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#348433 - 25/10/2011 21:06 Re: Nest Thermostat [Re: altman]
DWallach
carpal tunnel

Registered: 30/04/2000
Posts: 3728
Originally Posted By: altman
It is square, with a round bezel. Real round ones exist, but they cost.

Disclosure: I worked on that product too smile

You mean you worked on the Nest thermostat? Do tell!

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#348437 - 25/10/2011 21:33 Re: Nest Thermostat [Re: hybrid8]
Dignan
carpal tunnel

Registered: 08/03/2000
Posts: 12157
Loc: Sterling, VA
Originally Posted By: hybrid8
Just in case I misunderstood, the "typical" system I'm describing here has the furnace and AC coil ("the furnace") is in the basement and the AC evaporator somewhere outside. With basement ducts and 1st floor ducts in the basement ceiling. Then second floor ducts in the 1st floor ceiling. That means heat/cool come to the first and second floors via vents in each respective floor. This is what I understood that you were describing about your own system.

What I was saying about my system is that there is duct work only in-between our floors. So if you're on the first floor, the ducts are in the ceiling. If you're on the second floor, the ducts are in the floor. That's what I meant was a dumb design, and unlike other places I've lived.
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#348439 - 25/10/2011 22:00 Re: Nest Thermostat [Re: Dignan]
hybrid8
carpal tunnel

Registered: 12/11/2001
Posts: 7738
Loc: Toronto, CANADA
Ah! Gotcha. That's exactly backwards from what I have. What I described is what I meant is used in most homes around here, and I suspect a great many in the US as well. At least in places that use forced air.
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Bruno
Twisted Melon : Fine Mac OS Software

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#348441 - 25/10/2011 23:55 Re: Nest Thermostat [Re: Dignan]
tanstaafl.
carpal tunnel

Registered: 08/07/1999
Posts: 5403
Loc: Ajijic, Mexico
Originally Posted By: Dignan
We have two floors, with a thermostat on the first floor, and duct work in-between the levels. This is an awful design.
Yes.

My house in Alaska was very efficiently heated (we didn't concern ourselves too much with cooling. smile ) My heating bills were dramatically less than other people with similar sized homes -- sometimes by a factor of ten or more. I knew people whose heating bills in the coldest part of winter might run them as much as two or three thousand dollars in a single month.

My system was hot water baseboard with two "special" aspects. First, the boiler was a German unit made by Buderas. Buderas is unique in that they vary the boiler temperature depending on outside temperature, so instead of keeping my boiler at 190 degrees (F) all the time, it might run at 110 degrees if the outside temperature was, say, 40 degrees. Buderas claims, and I have no reason to doubt them, that they will put the same number of BTUs into a home as a conventional system, but at 75% of the fuel consumption.

The second thing that made my heating system efficient is that I had seven separate and distinct heating zones, controlled by seven thermostats. All of my interior walls were insulated, so rooms I wasn't using (big house, I was there by myself) I kept at about 40 degrees in the winter time. Of course all the outside walls were 6", heavily insulated, all the windows were triple pane glass. Entry was through the garage which was semi-heated by whatever heat leaked through the wall to the living/dining room. At 40 below zero outside temperature, the garage would drop down to about zero degrees, which is no problem with a properly prepared Alaskan car.

All in all, I had a pretty efficient house.

tanstaafl.


Attachments
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#348446 - 26/10/2011 01:34 Re: Nest Thermostat [Re: hybrid8]
Dignan
carpal tunnel

Registered: 08/03/2000
Posts: 12157
Loc: Sterling, VA
Originally Posted By: tanstaafl.
The second thing that made my heating system efficient is that I had seven separate and distinct heating zones, controlled by seven thermostats. All of my interior walls were insulated, so rooms I wasn't using (big house, I was there by myself) I kept at about 40 degrees in the winter time. Of course all the outside walls were 6", heavily insulated, all the windows were triple pane glass. Entry was through the garage which was semi-heated by whatever heat leaked through the wall to the living/dining room. At 40 below zero outside temperature, the garage would drop down to about zero degrees, which is no problem with a properly prepared Alaskan car.

You don't mention it specifically, but given the number of zones and my limited knowledge about what I see in that photo, am I correct in guessing you had radiant heating? One day I would LOVE to have radiant heating. THAT'S an efficient way to heat a house. You can heat the rooms you want, the heat stays nice and low where the people are, and in the winter you walk on nice warm floors.

