Posted By: SteamyTeaDJH
Was a simple polystyrene box with a roof tile on top. I then added different insulation under the tile and measured the temperatures as the solar input varied. Disregard Solar Shiny and Solar Matt as they are left over from a previous test.

How was the side of the box sealed to the foil and/or insulation? A photo/diagram would help me build a similar box.

As for oocalc not reading it have you tried Find and Replace,

Ah, that worked. Thanks for that excellent idea

or a copy of Excel, there are enough versions floating around.

Wash your mouth out! I don't have any M$ licences for anything.

Dave

The box is made from 50mm thick expanded polystyrene.
External measurements: 340L, 340W, 150H
Internal measurements: 240L, 240W, 100H
A roof tile was put on top with different 'finishes' under the tile.

There are some pictures of my original tests at, they were for trying out different finishes on the outside:
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5643&page=2

And here is a screen capture of a very bad drawing:

Derrick

No good will ever come of science, we have all we will ever need

Tom

I suspect from anecdotal observations, temperature differences, misunderstanding of the systems, the initial question, inability to collect/analysers data, differences in opinions, teasing a signal from data. I am sure the 'scientists' on here will go and research and synthesis what data is available and draw conclusions without the red herrings of cost, practicality of installation, other influential factors etc.

Have you had your simulation results back yet for your heat transfer design?

Biff, there would be no point. The reflective surfaces work only in combination with air gaps so as an installed insulation solution it would simply be a case of making what is currently the most effective thinnest passive insulation available into a thick one displaying an average "R" value
The effect of radiation is not refuted its just not as significant as some people would like us to believe. Carbon black added to EPS improves its thermal conductivity by about 5 milliwatts depending on the density of the EPS. With XPS the improvement is nearer 2 miliwatts, changing the density and cell size have more dramatic effects impacting on conduction and convection respectively

Posted By: SaintBiff, there would be no point. The reflective surfaces work only in combination with air gaps

I think a common misconception is the size of air gap needed. It is of the order of magnitude of the wavelength of infra-red light, i.e. not very much and so of approximately zero consequence.

Endlessly repeating the false assertion that a wide air gap is required above multifoils does not alter physics.

Posted By: Mike GeorgeNote the thermal resistance of the multifoil virtually doubles from 0.97m2K/W to 1.9M2k/W [page 4] with a minimum airgap of 20mm [page 8]

Maybe because that's the insulating property of that thickness of airgap. Up to a cetain point, air does insulate - but if the gap is too wide, convection currents reduce its effectiveness. Exactly the same mechanism as double/triple glazing. Which, if you think of it, is just like a multifoil (if the glass is coated). So any multifoil that claims better performance than triple-glazing is dubious to say the least.

Paul in Montreal.

Of course, as Paul points out, air is a good insulator. My point is that the air gap (after the first few nanometres) makes zero difference to the radiation related properties of a foil surface. The out going infra-red radiation does not 'know' how wide the air gap is beyond the first wavelength. (That's how low-e coatings work - the coating is half a wavelength thick so radiation leaving from the glass surface cancels out with that leaving form the outer side of the coating.)

Biff, I'd follow the guidelines from the BRE Convention for U value calculations
http://www.bre.co.uk/filelibrary/pdf/rpts/BR_443_(2006_Edition).pdf
para 4.8.2 recommends an air gap of at least 25mm and lets face it what's the most commonly used spacer, a batten.

Some very interesting points made that go a along way to making things clearer re the insitu performance of mf. Home made double glazing for the walls and roof, plus air barrier. Finaly, radiation takes third place in importance in a typical mf installation.

Just like to say that I've not really read a lot of this latest stuff but thoroughly approve of the surge in this thread, 750 not too far away now which really puts that magic 1000 well on the horizon!

Well done chaps, keep up the good work!

J

(Keith any possibility of some stats on this amazing thread; no. of posters, no. of words etc...? - [only if you have an idle moment ...])

As soon as the radiative component of overall heat transfer becomes (or is admitted to be) significant, then so also does frequency and amplitude of variation of the delta-t that is driving the transfer.
Radiant is at a minimum under steady-state delta-t (the unnatural state established at great effort in the hotbox), at a maximum under turbulent (real-life) delta-t.
I'm not sure that the v interesting pieces of research put up by djh on 22 May and 30 May ('1 day ago') have grasped that.

