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265 Comments
- JHW539, on 07/14/2009, -2/+48"Sure it's white, but it's plastic. The material alone is a conductor and likely to attract heat in the summer. "
NO. Just... NO. There has been a massive amount of research into reflective roofs. The fact the roof is plastic is irrelevant except as it impacts emissivity. I design and size cooling systems for commercial and industrial buildings, and the emissivity (correlated to color) of the roof directly impacts the heat gain calculations. Of course, you have to account for fouling (absortance goes up with the grime), but your comment is utterly divorced from the empirical data and basic physics.
And a silver roof is not always better - in fact bare metal is worse than metal painted black (unless it is a spectrally selective black coating as used in solar hot water collectors sometimes). But a silver "cool roof" formulation can be quite good. It's not about the color, it's the emissivity which is loosely correlated to color.
Let's design on actual data, not what sounds good to Joe Blow. I won't tell you the best way to manage a crew to make deadline, if you don't tell me that physics and a hundred years of empirical experimentation is wrong. Deal? - Angostura, on 07/14/2009, -6/+33Sorry old chum, but I don't think your anecdotage is stood up by the science. The fact is that all other things being equal, white surfaces reflect more sunlight than black and the surface will be cooler. It may only be a degree or two (too little difference to detect with the hand) but on a large scale that difference really ... makes a difference.
- DankBuddz, on 07/14/2009, -3/+27Actually, scientific research has showed that reflective surfaces divert electromagnetic rays back into space without being absorbed by the earth. This is called the Albedo effect, and this is what the proposal is supposed to simulate.
You can become less dumb by learning about it here:
http://en.wikipedia.org/wiki/Albedo
- glitchbit, on 07/14/2009, -3/+26So Michael Jackson was on to something after all.
- WasabiBomb, on 07/14/2009, -1/+24You clearly don't live in the south. Try opening a window when it's 100 degrees out with 100% humidity.
- Angostura, on 07/14/2009, -1/+21Ummm, no. The idea is that a significant proportion of the energy actually radiates out into space without heating the atmosphere. Chu does have a basic grasp of physics, I believe.
- SoCalDissident, on 07/14/2009, -1/+20Plastic is a good conductor? Last I checked, PVC was a great insulator, aka the opposite of a conductor
- inactive, on 07/14/2009, -3/+22The idea for roofs is fine, but remember that it snows in most of the country. White roads would be a disaster. It's hard enough to follow the blacktop during a storm.
- upnortherik, on 07/14/2009, -5/+23Stick to roofing, you don't know ***** about science.
- WasabiBomb, on 07/14/2009, -1/+18That's why I'll never live anywhere where I have to deal with an HOA. It's my house, let me do with it what I want.
- WasabiBomb, on 07/14/2009, -0/+16Next thing you know, they'll be telling you not to drink and drive, and that you have to slow down in school zones. Just another example of The Man keepin' a brother down.
- Angostura, on 07/14/2009, -0/+14I think (hope) that PxCxG was having a little joke.
- pathouston22, on 07/14/2009, -5/+19Most roofs with shingles are dark gray down here in the south - including mine. I laser thermometered it the other day, it was about 156 degrees - and it was a cloudy day. Ugh. Unfortently, putting a white roof on is not a viable option. Why? HOA nazis.
- inactive, on 07/14/2009, -1/+15Somewhere a hell of a lot nicer than where I live?
- Quintios, on 07/14/2009, -2/+16Sorry OP, but you couldn't be more incorrect in your statements.
White REFLECTS heat. Dark ABSORBS heat. This is a scientific proven fact. Your years spent on a hot roof prove that: 1. The roof is hot, and 2. It is radiating heat. Did you ever take temperature measurements on the underside of a white roof? If you had, you would see that the heat is being reflected, not absorbed. This is why, standing on a white roof vs. a dark roof, the temperature probably feels the same. But have you ever spent time on a mountain on a snowy day? Why is it you can go skiing sometimes without a jacket? Heat is being reflected off the snow and keeps you warmer. But the snow is still there and isn't melting. The radiation is being REFLECTED.
Standing on a white roof will be just as hot as standing on a dark roof. The black roof is radiating the heat it absorbed, and the white roof is REFLECTING the heat it DID NOT absorb.
My problem is that PVC degrades in sunlight. Over time it will yellow and crack.
Plastic is a heat conductor? No no no no no. It is an INSULATOR (thermally speaking, not electrically). Check thermal conductivities of that material vs. asphalt, metal, and fiberglass. You'll see where it falls in the range of capabilities and what it actually does. You even mention a vapor barrier as a "key ingredient to [thermal] efficiency". You contradict yourself as the typical vapor barrier is made out of... wait for it.. PLASTIC.
