Insulation- The Science

The Tardis factor (interiors, awnings, roofs etc)

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Tobias13
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Insulation- The Science

Post by Tobias13 »

Hi All,

I am due to start a refit in the New Year and whilst discussing the various options with the owner the age old debate of insulation in campervans was at large. Now whilst I have my own opinions, as many others do I wondered if any actual science has been applied.

Im not talking about calculations that can be done to calculate resistance this and resistance that etc., but to design an experiment and actually test different insulation materials to see how effective they are in a campervan environment.

Campervans are so variable, how much insulation, type, vapour barriers, windows etc etc etc, so , when I say ‘science’ I say this in the loosest term because to set up an experiment in the garage and accurately test the many variables involved is beyond my technical expertise, financial commitment and probably my time. Having said that, everyone loves an experiment!!

So this is what I propose:
• Construct a .7mm thick metal box with a removable 50mm cavity and lid. Box dimensions approx. 300mmx300mm plus 50mm cavity surrounding.
• Different insulation materials can be placed inside to test heat escape via conduction and air temperature retention inside the box.
• The heat source will be via a heat gun and I was planning to monitor the internal air temperature with a remote thermometer and the conductive heat escape with a laser temperature gun.

I would be interested in what people thoughts and opinions are on this, for three initial reasons:

1. To see if it is actually worth doing.
2. Technical opinions and the process to conduct the experiment (other than my initial thoughts)
3. To have a say in what gets tested and get involved.


My Thoughts,

In the home masonry surfaces are typically heated up via conduction and act like a storage heater releasing heat back to the building, providing the insulation behind it is effective and doing its job.

In a campervan there are very few surfaces that actually conduct heat apart from the metal body, and we typically cover these over to prevent moisture laden warm air condensing with cold surfaces and producing condensation.

In previous installations I have simply applied as much twin foil bubble to backs of panels etc. to reflect heat back into the van and also act as a vapour barrier, so my thoughts are that the foil insulation is effective enough to be used without further insulation within the voids etc. because heat loss occurs elsewhere such as windows, uninsulated surfaces and when you simply open the door. The theory being that only the air is warm and therefore when you open a door the heat is momentarily lost with little conducting materials being present to release heat back into the van.

Of course many people will have a different opinion and thoughts of what has worked for them and others etc., and as stated earlier testing every variable is probably impossible or not worth doing. :ok
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clift_d
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Re: Insulation- The Science

Post by clift_d »

Most of the data you're seeking to determine by experiment is available online without the hassle. For example, thermal conductivity values of different insulation types are available here:
http://www.greenspec.co.uk/building-des ... roperties/
Smaller thermal conductivity numbers at the above link mean better insulating performance.

With regard to bubble foil cavity wall insulations like AlReflex, the figures aren't really published by the manufacturer to allow a straight comparison. I suspect some of the performance of these insulations derives from the fact that the foil is located in the centre of the cavity so that there is an air gap either side of them. By sticking the foil to one of the inner faces of the van body cavity you will probably lose some of the performance benefits as a result, and so it may just be better to use something like a sleeved mineral wool or close cell XPS insulation instead.

But if you decide to go ahead with your experiment, I'd like to see pictures. :mrgreen:
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Tobias13
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Re: Insulation- The Science

Post by Tobias13 »

yup agree with your comments but was curious to see how it actually performed over a given time. my point being that there are many areas of heat loss in a van with windows, exposed metal etc and door is constantly being opened so figured there would be a point where the insulation hasn't actually had chance to work effectively. I guess the longest time would be at night, and then I would still be looking for ventilation to remove moisture.

that said, I came across this guy on youtube earlier and he pretty much nails the explanation. I'm sure there are calcs I could do to figure out the above but its not worth the hassle.

https://www.youtube.com/watch?v=hDZBJw7cV2U" onclick="window.open(this.href);return false;
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Re: Insulation- The Science

Post by a1winchester »

My experience with insulation and prevention of condensation relates to buildings, not camper vans, but the science is the same.
The YouTube video explains this pretty well, but there are a couple of other things to consider. If the loose fill fibreglass insulation becomes wet, it acts like a sponge and replaces the (insulating) air pockets with (conducting) water, so it looses it's insulation value.
In old houses, before the days of cavity walls, the only way to stay warm and dry was to heat the rooms very well. Then the condensation formed somewhere inside the masonry, and was driven away by the internal heat. With the advent of air cavities, the condensation (or dew point) occurred in the outer course of bricks and was prevented from entering the room by both the air cavity and the warmth of the internal rooms. However, the heat loss was less than for solid walls as the walls conduct less heat due to the cavity, provided that there was only a limited amount of ventilation to the cavity.
Next came insulated cavities. Some cavity insulation was 'blown' into conventional air cavities, and often did more harm than good, as it bridged the cavity, reduced air flow required to dry out the cavity, and acted like a wick to transfer moisture to the inner bricks. Cavity 'bats', like Celotex, used nowadays, are much better, as there is still a clear air cavity on the outside, but the insulation resistance of the wall improves a lot. So there is less need to heat the wall from the inside to ensure that the dew point remains in the outer skin of brickwork.
Transferring this technology to a van is difficult. Ideally, you would need that air cavity between the steel bodywork and the insulation to allow the condensation to escape. In my opinion, unless you can fully bond a closed cell insulation to the skin of the vehicle, you are asking for condensation problems. As the video suggests, areas of the vehicle which have prominent curves are difficult to insulate with closed cell insulation, (Alfas foam or similar might do the trick, but would be a hell of a job to remove if necessary)
So it seems to me that the old fashioned remedy of heating the room like a furnace is the best way to keep warm and reduce condensation. A dry heat source such as Propex is ideal for this. Gas heaters would be a very bad idea, as the end products of their combustion is Carbon Dioxide, Carbon Monoxide. and Water, none of which are desirable.
Any insulation used on the panelling needs to be closed cell. That foil backed bubble wrap stuff may feel warm to the touch, but is nowhere as good as Celotex, although it does score by being a medium for trapping air in closed cells, so could have some use in the curved areas. Plain bubble wrap would be just as good though.
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clift_d
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Re: Insulation- The Science

Post by clift_d »

Tobias13 wrote:that said, I came across this guy on youtube earlier and he pretty much nails the explanation. I'm sure there are calcs I could do to figure out the above but its not worth the hassle.

https://www.youtube.com/watch?v=hDZBJw7cV2U" onclick="window.open(this.href);return false;

His strategy for insulating his van seems a fairly sensible mix of techniques - see his Pt 2 video. He's using high performance rigid boards where the van side is flat enough to allow easy fitting, and mineral fibre where there is a lot of structure to go around, small pockets, or awkward shapes. They key thing he's doing is putting in a proper vapour barrier to the inner side of the van using foil reflective bubble wrap and foil tape for fixing. The vapour barrier stops any moist air getting into the insulation and condensation forming. Panelling would then be fitted over the insulation internally.
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Re: Insulation- The Science

Post by crazyhorse »

This looks ace, have watched his vids.

Fibre looks the best bet, with vapour barrier. What happens though if there is a leak from say a window or seam, the mineral fibe will get wrecked and hold the water. Fine on a sprinter, but for these might be an idea to to put foil inbetween the outide metal and inside also??
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