Turn thermostat down?
Please forgive me while I troll for a moment.....
Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. -- Christopher A. Young Learn more about Jesus www.lds.org .. |
Turn thermostat down?
On 2009-10-29, Stormin Mormon wrote:
Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i |
Turn thermostat down?
Stormin Mormon wrote:
Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. That is another one of those, " It Depends". In this case on how long you will be gone. ...lew... |
Turn thermostat down?
"Lewis Hartswick" wrote in message ... Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. That is another one of those, " It Depends". In this case on how long you will be gone. ...lew... You start saving energy as soon at the house temperature stabilizes at the lower temperature. Except for very short times, when you let the temperature drop and then immediately ramp it up again, you always save energy by lowering your house temperature. Here's what the DOE says about it: "A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save." -- Ed Huntress |
Turn thermostat down?
Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. |
Turn thermostat down?
On 2009-10-29, Pete C. wrote:
Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. i |
Turn thermostat down?
"Ignoramus10802" wrote in message ... On 2009-10-29, Pete C. wrote: Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. I Correct - whatever the net effect of insulation is, there is a net negative heat flux from the house to the outside. The flux is proportional to the temperature difference (the exact equation will depend on the radiation, convection and conduction components - radiation alone is governed by the Stephan-Boltzman equation). The larger the difference the greater the flux. Averaged over any period of time, any time spent with the thermostat set lower will yeild a lower internal temperature, hence less heat flux. Whether that is enough to show up in your bill is another question, but from a energy savings point of view, it is incontestible. |
Turn thermostat down?
"Ed Huntress" wrote in message ... "Lewis Hartswick" wrote in message ... Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. That is another one of those, " It Depends". In this case on how long you will be gone. ...lew... You start saving energy as soon at the house temperature stabilizes at the lower temperature. Except for very short times, when you let the temperature drop and then immediately ramp it up again, you always save energy by lowering your house temperature. Here's what the DOE says about it: "A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save." -- Ed Huntress True. Yet I still hear this type of "reasoning" all the time. Should be a simple concept even for the technically challenged, for example, people who argued here that you can compress air and allow it to expand (while doing no useful work) with no loss of energy. |
Turn thermostat down?
"Bill Noble" wrote in message ... "Ignoramus10802" wrote in message ... On 2009-10-29, Pete C. wrote: Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. I Correct - whatever the net effect of insulation is, there is a net negative heat flux from the house to the outside. The flux is proportional to the temperature difference (the exact equation will depend on the radiation, convection and conduction components - radiation alone is governed by the Stephan-Boltzman equation). The larger the difference the greater the flux. Averaged over any period of time, any time spent with the thermostat set lower will yeild a lower internal temperature, hence less heat flux. Whether that is enough to show up in your bill is another question, but from a energy savings point of view, it is incontestible. The confounding issue, though, is the thermal mass of the house. That's why the DOE explanation says that the savings occur when the temperature inside the house has stabilized at the lower temperature. When you shut off the furnace, the thermal mass of the inside of the house is what's giving up heat to the outside. That's stored energy that came from the furnace heat. When you raise the temperature, you have to restore that heat to the thermal mass. So with the furnace off and the temperature inside of the house dropping, you're losing stored heat. When you turn the thermostat back on, you have to restore that lost heat, which will also heat up the atmosphere inside of the house (which is a very small portion of the total inside thermal mass). That's what I read from their description, anyway, and it comports with things I've read about it from other sources. There is no (theoretical) net gain or loss when the thermal mass is put through the cycle of cooling down and heating up. The savings occur when the temperature is reduced and stabilized. This all assumes that a house is decently insulated and that the thermal mass of the house is substantial. Of course, the thermal differential between the inside and outside temperatures are always at work, suggesting that there is less heat loss with each degree of reduction of inside temperature, as you say. But the DOE's reference to actual testing agrees with the fact that, as soon as you turn the thermostat down, you begin losing *stored* heat, and when you turn it back up, 100% of that lost heat must be restored, regardless of actual thermal losses through the walls and ceiling. -- Ed Huntress |
Turn thermostat down?
On 2009-10-29, ATP* wrote:
True. Yet I still hear this type of "reasoning" all the time. Should be a simple concept even for the technically challenged, for example, people who argued here that you can compress air and allow it to expand (while doing no useful work) with no loss of energy. That would be almost possible if compressing and expanding was done very quickly, before compressed air cools. i |
Turn thermostat down?
