Modeling permeable pavements for urban heat island mitigation


#1

Hi All

I am working on modeling permeable pavements as mitigation for urban heat island. Permeable pavements are supposed to remain cooler compared to conventional pavements and contribute towards lowering ambient temperature through evaporative cooling. I would like to get pointers from you all on how can I model them in Dragonfly to validate their performance. As far as I know, phase change phenomena is a bit difficult to model in dragonfly. Is there any work around for doing this?

looking forward to hearing from you all on this.

Thanks in advance!
Ram


#2

Hi Ram,

  1. I am not at my machine so I might not be accurate about this. The only way to account for the contribution of a pavement in Dragonfly is by mentioning its albedo.

  2. It is my belief that the evaporative cooling effect that you expect to happen from the softscape of open paver will be very minimal and I don’t think it is accounted for in any of the components in the LB tools.

  3. Dragonfly does consider evapotranspiration from trees and green areas. However, the cooling effect due to evapotranspiration is reflected merely as substraction in the sensible heat in the urban canyon.

  4. I do not know what percent of the open paver is permeable in your case. Typically it is at least 50%. If it is more than that then a simplification will be to model this open paver surface as a green surface itself.


#3

Thanks for your response, Devang. I was thinking of an approach which is like this.

Model the permeable pavement as a green roof and get the surface temperature. Later use this temperature for calculating operative temperature through outdoor comfort recipe. What do you think about this?

Best,


#4

Ram,

Sure, that sounds like a good idea to me. I would do that myself. However, whenever I have attempted that, I have received surface temprature of the green roof similar if not greater than the rest of the paved area. That is obviously something that we don’t expect.


#5

True, Devang. I just ran the green roof algo and somehow the temperatures are not as expected maybe @chris can look in to this?
Best,


#6

@RamJoshi

I can’t help you with the green roof, however going back to your earlier questions about Dragonfly I have a few comments (even if you aren’t planning on using this method anymore):

I am not at my machine so I might not be accurate about this. The only way to account for the contribution of a pavement in Dragonfly is by mentioning its albedo.

One correction here is that DF/uwg does model the heat flux from paved surfaces, accounting for the monthly variation of ground temperatures at depths of 0.5, 1, or 2m, and the surface temperature of the pavement.

@devang is correct that it won’t model the evapotranspiration contribution of grass.

I don’t know if adding permeable pavements will have an effect on your model, but I think it is easy to find out! Check out this hydra example by Chris which allows you to quickly model the urban heat island using from parameters (i.e no need to model building geometries) which should allow you to quickly assess whether there is an impact from increasing the grass fraction to account for permeable pavements, vs non-permeable pavements.