Vegetation and soil – related parameters for computing solar radiation exchanges within green roofs: Are the available values adequate for an easy modeling of their thermal behavior?

Abstract

Several studies analyze the thermal performance of vegetated roofs, presenting either mathematicalmodels or experimental quantifications of heat transfer process through them, also showing the effectof vegetation and soil parameters on the thermal and energy performance of this type of roofing system.However, presently the level of availability of these parameters, has not been enough considered. Thiswork intends to investigate this underestimated issue of the green roofs’ thermal modeling, through theconsideration of the availability of parameters pertinent to the shortwave radiation exchange, which areadopted by models based on leaf area index (LAI) and on the fractional vegetation coverage (f). Fromthe analysis of these models, the importance of a precise knowledge of such parameters arises, despitethe availability of their values is still limited. In addition, the absence of a proper database includingseveral green roof plant species and information on their stage of growth, to which a technician possiblywill refer in the case of lack of field data, represents quite a worthwhile matter because it may lead toinaccurate estimations of the thermal loads for climatization of buildings equipped with green roofs. Inthis respect, the manuscript reports an estimation of the errors potentially occurring when not specificvegetation data are used. This evaluation is based on simulations, performed with the DesignBuilder©software, showing the energy effects produced by different assumptions in the green parameters (thatis by adopting experimental data revealed by authors and a potential mix of the literature availableparameters).Thus, the mission of the paper is to enlighten a difficulty that a technician possibly will encounterwhen performing an energy and thermal simulation of a green roof; therefore a strong call for makingthe current database more tailored on green roofs has also arisen.