Torso Simulator to test Heat Loss in Outdoor Gear – Radiation
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jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Re: Does condensation effect the reflection of radiation? on 06/26/2013 17:16:49 MDT Print View

"I am wondering if you might have tried a third condition which would be putting the foil under the insulation. If the foil is on top it would stop radiant, plus convection, plus some conduction heat. If the foil is under the insulation it would stop mostly radiant heat."

I did try insulation/foil/fabric. When there's no air space against the foil, you get very little benefit. It would be the same with foil under the insulation. You do get a degree or two like you do with any fabric layer, because there is a small air space because the fabric or foil is wrinkled a little. If you smashed the fabric or foil flat, then there would be no heat advantage. This is somewhat speculative because it exceeds my measurement accuracy.

And like I said, my measurement set-up is crude so it raises as many questions as answers.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: perforated reflective fabric -Omniheat on 06/26/2013 17:36:51 MDT Print View

"Columbia is using some kind of breathable reflective lining in their gear this year.

Omni-heat: http://www.columbia.com/Omni-Heat-Reflective/Technology_Omni-Heat_Reflective,default,pg.html"

They have dots of aluminized material with breathable in between. Good idea if the percentage of area covered by aluminized material is large enough. Cover more area to reduce radiant heat loss. Don't cover too much to prevent water vapor passage.

But, their reflective layer is inside the garment. Then you have no air space on either side of the reflective surface. I don't think that works. It will be little better than a non-reflective surface. The reflective surface needs to be on the outside, or if it's internal, there needs to be an air space next to it.

The concept that heat flows from your body to the outside and gets intercepted by a foil layer is not a useful model - that's just marketing spin...

Bradley Danyluk
(dasbin) - MLife
IR-reflectivity reduces condensation on 06/26/2013 19:57:55 MDT Print View

Hi,

Great article.

I've read it claimed a few times that a radiant barrier such as aluminized fabric can actually fight condensation forming on shelter walls, because the IR reflectively causes the fabric itself to become warmer (typically approaching the temperature of the air, rather than much cooler as it would be under an open sky).

Any thoughts or observations on this?

Edited by dasbin on 06/26/2013 19:58:33 MDT.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: IR-reflectivity reduces condensation on 06/26/2013 20:47:46 MDT Print View

"I've read it claimed a few times that a radiant barrier such as aluminized fabric can actually fight condensation forming on shelter walls, because the IR reflectively causes the fabric itself to become warmer (typically approaching the temperature of the air, rather than much cooler as it would be under an open sky)."

When I was testing on my patio under clear sky, the foil did not get dew but the eVent fabric did.

A surface, whether there's a human underneath or not, will radiate heat under a clear sky and get colder. As the night progresses, the temperature gradually drops, and at some point goes below the dew point, at which point some of the water comes out of the air and condenses on the fabric.

Of course it depends on the amount of water vapor in the air and the temperature and how clear it is.

If you're sleeping in a tent, you exhale water vapor which can similarly condense on the under side of the tent. If the tent was made of reflective material, it would be warmer so there would be less condensation.

Remember that my instrumentation is crude so this is all somewhat speculative, not a recommendation to do anything with any guarantee that anything will work.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: More than Radiation is going on. on 06/26/2013 21:14:34 MDT Print View

David, I agree. There are other smaller components going on than simple IR. The difficulty is seperating the two components: ie heat and radiation. Heat is defined as molecular movement. Infra Red is defined as a band of radiation. Even Jerry mixes the two. Take a look at his "Boundary Layer" graph. I interpret this as 0 IR absorption at 0" distance from the film, with an exponentially decreasing amount absorbed. But the effect of absorption is heat which he then plots...a bit confusing since he says he is only doing an IR study in a previous paragraph: "As everyone knows, heat loss is caused by conduction, convection, radiation, and evaporation. This article focuses on radiation. I will look into convection and evaporation in the future and probably will write something up about those."

Yes a painters drop cloth will do much the same, but this is sort of off topic and ignores the IR (the radiative heat loss,) which is really the focus of what Jerry is writing in this article.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: More than Radiation is going on. on 06/26/2013 22:07:51 MDT Print View

I'm not a physicist. Just trying to figure out how to stay warm with the minimum weight. And get some measurements rather than anecdotal information. I think some of you know more about all this than me - I'm not claiming to be the authority and have much to learn.

And sorry if I mix terms like "heat" and "radiation" - it's difficult to be consistent all the way through an article like this.

"Yes a painters drop cloth will do much the same, but this is sort of off topic and ignores the IR (the radiative heat loss,) which is really the focus of what Jerry is writing in this article"

If you look at "Difference in Heat Loss for Several Different Materials"

The "white" and "black" cases are white and black eVent, so there should be no convective heat loss. The air to torso temperature difference is about 46 degree F.

