[Travlin]

The 8.52W number is based on natural convection within the closed space. So no forced air. Forced air makes a massive difference in heat transfer (which is why we use fans etc. for cooling stuff).

I think your confusion is coming from the idea that the heat HAS to get in. Heat does not work like a pressurized hose. Heat transfer rate does not increase through a thermal bridge because you have added other insulation. The heat transfer through the thermal bridge is always constant (in a given scenario). The insulation does not affect sidewalls of the pillar at all. The heat transfer runs in parallel. The only way to reduce the heat transfer through a thermal bridge is to use a thermal break, as you have discussed. But the heat transfer through the open interior space can be significantly improved with insulation.

I appreciate you breaking it down like that. It helped significantly. I figured if this thread were up long enough, someone with the background could provide an angle that explained how it works in enough detail to cover the many aspects in play.

What Antoine and others recorded in photos and imaging supports how critically important it is to cover the bridge completely inside the van to retain heat in the Winter by creating a break point there, without Summertime imaging I'll presume the reverse direction will be helped as well. Most importantly, based upon what you have shared there appears to be more benefit to breaking the heat path inside than it was reflected in the tables of material heat transfer rates I referenced.

Thanks to Kabouter's skills in both the thermal and communication realms!

 

[harryn]

All of this points out the opportunity for the van mfgs to really help out the conversion community by using either carbon fiber or fiberglass to build the bulk of the van body vs the existing steel approach.

If the van skin and framework were relatively non thermal conductors vs the existing thermal conductor, imagine how much easier a conversion build would be.

 

[IanCH]

All of this points out the opportunity for the van mfgs to really help out the conversion community by using either carbon fiber or fiberglass to build the bulk of the van body vs the existing steel approach.

If the van skin and framework were relatively non thermal conductors vs the existing thermal conductor, imagine how much easier a conversion build would be.

Easier to get to an acceptable state, yes.

At the end of the day, the van is a very small space - and one would be wise to do as much as possible to insulate the van regardless of van body material. If you can throw a 1/4in of XPS or ez-cool in as a thermal break you should, its neither difficult or expensive.

Same for stuffing the body channels, its not very hard (yes I've done it) and not expensive at all so why not just go for it.

 

[bizeebawdy]

Reviving an aging thread... A builder was glad to accept my cash to eliminate >95% of any interiorly exposed surface metal with a disruption to thermal bridging heat transfer/loss. This involved applying 1/8 inch closed cell polyethylene to all metal surfaces and then 1/16 inch pretty woven material on the closed cell surfaces. Subjective assessment makes me believe that there is a significant benefit in reducing heat loss in cold weather and with both insulating cavities previously discussed AND attending to the disruption of thermal bridging, a year-round benefit will be realized. As one who space heats with only electricity, not liquid fuel, I have noticed far less electrical loads in cold weather. Now, off to the Missouri breaks for a few days to again evaluate the thermal breaks...

 

[jkmann]

This hardly qualifies as hard science ... but, I filled one ceiling channel with Havelock Wool and on the next sunny day the rib was much cooler than the unstuffed ribs. Since the ribs are separated by foam, the heat transmission from the bare roof panel through the open space of the rib is pretty different than if the transmission is just through the foam to the rib. It wouldn't actually be too hard to do the calculations on this. Have at it!

 

[Sweethiking]

I appreciate you breaking it down like that. It helped significantly. I figured if this thread were up long enough, someone with the background could provide an angle that explained how it works in enough detail to cover the many aspects in play.

What Antoine and others recorded in photos and imaging supports how critically important it is to cover the bridge completely inside the van to retain heat in the Winter by creating a break point there, without Summertime imaging I'll presume the reverse direction will be helped as well. Most importantly, based upon what you have shared there appears to be more benefit to breaking the heat path inside than it was reflected in the tables of material heat transfer rates I referenced.

Thanks to Kabouter's skills in both the thermal and communication realms!

 

[Sweethiking]

So in short, it's worth it to insulate the cavities to lower outside noises. We have heavy sideways rain here and high wind. The more insulation in the channels with lower the dcb significantly, especially in the roof channels.

 

[natecostello]

I appreciate you breaking it down like that. It helped significantly. I figured if this thread were up long enough, someone with the background could provide an angle that explained how it works in enough detail to cover the many aspects in play.

What Antoine and others recorded in photos and imaging supports how critically important it is to cover the bridge completely inside the van to retain heat in the Winter by creating a break point there, without Summertime imaging I'll presume the reverse direction will be helped as well. Most importantly, based upon what you have shared there appears to be more benefit to breaking the heat path inside than it was reflected in the tables of material heat transfer rates I referenced.

Thanks to Kabouter's skills in both the thermal and communication realms!

@Kabouter's analysis is incorrect. Here is my response to another time it was posted (albeit after it was posted in this thread):
<other post>

I am not sure what part you disagree with. Here is all the math and a pretty picture. The metal thermal bridge has a tiny cross sectional area, and therefore just can't move that much heat, even though it is made of a highly conductive material.