"ATP*" wrote in message ... "Ed Huntress" wrote in message ... "Lewis Hartswick" wrote in message ... Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. That is another one of those, " It Depends". In this case on how long you will be gone. ...lew... You start saving energy as soon at the house temperature stabilizes at the lower temperature. Except for very short times, when you let the temperature drop and then immediately ramp it up again, you always save energy by lowering your house temperature. Here's what the DOE says about it: "A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save." -- Ed Huntress True. Yet I still hear this type of "reasoning" all the time. Should be a simple concept even for the technically challenged, for example, people who argued here that you can compress air and allow it to expand (while doing no useful work) with no loss of energy. It's not as simple as a lab experiment in a vacuum jar, though, unless you put a big rock in the jar to represent thermal mass. g -- Ed Huntress |
Turn thermostat down?
"Ignoramus10802" wrote in message ... On 2009-10-29, ATP* wrote: True. Yet I still hear this type of "reasoning" all the time. Should be a simple concept even for the technically challenged, for example, people who argued here that you can compress air and allow it to expand (while doing no useful work) with no loss of energy. That would be almost possible if compressing and expanding was done very quickly, before compressed air cools. i But it has to be done *awfully* quickly. That's why there's a minimum cylinder size for diesel engines -- something like 300 cc. Below 3,000 rpm or so, the compressed air cools too quickly to ignite the fuel. And heat transfer gets worse as compression goes up. -- Ed Huntress |
Turn thermostat down?
Ignoramus10802 wrote: On 2009-10-29, Pete C. wrote: Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. i No, it isn't. It was documented on a well monitored high efficiency model home where the backup heat strips on the high efficiency heat pump were kicking in in order to provide a reasonable temp recovery time since the heat pump itself did not have the capacity. The electricity used during the temp recovery was more than would have been used on temp maintenance due to the switch to lower efficiency backup (100% vs. 300%+). |
Turn thermostat down?
"Pete C." wrote in message ster.com... Ignoramus10802 wrote: On 2009-10-29, Pete C. wrote: Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. i No, it isn't. It was documented on a well monitored high efficiency model home where the backup heat strips on the high efficiency heat pump were kicking in in order to provide a reasonable temp recovery time since the heat pump itself did not have the capacity. The electricity used during the temp recovery was more than would have been used on temp maintenance due to the switch to lower efficiency backup (100% vs. 300%+). But that only tells you that a lower-efficiency temperature-recovery system is...lower in efficiency. If you have that particular pair of heating systems, you have one situation. If you have a more-typical single heating system, you have quite another. In the case you've described, you aren't dealing just with the thermodynamics of the situation. You're also adding the complexity of multiple heat sources that operate under different circumstances. -- Ed Huntress |
Turn thermostat down?
Ed Huntress wrote: "Lewis Hartswick" wrote in message ... Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. That is another one of those, " It Depends". In this case on how long you will be gone. ...lew... You start saving energy as soon at the house temperature stabilizes at the lower temperature. Except for very short times, when you let the temperature drop and then immediately ramp it up again, you always save energy by lowering your house temperature. Here's what the DOE says about it: "A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save." -- Ed Huntress What you have there *is* a misconception in that it does not account for multi stage / mixed technology heating systems which are not that uncommon. A good example is a high efficiency heat pump with backup heat strips. Depending on the controls, such a heat pump may engage the backup heaters when it is unable to produce an acceptable rate of temp rise with just the heat pump, and this switches the effective efficiency from 300%+ to 100%, making it more costly to bring the temp back up to normal than it would have been to maintain it at normal. This situation was documented on a high efficiency model home. |
Turn thermostat down?
Ed Huntress wrote: "Pete C." wrote in message ster.com... Ignoramus10802 wrote: On 2009-10-29, Pete C. wrote: Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. i No, it isn't. It was documented on a well monitored high efficiency model home where the backup heat strips on the high efficiency heat pump were kicking in in order to provide a reasonable temp recovery time since the heat pump itself did not have the capacity. The electricity used during the temp recovery was more than would have been used on temp maintenance due to the switch to lower efficiency backup (100% vs. 300%+). But that only tells you that a lower-efficiency temperature-recovery system is...lower in efficiency. If you have that particular pair of heating systems, you have one situation. If you have a more-typical single heating system, you have quite another. That isn't a "pair of heating systems", nearly all heat pumps include backup heat strips for times when the heat pump is not able to produce enough heat such as very cold weather / high demand. In the case you've described, you aren't dealing just with the thermodynamics of the situation. You're also adding the complexity of multiple heat sources that operate under different circumstances. That complexity exists everywhere and that was my point - you have to do the actual analysis of the home in question to get the correct answer - you can't rely on blanket statements / myths. An additional complication is occupancy, since for folks who are retired or work from home, or a stay at home spouse, you loose half or more of your theoretical savings period with the occupants not being away during the day. |
Turn thermostat down?