The "mylar shiny side out" and "foil" cases are about the same, about 59 degree F air to torso temperature difference.

I think a painters drop cloth would produce about the same result as the black and white eVent. There is a 13 degree F increase in temperature difference that you get by eliminating radiative heat loss. A shiny surface is 13 degree F better than a painter's dropcloth.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Stephenson tents on 06/26/2013 22:39:38 MDT Print View

For Stephenson tents, they say regularly they have double wall with outside of inner wall aluminized.

That makes sense given my measurements. There's an air gap above the inner aluminized surface so that the inner wall will be warmer. Since it's warmer, there will be less condensation from the humans inside breathing.

I'll have to check that out, see if they sell fabric. They sold me some "fuzzy stuff" a few years ago. I wonder how reflective it is.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Step,henson tents on 06/27/2013 05:24:04 MDT Print View

Jerry, I have a tiny scrap of aluminized fabric (from OWFinc.) Not really sure why I kept it, but I would be happy to send it along. Send me a PM with your address. Maybe there is enough to stitch a couple pieces together for testing.

The mixed terms is OK. Once I got the hang of what you were writing about and why you were righting it. Often tests report results in terms of effect, it was just slightly confusing, though consistent. I believe a better test of thermal emisivity would be to directly measure the radiation, via, a detector, though. Like those used to measure houshold insulation. This should give you cleaner numbers to work with. There are a lot of questions, to me, about your Boundary Layer numbers, and insulations above and below. This looks more like cumulative convective heating of the air rather than pure IR absorption. From your standpoint, ie camping out, it is nice to know what will be most effective at keeping you warm.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Step,henson tents on 06/27/2013 08:17:23 MDT Print View

Those IR measurement devices are pretty cheap. Cooking stores. Harbour Freight had one for $40 or something. I've thought about getting one.

All I really care about is how warm I am. It doesn't really matter what the emissivity or IR radiation is. What matters is the temperature difference if I sleep under a nylon surface, reflective surface, etc. What is the temperature of the air away from me vs the temperature at the surface of the insulation?

I wonder if my temperature sensors are effected by radiation? Will they measure temperature of the air or will they have radiative cooling themselves and thus be cooler than the air?

Tim Hawthorne
(tim_hawthorne) - M

Locale: Southwest
Re: More than Radiation is going on. on 06/27/2013 11:11:31 MDT Print View

This may be controversial but I agree with David Thomas's analysis of the foil placed on top of insulation. It works because it stops convection heat loss, conduction heat loss and, for a human, evaporative heat loss. The amount of radiant heat loss stopped is insignificant because the body produces very very little radiant heat.

FOR THE HUMAN BODY, RADIANT HEAT BARRIERS DO NOT WORK WELL AT STOPPING RADIANT HEAT LOSS. Since there is very little radiant heat produced, there is essentially VERY LITTLE heat to stop. Don't believe the sales hype that radiant heat barriers keep you warm by stopping radiant heat. The barriers may work but they do it by stopping convection, conduction and evaporation. A painter's tarp, bivy bag, or other cover will work the same way.

peter vacco
(fluff@inreach.com) - M

Locale: no. california
the science books are wrong on 06/27/2013 11:44:52 MDT Print View

" convection as a heat transmission cause " ...this is one of those things that have been a thorn in my side for some time. the statment is as taught by every science book they ever forced upon me, and i suspect those books are wrong.
convection does not cause heat loss. convection itself is a movement Caused by heat, (or differentials of it.) convection to me looks more like an effect of soemthing else, not the something else that they claim it is. those books are wrong.

and also, "heat loss", if you look at it as drop in temperature, can be caused by expansion.

is an interesting thread.

cheers,
v.

Matt Dirksen
(NamelessWay) - MLife

Locale: Mid Atlantic
Re: Re: Torso Simulator to test Heat Loss in Outdoor Gear – Radiation on 06/27/2013 14:34:24 MDT Print View

http://www.homedepot.com/p/Reflectix-4-ft-x-125-ft-Heavy-Duty-50-g-Perforated-Radiant-Barrier-RB4812550/203927012#.UcyfwPlZd8E

Many companies which sell reflective barrier products for homes typically have perforated versions. These are due in-part to reducing the risk of condensation between the rafters of a house and the attic envelope beneath them.

Matt

Rod Braithwaite
(OddRod)

Locale: Salish Seashore
Nice work. on 06/28/2013 15:25:02 MDT Print View

Well written exploration of the topic.
Thanks.

Eric Blumensaadt
(Danepacker) - MLife

Locale: Mojave Desert
Kestrel Weather Meter on 06/28/2013 18:26:38 MDT Print View

I recommend using a Kestrel Weather Meter (4200 series).

