DIY Dehumidifier Chiller

Credit: Ted’s Aquarium

This chiller is made from a used dehumidifier. It works by keeping a small tank (the insulated box) of freshwater cold and then circulating the cold water through a heat exchanger in the sump as needed to cool the aquarium. In my case, I have used a coil of 1/2′ Polyethylene hose as the heat exchanger in the sump. There are other (more reasonable) variations to this if you don’t mind spending a little more money. I will discuss variations at the end of this documentation.

My unit is working perfectly and can produce 2300 BTU (about 1/6HP). With the amount of hose I have in the sump, I can utilize about 1/2 of the full capacity. It would take 35′ of hose in the sump for full capacity (assuming 55 degree chiller water temperature). The insulated tank works well, and even though the unit is always on, it only runs when it is needed – in other words, there is not a lot of waste in keeping the water cold all of the time.

Why a Dehumidifier?
I browsed the web for a long time looking for ideas, and I could not find any DIY chillers that made sense for my tank. Using a small refrigerator is one idea that you can find, but it is not powerful enough to cool anything but a small tank with a small heat load. I also found ideas about converting a window air-conditioner, but that would take me about 4 years to complete. I literally tripped over this idea in my workshop one evening when I walked into my basement dehumidifier – I still have the bruise to prove it. A dehumidifier is basically an air-conditioner that reheats the air after it is cooled. Normally, a 25Qt/Day unit is equipped with a compressor that operates around 1/6HP. The construction and refrigeration circuit design are perfectly suited to this project.

Dehumidifiers are readily available, cheap ($140 Bran’-spankin’-new), and are very easy to convert to a chiller. My project cost me about $60 in addition to the dehumidifier and was up and running with about 6 hours of work.

The down-side is that it is somewhat large, and probably a little less electrically efficient than a commercial chiller. Its not the sort of thing you want sitting around in your living room. There is also a small amount of maintenance (keeping the tank filled with water and an occasional cleaning. I have other ideas below that solve these problems, but I do not know if they will work as well. If you try one, please let me know how it turns out.

Unfortunately, if you want the tank temperature to be stable, you will STILL need a relatively expensive temperature controller to operate this unit and your heater . There is a possibility that you can tweak the snot out of this setup allowing the pump to run constantly and using your heater to make up the difference, but it would take a long time, a lot of experimentation and would not be electrically efficient. If you would like to try, I recommend setting the chiller thermostat to just below your water temperature, and if needed, shorten the tubing in the sump until the chiller can not quite keep up with the load. Then, turn down the chiller water temperature a little more until the water remains cool. You will be able to tweak the chiller water temperature as need throughout the year to try to minimize the time that your heater is on. Personally, I like the controller idea better.

Parts Needed
(1) Dehumidifier – a 25Qt/Day unit will operate at about 2300BTU or 1/6 HP.
(1) Water Cooler Thermostat – part number 30045K99 (I paid $12.00).
(1) 7-1/2 Gallon Vinyl Wastepaper basket.
(1) Smallest powerhead you can find.
(1) Powerhead or Pump capable of about 100GPH at 5′ head (I recommend RIO 2100 or 2500 or equivalent).
35′ of 1/2′ OD polyethylene tubing or black garden irrigation tubing.
-OR- 2′ of 1/2′ OD Titanium tubing – McMaster Part #89835K63.
Foil covered Insulation board.
Aluminum Foil Tape.
Wire Ties.
Pipe, 1/2′ ID vinyl hose, hose clamps and 1/2′ pipe insulation to suit your setup.

To Start, I constructed a box to fit the wastepaper basket using the insulation board and aluminum foil tape. This is the tape that is used to construct rigid duct work from fiberglass duct board. You can usually find it in the heating or plumbing department of your local Home Improvement store. Duct tape would probably work as well, but it would not stick (or look) as well. Be sure to leave a little space to allow the tank (wastepaper basket) room to expand when you fill it with water.

Any time you go to one of those home improvement places, there are always damaged pieces of Celotex insulation board – I made a deal with a salesperson to buy a damaged 4’x8′ piece for $5.00. I immediately cut it into three pieces so it would fit into my Jeep Wrangler anyway. If you are going to use this method to insulate the tank, be sure to get foil covered board – nothing sticks to bare Styrofoam well.

The dehumidifier I used had a really nice shelf on the back to hold the original condensate catch tank. I used this to sit the new tank onto. I drilled a few holes in the sheet metal frame of the unit and wire-tied the lip of the tank to the frame to hold it securely in place.

I VERY CAREFULLY bent the evaporator (cooling) tubing so that it all sat down into the new tank. I drilled a few holes in each side of the tank to secure the tubing to the bucket. I can not stress how important it is to be very careful here. One leak and it’s all over. Also, the aluminum tubing should not be bent (or unbent) too far or it will kink – try to find a way to minimize the amount bending at any one point.

