Cooler air for under Lm10

Last week, I was absolutely fed up of theoretical engineering, so I decided that a little practical work would be a good idea.

This guy was featured on both digg.com and slashdot, and I had been turning over his idea in my head for the past few days.

The idea behind it is that of a heat exchanger - passing heat from one fluid (like air) into another fluid (like water). When there are two different objects at different temperatures, heat will always go from the hot one into the cold one. This how a car radiator works - heat passes from the hot engine into the water in the radiator, and then the heat passes from the radiator into the air.

So this guy, who is a civil engineering student in Canada, came up with the idea to build a heat exchanger and stick it on the back of the fan in his room, to cool the air down faster. What he did was to take some copper tubing and attach it to the back of the fan in a spiral, and then run cold water through the spiral.

As the fan sucks air in, the air passes over the cold copper, and heat from the air passes to the copper and into the water inside it. This has the effect of cooling the air down, and therefore you too.

So, one afternoon early last week, I trotted off to the local ironmonger to get the materials.

The copper tubing was the biggest problem because the lady serving me couldn't find a flexible tape measure, and using a metal one just wasn't working... so she sent me off to the haberdashery to buy her a couple of tape measures but the haberdashery didn't have any... but then when I got back she managed to find it after all so that was OK...

The website said to use 25 feet, but I only got 20 because of the cost of it (student budget!). This was 5/16th of an inch in diameter, and cost 21 cents per foot. Actually I got it for 19 cents a foot because of the measuring problem, which works out to two free feet :-)

I also bought ten feet of plastic pipe, two jubilee clips, and a packet of 100 plastic ties because I had no idea how many I'd need. I only bought ten feet of pipe because I didn't intend running the waste water outside as shown on the website. I figured that by raising the feed bucket, I could get enough head (difference in pressure) to just run the waste water into a second bucket.

I did get some funny looks as I walked home with 20 feet of copper tubing casually slung over my shoulder, but hey, I've had my share of funny looks in the past, heheheh.

Back home, it was surprisingly easy to wrap the copper around the fan. There were a couple of hairy moments, but overall it was OK. The guy's suggestion to pre-bend the plastic ties didn't work for me, but I had taken the front cover off the fan so it wasn't too difficult to bend the ends back out so I could tie them off.

The biggest problem with copper in this case is that the more you bend it and mess around with it, the harder it gets, because the atoms inside are sliding around and building up at certain points (you see, I was paying attention during Metallurgy!) and eventually you get to a point where you can't manipulate it any more. There was one point when I thought a certain part was coldworked to death, but then managed to bend it again. *whew*

The other potential problem is that if you bend the copper tube too much, it will kink, and good luck trying to remove the kink! But copper is quite forgiving, and I imagine that you'd have to be bending it quite sharply to kink it. Anyway, I didn't have a problem with that.

Here you can see the coil on the back of the fan, attached with plastic ties (I cut the ends off the ties). That's all 20 feet of the copper there, it was just enough. It's important to leave enough space between the sections of pipe for the air to actually pass through the fan! I only needed about 12 ties to attach the pipe securely - if I had known, I would have bought 12 for 24 cents rather than 100 for Lm1.55! Oh well, I'm sure I'll have another project later that will call for more ties...

Admittedly it's not a particularly neat spiral and the coils could have been closer together, but it's not bad for a first try :-)

Once I had the coil mounted, I cut the plastic pipe into two lengths - I measured how much I needed for the feed bucket (from the copper inlet down to the floor, to make sure I had enough) and cut there, and left the rest for the waste water flowing out of the copper. I screwed on the jubilee clips without much trouble although they were a little big. Dad warned me not to tighten them too much or they'd kink the copper, so I didn't, but the plastic was fitting quite snugly onto the copper pipe anyways.

Here's the final setup:

You can see the fan on its stand, and yes, that's grey and white duct tape holding the casing together and attaching it to the broomstick that's holding the fan up. It's a very old fan!

The blue bucket is the feed water, and the whiteness on its lower half is condensation from the air. For a stand for it, I turned an eski upside down, and now just have it sitting on a chair. The orange bucket is the waste water bucket. Here's the waste feed:

To get the feed water cool, I used some ice batteries that Mum has; they are plastic and full of a fluid - you stick them in the freezer to freeze them, and then use them to keep stuff cool e.g. when you take food to a BBQ. Since then, I bought some for myself but my new ones don't seem to work as well as hers did.

