Tag Archives: cool cities

Cool Planet – Art Rosenfeld

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In Berkeley, we are fortunate to have such events as Science at the Theater, where Lawrence Berkeley National Lab researchers give talks on their work at the Berkeley Repertory Theatre. The lectures are free and get a pretty sizeable audience.

On Monday, October 11, I was in the audience as researchers from Lawrence Berkeley National Laboratory (and the beloved Art Rosenfeld) gave a presentation titled “Cool Roofs, Cool Cities.” The post below consists of Part 4 of my record of the presentation – Art Rosenfeld gives an overview of how cool roofs and cool cities can leader to a cool planet. All portions are included in chronological order.

An ellipsis (…) indicates that I was not able to capture the words or thoughts skipped. The presentation is transcribed as accurately as possible – punctuation choices are mine. I also added any images.

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I’m going to bring us into modern times and the question of global warming … Two thousand years ago, people tried to figure out how to keep houses cool, then a couple hundred years ago, we tried to figure out how to keep the cities cool, and now we’re trying to figure out how to keep the planet cool.

Taking a trip around the world … [looking at photos].

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Image credit: Wikimedia Commons

In Bermuda, they use sloped white roofs to collect water.

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Image credit: Wikimedia Commons

In Santorini, Greece, even the sides of the buildings are white.

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Image credit: Wikimedia Commons

In Hyderabad, people like to sleep on the roof to be cool at night.

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Here’s a Wal-Mart store in Northern California with white roof – they’ve done 4500 of their stores, and have 1500 to go.

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Here’s an overview of UC Davis … Since 2005, the CEC Title 24 has required that if a roof is flat, cool roofs are required …

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Image credit: Wikimedia Commons

Here’s the University of Tucson in the middle …  residential areas nearby also have white roofs … …

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Here’s Washington, DC (federal) … The House and Senate office buildings do not have white roofs.

The most fun was this – this is the Pentagon. I went to a hilarious meeting – I got invited to give a talk at the Pentagon. There were innumerable generals and such around …

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Now what about the Earth? … Part of what keeps the earth cool is ice and snow, which is decreasing in size … It would be nice to add some more white … …

Atmospheric climatologists have been aware of this issue for years, and back in the 1980s, Jim Hansen published a paper wondering whether cooling cities would make a difference – and he got an answer of about a 1/10th of a degree … But we weren’t so worried in those days … But we asked, maybe there’s a better way to sell this? … Look, carbon dioxide reflects heat, that’s called a positive radiation forcing onto the ground. And white roofs reflect heat … Carbon dioxide has a price … So we’ve got to do it per unit … 1000 square feet, winds up being about 10 tons of carbon. Suppose we multiply this by about 3 billion, since there are about 3 billion units of roof in cities, then avoid the heating effect of 25 billion tons of carbon dioxide…over the life of the roof. So let’s say 1 billion tons a year for 25 years … This winds up being 300 million cars off the road for 20 years … There are only about 600 million cars right now …

So what to do now? First, get other states to follow California… Arizona and Florida and Georgia have followed suit with cool roofs … The problem is a lot of the rest of the country, the hot part … the United States relies  on model building codes, and states are not required to adopt them. They can make them stronger and adopt them, but they are not required to adopt them. Texas doesn’t have any, the cities there have taken the lead …  DOE is going white, the Marine Corps is going white …

We’re going to launch a private club called 100 Cool Cities, with some DOE help, where were’ going to approach the 100 largest cities, which gets us  to a population of 200 million, where we’ll talk to them about cool roofs and try to get it into the building code … This will involve the Sierra Club, the Clinton Global Initiative, USGBC, ICLEI, the Energy Foundation, the Alliance for Climate Protection, ACEEE, and others …

Steve Chu will offer assistance to the first few countries to sign up to address this issue … …

So things are moving along nicely, and thank you very much.

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Part 1 is posted here. Part 2 is posted here. Part 3 is posted here.

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Cool Pavements – Melvin Pomerantz

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by energy • Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

In Berkeley, we are fortunate to have such events as Science at the Theater, where Lawrence Berkeley National Lab researchers give talks on their work at the Berkeley Repertory Theatre. The lectures are free and get a pretty sizeable audience.

On Monday, October 11, I was in the audience as researchers from Lawrence Berkeley National Laboratory (and the beloved Art Rosenfeld) gave a presentation titled “Cool Roofs, Cool Cities.” The post below consists of Part 3 of my record of the presentation – Melvin Pomerantz gives an overview of cool pavements. All portions are included in chronological order.

An ellipsis (…) indicates that I was not able to capture the words or thoughts skipped. The presentation is transcribed as accurately as possible – punctuation choices are mine. I also added any images.

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Now we’re talking about cool pavements … because they are a significant fraction of a city … including the streets, parking lots, driveways, and sidewalks.

