Reduction Of Heat Flux Green Roof

Extended life of the roof protects the roof from weather reducing maintenance costs.

Reduction of heat flux green roof.

Green roofs are more effective than conventional and white roofs for cooling buildings because they utilize a heat transfer mechanism known as evaporative cooling which is unavailable to most conventional roofs. Using green roofs in cities or other built environments with limited vegetation can moderate the heat island effect particularly during the day. 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. Green roofs reduce building energy use by cooling roofs and providing shading thermal mass and insulation.

Reduced urban heat island effect a green roof reduces the level of absorbed heat in dense concrete areas. A green roof or rooftop garden is a vegetative layer grown on a rooftop. However this difference was reduced to 5 with a snow layer. Green roofs reduce the heat flux through the roof and less energy for cooling or heating can lead to significant cost savings.

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. 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. Typically it can lower the need for air conditioning load to cool a building 7 by 10 to 30 percent. 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.

In summer the green roof protects the building from direct solar heat. 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 provide shade remove heat from the air and reduce temperatures of the roof surface and surrounding air. 2 reduced heating and cooling costs provides extra roof insulation.

Shading the outer surface of the building envelope has been shown to be more effective than internal insulation. Green roofs with silt clay soil required more than twice the amount of soil moisture than green roofs with sand to achieve similar roof heat transfer rates.