Today's my forumiversary, so I wanted to go ahead and post a writeup on the progress I've made on a project I hinted at a month ago. This cooling method revolves around the idea of harnessing the power of a standard window AC unit to effectively make an extremely powerful water chiller for (probably) cheaper than one would cost to buy outright. This method was inspired by this little-known tutorial, but with my own spin added in the later stages. I believe this should work well for glass terrariums as well as moderate-sized areas with some level of insulation because it's designed to be extremely scalable. For instance, I plan on using it to attempt to cool a section of a cabinet measuring roughly 30"x22"x17" (~48 gallons) with a 240mm PC radiator, but you could easily get a larger radiator or likely even chain multiple together for larger areas. You could even get more cooling power by using a larger AC unit and cooler, or by mixing food-grade glycol in with your water to cool your reservoir below freezing. FULL DISCLOSURE: I have NOT yet tested this to see just how well it performs as my testing area isn't fully enclosed yet, BUT both the water reservoir and the radiator surface cools from 72° to under 40° within 20 minutes. The only drawbacks I've noticed so far are obviously the noise of the AC unit (though it doesn't have to run very much), the copper tubes in the unit will frost up from condensation when running and then drip a bit after the unit kicks off, the system puts off a decent amount of heat and will need some ventilation, and the whole assembly is pretty bulky and not easy to move without damaging it unless you mount it all on a base of some sort.
~5000 BTU A/C unit w/ manual controls – But find a cheap used one instead, shouldn't be hard to locate one.
Cooler (~28qt or 15in+ interior width cooler) - Again, should be able to find one used on the cheap. Mine was like $8 from a pawn shop.
Aquarium pump – this model was probably overpowered, you could probably go with a lower GPH model depending how high you're sending the water.
240mm PC water cooling radiator – As mentioned, this part scales so you can go larger or use more than one if you want. Needs to have studs that fit 3/8" ID tubing.
(2) 120mm PC fans (for 1x240mm radiator) + PC fan power supply + PC fan splitter(s) - Just match this to your radiator.
3/8” ID - ½” OD vinyl tubing
90° elbows for tubing + (4) #4 hose clamps Not strictly required but makes for cleaner mounting. Again, match to your radiator setup.
Drill and ½” bit
1¼” hole saw - size needed for plug on pump linked, may be slightly different if using a different one.
Saw (Jigsaw, Sawzall, most hand saws, etc) - Literally anything that can cut the cooler wall. I used a jigsaw with a long blade.
Pliers (recommended) - makes pulling the knobs off easier
Ratchet and socket set - probably want long sockets for this
Great Stuff spray foam insulation - Pond and Stone preferred but nearly impossible to find right now
Flex Seal spray
Heat gun or hair dryer (optional) - not required but makes life easier
Latex gloves (recommended)
Time to Complete
~2-4 hours + 12 hours foam cure time + 48 hours Flex Seal cure time
TEST THE UNIT BEFORE STARTING. Especially if you got it used. I completely forgot to do this until I was nearly done, and while mine did work I wouldn't have been very happy if it hadn’t. Just plug it in a minute and make sure it cools first before proceeding. Step 2
Set knobs to max cooling (lowest temperature) and low fan speed (low cool), and remove rails and fins if attached. Step 3
Remove the knobs using pliers if you have them, remove the filter and any screws holding the front panel on, then remove the front panel by carefully prying the tabs on sides loose. Step 4
Remove all screws holding metal enclosure (but not the base) on, remove cover. Step 5
Remove the Styrofoam cover from the top of the fan behind the front panel heat exchanger, remove the screws holding on the heat exchanger behind front panel, then remove the nut from the fan rod using a ratchet and long socket (mine was 8mm). Step 6
Be EXTREMELY careful here, I can't stress this enough. First, very gently lift up on the metal heat exchanger to allow the Styrofoam piece underneath to lift up above the lip of the bottom panel and be removed, which in turn will allow the fan to be pulled forward and removed. The control box may need to be unscrewed from the base and moved aside, as well. If any of the copper tubes running to the heat exchanger are damaged during this process, the entire unit will be completely scrapped. Note: This step can be simplified by just destroying the Styrofoam, as it won’t be needed later. Step 7