With the fan running, there was an appreciable difference in the temperatures at the copper inlet and outlet. In fact, there was a fair amount of condensation at the inlet and none at the outlet, which is a good sign that it was working well because it shows that the water was entering the copper fairly cold, but gaining heat from the air by the time it exited. A normal bucketfull runs through quite quickly, but it's still cold enough (and the batteries are still frozen enough) to just pour the waste water back into the feed bucket and run it through a few more times.

This shot shows that there was condensation on the inner coils, but not the outer ones:

I don't have an appropriate thermometer so I can't really measure its performance, but it does seem to work decently as long as I get the feed water to be really cold to start with. Sticking some water the freezer and then pouring it into the feed instead of relying only on the batteries seems to help a lot. The colder the feed water is, the more it will cool the air.

The water runs through the setup without a pump because the whole thing is like a siphon - since the inlet to the plastic pipe (in the feed bucket) is higher up that the outlet (in the waste water bucket), the pressure in the air on the surface of the feed water pushes it through the pipes without needing a pump.

However this needs to be started up by sucking water through until the system gets going. I find this to be the worst part of all this - it's taking me a while to get the hang of it and I feel sick if I accidentally get the water in my mouth and swallow (tastes really bad). Little Sis suggested that I use one of the hand pumps that I use for balloon twisting, but adapting one for pumping water would be a real pain.

Then Dad gave me the idea of buying a little hand-pump that is usually used in small boats to get the fuel running between the tank and the engine. It's just a plastic bulb that you squeeze with your fist, and it's got a one-way valve inside so the fuel only flows in the direction you want it to.

One of those would make starting the siphon a lot easier, but I haven't got one yet. At Lm1.94 it's a decent investment though :-) Also, once the siphon is going, I could then use this hand-pump to periodically pump water from the waste bucket into the feed bucket without having to stop the whole process and then re-start it again. Oh yeah.

On the whole, it was a fun project. The cooling effect is nowhere near that of an airconditioner, but it definitely helps, and I think that I'll be very glad for it later in the summer :-D

• 20 feet of copper tubing: Lm 3.80

• 10 feet of plastic tubing: Lm 1.70 (I think they made a mistake with the price)

• two jubilee clips: Lm 0.20

• one packet of plastic ties: Lm 1.55

• four freezer batteries: Lm 1.08

• the feeling of nausea after ingesting water that has passed through 10 feet of plastic and 20 feet of copper tubing: Priceless

Comments

[Toni Sant]

Simply awesome! I wish this was the sort of thing I did whenever I wasn't blogging.

[MaltaGirl]

Thanks :-)

The great thing about this kind of project is that whether it works or whether it flops, it still makes for great blog fodder, lol!

[faħmu]

very cool..prosit..

[Dave]

I wonder if you worked out the extra heating for moving about to change buckets etc ;) a cool idea I saw somewhere for a personal cooler had a sort of necklace with peltier devices positioned over the arteries going up to the head - the idea to cool blood as it flows and get it distributed around the body .. i'm sure you can get peltiers for a decent price (if Greenweld still exist that is ;P) .. still thanks for sharing the experience! (& I had no idea how much copper tubing costs)

[MaltaGirl]

Lol @ extra heating :-)

The peltier necklace sounds uncomfortable, but when the temperature starts to hit the 40's anything that promises relief starts to look attractive!

I build one for a friend but I modified a couple of things. First, the use of 25” of copper tubing is counterproductive. I only used about 15” and split it between the front and the back. If you measure the airflow in front of the fan, you realize the strongest flow comes from the center and the edges have very little. So therefore, covering the front with 25” of tubing is pointless because as water passes thru the copper it starts to lose its temperature and the more of a distance to travel you have the more condensation and a rapid loss of temperature. My rig has a water pump that circulates the water around and extends the use of the fan. In addition, I used a 9qt cooler rather than a bucket or garbage can, which cannot preserve the temperature. You get better results by putting the tubing in the front rather than the back.

The other thing that makes this rig not very effective is the fact that summers in Canada are very mild compared to the US. In Florida, for example, this rig will have less than an hour worth of cooling power at 90+ temperatures. It also loses at lot of cooling power due to condensation. If you live in the Southeast, where the climate is moist and hot the condensation is so great that you have to lay a towel under the fan to prevent water from running all over.

My next project for fun involves the use of a radiator/condenser with a water pump some copper tubing and a 26qt cooler.

[Dro]

Have you posted this on Instructables.com?