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Insulation Panels

SteamyTea

Entry posted by SteamyTea in Thermal Testing

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It has been a cold week, so just after 12:30 on the 15th of January 2024, I started a small, but limited, experiment.

This was rather prompted by a comment by @Garald who wanted to insulate at the back of his book shelves, and mentioned our favourite insulation, multifoil.  @Gus Potter also has a project that may benefit a thin, easy and cheap to make, insulating panel.  I think I also made a comment to @saveasteading about this experiment, but can't remember in what context.

Now I have always been dubious of reflective type insulation.  Works great at high temperature, especially in a vacuum, it is how the cameras on the James Webb Telescope are kept cool.

But we are not Billionaires, so I used hardboard, pine, white emulsion paint, double sided tape, small screws, clingfilm and aluminium foil.

Basically I made some small St. Ives picture frames, put them face to face, separating the 24mm air gap with clingfilm in one, and aluminium foil in the other.  The total thickness of the test panels is 30mm.

 

image.png.0023fa4b1c31363ba2857cf3da16cf6b.png

 

Each side of the test material had temperature sensors (DS18B20s) inserted via holes in the frame.  These had been calibrated before hand and the analysis is based on the calibrated data.

Other sensors where fitted in the room and externally to log ambient temperatures (why being a cold week was so good).

The panels were then stuck to my kitchen window with double sided tape.

 

image.png.a3a62d63e45a21c04f953a7499ba032e.png

 

The position of the sensors allows for a combination of temperature differences to be logged, logging was at the minute interval but the analysis was based on 6 minute means.

A quick calculation to check the standard error showed that accuracy was a factor of at least 10 below the 0.1°C accuracy of the experiment.

 

The data analysis was based around temperature differences, but for some context, internal and external air temperature is also shown on the charts (right y-axis).  A frequency distribution line was also added, this is black line (right y-axis) and is called Ambient ∆T Probability Percentage.  The Ambient ∆T is the difference between the inside temperature and outside temperature.  This is also used for the 0.1°C temperature bins that create the x-axis.

Mean temperature differences between each side of the clingfilm or foil (shiny side towards warmer room) were also calculated and binned according to when they happened with respect to the Ambient ∆T.

This method is used as it is more relevant than a time series that can fluctuate during the day, it is the properties of the insulation that is being tested, not the absolute 'comfort' levels.

 

The below chart shows the total test period results. Test period (15/01/2024 12:26 to 19/01/2024 12:42)

 

image.png.9e63aa0f0bb67019c042c80e84def31d.png

 

Always remember that these are temperature differences and not absolute temperatures, except the Internal and External mean temperatures (yellow and green lines) and the probabilities (black line).  Those 3 are read from the right hand axis.

The Clingfilm is the red dots and the Aluminium Foil is the blue dots.  Linear trend lines have been added more for clarity than actual predictions.

A can be clearly seen, there is not much difference between the two datasets. The Clingfilm performs better overall with a mean difference of 2.5°C, to the Aluminium Foil's 2.3°C.

Above an Ambient ∆T of 19°C the Aluminium foil performed a little better.  This is actually saying, the colder it is outside, the Aluminium Foil performed better, which may be important comfort, but overall, there will be greater energy losses than with just using Clingfilm as a separator.

It is, purely from a climate change viewpoint, the overall energy reduction that is important.  Climate change has caused the mean temperature at my end of Cornwall to average -0.1°C for 4 days.  I have lived back here for 20 years and never known such a prolonged cold period.

 

I am now running a second test, using one panel without any separator at all, and the other one fully filled with silica micro balloons.  Micro balloons may sound exotic, but they are just filler used in the plastics industry.  I don't think the temperature differences are going to be so great next week, which is a shame as the greater the range that can be tested, the better.  I can always raise the temperature in the room to compensate, but as I raised it up to 24.5°C a few times, which resulted in only getting a mean of 23.5°C in the room, it will be a bit costly and not very environmental.

I shall post up the results of the second test next week, all going well.

 

 

Edited by SteamyTea

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Garald

Nice. Maybe do the same with 2cm-thick cork, comparing it to a 2cm air layer?

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SteamyTea
13 minutes ago, Garald said:

2cm-thick cork

Well I suspect that the tests I am now running will show that stopping air movement with a lightweight filler improves things.

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saveasteading
2 hours ago, Garald said:

2cm air layer?

There is a gap width at which air starts to circulate in the space  warm air rising on one side. 

Hence double glazing has a narrow gap for thermal effect and a wider gap for acoustics.

The skylights used in commercial roofs can be simple double skin boxes, but can be treble, but work better with an infill resembling....the best I can think of is wine box separators. That contains the air in pockets.

For this reason, the service void we've put on our walls will help insulation but perhaps not as much as the spreadsheet says.

 

Great work  @SteamyTea.

 

 

comment to @saveasteading about this experiment, but can't remember in what context.

Neither can I.

 

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Garald
27 minutes ago, saveasteading said:

There is a gap width at which air starts to circulate in the space  warm air rising on one side. 

