DIY fridge/cooler?

Interesting thread. If Aerogel or similarly effective insulation is used, would it be possible (by increasing its thickness far beyond usual standards) to reduce power-requirement to within the capacity of a small battery and solar recharging?

My thinking is that most yachtsmen graduate from the smallest and simplest (non-electric) cruising boats, straight to much bigger, more elaborate set-ups, where fairly hefty and complex 12v supply, wiring, maintenance and recharging is necessary...yet refrigeration is still typically only available for the duration of each cruise, when regular charging is available...

...whereas (planning ahead) I'd quite like to keep my first cabin-boat largely non-electric, but refrigeration can't be achieved without some power...

...so, if I was to regard the fridge as only a tiny place of long-term storage for a handful of foods/medicines which won't last at summer cabin temperatures, could the 20-litre space theoretically allotted to a conventionally power-hungry 12v cooler, be stuffed with insulation to allow, say, a 4-litre core to operate continuously without the limiting power-consumption and noise that yachtsmen are accustomed to?
 
dancrane said:
Interesting thread. If Aerogel or similarly effective insulation is used, would it be possible (by increasing its thickness far beyond usual standards) to reduce power-requirement to within the capacity of a small battery and solar recharging?

My thinking is that most yachtsmen graduate from the smallest and simplest (non-electric) cruising boats, straight to much bigger, more elaborate set-ups, where fairly hefty and complex 12v supply, wiring, maintenance and recharging is necessary...yet refrigeration is still typically only available for the duration of each cruise, when regular charging is available...

...whereas (planning ahead) I'd quite like to keep my first cabin-boat largely non-electric, but refrigeration can't be achieved without some power...

...so, if I was to regard the fridge as only a tiny place of long-term storage for a handful of foods/medicines which won't last at summer cabin temperatures, could the 20-litre space theoretically allotted to a conventionally power-hungry 12v cooler, be stuffed with insulation to allow, say, a 4-litre core to operate continuously without the limiting power-consumption and noise that yachtsmen are accustomed to?
Click to expand...

Insulation is key but there is a law of diminsihing returns. You could get all your stuff cold and simply put it in a well insulated cold box with a block of 'ice' and it would stay cold for a long time. The heat just needs to be kept out. Of course problems arise with things such as a lid where there is always going to be sub-optimal insulation and you are going to open it from time to time. Also there tends to be things which bridge the insulation such as pipes for the compressor. I am a big fan of insulation as once fitted it pays for itself with no running costs. My plan for a fridge would be to add significant layers of aerogel to achieve insulation properties many times that of a conventional fridge while maintaining similar capacity. The compressor will still have the same power requirements it just won't need to run as often.
 
dancrane said:
Interesting thread. If Aerogel or similarly effective insulation is used, would it be possible (by increasing its thickness far beyond usual standards) to reduce power-requirement to within the capacity of a small battery and solar recharging?
Click to expand...
If remember this previous thread correctly, skipper_stu is in the Med and running a fridge entirely off solar + house battery: http://www.ybw.com/forums/showthread.php?432158-On-the-hook-in-the-Algarve-and-solar-panels

If I understand this PDF correctly, aerogel is about twice as insulatey as other insulation boards (i.e. phenolic / polyurethane / polyisocyanurate bought from builders merchants) - see section 7, "Construction of a Cool Box" on page 11 - http://www.swingcat.co.uk/what/fridge_freezer_calculations.pdf

This thread inspired me to read up on the subject a couple of days ago, and it looks like most people are using 4 or 5 layers of 25mm (1") of builders merchants insulation - i.e. 4cm - 5cm total.

Would aerogel make that much difference?

Best use I can see is that it allows you to make the walls of your coolbox 1" thick instead of 2" - i.e. the fridge takes up less space / has more internal volume. I think keel cooling might well be the more effective. http://www.penguinfrigo.co.uk/shop/product/592/

pmagowan said:
The heat just needs to be kept out. Of course problems arise with things such as a lid where there is always going to be sub-optimal insulation and you are going to open it from time to time.
Click to expand...
The lid will never fit perfectly without a gap, so there will be losses there. But I read recently that opening the lid for short periods doesn't make that much difference.

This was explained in another comment in these forums I can't now recollect, but it stated that the heat storage capacity of air is low, partially because it's so light.

So if you open the door of a front-opening fridge and all the air flows out, then that will indeed need cooling again after you close the door. But doing so will take a fraction as much electricity as cooling the 300ml cans of soda also in there, because a can of soda is heavier than a cupboard full of air.

(The above is what I understand from recent reading - I don't pretend to be an expert, and am glad to be corrected.)
 
I think the heat gained from opening a top opening fridge is minimal but then we are talking about the margins here. The big gains are in the construction and suitable insulation. Obviously, being able to have 2 or 3 times the insulation in the same space is going to be a good improvement. Remember the compressor only has to remove the heat that the fridge gains once a steady state has been reached (i.e. all the stored produce has been cooled). You stop heat entering the box by having good insulaton, minimal themal bridges and minimal circulation of air from inside to outside.
 
Very many of us run fridges entirely powered by solar panels. My fridge is water cooled, which makes a big difference to power consumption. It is in most respects a standard Waeco 60 litre fridge, other than the water cooling. My total panel output is 125 watts, sufficient in summer but slightly lacking in autumn and no doubt far from sufficient in winter, when I am not in Greece. Commercial fridges are fairly poor so far as insulation is concerned but considerably more convenient than a top loading fridge. As usual, it's a compromise for the user's choice.

The specific heat of air is 1/1000 that of water. Cold air falling out of the fridge when the door is opened feels dramatic but the loss is rapidly restored once the door is closed again. Adding one can of warm beer to the fridge contents is considerably more power consuming than opening the door for 30 seconds.
 
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