I have a small log home. The logs are efficient insulators plus they
act as a heat sink. My heat is baseboard hot water and I have two
thermostats controlled by a homemade switcher. The "day" thermostat is
set to 65° and the night one is 57°. This does save some oil. My
question is about daytime if I leave the house. Does it make sense to
go on the lower setting for just four hours? It would use less oil
during that time but then it would use more to "catch up" when I get
home. What would be the minimum number of hours that would give the
best savings on oil?


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')

good article on setback stats:
http://www.energy.iastate.edu/news/p...backtherm.html




"---MIKE---" wrote in message
...
I have a small log home. The logs are efficient insulators plus they
act as a heat sink. My heat is baseboard hot water and I have two
thermostats controlled by a homemade switcher. The "day" thermostat is
set to 65° and the night one is 57°. This does save some oil. My
question is about daytime if I leave the house. Does it make sense to
go on the lower setting for just four hours? It would use less oil
during that time but then it would use more to "catch up" when I get
home. What would be the minimum number of hours that would give the
best savings on oil?


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')

"---MIKE---" wrote in message
...
I have a small log home. The logs are efficient insulators plus they
act as a heat sink. My heat is baseboard hot water and I have two
thermostats controlled by a homemade switcher. The "day" thermostat is
set to 65° and the night one is 57°. This does save some oil. My
question is about daytime if I leave the house. Does it make sense to
go on the lower setting for just four hours? It would use less oil
during that time but then it would use more to "catch up" when I get
home. What would be the minimum number of hours that would give the
best savings on oil?



http://www.mge.com/home/saving/thermostat.htm
http://www.energy.iastate.edu/news/p...backtherm.html
A common misconception associated with programmable thermostats is that a
furnace works harder than normal to warm the home back to a comfortable
temperature after the thermostat has been set back, resulting in little or
no savings. Years of research and numerous studies have shown that the fuel
required to reheat a home is roughly equal to the fuel saved as the home
drops to the lower temperature. This will result in fuel savings between the
times the temperature stabilizes at the lower level and the next time heat
is needed. The longer the house remains at the lower temperature, the more
energy saved.

---MIKE--- wrote:
I have a small log home. The logs are efficient insulators plus they
act as a heat sink. My heat is baseboard hot water and I have two
thermostats controlled by a homemade switcher. The "day" thermostat is
set to 65° and the night one is 57°. This does save some oil. My
question is about daytime if I leave the house. Does it make sense to
go on the lower setting for just four hours? It would use less oil
during that time but then it would use more to "catch up" when I get
home. What would be the minimum number of hours that would give the
best savings on oil?


---MIKE---

In the White Mountains of New Hampshire

(44° 15' N - Elevation 1580')

Hi,
First using programmable 'stat, decide what you want to do. Most
comfort, most saving or compromise. Then program the 'stat and tweak
it to your liking.

do you think that this would hold true for cooling a house?
"Edwin Pawlowski" wrote in message
t...

"---MIKE---" wrote in message
...
I have a small log home. The logs are efficient insulators plus they
act as a heat sink. My heat is baseboard hot water and I have two
thermostats controlled by a homemade switcher. The "day" thermostat is
set to 65° and the night one is 57°. This does save some oil. My
question is about daytime if I leave the house. Does it make sense to
go on the lower setting for just four hours? It would use less oil
during that time but then it would use more to "catch up" when I get
home. What would be the minimum number of hours that would give the
best savings on oil?



http://www.mge.com/home/saving/thermostat.htm
http://www.energy.iastate.edu/news/p...backtherm.html
A common misconception associated with programmable thermostats is that a
furnace works harder than normal to warm the home back to a comfortable
temperature after the thermostat has been set back, resulting in little or
no savings. Years of research and numerous studies have shown that the fuel
required to reheat a home is roughly equal to the fuel saved as the home
drops to the lower temperature. This will result in fuel savings between the
times the temperature stabilizes at the lower level and the next time heat
is needed. The longer the house remains at the lower temperature, the more
energy saved.

Joseph Meehan wrote:

Just not worth it...

Got physics? :-)

"---MIKE---" wrote in message
...
I have a small log home. The logs are efficient insulators plus they
act as a heat sink. My heat is baseboard hot water and I have two
thermostats controlled by a homemade switcher. The "day" thermostat is
set to 65° and the night one is 57°. This does save some oil. My
question is about daytime if I leave the house. Does it make sense to
go on the lower setting for just four hours? It would use less oil
during that time but then it would use more to "catch up" when I get
home. What would be the minimum number of hours that would give the
best savings on oil?

There's no minimum time. Turning the heat down always saves energy.

