Calculation of inertia and lower heating requirements

Heating, insulation, ventilation, VMC, cooling ... short thermal comfort. Insulation, wood energy, heat pumps but also electricity, gas or oil, VMC ... Help in choosing and implementation, problem solving, optimization, tips and tricks ...
crashback
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by crashback » 08/04/10, 22:16

Hi everybody!

Apparently everyone agrees with his:
the inertia should be seen as a buffer tank that smooths the temperature variations providing additional comfort.

There, in mid-season, it can be important to have the capacity to passively store this solar energy and benefit from it in the evening and until the morning (without having to restart the heating).


But if the heat that I store in my walls with good inertia I restore it at night, my temperature when I do not heat will be higher than temperature with walls with bad inertia (since the heat will be distributed outside). So when I start heating again I will consume less if my non-heating temperature is higher so I will make money.

So 4th question: how with the value of inertia I can know my non-heating temperature at night when my temperature when I stop heating is 20 ° C and outside 9 ° C?

You seem to have replaced the brick with thick polystyrene and therefore the heat takes 9 days, which seems high to me, because the defects (cladding and others) will short-circuit it.


I did not replace the brick with polystyrene I added polystyrene in external insulation but I found a great inertia after insulation because I found on a table a density of polystyrene of 1380kg / m3 and I am not too wary of where my improbable value, I will take the value of the density in the table post above.

I just changed my value and I find inertia after 80h work (the difference is probably due to the wooden cladding)



In any case, thank you all for your answers. It allows me to see a little more clearly.
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swift2540
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by swift2540 » 08/04/10, 23:05

crashback wrote:So 4th question: how with the value of inertia I can know my non-heating temperature at night when my temperature when I stop heating is 20 ° C and outside 9 ° C?

This is not how we do it. The best gain is 4 ° to 5 ° difference in temperature between day and night.
==> if TA = 20 ° during the day, then at night 15 ° to 16 °. If we drop less we do not take advantage of inertia, if we drop more we have to spend too much in the morning to heat the mass. (Walls, floor and ceiling)
Afterwards, it is the TA (or the ext probe) that gets by! It's up to him to say whether or not to restart the boiler at night.

crashback wrote:I just changed my value and I find inertia after 80h work (the difference is probably due to the wooden cladding)

Clearly yes, but it's won, that's the main thing!
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by dedeleco » 08/04/10, 23:51

After calculation I find an inertia before works: 71h

I just changed my value and I find inertia after 80h work (the difference is probably due to the wooden cladding)

To my physical common sense, putting a thick exterior thermal insulation in addition to the current brick and plaster walls, makes that the time of thermal equilibrium increases greatly given the significant additional insulation.
The calculation of 80h is the thermal penetration time through the insulated polystyrene alone but with the old wall to cool (or heat) behind the polystyrene with a good heat capacity, the time lengthens by a good factor, set by the thermal capacity of the wall divided by the low thermal flux through the polystyrene insulation. We will obtain a time varying as the inverse of the thickness of external insulation. The house is like a calorimeter.
So it is necessary in order of magnitude not to make too complex calculations, to evaluate the thermal capacities, thermal fluxes, time constants, and diffusivity of the various elements of the house in particular floor slabs and floors.
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by dirk pitt » 09/04/10, 09:37

swift2540 wrote:. If you drop less you don't take advantage of inertia, if you drop more you have to spend too much in the morning to warm up the mass (walls, floor and ceiling)


he is an urban legend!
physics says that the less you heat (so the more you agree to lower the temperature at night) the less energy you TOTAL.
on the other hand, there are other disadvantages such as the time to return to comfort temperature and the power required to do so, etc.
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Did67
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by Did67 » 09/04/10, 13:57

swift2540 wrote:
This is not how we do it. The best gain is 4 ° to 5 ° difference in temperature between day and night.
==> if TA = 20 ° during the day, then at night 15 ° to 16 °. If we drop less we do not take advantage of inertia, if we drop more we have to spend too much in the morning to heat the mass. (Walls, floor and ceiling)
Afterwards, it is the TA (or the ext probe) that gets by! It's up to him to say whether or not to restart the boiler at night.


Beware of ready-made recipes.

In the case of my house (high inertia, fairly good insulation), if I do not heat at all at night, I lose around 3 ° (around 21 to 18 °) by - 5 ° C outside!

I switch to "night" mode from 18 p.m.

If I put the day mode at 4 am, I did not go up until around 19 ° C around 7 am, and I approach 20 ° C around 10 am or 11 am!

To lose 4 or 5 ° C, I would have to wait 20 hours! And I would put 12 or 15 to win them again. Unliveable !!!

Nothing abnormal: high inertia (therefore a "large reservoir of calories) and fairly good insulation (so it" leaks "modestly). So if you have a large tank and it leaks little, it will take a long time. will also take a long time to refill!

So no "ready-made recipes": think and adapt ...

