Confusion about albedo and urban heat island

Site Grading & Site Design Vignettes and Multiple Choice

Confusion about albedo and urban heat island

Postby anonymous283 » Mon Apr 16, 2018 11:47 am

I keep reading that to lower the urban heat island effect (UHI), architects should use green roofs or light color painted roofs. This isn't the same as saying use high albedo materials, which I've also read, because vegetation doesn't have high albedo. I've also read the materials should be high in albedo and have a minimum reflectance of 0.3, but having a highly reflective material will also increase UHI - see question 17 which I answered C because of this confusion but they say D.

So in reality to lower the urban heat island effect the roof should be either a green roof, which is low in albedo and low in conductivity, or light/reflective painted, which is high in albedo and high in conductivity but not too reflective or mirror like because it will heat up adjacent taller buildings... Seems pretty confusing unless I'm missing something.

This leads back to my previous PPP question about how to moderate the microclimate on a site, which means the same thing as reducing UHI right? : viewtopic.php?f=4&t=52570&start=40 - posted at Wed Mar 21, 2018 7:30 pm.
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Re: Confusion about albedo and urban heat island

Postby anonymous283 » Tue Apr 17, 2018 8:15 am

I've read similar threads on here and found this one answered some of my questions: viewtopic.php?f=5&t=39407&p=135981&hilit=albedo#p135981 but jlu1985 says high conductivity would be best way to reduce uhi while ballast says high albedo in the attached question. No wonder so many people have a problem understanding this. So many contradictions.
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Re: Confusion about albedo and urban heat island

Postby anonymous283 » Tue Apr 17, 2018 8:52 am

I guess I'm gonna stick with high albedo for reducing UHI except for vertical surfaces or vegetation. Low albedo and high conductivity (vegetation) for moderating microclimate. Low albedo and low conductivity for thermal retention in arid places (and for cold?)
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Re: Confusion about albedo and urban heat island

Postby anonymous283 » Tue Apr 17, 2018 3:31 pm

Just when I thought I got it down another ballast question contradicts it - I answered C... I hope there aren't questions like this on the exam or else NCARB needs to release a study guide just for all these conditions since its very hard to research this information.
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Re: Confusion about albedo and urban heat island

Postby fare75 » Wed Apr 18, 2018 10:33 am

anonymous283 wrote:I keep reading that to lower the urban heat island effect (UHI), architects should use green roofs or light color painted roofs. This isn't the same as saying use high albedo materials, which I've also read, because vegetation doesn't have high albedo. I've also read the materials should be high in albedo and have a minimum reflectance of 0.3, but having a highly reflective material will also increase UHI - see question 17 which I answered C because of this confusion but they say D.

So in reality to lower the urban heat island effect the roof should be either a green roof, which is low in albedo and low in conductivity, or light/reflective painted, which is high in albedo and high in conductivity but not too reflective or mirror like because it will heat up adjacent taller buildings... Seems pretty confusing unless I'm missing something.

reminds me of the "Walkie Talkie" in London :lol:
https://www.theguardian.com/commentisfr ... skyscraper
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Re: Confusion about albedo and urban heat island

Postby cma52572 » Wed Apr 18, 2018 9:22 pm

thank you thank you thank you. I was going to post this same question. This is SO damn confusing to me. First I read you want Hi albedo hi reflectivity for heat island effect, but then I see ground surfaces you want low albedo HIGH conductivity like grass. (does grass really have high conductivity? Is this because of the water content?)

Ok, COACH!!! Can you please help with this one???

Sand has low conductivity so grass would be preferable to sand for ground cover (seemingly the conductivity is the main component making grass preferable). (I keep reading sand has low conductivity...does it?)

I'm thinking Desert Burning Man....ground is white and its sand and its hot. so is that high albedo low conductivity?

Obviously a big grassy lawn would be much cooler than a sandy beach or desert.

Now do the same rules apply to ground paving and ground landscaping cover??? Because it seems like if you are doing ground scape like concrete you would want high albedo.

For roof surfaces don't you want high albedo high conductivity? Like a light colored concrete? They are always talking about white roofs for mitigating heat island effect.

And why do they keep saying asphalt has HIGH albedo??? Asphalt is dark vs light concrete. Does dark asphalt have high albedo??? Isnt it absorbing the radiant energy more than reflecting it?

I am so so so confused on this. Id be so grateful if anyone could break this down for me like I'm a second grader. Ive already Googled it a million times and the info keeps contradicting itself.

Thanks
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Re: Confusion about albedo and urban heat island

Postby Coach » Wed Apr 18, 2018 11:50 pm

cma52572 wrote:Ok, COACH!!! Can you please help with this one???


I don't know jack about this topic.
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Re: Confusion about albedo and urban heat island

Postby cma52572 » Thu Apr 19, 2018 12:47 am

thanks Coach. I think I'm just gonna have to give it my best guess on the test via intuition.
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