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« The madness of Lord Deben | Main | More votes »
Tuesday
Jun302015

White wrong

President Obama's energy adviser [Stephen Chu] has suggested all the world's roofs should be painted white as part of efforts to slow global warming.

Telegraph, 27 May 2009

By using white roofing materials, [architects] could earn a point for helping a city like Philly stay cooler and therefore lower air-conditioning demand and natural-resource consumption for electricity generation. But the fact that they would spend more on heating costs was not always factored into the equation.

Philly.com, 29 June 2015

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Reader Comments (28)

Whitewash seems to be the favoured political solution, when global warmists run out of science.

Jun 30, 2015 at 3:20 AM | Unregistered Commentergolf charlie

Ignorance of the T^4 law is no excuse for the sheer wrongheadedness of this post:

The air conditioning power saving exceeds the winter solar heating loss by roughly a factor of 2 to 20, because , besides the difference in radiative flux due the the T^4 law, in winter, the sun is lower and the days are cloudier and shorter, significantly reducing solar gain. This commonsense program has saved householders billions while improving the quality of life . Details can be found in

Environ. Res. Lett. 5 (January-March 2010) 014005
doi:10.1088/1748-9326/5/1/014005
Radiative forcing and temperature response to changes in urban albedos and associated CO2 offsets

Surabi Menon1, Hashem Akbari1,3, Sarith Mahanama2, Igor Sednev1 and Ronnen Levinson1

Jun 30, 2015 at 5:01 AM | Unregistered CommenterRussell

The "green roofs not always the most energy efficient 'article linked by the Bish embodies your standard objection to climate models: it indulges an invented worst-case scenario.

The only sort of structure that loses money on a white roof is one that violates most building codes.
It takes an uninsulated south facing tin roof to undo the savings the ERL article details.

Jun 30, 2015 at 5:43 AM | Unregistered CommenterRussell

This appears to be a case for the black arab v white arab.
To answer the question as to why some arabs wore black robes without expiring of heat stroke, intrepid scientists inserted thermometers under both black and white robes. They found that white absorbed less heat, but was poorer radiating it. The black robes got hotter on the surface but radiated heat better.
NOTE this applies to thick robes with some insulating value.

Thus in theory, a white painted house roof would put less load on an air conditioner in summer, and less on heating in winter because it wouldn't radiate as much. However after sundown it would retain more heat than a black roof.
Moreover any heat coming into the house by other than through the roof (walls, doors, windows) and any internal release would be slower to be lost. If winter and summer were the same temperature then a white roof would make sense, but as they're not, it would be cheaper to insulate the walls etc. to decrease heat transfer.

Where I once worked they had 2 identical tanks, holding the same (water based) product. Both were exposed to 7 hours of Sydney sunlight in summer. Both were white painted, but one had hollow ceramic spheres in the paint adding some insulation. It certainly heated less in summer, about 1℃, but winter results were inconclusive as there was a higher temperature differential between outside temperatures and contents (- 20℃) in winter than summer (+15℃).

Jun 30, 2015 at 6:17 AM | Unregistered CommenterGraeme No.3

Graeme No.3
Like everything it's not a black and white issue, but is far more complex with a lot of variables going into the mix with each case being slightly different. In whch case the Philly.com paragraph has more merit than Stephen Chu's, although both are too simplistic.

Jun 30, 2015 at 7:51 AM | Unregistered CommenterSandyS

Bottomline : If it worked big biz would already be doing it WITHOUT subsidies
- Chu argued it saves CO2, so he means that the white-roofed building uses SIGNIFICANTLY less energy.
If that were true then the cost saving would be more than the hassle.
...And so every McDonalds, Wallmart, UPS depot etc would have a white roof.
..and cars businesses operate would have white roofs.

..But then some activists are so into conspiracy theories ..they believe
#1 That 'electricity from wind and solar is almost free and certainly cheaper than that from coal and gas which has to be paid for'
#2 'That big biz who are desperately into profiting from every penny, don't know that and choose to generate electricity with coal and gas that they have to pay for' .."cos they are stupid & evil"

Jun 30, 2015 at 8:04 AM | Registered Commenterstewgreen

Public Health England advocated a similar policy, of having light-coloured roofs in its Heatwave Plan.

