Seasonal thermal performance evaluation of the composite planted roof in subtropical area

Planted roof works as a passive technology of saving building as well as reducing the building energy consumption. Actual projects show that the structure of the planted roof, for example, the soil, may decrease the heat dissipation capacity of the planted roof, resulting in the temperature rise, higher than the non-planted roof when it is at night, in the bottom of planted roof and, thus, the energy consumption of planted roof might be increased. In regard of this, four novel composite planted roofs which combined water storage and ventilation technology were proposed. Theoretically, the innovative roofs can enhance the dissipation capacity of planting layer and reduce the reverse heat transfer at night. Four types of composite planted roof models have been tested under the subtropical climate in Guangzhou. The results show that the heat insulation effect of the composite planted roof performs better than the ordinary in summer. The average total heat flow, when in summer, of module A, B, C and D are 424.6 W/m2, 333.9 W/m2, 627.1 W/m2 and 292.7 W/m2 respectively. In comparison with the bare roof, the intake heat of the control room was reduced by 50.1%, 60.7%, 26.2% and 65.6% respectively. Also, the mechanical ventilation in soil layer can improve the insulation effect of the roof. However, the module with water storage and planting displayed the worst insulation performance. In addition, a mathematical model of the composite planted roof was established, and the average error between the calculated soil temperature value and the experimental data was less than 6%.