A while ago I stumbled upon a video showing some people in Bangladesh who had invented a kind of passive air cooler made from scrap bottles that could help poor people keep cool in the summer, you can read more about it here. I think it’s a neat idea so I figured I would try to build one of my own.  The version shown in the video fits in a window but I figured i could fasten it on the front of a fan for increased effect. This post is a build log detailing the process.

Materials:
As can be seen in the article you only need some plastic bottles and a backing board of some kind. I though 6 bottles would be enough but I ended up using 10 of them. The board I’m using is a kind of plastic board you can find in stationary stores here in Taiwan. They have a structure similar to cardboard which makes them light and sufficiently strong for small projects.

Materials and tools 

Step 1:
I made mine to match the size of the shell of the fan by taking the shell off the fan and tracing around it with a marker.

Tracing the edge

Step 2:
I measured the fan to find how far from the edge to place your bottle tops. I’m not sure what is the best placement but I chose to put them at the widest part of the fan blades.

Measuring the fan blades

Step 3: 
I cut out my backing board and drew a circle marking where I would place my bottle tops.

Backing board cut out

Step 4:
I cut the tops off all the bottles, trying to make it as even as possible.

  • Cutting the bottle tops
  • Mock up with my bottle tops. Here I realized I would need more than 6 of them.

Step 5:
I placed a bottle top roughly centered on the line I had drawn then traced around it with a marker and cut it out. After a test fitting I continued to do it all the way around.

  • Test fitting of first bottle top
  • All holes cut and ready

Step 6:
I used a hot glue gun to glue the bottle tops in place. I’m using a small glue gun for crafts which is safe and wont burn the plastic. The industrial kind might damage the plastic or your fingers.

  • Preparing the glue gun and all materials
  • Gluing in progress
  • All bottle tops glued in place

Step 7:
The fan I’m attaching this to has a large hole in the center of the shell (there used to be a cover but it has fallen off) with three smaller holes around it. These would work nicely as attachment points. I made two sets of holes, one matching the three holes in the fan shell and one slightly inside the original holes.

  • Marking the three holes 
  • I used an awl to make holes through the board in the correct places.

Step 8:
I used zip ties to attach the passive AC to the front shell and then put the shell back on the fan. The zip ties go through the backing board, loop around the edge of the big hole in the shell and then back through the backing board again.

  • Zip ties, better than duct tape when they can be used but less versatile
  • Zip ties in place

The result:
Here is the finished product mounted to the living room fan. Not too bad i would say.

The question is, did it work? Well, sort of… I felt the air coming out the nozzles was cooler than if I was just using the fan so the principle works. The problem is that the air becomes very directed, the normal fan gives you one big stream of air, with the passive AC you get 10 small streams and a lot of gaps between them where the air doesn’t move. Furthermore the streams of air from the passive AC don’t reach as far as that of the naked fan so you need more power to feel anything. Basically, while the temperature of the air coming out of the passive AC is lower than ambient, it doesn’t cool you down as well as a normal fan.

In the article they put big boards full of bottle tops over windows which should cool down the air inside the entire building. I think this is probably a better approach than the one I used. I might try this in the future to see if it works better.