Exploring the reduction of energy demand of a building with an eco-roof under different irrigation strategies

A passive system widely used to reduce the energy consumption of a building is the green roof. The main objective of this work was to determine the reduction of energy demand of a building with a green roof without plants, eco-roof, under 20 different irrigation strategies, compared to a traditional gravel ballasted roof, in southern Europe. Experimental data of heat flux collected during one year were used to calibrate two numerical models developed with DesignBuilder software. Evapotranspiration and volumetric water content were demonstrated to have a great impact on the heat flux reduction of the eco-roof. Moreover, evapotranspiration strongly depended on the climatic conditions. The annual heat flux results showed that the eco-roof improved the thermal performance of the building compared to the traditional roof, achieving a high reduction of annual energy demand, ED, up to 78.7%. The strategy that had the highest ratio between the annual ED to the lowest use of water was watering in alternate days for 20 min in the morning, obtaining an ED value of 46.7%. These results indicate that eco-roofs with a proper irrigation strategy could be used as an efficient passive system for the rehabilitation of old buildings.

Automated summary

The research demonstrates that evapotranspiration and volumetric water content have a significant impact on the reduction of heat flux in eco-roofs. The irrigation strategy plays a key role in improving the performance of eco-roofs. Eco-roofs can significantly reduce the energy demand of buildings and can be used as an efficient passive system for the rehabilitation of old buildings.