Originally Posted By: hybrid8
Ah! Gotcha. That's exactly backwards from what I have. What I described is what I meant is used in most homes around here, and I suspect a great many in the US as well. At least in places that use forced air.

Indeed, that's why my system is so f'ed up. We have ~9'-10' ceilings. If all my registers are open in the winter, it means that the first floor is being heated from the top-down, which is stupid because the heat takes forever to fall to where the people (and the thermostat) are, and it's primarily the top of the room that's getting the heat, which is very inefficient. Meanwhile, the top floor is being continually heated from the proper direction, but it keeps heating far past the point it needs to because the first floor hasn't warmed up enough.

Sorry, I really hate our system...


Edited by Dignan (26/10/2011 01:35)
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#348450 - 26/10/2011 02:15 Re: Nest Thermostat [Re: tanstaafl.]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 14119
Loc: Canada
Originally Posted By: dignan
am I correct in guessing you had radiant heating?

Originally Posted By: tanstaafl.
My system was hot water baseboard


So, yeah, radiant heat.
Not "in floor", but radiant nonetheless.

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#348451 - 26/10/2011 02:23 Re: Nest Thermostat [Re: mlord]
Dignan
carpal tunnel

Registered: 08/03/2000
Posts: 12157
Loc: Sterling, VA
Originally Posted By: mlord
Originally Posted By: dignan
am I correct in guessing you had radiant heating?

Originally Posted By: tanstaafl.
My system was hot water baseboard

So, yeah, radiant heat.
Not "in floor", but radiant nonetheless.

Oops, missed that...
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Matt

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#348462 - 26/10/2011 04:18 Re: Nest Thermostat [Re: canuckInOR]
Roger
carpal tunnel

Registered: 18/01/2000
Posts: 5620
Loc: London, UK
Originally Posted By: canuckInOR
The pictures don't show a dismantled view.


Yeah, you're right. The picture in the engadget link shows a round device in the guy's hand, which threw me. Looking more closely, the bezel leaves plenty of room for a square device inside, though...

Still looks really nice, though.
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#348464 - 26/10/2011 06:18 Re: Nest Thermostat [Re: Roger]
Cris
pooh-bah

Registered: 06/02/2002
Posts: 1896
Loc: Leeds, UK
So will this work in the UK ???

Living on my own as I do at the moment, and being a man, I don't tend to touch the thermostat. But with a chance of circumstance just around the corner I like the idea of keeping costs as low as possible.

Cheers

Cris

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#348465 - 26/10/2011 07:11 Re: Nest Thermostat [Re: Dignan]
BartDG
carpal tunnel

Registered: 20/05/2001
Posts: 2595
Loc: Bruges, Belgium
Originally Posted By: Dignan

You don't mention it specifically, but given the number of zones and my limited knowledge about what I see in that photo, am I correct in guessing you had radiant heating? One day I would LOVE to have radiant heating. THAT'S an efficient way to heat a house. You can heat the rooms you want, the heat stays nice and low where the people are, and in the winter you walk on nice warm floors.

We paid a lot of attention to our choice of heating system when we built our house. We ended up choosing a Geothermal heat pump system. (which is effectively the same technology you'll find in a refrigerator, but then reversed) This effectively means three holes of 100 meters deep were drilled in our garden, in each of which four tubes were put. (vertical ground loops) The tubes were connected to each other prior of being put inside the ground, effectively making for a 400 meters long circuit inside the ground. Then the three circuits were connected to each other, resulting in a circuit of 1200 meters. After the tubes were put into the ground, a cement compound was injected into the drilled holes, so nothing would ever touch the tubes.

In-house, floor heating was put everywhere throughout the house. Then, the tubes were filled with water, with a bit of glycol added to it.
The system is as simple as it is brilliant. Water flows through the underground conducts, effectively reaching the temperature of the earth at that specific depth, which is always about 6 to 10 C (40 - 50 F). That water then gets compressed by the heat pump, which effectively raises the temperature of the water. One circuit is heated up to about 30 - 35 C (85 - 95F) and flows through the heating tubes under the floors. This is more than enough to heat up the whole house to a nice comfortable temperature of 20 - 24 C (70 - 80F), or more if necessary (like in the bathroom). The other circuit is heated up to 55 C (130 F) and is stored in a 180 litre boiler for hot tap water. I had my doubts in the beginning that 55 degrees would be enough, but it turned out to be MORE than adequate, to bathe, to do the dishes, anything you need it for really.

