Evaporation powered fridge

[Daox]

Found this the other day. Not sure how well it would actually work. Anyone have thoughts/ideas?

[Xringer]

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..?.

[Ryland]

It's not going to lower the temp down past the dew point, ever, even with a fan.

[Xringer]

78.3 °F
Overcast
Humidity: 75%
Dew Point: 70 °F

Humm, Not so good..

[NiHaoMike]

It's possible to use it in hybrid refrigeration, where evaporative cooling is used to cool the condenser.

[AC_Hacker]

Originally Posted by Daox

Found this the other day. Not sure how well it would actually work. Anyone have thoughts/ideas?

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.

Originally Posted by Xringer

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.

In the early part of the 20th centure, the Coolgardie safe was very popular in Australia, in areas where there was no electricity.

Originally Posted by Ryland

It's not going to lower the temp down past the dew point, ever, even with a fan.

A ten or fifteen degree drop can be quite useful and comfortable. Biggest plus is that no electricity is required.


In this post, I made a suggestion regarding Direct Evaporation to Peakster:

Hey Peak,

It may be a bit late in the season for this, but if you put a soaker hose or yard sprinkler on the roof of your place and a timer that will activate it every 20 minutes or so, for about a minute or two duration (the right timer is the toughest part of the system to obtain, but they do exist), the evaporation of the water will give you a considerable amount of cooling for not so much money.

I suggested this to a friend that was suffering from the heat in her convenience store job. After the sprinkler setup, the inside temp dropped ten degrees. Seventy five-degrees is much easier to live with than eighty-five degrees.

-AC_Hacker

Originally Posted by NiHaoMike

It's possible to use it in hybrid refrigeration, where evaporative cooling is used to cool the condenser.

Have you found any references that would suggest if this has been used? Any idea as to the benefit?

-AC_Hacker

[NiHaoMike]

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.

[AC_Hacker]

Originally Posted by NiHaoMike

...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. ...it has an equivalent SEER rating of about 40.

My SEER to COP conversion may be a bit flawed, but a SEER of 40 seems to indicate a COP of around 9.24.

Not too shabby.

Tell us more.

How about some photos and more detail on this system...

-AC_Hacker

[NiHaoMike]

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.