 ThinkTek Hawaii, Code Green. This is a Monday, January 5th, I believe New Year 2021. Got a very, very hot topic for us today, namely cool roofs and cool walls. And my guess is maybe, I think I'm prejudice, maybe the world's leading expert on reflective surfaces like walls and roofs and their effect on the immediate temperature surrounding and perhaps we are going to see if he can give us a really a worldwide perspective on cool reflective surfaces. He is Dr. Ronan Levinson, staff scientist with Lawrence Berkeley Laboratories and leader of the Heat Island group. Welcome, welcome to you, Dr. So thank you, Howard. Have you. Yeah. Great to be here. So Ronan, why don't you start with a little background about what the Heat Island study is all about? I don't I think maybe Dr. Akbari started it and you were his understudy and then you took over or were you co-founders with Dr. Akbari? Well, Dr. Hashem Akbari started the Heat Island group at Lawrence Berkeley National Laboratory about three decades ago. But the study of urban heat islands dates back to the 19th century and it's been well documented all the way around the world. We'll have a slide coming up to graphically illustrate that after a while. And you want to give us the background about why cities become hotter than the countryside? Absolutely. Actually, this would be a good time to throw up the second slide. Okay. All right. Here's a picture of what we call the summer urban heat island and in this cartoon you can see that the air temperature near the ground in the downtown area is about two to three degrees Celsius higher than the air temperature in the far country side. And you might ask, well, why is it hotter in our cities than outside our cities? And if we go to the next slide, we can see part of the answer. One of the reasons is that we have many dark surfaces. This is an aerial picture of Sacramento, California. And it just so happens that in Sacramento, about 60% of the surface is manmade, either pavement or roofs. And less than a third of it is vegetation, even though Sacramento is a pretty green city. And if you have dark, dry surfaces, they absorb a lot of sunlight, they get warm. And in turn, they heat the air. If you had surfaces that were more reflective to sunlight, which could be light colored surfaces or certain sorts of specialty surfaces, or if you had wetter surfaces such as trees or lawns that evaporate water, you have the potential to absorb less sunlight and to dissipate more of the absorbed heat by evaporating water. Trees are good for shade, too. Very definitely. A lot more comfortable. And I can testify Sacramento was a nice green, green city. There's something that struck me when I was there was all the trees all over the place. So a lot of cities that you surveyed could have a more extreme difference. That's true. Yeah. And just as a very local instance, I'm very blessed to live in the back of Manoa Valley, which is, and I get over a hundred inches of rain a year. And generally, the temperature at my house is about seven degrees cooler than it is downtown, just three miles away. And we've noticed the same thing. We performed what are called transects in Los Angeles, which just means that you travel from point to point, either with a car or sometimes I've seen in Europe on a bicycle, and you measure the air temperature as you move through the city. And the measured air temperature in some of the places like parks that had a lot more vegetation and a lot less manmade surface, fewer pavements, fewer roofs, they were several degrees Celsius cooler than other parts of LA. And in fact, Howard, I believe that a survey like that was done in Hawaii. Could you tell us a little bit about that? Ironically, it's done or headed by a good friend of mine who works for the Office of Resiliency in the city of Honolulu. And I work with them all the time on all kinds of climate related matters. And I didn't even know about this study. You had to point it out to me. But they did a point by point by point study of several neighborhoods on Oahu. And for one thing, they recorded record high temperatures. I was born and raised here. And if the temperature ever got up in an August to 90 degrees, that would make the headlines. They recorded a temperature. I think I know the neighborhood of 95 degrees, which is astoundingly hot for us. So that study will be out in another month or so. And, Dr, I'm sure that we want to share that study with you. It'll definitely add to your body of knowledge there. Yeah. Especially, I gather you travel here pretty frequently. Well, not as frequent as I'd like, but I was happy enough to spend a little vacation time on Oahu and on Maui about a year and a half ago. Mm-hmm. Yeah. So why don't we get into all of the slides? Well, let's see. Do you have anything first worldwide to say about the heat island effect? Because a lot of the world's population lives in climates that are much hotter than ours, ours being either Hawaii or most of the mainland. Yeah. Well, the big picture is that first the climate as a whole is warming, and our cities are getting hotter too. And in some parts of the world, they're taking aggressive steps to try to mitigate the problem. For example, Japan has been a leader in