Of course, this system works best when the house is insulated VERY good, which is what we did: 10 cm (about 4 inches) of the most efficient polyurethane insulation, which works very good. (in total, our walls are about 40 cm thick - all brick).

This system has a high startup costs because of all the materials that are needed (LOTS of tubes!), and the drilling of the holes also doesn't come cheap. But after that, you get a system which is very efficient. The heating pump works electrical, so obviously my electrical bill goes up. BUT... I do not use gas, diesel, wood or any other of the classical combustible fuels. That's why our house also does not have a chimney. Absolutely NO risk of CO intoxication or fire hazard, since no fire is involved in producing this heat. (our fire/home insurance loves this, and this is reflected greatly in our annual bill!) My monthly electrical bill is about the same as what my neighbour pays... but mine includes my heating and hot tap water production: his does not. The system is also maintenance free for its entire life cycle. (which is about 25 years)
Another big benefit: in the summer, the system can be reversed and the floor heating can actually be used to cool the house, at a fraction of the cost of what air-conditioning would cost me. (since the water is cooled via the earth) This works VERY well and I would want to be without it any more. Last summer, when the outside temperature was about 30-35 (85-95) degrees for weeks, this system had no trouble of keeping our house at a steady 20 - 21 degrees (68 - 70 F)... at only the cost of a circulation pump of a few watts that needed to run.

This system is essentially capable of keeping our house at a more or less constant temperature of 21 degrees all year long, at about half the price of what gas or diesel would have cost me. I never need to worry about setting the thermostat or turning the heat off when I leave the house: the system is always running because it would consume more energy when I would turn it on/off all the time then to simply let it run at a constant temperature (again, the refrigerator analogy). Since the heat is radiant floor heating, it's a very pleasant and comfortable heat as well.

You can see some pics here of the holes getting drilled and the setup. This is not our house, but these people worked with the same firm as we did, so the used method is identical (in fact, the workers on the photos are the same who did the drilling at our place smile.

We simply LOVE this system and are very happy we ended up choosing it. It also takes a lot of the stress off because once it's paid for, there's no need to fear the 'dreaded monthly heating bill' any more.
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#348466 - 26/10/2011 07:18 Re: Nest Thermostat [Re: Cris]
andy
carpal tunnel

Registered: 10/06/1999
Posts: 5797
Loc: Wivenhoe, Essex, UK
Originally Posted By: Cris

Living on my own as I do at the moment, and being a man, I don't tend to touch the thermostat.


So I'm not the only person in the world whose partner believes a thermostat is an on off switch then ?

"I've turned it to 25, so that the house warms up quicker" frown

I have finally managed to convince Eryl that the oven temperature dial isn't a switch, but convincing her that the same applies to the heat thermostat is a work in progress wink
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#348467 - 26/10/2011 09:32 Re: Nest Thermostat [Re: Cris]
sein
old hand

Registered: 07/01/2005
Posts: 890
Loc: Sector ZZ9pZa
Originally Posted By: Cris
So will this work in the UK ???

Its not going to work in the UK out of the box as it is designed for 24V AC North American HVAC systems.

It seems to be able to control from Single Stage Heating up to 2-Stage Heating, Cooling and Ventilation.

I have put together a reasonably simple 24V AC Transformer and Relay fitted in a small enclosure which should allow the Nest to control common heating systems in the UK (and will hopefully offer more relays for people who have air conditioning systems and home ventilation / heat recovery systems). I hope to be offering these through my company pre-wired, labelled and with full instructions for getting it working here - just waiting on my pre-ordered Nest to arrive and make sure I get it working as expected and have everything in place to offer it here as a kit. There are still some details to work out (have contacted Nest yesterday, hopefully speak to them again today), but watch this space.
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#348468 - 26/10/2011 11:00 Re: Nest Thermostat [Re: wfaulk]
frog51
pooh-bah

Registered: 09/08/2000
Posts: 2091
Loc: Edinburgh, Scotland
Originally Posted By: wfaulk
...inflatable bladder...pneumatic tubing...a big fan...a long piece of string, and a small "parachute".


Reminds me of this sequence from Brazil
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MkIIa, blue lit buttons, memory upgrade, 1Tb in Subaru Forester STi
MkII, 240Gb in Mark Lord dock
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#348469 - 26/10/2011 11:10 Re: Nest Thermostat [Re: andy]
frog51
pooh-bah

Registered: 09/08/2000
Posts: 2091
Loc: Edinburgh, Scotland
Originally Posted By: andy
So I'm not the only person in the world whose partner believes a thermostat is an on off switch then ?


