Reduction Of Heat Flux Green Roof

Heat flux reduction depends on the building and roof insulation and moisture in a green roof s soil medium.

Reduction of heat flux green roof. In summer the green roof protects the building from direct solar heat. In a plot study when comparing green and traditional roofs for two weeks in the winter researchers found a 23 reduction in heat flux through the green roof relative to the reference roof in conditions with no snow cover. The average 24 h effect of sedum covered green roof was a 0 2 c increase of air temperature 15 cm above the ground. This suggests that extensive sedum covered green roofs might help decrease air temperatures at night when the urban heat island is strongest but possibly contribute to high daytime temperatures.

A green roof or rooftop garden is a vegetative layer grown on a rooftop. The best net heat flux gains for vegetated green roofs were 4 7 w m 2 for the sand roof and 7 8 w m 2 for the silt clay roof. Typically it can lower the need for air conditioning load to cool a building 7 by 10 to 30 percent. Also under the described laboratory conditions the uninsulated green roof samples with plants showed an average heat flux reduction of 25 compared to samples without plants.

Green roofs can reduce the flow of stormwater from a roof by up to 65 and delay the flow rate by up to three hours. When water changes from a liquid to a gas energy is needed to overcome the molecular force of attraction between the particles. 2 reduced heating and cooling costs provides extra roof insulation. Extended life of the roof protects the roof from weather reducing maintenance costs.

Reduced urban heat island effect a green roof reduces the level of absorbed heat in dense concrete areas. Shading the outer surface of the building envelope has been shown to be more effective than internal insulation. Using green roofs in cities or other built environments with limited vegetation can moderate the heat island effect particularly during the day. However this difference was reduced to 5 with a snow layer.

Green roofs reduce building energy use by cooling roofs and providing shading thermal mass and insulation. Green roofs reduce the heat flux through the roof and less energy for cooling or heating can lead to significant cost savings.