Reduction Of Heat Flux Green Roof

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

Reduction of heat flux green roof. Green roofs reduce building energy use by cooling roofs and providing shading thermal mass and insulation. 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. 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 effect that the green roof media has on the thermal performance of the roof system was evaluated.

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

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

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