Intro: Personal Solar Powered Air Conditioner
The purpose of this Instructable is to create a personal air conditioner for outdoor use. The 'cool' comes from an ice/water reservoir stored in a thermos. Copper tubing is used as a heat exchanger, a small water pump moves the ice water and a small fan distributes the cool air. The entire system is run from a solar panel from Brown Dog Gadgets. An off-the-shelf USB Y connector can be used to connect the components so that no soldering is needed.
Step 1: The Thermos
Any insulated cooler can be used. It should be portable and ideally have a pouring spout at the top to allow the copper tubes to go in an out without a lot of drilling. The same spout can be used to collect any condensation on the copper coil and add that water to the reservoir.
Step 2: The Power Source
Brown Dog Gadgets makes a series of portable solar cell panels with built in voltage regulation to supply +5V at a USB connector. The one that I have chosen can supply 1A in full sunlight or 5W.
Step 3: Power Distribution
To make the project easy, I have decided to use the USB connectors without any fixed wiring. Since a fan and pump are both powered, I purchased a 'Y' adapter that splits the single power connector on the solar panels into two paths. To allow me to make current measurements, I also purchased a USB voltage/current monitor.
Step 4: The Pump
I purchased a small, USB powered submersible pump, typically used in fountains. The specs are: 5V at 300ma (1.5W). The one on the right was from a previous build and fit the tubing better.
Step 5: The Fan
The first unit that I made focused on very low current and very low noise since I wanted to use it at music festivals. After some testing, I decided that the fan speed was too low and to get any cooling effect you needed to be within about 8" from the fan. The fan I bought for this project is a Thermalake brushless 5V with variable speed. It has a USB cable and specs of 550ma (2.75W) at its highest rate. The fan on the right of the photo was larger, noisier and didn't seem to move any more air.
Step 6: The Cool Exchanger
The ice water is pumped out of the reservoir through a spiral coil of small diameter copper tube. The diameter of the spiral should match the diameter of the fan. The center area will not have any air moving across it so be sure to check the fan as you are bending the tubing. I used a fairly thick walled tube and made very small bends. Care must be taken not to kink the tube or else the water flow will be stopped. I wasn't sure of the length to cut the tubing (you could mock it up using string, use calculus or guess) so I just started at one end and kept bending until I was done. Be sure to start with a long straight to go into the thermos and another long straight to return to the thermos. These should be adjacent and close enough to fit down the thermos spout hole. The spout hole should be centered under the fan since water will condense on the coil (if all goes well) in a humid environment and it would be better if this drips into the reservoir instead of down the side of the thermos. When you cut the tubing, use a fine tooth saw. You have to be careful not to crush the end of the tube as you might with a wire cutter.
Step 7: Test the Components
It is good if, on paper, the specs of the pump and fan together show a current that is less than the 1A advertised for the solar panel. I would say to aim for 800mA so that the cooler is running at full capacity even if the panel alignment to the sun isn't perfect. I have found that a USB tester (purchased from Ebay for around $6 is invaluable. It shows the voltage and current at a USB port and updates about once per second. Using a 1A wall charger, I took separate measurements for the fan and pump. Be sure to submerge the pump before running it to minimize wear. Everything worked fine and the currents were within the specs.
Step 8: Fan Assembly
The pump should have its USB cable fed up through the thermos spout hole. I had to widen the hole a bit with wire cutters to get the cable through. The excess cable can stay inside the cooler. Take the heat exchanger coil and use zip ties to attach it to the outward blowing side of the fan so that condensed moisture isn't sucked into the motor. Position the fan on top of the thermos so the two ends extend down into the cooler. I have mounted my first one with two small angle brackets but but used zip ties on the second one. Both methods worked fine.
Step 9: Pump Assembly
I found some aquarium tubing that connected one side of the tubing to the output port of the pump. If you don't get a good match, InstaMorph can be used to mold a mating connector between two parts. I roughed up the surfaces with sandpaper to give the InstaMorph more grip and put a piece of tubing inside the pump hole and outside the copper tube to keep things aligned with I modeled the connection.
Step 10: Electrical Connections
The pump and fan are each connected to one branch of the Y cable. The center is connected to the solar panel output port. If you need more distance, you can pull some of the cable out out the thermos and extend the fan cable.
Step 11: Final Testing
Half fill the thermos with either water for testing or ice water for the real deal. Bring the assembly out into bright sunlight. The fan should immediately start to spin and the pump should be circulating water. You can use the USB monitor to see how much current is being drawn. If the sun isn't available, you can test the operation with the wall supply you used for earlier testing. On a hot, humid day I found that the coil cools in under a minute and water condenses on it within two minutes. The ideal thermal transfer should result in the last part of the coil not condensing much water. This means the water has reached the outside temperature. Some pumps will let you adjust the flow rate. Fan speed will also regulate the heat transfer.