If you look at this picture and the one above, you can see the wire ties holding the cooling coil, and the way I ‘adjusted’ the coil without doing any tight bends or major straightening – it is not pretty, but at least I don’t have to figure out where to buy R-500 to recharge the unit after a leak.

Above, you can see the small power head I put in the tank to keep the water from stratifying. I wired this directly into the incoming power cord so it runs as long as the chiller is plugged in – without requiring an additional outlet.

To the right, you also can see the capillary from the new thermostat that will be used to keep the water in the tank at about 55 Degrees. The thermostat is adjustable, but it is important to get as much of the capillary as possible into the water.

I removed the humidistat and installed the new thermostat in the same location. The wires pulled off of the humidistat and onto the thermostat without changing a thing. I had to drill two ne hole in the frame for the mounting pattern of the thermostat, but now I can adjust the temperature on the unit through the hole left by the humidity control knob.

Typically this thermostat is used with its entire capillary tube in contact with the water. In my installation, only about 2/3 is in the water so I had to adjust the small calibration screw (inside the thermostat – next to the large adjustment knob) to get it to operate in the range of about 50-60 degrees

Above, you can see that I have added the circulation pump into the tank and also attached a return line. The hoses are 1/2′ ID so to allow me to slip the plastic tubing into them and use hose clamps to prevent leaks. I bent the cooling coil to insure that there was room for the RIO 2100, and that nothing was rubbing or rattling. Ugly, huh?

To the left is the coil of tubing in the sump. Don’t be alarmed – the sump level varies during the day because of my wave maker. The chiller is about 12′ away from the sump, so I insulated the tubing between the chiller and the sump with 1/2′ foam pipe insulation to prevent sweating and capacity loss.

Finally, the pump is hooked up to the sump coil, and the chiller tank is filled with tap water. Do not use RO, distilled or saltwater in the chiller tank – they will corrode the aluminum cooling coil.

I added a gallon of Propylene Glycol antifreeze to the chiller tank to help keep the water clean and protect the aluminum coils. Even though propylene glycol is non-toxic, you should still take great care to insure that none can accidentally get into your aquarium – this means making all connections away from the sump in case there’s a leak. If you are not sure about this, do not do it – it is not really necessary and certainly not worth the risk.

If you DO opt for antifreeze, DO NOT use ethylene glycol (automotive antifreeze) – you should not have that stuff within 50′ of your aquarium (or any other living thing).

The Rio 2100 pump is plugged into a temperature controller. The pump runs whenever cooling is needed by the aquarium. The chiller turns on and off as needed to keep the water in the chiller tank at 65 degrees – I could go colder, but it would only waste energy since I don’t need that much capacity.

Titanium heat exchanger:
In order to make the system more efficient in the sump, 2 feet of 1/2′ Titanium tubing will do the same job as 35′ of plastic tubing. Titanium tubing is expensive ($35 for 5′), and I do not know much about bending or cutting it. It would obviously be nice for small sumps. You could theoretically cut the tube into a few (or many) pieces and use hose to connect them together as needed to fit in to the sump. If you do this, you will need to be very careful to make tight joints to prevent the chiller water from leaking into the sump. Definitely do not use any chemicals in the chiller water if you plan to try this – unless you can make all joints outside of the sump.

You can use a much smaller pump with this variation because there is less pressure loss through the much shorter run. The object is to get about 100gph for maximum efficiency.

Tankless System:
Conceivably, you could pump the aquarium water through many small (6′ ?) pieces of Titanium tubing, interconnected with hose and strapped to the cooling coils of the dehumidifier. I suppose you could also bend a single piece as an alternative, but I do not know if Titanium tubing can be easily bent.

You would have to try to find a way to maximize contact between them by running the Titanium tubing in parallel with the aluminum dehumidifier coils (typically up and down). I would recommend trying to bend the aluminum tubes slightly so that two or four of them could be strapped around one Titanium tube with wire ties. The entire cooling coil would have to be fully insulated without restricting air flow to the condenser coils. To maximize efficiency, you would want to have the aquarium water start at the warm end of the cooling coil and work its way to the cold side. (the cold side is the side with the small copper capillary connected to it). I have no idea how efficiently this would work. If you do not transfer enough heat, the dehumidifier will shut down on low pressure.

The nice things about this scenario are that there is no cooling water to maintain, and you do not need to replace the humidistat with a thermostat – just turn it all the way up or short it out.

You will definitely need to use an aquarium temperature controller to start and stop the chiller in this method. The pump can run continuously or turn on and off with the chiller.

I am really interested to know if anyone tries this (or can offer more information about working with Titanium). Please email me with results or information!

Blane Perun

Diver - Photographer - Traveler

Whale in Ocean