Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Countering climate change with cool pavements

news.mit.edu

Post reply on HN
Print view View original

71–80 of 80 posts

Re: Countering climate change with cool pavements

#71

Post by marcus_holmes »

axelroze wrote: post #66
ToJans wrote: post #59

Earlier quoted context omitted.

FYI I've brainstormed on an innovation use case once that would allow citizens to use an app to suggest things like planting trees everywhere using AR etc. When discussing with academics, I was flabbergasted to find out that in street canyons, trees can have a negative effect because they reduce air flow. So, apparently it's not as simple as "just plant some trees"...

They can also be a hazard as they can crash much easier during a storm, earthquake or hurricane. Especially if they are dry and not alive any more. IMO solving overheated cities is not just more trees but less population density. Less buildings, less concrete, less asphalt. Less generation of heat and pollution in the first place. Less is more essentially.

Less population density means more transport, though, as the city is so spread out. More cars, more roads, more parking, more infrastructure generally.

Smaller, denser cities are more walkable and have more room for parks.

Small, single-family buildings are incredibly energy-inefficient. Large 5-story apartment blocks are way more efficient.

I moved from Perth, Australia to Berlin, Germany - the difference is astounding. Living in Perth without a car was painful. Living in Berlin without a car is normal. The hot water heating is communal, even in some areas provided for entire city blocks, while every house in Perth has its own reverse-cycle air conditioning setup. High density living is just more efficient per person.

Re: Countering climate change with cool pavements

#72

Post by berikv »

elric wrote: post #57
berikv wrote: post #8

Why wouldn’t you just plant some trees. You don’t need any fancy pavement if it is below a tree.. European cities are filled with trees to cool the streets below them. Obviously, you’d need smaller streets that fit pedestrians and bicycles instead of massive urban highways for trees to be effective.

> European cities are filled with trees Bit of an overly broad generalization. Some European cities, sure. But many are desolate and devoid of trees. Many old cities have very narrow streets, which aren't great for trees. A few shrubs, maybe. Wider strees in Belgian cities are generally devoid of trees, because parking spaces are apparently more important -- and we wouldn't want to impede the view of shops and billbo…

Turns out your right, the story is much more balanced. This page has data on tree cover per capita, and it isn’t Europe on top US on the bottom : https://datadrivenlab.org/urban/issue-profiles/urban-tree-co...

Re: Countering climate change with cool pavements

#73

Post by skocznymroczny »

elric wrote: post #57
berikv wrote: post #8

Why wouldn’t you just plant some trees. You don’t need any fancy pavement if it is below a tree.. European cities are filled with trees to cool the streets below them. Obviously, you’d need smaller streets that fit pedestrians and bicycles instead of massive urban highways for trees to be effective.

> European cities are filled with trees Bit of an overly broad generalization. Some European cities, sure. But many are desolate and devoid of trees. Many old cities have very narrow streets, which aren't great for trees. A few shrubs, maybe. Wider strees in Belgian cities are generally devoid of trees, because parking spaces are apparently more important -- and we wouldn't want to impede the view of shops and billbo…

In Poland, there is a trend (referred to as "betonoza") to replace city squares which had trees with concrete squares devoid of any vegetation. There are several reasons for that. Main reason seems that it's easier to get government/EU money for such 'renovation'. Second reason is that it's considered more prestigious to have a concrete square, because that's what other famous cities have.

Re: Countering climate change with cool pavements

#74

Post by elric »

skocznymroczny wrote: post #73
elric wrote: post #57

Earlier quoted context omitted.

> European cities are filled with trees Bit of an overly broad generalization. Some European cities, sure. But many are desolate and devoid of trees. Many old cities have very narrow streets, which aren't great for trees. A few shrubs, maybe. Wider strees in Belgian cities are generally devoid of trees, because parking spaces are apparently more important -- and we wouldn't want to impede the view of shops and billbo…

In Poland, there is a trend (referred to as "betonoza") to replace city squares which had trees with concrete squares devoid of any vegetation. There are several reasons for that. Main reason seems that it's easier to get government/EU money for such 'renovation'. Second reason is that it's considered more prestigious to have a concrete square, because that's what other famous cities have.

My city recently renovated a huge square, got rid of all the trees and shrubs and plants, and turned the whole thing into a giant concrete wasteland. The mayor was quoted as saying that "not every square needs trees" ... It's mind boggling.

Re: Countering climate change with cool pavements

#75

Post by Nbox9 »

agurk wrote: post #65
na85 wrote: post #58

Earlier quoted context omitted.

>Pavement is a very poor conductor, energy doesn’t move easily through it. Oh dear I'm certainly not proposing running electricity through the pavement itself. I'm suggesting you harvest the heat from the asphalt with e.g. a thermocouple and use that to produce a voltage. >The Delta between ambient air temp and pavement temp low. Perhaps, but not between the pavement and the soil a foot or so underneath.

