I reworked the previous version. The design is basically the same. I just improved the construction.
The main construction materials used were:
• Aluminum repair roll ($10-15)
• Nuts, bolts, screws and washers ($10-15)
• Durable waterproof silicone: GE Silicone II - for adhesion to steel, aluminum, and wood - it's the type of high quality silicone used for aquariums (~$15)
I also used wood I had lying around. So that did reduce the price a bit. Total cost: $35-45.
Like before, the heat exchanger is made from straight sections of aluminum bent into a U-shaped channel. To maintain the gap around the edges I used slender lengths of wood, 1.8 cm wide x 1.8 cm thick. The lengths of wood, and the 2x4 shown also serve to strengthen and maintain the shape of the exchanger (Figure 1 and 2 ). A copious amount of silicone was used to seal all gaps around the edges and bolts to prevent water from entering. I also coated the exposed faces of the wood with silicone as I didn't want the water to be in contact with it.
The width of the heat exchanger is 25 cm. The flow length (along the U-shape) is approximately 60 cm. The inside gap is 1.8 cm.
Attached to the heat exchanger is a duct (Figure 2) which feeds air into the heat exchanger by way of a fan (Figure 3). The sides of the duct are oriented so that the wood grains run in the direction of the air flow. This helps reduce friction and pressure drop of the air before it enters the heat exchanger.
The top plate of the duct has a hole in it which is slightly larger than the fan diameter at the lip, allowing the fan to sit snugly inside (Figure 4). The gap between the top plate and duct is sealed with silicone to prevent air from escaping while the fan is running. The junction at the duct and heat exchanger interface is also sealed with silicone to remove external gaps, to prevent air from leaking.
A rubber mat is placed on the bottom of the container (30 cm diameter, 34 cm high) to prevent the aluminum from being scratched by the bottom of the steel container (Figure 5). The heat exchanger + duct + fan assembly is then placed inside the container (Figure 6). Figure 7 shows a close-up view of the air exit.
Supports (Figure 8) are used to keep the unit vertical. Ice, in addition to water, can then be placed inside the container (Figure 9). This serves as the cooling medium. You can also use ordinary tap water without adding any ice. In my area the average temperature of tap water in summer is roughly 20 degrees Celsius.
I made 40 bags of ice outdoors, on one really cold night this past winter (it was minus 20 degrees Celsius), and stored them in the freezer (Figure 10). This way I won't have to make, or buy any ice. Alternatively, you can also leave water outside overnight, allowing it to cool, and use it the following day if it's hot out.
With ice-water temperature between 10-12 degrees Celsius and ambient (room) temperature between 20-28 degrees Celsius, the air cools 3-7 degrees between inlet and outlet. To achieve greater cooling the gap of the heat exchanger would have to be smaller than 1.8 cm to increase the heat transfer rate. The drawback to this is that the air will flow through the exchanger at a slower rate, due to the greater pumping effort required. In the previous version the gap was roughly 1 cm, but the exiting air speed was less than ideal, even with the fan running at maximum. So I would need a more powerful fan (possibly a blower) to compensate for a smaller gap, and maintain suitable air speed.
I found that you need frequent water exchange or a constant supply of ice to maintain a low cooling-medium temperature. One way to do this without too much hassle is to have a big tank of water set up outside to cool overnight, and insulated during the day so that it doesn't heat up. You can then circulate the water from this tank though the container, via a small pump, to maintain the "sink" temperature for the heat exchanger. You can size the outdoor tank so that this lasts you all day and so that it has enough time to cool down during the night. Or you could run a hose from a water spigot to your container, and turned on low, while simultaneously draining it into a nearby drain, thereby keeping the "sink" water cool.
A note on condensation: On humid days water will likely condense on the inside of the heat exchanger, and pool on the bottom. So you may have to pour it out every few hours or so, depending on how much water condenses (it probably won't be a lot). And it's also a good idea to place old newspapers underneath the container to catch condensate accumulating on the outside of the container.
** Update July 09, 2008
Instead of using a metal container I switched to using a cooler (capacity 15 litres). The heat exchanger fits nicely inside and is held upright by horizontal wooden supports. The cooler works better than the container because it's insulated. To insulate the top area I just placed a towel around to help keep the "cool" in. See Figures 11-14. Surprisingly, the temperature drop was better than with the metal container. With ice-water temperature of 7 degrees Celsius, and ambient temperature of 26 degrees, the exiting air temperature was 16 degrees! Very decent.
This unit works great for local cooling. Better than a fan but not as good as a store-bought A/C. But if you just want to keep yourself cool then just put it beside you, and it's all you need.
Have a look at Cost To Make Ice For Homemade Air Conditioner.
Other related posts:
Homemade Air Conditioner Version 1
Homemade Air Conditioner Version 4