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Title
Hygrothermal Simulatons of Cool Reflective and Conventional Roofs
Hygrothermal Simulatons of Cool Reflective and Conventional Roofs
Date
9/2011
9/2011
Author(s)
Hamed Saber; Michael Swinton; Peter Kalinger; Ralph Paroli
Hamed Saber; Michael Swinton; Peter Kalinger; Ralph Paroli
Page(s)
Keyword(s)
hygrothermal modeling; white roof; black roof; energy savings; modified bitumen; heating degree days; HDD
hygrothermal modeling; white roof; black roof; energy savings; modified bitumen; heating degree days; HDD
Abstract
When solar radiation hits a roof surface, a part of solar energy is reflected and part is absorbed. The absorbed part of solar energy results in an increase in the roof’s surface temperature. Cool reflective (white) roofs use bright surfaces to reflect the incident short-wave solar radiation, which lowers the surface temperature compared with conventional (black) roofs with bituminous membranes. As such, white roofs help reduce the urban heat island effect during the summer. The question is: “Do white roofs lead to moisture-related problems in northern and southern climates?” To answer this question, numerical simulations are conducted to compare the hygrothermal performance of white and black roofs under different outdoor and indoor conditions. The outdoor conditions are obtained from the weather database of the National Research Council of Canada, Institute for Research in Construction (NRC-IRC). The indoor conditions are taken based on European standard (EN 15026) and American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) recommendations for conditioned space. The roof types considered in this study are polymer-modified bitumen roof systems. The numerical simulations were conducted using the NRC-IRC’s hygrothermal model called “hygIRC-C.”
When solar radiation hits a roof surface, a part of solar energy is reflected and part is absorbed. The absorbed part of solar energy results in an increase in the roof’s surface temperature. Cool reflective (white) roofs use bright surfaces to reflect the incident short-wave solar radiation, which lowers the surface temperature compared with conventional (black) roofs with bituminous membranes. As such, white roofs help reduce the urban heat island effect during the summer. The question is: “Do white roofs lead to moisture-related problems in northern and southern climates?” To answer this question, numerical simulations are conducted to compare the hygrothermal performance of white and black roofs under different outdoor and indoor conditions. The outdoor conditions are obtained from the weather database of the National Research Council of Canada, Institute for Research in Construction (NRC-IRC). The indoor conditions are taken based on European standard (EN 15026) and American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) recommendations for conditioned space. The roof types considered in this study are polymer-modified bitumen roof systems. The numerical simulations were conducted using the NRC-IRC’s hygrothermal model called “hygIRC-C.”