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Home > Archive > Alternative Power sources > November 2005 > Set Back Thermostat To Save Energy?
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Set Back Thermostat To Save Energy?
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| John Gregory 2005-10-26, 10:21 am |
| I've teetered on this issue for years and finally settle on leaving the
house at constant temperature to conserve heat. Now, faced with expected
gargantuan increases in the cost of natural gas, I find my self revisiting
the issue.
My four leave cap cod (1800 sq ft prox) is set at about 70 degrees. My
setback thermostat was reloaded with its battery two days ago so it would
drop the temperature 5 degrees from midnight to 6:30AM. Because it has two
sets of set back detents, it also drops the temperature from 4 PM to 5:30PM;
that was as narrow a period I could get by placing the start/stop detents
side by side.
When the heat came on the past two day, it seemed my furnace ran
continuously from 6:30AM to about 8AM in order to regain those 5 degrees.
Now. I haven't measure this by tying on some measurement devices that would
capture the number of cycles and their duration (is there such a devise
available retail?) but I'm sensitive enough to recognize that furnace
blowing air throughout the house and it sure seems like it's on full blast
for an hour and a half. (I realize it can't be but the cycle times are
awfully short while it's trying to satisfy the 70 degree setting).
What do the mathematicians have to say about this. those with knowledge of
this heat loss/regain problem?
| |
| barry@sme-online.com 2005-10-26, 11:21 am |
| This really has been beaten to death. (Insert obligatory suggestion to
DAGS.)
My Honeywell programmable t-stat of about 5 yrs back supposedly runs
adaptively. And, it does seem to do so. Meaning, when approaching
scheduled temp rise, it starts early, cycling according to its own
scheme, to be at set temp at scheduled time.
That seems to be similar to what you're seeing.
In fact, it can be shown mathematically that the best overall
efficiency can be obtained by having the furnace either on or off for
longest blocks of time possible. Assuming that burner firing rate is
just sufficient to make it on rise to setpoint- that's the sticky part.
Net effect can be measured most simply by reading your gas meter- note
consumption over several days with each scheme, with similar outside
temps. (When meter seems broken and/or monthly bill is tiny, you're
onto something.)
Multitude of variables make calculating all this "interesting"- firing
rate, airflow rate, fan-switch settings, presence/absence of flue
damper, etc., etc. Definitely of theoretical interest.
Bottom line: so long as you're not relying on resistive-electric
heat-strips to recover temp, you're best off with max setback possible
short of freezing pipes. Works for me.
Low firing-rate helps. Ditto flue-damper, clean air-filter,
throttling/closing registers where heat is needed less and it doesn't
affect t-stat. Ditto alternate heat source, such as clean, efficient
wood, pellet, whatever stove. Ditto max insulation and sealing all
leaks possible. Etc., etc. (Many blanks here for others to fill.)
Enjoy staying warm. May it be a rewarding challenge rather than an
obsession.
HTH,
J
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| nicksanspam@ece.villanova.edu 2005-10-26, 1:21 pm |
| John Gregory <jaygreg90@hotmail.com> wrote:
>I've teetered on this issue for years and finally settle on leaving the
>house at constant temperature to conserve heat. Now, faced with expected
>gargantuan increases in the cost of natural gas, I find my self revisiting
>the issue.
Good. Night setbacks save energy. So does zoning.
Nick
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"John Gregory" <jaygreg90@hotmail.com> wrote in message
news:E2L7f.95952$tD4.48089@tornado.ohiordc.rr.com...
> I've teetered on this issue for years and finally settle on leaving the
> house at constant temperature to conserve heat. Now, faced with expected
> gargantuan increases in the cost of natural gas, I find my self revisiting
> the issue.
>
>
>
> My four leave cap cod (1800 sq ft prox) is set at about 70 degrees. My
> setback thermostat was reloaded with its battery two days ago so it would
> drop the temperature 5 degrees from midnight to 6:30AM. Because it has two
> sets of set back detents, it also drops the temperature from 4 PM to
5:30PM;
> that was as narrow a period I could get by placing the start/stop detents
> side by side.
