On Mar 27, 9:16*am, Doug wrote:
On Tue, 26 Mar 2013 13:13:37 -0700 (PDT), "





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.

It would also seem to me that it's junk science to suggest
that lighter roofs lead to a cooler world. *X amount of solar
radiation is hitting the earth. *Almost all of it is going to go
into heating it.
So, it's hard to believe that because something is white
that radiation is going back from earth to outer space.

I've seen many model homes around Houston boasting energy saving
features and they don't have white roofs so I think that proves you
right. *Our typical summer days are 95F but two or so years ago, we
often had 102F summer days.- Hide quoted text -

- Show quoted text -


Now it gets interesting. I went looking for the study done
in Florida that I read just a month or so ago. I found the
same study again, or I should say part of it. The original
study that I saw consisted of instrumenting and monitoring
the energy usage of 6 side by side houses in FL that were
identical except for the roof type and/or color. As I
posted earlier, the study showed that on a yearly basis,
having a white shingle roof versus a dark grey one
resulted in a 10.8% reduction in energy usage.

http://www.fsec.ucf.edu/en/publicati...es/roofing.pdf


But here is the interesting part. That 10.8% number is
with the houses set at 77F and UNOCCUPIED.
In the SAME study, when I previously saw it, it also
contained a section on the results
when the homes were then monitored OCCUPIED,
but with the thermostats still set at 77F. And
when occupied, the yearly energy savings dropped to just
a few percent. The reason for that is obvious. The amount
of energy saved by the white roof is going to be the same
whether occupied or unoccupied. But when occupied
the energy usage overall is going to be higher, due to
opening doors, cooking, appliances, etc. So the percent
savings of the actual energy usage is going to be a lower
percentage.

It's interesting that part is gone. Now why might that be?
Maybe it's because it's too real. I'm getting a new roof and
was curious about the difference between a grey or black
shingle. When I saw that in a real house, in FL of all places,
going from dark grey to white only resulted in a few percent
savings, I said forget it, the difference between black and
grey isn't going to matter. And keep in mind
that is for FL. I'm in NJ and in northern climates, what you
save in summer is partly offset by increased heating costs
in winter......