Ignoramus10802 wrote:
i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. No, there is quite an element of truth! You have to compare the thermal mass of the house and the heat loss. If the house had enormous thermal mass, like lots of stone floors and massive stone fireplaces (some people build houses intentionally to have very high thermal mass) then although the furnace could warm the air quickly to make you comfortable, it would still run for hours to warm up all that mass. If you have a lot of thermal mass and low heat loss (good insulation) then turning the thermostat down for a couple hors gives no benefit. If you have low thermal mass and lots of heat loss, then turning it down for even a couple hours will give significant benefit. Jon |
Turn thermostat down?
Ed Huntress wrote:
The confounding issue, though, is the thermal mass of the house. That's why the DOE explanation says that the savings occur when the temperature inside the house has stabilized at the lower temperature. Yes, if the house has only dropped a couple degrees when you get back, then there's little benefit. if the house cools rapidly to the lower temperature and stays there for, say, 7 hours before you return, then you get a benefit. Of course, if your house cools off very quickly, then you might do best to invest in insulation. We had a big ice storm a couple years ago, and found we could be moderately comfortable for about 8 hours before firing up the generator to bring the furnace online. I think that means our insulation is doing pretty well. Jon |
Turn thermostat down?
"Pete C." wrote in message ster.com... Ed Huntress wrote: "Lewis Hartswick" wrote in message ... Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. That is another one of those, " It Depends". In this case on how long you will be gone. ...lew... You start saving energy as soon at the house temperature stabilizes at the lower temperature. Except for very short times, when you let the temperature drop and then immediately ramp it up again, you always save energy by lowering your house temperature. Here's what the DOE says about it: "A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save." -- Ed Huntress What you have there *is* a misconception in that it does not account for multi stage / mixed technology heating systems which are not that uncommon. Yeah, they are uncommon, in residences. Heat pumps of all types, cumulatively, are used in about 8% of the residential homes in the US. http://www.eia.doe.gov/emeu/recs/rec.../alltables.pdf A good example is a high efficiency heat pump with backup heat strips. Depending on the controls, such a heat pump may engage the backup heaters when it is unable to produce an acceptable rate of temp rise with just the heat pump, and this switches the effective efficiency from 300%+ to 100%, making it more costly to bring the temp back up to normal than it would have been to maintain it at normal. This situation was documented on a high efficiency model home. I'm aware of the principles at work. They just aren't common. -- Ed Huntress |
Turn thermostat down?
"Pete C." wrote in message ster.com... Ed Huntress wrote: "Pete C." wrote in message ster.com... Ignoramus10802 wrote: On 2009-10-29, Pete C. wrote: Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. i No, it isn't. It was documented on a well monitored high efficiency model home where the backup heat strips on the high efficiency heat pump were kicking in in order to provide a reasonable temp recovery time since the heat pump itself did not have the capacity. The electricity used during the temp recovery was more than would have been used on temp maintenance due to the switch to lower efficiency backup (100% vs. 300%+). But that only tells you that a lower-efficiency temperature-recovery system is...lower in efficiency. If you have that particular pair of heating systems, you have one situation. If you have a more-typical single heating system, you have quite another. That isn't a "pair of heating systems", nearly all heat pumps include backup heat strips for times when the heat pump is not able to produce enough heat such as very cold weather / high demand. Again, you're talking about 8% of homes, at most. In the case you've described, you aren't dealing just with the thermodynamics of the situation. You're also adding the complexity of multiple heat sources that operate under different circumstances. That complexity exists everywhere and that was my point - you have to do the actual analysis of the home in question to get the correct answer - you can't rely on blanket statements / myths. No, it doesn't exist everywhere. It only exists where you have multiple heating systems operating at very different levels of efficiency -- 8% of homes, at most. An additional complication is occupancy, since for folks who are retired or work from home, or a stay at home spouse, you loose half or more of your theoretical savings period with the occupants not being away during the day. |
Turn thermostat down?
Pete C. wrote:
No, it isn't. It was documented on a well monitored high efficiency model home where the backup heat strips on the high efficiency heat pump were kicking in in order to provide a reasonable temp recovery time since the heat pump itself did not have the capacity. The electricity used during the temp recovery was more than would have been used on temp maintenance due to the switch to lower efficiency backup (100% vs. 300%+). OK, this is a killer example, where the furnace efficiency goes down the tubes when it needs to raise the temp suddenly. It might be possible to stage the temp rise to avoid that with a suitable thermostat. But, many other heating systems have no such penalty for a rise in temp setting, such as a traditional gas forced-air furnace. Jon |
Turn thermostat down?
