On 3/26/2013 3:13 PM, wrote:
On Mar 26, 4:03 pm, Metspitzer wrote:
The idea of painting roads and rooftops white in order to combat
carbon emissions has been around for years. It is surprisingly simple
and effective and yet has not been implemented much.

A study at the Lawrence Berkeley National Laboratory found that cooler
pavement and roofs leads to cooler cities and an overall cooler world.

Since buildings with white roofs reflect far more sun than those with
black roofs, these buildings stay cooler. Less air conditioning has to
be used, lowering the overall energy required to run the building.

Also buildings with black roofs heat the space below them and this
heat is carried spread by the wind. This raises the ambient air
temperature in what is known as the urban heat island effect. Black
roofs also radiate energy back into the atmosphere to be absorbed by
clouds. This heat is then trapped by the greenhouse effect.

As such, white roofs is one of the quickest and most cost-effective
ways to reduce our carbon emissions. In an initiative launched by the
Energy Department, the federal government hopes to exemplify the
benefits by using these light roofs on their buildings.

http://newscenter.lbl.gov/news-relea...-roofs-offset-...



I say it's total BS. The best study I saw on roof color was
done in FL. They took a bunch of identical houses, put varying types
and color of roofs on them, fully instrumented
the houses, and measured during AC season.

The conclusion was that if you had a shingle roof, it made
about a 10% difference in energy usage if you had a black
rood or a white roof. And that was the energy usage with
the houses unoccupied. They did another test when they
were occupied and the energy usage difference dropped to
just a few percent. Which makes sense, because when
occupied the energy usage is going to be higher, because
people are opening door, turning on TVs, cooking, etc.

Your recollection of the study's findings is not completely correct.
You're right that in its initial testing of unoccupied homes, it found
an approximate 10% energy savings using a white roof. But it also
found that while occupying the homes increased energy usage overall,
there was no change to the amount saved by the lighter roofs:

"Additional monitoring took place over a month long period with the
homes occupied, but the thermostat set points were kept exactly the
same as in the unoccupied monitoring period. Although average cooling
energy use rose by 36%, analysis indicated no decrease to savings or
demand reduction from the highly reflective roofing systems. The added
heat gains from appliances and people increase cooling system
run-time, with longer periods for the duct system to exchange heat to
the often hot attic space."

And the study's conclusion:

"In summary, this evaluation strongly confirms the energy-saving
benefits of using more reflective roofing systems in Florida.
Selection of colors with higher solar reflectance will result in
tangible cooling energy savings for customers. This is particularly
true for roofing materials such as tile and metal which are currently
available with solar reflectances of 65%-75%. The selection of
reflective roofing systems represents one of the most significant
energy-saving options available to homeowners and builders. Such
systems also strongly reduce the cooling demand during utility
coincident peak periods and may be among the most effective methods
for controlling demand."

http://www.mcelroymetal.com/content/...ight_Study.pdf