>
>
>
> When the heat came on the past two day, it seemed my furnace ran
> continuously from 6:30AM to about 8AM in order to regain those 5 degrees.
> Now. I haven't measure this by tying on some measurement devices that
would
> capture the number of cycles and their duration (is there such a devise
> available retail?) but I'm sensitive enough to recognize that furnace
> blowing air throughout the house and it sure seems like it's on full blast
> for an hour and a half. (I realize it can't be but the cycle times are
> awfully short while it's trying to satisfy the 70 degree setting).
>
>
>
> What do the mathematicians have to say about this. those with knowledge of
> this heat loss/regain problem?
Set back detents? sounds like a pretty simple stat. Maybe not what is
needed in your situation. Which of course we can not see. My utilities
make large bones about more than 5 degrees for more than 8 hours saves 10%.
But I am air conditioning.
An adaptive stat is a really good idea. The stat tends to learn how long it
takes to make set point.
Check your local utilities web page. Regional issues are a factor.
| |
| nospam.clare.nce@sny.der.on.ca 2005-10-26, 5:21 pm |
| On Wed, 26 Oct 2005 12:57:08 GMT, "John Gregory"
<jaygreg90@hotmail.com> wrote:
>I've teetered on this issue for years and finally settle on leaving the
>house at constant temperature to conserve heat. Now, faced with expected
>gargantuan increases in the cost of natural gas, I find my self revisiting
>the issue.
>
>
>
>My four leave cap cod (1800 sq ft prox) is set at about 70 degrees. My
>setback thermostat was reloaded with its battery two days ago so it would
>drop the temperature 5 degrees from midnight to 6:30AM. Because it has two
>sets of set back detents, it also drops the temperature from 4 PM to 5:30PM;
>that was as narrow a period I could get by placing the start/stop detents
>side by side.
>
>
>
> When the heat came on the past two day, it seemed my furnace ran
>continuously from 6:30AM to about 8AM in order to regain those 5 degrees.
>Now. I haven't measure this by tying on some measurement devices that would
>capture the number of cycles and their duration (is there such a devise
>available retail?) but I'm sensitive enough to recognize that furnace
>blowing air throughout the house and it sure seems like it's on full blast
>for an hour and a half. (I realize it can't be but the cycle times are
>awfully short while it's trying to satisfy the 70 degree setting).
>
>
>
>What do the mathematicians have to say about this. those with knowledge of
>this heat loss/regain problem?
>
Get a GOOD digital setback thermostat, like a Honeywell, with a
totalizer on it. It will tell you how many minutes per day the furnace
runs. Gives you today, yesterday, and total season.
Real easy to see how much difference the setback makes that way.
| |
| John Gregory 2005-10-27, 3:21 am |
| >>totalizer<<
Oh? Sounds like what I'm after to measure this project. Lowe's? Home Depot?
I've got a Honeywell now but it has plastic clips to insert around the rotor
(clock) to start and stop the setback. Probably 10 to 15 years old.
I've paid closer attention to the furnace operation since writing this and
I've pulled the battery from the T-stat. It's 39 degrees outside here in
Northern Ohio (1:45AM) and my furnace comes on about twice an hour for about
5 minutes each time. If I'm correct that - with the setback - my furnace
starts at 6:30AM and fights until 8AM to regain the heat it lost over the
past 6 hours, it seems to me I'm ahead operating without the setback or at
least even.
<nospam.clare.nce@sny.der.on.ca> wrote in message
news:vslvl1t99h9djckqheij6tbrokul4bcrns@4ax.com...
> On Wed, 26 Oct 2005 12:57:08 GMT, "John Gregory"
> <jaygreg90@hotmail.com> wrote:
>
> Get a GOOD digital setback thermostat, like a Honeywell, with a
> totalizer on it. It will tell you how many minutes per day the furnace
> runs. Gives you today, yesterday, and total season.
