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Abstract
It is well known that the mass of a ballasted roof can peak roof temperatures and delay theheat flow into a building. Although they perform similar functions, ballasted roofs do not meet the traditional requirements of high solar reflectance and high thermal emittance set out by the EPA and other orgniazations regarding being a "cool roof." To address whether ballasted roofing systems offer similar energy efficiency benefits as cool roofs, a project to perform side-by-side experiments was intiated. Different weightings of ballasted roofs were compared to a paver system and black and white membranes. These six test sections were constructed and installed on the Roof Thermal Research Apparatus (RTRA) and were monitored for thermal performance for a twenty-four month period. Data collecction includes continuous monitoring of temperatures, heat flows, and weather conditions as well as periodic verification of the surface properties of solar reflectance and thermal emmitance. These data will answer what impact a ballasted roof has on the heat flow into a building and on the roof surface temperature. Furthermore, comparisons between the ballasted and unballasted membranes will allow for an assessment of whether ballasted systems perform as well as white membranes and are deserving of a "cool roof" status within the codes. This report also describes the modeling of the thermal performance of all six systems with the Simplified Transient Analysis Roofs (STAR) program. STAR does well for lightweight roofs with exposed membranes. Reasonable values of effective heat capacity and thermal conductivity were sought for the ballasted systems that yielded good agreement between the predicted and measure membrane temperatures and insulation heat fluxes. Goodness of agreement was judged by average differences over six month periods between mid-April and mid-October. Modeling of ballasted roofs was desired so that experimental results measured in East Tennessee could be generalized to other climates across the United States.
It is well known that the mass of a ballasted roof can peak roof temperatures and delay theheat flow into a building. Although they perform similar functions, ballasted roofs do not meet the traditional requirements of high solar reflectance and high thermal emittance set out by the EPA and other orgniazations regarding being a "cool roof." To address whether ballasted roofing systems offer similar energy efficiency benefits as cool roofs, a project to perform side-by-side experiments was intiated. Different weightings of ballasted roofs were compared to a paver system and black and white membranes. These six test sections were constructed and installed on the Roof Thermal Research Apparatus (RTRA) and were monitored for thermal performance for a twenty-four month period. Data collecction includes continuous monitoring of temperatures, heat flows, and weather conditions as well as periodic verification of the surface properties of solar reflectance and thermal emmitance. These data will answer what impact a ballasted roof has on the heat flow into a building and on the roof surface temperature. Furthermore, comparisons between the ballasted and unballasted membranes will allow for an assessment of whether ballasted systems perform as well as white membranes and are deserving of a "cool roof" status within the codes. This report also describes the modeling of the thermal performance of all six systems with the Simplified Transient Analysis Roofs (STAR) program. STAR does well for lightweight roofs with exposed membranes. Reasonable values of effective heat capacity and thermal conductivity were sought for the ballasted systems that yielded good agreement between the predicted and measure membrane temperatures and insulation heat fluxes. Goodness of agreement was judged by average differences over six month periods between mid-April and mid-October. Modeling of ballasted roofs was desired so that experimental results measured in East Tennessee could be generalized to other climates across the United States.
Date
9/2007
9/2007
Author(s)
A Desjarlais; T Petrie; J Atchley; R Gillenwater; D Roodvoets
A Desjarlais; T Petrie; J Atchley; R Gillenwater; D Roodvoets
Page(s)
23
23
Source
Oak Ridge National Lab
Oak Ridge National Lab
Keyword(s)
ORNL; SPRI; energy performance; ballasted; cool roof; STAR program;
ORNL; SPRI; energy performance; ballasted; cool roof; STAR program;