Reduction Of Heat Flux Green Roof

Peak membrane temperatures were reduced by the green roof and were delayed by 5 h relative to a traditional roof 11.

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. 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 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. In summer the green roof protects the building from direct solar heat.

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. 1 3 these temperature reduction and energy efficiency benefits are a key contributor to the growing popularity of green roofs in the. 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. New york has recently approved a tax abatement of up to.

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. The effect that the green roof media has on the thermal performance of the roof system was evaluated. 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. 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.

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. The hamerschlag hall green roof was found to lose 26 less heat than the control roof in heating months. 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.

Shading the outer surface of the building envelope has been shown to be more effective than internal insulation. 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.