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Author: Subject: Improvised Airconditioning
vulture
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[*] posted on 13-6-2006 at 12:59
Improvised Airconditioning


It's very hot here in Belgium at the moment, ofcourse it's only that hot when I have exams, go figure.

Anyway, I was thinking of airconditioners and thought about improvising something with labequipment, more for fun than anything else.

So I figured, what if I put some water in my large dessicator, connect the vacuum pump and constantly evacuate it to about 100mbar. A fan would blow the room air over the dessicator and the "exhaust" from the vacuum pump would simply be vented to the outside, properly sealed ofcourse.

I'm foreseeing a few major problems:
- 100mbar is not enough to make water boil at room temperature (30C now)
- the heatconductivity of thick dessicator glass is rather poor

Let's see if anyone else has some bright ideas for a poor mans airconditioning (no cryogenics or liquid propane stuff etc)...




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12AX7
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[*] posted on 13-6-2006 at 13:20


Water is a crap-ass refrigerant, because it boils at such a low pressure, and tends to freeze at exactly useful temperatures.

Best way to improvise a refrigerator is to take apart a 'fridge and rebuild it. :P

I'm guessing it's also nicely humid (about like Wisconsin in summer, although pleasantly not today ;) ), so a swamp cooler won't interest you...

Tim




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Mr. Wizard
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[*] posted on 13-6-2006 at 14:54


I have a couple of 'swamp coolers' (evaporative coolers) on my home. Water is pumped over three or four open pads with holes .5 to 2.0 mm in it. A 1/3 to 3/4 horsepower motor drives a belt driven squirrel cage, to move 5000 cubic feet of air per minute. The temperature outside is 94F (34.4C) and it is 73F (22.8C) inside. I live in the desert south west of the US, and the units are very practical for all but a month of very humid weather. As 12AXT noted, they are not comfortable when the humidity gets above 20%. A quick test with a wet bulb thermometer would tell you what you could achieve. They are very economical, and in dry heat I have regularly seen 74F (23.3C) inside while it was 104F (40C) outside. Just about any idea involving boiling refrigerants will quickly empty your wallet. Even the commercial units I have on my house , which are quite efficient, cost a fortune to run, even at $0.10 /KWHr. The units are rated 3.5 and 3.25 'tons',an antiquated term, which means they can equal the cooling of that many tons of ice per day.

Often much comfort is given by a common ceiling or desk fan. Unless the humidity level is 100% you will realize some cooling. Has anyone heard of water misters? They hook up to a regular water line and use only a few liters of water per hour to create a fog like mist, suitable for cooling outdoor areas. I was going to build a multi stage evaporative cooler , where one stage pre-cooled the air going in to the next stage, but I realized the relative humidity levels would quickly rise as the air was cooled and would not yield much additional cooling.
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Magpie
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[*] posted on 13-6-2006 at 15:28


I agree that evaporative coolers ("swamp coolers") can be very economical and useful where the relative humidity is low enough. I lived in the southwest US for a while where they were used effectively.

I now also live in a Western desert area but due to crop irrigation the humidity stays at about 40% RH all year. I don't have a swamp cooler but my neighbor does. It seems to do the job quite well for him even at 40% RH.




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Mr. Wizard
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[*] posted on 13-6-2006 at 17:07


Increased RH does make the home less comfortable. I agree the coolers will still work at even 40% RH but the comfort level will be much less, as your clothes start sticking to your body, door frames start to swell from the moisture and potato chips get limp.

What sort of RH are we talking about in Belgium today?
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franklyn
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[*] posted on 13-6-2006 at 17:39
Quick and Dirty


Quote:
Originally posted by vulture
Let's see if anyone else has some bright ideas for a poor mans airconditioning

To chill , while working in the suffocating heat produced by
industrial vacuum ovens used for curing dielectric resin in
potted core inductive devices, the foreman rigged a copper coil
immersed in an alchohol bath containing dry ice. One end was
connected to the central compressed air supply and the other had
a bleed valve to allow a jet of freezing air out.
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Rosco Bodine
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[*] posted on 14-6-2006 at 10:00


If you can get an old large diameter parabolic satellite dish and drive mount , perhaps you could cover the dish
with reflective mylar and use it as a heliostat solar collector on a rooftop , with an ammonia cycle boiler coil at the focal point of the dish where the feed horn would usually mount . You would need a good sized reservoir for storing the charged refrigerant between cycles . Since the refrigeration system has no moving parts it would last practically forever .....and since it is solar powered it would have no operating cost . A small solar panel and battery could supply all the electricity for the dish aiming motors and for the small fan motor on the evaporator . Most of the system could probably be
assembled from scrounged parts cannibalized from
junked equipment at a scrap yard .

http://www.nh3tech.org/absorption.html
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unionised
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[*] posted on 14-6-2006 at 11:41


So far as I can judge you could still use a swamp cooler sort of thing (the efficiency would suck; here in the North of the UK it's 15c outside anyway so it wouldn't matter; but it's also 75RH).

Dribble water over a cloth wrapped round a big metal pipe, put it outside and set a fan to blow air over it. This should cool the pipe. Get another fan to blow air through the pipe into your house.
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Pommie
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[*] posted on 18-6-2006 at 19:35


A more chemical based system could use lithium chloride.

Heres a paper on it.

Mike.

Attachment: LiCl solar cooling paper.pdf (409kB)
This file has been downloaded 1308 times

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gsd
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[*] posted on 18-6-2006 at 20:52


Why not use the Ranque-Hilsch vortex tube extensively discussed in this forum and so beautifully condensed in a practicable format by tecnotacho at his website:

http://www.tecnotacho.com/projeto1.htm

with the necessary modifications to adapt it to cool the air ?
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franklyn
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[*] posted on 7-7-2007 at 22:07


Here is another approach _
http://www.solarmirror.com/fom/fom-serve/bags/solar-icemaker...

.
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Pyridinium
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[*] posted on 7-7-2007 at 23:23


If your building were well insulated and you had a few hundred kilos of ammonium nitrate and some water, you could make the place nice and cool... ah, well, nevermind. A couple hundred kilos of NH4NO3 might give the wrong impression these days.

I think KSCN gives a pretty cold solution as well. Again, you'd need quite a bit of it. Then you could evaporate the solution out in the sun, bring the crystals inside, and do it over again :-D

You could always rig up a giant Peltier cooler, with the hot side facing outside your building... and running at a huge electricity cost, of course.
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DerAlte
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[*] posted on 7-7-2007 at 23:38


Here we rarely have temps above 100F But I'd much rather be in Tucson. We commonly have 95F but also 70% RH. That feel's like Death Valley at midafternoon on a hot day - a heat index of 122F. For 4 months per annum, too. Pray for rain! It can then drop as low at 78F with 100% RH.

Regards,

DerAlte

[Edited on 7-7-2007 by DerAlte]
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