Exact calculation of thermal insulation

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chatelot16
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Exact calculation of thermal insulation




by chatelot16 » 24/01/16, 16:53

Hello

this problem arises once again in this subject where we talk about thin insulation https://www.econologie.com/forums/willy-furt ... 14-10.html

the standard method of insulation is done with the notion of thermal resistance, as if the heat flow through an insulation was proportional to the temperature difference

alas the real life is more complicated, and one can not progress with a wrong method of calculation

Although the standard method is good for advising building professionals in the current state of the art, more detailed calculations should be made to find all possible ways of progress.

which has already seen a detailed measurement of insulation: ie thermal flow measured at different temperatures?

in general the insulation manufacturer hides behind the norms and do not give detailed information, but this kind of measure has had to be done

for the electrical resistance, one does not ask any question because the current is exactly proportional to the tension: when one buys a resistance of 10 ohm this resistance is constant for all the possible tension

if the thermal data are eclipsed by the standards of the building it should be for the other field of insulation: insulation of furnace or insulation of cryogenic material, or given the large temperature difference aproximation are not tolerable

please
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by Did67 » 24/01/16, 17:34

I'm not a job, you know it.

Nevertheless, it seems to me for heat, the issue of flows is a little complicated than for electricity.

Indeed, the heat moves from 3 ways:

- Conduction: gradually, in a solid or immobilized fluid, the heat goes from the warmest to the coldest ...

- convection: in a fluid, it moves, the hotter rises and takes the place of the colder, and "carries" the calories with it; we can also "manage" this flow by "pumping" (aerolic)

- radiation: without any material support, a hot body emits radiation which "evaporates" in a vacuum ...

Thin insulators are effective against radiation. In a certain way too, against conduction. But being thin, in general, they only imprison a very thin layer of still air. Forcibly less insulating than a very thick layer of the same material ...

But thick insulators are not made in the same material ...

So it gets bored ...

I isolated attics with thin insulation cited in one of the controversial wires. In the standards: without contact. Air screen in front. Air screen behind .... Ben summer, my attic is an oven! I exaggerate a little. Say, it's far from the expected comfort. I also have creepers isolated by glass wool (a double layer of 30 cm): it is, in summer, much more efficient because of the phase shift. The hot wave arrives in the evening quad I can open ...


In a well-insulated house, there is also the issue of waterproofing when, like last week with us, a cold north-easterly wind blows. So the slightest "hole" (an uninsulated socket, a keyhole, a slightly damaged window seal that "whistles") results in a collapse in air temperature (and comfort, even with PCBTs , even if to a lesser extent, because the radiation of PCBT remains effective) ...

So yes, it's horribly complicated.

And, by manipulating the data a little, we can make believe a lot of things. When I bought the thin insulation, "notices" showed an insulating power equivalent to x cm of glass wool. I see that it is not "the same"!
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by chatelot16 » 24/01/16, 18:06

that's why I'm looking for detailed measurement results, not a result put in the form of thermal resistance

there must be measures already made: for example 10cm of glass wool between 2 tole and complete waterproofness, measurement of the flow at different temperatures, and we will see in which range of temperature is linear

of course this result will be falsely optimistic because in real life the walls are not waterproof and unventilated glass wool may accumulate moisture: it is necessary to ventilate with outside air and if the ventilation has too much of debit it adds a loss of energy

this loss by ventilation must be known by the architects or the cstb to quantify the difference between waterproof box-glass wool and glass wool with ventilation

this result of the influence of the ventilation concerns me to know if layers waterproof and an artificial ventilation would be interresting

Another result of interressant measurement: influence of the thickness: I can not believe that the thermal resistance increases exactly with the thickness of the ordinary glass wool ... the glass wool is not waterproof, there is necessarily a small convection, which should make the insulation a little worse than expected when you increase the thickness ... remains to see the true result

I do not imagine that I am the first to ask myself these questions: these measures must have already been made! but where do you find the results?
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by Did67 » 24/01/16, 18:33

It seems to me that more and more, certification tests and certifications are paying, at the expense of companies.

In the absence of public research, public data are scarce ...

And so the data is "captured" and you will never see them ... What you will see are the extracts which "suit" the manufacturer ...

Even the "standards" are paying!

Surely, that exists.

Not sure it's so easy!

Not to mention the fact that the specifications of the test protocols are often the result of the lobbying of the manufacturers who are behind, to the point that the results obtained have very little to do with reality, in the real world in which we live!

Look at the miserable tests that we have on the polluting emissions of vehicles! And yet you or me, we could write a repository ... No doubt we would fight to know what "dose" of motorway, home-work shuttle over what distance, how many "km of ballad in the Vosges on weekends. end "... But we would agree that there are the tires" imposed "at the time of homologation, at the pressure indicated in the frame of the door, all the accessories fitted to the model, the air conditioning as soon as 'it's hot, etc, etc ...

We would obtain a result that would still be contested and questionable. The excitement that makes the tires squeal would emit more. The ultra-Zen driver who only does the "high road", never commutes, less ...

So I doubt ...
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by izentrop » 24/01/16, 19:43

What is important for perfect insulation and not done before is the airtightness.
The thin insulation by its tight side can realize it but sometimes at the risk of rotting a frame.
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by Obamot » 24/01/16, 19:53

Yes, the hermeticity in a building must be perfect, but it is only relative. A total waterproofness is an absurdity ... total!