On 2009-10-29, Jon Elson wrote:
Ignoramus10802 wrote: i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. No, there is quite an element of truth! You have to compare the thermal mass of the house and the heat loss. If the house had enormous thermal mass, like lots of stone floors and massive stone fireplaces (some people build houses intentionally to have very high thermal mass) then although the furnace could warm the air quickly to make you comfortable, it would still run for hours to warm up all that mass. So what? If you have a lot of thermal mass and low heat loss (good insulation) then turning the thermostat down for a couple hors gives no benefit. If you have low thermal mass and lots of heat loss, then turning it down for even a couple hours will give significant benefit. Jon, with all respect, I must say that you are mistaken here. From the law of conservation of energy, heat input into the house == heat loss from the house The lower is house temperature, the lower is the heat loss. i |
Turn thermostat down?
"Jon Elson" wrote in message ... Ed Huntress wrote: The confounding issue, though, is the thermal mass of the house. That's why the DOE explanation says that the savings occur when the temperature inside the house has stabilized at the lower temperature. Yes, if the house has only dropped a couple degrees when you get back, then there's little benefit. if the house cools rapidly to the lower temperature and stays there for, say, 7 hours before you return, then you get a benefit. Of course, if your house cools off very quickly, then you might do best to invest in insulation. We had a big ice storm a couple years ago, and found we could be moderately comfortable for about 8 hours before firing up the generator to bring the furnace online. I think that means our insulation is doing pretty well. Jon Either that, or you live in a cave. You could judge how much of it is insulation effectiveness and how much is high thermal mass if you had a few thermometers, a clock, a calculator, and more time on your hands than anyone should have. d8-) -- Ed Huntress |
Turn thermostat down?
"Ignoramus10802" wrote in message ... On 2009-10-29, Jon Elson wrote: Ignoramus10802 wrote: i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. No, there is quite an element of truth! You have to compare the thermal mass of the house and the heat loss. If the house had enormous thermal mass, like lots of stone floors and massive stone fireplaces (some people build houses intentionally to have very high thermal mass) then although the furnace could warm the air quickly to make you comfortable, it would still run for hours to warm up all that mass. So what? If you have a lot of thermal mass and low heat loss (good insulation) then turning the thermostat down for a couple hors gives no benefit. If you have low thermal mass and lots of heat loss, then turning it down for even a couple hours will give significant benefit. Jon, with all respect, I must say that you are mistaken here. From the law of conservation of energy, heat input into the house == heat loss from the house The lower is house temperature, the lower is the heat loss. i This is more equations than I care to handle, but a house with very good insulation and high thermal mass is not going to benefit noticeably until the temperature has dropped and stabilized. Otherwise, all you're doing is cycling the cooling and warming of the thermal mass. -- Ed Huntress |
Turn thermostat down?
On Thu, 29 Oct 2009 12:46:13 -0400, "Ed Huntress"
wrote: "Bill Noble" wrote in message ... "Ignoramus10802" wrote in message ... On 2009-10-29, Pete C. wrote: Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. I Correct - whatever the net effect of insulation is, there is a net negative heat flux from the house to the outside. The flux is proportional to the temperature difference (the exact equation will depend on the radiation, convection and conduction components - radiation alone is governed by the Stephan-Boltzman equation). The larger the difference the greater the flux. Averaged over any period of time, any time spent with the thermostat set lower will yeild a lower internal temperature, hence less heat flux. Whether that is enough to show up in your bill is another question, but from a energy savings point of view, it is incontestible. The confounding issue, though, is the thermal mass of the house. That's why the DOE explanation says that the savings occur when the temperature inside the house has stabilized at the lower temperature. When you shut off the furnace, the thermal mass of the inside of the house is what's giving up heat to the outside. That's stored energy that came from the furnace heat. When you raise the temperature, you have to restore that heat to the thermal mass. So with the furnace off and the temperature inside of the house dropping, you're losing stored heat. When you turn the thermostat back on, you have to restore that lost heat, which will also heat up the atmosphere inside of the house (which is a very small portion of the total inside thermal mass). That's what I read from their description, anyway, and it comports with things I've read about it from other sources. There is no (theoretical) net gain or loss when the thermal mass is put through the cycle of cooling down and heating up. The savings occur when the temperature is reduced and stabilized. This all assumes that a house is decently insulated and that the thermal mass of the house is substantial. Of course, the thermal differential between the inside and outside temperatures are always at work, suggesting that there is less heat loss with each degree of reduction of inside temperature, as you say. But the DOE's reference to actual testing agrees with the fact that, as soon as you turn the thermostat down, you begin losing *stored* heat, and when you turn it back up, 100% of that lost heat must be restored, regardless of actual thermal losses through the walls and ceiling. Savings begins the instant inside temperature is reduced, whether or not it is stable at a lower setpoint. This is true regardless of how well the house is insulated, what the thermal mass might be, who the president is, which party controls congress or whether DOE likes it or not. Rate of heat loss at any (and every) instant depends upon temperature gradient from inside to outside. Whether or not the savings on the energy bill is noticable is another question depending on how much the setback was for how long. I wonder how much the DOE spent on a study to address what would be an easy test question in thermodynamics 101. |
Turn thermostat down?