countermeasures to urban heat islands. And the strategies that are applied around the world are pretty similar. One adds shade trees, makes roofs more reflective, often white, though not always white. Some places have been looking at campaigns to make the pavements more reflective. If you live in a climate that has rain in summer, which doesn't work for California, but does work for many other places, some have looked at using porous pavements that let the water sink in during a rainstorm and then slowly evaporate for several days after providing cooling. Is America leading the way in this research? No, studies on urban heat island mitigation are done around the world. And just to give you an example of how broad it is, there's a conference that takes place every year or two, looking at countermeasures to urban heat islands. And when it was held in Singapore back in 2018 or so, maybe 2016, there was a huge attendance from Asia, many from Japan, many from China, because everyone is trying to make their city cooler in summer. It's not restricted to Asia. I would say the Europeans were probably the first to notice this. I believe some of the earliest heat island effects were recorded in places like London. It's been a strong area of interest in the United States for, I would say, the last 30, 40 years. And in part it's because some of the measures that can be used to cool the air in the city also provide a direct cooling benefit to the homes. So if you were to replace your dark hot roof with a white cooler roof, yes, you'll help lower the air temperature in the city. But even more importantly, from your perspective, you get a cooler home or use less air conditioning if your home is air conditioned. So I think that's driven a lot of the popularity of heat island countermeasures, the direct benefit that people receive to their own residents. Absolutely. Where in Honolulu we're seeing, just by substituting a reflective coating on the roof for what had been a dark, absorptive coating, the interior temperature drops a minimum of eight degrees. And I've seen the recordings of dropping by 12 degrees. That's from discomfort to comfort. Absolutely. Just on a personal note, something I've been working on with the US or the State Department of Education is to apply cool roofs to all the classroom buildings. And that can be very important because if school building is over warm, I think the students tend to fall asleep. And yeah, there are a lot of instances of sweating, just sweating so badly that the paper they were trying to write on became wet makes writing rather difficult. That's a big thrust of some of the research now. I was looking at how cool surfaces, along with other kinds of passive measures for reducing unwanted heat in buildings, can make buildings more comfortable and during a heat wave safer. And this is a really big deal because we've relied on air conditioning to keep our buildings cool and comfortable when it gets very hot. And don't get me wrong, I enjoy air conditioning, especially on a very humid day. But here in California, on the hottest days of the summer, the grid has trouble keeping up and we have rolling blackouts. So you might own an air conditioner, but not be able to run it. In fact, we also, thanks to wildfires, now have to deal with public safety power shutoffs where the grid is turned off preemptively to reduce the risk of a transmission line starting a wildfire. And these public safety power shutoffs often coincide with really hot weather. So anything that we can do through a passive measure that doesn't rely on grid power is, I think, helpful for making people more comfortable and safer. Now, what we've been doing, we, being the Hawaii Energy Office, is emphasizing number one cool rooms combined with ceiling fans. I'm thinking in particular of school buildings because they're neither heated nor cool here in Hawaii. And there is a big push, especially by parents, the air condition, all of the every classroom in the state. And that is tens of thousands of classrooms. And there is just no way we can number one afford the air conditioner, the installation, and number two, if they were in, we couldn't afford the electricity bills anyway. So ceiling fans use maybe one 20th as much energy as there's an AC to cool a comfortable space. So that's something we've been certainly pushing and working on. I'm glad you brought that up because my colleagues at the University of California, just down the hill from Berkeley Lab, we've been working with them on a project looking at a number of passive cooling measures. One of them happens to be cool surfaces like reflective roofs and reflective walls. But another is ceiling fans. And what they found is if you turn on a ceiling fan, you can increase the temperature at which people will stay comfortable by about two degrees Celsius. And this makes a big difference in reducing the number of hours each summer when people in a building aren't comfortably warm. It's what you expect from your everyday experience. If it's too hot, you turn on a fan. If it's too hot, you stand in the shade. A lot of the things that we do for heat island countermeasures and for saving energy are really pretty obvious if you think about them. It's just