DWC Hydroponic roofs for building decarbonization: a parametric dynamic thermal analysis

This study investigates the potential of a modular Deep Water Culture (DWC) hydroponic roof as a passive strategy for building decarbonization and energy demand reduction. The proposed system represents an alternative to conventional green roofs, combining the thermal inertia provided by a water layer with the principles of Building-Integrated Architecture (BIA). A parametric dynamic thermal analysis was carried out to evaluate the influence of the hydroponic water depth on the energy and thermal performance of buildings. To this aim a validated TRNSYS model, calibrated against on-site experimental measurements was used. Three different water depths in the hydroponic tray (20 cm, 30 cm, and 40 cm) were analysed in combination with three roof typologies: an uninsulated reinforced concrete slab with hollow clay blocks, an insulated concrete roof and a lightweight prefabricated roof. Seasonal heating and cooling energy demands, surface temperatures, time lag and decrement factor were investigated. The results demonstrate that a water depth of 20 cm represents the optimal configuration across all roof typologies leadings to a reduction in cooling energy demand of up to 45%, an increase in time lag from 7 h to 14 h and a decrease in peak external surface temperature exceeding 10 °C during summer. Increasing the water depth beyond 20 cm does not provide additional benefits and may even degrade summer performance due to excessive thermal resistance and heat storage effects. The most significant improvements were observed for lightweight roofs, which inherently lack thermal inertia.