Stormin Mormon wrote:
Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. OK, Stormin, let's have your point of view now. Poll question: How many guys here have wives who mistakenly think that when warming up a cooled down house the rate of temperature change produced by a typical home heating system will be faster if they shove the thermostat setting all the way up to 90F than if they just move it to the appropriate setpoint. Then of course, they forget to reset it when the place reaches a comfortable temperature which some time later causes the man of the house to snarl, "Why the hell is it so damn hot in here?" And visa versa for A/C of course. It can't just only happen to me. G Jeff PS, I realize there may be some HVAC systems (and some wives too of course) which don't conform to the above scenario, but they sure aren't in the majority around here. -- Jeffry Wisnia (W1BSV + Brass Rat '57 EE) The speed of light is 1.8*10e12 furlongs per fortnight. |
Turn thermostat down?
jeff_wisnia wrote: Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. OK, Stormin, let's have your point of view now. Poll question: How many guys here have wives who mistakenly think that when warming up a cooled down house the rate of temperature change produced by a typical home heating system will be faster if they shove the thermostat setting all the way up to 90F than if they just move it to the appropriate setpoint. Then of course, they forget to reset it when the place reaches a comfortable temperature which some time later causes the man of the house to snarl, "Why the hell is it so damn hot in here?" And visa versa for A/C of course. It can't just only happen to me. G Jeff PS, I realize there may be some HVAC systems (and some wives too of course) which don't conform to the above scenario, but they sure aren't in the majority around here. One of my tests for a potential girlfriend is to have here explain how a thermostat operates. Few pass this test of course, but it sure saves a lot of time and money. |
Turn thermostat down?
"Don Foreman" wrote in message ... On Thu, 29 Oct 2009 12:46:13 -0400, "Ed Huntress" wrote: "Bill Noble" wrote in message ... "Ignoramus10802" wrote in message ... On 2009-10-29, Pete C. wrote: Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. I Correct - whatever the net effect of insulation is, there is a net negative heat flux from the house to the outside. The flux is proportional to the temperature difference (the exact equation will depend on the radiation, convection and conduction components - radiation alone is governed by the Stephan-Boltzman equation). The larger the difference the greater the flux. Averaged over any period of time, any time spent with the thermostat set lower will yeild a lower internal temperature, hence less heat flux. Whether that is enough to show up in your bill is another question, but from a energy savings point of view, it is incontestible. The confounding issue, though, is the thermal mass of the house. That's why the DOE explanation says that the savings occur when the temperature inside the house has stabilized at the lower temperature. When you shut off the furnace, the thermal mass of the inside of the house is what's giving up heat to the outside. That's stored energy that came from the furnace heat. When you raise the temperature, you have to restore that heat to the thermal mass. So with the furnace off and the temperature inside of the house dropping, you're losing stored heat. When you turn the thermostat back on, you have to restore that lost heat, which will also heat up the atmosphere inside of the house (which is a very small portion of the total inside thermal mass). That's what I read from their description, anyway, and it comports with things I've read about it from other sources. There is no (theoretical) net gain or loss when the thermal mass is put through the cycle of cooling down and heating up. The savings occur when the temperature is reduced and stabilized. This all assumes that a house is decently insulated and that the thermal mass of the house is substantial. Of course, the thermal differential between the inside and outside temperatures are always at work, suggesting that there is less heat loss with each degree of reduction of inside temperature, as you say. But the DOE's reference to actual testing agrees with the fact that, as soon as you turn the thermostat down, you begin losing *stored* heat, and when you turn it back up, 100% of that lost heat must be restored, regardless of actual thermal losses through the walls and ceiling. Savings begins the instant inside temperature is reduced, whether or not it is stable at a lower setpoint. This is true regardless of how well the house is insulated, what the thermal mass might be, who the president is, which party controls congress or whether DOE likes it or not. Rate of heat loss at any (and every) instant depends upon temperature gradient from inside to outside. The point is that what you're talking about is insignificant in most homes. That's what the DOE statement is all about: cycling of the heat mass overwhelms the effect of the insulation, until the temperature is reduced and stabilized for a while. Otherwise, all you're doing is cycling the heat retention of the thermal mass, with relatively much less actual savings as the temperature drops in the house. Whether or not the savings on the energy bill is noticable is another question depending on how much the setback was for how long. I wonder how much the DOE spent on a study to address what would be an easy test question in thermodynamics 101. Probably enough to know that you learned your thermodynamics with a calculator and a vacuum jar, rather than a house. g I've seen those studies for years, Don, starting with a book I read in the '70s, titled something like _Low-cost, Energy-efficient Shelter_. What the DOE says is widely known. -- Ed Huntress |
Turn thermostat down?
