Reduction Of Heat Flux Green Roof

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.

Reduction of heat flux green roof.

Green roof temperatures can be 30 40 f lower than those of conventional roofs and can reduce city wide ambient temperatures by up to 5 f. The hamerschlag hall green roof was found to lose 26 less heat than the control roof in heating months. Green roofs reduce the heat flux through the roof and less energy for cooling or heating can lead to significant cost savings. 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.

In summer the green roof protects the building from direct solar heat. 6 the report concluded that a combined strategy of implementing green roofs and maximizing the amount of vegetation in new york by planting trees along streets and in open areas offers more potential cooling than any one strategy. 1 2 in addition green roofs can reduce building energy use by 0 7 compared to conventional roofs reducing peak electricity demand and leading to an annual savings of 0 23 per square foot of the roof s surface. The green roof caused a mean reduction of 4 96 c proving that green roofs contribute to reducing indoor room temperature and thermal lag promoted by the green cover where the heat input takes.

Green roofs reduce building energy use by cooling roofs and providing shading thermal mass and insulation. 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. The average 24 h effect of sedum covered green roof was a 0 2 c increase of air temperature 15 cm above the ground. Research by david sailor at portland state university also concluded that low latent heat flux due to lack of vegetation in urban areas is the most significant contributing factor to the uhi phenomenon.

In toronto researchers found that average daily heat flow through a green roof was reduced 70 90 in the summer and 10 30 in the winter relative to a traditional roof. 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. 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. The allegheny county office building green roof was found to lose 8 2 less heat than the control roof in heating months and gain 75.

Peak membrane temperatures were reduced by the green roof and were delayed by 5 h relative to a traditional roof 11. 1 3 these temperature reduction and energy efficiency benefits are a key contributor to the growing popularity of green roofs in the.