Conductor can be used to describe more energy types than electricity. In this case they were referring to heat energy. This would be important as if you moved the energy from the hot pavement to a cold source you're cooling the small part where you're taking heat from. As pavement is a poor heat conductor all the energy in the surrounding mass of pavement would flow only very slowly to the patch you were using. This…

Confirming that I was using conductor to mean heat transfer instead of electrical transform.

You could theoretically build a power plant by building a pipe through the pavement (does this reduce the structural integrity of the pavement?) or directly underneath and touching (surface area and high heat transfer would be the desired quality of the pipe). Inside the pipe is a liquid and a set of conditions such that as the liquid heats up next to the pavement it will turn into a gas. You could then capture the extra pressure generated by the gas via a turbine. There would be a condensing section of pipe (typically above the boiling section so gravity can move the cool liquid back down) so it’s a closed system. The primary problems with this setup are:

1. You’d have to change the liquid or change the pressure inside of the tube to adjust for the difference in temperature. Imagine a place like Houston where the pavement might be 150F or it might be 50F. The conditions of the power plant vary.

2. The material cost is stupid high for the amount of power it would generate. It would probably be a better use of materials to capture the heat waste of kitchens boiling water.

3. The labor cost is stupid high for the amount of power it would generate.

4. I’m really concerned about how this will change fundamental goal of pavement (to provide a solid, long living, smooth material for roads and building foundations.). It’s actually possible that reducing the size of the heat fluctuations will make the material more stable. I think it’s just as likely that adding complexity to the system will make the pavement less stable, but if you are going for the 2% of doubt a reduction in maintenance cost would be able to modify the $/Watt function you’d be fighting wind/solar/hydro for.

I’d really like to stress than 2 and 3 will combine to make Wind 10x-1000x cheaper.

Re: Countering climate change with cool pavements

#77

Post by karmelapple »

harmmonica wrote: post #13
clairity wrote: post #3

> “Conversely, by reflecting light — called incident radiation — onto nearby buildings, cool pavements can warm structures up, which can increase AC usage in the summer and lower heating demand in the winter.” this is one of the reasons why i'm an advocate for street trees, and urban foliage in general (cuts down both incident and reflective radiation), and why i'm maddened when i see urban trees cut down or cut back…

from one LA resident to another, amen to that. we were just walking down our street this morning and discussing, for the umpteenth time, whether our neighbors would actually be willing to take care of trees if we went out and bought them and planted them. the problem, as other commenters have pointed out, is that they do require upkeep, but since they're living/breathing things the more hardy ones can really be abuse…

Here’s a very relevant 99% Invisible podcast episode about trees, shade, and plenty about Los Angeles: https://99percentinvisible.org/episode/shade/

Re: Countering climate change with cool pavements

#78

Post by clairity »

Tempest1981 wrote: post #69
clairity wrote: post #56

Earlier quoted context omitted.

i just learned that a huge, grand old tree in my neighborhood is a species of ficus, and indeed, the sidewalk next to it is a buckled, gnarled mess. but i’d rather deal with that problem than harm the tree (it seems like it would be pretty straightforward to build a concrete ramp over the roots, like a mini-bridge).

See if you can get a rubber sidewalk: https://www.npr.org/templates/story/story.php?storyId=561579... (2006)

that's neat, like the temporary flooring used for outdoor 3-on-3 basketball tournaments. a concrete bridge would probably be smoother, more durable, and require less maintenance, but the interlinked rubber segments would be easier to reuse/reposition over time and being semi-permeable is a useful property for other reasons.

Re: Countering climate change with cool pavements

#79

Post by harmmonica »

clairity wrote: post #56
harmmonica wrote: post #44

Earlier quoted context omitted.

like parent commenter said LA actually has a list of acceptable “street trees” that they’ve approved so they don’t kill the sidewalks. some of the most glorious trees you’ll see here are ficus, but those are not on the list because they do blow away sidewalks, streets, utilities. unbelievable shade trees though that require very little water.

i just learned that a huge, grand old tree in my neighborhood is a species of ficus, and indeed, the sidewalk next to it is a buckled, gnarled mess. but i’d rather deal with that problem than harm the tree (it seems like it would be pretty straightforward to build a concrete ramp over the roots, like a mini-bridge).

ah super cool. fully agree that taking a tree like that out would be a travesty. and I'm not insensitive to the infirm or disabled when having to deal with broken sidewalks, but taking those trees out would be a sin when there are other ways to address the root damage like the ramp you suggest or those rubber tile things.

Re: Countering climate change with cool pavements

#80

Post by ClumsyPilot »

godelski wrote: post #12
ClumsyPilot wrote: post #11

Earlier quoted context omitted.

"now have biological contaminants, there's bugs and fungus" Dude, we have rats running around, pigeons nesting and pooping, what biological contaminants?

Just because biological contaminants exist doesn't mean adding more creates more issues. More trees also means more rats and pigeons. What's your argument? That just because we already have a bad thing doesn't mean that a similar bad thing isn't bad? That doesn't make much sense and is a pretty lazy argument.

Either way, rats and pigeons feed on garbage, they dont eat oak trees.

We need to have less takeaway left on the street and garbage bins that are cleaned up on time.

Post reply on HN