It measures relative humidity, temp, air density, etc. for a much better, more accurate take on atmospheric conditions

Tanner M
(Tan68)
Re: Re: - Omniheat, divers are sold this as well on 07/02/2013 08:23:13 MDT Print View

The diving industry likes to sell aluminized stuff. At least they used to. Haven't looked in a while. I think one brand marketed titanium something. Really, I can't remember if I bought the hype then or not... I know I couldn't afford it. Minimizing water flow through a wet suit is most important. Titanium or not, don't want to heat up a new volume of water if the warm water flushes out.

> jerry adams:

> > Omni-heat: http://www.columbia.com/Omni-Heat-Reflective/Technology_Omni-Heat_Reflective,default,pg.html"

> They have dots of aluminized material with breathable in between. Good idea if the percentage of area covered by aluminized material is large enough. Cover more area to reduce radiant heat loss. Don't cover too much to prevent water vapor passage.

Edited by Tan68 on 07/02/2013 08:44:33 MDT.

Tanner M
(Tan68)
Re: Link to site & Painter's tarp on 07/02/2013 08:43:36 MDT Print View

This site has some interesting information:
http://www.windowoutdoors.com/WindowOutdoors/Window%20Outdoors.htm

I wonder that the painter's tarp might also transfer less heat than a foil blanket. Both are impermeable barriers. The tarp doesn't reflect radiation but the foil blanket does. However, I imagine the foil blanket will conduct heat better/faster than a plastic tarp.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: the science books are wrong on 07/03/2013 13:32:14 MDT Print View

"convection does not cause heat loss..."

Convection can disrupt the boundary layer of air on the outside of your sleeping bag which adds about 10 degrees of temperature.

Convection can also blow through your fabric and carry away some of the warm air inside your insulation.

Convection can increase the minimum temperature you'll be comfortable. An outfit could be comfortable in still air, but if it was windy you could be cold.

Samuel C. Farrington
(scfhome) - M

Locale: Chocorua NH, USA
heat retention on 07/04/2013 21:21:41 MDT Print View

Jerry,
Nice article. Wow, you have been busy with this topic.
Do you think you resolved the question of whether a radiant barrier, like Heatsheets, is worth its weight in terms of heat retention. It weighs a little less than one oz/sq/yd. When placed most effectively in a bag or quilt, Will it provide more heat retention for its weight than Primaloft One or high loft down?

It was mentioned that Heatsheets are mylar. Doubt it, as it behaves more like polyethylene, and bonds like polyethylene, not at all like mylar.

From reading David Thomas' posts and your article, it seems that the answer to the above question is negative. If that is so, the better design would just add a little more Primaloft One or down rather than a reflective barrier.

Note: A meat tenderizer with lots of little spikes is one way to make Heatsheets vapor permeable.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: heat retention on 07/04/2013 22:55:53 MDT Print View

I think a reflective layer facing out will provide more warmth for it's weight than primaloft or even down. Also a lot less volume packed. I think that's a great emergency gear item in case you get injured and can't continue walking.

The only problem is it doesn't breath so it will condense inside and get everything wet. So, better to just add a little more insulation. And radiation only accounts for a small amount of heat loss so you don't have to add that much insulation.

I was looking at heatsheets website. They said it reflects back 65% of the heat from your body. They have pictures of runners wearing heatsheets. If there was a one inch air gap between human and heat sheet, then it would reflect back all the radiation. It looks like there's an air gap some places but, for example, where it rests against the shoulders, there's no air gap, so it doesn't work. Maybe overall, it averages that 65% of the area has an air gap...

I think if they got rid of that obnoxious advertising on the outside of the heatsheets and just had a reflective layer, it would work better...

Meat tenderizer - good idea, lots of holes quickly. One thing is, I would like to be able to make a known amount, like 5% or 10% of the surface area be holes.

Matt Dirksen
(NamelessWay) - MLife

Locale: Mid Atlantic
Re: heat retention on 07/04/2013 22:58:41 MDT Print View

Please do not forget that relative humidity has an equal part to play with heat retention, when it comes to overall "comfort". This is what our psychometric charts have been offering us for over a century now. If our bodies are warm enough, but we are in an environment where we are too humid, we won't be comfortable, and will most likely not fall sleep.

It seems that RH is simply neglected in these quantitative measurements. I'd hate to see conclusions being formed based on half of a picture. If IR barriers actually worked a practical scale, all our cars, buildings, and homes would be shiny now. The reality is that IR barriers are more effective at reducing solar heat gain than preserving human generated warmth.

Fwiw, there were sleeping bags made with high emissive fabrics back in the 80's (Kelty comes to mind.) They are gone now because they ignored the importance of vapor permeability. Furthermore, you will find less building codes requiring vapor barriers, simply due to the fact that building science has now concluded that they cause more harm than good to our environments.

If you want to stay warmer in a sleeping bag, have an overbag, make sure you have a good conduction barrier (ground pad), a good draft coller, and don't toss and turn. The sudden air exchange in a bag will render any heat retention pretty much eliminated.

Matt