Hello, so I am trying to develop a simple model for calculating the cooling impact of green roofs, but am having trouble trying to incorporate the variable of building height. Specifically, I am trying to find the relationship between building height and green roof cooling impact, where I could calculate how a green roof's cooling effect/impact will change based on how high up it is, such as comparing the cooling effect of a green roof on a one-story building compared to the cooling effect of the same green roof on a 10-story building. The theory and general consensus I have found throughout the literature is that the higher the green roof is off the ground, the lower its cooling impact is on reducing the urban heat island effect. If we are just talking about land surface temperature here, this would seem quite intuitive, e.g. we would want the green roof cooling to be closer to the ground where people actually need it.
The trouble I am having is finding that actual quantitative relationship between green roof cooling impact and building height, such as a specific multiplier or coefficient I could use to multiply a green roof's cooling effect by to account for its height off the ground. Would anyone know if such a relationship has actually been documented in the literature?
I have seen this paper "Impact of Morphological Characteristics of Green Roofs on Pedestrian Cooling in Subtropical Climates" by Zhang et al. (2019) that concludes the reduction in green roof cooling effect the higher the building height is: Article Impact of Morphological Characteristics of Green Roofs on Pe...
I have also seen this paper "Effect of vegetation biomass structure on thermal performance of tropical green roof" by C.Y. Jim (2012) that describes the relationship between building height and green roof cooling effect as a "height-decay function", where the green roof cooling "decays" the higher it is off the ground:
Article Effect of vegetation biomass structure on thermal performanc...
And then this paper "Green-Roof Effects on Neighborhood Microclimate and Human Thermal Sensation" by Peng and Jim (2013) that describes that height decay as linear:
https://www.mdpi.com/1996-1073/6/2/598/htm
It is great to see that this important relationship between building height and green roof cooling effect has been well studied, and I can see that the consensus is that yes, the cooling effect of a green roof will be reduced as a function of how high the green roof is off the ground (if we are talking about its effect on land surface temperature). However, I cannot find in these papers or anywhere else in the literature what these coefficients, relationships, or functions actually are, such as a percentage cooling effect reduction per meter of building height, or something like that. I am looking for something that I could simply multiply a green roof cooling impact by to account for the height of the building. Would anyone know is such a quantitative relationship has been documented?
Thank you!
Dear Lino Sanchez
As you have said, Apart from green roof structures, building characteristics and configurations can also influence cooling effects of green roofs. Overall, the cooling performance decreases along building height, and the cooling effects on pedestrian air temperature are negligible when the building height exceeds 60m.
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