Reduction Of Heat Flux Green Roof

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.

Reduction of heat flux green roof.

Green roofs reduce building energy use by cooling roofs and providing shading thermal mass and insulation. The hamerschlag hall green roof was found to lose 26 less heat than the control roof in heating months. 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 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.

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. The average 24 h effect of sedum covered green roof was a 0 2 c increase of air temperature 15 cm above the ground. Green roofs reduce the heat flux through the roof and less energy for cooling or heating can lead to significant cost savings. New york has recently approved a tax abatement of up to.

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. 1 3 these temperature reduction and energy efficiency benefits are a key contributor to the growing popularity of green roofs in the. In summer the green roof protects the building from direct solar heat. 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.

The effect that the green roof media has on the thermal performance of the roof system was evaluated. Peak membrane temperatures were reduced by the green roof and were delayed by 5 h relative to a traditional roof 11. Shading the outer surface of the building envelope has been shown to be more effective than internal insulation. 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.

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. 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.