Cool Roofs – Melvin Pomerantz


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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5 comments on “Cool Roofs – Melvin Pomerantz

  1. […] Zero Resource Use less. Use data. « Cool Roofs – Melvin Pomerantz […]

  2. […] 1 is posted here. Part 2 is posted here. Part 4 will be posted […]

  3. […] 1 is posted here. Part 2 is posted here. Part 3 is posted […]

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