You also talk about efficiencies in thermal resistance in a roof. The article isn't talking about how to keep a building cool, it's talking about reflecting radiation back into space. Granted, keeping a building cool with materials will reduce your cooling bill and will therefore also reduce its carbon footprint. - qiaohua, on 07/13/2009, -2/+16That seems easy enough, as long as I don't have to get off my couch.
- OLTP, on 07/14/2009, -1/+14White roofs is not a novel idea. Thermochromic roofs are a novel idea. To have a white roof when it's hot out, and a dark roof when it's cold out, then you'd save on both A/C and heating!
- DrDash, on 07/14/2009, -2/+15I live in Arizona, and color does matter. Painting a roof white (we use a product called cool-coat) does make a difference. Just like the color of your car (same materials) make a difference. Is it huge, no. Is it expensive or hard, no but it is surprising how many businesses and such do not take advantage.
- dsmx, on 07/14/2009, -1/+14Air conditioning only works when you don't open any windows. So most buildings that were designed from the beginning to be air conditioned won't have windows you can open easily.
- InetRoadkill, on 07/14/2009, -0/+13My house (in S. Texas) was originally stained a dark brown and had a brown asphalt shingle roof. I painted the house a light gray and replaced the roof with white shingles. My utility bill during the summer dropped $50 to $100 a month. It does make a difference.
- Elset, on 07/14/2009, -0/+13Opening a window on a 90 degree humid day does not cool down your house
- drmephesto, on 07/14/2009, -5/+17It's truly sad to see how many retards posts comments on digg. Stupid, retarded moronic f*ckwits, oozing out of every nook and cranny.
Lets go back to basics, for all the losers who didn't make it out of junior high, ok?
Electromagnetic radiation from the sun can be absorbed by materials; the ability of a material to absorb a certain spectrum of radiation is defined but its molecular electronic structure. No retards, this is nothing to do with heat conductivity. It is to do with the excitation of an electron in a molecules molecular orbital to a higher energy molecular orbital and its subsequent conversion of this energy to molecular vibrations during its transition back to its ground state.
Materials that are unable to absorb incoming photon and convert them to heat are brighter, white for example. The white you see is the energy the would have become heat, had it not bounced off. If an object is black, it has absorbed all the energy in the visible spectrum. Thats why there is discussion of pumped seawater into the atmosphere to generate clouds. Clouds are white, and would reflect heat back into space.
Or not. Maybe you guys should elect nick2525, the roofing contractor, to government office. His deep understanding of the physics of polymer light absorption clearly demonstrates the he can solve the big issues. - DankBuddz, on 07/14/2009, -0/+12http://coolwilliamstown.org/images/web_greenhouse_ ...
Us "hippies" enjoy learning about subjects before we criticize others.
Anyone with a high school science education who understands the greenhouse affect realizes that solar radiation is shortwave, and can be reflected back into space through there atmosphere. However, once the radiation is absorbed into the earth, it is then converted into longwave radiation, and this is when it can be trapped in the atmosphere.
I don't think conspiracy theorist websites cover such subjects as "science", but they should really look into it. - DankBuddz, on 07/14/2009, -0/+12Kind of weird how multiple different forcing could all contribute to the same issue.
- DankBuddz, on 07/14/2009, -2/+14Yeah, the color of your roof is one of the most important sections in the handbook for world domination and control of the human race.
- MaxxusFlamus, on 07/14/2009, -0/+11It's not simply reflecting light to reduce surface temperature, but it's also reducing the amount of energy required to cool the building.
- nick2525, on 07/13/2009, -40/+51It seems like a good idea in theory. However, I can tell you (as a roofing contractor by trade) white roofs alone will not help much.
I find it funny how the picture at the top of the article has a roofer installing a white PVC roof. PVC stands for "Polyvinyl chloride", which is a form of plastic. Sure it's white, but it's plastic. The material alone is a conductor and likely to attract heat in the summer. Ever tried to sit in a vinyl tent on a hot day?
The majority of roofing materials used in North America are various types of asphalt roofing. I can tell you it doesn't matter weather it's a white roof or a black roof, you can fry an egg on it on a moderately hot day.
It is not the color of the roof that will make a building more efficient but the type of material used and the quality of the building envelope. I'd say more emphasis needs to be put on the thermal resistance value of the insulation used in roofing construction. Vapor barriers and ventilation quality are also key ingredients to efficiency.
Conspiracy theory: Obama's top energy advisor is invested in white paint!
/s - WasabiBomb, on 07/14/2009, -1/+12Please explain how white roofs and properly inflated tires can't possibly save us money. What the hell is it with you Internet Tough Guys, anyway?
