Bangladeshi air cooler made from plastic bottles uses no electricity
inhabitat.com
inhabitat.com
My guess is that it allows a relatively high level of ventilation but blocks the sun that would otherwise come in through the open window. So more or less the same effect as an awning.
Of course all of this still takes energy and I'm not motivated to do the math, but cooling a room by 5 deg C still takes the same amount of energy whether it's powered by wind or electricity.
The heating is inherent to the compression. Adiabatic means something else.
To make air based refrigeration work, you would have to compress the air and transfer the extra heat somewhere else. Then you would get cooling when you let the air expand again.
... which is all still moot as the air would not be compressed enough to matter in this case.
Some of my favourites in this category are the Q Drum (a rollable water container) and the GravityLight (a lamp powered by gravity).
If you lift a 20 kg weight by two meters, you gain a potential energy of 20 * 2 * 9.8 = 392J. Amazon seems to be selling "60W equivalent" LED lights which consume 8.5W. (I think that's about the realistic minimum for reading or cooking.)
Assuming 100% efficiency, you can power this LED light for 46 seconds.
The efficiency of its LED lamp is about 210 lm/W whereas for an average consumer lamp it is less than 100 lm/W.
More important is that the brightness of this LED is just 16 lumens compared to 400 lumens for the average consumer lamp.
The device itself only generates 0.075W. This is well within your potential energy calculations.
While this is not the same level of brightness that westerners are used to, it is sufficient for reading and other activities.
The device has an extension point to attach a cable to task-specific spotlights, used for reading for example. Or to power a radio.
Tech Specs: http://gravitylight.org/techspecs
A single 1.5V AA alkaline battery can provide the same output (50 mA * 1.5V = 75 mW), and it can provide up to 2600 mAh, which equals 52 hours, or almost a month if you need the light on for two hours every day.
So a family can simply buy a (very small) LED light and a single rechargeable AA battery. They probably could find a shop to recharge the battery once every month, with minimal fee. Sounds much more reasonable than buying a 12.5kg pulley that needs to be reset every 20 minutes.
* The fact that I've never heard of these amazing "single AA battery powered lights" sweeping through African homes makes me doubt your claim that it's "sufficient for reading and other activities". (Many Africans have cell phones; many more should be able to afford an AA battery.)
Sure there are many parts of Africa with good infrastructure, but just because you are living in Africa in the 21st century does not mean you are now surrounded by power lines!
The nearest power socket might be a few dozen or even hundreds of miles away. How are you going to get there and back? If you don't succeed in charging your battery today because of floods or storms, will you go without lighting?
And there is also cost and access to credit to account for. The GravityLight is targeting $5 price point, whereas a basic solar charging pack in Uganda costs approximately $150 USD on finance [1].
Compared to batteries, GravityLight has no operating costs. It also does not degrade over time, lose charge when it is unused, or unexpectedly stop working when the battery runs out. This might be an important consideration for some.
As for whether the device can produce adequate lighting. A candle or simple kerosene wick lamp will produce around 8 lumens of light output [2] compared with the 16 lumens of the GravityLight. So this is pretty good.
Each community has different needs and circumstances. Providing people with more alternatives to kerosene fuel will allow them to choose the solution that is right for them.
[1] http://www.fenixintl.com/uganda/ [2] http://evanmills.lbl.gov/pubs/pdf/offgrid-lighting.pdf
And I think you're right about solutions being obvious only in retrospect. The simple fact that I can understand a solution as soon as I see it doesn't mean I'll think of the solution as soon as I encounter the problem. Or ever.
In my coding, it's always easier to "see" the complex bad solution than the simple and elegant good solution.