emissions due to Amazon deforestation and other land use change. While the sink has weakened in some regions since 2000, our analysis suggests that Amazon nations which are able to conserve large areas of natural and semi-natural landscape still contribute globally-significant carbon sequestration. CONCLUSIONS: Mature forests across all of Amazonia have contributed significantly to mitigating climate change for decades. Yet Amazon nations have not directly benefited from providing this global scale ecosystem service. We suggest that better monitoring and reporting of the carbon fluxes within mature forests, and understanding the drivers of changes in their balance, must become national, as well as international, priorities

Optimum integration of albedo, sub-roof R-value, and phase change material for cool roofs

A cool roof aims to reduce total seasonal cooling loads and peak summer loads. It is often rated just in terms of its solar reflectance Rsol (or albedo), with some impact of infrared emittance considered. However the sensitivity of cooling loads to Rsolvaries as the R-value of sub-roof insulation changes. Knowing joint impacts led to better integrated energy savings design with R-value chosen on the basis of Rsol and local climate. This study extends previous work (Gentle et al., 2011) (Smith et al., 2012) (Aguilar et al., 2012) by considering the impact of phase change materials (PCM) within a roofing module on energy savings. The aim is to show how building simulation helps pinpoint the optimum combination. Copyright © 2011 by IPAC'11/EPS-AG

Multi-parameter sensitivity analysis: A design methodology applied to energy efficiency in temperate climate houses

Quantified sensitivities of heating and cooling loads to different variables that influence heat gain and loss in a building provides a valuable basis for energy efficient design, especially in temperate climate zones where particular parameter settings could be beneficial in one season while reducing performance or neutral in the other. In doing so it is important in this multi-parameter design space to consider impact of changes in each parameter when other variables also change. Such 2-variable up to n-variable correlation is called factorial analysis. The methodology is introduced using three variables (roof solar absorptance, air exchange rates, and sub-roof R-value) in a simple structure with all other parameters fixed. Sensitivity is via impact of changes on each of heating load, cooling load and annual total. Knowledge of factorial effects is shown to be important and lead to simple strategies that provide large benefits in both seasons. They also show that some standard approaches to saving energy (e.g. raising R significantly), while useful are often unnecessary, unless poor settings are made in other parameters. © 2012 Elsevier B.V. All rights reserved