"jeff_wisnia" wrote in message ... Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. OK, Stormin, let's have your point of view now. Poll question: How many guys here have wives who mistakenly think that when warming up a cooled down house the rate of temperature change produced by a typical home heating system will be faster if they shove the thermostat setting all the way up to 90F than if they just move it to the appropriate setpoint. [raises hand] Then of course, they forget to reset it when the place reaches a comfortable temperature which some time later causes the man of the house to snarl, "Why the hell is it so damn hot in here?" [raises sweaty hand] And visa versa for A/C of course. [raises blue, shaking hand] It can't just only happen to me. G Jeff PS, I realize there may be some HVAC systems (and some wives too of course) which don't conform to the above scenario, but they sure aren't in the majority around here. -- Jeffry Wisnia (W1BSV + Brass Rat '57 EE) The speed of light is 1.8*10e12 furlongs per fortnight. -- Ed Huntress |
Turn thermostat down?
On 2009-10-29, Don Foreman wrote:
Savings begins the instant inside temperature is reduced, whether or not it is stable at a lower setpoint. This is true regardless of how well the house is insulated, what the thermal mass might be, who the president is, which party controls congress or whether DOE likes it or not. Rate of heat loss at any (and every) instant depends upon temperature gradient from inside to outside. Very well put. Whether or not the savings on the energy bill is noticable is another question depending on how much the setback was for how long. I wonder how much the DOE spent on a study to address what would be an easy test question in thermodynamics 101. That study might have been a part of economic stimulus. i |
Turn thermostat down?
On 2009-10-29, Pete C. wrote:
One of my tests for a potential girlfriend is to have here explain how a thermostat operates. Few pass this test of course, but it sure saves a lot of time and money. Huge savings on flowers and condoms, too. i |
Turn thermostat down?
"Ignoramus10802" wrote in message ... On 2009-10-29, Don Foreman wrote: Savings begins the instant inside temperature is reduced, whether or not it is stable at a lower setpoint. This is true regardless of how well the house is insulated, what the thermal mass might be, who the president is, which party controls congress or whether DOE likes it or not. Rate of heat loss at any (and every) instant depends upon temperature gradient from inside to outside. Very well put. But it has little to do with the question of whether you get any significant energy savings from turning down the thermostat for relatively short periods of time. Again, if you shut it down for eight hours and the temperature drops, say, 12 - 15 degrees F (typical for my house), you will spend hours waiting for the temperature to climb back up -- and (you do the calculus, not me g) the benefit you get from it is LESS than the theoretical savings you would have if you lived in a vacuum bottle and the temperature had dropped only 6 or 7 degrees for all of that time. Meanwhile, you're freezing your butt off, part of the time at close to 12 degrees lower than your regular setting. Are we together on this, Dr. Algebra? Whether or not the savings on the energy bill is noticable is another question depending on how much the setback was for how long. I wonder how much the DOE spent on a study to address what would be an easy test question in thermodynamics 101. That study might have been a part of economic stimulus. You guys had better figure in thermal mass and look up some values for thermal mass versus R-values in a typical house. The calculation is not as simple as you make it out to be. For a short time, as DOE says, the saving is trivial. -- Ed Huntress |
Turn thermostat down?
"Ignoramus10802" wrote in message ... On 2009-10-29, Pete C. wrote: One of my tests for a potential girlfriend is to have here explain how a thermostat operates. Few pass this test of course, but it sure saves a lot of time and money. Huge savings on flowers and condoms, too. i My test was whether she could double-clutch a racing crash box transmission -- or if she was teachable and wanted to learn. -- Ed Huntress |
Turn thermostat down?
On Oct 29, 2:59*pm, jeff_wisnia
wrote: How many guys here have wives who mistakenly think that when warming up a cooled down house the rate of temperature change produced by a typical home heating system will be faster if they shove the thermostat setting all the way up to 90F than if they just move it to the appropriate setpoint. |
Turn thermostat down?
