Thermal conductivity numbers for boat fridge construction

[GILow]

Hi all,

There are lots of threads on building boat fridges, and I've been trawling them with some care, but I cannot find the range of thermal conductivity numbers people are finding work well (enough) for insulation material.

Obviously there are the super high spec products like Aerogel and Vacuum panels, but for more conventional foam insulation, I wonder if anyone has an idea of what the threshold is for "adequately low" thermal conductivity.

For instance, my preferred two part, 94% closed cell foam is rated at 0.0256 W/mK, but I have no idea if this is good or not.

Does anyone have some working figures?

Matt

[coopec43]

Why don't you google:

"thermal conductivity freezer insulation comparison"

It's not hard!

[GILow]

Originally Posted by coopec43

Why don't you google:

"thermal conductivity freezer insulation comparison"

It's not hard!

Why don’t you read the question?

It’s not hard.

[GordMay]

From ☞ 5. Thermal insulation materials, technical characteristics and selection criteria

FIGURE 5.4 Comparison of typical insulation thickness for shore-based chilled and ice stores operating at average ambient air temperatures of 20 °C, 30 °C and 40 °C (thickness rounded up to nearest 5 mm)

[coopec43]

Originally Posted by GordMay

From ☞ 5. Thermal insulation materials, technical characteristics and selection criteria

FIGURE 5.4 Comparison of typical insulation thickness for shore-based chilled and ice stores operating at average ambient air temperatures of 20 °C, 30 °C and 40 °C (thickness rounded up to nearest 5 mm)

I've already given GILow a link to that article but apparently it is not what he wants. (As far as I am concerned I think it is an excellent article)

Obviously I am misreading GILow's comment but I don't know how?

[GILow]

Originally Posted by GordMay

From ☞ 5. Thermal insulation materials, technical characteristics and selection criteria

FIGURE 5.4 Comparison of typical insulation thickness for shore-based chilled and ice stores operating at average ambient air temperatures of 20 °C, 30 °C and 40 °C (thickness rounded up to nearest 5 mm)

Thank you GordMay, I’ve seen that and many similar articles.

It was during my searching that I hit on the bit that is confusing me. According to most of the credible data I can find, the quoted thermal conductivity figures for most of the good materials does not vary that greatly. In fact, I found articles claiming a higher thermal conductivity in aerogel than my two part poured foam.

Yet aerogel, I am pretty sure, has been spoken of here on CF as a kind of gold standard, if you can afford it.

Hence my question was to hopefully illicit a response from some of our refrigeration gurus to get them talking about the numbers and the rationale they use.

I feel like I am missing a subtlety.

[jimbunyard]

Know next to nothing about this, but on the list here for 'low temperature insulation materials', the old standard glass fiber is right up there with the lowest 'K values' among common materials...

http://tiac.ca/wp-content/uploads/20...Section-02.pdf

[coopec43]

Originally Posted by jimbunyard

Know next to nothing about this, but on the list here for 'low temperature insulation materials', the old standard glass fiber is right up there with the lowest 'K values' among common materials...

http://tiac.ca/wp-content/uploads/20...Section-02.pdf

Jimbunyard


Aerogel is apparently more expensive than gold (NASA used it on their Mars Rover).

For our purposes glass is good but polyurethane is better.


Vacuum insulated panels have the highest R-value, approximately R-45 (in U.S. units) per inch; aerogel has the next highest R-value (about R-10 to R-30 per inch), followed by polyurethane (PUR) and phenolic foam insulations with R-7 per inch. They are followed closely by polyisocyanurate (PIR) at R-5.8, graphite impregnated expanded polystyrene at R-5, and expanded polystyrene (EPS) at R-4 per inch. Loose cellulose, fibreglass (both blown and in batts), and rock wool (both blown and in batts) all possess an R-value of roughly R-2.5 to R-4 per inch.
Straw bales perform at about R-1.5 per inch. However, typical straw bale houses have very thick walls and thus are well insulated (WIKI)


My understanding is that most household fridges would have polyurethane foam.

[john61ct]

The keys are **per thickness** as well as availability & cost.

R-values are not constant across all temperature ranges, so stats from home construction will vary from refrigeration use cases.

Tests have shown the most effective bulk insulation at reasonable price for freezer / fridges is polyiso.

But with a 1/2" of XPS, aka Dow styrofoam/blue board, as an inside layer to buffer the polyiso from the most extreme cold temps.

[senormechanico]

Polyisocyanurate foam may have a higher R rating, but it absorbs water.
Aerogel does not, neither does blue or pink closed cell foam.
That is a big deal on a boat, but not so much in a house.

[john61ct]

Yes, proper encapsulation of the foam is critical.

You don't want incomplete vapour barriers nor intrusion of water from either side, no matter what kind of foam you choose.

[john61ct]

http://www.kollmann-marine.com/insulation.aspx

http://www.kollmann-marine.com/Refri...hp?topic=342.0

http://www.cruisersforum.com/forums/...st-193232.html

http://www.cruisersforum.com/forums/...ml#post2450446

http://www.cruisersforum.com/forums/...ml#post2444073

[GILow]

Originally Posted by john61ct

Kollmann Marine

Insulation Ice Test

http://www.cruisersforum.com/forums/...st-193232.html

http://www.cruisersforum.com/forums/...ml#post2450446

http://www.cruisersforum.com/forums/...ml#post2444073

Thanks John61ct, most of those articles are familiar to me. I particularly liked the thread where our three main CF refrigeration gurus chimed in. Mostly in agreement in that thread, which is rare.

[GILow]

Originally Posted by john61ct

Yes, proper encapsulation of the foam is critical.

You don't want incomplete vapour barriers nor intrusion of water from either side, no matter what kind of foam you choose.

This is why I like the builder's film approach. It solves two problems, namely vapour intrusion AND prevents the two part foam from sticking to the hull.

[LouK]

Please note that closed cell polyiso is non-hygropobic, does not absorb water & this is why it is used in roofing all over America. It’s also the reason why ‘blueboard’ Or other open cell foams are not used in roofing systems- as they do absorb water & thus would blister the membrane during the summer.

In compact assemblies or membranes like a roof or your ice box, polyiso is hard to beat.