"Don Foreman" wrote in message
...
On Fri, 30 Oct 2009 14:58:11 -0400, "Ed Huntress"
wrote:


"Don Foreman" wrote in message
news
On Fri, 30 Oct 2009 13:17:41 -0400, "Ed Huntress"
wrote:



As I said, I'm aware of the physics, Don. But the questions, which have
gone
all around the barn, are about whether it's worth it. And the answer is
that
it's much more worthwhile if your periods of turning the furnace off (or
the
thermostat 'way down) are quite long.

DOE addressed the question accurately: if you have two periods of
reduced
heat per day -- the time you're at work and the time you're sleeping at
night -- you'll typically save 10%. That's a figure that's been tested
and
reported for decades.

That's as good as any generalization. Savings vary a lot with how
much the homeowner sets back and for what percentage of the time. The
length of each period is only relevant if it is small or comparable to
the time constant of the enclosure. If the period is short enough
that the space can only cool 5 degrees, then lowering the setpoint
more than that has no effect or benefit.

But the assertion about not saving anything until the house is
stabilized at the lower temp is wrong...

I should have said "anything significant." Somehow significance stuck in
my
mind throughout that discussion.

...and the stuff about cycling
thermal mass requiring net energy is also wrong.

I don't know who said that, but it wasn't me. Or if I did, then I
misspoke.

Just to make sure we agree he If you read what DOE actually says, it's
perfectly accurate. They don't get into thermal masses or hypothetical
examples. They're talking about real savings, based both on theory and,
more
importantly, on real tests run over a period of decades.

I don't know which DOE study you refer to here since there were
several, but I have no quarrel with findings based on actual data.
Honeywell did their own studies with similar findings.

Precis of findings:
How much does a setback stat save? It depends.
Are the savings significant? Maybe.
10% of not much is hardly any.
10% of a whole bunch is some.
Buy a Honeywell Chronotherm. Your family deserves the best.

Some gov't studies are almost laughable when they wander off into the
weeds trying to offer an impressive technical explanation of what the
data says and why, which more often is really the writer's attempt to
impress by verbose technobabble obfuscation. It's well known in
contract research labs that the gov't wants big thick reports for
their research buck. Hell, the proposals alone sometimes look like
phonebooks. It's widely suspected that nobody actually reads these
reports, they just weigh them and assign a grade.

Makes me think of a notorious DOH or OSHA study that spent 3/4 mil
finding that pig**** is slick. (Safety issues in pig farms or
something like that).


That probably was a report about Chicago's Grant Park in 1968. g

--
Ed Huntress