Nick

On Dec 9, 11:01 pm, "Cshenk" wrote:


1- when you shut down at night to 57, it takes 3 hours or more before the
temp hits 57 but in the morning when you bring it up, it rewarms pretty much
in 15 mins or less.
- may not save you that much

2- when you shut down at night to 57, it takes 1 hour or less to hit that
temp and takes at least 15 mins, maybe more to rewarm.
- will save you money

I'm not getting this, can you explain further?

He probably can't, because at best it's a working hypothesis.

Based on scientology or something, not on math/physics.

John

Joe wrote:
On Dec 9, 11:01 pm, "Cshenk" wrote:

1- when you shut down at night to 57, it takes 3 hours or more before the
temp hits 57 but in the morning when you bring it up, it rewarms pretty much
in 15 mins or less.
- may not save you that much

2- when you shut down at night to 57, it takes 1 hour or less to hit that
temp and takes at least 15 mins, maybe more to rewarm.
- will save you money

I'm not getting this, can you explain further?

"---MIKE---" wrote
I have a small log home. The logs are efficient insulators plus they
act as a heat sink. My heat is baseboard hot water and I have two
thermostats controlled by a homemade switcher. The "day" thermostat is
set to 65° and the night one is 57°. This does save some oil. My
question is about daytime if I leave the house. Does it make sense to
go on the lower setting for just four hours? It would use less oil
during that time but then it would use more to "catch up" when I get
home. What would be the minimum number of hours that would give the
best savings on oil?

It would depend on how much drop in temp you get over 1 hour, and 4 hours.

2 scenarios he

1- when you shut down at night to 57, it takes 3 hours or more before the
temp hits 57 but in the morning when you bring it up, it rewarms pretty much
in 15 mins or less.
- may not save you that much

2- when you shut down at night to 57, it takes 1 hour or less to hit that
temp and takes at least 15 mins, maybe more to rewarm.
- will save you money

"Edwin Pawlowski" writes:

http://www.mge.com/home/saving/thermostat.htm
http://www.energy.iastate.edu/news/p...backtherm.html
A common misconception associated with programmable thermostats is that a
furnace works harder than normal to warm the home back to a comfortable
temperature after the thermostat has been set back, resulting in little or
no savings. Years of research and numerous studies have shown that the fuel
required to reheat a home is roughly equal to the fuel saved as the home
drops to the lower temperature. This will result in fuel savings between the
times the temperature stabilizes at the lower level and the next time heat
is needed. The longer the house remains at the lower temperature, the more
energy saved.

Of course, you need to take into account that this talks about *energy*
used, not cost. If energy costs the same any time of the day, no
matter what the temperature differential (typical for gas or oil heat),
then energy and cost are the same. But there are some systems where
this isn't true. Pure resistive electric heat can cost different
amounts at different times of the day in some locations.

And heat obtained from a heat pump gets a lot more expensive if the
house gets cold enough to bring on the resistance heaters instead of
just running the compressor (that's a case where it actually uses more
energy for the same heat output, since the resistance heater is much
less efficient than the heat pump heat). You may be better off letting
the heat pump run some during the day to keep the house warm enough so
that when the setpoint comes up at 5 PM (or whenever), the resistance
heaters are not used.

So the minimum-cost option can depend on the system type.

Dave

"Cshenk" wrote in message
...

"Joe" wrote
1- when you shut down at night to 57, it takes 3 hours or more before
the
temp hits 57 but in the morning when you bring it up, it rewarms pretty
much
in 15 mins or less.
- may not save you that much

2- when you shut down at night to 57, it takes 1 hour or less to hit
that
temp and takes at least 15 mins, maybe more to rewarm.
- will save you money

I'm not getting this, can you explain further?

It takes a certain amount of time to reheat back to your 65 in the
morning. It takes a certain time to drop back to 57 when you cut the heat
back.

Unless we know how long those 2 are, no one can answer your question as it
depends on the insulation and heating efficiency of your home.

The best any can do with what was posted is ask how long it takes to drop
to 57, and how long it takes to heat back to 65.


What difference does it make how long it takes to drop to 57? The furnace is
not working at all at that time. Only when the temp is reset to 65 the next
morning does the furnace come on continuously till the temperature in the
house climbs to 65.

Cshenk wrote:

"Joe" wrote

It takes a certain amount of time to reheat back to your 65 in the morning.
It takes a certain time to drop back to 57 when you cut the heat back.

Unless we know how long those 2 are, no one can answer your question as it
depends on the insulation and heating efficiency of your home.

Nonsense. Any setback saves energy, no matter how short.