Ed Huntress wrote:
"Ignoramus10802" wrote in message ... On 2009-10-29, ATP* wrote: True. Yet I still hear this type of "reasoning" all the time. Should be a simple concept even for the technically challenged, for example, people who argued here that you can compress air and allow it to expand (while doing no useful work) with no loss of energy. That would be almost possible if compressing and expanding was done very quickly, before compressed air cools. i But it has to be done *awfully* quickly. That's why there's a minimum cylinder size for diesel engines -- something like 300 cc. Below 3,000 rpm or so, the compressed air cools too quickly to ignite the fuel. And heat transfer gets worse as compression goes up. That statement may not be entirely correct, Ed. Remembering waaaay back to my childhood playing around with control line model aircraft. before the glow plug engine was developed we had but two choices, conventional spark plug engines and diesel engines. The diesels were never very popular, but they are still being made for thos who want to add a bit of "authenticity" to replicas of vintage model aircraft. Those are surely far below 300 cc, but the fuel they burn may not be quite the same as what cars and trucks use. G http://www.eifflaender.com/enginepics.htm I also remember my not terribly successful efforts at flying RC models back then. My ham ticket let me do that legally on 28 Mhz (the 10 meter ham band) using a one tube receiver in the plane which triggered a rubber band energized "escapement" that moved a combination rudder-stabilizer at the rear of the plane. How the heck I just remembered that the tube used in those receivers was an RK61, a gas filled triode, I'll never understand. http://tubedata.milbert.com/sheets/138/r/RK61.pdf Thaks for the mammaries though. Jeff -- Jeffry Wisnia (W1BSV + Brass Rat '57 EE) The speed of light is 1.8*10e12 furlongs per fortnight. |
Turn thermostat down?
On 2009-10-29, Ed Huntress wrote:
"Ignoramus10802" wrote in message ... On 2009-10-29, Don Foreman wrote: Savings begins the instant inside temperature is reduced, whether or not it is stable at a lower setpoint. This is true regardless of how well the house is insulated, what the thermal mass might be, who the president is, which party controls congress or whether DOE likes it or not. Rate of heat loss at any (and every) instant depends upon temperature gradient from inside to outside. Very well put. But it has little to do with the question of whether you get any significant energy savings from turning down the thermostat for relatively short periods of time. Again, if you shut it down for eight hours and the temperature drops, say, 12 - 15 degrees F (typical for my house), you will spend hours waiting for the temperature to climb back up -- and (you do the calculus, not me g) the benefit you get from it is LESS than the theoretical savings you would have if you lived in a vacuum bottle and the temperature had dropped only 6 or 7 degrees for all of that time. Meanwhile, you're freezing your butt off, part of the time at close to 12 degrees lower than your regular setting. Are we together on this, Dr. Algebra? Sure. Savings would be there, t possibly too small to overcome inconvenience. The solution to this has been well known and it is thermostats with a time schedule function. Whether or not the savings on the energy bill is noticable is another question depending on how much the setback was for how long. I wonder how much the DOE spent on a study to address what would be an easy test question in thermodynamics 101. That study might have been a part of economic stimulus. You guys had better figure in thermal mass and look up some values for thermal mass versus R-values in a typical house. The calculation is not as simple as you make it out to be. For a short time, as DOE says, the saving is trivial. Yes, but it is still there, which is the point. i |
Turn thermostat down?
On Thu, 29 Oct 2009 12:46:13 -0400, "Ed Huntress"
wrote: "Bill Noble" wrote in message ... "Ignoramus10802" wrote in message ... On 2009-10-29, Pete C. wrote: Ignoramus10802 wrote: On 2009-10-29, Stormin Mormon wrote: Please forgive me while I troll for a moment..... Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway. Imagine for a minute that you have to leave house for a month. Would it be energy efficient to turn thermostat down? Of course, as less heat will be produced for a whole month, with only a few minutes to catch up. The same applies to only one day. i It's far more complicated than that. Factors such as insulation / heat loss, type of heating, multi-stage heating, electric backup heat on heat pumps, etc. all come into play in determining the away duration and temp reduction where savings begin, and in some cases (typically high efficiency homes) it can require a multi day absence to see any savings. This is patently untrue. I Correct - whatever the net effect of insulation is, there is a net negative heat flux from the house to the outside. The flux is proportional to the temperature difference (the exact equation will depend on the radiation, convection and conduction components - radiation alone is governed by the Stephan-Boltzman equation). The larger the difference the greater the flux. Averaged over any period of time, any time spent with the thermostat set lower will yeild a lower internal temperature, hence less heat flux. Whether that is enough to show up in your bill is another question, but from a energy savings point of view, it is incontestible. The confounding issue, though, is the thermal mass of the house. That's why the DOE explanation says that the savings occur when the temperature inside the house has stabilized at the lower temperature. When you shut off the furnace, the thermal mass of the inside of the house is what's giving up heat to the outside. That's stored energy that came from the furnace heat. When you