The idiots.

Jun 30, 2015 at 8:05 AM | Unregistered CommenterJoe Public

Expect EPA legislation to require you to paint it white in Spring and black in Autumn, every year. Using approved operators....oh...and with large fines for non-compliance.

Jun 30, 2015 at 8:07 AM | Unregistered CommenterJack Savage

There's a fundamental rule of thumb that tells you which gullible energy source gets funding and its not that which reduces the most CO2 output, instead it is the one that funnels most public money into the pockets of con-men gullibles pushers.

So, I will bet this great "insight" has behind it a pushy salesman selling paint.

Jun 30, 2015 at 8:50 AM | Registered CommenterMikeHaseler

SandyS:

Of course it is more complicated, I was just trying to be polite.

What Russell forgets is that people want to be comfortable in their homes. If it is 35℃ outside, and they can afford an air conditioner, it will be on. Especially if it is very humid also, because air conditioners are good dehumidifiers.
If it is very cold outside then the heating will be going. The use of a white roof seems unnecessary if you have 20 cms. of snow on the roof (that's that white fluffy stuff full of air, so a good insulator).

The heat balance will depend on the difference in inside and outside temperatures. If 23℃ is the preferred inside temperature then it will require less energy to reach it if the outside temperature is 35℃ than if it is, say -15℃ (a difference of 12 v 38 as Newton could have used to illustrate his law of cooling).

Another problem is that hot air rises into the roof space, where the solar heat can boost its temperature. Here in Australia where we get some higher temperatures than in, say Scotland, the air space can reach 65℃. A white roof reducing radiation might work? but it is simpler and more effective to install a solar powered fan to exhaust the roof air and replace it with fresh air from outside, even though that is hot, but nowhere near what was evacuated.

And the same applies internally. There must be fresh air coming in, and even with a heat exchanger - at extra cost - that means a bit more energy needed. Also, there is far more area in the walls +windows +doors than on the typical house roof. More energy needed to compensate.

I have no objection to people painting their roof white, provided they clean it regularly, but I think there are more cost effective ways of saving energy.

Jun 30, 2015 at 8:53 AM | Unregistered CommenterGraeme No.3

Is this a business opportunity for rotating roof tiles?

Jun 30, 2015 at 8:58 AM | Unregistered CommenterJamesG

If your loft is reasonably well insulated, it should make precious little difference whatever colour is your roof.

Jun 30, 2015 at 9:01 AM | Registered CommenterMartin A

@ Graeme No.3 at 6:17 AM.
Oh the humanity! I’m sorry, my heart goes out to the intrepid scientists who had the job of checking those thermometers.

Jun 30, 2015 at 9:35 AM | Unregistered CommenterChris Hanley

I lived in a flat roofed villa (so called) in the Oman and built by an Austrian Co. The roof was concrete slabbed to walk upon.

The main bedroom in the hottest part of the year (May thru Sept) was unbearable and would require 3 air cons. Only 1 designed in. The 2nd bedroom was surrounded by shrubs and some tallish trees. That room was always too cold with a small aircon running - no fan only. No chance in opening a window in that place!

Close by was the Royal Guard barracks that were fed by main plant air con (turbines) and likely the biggest plant in the world at that time (1980's). i knew the air con engineer who said most every time he visited the barracks, doors and windows were wide open. He wondered why he was eating through his turbine systems so fast...well?

Jun 30, 2015 at 9:47 AM | Unregistered CommenterEx-expat Colin

Corollary to Mike Hassler's observation, for every white roof booster there should be an asphalt lobbyist preaching the black roof and maccadam gospel.

Sure enough- K Street boasts a National Asphalt Tile Association.

Jun 30, 2015 at 10:05 AM | Unregistered CommenterRussell

Graeme No.3
I was agreeing with you that it's horribly complicated, so sorry if you thought I having a pop.

