Where's the air conditioner go?
July 10, 2010 12:31 AM   Subscribe

Bush league air conditioner -- a block of ice and a box fan. Where does the ice go for maximum efficiency?

A block of ice is now sitting in my freezer waiting to be used on this overheated, AC-less night. I think it should go behind the fan. Other people say in front. Which side will give me the most bang for my cooling buck? I'm trying to do the physics but I'm too stupid.

Previously (kind of, but not really)
posted by zvs to Home & Garden (12 answers total) 2 users marked this as a favorite
I would posit that you want the ice close behind the fan - then, most of the air going through the fan would have been close to the ice.

In front of the fan would be less good because the ice would block airflow.

Or you could always put the ice in a bag and just hold onto it!
posted by Earl the Polliwog at 12:38 AM on July 10, 2010

That depends on what you mean by "bang for your buck". Fact is, that block melting is going to use up a certain amount of energy; this energy will come from the air in the room which will therefore cool down. As long as the doors to the room remain closed the end effect will be the same: soon after the ice is melted the temperature will average out, and all the air will be fractionally colder than before.

Where you place the ice will only marginally impact the end result - the sooner the ice melts, the sooner it will start averaging out. If it melts slower, it will last longer, the breeze will not be as cool, but the end result will still remain the same. So you'll have to try it out and see what pleases you most: a stream of really cold air that will be gone soon or some luke-warm air that will last longer, but unless you have a giant hunk of ice that won't completely melt during the night the end result will always be the same, no matter whether you place the ice in relation to the fan.
posted by PontifexPrimus at 1:00 AM on July 10, 2010 [1 favorite]

Best answer: It depends on what you want.

The phase transition of the ice turning into water (and eventually evaporating) is obviously going to absorb the same amount of thermal energy from the room no matter where you put it. But I imagine putting the ice in front of and slighty below the fan, so the airflow is washing direct over it, will produce the coldest fan-wind (and make the ice melt fastest). Putting the ice behind the fan wil be similar, but probably slower as the blast of air will be less focussed.

Even better would be to put the ice in front of and slight above the fan, so the cold air gets blown towards you as it falls away from the ice, but that might be more difficult to set up without getting water everywhere.
posted by A Thousand Baited Hooks at 1:07 AM on July 10, 2010

The melting ice will increase the humidity in the room and (depending on where you are) may actually make your room feel hotter by increasing the heat index.

This doesn't really answer the question, but--- stick your pillowcase and bedsheet in a plastic bag and put them in your freezer for a while.
posted by at the crossroads at 1:21 AM on July 10, 2010

In my experience, this is ineffective enough to be a waste of time. You're not going to cool your house down with a block off ice. It'll remove some heat, but it'll accomplish the same work no matter how you position it.

If your house has poor insulation and it's much cooler outside, I suggest just going outside or using your fan to ventilate the area by putting it in an open window.. If it's warmer outside, the dismal amount of heat you remove with your block of ice will be replaced with outside heat.

That said, you can put the fan blowing on the block of ice and sit directly in front of it. That'll help cool *you* down. But if I were that desperate I'd take a cold shower, which is much more effective.
posted by cj_ at 2:47 AM on July 10, 2010

Be aware more heat was released by the freezer pumping heat away plus inefficiencies than you could ever possibly get back. Also, if you want to stay cool, one thing you can do is set your fridge/freezer to a warmer setting.

This is true but only a real problem if his freezer is in his bedroom.
posted by pullayup at 4:14 AM on July 10, 2010

This last week I've been trying it. I finally put the ice in baggies, stuck a few baggies in a pillowcase, and wore the pillowcase around my neck. After that I stopped caring about my fan.
posted by SMPA at 4:42 AM on July 10, 2010 [1 favorite]

A block of ice lasts longer than ice cubes because it's more efficient in insulating itself - blowing a fan over it will pull some 'cold' off of it, but the slowness of it melting won't transfer as much heat away from the air. Create more surface area by breaking the block up, or use a bunch of ice cubes, and you'll cool the air faster, and get more water puddles sooner.

Cooling the air, then hoping to transfer the air to you, and then hoping the air will cool your body, is a pretty inefficient way of doing things. Here's a suggestion: Put the block of ice in a large bucket of water. Soak your shirt or a towel in it, and then put that over your shoulders. The cold water will cool you more directly, plus (depending on local humidity) evaporation will draw heat away from your skin, too. If you've got a dehumidifier, run that in your room.

If you've got a freezer, use it to make juice pops or koolaid popsicles -- it'll cool your body from the inside, not necessarily making the room feel cooler, but your body won't work so hard at cooling itself down. It helps pandas.
posted by AzraelBrown at 6:09 AM on July 10, 2010

Sounds like you're trying to simulate a swamp cooler (evaporation cooler). As said above, it won't really work that well.

Since it's a box fan, you could stretch a moist towel over the front of it and keep it moist. That would work better than the ice, but might be a pain to keep damp. However, be warned of the risk of electrocuting yourself and anyone else nearby, since a box fan isn't insulated against water like a swamp cooler is. If you try this, let us know if you make the news.

It also won't work in a wet climate. Unless your existing humidity is fairly low (20% or less, I would think) I wouldn't bother.
posted by krisak at 6:11 AM on July 10, 2010

Best answer: I stumbled across this yesterday: Making Your Own Air Conditioner to Beat the Heat.

Haven't tried it myself, so no guarantees, but if you have or can get hold of the cheap supplies it might be worth a shot.
posted by trip and a half at 7:28 AM on July 10, 2010 [1 favorite]

I can't find it online, but I remember seeing a cooler like the one trip and a half posted, with two trash cans and a siphon instead of a pump.

I've tried various methods of this in the past. It never works as well as you'd like.
posted by Hactar at 8:57 AM on July 10, 2010

Response by poster: Thanks, all. I considered the homemade A/C but honestly it was too much of a money sink to bother -- summer in Seattle is not wrought with hot days, we just had a few.

And I should've been clearer, we really just needed it to get to sleep -- it's not so hot in here that it's unbearable during the day, and we had popsicles/damp clothes/etc. The ice worked reasonably well (my freezer is separated from my bedroom) to get us through the night. It was a pretty big block.
posted by zvs at 10:39 AM on July 10, 2010

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