I have set up a hot plate test for multi foil. Put my temperature probes in between the layers and taken measurements at steady state.

Then I took the wadding out of the multifoil and reassembled it between newspaper!

Here are the multifoil results

Great fun! Suggest you keep foils 1 and 6 and just replace the internal foils, 2-4, with paper. It's the added value of the internal foils that are the real issue. The outer ones probably are worth the money.

Second run with newspaper 74;60;52;40;35;27

Th outer foil layers are much thicker on the multifoil and black inside result with newspaper insde layers = 72;69;61;53;43;36;29 hot plate 74 air 20

stupid question


is there a difference in performance if the actual drop is constant?

ie, will an insulation (standard or foily) perform the same from -10>-35, +20>-5, +30>+5, +60>+35 etc

that was my thought.

it would make sense that the insulation would deal with the same differential in the same way, however, extreme temperatures (low or high) may have a base effect on the material itself, rending it more or less effective.

I believe radaition dominates convection/conduction at higher temperatures.

It's very rarerly I have my thermostat set at 70 deg C and it's 30 outside ;-)

I'd have thought the only way to be sure whether the temperature diffs are affected by real world temperatures is to carry out a real world temperature test. If you keep you eyes open you might find a fridge on freecycle which you can cut a hole in/take the door off, depending on how big your "multifoil test rig" is.

The temperature outside the fridge will be your real internal room temperature, whilst the internal fridge temp should make a good substiture for "outside". Probably around 5 degrees - which is what "outside" is most of our cold period. I think if you want to go colder than abotu 2 deg C you'll need a freezer, but have to switch it off as it passes zero or it will get down to minus 40. (Which would be more relevant for Paul in Montreal!)

Simon

sounds expensive but exactly the sort of thing BRE should have already done to me.

Posted By: tonysounds expensive but exactly the sort of thing BRE should have already done to me.

They explain why it wouldn't give accurate results here...

http://www.foam-insulation.co.uk/building-regulations/BRE-multi-foil-insulation-measured-u-values.pdf

"The thermal properties of insulation materials are commonly tested by measuring samples of the product in
a hot-plate apparatus conforming to BS EN 12667 [3]. The performance of products with foil facings,
however, includes the effect of the surfaces on the thermal resistance of adjacent air spaces. These effects
will not be allowed for in a normal hot-plate test where the surfaces of the test sample are adjacent to the
hot and cold plates of the apparatus. Also, if the surface of the material is not flat, as is often the case with
multi-foil insulation products, parts of the surface will be in contact with the hot and cold plates while other
parts will have air pockets between the product surface and the surface of the hot and cold plates. This
combination of direct contact areas and areas with air pockets make any test result difficult to interpret and
apply to the product and its intended application.

A hot box test, on the other hand, can be done on a larger scale and in particular the test sample can
consist of a more complete construction. The test method is defined in BS EN ISO 8990 [4]. In the test
conducted by NPL the multi-foil insulation was placed between two plywood sheets, and had an airspace
on either side of it, as would be the case in normal use of this product. The reported result is the thermal
resistance of the product itself plus the two adjacent airspaces."

My blessings on the project

Posted By: tonyLooks not much difference between the two so is foil doing anything?

Actually it looks like the newspaper is doing better as the air-side surface temperature is higher - this means that less energy is flowing through the newspaper so it's insulation value is higher in this case.

Paul in Montreal.

Am I missing something?

You are measuring the temperature gradient from a warm place to a cold place, but not measuring the rate of energy flow along that gradient.

Posted By: biffvernonYou are measuring the temperature gradient from a warm place to a cold place, but not measuring the rate of energy flow along that gradient.

Indeed. You need another standard resistance in series and then measure the /voltage/oops temp diff across that to work out the rate of energy flow. How about a polystyrene tile on top of each stack, for example? But don't forget the air spaces.

Posted By: Ed Daviesput a "known" piece of insulation under both of the samples

I like the diagram :) But don't forget the multifoil needs an airspace to work. Otherwise he'll just get disappointing results that the believers will decry.

Ed's experiment is nice because you just have to see whether the ice melts more under one pile or the other.
Just recording the temperature gradient doesn't do it. Seeing how much ice turns to water really is a measure of energy flow.

djh, I've made this point before and nobody has countered it though many have ignored it - the airspace is not what it's cracked up to be. As far as the foil is concerned the only airspace that matters is one that is one infra-red wavelength across (and that is really small). Any further air space adds insulation, like any air does, but does not affect the effectiveness of the foil.