Economic comparison of cool and grey roofs of a small office building in the USA

Abstract

EnergyPlus V9.0 simulations of a typical small office building prototype in five USA cities (Albuquerque, Atlanta, Buffalo, San Diego, Rochester) indicate that adding a cool roof (albedo 0.6) for an aged grey roof (albedo 0.2) would reduce the annual energy and annual energy cost in all hot dry or humid cities (Albuquerque, Atlanta, San Diego) and in severe cold or mixed humid cities (Buffalo, Rochester). The CO2, SO2, and NOX savings are positive in all selected cities. This work considers the economics of using cool roofs of an office building in the USA by performing a 20-year life-cycle cost analysis that compares each type of roof to a grey roof. The 20-year net present values (NPVs) of annual conditioning (heating + cooling) energy cost savings were calculated. The life cycle cost savings (NPV of annual streams – initial cost premium) of cool roofs have both positive and negative values. The NPV with the cool roofs is from -17.3 USD/m2 in Rochester to 6.5 USD/m2 in San Diego. Among the five cities in the USA, Albuquerque, Atlanta, and San Diego were able to apply the cool roofs since they all have positive NPV, while Buffalo and Rochester were unsuitable to apply the cool roofs methods because of the negative NPV. Owners concerned with urban heat island mitigation and slowing climate change may prefer cool roofs