raise the temperature, you have to restore that heat to the thermal mass. So with the furnace off and the temperature inside of the house dropping, you're losing stored heat. When you turn the thermostat back on, you have to restore that lost heat, which will also heat up the atmosphere inside of the house (which is a very small portion of the total inside thermal mass). That's what I read from their description, anyway, and it comports with things I've read about it from other sources. There is no (theoretical) net gain or loss when the thermal mass is put through the cycle of cooling down and heating up. The savings occur when the temperature is reduced and stabilized. The furnace is supplying an average of so many BTU when it is running (assuming the usual on/off type of furnace). The house is losing so many BTU when it is at temperature T0 inside, and the losses will always Be LESS when the temperaure is closer to the outside temperature (assumed to be lower, of course). When the house is cooling, the thermal mass is supplying part of the heat to the outside. When the house is heating up, the furnace is supplying heat to warm the thermal mass, PLUS the heat which is being lost to the outside. The heat lost to the outside during the cooling *that is supplied by the thermal mass* is made up for that part of the heat supplied by the furnace to heat the house back to T0, so that part IS a wash. What's missing is that for for every second the house is at a lower temperature than T0, the heat loss to the outside is less, so even if it cools down and immediately is heated up there will be an energy saving. If it was linear (which it isn't, but bear with me) then say the outside temperature was 25F and the internal temperature was 75F. The loss is k*(75-25) = k*50, where k is a constant. Now allow the house to cool to 50F over an hour, then heat it back up again to 75F over another hour. The heat loss to the outside during that time is k*(62.5-25) = 37.5*k, which is 25% less (62.5F is the *average* inside temperature over those two hours). Chances are the heat loss is actually worse than linear (convection and radiation are worse, and conduction is linear), so this should be conservative. Now if it's 25% of 2/24 of a day, that's not very much (about 2% saving) but it is going to be a saving. This all assumes that a house is decently insulated and that the thermal mass of the house is substantial. Of course, the thermal differential between the inside and outside temperatures are always at work, suggesting that there is less heat loss with each degree of reduction of inside temperature, as you say. But the DOE's reference to actual testing agrees with the fact that, as soon as you turn the thermostat down, you begin losing *stored* heat, and when you turn it back up, 100% of that lost heat must be restored, regardless of actual thermal losses through the walls and ceiling. Yes, that *part* of it is a wash. |
Turn thermostat down?
On Oct 29, 8:22*pm, "Ed Huntress" wrote:
I've seen those studies for years, Don, starting with a book I read in the '70s, titled something like _Low-cost, Energy-efficient Shelter_. What the DOE says is widely known. -- Ed Huntress What the DOE says is widely known, but incorrect. Don has explained the problem correctly. Thermal mass and insulation determine the thermal time constant, which affects how much saving results. But has no effect on whether there is a savings. As Pete C. points out there are some heating systems that change efficiency depending on the demand. Heat pumps are one case. Another case is modulating furnaces. These will be less efficient at higher loads. But the common furnace located in a non heated area, will be somewhat more efficient as the furnace will run for a longer time before shutting off and loosing heat to the unheated area. Dan |
Turn thermostat down?
On Thu, 29 Oct 2009 15:59:36 -0400, jeff_wisnia
wrote: Poll question: How many guys here have wives who mistakenly think that when warming up a cooled down house the rate of temperature change produced by a typical home heating system will be faster if they shove the thermostat setting all the way up to 90F than if they just move it to the appropriate setpoint. One minute of this video http://www.youtube.com/watch?v=TbMmj5YZ8-U, commencing at 2:47, explains everything. As for the poll, *my* wife understands how most thermostats operate, and she had a good laugh when we watched that episode of Peep Show. Watch the whole episode if you want to see a really good poem about GWB. Wayne |
Turn thermostat down?
wrote in message ... On Oct 29, 8:22 pm, "Ed Huntress" wrote: I've seen those studies for years, Don, starting with a book I read in the '70s, titled something like _Low-cost, Energy-efficient Shelter_. What the DOE says is widely known. -- Ed Huntress What the DOE says is widely known, but incorrect. Don has explained the problem correctly. Thermal mass and insulation determine the thermal time constant, which affects how much saving results. But has no effect on whether there is a savings. As Pete C. points out there are some heating systems that change efficiency depending on the demand. Heat pumps are one case. Another case is modulating furnaces. These will be less efficient at higher loads. But the common furnace located in a non heated area, will be somewhat more efficient as the furnace will run for a longer time before shutting off and loosing heat to the unheated area. Dan Hot water reset systems also operate at higher efficiency if the demand is lower, since the water temperature is reduced, resulting in a greater delta t in the boiler and more efficient heat transfer. With the right insulation and very limited air changes a steady state high efficiency heating plant without a setback might be more efficient. But very few residential systems operate like that. |
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