On the other hand, as Dirk says, I lose more calories than if I could lower more and faster. It is therefore in this sense that the recommendation often made "not to lower with heated floors" should be taken. Not that it would not save money, but it is not feasible (in a manner compatible with a sufficient comfort for the inhabitants). So impossible to save as much as you would like to do (just as it is impossible to consume less with a large 4 x 4 than with a C1! Even if you can consume less when driving "soft" than 'driving like a bully !!!). Ultimately, lower or not, under the circumstances I am describing, the gap is peanuts. By force of circumstances (inertia).
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by dedeleco » 09/04/10, 14:17

The savings depend on the cold we tolerate when sleeping in a quick response house (a few hours) otherwise it is illusory if the response time is long more than one night (unless you turn off all heating at night)! !
Personally my feeling of cold is very much a function of my physical activity which heats up !!
Sleeping still gives me a strong feeling of cold and I can't stand the cold air in the lungs while sleeping, like my wife: result I heat as much at night and I don't understand this type of saving !!!
On the contrary, the day with physical activity, I am hotter and I can stand the cold more !!
If I saw wood with a hand saw or if I jog hard, I can handle zero degrees !!
So the heating must be adapted to the actual physical activity to save !!!

Otherwise try to keep the summer heat for the winter in the ground deep !!
It is the best possible economy, old house become passive.
There are ways to create innovative companies on this market better than insulating exterior walls.

The site indicated by Aumicron is to read and learn for the physical principles:
http://www.fiabitat.com/construction-ma ... me.php#5b4
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by swift2540 » 10/04/10, 01:19

@ dirk pitt and Did67,
please don't type!
If we mix the viewing angles and the parameters, we won't understand each other, that's for sure.
I was a little quick, I start again.
In a thermal colander, 4 to 5 ° drop in temperature is the greatest energy saving if the heating is reactive (radiator).
-Beyond, the mass will be too cooled and the heating must be restarted too early for warming in the morning, otherwise discomfort. (Assuming that I want my 20 ° when I get up, of course).
So, in addition to the possible / probable discomfort (radiating cold walls), the energy gain is zero. We pay in the morning for what we earn at night.
-By this, (eg a night at 12 °, impossible to lose 5 °), well since the boiler does not restart, the gain is maximum possible.
If we have a house that is well or very well insulated, we will be “below it” all year round, so heating is completely cut off, therefore maximum savings possible.

Then we will work on the evening cut-off time.
The more the house has inertia, the sooner we can cut.
Ex: I want 20 ° until 23H
In a not insulated house, I heat until 22:30 p.m. '
In a little insulated house, I heat until 21:30 p.m.
In a well insulated house, I heat up to 20 p.m.
And it's always 20 ° at 23 p.m.
And as the inertia of the house + the good insulation allows not to lose 5 °, the start time for "good comfort" is always the same.
Which represents a 2nd gain in consumption 8)

And to guarantee as much as possible the gain, some outdoor sensors have a "boost" function + 25% 1st heating time (not usable with a condensing boiler)

Now, if the heating is not very reactive (underfloor heating), there it becomes a headache and to be studied on a case by case basis. Hence the recommendation not to cut the night.

These explanations are valid ONLY if we use the postulate "I want my comfort from such hour to such hour, identically".
Then, it's up to everyone to develop their comfort equation> <economy ...
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by Did67 » 10/04/10, 13:11

swift2540 wrote:@ dirk pitt and Did67,
please don't type! ...


For my part, I do not type.

Just a flat compared to your recipe stated as a general rule (at first). Because many people take at face value what some write on the net.

Under the conditions you have now (reactive house, "powerful" heating without inertia), what you said is true.

Even if we could nuance here and there ... but hey.

I prefer that everyone understands the principles and tweaks their own settings rather than applying recipes. But I may be naive (and annoying because long in my posts!).

Already this starts with the heating curve for those who have an external sensor control - almost none is adjusted beyond the "pifometric" setting set by the installer depending on the type of heating !.

And then, each one its rhythms and its requirements. Whoever starts his day with a gym session will probably endure a 19 ° shower and save money (if he wants to).

And each his own house: inertia or not, radiators or floors etc ...
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by swift2540 » 10/04/10, 23:08

8) I knew we would agree : Mrgreen:
When you write
Because many people take at face value what some write on the net.

I answer you and therein lies the problem
Many disembark, seek a quick and simple answer, and above all non-binding.
So now I start on the principle
simple question = simple answer
sharp question = sharp answer
This will imply that the person requesting it posts several messages, makes tests and sends them back to us to refine.
Remember the discussion on class A circulators in another thread:
a class A circ consumes less; yes but at home I have such a problem; then try such a setting; ...; Yes it works
Here it is the same, no details, no report.
However it is obvious that there are never 2 identical houses. Even if ditto in appearance (ex: cited), the thickness of the tiles or wallpaper, the (un) happy treatment of thermal bridges, the height of the front door compared to the ground (therefore the passage of air), ... will change the settings.
So correct answer yes, but very (too much?) General, yes too. To be refined on a case by case basis.
==> To those who read these messages, do not hesitate to come and ask questions to get as much information as possible, it is the only way to arrive at a correct setting.
@ soon
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