Heat transfer in a lightweight extensive green roof under water-freezing conditions

This paper presents a study of the thermal response of lightweight extensive green roofs with lightweight mineral wool growing media in wintertime in water-freezing conditions. A model of green roof heat and mass transfer was developed, which considers sensible as well as latent heat accumulation in plants and lightweight mineral wool growing media using an apparent heat capacity method. The model was validated with in-situ experiments. The influence of latent heat storage on the thermal response of a green roof was studied for different climatic conditions. The results of numerical analyses showed that the process of water freezing further improves the energy efficiency of green roofs, because the peak heat flux at the inner surface of the roof is up to 30% lower in comparison to the non-vegetated roof. It is shown that latent heat storage significantly contributes to decreasing heat losses during wintertime, which are approximately 5% to 20% lower in comparison to non-vegetated roofs. (C) 2018 Elsevier B.V. All rights reserved.