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09-30-10, 07:19 AM | #1 |
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Evaporation powered fridge
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09-30-10, 09:45 AM | #2 |
Lex Parsimoniae
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When I was a little boy, way back around 1950..
We would drive around south Texas with a canvas water bag tied on the front bumper. The water slowly weeping out of the fabric would evaporate as we roared (50 MPH) along the roads between Del Rio and Junction. Even when it was hot out, (90-100 dF) the water in that bag stayed cool. I guess the faster you drove, the cooler the water.. It worked pretty well, but I'm not sure that it was cool enough to keep milk from going bad.. Maybe.. When hiking in the boondocks, I used WW2 GI canteens. (Alzheimer source?) . Whenever there was a waterhole, I always soaked the canvas cover, so it would evap cool the water. Other wise, I would be trying to drink 100 degree water! Before the evap water was gone, the water in the canteen was drinkable, not really lukewarm.. But when the cover was dried out, the water would almost be un-drinkable within an hour or two.. If you had water to spare, you just re-soaked the cover.. The process works, but it's not really going to keep your cottage cheese from turning into gunk.. My guess, wire up a PV to a tiny water pump (if there is no city water pressure) and connect some DC fans to blow over the evap surfaces. And you might keep the insides down at 70 on a 90 degree day.. I guess it all depends on the design.. Maybe a heat-pump.?. A heat-tube to circulate coolant inside an insulated container. It would collect heat inside of the food compartment. On the outside, the tube would be covered with a wet fabric. Hot air would be blown across the covered tube, to force fast evap..?. |
09-30-10, 02:10 PM | #3 |
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It's not going to lower the temp down past the dew point, ever, even with a fan.
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09-30-10, 02:14 PM | #4 |
Lex Parsimoniae
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78.3 °F
Overcast Humidity: 75% Dew Point: 70 °F Humm, Not so good.. |
09-30-10, 10:44 PM | #5 |
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It's possible to use it in hybrid refrigeration, where evaporative cooling is used to cool the condenser.
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10-01-10, 01:50 PM | #6 | |||||
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Quote:
Actually what you have is a Pot-in-Pot cooler, invented by Mohammed Bah Abba of Nigeria.check out this article. Very effective in hot dry climates. Especially appropriate tech for certain regions of Africa. They greatly extend the marketable life of produce. Quote:
In the early part of the 20th centure, the Coolgardie safe was very popular in Australia, in areas where there was no electricity. Quote:
In this post, I made a suggestion regarding Direct Evaporation to Peakster: Quote:
Quote:
-AC_Hacker Last edited by AC_Hacker; 10-01-10 at 01:57 PM.. |
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10-01-10, 10:44 PM | #7 |
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I'm not aware of small scale use of hybrid refrigeration, but a friend of mine has built a hybrid A/C. It uses a switched reluctance centrifugal compressor (operating at about 75,000 RPMs) with a water-based refrigerant. (There is an unspecified amount of ethanol mixed into the water to act as antifreeze and I assume to carry lubricant through the system.)The condenser is cooled by a separate open evaporative system. Last time I checked, it has an equivalent SEER rating of about 40. Then again, there's a good reason my friend is nicknamed "the fridge girl".
For refrigeration, it would probably be better to use something like R-410a and a common inverter drive compressor with an evaporative condenser.
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10-02-10, 02:28 PM | #8 | |
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Not too shabby. Tell us more. How about some photos and more detail on this system... -AC_Hacker |
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10-03-10, 05:37 PM | #9 |
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It's too bad my friend doesn't want to share all the details. But from my understanding, most of the efficiency gain is simply because the evaporative cooling allows the condensing temperature to be much lower than ambient, allowing the heat pump to operate with a lower delta T. In hot, dry climates like Arizona, I can easily see it offering as much efficiency as a (theoretical) 40 SEER conventional system. If you want 70F evaporating temperature at 100F ambient, an evaporative condenser with 85F condensing temperature would offer half the delta T of an ideal heat exchanger.
The efficiency gain wouldn't be as high for refrigeration but there would still be some.
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