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  #21  
Old 11-21-2014, 10:48 PM
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Yea, But....Imagine making a cover that's 3,4 or even 5x the thermal efficiency of the store bought cover thus reducing the duty-cycle of the compressor. You could, in all probability, eliminate the need for a second battery. Plug that into your cost effectiveness equation.....
If I'm going that far, I'm just going to buy a small solar panel.
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  #22  
Old 11-21-2014, 10:58 PM
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Originally Posted by Seldom Seen View Post
Yea, But....Imagine making a cover that's 3,4 or even 5x the thermal efficiency of the store bought cover thus reducing the duty-cycle of the compressor. You could, in all probability, eliminate the need for a second battery. Plug that into your cost effectiveness equation.....
If that was what Drew was making but it sounds like to me he's copying the Engel one, which is soft sided wrap of reflective inside with maybe an inch of batting behind a heavy nylon outer. Adding even this level of bag does help reduce run time because the fridge itself is also insulated with a layer of styrofoam in it's walls.

DIY isn't often about the bottom line, though you still have to be realistic. It would be cool to build a substantial box around my fridge but I admit that it already consumes a lot of bed space so I don't know that I could fit a MT45 if it had a Yeti sort of enclosure. I can barely open the lid as it is with the 'Nest closed.

I'd also think you'd have to consider how to get the compressor heat away so that it doesn't get trapped and work against you by heating the insulation, negating any benefit, or causing poor cooling and overheating of the motor. Maybe a fan and some ducting.
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  #23  
Old 11-22-2014, 12:25 AM
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I'd also think you'd have to consider how to get the compressor heat away so that it doesn't get trapped and work against you by heating the insulation, negating any benefit, or causing poor cooling and overheating of the motor. Maybe a fan and some ducting.
I think this is a big deal....

getting the heat out and away from the coils is huge.

think about what your fridge does in an enclosed space vs. ventilated.
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Old 11-22-2014, 12:58 AM
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When did I say to cover the ventilation grills with insulation?

If there is enough ventilation with the OEM cover you can defiantly maintain the same CFM with a DIY cover thus keeping the compressor compartment at the same temp. Going the DIY route would allow for a substantial increased R value around the refrigerator compartment. I'm thinking ~1 1/2 inches of ensolite for a R of ~9 over the maybe 1 or 2 of the OEM cover.

I know there are enough people that are just getting buy running their fridges on 1 battery and wishing for a dual battery system "just in case". By increasing the efficiency of the fridge will most defiantly decrease the power consumption to the constraints of a single battery system.

Last edited by Seldom Seen; 11-22-2014 at 01:50 AM.
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Old 11-22-2014, 08:22 AM
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You greatly overestimate Ensolite insulation. The typical blue stuff (Ensolite PVC-NBR-CR) has thermal conductivity (k-factor) of 0.231 BTU-hr/sqft-F, so typical sleeping pads that are 1/2" have an R-value of about 2.2. It's not really that great of an insulator but being foam and closed cell it's got high practical value in wet environments and is very durable and doesn't compress (which is why it's absolutely invaluable to park your butt on eating lunch sitting on the snow on a ski tour!). A 1.5" thick layer would have an R-value of 6.6.

http://www.rubberlite.com/themes/sit...IV1_030512.pdf

There are tons of Ensolite compositions, so you may have something else in mind. They make a denser automotive damping foam that would be a good choice and probably closer to your R-value, but I assume you mean the stuff that's easy to get anywhere.

In comparison regular cotton has a k-factor of 0.27 BTU-hr/sqft-F, a 1/2" thick layer of cotton has an R-value of 1.9. But this would not be practical, so dense packed cotton batting is used, which is lighter and easy to work with. This changes the k-factor because air is partially used as the insulator. Standard air has a k-factor of 0.167 BTU-hr/sqft-F and therefore an equivalent R-value of 3 for 1/2". Even the cheap quilting batting has an R-value of around 3.5 in typical use (bed blankets). Cotton is terrible because it doesn't handle moisture well at all, but actually is alright at insulation.

