A heat transfer model for assessment of plant based roofing systems in summer conditions

This paper presents a quasi-steady state heat and mass transfer green roof model that can be incorporated in different energy simulation software or calculation procedures. The model considers heat and mass transfer processes between the sky, plants, and substrate. This paper also presents new equations to calculate (1) substrate thermal conductivity for green roofs, (2) substrate resistance to calculate green roof soil evaporation, (3) and set of compiled stomatal resistance functions to calculate plants' transpiration. The model is validated with robust experimental data that consists of surface temperatures, conduction heat flux, convection heat flux, net radiation and evapotranspiration. The data was obtained from laboratory experiments using a new "Cold Plate" apparatus set in an environmental chamber. The validation shows that the model predicts the heat and mass transfer accurately, except that it tends to underestimate peak evapotranspiration rates. (C) 2011 Elsevier Ltd. All rights reserved.