Irrigation proposals for improving the energy performance of green roofs in Mediterranean climate

The evapotranspiration and cooling energy saving potential of green roofs is very great in the Mediterranean climate, due to high levels of solar radiation. However, the low rainfall limits these losses. The main goal of this research is to determine the energy savings achieved by increasing water availability by installing an irrigation system. It is proposed the computer simulation of a building renovated with three construction systems, according to real scaled models. Irrigation proposals are studied from two perspectives: (1) different irrigation rates for each green roof system and (2) different irrigation schedules. From the perspective of irrigation rates (1) it is observed that increased water input in extensive green roofs does not lead to increased evapotranspiration heat losses due to their limited water storage capacity. In extensive green roofs, increasing the water supply above the storage capacity implies increasing water outflow, but not heat losses. In relation to the irrigation schedules (2) the models with daily annual irrigation achieve very limited total savings, less than 1% compared to self-sustaining models. However, a daily irrigation system only during cooling periods achieves greater total savings, between 1% and 2% compared to self-sustaining models. The system is optimised by increasing energy savings and reducing water consumption. On green roofs in the Mediterranean climate, the increase in available water does not necessarily imply an increase in total energy savings. In these cases, it is essential to find a balance between limiting water consumption and reducing energy consumption.