>
> Real easy to see how much difference the setback makes that way.
| |
| nicksanspam@ece.villanova.edu 2005-10-27, 10:21 am |
| John Gregory <jaygreg90@hotmail.com> wrote:
>... It's 39 degrees outside here in Northern Ohio (1:45AM) and my furnace
>comes on about twice an hour for about 5 minutes each time. If I'm correct
>that - with the setback - my furnace starts at 6:30AM and fights until 8AM
>to regain the heat it lost over the past 6 hours, it seems to me I'm ahead
>operating without the setback or at least even.
You are probably incorrect. Newton worked most of this out 300 years ago.
Nick
| |
| barry@sme-online.com 2005-10-27, 2:21 pm |
| Don't cheap out on the t-stat. Can you say "programmable" to the
sales-person? Seems you're talking a glorified light-timer.
Re your conclusion- I say again "read the meter." (Assuming you've a
gas meter, since you've yet to tell the full story.) Read meter. Run
plan A for x-days and read meter. Do same for plan B. If weather
approx. same, compare results. Next!
Fact is, unless resistive electric heating enters picture, the deeper
and longer the setback, the less energy consumption. Period. DAGS-
"thermostat setback" nets 1120 hits.
Seems you're obsessing about one aspect of situation. Msef, I druther
obsess about an automatic stack damper, which can save about 50% with
some gas systems.
HTH,
J
| |
| nospam.clare.nce@sny.der.on.ca 2005-10-27, 10:21 pm |
| On Thu, 27 Oct 2005 05:45:25 GMT, "John Gregory"
<jaygreg90@hotmail.com> wrote:
>Oh? Sounds like what I'm after to measure this project. Lowe's? Home Depot?
>I've got a Honeywell now but it has plastic clips to insert around the rotor
>(clock) to start and stop the setback. Probably 10 to 15 years old.
>
>I've paid closer attention to the furnace operation since writing this and
>I've pulled the battery from the T-stat. It's 39 degrees outside here in
>Northern Ohio (1:45AM) and my furnace comes on about twice an hour for about
>5 minutes each time. If I'm correct that - with the setback - my furnace
>starts at 6:30AM and fights until 8AM to regain the heat it lost over the
>past 6 hours, it seems to me I'm ahead operating without the setback or at
>least even.
>
VERY difficult to get a system that is as cost efficient without
setback as with. Over a 7 hour setback, each degree C should save you
1% on your heat costs if your furnace is running anywhere near design
spec.
><nospam.clare.nce@sny.der.on.ca> wrote in message
>news:vslvl1t99h9djckqheij6tbrokul4bcrns@4ax.com...
>
| |
| Solar Flare 2005-10-27, 11:21 pm |
| If the temp outside is 65F you may save 100% on your heating costs for each 1
degree setback inside.
No credits though...LOL
<nospam.clare.nce@sny.der.on.ca> wrote in message
news:ior2m1t9hsrb03732idhokgf7rvns6rudd@4ax.com...
> setback as with. Over a 7 hour setback, each degree C should save you
> 1% on your heat costs if your furnace is running anywhere near design
> spec.
>
| |
| daestrom 2005-10-28, 2:21 pm |
|
"John Gregory" <jaygreg90@hotmail.com> wrote in message
news:E2L7f.95952$tD4.48089@tornado.ohiordc.rr.com...
> I've teetered on this issue for years and finally settle on leaving the
> house at constant temperature to conserve heat. Now, faced with expected
> gargantuan increases in the cost of natural gas, I find my self revisiting
> the issue.
>
>
Opinions vary. But generally, if the length of time is fairly long, like
overnight, they can save you money. Remember the way it works isn't how
long your furnace is off/on, it's how cool your house gets. And a cooler
house uses/loses less energy.