I use it as an on-off switch: turn it below 15 for the summer so we don't use it from April to September then back up to 18 or 19 for the winter.

Simples. And we just have one thermostat, in the main hall, but at least I do have a timer so it comes on in the morning and evening for hot water for the showers.

Somtimes I'm quite glad we don't need to think about aircon in this country :-)
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MkIIa, blue lit buttons, memory upgrade, 1Tb in Subaru Forester STi
MkII, 240Gb in Mark Lord dock
MkII, 80Gb SSD in dock

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#348472 - 26/10/2011 11:51 Re: Nest Thermostat [Re: andy]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 14119
Loc: Canada
Originally Posted By: andy
"I've turned it to 25, so that the house warms up quicker" frown

That one sounds like a great dumb line, but in fact is true. The house does warm up more quickly on a higher temperature setting than on a lower one, at least with forced air systems.

The reason is thermal mass. At a 20C setting, the furnace heats up the air to 20-21C, then turns off. The air quickly chills back to 17C as the cold walls/floors absorb the heat, and then the furnace comes back on again 5-10 minutes later to repeat the cycle.

Setting it to 25C gives a single long blast of warmth, enough to get the walls/contents of the house closer to 20C in one go, after which one sets the thermostat back down to 20C.

Cheers

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#348474 - 26/10/2011 12:00 Re: Nest Thermostat [Re: mlord]
andy
carpal tunnel

Registered: 10/06/1999
Posts: 5797
Loc: Wivenhoe, Essex, UK
That might apply to forced air systems, it certainly doesn't to any radiator based system I've ever used.

I've never come across a forced air system in the UK, radiators are what you get in 99% (made up statistic) of UK homes.
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#348475 - 26/10/2011 12:07 Re: Nest Thermostat [Re: andy]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 14119
Loc: Canada
Yeah, especially with older cast iron radiators. Good system, that was.

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#348476 - 26/10/2011 12:13 Re: Nest Thermostat [Re: andy]
hybrid8
carpal tunnel

Registered: 12/11/2001
Posts: 7738
Loc: Toronto, CANADA
The homes in Canada are made out of kindling and papier-mch, everything is hollow, so it's easy to install forced air systems. wink
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Bruno
Twisted Melon : Fine Mac OS Software

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#348479 - 26/10/2011 12:18 Re: Nest Thermostat [Re: hybrid8]
andy
carpal tunnel

Registered: 10/06/1999
Posts: 5797
Loc: Wivenhoe, Essex, UK
And they were mostly built after modern heating systems were invented wink
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#348480 - 26/10/2011 12:18 Re: Nest Thermostat [Re: mlord]
wfaulk
carpal tunnel

Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
It's kinda more efficient to keep the house at the same temperature all the time in order to avoid that situation.
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#348481 - 26/10/2011 12:56 Re: Nest Thermostat [Re: wfaulk]
tanstaafl.
carpal tunnel

Registered: 08/07/1999
Posts: 5403
Loc: Ajijic, Mexico
Originally Posted By: wfaulk
It's kinda more efficient to keep the house at the same temperature all the time in order to avoid that situation.
Not so.

The only reason you put heat in a house at all is to replace the heat that has been lost through radiation, either into the ground or into the air surrounding the house.

The amount of heat lost through radiation is proportional to the fourth power of the difference in temperature (in degrees Kelvin) between the radiating body and the outside source that is absorbing the heat. Lessening this difference greatly reduces the amount of heat loss.

It is more efficient to minimize this difference whenever practical by allowing the house be cool (or in my Alaskan example, downright cold) when not in use.

tanstaafl.
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#348482 - 26/10/2011 13:08 Re: Nest Thermostat [Re: BartDG]
tanstaafl.
carpal tunnel

Registered: 08/07/1999
Posts: 5403
Loc: Ajijic, Mexico
Originally Posted By: Archeon
This system has a high startup costs...
If you don't mind my asking, what did your system cost?

Also, what are the climate conditions where you live, how cold in the winter, how warm in the summer?