I appreciate you taking the time to show your work. Some observations:

1. Conductivity of carbon steel can be higher that what you assumed. As much as double. But for consistency I used your value.
2. Your pillar sidewall area is a little off from mine, but that probably comes down to the definition of 16 ga. This has a negligible effect.
3. For the "insulated case" the value of the two resistors in parallel are 3 C/W (pillar sides) and 93 C/W (insulation). So I think we can agree for the insulated case, heat transfer is dominated by pillar sides.

4. I disagree with your model of the un-insulated case. What you have modeled is a 5"x12" uninsulated patch of the outer wall. I say this because you assume a T-bulk equal to the interior of the van. In that case, the effective resistance is 2.5 C/W, which is lower than the pillar sides above, and thus does become dominant. In reality, T-bulk of the air inside the pillar will be substantially lower than the 65F inside the van. We can say this confidently because there is at least one boundary layer between T-bulk in the panel and the panel face. If I assume that the outer wall and the panel face are at your two bounding temperatures (65F and 25F), I can assume two symmetric boundary layers on the interior of the outer wall and panel face. This would place T-bulk in the panel halfway between them. That cuts your convective heat transfer in half (and doubles its effective resistance such that it is higher than the panel sides). Any additional insulation on the outside of the panel face (ie the thermal break) is going to reduce that delta between T-bulk and the outer wall, further reducing convective heat transfer.

For the un-insulated case, if the air volume inside the pillar is restricted from free flow into the van (which it should be as trapped void), the effective resistance from free convection occurring within the pillar is multiples higher than the resistance of the pillar sides. Thus the metal pillar sides will still dominate the heat transfer.

If you think I've made some errors in the above assumptions please point them out.

</other post>

Link to post:

A different kind of insulation discussion - thermal breaks

I've been reading / watching / etc. a bunch on building up a van, and one thing I've been trying to sort out is the thermal breaks and the interior walls - specifically on how to insulate in front of the wide ribs on the side / rear. I've filled them with Havlock wool, but there is still the...

www.fordtransitusaforum.com

If I'm wrong, I'd love to be shown that. My counter was never responded to in the other thread. In the meantime I'll keep focusing on covering thermal breaks, and insulating channels when its not too much trouble.

(edit on orginal - corrrected spelling of negligable)

 

[Kabouter]

@Kabouter's analysis is incorrect. Here is my response to another time it was posted (albeit after it was posted in this thread):
<other post>



I appreciate you taking the time to show your work. Some observations:

1. Conductivity of carbon steel can be higher that what you assumed. As much as double. But for consistency I used your value.
2. Your pillar sidewall area is a little off from mine, but that probably comes down to the definition of 16 ga. This has a negligible effect.
3. For the "insulated case" the value of the two resistors in parallel are 3 C/W (pillar sides) and 93 C/W (insulation). So I think we can agree for the insulated case, heat transfer is dominated by pillar sides.

4. I disagree with your model of the un-insulated case. What you have modeled is a 5"x12" uninsulated patch of the outer wall. I say this because you assume a T-bulk equal to the interior of the van. In that case, the effective resistance is 2.5 C/W, which is lower than the pillar sides above, and thus does become dominant. In reality, T-bulk of the air inside the pillar will be substantially lower than the 65F inside the van. We can say this confidently because there is at least one boundary layer between T-bulk in the panel and the panel face. If I assume that the outer wall and the panel face are at your two bounding temperatures (65F and 25F), I can assume two symmetric boundary layers on the interior of the outer wall and panel face. This would place T-bulk in the panel halfway between them. That cuts your convective heat transfer in half (and doubles its effective resistance such that it is higher than the panel sides). Any additional insulation on the outside of the panel face (ie the thermal break) is going to reduce that delta between T-bulk and the outer wall, further reducing convective heat transfer.

For the un-insulated case, if the air volume inside the pillar is restricted from free flow into the van (which it should be as trapped void), the effective resistance from free convection occurring within the pillar is multiples higher than the resistance of the pillar sides. Thus the metal pillar sides will still dominate the heat transfer.

If you think I've made some errors in the above assumptions please point them out.

</other post>

Link to post:

A different kind of insulation discussion - thermal breaks

I've been reading / watching / etc. a bunch on building up a van, and one thing I've been trying to sort out is the thermal breaks and the interior walls - specifically on how to insulate in front of the wide ribs on the side / rear. I've filled them with Havlock wool, but there is still the...

www.fordtransitusaforum.com

If I'm wrong, I'd love to be shown that. My counter was never responded to in the other thread. In the meantime I'll keep focusing on covering thermal breaks, and insulating channels when its not too much trouble.

(edit on orginal - corrrected spelling of negligable)

I am interested in getting this correct, but I am missing a lot of what you are saying. What values are C/W? Thermal Resistance values I think (but in Celsius). You are very correct about the resitance values. WHat you are missing (I think) is the same factor that most poeple miss. The CROSS-SECTIONAL AREA is the biggest factor here. I never stated that metal conducts at the same rate. But the fact that the air or insulation gap is SOOOOO much larger in our case drops the importance of the thermal bridge.