- anonymous1986, on 07/14/2009, -1/+11Yes, clearly you should have been given the job instead of Chu.....
- askantik, on 07/14/2009, -2/+12"I can tell you (as a roofer by trade)" um, not dogging you or anything, but just because you put a roof on a house doesn't mean you know about reflecting light and the thermal properties of various materials and which would help reflect light at the correct angle to send it back into the atmosphere...
- kimbja98, on 07/14/2009, -0/+9That's because heat is in the IR, rather than the visible spectrum. It is common that white things happen to reflect IR too but it's not always true. Silver surfaces work best for reflecting heat...perhaps someone should engineer a material that reflects IR but is coloured in the visible range to look nice.
- xeriscaped, on 07/14/2009, -2/+11I have found living in Tucson that a white roof does make a difference. My house initially had a silver roof, but I switched to white and have noticed a difference in temperature when I am on the roof switching between the swamp cooler and AC in the summer.
This change should be part of new building codes. - inactive, on 07/14/2009, -0/+9Tile is very expensive, tricky to work with, and heavy. Asphalt roofing is cheap and easier to work with. If you want to build a lot of structures cheaply, quickly, and easily, tile is not a good choice.
- nathanbutnet, on 07/14/2009, -3/+12Yea, nobel prize winners are usually known for throwing out ridiculous ideas with no scientific support.
- Scrappy1850, on 07/14/2009, -1/+10i doubt anyone is going to "paint" the roads. just use a lighter colored asphalt.
- drmephesto, on 07/14/2009, -0/+81) yes, its quite big.
2) the reflected light doesn't get absorbed by the atmosphere very much, otherwise it would not have reached the ground in the first place.
3) its a white roof, not a mirror. look around a city, and you will find a white billboard or something. is it bliding you?
4) yes, tan would be better than black. concrete color even better. - inactive, on 07/14/2009, -0/+8This would be more applicable for large scale commercial and industrial structures than homes. Think factories, shopping malls, grocery stores, office buildings, etc. In some places you'll see fine white gravel on roofs of these structures.
- gimpbully, on 07/14/2009, -0/+8can you trap atoms?
chu can. - kentifer, on 07/14/2009, -0/+8I want to know what the difference would be between a roof top garden and a white roof top.
The garden would probably cost more, I'm sure, but what about the effects it would have in slowing global warming? - anillop, on 07/14/2009, -0/+7Yeah the nerve of this administration coming up with non-government solutions to problems. You would think Republicans would be more open to cost effective non government solutions, but apparently the chance for hypocrisy is just too good for them to pass up.
- WasabiBomb, on 07/14/2009, -7/+14Since you're obviously an idiot, I fail to see why any of us should invest any time in trying to explain to you how you're wrong.
- enotswhat, on 07/14/2009, -1/+8roads
- Angostura, on 07/14/2009, -2/+9Have you ever seen a picture taken from space of Europe and North America during the night? It gives you a nice feel for just how significant human population is.
- anillop, on 07/14/2009, -0/+7Yes because it is quite common for Nobel Prize winners to be morons.
- SquigglyP, on 07/14/2009, -0/+7I think your average parking lot's color has less an effect on climate change as the number of trees they cut down to put it there.
- rolf, on 07/14/2009, -1/+8Not much, the winter is colder because you get less sun and at a less direct angle. Also, heat tends to rise, so only the very top top gets any heat from the roof but in the summer it can become so extreme that it builds up in the attic and any hot air rising from the house below stays in the house since it's still colder.
Basically, you can gain some cooling in the summer and there's not much to lose in the winter (opening your window shades during day probably would have more effect to heating your house in the winter). - ShadowFusion, on 07/14/2009, -2/+9I think we should just build giant domes over the major cities so we don't have to deal with annoying things like the sun, rain, and wind
http://www.huliq.com/1/81975/experts-say-houston-d ... - tamman2000, on 07/14/2009, -0/+7Well, we will use less foreign oil and less smog/acid rain forming coal if we need less electricity to stay cool, so even if you don't believe in global warming, there are still very good reasons to get behind this.
- gimpbully, on 07/14/2009, -0/+6nope, just keep the tinfoil on your head, it'll be alright.
- Johnagain, on 07/14/2009, -0/+6I am currently finishing up a buildign project where they are installign a green roof - green in every respect. The roof consists of structure, covered by torch-down rolled roofing tokeep the water out. On top of this is root barrier, followed by drainage rock, a foot or soil, and groundcover type plants. The roof will be green in color, "green" in that it makes oxygen, "green" in that all the extra material on the roof serves as an insulator.
No, I don't have a point. I just wanted to share. -
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