My system was very expensive to install, but most of the expense was labor since it was replacing impossibly costly to operate electric baseboard heat, which meant that they had to knock holes through walls and floors/ceilings, and install many hundreds of feet of copper pipe, make more holes to run the wiring for the thermostats, etc. All of this in a 20-year-old house while people were living in it. Ugly... And that Buderas furnace wasn't cheap, either. But there really was no option. Had I continued with electric resistance heating, the house would have been literally unsalable. I saw the real estate crisis coming and knew I had to get out before the crash, and in Alaska nobody would even look at an electrically heated house.

My installation, parts, labor, and repair of demolition required for running the pipes came to about $23,000.

tanstaafl.
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#348487 - 26/10/2011 13:33 Re: Nest Thermostat [Re: wfaulk]
mlord
carpal tunnel

Registered: 29/08/2000
Posts: 14119
Loc: Canada
Originally Posted By: wfaulk
It's kinda more efficient to keep the house at the same temperature all the time in order to avoid that situation.

Err, no, it isn't. Major fuel/cost savings from turning the heat way down during nights.

Cheers

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#348488 - 26/10/2011 13:56 Re: Nest Thermostat [Re: tanstaafl.]
peter
carpal tunnel

Registered: 13/07/2000
Posts: 4153
Loc: Cambridge, England
Originally Posted By: tanstaafl.
The only reason you put heat in a house at all is to replace the heat that has been lost through radiation, either into the ground or into the air surrounding the house.

The amount of heat lost through radiation is proportional to the fourth power of the difference in temperature (in degrees Kelvin) between the radiating body and the outside source that is absorbing the heat. Lessening this difference greatly reduces the amount of heat loss.

Most heat loss into the air, and all heat loss into the ground (unless the ground near you is transparent to far IR, which it isn't) is through convection or conduction respectively -- not radiation. Energy flow through both convection and conduction goes linearly with the temperature difference, not to the fourth power. But even so, I think your actual point still stands...

Peter

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#348490 - 26/10/2011 14:12 Re: Nest Thermostat [Re: tanstaafl.]
BartDG
carpal tunnel

Registered: 20/05/2001
Posts: 2595
Loc: Bruges, Belgium
Originally Posted By: tanstaafl.
Originally Posted By: Archeon
This system has a high startup costs...
If you don't mind my asking, what did your system cost?

About 38.000 euro, of which 12.000 euro for the drilling alone. But the government was kind enough to subsidize about 9000 euro of the total, so it cost me about 29.000 euro. This could have been 3000 euro less even if I had been smart enough to have a heat-loss calculation done beforehand. As it is now, our heat pump is a 12Kw model. I'm pretty sure though that, because of the good insulation we had installed, a 6Kw model would have been sufficient. This 6Kw model is 3000 euro cheaper.
Also. This system is heating about 320 square meters of space.
Originally Posted By: tanstaafl.

Also, what are the climate conditions where you live, how cold in the winter, how warm in the summer?

Summers have temperatures of up 35 to 40 degrees - 95 to 105F (40 being rather exceptional), winters go from minus 10 to minus 15 - 15 to 5 F (again, 15 being rather exceptional). The humudity is also pretty high here, making the heat in the summer pretty unbearable.
Originally Posted By: tanstaafl.

My system was very expensive to install, but most of the expense was labor since it was replacing impossibly costly to operate electric baseboard heat, which meant that they had to knock holes through walls and floors/ceilings, and install many hundreds of feet of copper pipe, make more holes to run the wiring for the thermostats, etc. All of this in a 20-year-old house while people were living in it. Ugly... And that Buderas furnace wasn't cheap, either. But there really was no option. Had I continued with electric resistance heating, the house would have been literally unsalable. I saw the real estate crisis coming and knew I had to get out before the crash, and in Alaska nobody would even look at an electrically heated house.

My installation, parts, labor, and repair of demolition required for running the pipes came to about $23,000.

I don't know how long it's been since you had that 'upgrade' done, but I can tell you take the cost of parts has gone up tremendously since the year 2000. Most things have doubled in price, sometimes even tripled. Same with the labour costs. Some of those workers are not ashamed to charge you 50 euro/hour ex. VAT! At those prices, if they show up with two, work 8 hours and have two days of work, they easily charge you MORE than most people make in a MONTH! In labour alone! I don't think this is very reasonable anymore, but what can you do? I do know that people won't be able to cope with these ever increasing prices much longer. At the rate this goes, my kids will not be able to build their own house any more (unless they do everything themselves).