Again, I am not saying that a thermal break is a bad idea (I installed one), I am just stating that it is very wrong to tell people that filling the voids is useless. The math is all there. You can argue confined space and free flowing air, but it doesn't really matter. According to the dimensions, this would be freely convective trapped air space (how I calculated it). But even stating stagnant air, it is still 5x more energy efficient to insulate the space.

 

[natecostello]

On mobile so just a quick response for now: for your free convection trapped air space you need to account for two boundary layers. Thus the T-bulk in the trapped air is not the T-bulk in the van. This will lower the delta t and thus the heat transfer through the air portion of the insulated void. That was the error in your calc from what I recall off hand. When you correct that error you will find the heat transfer through the void metal sides dominates, even when you account for its thinness.

 

[Kabouter]

The exterior van metal face and the interior metal face of the rib are accounted for in the math. I am not sure what the T-bulk that you are talking about is, do you mean the temperature at various points within the rib? The location of temperature internally does not matter in this calculation. Just run the math the way you are thinking and then maybe our confusion will make sense.

Here is the thermal resistance diagram I am using.

 

[natecostello]

When you are doing convection calculations, T-bulk is the boundary condition temperature. To be clear, I don’t disagree with your insulated channel case. I disagree with the uninsulated channel case. For that case you have your outside air temp (outer T-bulk). Then a boundary layer, the then van metal. Then in parallel: the rib, free convection boundary layer to a channel T-bulk to a free convection boundary layer, then those to paths meet at the outer face of rib. Then whatever you have outside the rib, then a boundary layer to interior T-bulk.

Does that make sense? If you reread the bullet 4 in my post above it might help.

 

[natecostello]

The exterior van metal face and the interior metal face of the rib are accounted for in the math. I am not sure what the T-bulk that you are talking about is, do you mean the temperature at various points within the rib? The location of temperature internally does not matter in this calculation. Just run the math the way you are thinking and then maybe our confusion will make sense.

Here is the thermal resistance diagram I am using.
View attachment 166691

@Kabouter, I'm reproducing your calc exactly, and will extend for the un-insulated void case from there, so hopefully it is easier to get from yours to mine. However I did find a few math errors in your pdf in doing this. When you plug in values for thermal resistance you inadvertently moved the decimals on the outerwall and pillar face value so they are off by 4 orders of magnitude. Check your numbers, they should be 0.000718 K/W and 0.000861 K/W. When you plugged them in you used 7.18 K/W and 8.61 K/W. This changes the heat flow to 2.11W for the 22K (or C) delta T you imposed vice the 0.84W you calculated.

 

[Kabouter]

Well done Nate! I did indeed fail to move my decimal. The overall point still stands but the factor is different. With the dimensions of the rib and column cavities, the convection coefficient would be for contained free air. That is, the air itself is trapped, but can also move within the cavity. Truly trapped air would be what the insulation is providing. I used a coefficient of 10 W/m2K which is the very lowest end of free air. I do not believe there would be additional boundary cases in this instance, but if you want to model that I would love to see it.

TLDR: Insulated cavities will be approximately 4x more energy efficient than uninsulated.

 

[Go Transit Further]

Wow, this whole thread was a tough read. Still not sure if it matters, but I am glad I pulled thinsulate through MY channels.

 

[JacktheTransit]

After many years debating filling channel/cavities with thinsulate. What is the mindset in 2025? Are we still advocating for or against filling cavities? Perhaps the only answer is for $100 more, do it and don't think about it?

 

[dhally]

After many years debating filling channel/cavities with thinsulate. What is the mindset in 2025? Are we still advocating for or against filling cavities? Perhaps the only answer is for $100 more, do it and don't think about it?

Personally, I just couldn't help myself. But I left some bare metal too.

 

[gregoryx]

After many years debating filling channel/cavities with thinsulate. What is the mindset in 2025? Are we still advocating for or against filling cavities? Perhaps the only answer is for $100 more, do it and don't think about it?

... at the expense of them being available for wiring later if necessary... might as well fill them. But it is a pain for fairly small return, as the gents above proved, mathematically.

 

[Kabouter]

I think it matters if you are really going to experience weather extremes. For me, Skadi takes me to sub-zero temperatures as her primary use case. Getting to fill stations is very inconvenient, so maximizing insulation allows me to stay comfortable longer, on less propane. I don't know the exact surface area of the van that is covered by ribs, but it is not insignificant, and those ribs transfer about 4X the heat if left uninsulated.

For 90% of people, it probably makes very little difference. The only two cases I can see making any real difference are winter focused vans, and summer vans that intend to run AC a lot when not connected to shore power. Pretty uncommon use cases.

 

[gregoryx]

... propane.
...

There's the problem.

Yeah, I'm sure I'm wasting a few drops of gasoline in every sub-freezing (sub-zero in some cases... but that's rare in freedom-degrees), but it's all from the same tank.

With all the math you guys did, it would be much more interesting if you wrapped it back up and compared the losses of JUST the ribs versus everything else. I'm guessing very small percentages overall. Huge numbers compared to nothing... but these are small portions of the whole story.