With the heat of summer in full force it can be tempting to try and devise ways to keep cool on your own without resorting to buying an air-conditioner, or paying the electrical bill to operate one. This is especially motivating as the push for more environmentally friendly energy usage has never been stronger.

Here’s a cheap and simple way to build an air-conditioning unit using simple household items. To build the unit, the items and materials you will need are:

• Fan
• Wood (pieces of 2x4)
• Metal container (such as a garbage can, approximately 15 inch tall by 13 inch diameter)
• Circular saw
• Nails and a hammer
• Aluminum metal repair roll, thin sheet (18 inch x 5 ft, available as a standard size at a hardware store)

At this point you may want to go to my website http://assortedtips.blogspot.com/2007/08/making-homemade-air-conditioner.html . It will give you a better understanding of what’s going on, as there are pictures there for you to look at.

The fan I used is roughly 8 inches in diameter. This diameter will roughly dictate the size of the opening for the duct (but fan size is not critical). This opening will be made out of pieces of 2x4.

Using the circular saw (making sure to wear eye and ear protection and following safe operating procedure) cut pieces of 2x4 and nail them together to make an 18 inch x 8 inch frame. The aluminum roll will attach to this frame, to form a spiral duct.

To form the spiral duct align the outermost end of the aluminum roll with one of the 18 inch sides of the 18x8 inch frame, such that the inside surface of the roll touches the side of the frame. Adjust the alignment so that the edges of the roll and frame are flush, and then nail them together. Now, align the other end of the roll to the other side of the frame, such that the outside surface of the roll touches the side of the frame. Once again, make sure the edges are flush and nail them together. You should now have a spiral shaped duct.

Next, put the metal container inside the spiral duct, adjusting its position and that of the opening so that the air blows roughly tangentially past the container on its way in, and with ample room to exit. Now, fill the container with cold water and put a lot of ice in it. The temperature of the water should drop to a few degrees above freezing. The outside of the container will quickly become cool, since metal is an excellent conductor of heat.

Lastly, place the fan in front of the opening, and put a sheet or whatever you have (which serves as a lid) on top of the duct, leaving a small opening for the air to blow out of, after making its way around the duct. You may also want to seal part of the opening above the fan with an old newspaper so that there’s no unnecessary gap above the fan where air can escape before being cooled. This is a crude design for sure, but it allows for easy fine-tuning, before making something more permanent.

Now, turn the fan on and the air coming out should be cooler. For my own unit I measured the exiting air as 2-3 degrees cooler than the air going in (I used a digital kitchen thermometer to measure). The ice in the container should last a few hours, and when you’re done you can dump the water down the drain.

The advantage of this design is that you are utilizing the entire surface area of the metal container to cool the air.

The dimensions and sizes I used work together nicely. But of course, many variations are possible.

Some tips:

• You can put salt (NaCl) into the container along with the ice. Due to the endothermic reaction between salt and water, you will get a further lowering of temperature. It may be a useful experiment, to see how much salt to add to get a target drop in temperature.
• Setting fan speed on low rather than high may result in cooler air coming out since the air stays in contact with the cold container longer.
• Well-placed fins inside the duct may help to improve the flow and mixing time, thus improving the amount of cooling. This would be a good project for future work.
• In winter you can make blocks of ice outside, and store them in your freezer for when you need them in the summer. I figure that to hold you over on those really hot days you need around 30 ice blocks, each 4x8 inches, and one block for each sitting. Remember, this is free ice and you won’t be loading your freezer.

© 2007 Vittorio Norman

Vittorio Norman has a blog at http://assortedtips.blogspot.com