We need to understands that they are a composite material … they are aggregate, an array rocks of different sizes … We then have to hold them together. So we have to glue the rocks and sand together by coating each rock with a  binder of some sort. For “asphalt”, the binder is asphalt, which is a petroleum product …  We can also bind the rocks together with cement, which is a mineral product, and we call that concrete … The key thing is that because you’re coating the aggregate, you mostly see the color of the binding … Our target is the binder.

Of the third of the city that is covered with pavements of various kinds, 50% is streets, 40% are exposed parking, and about 10% are sidewalks … Because it covers about 90% of the paved city streets, our target is the asphalt concrete.

Image credit: Wikimedia Commons

Start with fresh asphalt concrete … which is very black and has a solar reflectance of about 5%. As it ages, sunlight breaks it downs … Typically, its solar reflectance goes up to about 15% … The question is can we do any better … If you use a light-colored aggregate, it will show as the binder wears off … can use seashells, or porcelain … For old pavement, which required resurfacing periodically … we can put on a layer of asphalt emulsion, and put light-colored aggregate on top. That is called a “chip seal” … One issue is that aggregate is heavy, so it’s expensive to ship. So we want to use rock that’s nearby, and it may not be white … If the road stay cool, it doesn’t deform as much …

An example is from San Jose … They happen to have a quarry nearby that has white rock, and they’ve used a chip seal …

The other type of road, a little less common, is cement concrete … Fresh cement has a solar reflectance of about 35% … as it ages, it gets darker and reflectance drops to about 20% … The fine aggregate tends to float to the top … If you have light-colored fine aggregate, you can get an initial solar reflectance of about 40% …

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Part 1 is posted here. Part 2 is posted here. Part 4 is posted here.

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Cool Roofs – Melvin Pomerantz

5
by energy • Tags: , , , , , , , , , , , , , , , , , , ,

In Berkeley, we are fortunate to have such events as Science at the Theater, where Lawrence Berkeley National Lab researchers give talks on their work at the Berkeley Repertory Theatre. The lectures are free and get a pretty sizeable audience.

On Monday, October 11, I was in the audience as researchers from Lawrence Berkeley National Laboratory (and the beloved Art Rosenfeld) gave a presentation titled “Cool Roofs, Cool Cities.” The post below consists of Part 1 of my record of the presentation – Melvin Pomerantz gives an introduction to the heat island effect and cool roofs. All portions are included in chronological order.

An ellipsis (…) indicates that I was not able to capture the words or thoughts skipped. The presentation is transcribed as accurately as possible – punctuation choices are mine. I also added any images.

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What I’m going to talk about is a very familiar experience to a lot of you – when you go into the center of a city, it’s a lot warmer … That effect, namely the temperature … tends to be anywhere from 5-7 deg F warmer in the city than outside the city …

Image Credit: Wikimedia Commons

The heat has not only an effect of causing discomfort, but has economic effects, too … Looking at some SMUD data … went up to about 107 degrees that day … As the day goes on, it gets hotter and hotter, and the demand for electricity gets higher and higher … finally it cools down and people turn off their air conditioners a little bit. … To get this power, you need about 5.5 power plants, but the power used in January is much less, so the power company has to have in reserve all these power plants. So there is capital involved in having these in reserve … And the ones in reserve are generally the oldest, most polluting plants … so it’s an unfortunate effect …

Another effect that goes on is that when things are very hot, there are actually deaths … Chicago in 1995, there were 739 deaths attributed to the heat wave – almost all occurred on the top floor of buildings with black roofs …

So what can we do about it? … How is the air heated in the first place? The sun does not heat the air directly … Sunlight travels very well through the atmosphere … There are opaque surfaces – the light comes in from the sun and strikes a surface … some stays in the surface and heats the surface, then the air comes along and touches the surface and heats up … The surface is acting as a converter, so if we can modify the surface, we can get a handle on it … If you have a building underneath a roof, that heat travels into the building, then you have to run on the air conditioning. …  Also pavements suffer if it gets too hot … the pavement needs to handle the deterioration that the heat causes … …

One way to look at this is to look at the solar reflectance … If you have no light coming out, it’s black … if it all comes out, it’s very bright. If the light is not all caught by the material, it has a higher solar reflectance, and it’s cooler … If you decrease the solar reflectance, the temperature can rise 80-90 degrees F over the ambient air – and you don’t want that … …

There’s another feature, which is that once the surface is warm, it radiates … there are gases in the air which absorb this thermal radiation, and it’s like a blanket. It’s blocked by the gases in the atmosphere… this is the atmospheric greenhouse effect. If we can affect the light from sticking in the surfaces, we reduces the greenhouse effect, too, and keep the planet a bit cooler …

Image credit: Wikimedia Commons

What can we make cooler? … Looking again at Sacramento … about 39% of what we could see from the sky was pavements … … … If we reflect sunlight, it mostly passes back out of the atmosphere without heating the air…

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Part 2 is posted here. Part 3 is posted here. Part 4 is posted here.

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