In article
,
wrote:

On Aug 8, 7:34*pm, Smitty Two wrote:
In article
,





wrote:
On Aug 8, 12:46*pm, Smitty Two wrote:
In article
,

wrote:
On Aug 7, 9:47*am, ransley Mark wrote:
On Aug 6, 8:31*pm, "Jordan" wrote:

I just started thinking about getting an electric water heater
timer
for
my
3 year old 30 gallon water heater. *I checked some of the reviews
for
the
Intermatic timers and it looks like everybody loves them and they
say
they
practically get their $40 bucks back each month.

Are timers all they seem to be cracked up to be and will turning
off
the
water heater from 10 PM to 8 AM really save a family of 4 a big
chunk
of
change each month?

Nobody is getting 40 back, My total bill for the electric tank was
under 40 a month, I know because that is how much it went down when
I
switched to Ng. Do a test, my tank still had warm water in it after
5
days when I would leave and turn off the power. See how much it
drops
overnight, you will be just reheating it and may save nothing.

Of course it has to be reheated, but once again, that DOES NOT
TRANSLATE INTO SAVING NOTHING. * In fact, the more it has to be
reheated, the MORE he saves.

Sorry, not true.

Exactly what is not true? * This is what you stated:

"See how much it drops overnight, you will be just reheating it and
may save nothing.

I didn't say that. We're getting into quote confusion, now.





'

That is what is not true and doesn't make any sense. *Of course it has
to be reheated the next morning. * The point, once again, is that it
takes less energy to then reheat it in the morning than it does to
maintain it at the normal set temp all night. * This is exactly the
same concept and simple physics as turning back a thermostat overnight
on a home heating system. * Are you going to tell us that doesn't save
energy too?

And again, let me state the disclaimer, I'm not saying he's going to
save a lot of energy. *I'm not saying it's worth it to install a
timer. * Maybe it is, maybe it isn't depending on exactly how much
energy he can save. * But that is a totally different argument than
saying turning off the water heater doesn't save any energy because it
has to be reheated.

It's the change in *rate* of heat loss that determines
the savings. The rate slows, slightly, as the temperature difference
between the water in the tank and the surrounding air decreases. But
that difference is essentially negligible.

IOW, looking at a loss of 20 degrees in 10 hours overnight: if it loses
10 degrees in the first five hours and another 10 in the second five
hours, there is absolutely *zero* savings.

Let's look at the previous example you gave he

Let's say your HW is at 130 degrees, and it cools to 110 overnight in
the tank with the heater off. Do you *really* think that the slope of
temp over time isn't close enough to linear to disregard its
shallowing
in this *real world* consideration?

The rate of heat loss is proportional to the temp difference. * Let's
assume it's in a basement at 60 degrees. *At 130 degrees, the temp
differential is 130-60, or 70 degrees. * At 110, it's 110-60 or 50
degrees. * So the temperature differential has gone from 70 to 50, or
about a 30% difference at the end of the period. * * It's a decaying
exponential so more of that 30% benefit occurs in the earlier period
than in the later. * But even if you assumed it was linear and went
from 0 decrease to 30% at the end of the period, *the tank would have
an average of about 15% less heat loss over say 6 hours. * That isn't
zero and it's not negligible either. *Again, whether it makes it
worthwhile to install a timer is a completely different discussion.

*However, if it loses 10.1
degrees in the first five hours and 9.9 degrees in the second five
hours, then you'll save by turning it off overnight. How much? Maybe a
penny. Likely not even that.

Clearly that can't happen. because the rate of heat loss is
proportional to the temp difference and it's a natural log decaying
function, which according to physics and math isn't close to being
linear. *In other words, it's going to lose much less in the second
five hours.

I'm pretty sure that if you look at a short enough section of a
logarithmic curve, it approaches a straight line. I think the WH cooling
graph overnight fits that approximation. Yes, it's an approximation. I
was the first one to acknowledge that I am approximating. So what?

In your own water heater example that you gave, with a timer, the
temperature delta goes from 70 to 50. That's a very significant move
on a decaying exponential curve and isn't approaching a straight
line. If what you're saying were true, what about a house setting
back the temp overnight? Let's say it's 22 deg outside, 72 inside
during the day. That's a delta of 50. At night we set it back to
62. The delta is now 40. So, it's widely accepted that a delta of
going from 50 to 40 saves a reasonable amount of energy, but a delta
going from 70 to 50 is so insignificant that it matters not a whit?
What kind of physics is that?

What kind? It's real world physics. IOW, logic is applied to it.
The average air temperature in the home changes when you set back the
thermostat at night. The average temperature of the water heater in the
tank that you *use* (disregarding taking a cold shower in the morning if
you got up earlier than the tank recovered) *doesn't change.*

You have to factor in that 100% of the heat loss from the house is
unintentional, while maybe 10% (at the most, it's probably more like 5%
or 3%) of the heat loss from the WH is unintentional.