that we have to do them. And it's nice when we can put the scientific data behind that also. Exactly. The politicians, they always, when you propose anything like this, they always want to know what's the cost and what's the benefit with a good reason. This is taxpayer's money they're dealing with. That's a very valid question. And plus Howard, as you know very well, when one of the strongest ways to make our buildings more comfortable is to have better energy standards for buildings. But if we're going to propose an improvement to building energy standards, it has to be justified with science and engineering. My colleagues and I are working on exactly that very thing. Even as we speak here, we've just adopted a new standard. Now we've got to put some good numbers behind it. So should we talk a little bit about some of the more recent advances like cool walls? Absolutely. I believe you have a slide show all prepped up for us. We've already seen some of the slides, but we begin with that. I've got a few pictures just to help tell the story. So why don't we go to the next slide. Now, many people are probably familiar with the idea of cool roof and you can get cool versions of most, if not all, roofing products. Your clay tiles that people use, these are often cool. If it's a commercial building that has a flat roof, you can get a white version of a single-ply membrane at no extra cost when you're choosing your roofing product. And there are even cool-ish asphalt shingles. And asphalt shingles go on about 80% of residential roofs. Cool roofs are pretty well understood solution and they're very helpful for cooling the building, for cooling the city, and cooling the planet. But it turns out that cool walls are just as helpful. Why don't we take a look at the next slide. If I have a cool exterior wall that doesn't mean that the wall is bright white, it just means that I'm looking at a wall that could be an off-white or a dull white reflecting about 60% of the sunlight that it receives. And that's nice improvement over a conventional wall which might reflect 25% of sunlight. Here's a picture of a building just down the street for me that has a combination of different color walls, some lighter than others. And if you make the wall cooler, you can reduce the need for air conditioning, which will save you energy. It will save carbon and save money. Let's look at the next slide. Going back to the idea of the science that's very helpful. So we looked at the effect over the course of the entire year of cool walls on the energy and carbon and energy cost expenditures over the course of the year, looking at cooling in the summer, heating in the winter, fans all year round. And what we found is that in the southern half of the mainland United States, cool walls are a clear win. And it's also true for Hawaii. And if we look at the next slide, we also found that cool walls would have an effect on reducing the urban heat island comparable to those from cool roofs. And you might wonder about why would a cool wall be as effective as a cool roof? For example, on average, walls get about half as much sunlight per unit area as roofs do. So since they get less sunlight, wouldn't they be less effective as a solution for saving energy? Well, the first assumption is right, but what balances it is that walls also have only about half as much insulation as do roofs. It's just harder to insulate a wall cavity to thinner and it's more awkward. So the less sunlight and less insulation balance out, so you get energy savings from cool walls that are similar to those from cool roofs. Then if we look quickly again at that slide, here we go, with the urban heat island effect, yes, the walls get less sunlight, but the walls are closer to the ground, they're closer to people. I mean, on average, the height of the wall is half that of the roof. And there are some other effects in play too. But we found that the use of cool walls in LA as a heat island mitigation strategy was about 85% as effective as use of cool roofs. So it's a win for cooling the outside air as well. Then if we look at our next slide, a nice thing is that cool walls are not an exotic option. You can go to your paint store and buy cool exterior wall paints today. You just have to look for the lighter colors. And nothing exceptionally bright, these are colors that you might see on walls that you pass every day. And there are also some options in darker colors, things that aren't white, which will do a good job as well staying cool. Because while they don't reflect as much of the light that you can see, they do strongly reflect the invisible half of sunlight. So in this diagram, I'm showing some different mostly exterior wall paints. And I've divided up the wall technologies into two tiers. The lower tier cool walls, which is a designation I just made up, would reflect between 40% and 60% of sunlight. And a higher tier cool wall is something that reflects at least 60% of sunlight. These aren't official yet, but I'm hoping that as cool walls become part or increasingly part of our standards and our utility programs, we'll have some definitions like that to help people make choices. So that's a little bit of an introduction to cool walls. And I believe