I also subscribe to that! That's why thin insulators don't work! A vapor barrier must be installed hermetically (without allowing "free air" to pass through), but in itself it is not waterproof! If not that's right Izentrop, hello the "dewar vase" effect, hello mold in the thermos!

Yes, the VIPs in their Sunday best are smart, they always use the same example, that of the polar jacket with reflective sheets of aluminum! obviously it's thin it isolates and it returns some of the heat produced by the body, but precisely they forget to say that there is the human body that inside, produces about 200'000 joules / hour of heat constant!

Let's talk about how a "positive energy" construction is heated from the inside, which produces more than it spends (leaving aside external inputs such as thermodynamic solar panels)

For an adult it is approx. 60 Watts of heat production, ie for 1 day at the rate of 1'500 calories absorbed 1'200 x 4,2kJ x 24h = approx 5'000'000 Joules / day. Only here, all the calories that we eat do not turn into heat, so the calculation above is wrong. In addition, our own heat cools because it also undergoes a convection effect. There is also dissipation of heat by the water vapor released by the human body. In fact it's a little more, but there is energy that is dissipated in urea and methane release well known, as they can be ... odorous, etc! ^ _ ^

And when the inhabitants are not there, the laws of physics take back their rights, the reflective aspect of thin insulation is no longer useful!

But there are still other parameters that come to play the festive troubles.

It depends on the coef. thermal loss of the insulated area by the thin insulation and of course the outside temperature of the habitat. We arrive at e calculationsXStrong energy complex to establish the equilibrium temperature in the isolated zone which is to know what will remain when the heat generated inside will exactly balance the heat losses towards the outside (and this according to the temperature of comfort, which we have proposed to achieve inside) and all this depends on the properties of the walls ... and there no miracles, a thin insulation barely reaches R = 1 (if we want a industrial product in "economic quantity"). 200mm of glass wool is R = 6,5 if it is correctly installed in the rules of the art, there is no picture!

Every day that nature does, also sees the rising of one side of the pigeons and the other of the hunters! Thin insulation is a pure scam (tells us Yves35 in the forum opposite), they do not have ACERMI certification and he is right.

You can do all the insulation with a R = 6,5 certified you will not find one that is a thin insulation, they all average among the best 200mm (there's better but it costs an arm.)

That's where you can find certified insulation and compare with what we offer:
http://www.acermi.com/isolants-certifies/rechercher/

Take a thin paper wall, the influence of 60 W on the indoor temperature is negligible, while at the other extreme, the same energy placed in a Dewar vase, the temperature will go up, very high ...
I suggest Willy to compare his thin insulation to the insulation of a dewar vase >>> should stop pretending anything M. FURTER !!!

In the building industry, we have always encountered the same recurring problem, that is, as in many sectors "the customer is always right", suddenly, if this is true and applied, he must also be right against the laws of physics!

This is what is complicated, what people without experimentation or experience, come to you with the peremptory statements they take for truths against all odds.

But the golden rule applies: "they are always right"

Bein let them be right in their corner : Mrgreen: : Cheesy:
Last edited by Obamot the 24 / 01 / 16, 20: 02, 2 edited once.
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by hic » 24/01/16, 20:00

Did67 wrote:
I isolated attics with thin insulation cited in one of the controversial wires. In the standards: without contact. Air screen in front. Air screen behind .... Ben summer, my attic is an oven! I exaggerate a little. Say, it's far from the expected comfort. I also have creepers isolated by glass wool (a double layer of 30 cm): it is, in summer, much more efficient because of the phase shift. The hot wave arrives in the evening quad I can open ...!

Hi Did67

there is a greenhouse effect in the attics,
even more so if a reflected reflector 95% of the heat
which increases the temperature and cancels the insulation (which is a problem close to the on insulation

are your tiles ventilated according to the 'wall trombe' principle?
Last edited by hic the 24 / 01 / 16, 20: 34, 2 edited once.
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by izentrop » 24/01/16, 20:02

obamot wrote: Hello mold!
Good sealing is accompanied by good insulation and good ventilation.
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by Christophe » 24/01/16, 20:07

The Belgian K building method is an interesting method to give in 1 single digit the overall thermal performance of a building.

The notion of habitat form, for example, is taken into account: the more a building has outward surfaces in relation to its living space, the more this calculation penalizes it (an aspect that would not be taken into account when the average of the losses of the isolated surfaces, ie the BBC method which imposes thicknesses of insulation but does not speak about the form!).

It also takes into account thermal bridges.

Depending on the housing, it requires a few hours of measurements all the same.

Method: http://www.energieplus-lesite.be/index.php?id=15007

Xls free and 100% functional to do it at home: https://www.econologie.info/share/partag ... 3tHism.xls

I had arrived at a K45 about me, despite some big thermal bridges.

It's interesting to see how increasing the insulation of some surfaces no longer influences the K from a certain point in time. That is to say that putting 50 cm in the attic instead of 30 cm will bring very little overall performance to the building. This is called on insulation ...

I still have my version completed somewhere, if you're interested I'll find you ...
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by Obamot » 24/01/16, 20:11

Yes Yes Yes :D

Reason, I have a project of mass stove and ITE in the pipeline ...

If one of these 4, you could a little coach around this spreadsheet, it interests me to discover another method!

;-)
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