This is 300-year-old high-school physics :-)

Nick

wrote in message

Nonsense. Any setback saves energy, no matter how short.

This is 300-year-old high-school physics :-)

Nick

Is there any limit to what the setback temperature should be?

"Joe" wrote
1- when you shut down at night to 57, it takes 3 hours or more before the
temp hits 57 but in the morning when you bring it up, it rewarms pretty
much
in 15 mins or less.
- may not save you that much

2- when you shut down at night to 57, it takes 1 hour or less to hit that
temp and takes at least 15 mins, maybe more to rewarm.
- will save you money

I'm not getting this, can you explain further?

It takes a certain amount of time to reheat back to your 65 in the morning.
It takes a certain time to drop back to 57 when you cut the heat back.

Unless we know how long those 2 are, no one can answer your question as it
depends on the insulation and heating efficiency of your home.

The best any can do with what was posted is ask how long it takes to drop to
57, and how long it takes to heat back to 65.

On Dec 10, 9:48 pm, "Edwin Pawlowski" wrote:
wrote in message

Nonsense. Any setback saves energy, no matter how short.

This is 300-year-old high-school physics :-)

Nick


Assuming, as someone earlier pointed out, that fuel costs are
constant, which is usually the case. For example, if you had a
situation with a heat pump where by turning it down too much it
resulted in secondary electric kicking in during recovery, it could
negate the cost savings. Or if you had differing rates for
electricity for a heat pump during different periods, etc.


Is there any limit to what the setback temperature should be?

Only what you can tolerate from a comfort level when you're there and
what the house can tolerate when you're not. If I'm away for an
extended period, I set it down to 45. One factor is as the house
cycles, you may get more drywall cracking do to expansion/contraction.

On Tue, 11 Dec 2007 02:48:04 GMT, Edwin Pawlowski wrote:

wrote in message

Nonsense. Any setback saves energy, no matter how short.

This is 300-year-old high-school physics :-)

Nick

Is there any limit to what the setback temperature should be?

Freezing. If you can't feel the difference, let it set back to 35-40 degrees.
You don't want it to get cold enough to burst the plumbing.

I personally prefer something above 60 at night.

(Dave Martindale) wrote:

... You may be better off letting the heat pump run some during the day
to keep the house warm enough so that when the setpoint comes up at 5 PM
(or whenever), the resistance heaters are not used.

Maybe not, in a high-conductance house with a low thermal mass and a long
setback and high-capacity resistance heaters. In the example below, a low-
capacity heat pump barely returns the house to 70 F on a cold day, running
through almost the whole setback time. Heat pumping alone uses 19% more
energy as it slowly raises the house temp from 60 to 70 F with a higher
average setback temp than the same heat pump with a final 8 minute goose
from resistance heaters, just before 5 PM.

20 G=1200'house conductance (Btu/h-F)
30 C=2400'house capacitance (Btu/F)
40 TH=70'normal house temp (F)
50 TS=60'min setback temp (F)
60 SBT=12'setback time (hours)
70 TA=40'outdoor temp (F)
80 RC=C/G'time constant (hours)
90 TC=-RC*LOG((TS-TA)/(TH-TA))'cooling time (hours)
100 TWP=SBT-TC'heat pump warming time (hours)
110 THP=(TH-TS*EXP(-TWP/RC))/(1-EXP(-TWP/RC))'equiv. heat pump temp (F)
120 HPC=(THP-TA)*G'heat pump capacity (Btu/h)
130 COP=3'heat pump COP
140 HPE=HPC*TWP/COP'heat pump energy (Btu elec.)
150 RHC=5*HPC'resistance heat capacity (Btu/h)
160 THR=TA+(RHC+HPC)/G'equiv. resistance + heat pump temp (F)
170 TWR=-RC*LOG((THR-TH)/(THR-TS))'resistance + HP warming time (hours)
180 REE=RHC*TWR'resistance heater energy (Btu elec.)
190 HPA=(TS-TA)*G*(SBT-TC-TWR)'heat pump setback energy (Btu)
200 HPW=HPC*TWR'heat pump warming energy (Btu)
210 HPT=(HPA+HPW)/COP'heat pump total energy (Btu elec.)
220 RET=REE+HPT'total energy with res. assist (Btu elec.)
230 PRINT SBT,TC,TWP,TWR
240 PRINT HPC,RHC,HPE,RET,HPE/RET

setback cooling heat pump warming
hours hours hours hours

12 .8109303 11.18907 .1288909

heat pump resistance Heat pump HP+res HP alone/
Btu/h Btu/h alone Btu Btu (HP+res) Btu

36044.78 180223.9 134435.9 113259.3 1.186974

Nick