maybe it wasn't in these slides, but other literature that I've seen compares the need to clean the walls versus need to clean the roofs. And I think it's virtually nil. Exactly. If you go to our next slide, what a terrific setup. Here we look at exactly that question. So people who work with cool roofs know that especially for a flat white roof, in many places the roof will get dirty over time because things fall out of the air and because you get growth on the roof. Now, these can be addressed when some of the white roofing materials are made. There are biosides that could be included. And they also tried to ensure that the softer white products don't leach so much of the plastic out to the surface, which is very nutritious for microorganisms. But it is well understood that white roofs will become less reflective over time. And when we model all of the benefits from white roofs, we assume they get soiled on day one. So we're kind of conservative that way. But if we were to take another look at this slide, what we decided to do was check with cool wall products, how well would they stay clean and reflective? And we exposed them in a place that was hot and dry in Arizona, a place that was hot and wet in Florida, and a place that was more temperate but had higher pollution in Ohio. And the end result is that after three years, which is the period that we used for testing these sorts of products, the average reflectance loss was only two percentage points. Whereas for a white roof, it might be something like 20 percentage points. And this agrees with common sense. A roof is horizontal or close to horizontal. So when you get puddles on it and the water evaporates, you get dirt left behind. But walls are vertical. And so the water runs down the wall. I always say if you have a puddle on your wall, we have much bigger problems. Yes. Just maybe the terrific example of that is in Guam. I spent a good deal of time there. And they are a hot humid climate. Typically gets up around 90 degrees in the day. And it feels like about 90% relative humidity. And the typical residential architecture calls for a flat roof. And there's lots of rain. Rain puddles there. Rain or the water begins to evaporate. But it's still nice and moist. This is a tropical climate. What happens to that nice moisture? It breeds all kinds of microorganisms. And then the sun cut with your start out green. And then the sun comes down and bakes it. And you end up with a black, largely black roof. Exactly. So in our latest tropical building code, we call for at least a gentle slope on the roof. No such thing as flat roofs anymore. That's a very good move. Having some pitch to shed water is key. Another key thing is that if you have a roof with insulation that goes above the roof deck, and then some sort of a surfacing material above it. So maybe you've got some board insulation and there's a membrane on top of the board insulation. You want to make sure that the membrane stays flat and straight. If you have depressions in the membrane, that's where you get puddles. So some of it is just construction practice. And others is be kind to your roof. Don't walk on it and put divots in it. Yeah. Yeah. And something I wanted to... Well, we didn't talk about emittance. This is the fact that the surface, be it a wall or a roof, will absorb some of the radiant heat, the solar heat. But then a lot of that gets re-emitted back to the atmosphere. Can you talk a little bit about that? And how important that is when you're looking at reading roofs or material. Yeah. So Howard, you're exactly right. Some of the sunlight will get absorbed and you want to make sure that the roof can reject as much of that absorbed sunlight as possible, preferably up instead of down, because what goes down heats the building. So to go up, you have two choices. There's convection where the air blows over the roof and the heat is carried away into the air. That's good for your building. It's not great for the city. And the other option is every surface is radiating heat as a function of its temperature. And how efficiently it radiates heat compared to a perfect emitter, we call that its thermal emittance. And most of your surfaces for the building, unless they're metal, are about 90% efficient in radiating that unwanted heat away to the sky if it's a roof. There are, however, some materials, not many, but mostly bare metals that are not good emitters. And those will get hot in the sun compared to something that is equally reflective, but is a good emitter. And the way that I used to explain this to people when you could still find metal bumpers on cars is if you have a white car with a shiny metal bumper, then the white car shell, the painted metal and bare metal bumper, each reflecting about 60% of the sunlight. But if you were to touch that bare metal bumper, it gets much hotter in the sun than the white shell. And that's because bare metals are poor emitters of radiation. The big story is the reflectance. If you have something that's highly reflective, that's most of the battle. You do, however, want to make sure that what you're not doing is putting something like bare aluminum as your surface of the building, because that's not going to be as cool as you would