Note that in saying "frequency and amplitude of variation of the delta-t" we're not talking about the kind of slow variation that can be achieved by varying temps in a hotbox - that's so slow as to count as near enough steady-state. That was the ridiculous 'error' made in the infamous NPL study that was commissioned to discredit multifoils.

Paul, in a mix of radiant, conductive and convective, when there's a disturbance in the delta-t, across a void space, it has to be re-equilibriated. The radiant component starts delivering energy instantly to the suddenly-colder end of the couple, whereas there's a time-lag before conductive and convective get there. By then the radiant component may have already done much or all of the transfer necessary to complete the re-equilibriation. The delta-t driver for the conductive and convective may even peter out before they get there.

Posted By: fostertomAs soon as the radiative component of overall heat transfer becomes (or is admitted to be) significant, then so also does frequency and amplitude of variation of the delta-t that is driving the transfer.
Radiant is at a minimum under steady-state delta-t (the unnatural state established at great effort in the hotbox), at a maximum under turbulent (real-life) delta-t.

Posted By: fostertomin a mix of radiant, conductive and convective, when there's a disturbance in the delta-t, across a void space, it has to be re-equilibriated. The radiant component starts delivering energy instantly to the suddenly-colder end of the couple, whereas there's a time-lag before conductive and convective get there. By then the radiant component may have already done much or all of the transfer necessary to complete the re-equilibriation. The delta-t driver for the conductive and convective may even peter out before they get there.

Tom, I agree with some parts of what you say here. But I'm not so sure about other parts, such as "significant" in the context of variations. Remember that some of the experiments measure diffusivity directly. Rather than get into another sterile debate, I suppose you must have a basis for your belief, so could you post the references so we can all read them.

Thanks, Dave

Thanks. Paul, for engaging with what I’ve been saying for a couple or three years – no one else has, on this forum (and I don’t think I’ve said it anywhere else).

Posted By: Paul in Montrealyou talk of a void space. In real-world materials, there is no void space, it is filled with something - most likely air or another gas

Yes, that's what I meant, not a vacuum.
So when, after a period of steady-state transfer across plus around the perimeter of such a gas-filled void, one 'shore' of the void changes in temp because a temp wave has reached it via the solid material 'inland' (I'm going into a flat-earth analogy here), delta-t across the void increases and a new equilibrium has to be established.
The total rate of heat transfer across plus around the perimeter of the void will increase and eventually as a result the far 'shore' will also rise in temp, until a new steady-state equilibrium is established.
That transfer will be by convection thro the gas that fills the void;
by conduction thro the gas that fills the void and also thro the solid material that surrounds the void;
and by radiation across the void.
The radiant mode gets transferring instantly; the convective and conductive modes take time to have any effect on the far 'shore'.
By the time they do, the radiant mode will have already done much or all of the work of re-equilibriation, and may even have wiped out the temporarily raised delta-t that was driving the conductive and convective transfer.

Posted By: Paul in Montrealyou talk as if an external change suddenly causes the radiative transfer of energy to be activated

All three modes were already activated; the external change causes all three modes to increase equally, more or less pro rata.
The point is that the increase of the radiant component then gets there sooner than the increase of the convective and conductive components, hence the radiant does much or all of the work of re-equilibriation neither helped nor hindered by the tardy convection and radiation.
This 'gets there sooner' advantage only applies to the increased portion of the transfer, attributable to the suddenly increased delta-t;
the 'base load' portion of the transfer, attributable to the pre-existing steady-state, ploughs on unchanged.

Thus the radiant component trumps the other two only in respect of the increased portion of the transfer, and that increased portion only exists when delta-t is suddenly disturbed, from the pre-existing steady-state.

So under steady-state I don’t doubt that radiant does play its significant but minority role, as calcd by the conventionally understood physics of convection (tricky), conduction (simple) and radiation (simple).

When a new isolated temp wave comes through, disturbing the steady-state, that variant portion is effectively handled by the radiant component (where there are voids and pores - obviously not within the solid), until re-equilibriation. This is superimposed on the ongoing steady-state regime (which again prevails after re-equilibriation), so you might say is interesting but insignificant.

But when new temp waves are coming through constantly, steady-state hardly exists, so a high proportion of the constant re-equilibriation is handled by the radiation component, while the convective and conductive are reduced to impotence, constantly setting off in a new direction but never getting there, before a new disequilibrium arises.

Don’t ask for my sources – this is all out of my head. It’s like – I don’t need a peer reviewed research project to tell me that if A is faster than B, then A gets there sooner.