Show me some data that says a well-insulated tank in a heated area of a
house loses so much heat overnight that a person could save any
significant amount of money. Otherwise, let's just agree to disagree on
this one.- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -


As I recall, the point of contention here was NOT whether a timer
saves a significant amount of money. It was about statements you made
that defy physics:

I never made any statements that defy physics. I stated right off the
bat that I was *intentionally ignoring* the decaying heat loss curve
because it wasn't significant to the question of whether the OP could
save money. As I estimated yesterday, he could save about eight cents,
not enough to power the timer.


"I don't think it'll save you a plug nickel. The amount of heat lost
during those 10 hours is exactly the amount of heat that has to be
put
back in. It doesn't matter one whit whether it's done all at once in
the
morning, or incrementally throughout the night. "

From simple physics, that statement is false. Had you said, I don't
think the energy saved is enough to make it worthwhile, we wouldn't be
having this disagreement.

We seem to be having it, though. And the phrase *I don't think you'll
save a plug nickel* translates to *I don't think the energy saved is
enough to make it worthwhile.*


"For all intents and purposes*, you don't save until it's been off
long enough to
cool down to whatever temp your cold water supply is. "

Which is also false. From physics, there is nothing special about it
cooling down to the cold water temp, any more than a house needs to
cool down to the 20 degree outside temp in winter to save money by
setting back the thermostat at night.

Like hell there isn't anything significant about it. Heat loss stops
altogether at equilibrium. That's the jacuzzi heating logic. Use it
daily, keep it hot. Use it monthly, let it cool.



"Every speck of heat lost through the night
has to be replaced. Do it in small chunks, or do it all at once. Same
amount of energy is expended, disregarding the *very* minor
difference
noted (that rate of heat loss decreases as temp. differential
decreases.) "

Same could be said for the house setback example, which then lead to
the distraction of air in a house somehow being used? The fact that
the rate of heat loss decreases IS the whole point. I've said right
from the start that whether the savings would actually make it
worthwhile to do is another question. But you seem to seek to
obfuscate and dismiss the physics, rather than focus on what is
occuring and then figure out if it's worthwhile.


"It will use just as much electricity if it comes on for one hour
every
day, making up the whole 50 degrees at once, or if it comes on for
six
minutes, 10 times per day, increasing the water temp in the tank 5
degrees each time. "

Another false statement. If you had said it will use only a small
amount less if heated only once a day, then it would be true. But
as it stands, it's obviously false.

"It doesn't matter one whit whether it's done all at once in the
morning, or incrementally throughout the night. "

Again false and defies basic physics.

Huh? You must mean your decaying heat loss curve, again. The one that's
insignificant as far as saving any money. Or is there another issue you
have with that?


Now as for whether you can actually save money and how much, I
already showed you the DOE website, where it says you can save money
by installing a timer to either:

A - Lower the temp at night

B- Have the water heater run during periods when electricity is lower,
if that is available

But you just dismissed it.

I dismissed A. It's nonsense. B, I agree with 100%

Here it is again:

http://www.eere.energy.gov/consumer/your home/water
heating/index.cfm/mytopic=13110
If you have an electric water heater, you can save an additional 5%*
12% of energy by installing a timer that turns it off at night when
you don't use hot water and/or during your utility's peak demand
times.

I would interpret that to mean that the low end, 5% savings is
achieved by using a timer with flat rate electric.

Nuts. Standby losses are so low in a modern water heater that even
though I speculated that 10% of the total energy used goes to counter
them, I'd say it's 5%. So the DOE thinks a timer will eliminate standby
losses altogether? Since you seem to like to pick on my understanding of
physics, I'll suggest yours needs a tune-up if you believe that.

And the 12% high
end is achieved by using a timer to get off-peak lower rates.
Whatever the numbers, clearly DOE, by the use of the words and/or,
endorses using timers even when you don't have a rate differential.
So, I would say that means they don't agree with you that it doesn't
matter a whit.



Here, from Popular Mechanics:

http://www.popularmechanics.com/home journal/how to/4217039.html?series=25
2. Night Wise
Put a timer on your electric water heater that turns it off while
you¹re asleep or keeps it off during peak hours‹especially if you sign
up for time-of-use pricing.


From the state of California:

http://www.fypower.org/res/tools/energy tips results.html?tips=water-heating
For electric water heaters, install a timer that can automatically
turn the heater off at night and on in the morning. A simple timer can
pay for itself in energy saved in about one year. More expensive,
multisetting timers are also available.


Do I think this means it's worth the trouble, expense, etc to actually
do? Not necessarily. But I do think it justifies the physics of
what is going on and shows that these sources do think the energy
savings are non zero and matter more than a whit.