And Buderus is really a high quality brand. They make heat pumps as well, but we decided to go with Nibe instead, since heat pus are Nibe's core market.
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#348491 - 26/10/2011 14:13 Re: Nest Thermostat [Re: tanstaafl.]
wfaulk
carpal tunnel

Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
There are several things wrong with your assessment. First, far more heat is lost through conduction than radiation: the outside air touching your house, especially your windows. Second, you fail to take into account the energy required to reheat the walls, which have far more mass than the air in the house. If you're reheating the walls every afternoon when you get back from work, rather than minimizing the temperature difference between the walls and the (interior) air.

I'll admit that these calculations may be very different in significantly colder climates.
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#348492 - 26/10/2011 14:43 Re: Nest Thermostat [Re: wfaulk]
BartDG
carpal tunnel

Registered: 20/05/2001
Posts: 2595
Loc: Bruges, Belgium
I agee with Bitt: if your house is well insulated, and you are using a radiant heat solution, then it will definitively be cheaper to just set it at a constant temperature and forget it than to switch it on and off all the time. The energy needed to re-heat the cooled off mass of the house is enormous.

This of course does not apply if you have a non-brick, badly insulated and heated by forced air systems/radiators house.
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#348496 - 26/10/2011 16:01 Re: Nest Thermostat [Re: wfaulk]
peter
carpal tunnel

Registered: 13/07/2000
Posts: 4153
Loc: Cambridge, England
Originally Posted By: wfaulk
I'll admit that these calculations may be very different in significantly colder climates.

I don't think the actual temperature difference matters. Look at it from a conservation of energy viewpoint: the total heat lost from the house to its environment (by conduction and convection) must equal the total heat produced by the heating system, as (effectively) none of it goes anywhere else.

And if you keep your house heated the whole time, the steady state is when the inside surface of your walls is at room temperature all the time. This means that the temperature difference measured across your walls is always as high as possible (for it to be any higher, the inside surface would have to be above room temperature, which never happens).

But the heat flow (heat loss) is proportional to the temperature difference across the wall. So heat flow, under this plan, is always at maximum, 24 hours a day. Which means that any other plan -- even letting the house cool down for only an hour before turning the heat back on -- causes less heat flow into the environment, and thus less heat production by the heating system, and thus lower bills.

The energy needed to reheat the walls, while no doubt a lot, is not as much as the energy needed to keep them permanently warm.

Peter

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#348497 - 26/10/2011 16:44 Re: Nest Thermostat [Re: wfaulk]
tanstaafl.
carpal tunnel

Registered: 08/07/1999
Posts: 5403
Loc: Ajijic, Mexico
Originally Posted By: wfaulk
There are several things wrong with your assessment. First, far more heat is lost through conduction than radiation: the outside air touching your house, especially your windows. Second, you fail to take into account the energy required to reheat the walls, which have far more mass than the air in the house. If you're reheating the walls every afternoon when you get back from work, rather than minimizing the temperature difference between the walls and the (interior) air.
Let me re-state it more simply.

No matter if you lose heat through conduction or radiation or just leaving your windows open, your heating system must replace whatever heat you lose. The amount of heat you lose depends entirely on the difference in temperature between your house (the heat source) and the outside (the heat sink). Think about it. If you were keeping your house at 70 degrees, and it was 70 degrees outside, you would lose no heat at all. It is temperature differential and nothing else that determines heat loss.

You are correct that the walls have more thermal mass, but that is irrelevant. All that matters is how much heat is lost to the outside. The warmer the air inside, the more heat that will radiate be conducted outside and have to be replaced. [Yes, you and Peter are quite correct about the conduction vs radiation issue. For whatever reason I didn't think about the outside air actually touching the house. blush )

It is astonishing (and rather appalling) to put this question to Google and see the amount of misinformation out there being propagated as fact. Even a slight knowledge of thermodynamics (all that I have) proves that any opportunity to lower your in-house temperature saves heating cost.

tanstaafl.
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#348499 - 26/10/2011 17:22 Re: Nest Thermostat [Re: peter]
wfaulk
carpal tunnel

Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
If you were heating your house with room temperature air, I totally agree. But I think because you're heating air to well above the target temperature, you're losing a lot of efficiency.

Argh. I'd really like to do some math and figure this out, but I just don't have the time right now. Things that may need to be taken into account are the amount of energy it takes to heat air vs. walls and temperature differences between outside, inside, and heated air.
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Bitt Faulk

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