Insulating a portable fridge

Submitted: Thursday, Jan 17, 2019 at 13:06
ThreadID: 137687 Views:1505 Replies:5 FollowUps:6
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Hi all.....

Owning a number of Engel fridges (running as fridges only), my circumstances have changed and have decided to run my older 39 litre as a dedicated freezer, which brought an idea to my head to possibly coming up with a way of further insulating so it better holds temperature meaning less compressor run time = less power to run.

Currently, My dedicated fridge is an 11 yo 40 litre model that has an Engel supplied transit bag, which sometimes when a hand is plased between the outer side of the fridge wall and transit cover, condensation is present for which i cant understand why, and definitely dont want happening when i modify the other model into "freezer only" .

The reason, this model was my grandfathers (1982 cream metal body/olive green lid) and is in fine condition for its age. Whatever form of insulation i put around it (thinking polystyrene) if condensation occurs, could result in rust on the body and lid. I then thought of a possible treatment applied to the surfaces to prevent rust but an unsure what that could be.

Finally, another reason why the extra insulation is because the unit will live on the back of my ute within a canopy where temperatures can and will be the highest of ambient.
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Reply By: RMD - Thursday, Jan 17, 2019 at 14:07

Thursday, Jan 17, 2019 at 14:07
I have an early 39L grey Engel and added two fans. Both are 12v computer fans and wired in series. Only around 100ma draw additional to compressor and connected via a small rectifier to compressor wires.
Insulation in Engels is minimal and mine does get condensation between the steel case and the additional insulation. I made the cover. If run as a freezer I cover the case with heavy thickness of sleeping bag or similar with a refective over cover the divert radiant heat.

Now freezes to -18 in 30C +. Never before did it reach anywhere near that coldness and ran 24/7 and still couldn't freeze well.
AnswerID: 623250

Follow Up By: Cobba123 - Friday, Jan 18, 2019 at 16:44

Friday, Jan 18, 2019 at 16:44
Thanks for the reply..... Yes, I have been reading up on the modification of adding fans to the older models on this forum and thanks to those that have provided valuable information..... I have already ordered everything needed to upgrade my older Engels..... For those that might want to do it as well, 24v AC to 12v DC rectifying circuit boards are readily available on EBay real cheap (just hoping good enough for the job) as well as 12v DC computer fans..... I am also going to throw an additional 24v AC fan in my 40 litre Engel......
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Reply By: Allan B (Sunshine Coast) - Thursday, Jan 17, 2019 at 16:07

Thursday, Jan 17, 2019 at 16:07
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Hi Cobber,

The metal outer cover of the fridge will normally be near ambient temperature when the fridge is operating. If you place thermal insulation over the case the metal temperature will fall due to heat transfer to the case interior. This will reduce the case to below the dew point and condensation will form. This is what you have experienced.

The only way to prevent the condensation is to seal the outer insulation so that moisture-laden air cannot access the metal case. To achieve this the insulation must be 'closed-cell' type through which air will not pass or the insulation must have an outer sealing skin. Then the edge of the insulation must be sealed to the metal case to prevent ingress of air there.

A "treatment applied to the surfaces" may prevent rust but will not stop condensation which could then saturate your insulation and defeat its effect.

Cheers
Allan

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AnswerID: 623255

Follow Up By: Cobba123 - Friday, Jan 18, 2019 at 16:55

Friday, Jan 18, 2019 at 16:55
Thanks Alan for the very informative reply and taken on board..... I have found a product called foil board (used in construction industry)...... it’s basically expanded polystyrene (15mm) sandwiched between two layers of building foil. Given what you have said about “air gaps and proper sealing edges and seams”, I reckon purpose built sarking (the highly adhesive foil tape used for joining construction blankets and sarking) should work well for me here...... The only problem I have is that once I wrap the body of the Engel in this stuff it’s outer integrity is going to be fragile...... May need to consider a thin layer of something else that can take a knock or two .....
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Reply By: Crusier 91 - Thursday, Jan 17, 2019 at 16:32

Thursday, Jan 17, 2019 at 16:32
I used yoga mat cut to size and line the inside of fridge to soften rough rides and insulate. Also used an old -2 degree wetsuit cut to size to fit the inside top of fridge.
Cheers.
AnswerID: 623257

Reply By: tim_c - Friday, Jan 18, 2019 at 10:43

Friday, Jan 18, 2019 at 10:43
Can you leave a small air gap between the fridge and the additional insulation? This would allow any condensation to drain and dry, reducing the likelihood of rusting the fridge casing. The air gap may also be slightly beneficial in assisting the insulation.
AnswerID: 623274

Follow Up By: Allan B (Sunshine Coast) - Friday, Jan 18, 2019 at 10:50

Friday, Jan 18, 2019 at 10:50
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Hi Tim,

If you leave an air gap between the fridge casing and the insulation then condensation may drain but constant moisture forming on the casing would encourage rust.
Better to seal the air gap so no moist air can enter and condense there.

Any air gap will not enhance insulation but may degrade it.
Cheers
Allan

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Follow Up By: tim_c - Friday, Jan 18, 2019 at 11:56

Friday, Jan 18, 2019 at 11:56
If an air gap will not enhance insulation but may degrade it, why would anyone pay extra for double-glazed windows?
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Follow Up By: Allan B (Sunshine Coast) - Friday, Jan 18, 2019 at 12:11

Friday, Jan 18, 2019 at 12:11
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Double-glazed windows are sealed around their perimeter.
Their value as an insulator lies in air (or other gas or even vacuum) between the glass panes being superior insulation to just a single glass pane through which heat can more easily transfer.

Perhaps I could have said "Any air gap will not enhance insulation but may degrade it" if not sealed around the perimeter.

An unsealed air gap will allow the circulation of warm air within the gap with can then transfer through the fridge wall to the contents.
Cheers
Allan

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Reply By: Member - John - Friday, Jan 18, 2019 at 10:51

Friday, Jan 18, 2019 at 10:51
I used stick on 25mm insulation/foam from Clark Rubber, had reflective silver on the outside, being stuck on, precluded air and condensation. Sealed the edges with 100mph tape. seemed to work well.
John and Jan

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Follow Up By: Cobba123 - Friday, Jan 18, 2019 at 16:56

Friday, Jan 18, 2019 at 16:56
Yes, similar to my reply to Alan...
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