Hence double glazing has a narrow gap for thermal effect and a wider gap for acoustics.

 

Sure. Yet the optimal width seems to be about 2cm (somewhat confusingly, since that's the sort of gap that is commonly used in double glazing optimized for acoustics):

 

https://www.sciencedirect.com/science/article/pii/S1876610218307963#:~:text=The optimal thickness of the,depending on the climate condition.

 

At any rate, that doesn't mean that 2cm of cork wouldn't be better than 2cm of circulating air. I'd just like to see an experiment where the two are compared.

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saveasteading
13 minutes ago, Garald said:

to see an experiment where the two are compared.

Want to forecast?

 

14 minutes ago, Garald said:

(somewhat confusingly, since that's the sort of gap that is commonly used in double glazing optimized for acoustics.

Too late for any checking, but i think 20mm for acoustics is a pragmatic choice to compromise between  thermal and acoustic properties snd to suit window frames. Ie  a bigger gap works better for sound but is rubbish for heat, so choose something inbetween.

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SteamyTea
6 hours ago, saveasteading said:

There is a gap width at which air starts to circulate in the space  warm air rising on one side. 

Hence double glazing has a narrow gap for thermal effect and a wider gap for acoustics.

 

5 hours ago, Garald said:

Yet the optimal width seems to be about 2cm (somewhat confusingly, since that's the sort of gap that is commonly used in double glazing optimized for acoustics):

When I was getting a new unit for my back door, I wanted 16mm gap as I read, somewhere, that was the optimal gap.  I was convinced that 20mm was better because of the sound transmission.

 

This experiment was really about the difference between reflective and transparent barriers though.

 

5 hours ago, saveasteading said:

Want to forecast

Not really, because the differences are too small to be meaningful.

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SteamyTea
4 minutes ago, saveasteading said:

So that's your forecast.

Reading off the above chart.

At a temperature difference of 25°C, the foil will perform better.

 

Though I am not sure what the question really is.

 

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Garald
42 minutes ago, SteamyTea said:

Reading off the above chart.

At a temperature difference of 25°C, the foil will perform better.

 

Though I am not sure what the question really is.

 

 

I don't think that was my question, but my proposal would be: do a comparison of

a) a 20mm air gap (change to 24mm here and in what follows if you prefer)

b) a 20mm air gap + the same reflective material that is used in commercial-grade reflective insulation (would have to detach it from the rest of the insulation)

c) a 20mm air gap + a space blanket (cheap and likely to be used in DIY projects; at least I would be more likely to use that than aluminum foil)

d) 20mm of cork (again, good for DIY, since risks would seem to be negligible, no?)

e) 20mm of rock wool

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SteamyTea
36 minutes ago, Garald said:

my proposal would be: do a comparison of

Basically what I intend to do.

37 minutes ago, Garald said:

a space blanket

I remembered I have some of that, I know it is great for covering a tent when it is sunny.

 

I also intend to fill one up with different solid materials and see what happens.

 

Almost like being back at University, I never understood people that wanted to do anything outside of the laboratory.

I should have studied Mathematics, then the lab is just paper, pencil, eraser and maybe a laptop to type it up on.

Wonder if I could get a job doing that with my statistical analysis skills, the only skills in statistics is counting and explaining after all.

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MikeSharp01
5 hours ago, SteamyTea said:

This experiment was really about the difference between reflective and transparent barriers though.

So what is the highest order learning here - are the multifoil blanket insulation products looking like they are all they are cracked up to be?

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SteamyTea
4 minutes ago, MikeSharp01 said:

So what is the highest order learning here - are the multifoil blanket insulation products looking like they are all they are cracked up to be?

No.

They may, possibly, help reduce convection currents, but overall, perform no better than a bit of clingfilm.

 

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saveasteading
4 minutes ago, MikeSharp01 said:

multifoil blanket insulation products looking like they are all they are cracked up to be?

I'd use them in my garden shed t garage but that's all.

I went to a lecture by them, oddly supported by the bco department. ( free sandwiches from the company?)

They were very poor at answering questions.

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SteamyTea
6 hours ago, saveasteading said:

They were very poor at answering questions

That is a shame, but not surprising as it was probably organised by the sales team, or worse, the PR department.

 

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Garald

My understanding is that reflective insulation works against heat loss by radiation - and so it makes sense to use it in a setup where that has become the dominant means of heat loss, due to measures taken against other means. Thus the air layer. Of course experiment is (or rather: experiments are) the ultimate judge.

 

Of course reflective insulation + stopping convection are about the only things that one can do effectively with a thin layer of anything, so there's that.

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saveasteading
11 minutes ago, Garald said:

reflective insulation works against heat loss by radiation

That's the issue. These multi-layer products have foil on the outside, bouncing rays back into a room, but also in the middle where they bounce it onto the thin foam sitting next to it, from where it can conduct .

also their explanations of why it can't have a U value but that doesn't matter. were unconvincing. They were basically saying that the approved test methods aren't fair.

That was 4 years ago, say maybe there is progress.

 

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