If you have a superinsulated house, so good that when you turn the furnace
off overnight for 10 hours, the temperature only drops 2 degrees, then a
set-back thermostat won't save you much more energy. Even if you set it to
45F or lower, the house is only dropping 2 degrees so the energy lost to the
environment is not much less than when you keep temperature constant.
On the other hand, a drafty, poorly insulated house that cools down 15 to 20
degrees in just six hours, then for those six hours the difference between
the inside temperature and the outside temperature is less than if you had
kept the temperature up all night. So the house lost less energy to the
environment. In other words, setting down the thermostat saves money.
Programming a setback the setpoint and then restore it to normal for short
periods of time doesn't do much good. The house doesn't cool down, so the
amount of heat lost is not changed much.
Of course, if you insulate better, then the house doesn't cool down as much,
so the 'set-back savings' aren't as good. If the house cools off pretty
fast, you can save money with a set-back thermostat, but you might save even
more with better chaulking and insulation.
daestrom
| |
| daestrom 2005-10-28, 2:21 pm |
|
"John Gregory" <jaygreg90@hotmail.com> wrote in message
news:VPZ7f.96810$tD4.20211@tornado.ohiordc.rr.com...
> Oh? Sounds like what I'm after to measure this project. Lowe's? Home
> Depot? I've got a Honeywell now but it has plastic clips to insert around
> the rotor (clock) to start and stop the setback. Probably 10 to 15 years
> old.
>
> I've paid closer attention to the furnace operation since writing this and
> I've pulled the battery from the T-stat. It's 39 degrees outside here in
> Northern Ohio (1:45AM) and my furnace comes on about twice an hour for
> about 5 minutes each time. If I'm correct that - with the setback - my
> furnace starts at 6:30AM and fights until 8AM to regain the heat it lost
> over the past 6 hours, it seems to me I'm ahead operating without the
> setback or at least even.
Hmmmm, 90 minutes to recover. If your measurements on the other run time
are correct, that's equal to 9 hours of running 10 minutes an hour to
maintain the temperature. Doesn't seem quite right.
You might want to check those times a little closer. What you're describing
is a house that loses more heat when it cools off than when it stays warm.
And that just doesn't add up.
daestrom
| |
|
| daestrom wrote:
>
> "John Gregory" <jaygreg90@hotmail.com> wrote in message
> news:E2L7f.95952$tD4.48089@tornado.ohiordc.rr.com...
>
> Opinions vary. But generally, if the length of time is fairly long, like
> overnight, they can save you money. Remember the way it works isn't how
> long your furnace is off/on, it's how cool your house gets. And a cooler
> house uses/loses less energy.
>
> If you have a superinsulated house, so good that when you turn the furnace
> off overnight for 10 hours, the temperature only drops 2 degrees, then a
> set-back thermostat won't save you much more energy. Even if you set it
> to 45F or lower, the house is only dropping 2 degrees so the energy lost
> to the environment is not much less than when you keep temperature
> constant.
>
> On the other hand, a drafty, poorly insulated house that cools down 15 to
> 20 degrees in just six hours, then for those six hours the difference
> between the inside temperature and the outside temperature is less than if
> you had
> kept the temperature up all night. So the house lost less energy to the
> environment. In other words, setting down the thermostat saves money.
>
I can just picture someone opening his windows to save energy :-)
> Programming a setback the setpoint and then restore it to normal for short
> periods of time doesn't do much good. The house doesn't cool down, so the
> amount of heat lost is not changed much.
>
> Of course, if you insulate better, then the house doesn't cool down as
> much,
> so the 'set-back savings' aren't as good. If the house cools off pretty
> fast, you can save money with a set-back thermostat, but you might save
> even more with better chaulking and insulation.
>
> daestrom
| |
| Solar Flare 2005-10-29, 1:21 am |
| For me and most people here the money savings is secondary. The primary idea of
the setback is to have a cooler house for comfort when sleeping. I have
automatic setbacks and I also have a window open in my bedroom to keep it cooler
and fresher.
