
Bangladeshi air cooler made from plastic bottles uses no electricity - infodroid
http://inhabitat.com/this-amazing-bangladeshi-air-cooler-is-made-from-plastic-bottles-and-uses-no-electricity/eco-cooler-plastic-bottle-air-conditioner-3/
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upofadown
Anyone know how this is supposed to work. The part about "compressing and
cooling the air" doesn't make any sense. The air wouldn't be compressed and it
it was it would get warmer, until it wasn't compressed any more.

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.

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HeyLaughingBoy
It's the expansion of the compressed air that cools it. IANAME (I'm not a
mechanical engineer) but thinking through the physics of it, you need a fairly
strong airflow since the compression has to be adiabatic (air must be
compressed quickly enough so it doesn't heat up), then once it expands, it
cools.

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.

~~~
upofadown
>air must be compressed quickly enough so it doesn't heat up

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.

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andrewl
I love solutions like this. I look at them and think "It's so simple and
obvious! I could have invented that." But I never do invent them.

~~~
infodroid
Maybe such solutions are only really obvious in retrospect!

Some of my favourites in this category are the Q Drum (a rollable water
container) and the GravityLight (a lamp powered by gravity).

[1] [http://www.qdrum.co.za](http://www.qdrum.co.za) [2]
[http://gravitylight.org](http://gravitylight.org)

~~~
yongjik
"Gravity light" will never be something more than a curious gadget.

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.

~~~
infodroid
The device does not use a typical consumer LED lamp.

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](http://gravitylight.org/techspecs)

~~~
yongjik
So, according to the tech spec, it has 0.075 W output = 75 mW.

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.)

~~~
infodroid
The problem is that the cheapest source of lighting for many poor communities
is hazardous biomass fuels like kerosene. And unfortunately good alternatives
like solar may not be a viable option for everybody.

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/](http://www.fenixintl.com/uganda/) [2]
[http://evanmills.lbl.gov/pubs/pdf/offgrid-
lighting.pdf](http://evanmills.lbl.gov/pubs/pdf/offgrid-lighting.pdf)

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gameofdrones
thunderf00t will debunk this as not a sanitary napkin-making machine-scale
revolution.