hope for. But a nice thing is you can figure this out for yourself just with your fingers. Well, be careful, don't burn yourself. But this is not rocket science. Yeah. And are you, by any chance, as I am a fan of TIO2 titanium dioxide added to reflective coatings? Well, most reflective coatings get their reflectance from titanium dioxide, rutile. That's the almost universal white. It's relatively inexpensive. It's non-toxic. And it's a very strong white. So if you have anything in your daily life that is white other than paper and ceramic, it's probably white because there's TIO2 making it so. So a white membrane roof became white because TIO2 was added to the plastic. A white paint is white almost always because TIO2 is incorporated in the paint. So that's your go-to light color pigment. And sometimes it gets mixed with other colors in order to make pastels. And as I understand it, when we're talking about emittance, when the radiant heat penetrates into a coating, say a roof coating, it's the TIO2 molecules in there that cause the radiant heat penetrating to reflect back out to the atmosphere. Is that a good explanation of how TIO2 works? Incidentally, a sunscreen full of TIO2 also. It is, although it's a little bit different. TIO2 comes in different particle sizes. The particle sizes that are good scatterers for sunlight that cause that reflection to happen. Those are usually bigger TIO2 particles. But you're right. When sunlight enters a white paint, the paint itself is pretty transparent. Sorry, the paint vehicle like the acrylic is pretty transparent. But then it strikes a TIO2 particle and it changes direction. So you get, we call back scattering and this makes it reflective. The TIO2 that's in a sunblock, those are very small TIO2 particles. And they're present not because they scatter sunlight, but because TIO2 in any size is a really good UV absorber. So the function of the really small TIO2 particles in a sunblock that is, you know, once you rub it in clear is to absorb the UV so that the UV isn't absorbed by your skin. And those of us who live in a climate like Hawaii with fair skin can attest firsthand to the importance and the effect of UV light. If you could see my arm clearly, the arm of many colors. Because there you go. The sunburn that it's endured. And finally, we've only got a couple of minutes or maybe a minute. Cost effectiveness. As I see it, applying say a coating to either a roof, dark colored roof or to a wall, it has virtually the same expense as does a darker color. It does. So there usually isn't a cost premium for choice of color. But what I recommend is that if you have a roof, unless the roof is about to leak, don't think of coating your existing roof. I mean, you could do that. But your most economical choice is to choose a lighter colored replacement product when your roof comes to the end of its life. And most roofs get replaced about every 20 years, which means that in 20 years, we could turn over all the roofs and make them cool. You might do the same thing with your walls when it's time to repaint your outside wall for any reason. Just think of going to a lighter, more reflective color. Makes it a no cost solution for cooling your building. Precisely. One of the provisions in Hawaii's energy codes residential, well no commercial buildings also, is if you the energy code requires exterior insulation, insulation that's on the outside of the wall of the roof, and instead of that plus the interior insulation, instead of that exterior insulation, we say just get a reflective coating on there. And our studies have shown that the reflective coating is has virtually the same cooling effects as does the insulation, but at a much, much, much greater cost effectiveness. Exactly. Yeah. So I think that's we're operating our code again and I think that's going to be a pretty easy sell for the building industry. Exactly. Very inexpensive. Plus it doesn't trap the heat that might be generated inside the building because you have heat that's produced in the building when sunlight comes through windows or because you have people or each person's like 100 watt light bulb. And you have all sorts of equipment and all of those generate heat. And when you add insulation to the building, you help keep the external heat out, but you also trap the internal heat within. Precisely. And we, as an energy codes guy, we've added such provisions to the national code and we will continue to do so. And we've got just about time to say Aloha, maybe we can bring your, your introductory slide up again for for Dr. Levinson. Here it is. People, if you have further questions, you can, you know how to contact me, but there's Dr. Levinson's contact information. And both of us are pretty gosh darned passionate about this as a means of reversing global warming and promoting global cooling. So on that cheery note, thank you so much Dr. Levinson. It's been a huge, huge, huge honor having you as our guest. And bid you fond Aloha. And one of these days will actually get together physically again to have more cool wall meetings. So Aloha to everyone. Thank you for attending and send me any questions that you have. Thank you very much for the chance to be with you. Better new year to all.