Most important step here. Fully detach the control box from the heat exchanger, including all wires and temperature probe which can just be bent out of the way indefinitely. Then extremely carefully bend the copper tubing leading to the heat exchanger so that it sits forward of the unit by just enough to clear the cooler wall thickness. Again, be extremely careful not to damage the tubing as that will let the refrigerant leak out making the unit worthless. On my unit the tubes had some kind of hard plaster attached to them, if this is present then you can carefully break it off. Step 8
These next couple of steps will be pretty messy so make sure to have a vacuum on standby. First, line up your cooler in line with the AC unit as it will be installed (front or either side works here), then with a sharpie make a mark on the cooler in front of the copper tubes where they’ll need to pass through the cooler wall. Then, cut the slot out going upwards towards the cooler lid. I started by drilling the bottom out with a ½” bit then cut the rest with a jigsaw, but you can do this any number of ways. Step 9
Next, drill 3 holes in the lid: use the ½” drill bit to make 2 holes to run tubing in and out – you may need to wobble the bit some for the tubing to fully fit through – then make 1 more hole with a 1 ¼” hole saw or larger to fit the power plug for the pump. Step 10
Thoroughly vacuum out the inside of the cooler, then lift the AC unit and slide the tubing down into the slot in the cooler so that the heat exchanger is sitting inside the cooler. You may want to reattach the control box back before moving the unit during this step. Step 11
Wrap duct tape very thoroughly around the tubing and up both the inner and outer walls to cover the slot, leaving the top open for now. Slowly fill the gap with spray foam, starting at the very bottom and working your way up. Wrap a piece of tape across the very top at the end. Let cure for at least 8 hours before proceeding. NOTE: Wear disposable gloves and clothes you don’t care about for this step. If you’ve never used this stuff before, it is EXTREMELY sticky and will literally never come off if it gets on your clothes. Step 12
After letting the foam cure, use Flex Seal spray to thoroughly coat the inside of the cooler where taped to fill any remaining gaps or cracks and help seal the tape edges. Let this fully cure for 48 hours before proceeding to Step 13.
Step 12.5 (if needed)
If you got your AC unit used, at this point you can move the fan assembly over to vacuum up any debris underneath and check the rear radiator for lint or debris. If yours, like mine, had a large amount of debris underneath the fan, do yourself a favor and don’t skip this step and clean it out as best you can before powering the unit on, or else you’ll risk that debris being thoroughly redistributed around your work area. Fan assembly removal should be simple – mine only required 4 screws - 2 top, 2 side - to be removed before being able to lift it up to clear the slot on the side of the rear radiator. Just reattach it when done. Step 13
Run a length of tubing down through one of the holes from the top of the lid, then attach to the pump. This will be your cool water line going to the radiator, so make sure the tube is long enough to reach where the radiator will be mounted in the enclosure. Place the pump in the bottom of the cooler with the intake preferably facing the heat exchanger, then run the pump’s power cable out through the hole in the lid. Note: If, like mine, your pump only comes with a ½” fitting, you can use a hair dryer or heat gun to soften the end of the tubing enough to slide over the fitting. Alternatively, you can soak the end of the hose in boiling water to soften it. Step 14
Run a second length of tubing down into the cooler with the end below the expected water level, ideally away from the pump intake. This will be the return line from the radiator, so it should be just slightly longer than the other line.
Mount the radiator as desired, then attach ends of both tubes to the radiator. If you're using the 90° elbows, cut two 1.5" or longer pieces of hose off from a scrap piece and attach the elbows with hose clamps. Attach the 120mm fans to the radiator, plug them into a splitter, then plug the splitter into the fan power supply. Move the cooler and AC unit into place. Step 16
Add water until it reaches the bottom of taped area, then slowly add more while checking for leaks until the heat exchanger is mostly submerged. Plug in the AC unit and pump temporarily to make sure everything works.