Peltier Fridge
Deveak
Solar Expert Posts: 38 ✭✭
In before a wave of "Its not efficient!"
Yes modern compressor based refrigerators are more efficient, so are dc fridges. The problem i see with both is, cost and for the AC fridges, inverters. Insulation is cheap. I have limited skills but i am pretty sure for 2-300 bucks i could build a EXTREMELY well insulated peltier fridge. If i could get the kw draw under 500 watts a day for a 5 cubic foot box i would consider it a resounding success. I found a simple 12 volt thermostat for kegerators. 15 bucks, the peltiers themselves, 5-20 bucks depending on quality and since its solid state, i would go cheap. I can replace most of the parts for pennies, service it myself and being a solid state component they have long life. Also the custom gaming computer market has a DEARTH of cooling options that fit the peltier perfectly since it heats and cools just like a cpu. The trick is finding a low power efficient cpu cooler. My question is what is to stop me from say, getting two units, running a 5 cubic foot fridge with them, using the thermostat to either turn it off or lower the voltage (makes it more efficient for most peltiers)to maintain the tempature when it gets there and building the box with 8-12 inches of foam board and mylar on the outside. Double rubber seal on the door. Yes its not a efficient at cooling per say but if it barely has to work to cool the box it lowers my daily wattage. I've seen peltiers with a temperature difference over 70 degrees. Seems a much better option and more long term than going dc or even ac compressor based fridges. A actual freezer may be an issue.
Yes modern compressor based refrigerators are more efficient, so are dc fridges. The problem i see with both is, cost and for the AC fridges, inverters. Insulation is cheap. I have limited skills but i am pretty sure for 2-300 bucks i could build a EXTREMELY well insulated peltier fridge. If i could get the kw draw under 500 watts a day for a 5 cubic foot box i would consider it a resounding success. I found a simple 12 volt thermostat for kegerators. 15 bucks, the peltiers themselves, 5-20 bucks depending on quality and since its solid state, i would go cheap. I can replace most of the parts for pennies, service it myself and being a solid state component they have long life. Also the custom gaming computer market has a DEARTH of cooling options that fit the peltier perfectly since it heats and cools just like a cpu. The trick is finding a low power efficient cpu cooler. My question is what is to stop me from say, getting two units, running a 5 cubic foot fridge with them, using the thermostat to either turn it off or lower the voltage (makes it more efficient for most peltiers)to maintain the tempature when it gets there and building the box with 8-12 inches of foam board and mylar on the outside. Double rubber seal on the door. Yes its not a efficient at cooling per say but if it barely has to work to cool the box it lowers my daily wattage. I've seen peltiers with a temperature difference over 70 degrees. Seems a much better option and more long term than going dc or even ac compressor based fridges. A actual freezer may be an issue.
Comments
https://en.wikipedia.org/wiki/Thermoelectric_cooling
And only cool by ~20C/36F per stage.
Mechanical refrigeration is still the most (electrically) energy efficient (with good insulation).
-Bill
We have a12/24 VDC fridge in our RV (danfoss compressor). It is an energy miser. I did add an extra 2" of XPS foam to the sides, back, top and bottom. We're in NM where it is sometimes hot. When I was testing the most KwH in a 24 hour period was 480 watt/hours and that was a hot day. With a normal indoor temperature the use dropped to less than 300 watt/hours. That is for a 4.2 cu ft interior fridge. There are a few different makes and they do vary in energy consumption with how well the condensor coils are cooled.
As mentioned in the posts above, Peltiers do exist with larger differentials (the cheap coolers just use the cheaper Peltiers), and you can stack them for a larger total differential.
If you don't have "enough heat removal" capacity, the "warm items will heat up the rest of the food/defrost the freezer/etc... It is not just about insulation.
If all your food is pre-chilled (we would freeze meat/juices/etc. for trip/camping--Expecting them to thaw/keep rest of the food cool during trip, in a Peltier cooler.
-Bill
edit: I looked at a dc powered danfoss compressor conversion as well prior to getting my current setup, but the numbers to do the conversion just didn't pan out in terms of the cost to do such a conversion. I'm happy I went with the ac powered freezer-turned fridge, it works wonderfully and at such minimal cost. Prior to finding this solution, I couldn't figure out how to make a battery storage system work, the amount of batteries I'd have to get was just way too high given my need to refrigerate food. Now, it's a real possibility to get rid of the grid connection entirely!
But not to worry Deveak, I had to learn a bunch of things the hard way too.
-Bill
That was my experience with chest type conversions. The vertical type I have now is designed using the evaporater tubes to form the racks on which the items are placed, so the condensation forms directly on the racks. If I run it at the freezing point, the condensation forms ice. When enough builds up. I place a heavy towel under each rack, turn off the power to the "fridge" and wait. About 6 or 8 hours later most of the ice has melted into the towels and it's ready to go again.
Wayne, I was thinking about that upright freezer too! glad to see someone else thought of the same thing. The price was about the same either way, but I've got 2 kids whose noses are constantly in and out of the thing, so I figured I'd save more energy by having the horizontal storage and not have the cold air spill out every time they checked the fridge.
-Bill
Bill, I've been thinking of trying that for some time. The top "shelf" is the last to cool off, (cooling starts with the middle shelf) and since the thing only runs about 5 minutes every 50 or 55 minutes, it shuts off again before the liquid refrigerant gets to the top shelf. One of these days - - - - -
And like "kaipo-boy" says, vegies seem to last forever when the temp is set at or very near freezing. In fact. everything lasts far, far longer than in any normal fridge I've ever owned or had anything at all to do with. Not kidding. The result is something that gives results sort of halfway between a fridge and a freezer. One more reason I'd never be satisfied with a normal fridge again.