Jun 30, 2015 at 12:23 PM | Unregistered CommenterSandyS

SandS:

No I didn't think that, it was just another chance to have a go at Russell, who seems to have disappeared.

Where the Botzmann coefficient comes in I don't know. The obvious starting point would be Newton's law of cooling - I'd better put that in, in case he ever reads the responses - and some practical experience. He would appear to be very short of the latter, like so many believers in the Global Warming scam.

Jun 30, 2015 at 12:33 PM | Unregistered CommenterGraeme No.3

vvussell, with your expert knowledge of increasing solar reflectivity, why are you not marketing your scheme? Or are comments here part of your protective bubble?

Jun 30, 2015 at 12:44 PM | Unregistered Commentergolf charlie

Yep, why paint an insulated roof ? it's a waste of money
@Martin A was spot ...................................Jun 30, 2015 at 9:01 AM |
If your loft is reasonably well insulated, it should make precious little difference whatever colour is your roof.

Jun 30, 2015 at 2:07 PM | Registered Commenterstewgreen

So; in a country that is mostly cool, some crackpot insists that white roofs are better.

What does he recommend for places that are hot most of the year?

Why not paint the asphalt streets too? Make them slippery when it rains, that'll help the green dream for reducing population.

As usual, the green plans for the rest of us are bogus; full of hype and hymn but little substance.

Jun 30, 2015 at 2:37 PM | Unregistered CommenterATheoK

"as part of efforts to slow global warming"

That's the daft bit. How much paint (and how many roofs) would you require to make a measurable difference, Mr Chu..?

Jun 30, 2015 at 3:02 PM | Registered Commenterjamesp

How much would this change the Earth's albedo? There must be a lot of roofs around the world; wouldn't want this simple nature trick to plunge the planet into a new ice age or anything..or would they?

Jun 30, 2015 at 3:23 PM | Unregistered Commenterchris moffatt

I can just see all the dirty white roofs, it would be charming, with dark streaks from the leaves on them. Perhaps there is a reason there are lots of white houses but no white roofs anywhere, ever.

Jun 30, 2015 at 3:34 PM | Unregistered CommenterCraig Loehle

Here on the West coast of the U.S., commercial buildings usually have flat roofs. These are usually covered either with light colored, fine gravel embedded in the pitch type material used to seal the roof, or painted with aluminium paint.

I don't think I have ever seen a black/dark flat roof.

Now houses are a different matter, because they are traditional sloped roofs covered with typically dark roofing material.

Jun 30, 2015 at 4:21 PM | Unregistered CommenterPhilip

Philip, white or silver paint on flat felt and asphalt roofs, has been used in the UK for over 30yrs. The idea was to reflect the sun, and prevent damage due to UV light, and thermal expansion and contraction.

Its success was not dramatic, but could to know that failed technologies can be repurposed, in the name of global warming.

Jun 30, 2015 at 6:49 PM | Unregistered Commentergolf charlie

Paint roofs white, reduce local rainfall.
“Seasonal hydroclimatic impacts of Sun Corridor expansion,” published in the Sept. 7, 2012 issue of Environmental Research Letters. http://iopscience.iop.org/1748-9326

Ignore heating, reduce rainfall, being a Climate Scientist (TM) is EASY, because you don't have to think about consequences, trade-offs or cost-benefit analyses.

Jul 1, 2015 at 3:07 PM | Unregistered CommenterLeo Morgan

@ex-expat Colin. I too lived in Oman in the mid-80s. I recall the old houses in Muscat itself were built with wind-towers. Basically a very wide chimney up through the house which created a natural ventilation flow and keeping things relatively cool.

Jul 2, 2015 at 4:45 PM | Registered Commenterdavidchappell

Stewgreen writes:

Bottomline : If it worked big biz would already be doing it WITHOUT subsidies

Why yes they are

This is a suburban mall in Washington DC.

Jul 4, 2015 at 2:05 AM | Unregistered CommenterEli Rabett

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