The well-worn idiom reads necessity is the mother of invention. Last week the central air conditioning unit for our loft finally konked out. The system had been installed thirty years ago with the original 1979 conversion of the commercial building into residential use. Ours is the last of the original A/C units on the roof. And up until last week, it still worked rather well. It was noisy, and sometimes cantankerous. It usually needed a mild servicing call in the spring each year. But it functioned. It cooled the loft effectively.
Our only real trouble with it came in 2005. The A/C blower mechanism decided it was going to leak sporadically over the top of our bathroom that spring. Whirl — already taxed with taking care of me after the brain injury — spent considerable amount of time and energy maintaining the house and managing the leaks until we finally found the cause and corrected it. An archaic drainage system had clogged up and would overflow from time to time depending on the humidity. That was the catalyst to start our planning to replace it. We put a new A/C system in our budget and started socking money away. Our intent was to upgrade the entire system in 2009 or whenever the unit died. Whichever came first. As it turns out the deadlines came due at almost the same time. Almost.
We just wish the unit had hung in there for two more weeks.
Rather than pay to repair the old unit only to replace it a few weeks later, we decided to build our own air conditioning unit on the cheap based of some plans originally attributed to some college students in Calgary.
Tools and Components : Styrofoam Cooler (1), Box Fan (1), Copper Tubing (3/16 inch; 50 feet), Zip Ties (60), Aquarium Pump (1), Aquarium Tubing (20 feet), Mini Tubing Cutter (1), Scissors (1)
Rigging the Tubing : We began by positioning the coil of copper tubing on the front of the box fan. We aquired 50 feet of 3/16ths inch tubing and took advantage of the grid-like guard that existed on the front of the fan to anchor the tubing. We used zip ties on the cross-hatches, beginning on the outside edge and methodically spiraled toward the center.
Cutting the Tubing : We could have planned a tighter spiral that left us with less leftover tubing. However we decided to cut the excess with the mini tube cutter and leave it off. We connected the aquarium tubing to the ends of the copper spiral with the feed starting at the outside edge and the return from the other end of the spiral.
Trimming the Zip Ties : I liked the look of the the forest of zip ties. It gave the whole design some motion. However the noise of the box fan was already considerable. When the flapping of the free zip ties was added to that, it was too much. We quickly cut down all the zip ties.
Filling the Tank : The experiment attracted the attention of our two cats. At several moments throughout the project I felt like they were our foremen, directing our efforts. We submerged the aquarium pump in the water and connected it up to the vinyl leads to prove out the entire closed system.
Adding Ice : The pump is not particularly powerful, but given enough time it was able to provide a constant — if somewhat weak — flow from the water reservoir through the copper spiral and back to the return. The last step of the process was to get that water cold. We added a lot of ice to chill the water as much as we could.
Success! : Turning on the fan and the pump yields a small but refreshing breeze of of chilled air. It does not replace our failed A/C unit but it does provide significantly cooler air than what comes off of our unmodified control fan. A more powerful water pump would propel the cold water through the copper tubing faster and provide for more effective overall cooling.
The complete gallery of photographs includes a few more images than what I’ve included here. The unit is not pretty. It will not cool down the big expanse of the loft, but it was a fun experiment and cost about $50 in parts altogether. And more than half of that total was spent on the tubing.
Beta|Erinyes 
I thought about doing this in my computer room to hel with the cooling in the summer. Adding some salt to the water can help lower the freezing point of the water making the unit slightly more efficiant. I’m sure you can find a vole to salt ratio somewhere. I’m glad to hear they work out alright.
That’s a good idea. I really think the critical piece is the power of the pump. It was interesting to track the cooling/warming process through the copper spiral. It would reach a threshold where the ambient air temperature’s warming would override the cooling process of the water. You could track it by watching the dew point move around the spiral.
I think a more powerful pump would propel the cold water through the pipe faster and allow for more effective dispersion of the coolant. I also wonder how effective an aquarium pump will be near the freezing point. But that’s why we experiment!
Great job and post! I agree that optimizations are possible. It would be interesting to try and increase the surface area of the cooling surface as well. Finding “finned” tubing does this well, but really increases the cost and safety of operating the chiller. I agree that trying a more robust pump is the easiest mod to try first. Falls here, and winter is far behind…