On Friday, July 4, 2014 4:11:00 AM UTC-4, rickman wrote:
On 7/4/2014 12:28 AM, Jeff Liebermann wrote:

On Thu, 03 Jul 2014 18:40:06 -0700, RobertMacy

wrote:



Ceiling exhaust fan !!! when it's 105 outside no way!!! you want me to

suck in outside air at those temps??!!



Let's see at night 81 during day 105, making the average high side of 93,

sounds about right.



I thought it gets kinda cold at night in Az. I've only been there

once. It was quite hot during the day, but we nearly froze sleeping

in the car at night.



Since I painted my house a darker color and take advanatage of 'night time

radiation' the average in our house has dropped substantially. Who would

have thought? dark house = cooler average, light colored house = hotter

average. but true we noticed a difference the moment the house was painted.



In some areas, white rocks and white roofs are required by code to

reduce air conditioning requirements. It's suppose to reflect the

sunlight instead of absorbing it. Now, you're telling me that the

collective wisdom of the local planning department might be wrong? Are

you sure?



I initially thought he was wrong, but consider the two situations. In

the day the house is absorbing sunlight radiated from the Sun at many

thousands of degrees. At night the house is radiating heat into the

void at around -273�C. I'd say the more significant factor is the

daylight situation, but the devil is in the details and I would love to

see some real data on the situation.



--



Rick

There is a study that was done in Florida on identical houses
where they measured temps and energy usage with a variety of roofs.
Between white shingled roofs and black it resulted in something like
a 10% savings in AC energy at the peak in summer, with the houses
unoccupied. When houses were occupied, that savings got cut in
half. The reason I would suspect is that with the houses occupied,
a lot more AC is used, so while the savings amount is about the same,
the percentage is going to be less, because the overall usage number
is higher.

From which I concluded, it doesn't make much difference, at least for
me. I'm in NJ and the study was in FL, where the temps are much higher
over a much longer period. To make a roof choice color based on saving
$15 a year didn't make any sense to me.