Now I just lied with the above statement, as my setback, when I am at work, is
only for one purpose...to save money.
oooops.
"Eric" <nospam@email.com> wrote in message
news:7eednff70-lGNf_eRVn-pg@comcast.com...
> daestrom wrote:
>
>
> I can just picture someone opening his windows to save energy :-)
>
>
| |
| nicksanspam@ece.villanova.edu 2005-10-29, 4:21 am |
| Eric <nospam@email.com> wrote:
>daestrom wrote:
>
>
>I can just picture someone opening his windows to save energy :-)
I can picture someone minimizing the mass in a superinsulated house and
air conditioning it at dusk in wintertime, pumping the little heat stored
in the building mass into a well-insulated warm water storage tank for
recovery at dawn.
Or doing something similar with a stratified heat storage tank and fin-tube
pipes near the ceiling, pumping enough cool water up from the tank bottom
during the day to keep a room near a sunspace from exceeding 70 F, then
pumping more up at dusk to cool the room to 50, then pumping warm water up
(or letting it thermosyphon) from the top of the tank the next morning to
heat the room to 70, with the help of a slow ceiling fan.
Nick
| |
| Solar Flare 2005-10-29, 1:21 pm |
| Controllable thermal mass would be in order in some climates.
<nicksanspam@ece.villanova.edu> wrote in message
news:djv4v7$668@acadia.ece.villanova.edu...
> Eric <nospam@email.com> wrote:
>
money.[color=darkred]
>
> I can picture someone minimizing the mass in a superinsulated house and
> air conditioning it at dusk in wintertime, pumping the little heat stored
> in the building mass into a well-insulated warm water storage tank for
> recovery at dawn.
>
> Or doing something similar with a stratified heat storage tank and fin-tube
> pipes near the ceiling, pumping enough cool water up from the tank bottom
> during the day to keep a room near a sunspace from exceeding 70 F, then
> pumping more up at dusk to cool the room to 50, then pumping warm water up
> (or letting it thermosyphon) from the top of the tank the next morning to
> heat the room to 70, with the help of a slow ceiling fan.
>
> Nick
>
| |
|
| A question that's been bugging me for a while... is air-circulated=20
central heating more or less efficient than water-circulated central=20
heating?
I seem to remember reading that heating by convection requires higher=20
temperatures to reach the same "confort feeling", so wouldn't it make=20
sense to have water based central heating?
And would this have an impact on the best amount/duration of set-back=20
for a specific house?
Sorry about the question a little of-topic....
Mel
Solar Flare a =E9crit :
> Controllable thermal mass would be in order in some climates.
>=20
> <nicksanspam@ece.villanova.edu> wrote in message
> news:djv4v7$668@acadia.ece.villanova.edu...
>=20
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>=20
> money.
>=20
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>=20
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>=20
| |
| nicksanspam@ece.villanova.edu 2005-11-03, 4:21 am |
| Mel <melodie@pasdespam.chezmoi> wrote:
>... is air-circulated central heating more or less efficient than
>water-circulated central heating?
I'd say they are about the same, in principle. For solar heating,
air can be a lot simpler than water.
>I seem to remember reading that heating by convection requires higher=20
>temperatures to reach the same "confort feeling", so wouldn't it make=20
>sense to have water based central heating?
Moving air makes people feel cooler, although slow-moving air makes little
difference, and most people prefer a little airflow for comfort. Radiators
usually contain higher temp water than air system temps. Lower temp furnaces
can be more efficient, with less heat going up the chimney.
>And would this have an impact on the best amount/duration of set-back=20
>for a specific house?
It seems to me that air is better for setbacks. Less thermal mass, so
the setback begins sooner, and after a setback, some clever (Honeywell)
thermostats average air and wall temps and initially overheat the room
air to make up for cold walls until the walls catch up. This allows
delaying the end of a setback, which saves energy.
Nick
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