What is the best way to evaluate van window insulation materials?

Question

I'm trying to make insulation for my van's windows to make it livable in very cold weather. There is a lot of conflicting information about the efficacy of various insulation materials that vary even further based on how they are installed.

I would like to design an experiment that could roughly measure the performance of various configurations of insulation materials. I know it can't be perfect, but I wonder if I could get something meaningful.

I presume that the basic structure of the experiment would be to setup a heat source that could be placed one one side of the insulation, turn it on for a fixed period of time, and then measure the change in temperature on the other side using an infrared thermometer. Where I get confused is how to account for the various types of heat transfer.

The heat sources in the van will be two human bodies and a forced dry air furnace (combusting outside and circulating air inside).

As I understand it, human bodies emit their heat primarily through radiation. The furnace will be circulating warm air throughout the van, which of course is convection. I guess the warm air will then come in contact with the walls/windows of the van, which will absorb the heat via conduction, conduct it through the walls of the van or windows (and any insulation), and then finally radiate the heat out into the outside world?

The most promising insulation prospect that satisfies our requirements of ease of production, access to materials, price, comfort, ease of mounting in windows, etc, is a layered construction of two pieces of radiant barrier (Reflectix) sandwiched around a layer of corrugated plastic to serve as an "air gap", even though of course it isn't truly an empty gap.

The questions I would like my experiment to answer are:

• what constitutes an "air gap"?
• How big it has to be for the insulation to be effective?
• Can there be any kind of thin fabric coating the Reflectix on one side or the other, or does that ruin the effect?
• How does it compare to other types of common insulation (foam board, etc)?

And then the questions I have questions about the construction of the experiment are:

• Is the core idea reasonable?
• Which heat source would be best? Some options I have considered are a stove top, a toaster, a hair dryer, etc.

Any advice would be very much appreciated!

Answer 1

you are proposing a significant amount of work here. Best to place things in perspective, as follows.

Conductive heat transfer is directly proportional to the area through which the transfer is occurring. Let's break the van down into to two areas- the metal area of the van body and the glass area of the van body, and compare them.

What you will probably find is that if the van had no windows at all, the amount of change in the heat transfer through its area would be altered by about 10% to 15% because that's how much glass area you have.

(Now, at this point we must ask is your van insulated, or not? If not, you can see that the big payoff will be if you insulate not the windows but instead the walls and floor of the van first. Note also that the conductivity of the uninsulated metal walls of the van is actually greater than that of the glass windows!)

Next we realize that the thermal conductivity of glass is not infinite; if it is halfway between zero and infinity then the difference falls to half of that- 5 to 7.5%. More accurate estimates can be had with more accurate input data, but you get the idea. Bottom line is this:

The net gain from insulating the windows is not going to be big, and insulating them in an uninsulated van will be pointless. So let us know more about your van and then we can take another shot at your question.