I have just one battery and have run my Engel from it for going on 7 years now. Dunno, a second battery is a luxury I've never had. You lose far more heat opening the fridge and waste a lot letting the sun warm up the cover than the thermal loss through the insulation. Getting in and out of the fridge quickly and as little as necessary is the main thing you do to reduce cycling. At night my fridge might run 15% duty cycle (10 minutes per hour) even in the summer.

My mention of the vents is that you have to leave them exposed is all. If you make the outer box too thick the heat from the compressor does not evacuate and just heats up the space between the fridge and insulation, which then does more harm than good. It traps a layer of higher than ambient air right next to the fridge.
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Last edited by DaveInDenver; 11-22-2014 at 08:57 AM.
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  #26  
Old 11-22-2014, 08:54 AM
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mr. smartypants engineer...


Quote:
Originally Posted by DaveInDenver View Post
You greatly overestimate Ensolite insulation. The typical blue stuff (Ensolite PVC-NBR-CR) has thermal conductivity (k-factor) of 0.231 BTU-hr/sqft-F, so typical sleeping pads that are 1/2" have an R-value of about 2.2. It's not really that great of an insulator but being foam and closed cell it's got high practical value in wet environments and is very durable and doesn't compress (which is why it's absolutely invaluable to park your butt on eating lunch sitting on the snow on a ski tour!). A 1.5" thick layer would have an R-value of 6.6.

http://www.rubberlite.com/themes/sit...IV1_030512.pdf

There are tons of Ensolite compositions, so you may have something else in mind. They make a denser automotive damping foam that would be a good choice and probably closer to your R-value, but I assume you mean the stuff that's easy to get anywhere.

In comparison regular cotton has a k-factor of 0.27 BTU-hr/sqft-F, a 1/2" thick layer of cotton has an R-value of 3.7. But this would not be practical, so dense packed cotton batting is used, which is lighter and easy to work with. This changes the k-factor because air is partially used as the insulator. Standard air has a k-factor of 0.167 BTU-hr/sqft-F and therefore an equivalent R-value of 3 for 1/2". Even the cheap quilting batting has an R-value of around 3.5 in typical use (bed blankets). Cotton is terrible because it doesn't handle moisture well at all, but actually is quite good at insulation.

I have just one battery and have run my Engel from it for going on 7 years now. Dunno, a second battery is a luxury I've never had. You lose far more heat opening the fridge and waste a lot letting the sun warm up the cover than the thermal loss through the insulation. Getting in and out of the fridge quickly and as little as necessary is the main thing you do to reduce cycling. At night my fridge might run 15% duty cycle (10 minutes per hour) even in the summer.

My mention of the vents is that you have to leave them exposed is all. If you make the outer box too thick the heat from the compressor does not evacuate and just heats up the space between the fridge and insulation, which then does more harm than good. It traps a layer of higher than ambient air right next to the fridge.
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  #27  
Old 11-22-2014, 08:57 AM
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Not smart enough, there were mistakes...
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  #28  
Old 11-23-2014, 10:52 PM
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Heh...that's where I was going, I just didn't type it all out.
Think of it like this: The manufacturers compete with amp draw/efficiency/size/etc.
They have pretty much nailed the ideal size ratio for the insulation to what most customers will tolerate. Adding insulation will be negated if you have air movement at all. That means, where the insulation turns from from fridge side to fridge grille vent, you will need an air-tite gasket of some sort. Same thing for the zipper and the bottom of the fridge.

Think of it like this, a vacuum coffee mug works so well because there is ZERO air movement. And it does all of that in about a 1/4" of space.

Temp isn't exactly like sound, but sound can be transmitted through a solid barrier by just a tiny hole, and essentially render the whole barrier useless.
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  #29  
Old 11-26-2014, 09:34 AM
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Meh, I want to build something. It'll be unique and how want it, it'll keep the fridge from getting dinged up more than it already is and, I get to learn in the process.for me, it's a win-win. Btw, couldn't source the zippers I needed so its turning into a Christmas project. I was actually planning on a CPU type fan inside the cage blowing on the compressor, but I digress.
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