DIY Chiller idea

Hey all,
I'm really interested in getting an axolotl, I've read through a lot of information regarding it and one issue that's really putting me off is keeping the tank at <=20 degrees celcius. So I've looked at chillers and some information about them... one page suggested that there are no viable DIY solutions. I think that's a load of ****

I live in Melbourne Australia, and last summer I think the heat peaked at around 45c. The ambient temperature where'd I'd keep the axolotl probably peaks at around 40 at the most on such a day.

I've been looking at the cost of peltier (TEC) modules on ebay, and some are quite affordable. Being into computers I've naturally got plenty of DC PSU's and cooling devices for them, so I'd only need the straight modules. Looking at some videos on youtube, an under-powered 46w module got to -16c. On ebay I can get 60w modules for <$3ea. + post of about $5.

So what if I were to stick say, 4 of these to the side of the glass tank (77*30*40cm - 92 litres)? Obviously glass is a good thermal insulator so there would be issues, but it beats spending $500 on a commercial chiller! And in the worst case scenario ice can always be added to tank.

Has anyone else even considered this? Any thoughts on whether or not it would work?

And as a side note, I've read that this forum is the best place to get them - but how hard pressed would I be to get 1 or 2 GFP modified axies in Melbourne?

Thanks

Edit: A 2D diagram as to how it could possible be integrated:
(It seams I can't link to websites, so I've broken the link - http://img265.image shack.us/img265/8782/41054955.png)
Pros are that it could be seamlessly implemented into any aquarium, and being affordable Of course there would have to be a fairly large cooling setup to the left of the TECs (Green on the diagram). The orange bit could be aluminium for affordability, or copper would work better. Diamond more so It just acts to spread the 'cold' (In physics terms that's not right - but it'll do) to have a larger interface between the 'cold' and the glass. The insulation just stops that 'cold' from being lost to the air etc and since glass isn't a good thermal conductor it needs every bit it can get.

Edit: I've had a better look at commercial products are available, and I see how they manage to do it. Doing it through the glass is pretty crappy - so it seams having a loop of coolant going around is the way to go. I can do that as well, I have a small 12v pump - I'd just need some small copper tubing, fill it with water and stick peltier modules to a reservoir and have a closed loop run through the tank)

There are a number of threads here that cover this method pretty well. (The most recent detailed one being this one here)

Plug "peltier" into the forum search function and you can learn all about the pros and cons of such a system.

Hmmm so it seams it isn't the best for a 92 litre tank. Say the tank was only 3/4 full which it would be, that's still 69 litres. It would still be a good project to do considering the fairly cheap cost, and currently I have a lot of spare time.

I thought a lot more just after posting the OP, and realised that through-the-glass is definitely not going to work.

Consider this -
http://img204.image shack.us/img204/1079/74330905.png

Everything but copper pipe and the peltier modules would be reused, even the pump which I bought a few months back for a project like this.

With sub-zero temperatures water would freeze, but consider that all pipe joins would be outside of the tank then I think anti-freeze could be safely used?if leaks occured they'd be outside of the tank. And with a regulated ATX (computer) PSU - I can hook everything up in parallel have switches to enable and disable each module allowing me to vary the coolant temperature with some stepping.

I don't have any axies atm, so there is no urgency to get any cool. So I might make a prototype and see how it works.

If you are technically very confident, i think its an interesting project. However, be cautious of electrical wirings coming into contact with water. A short circuit or electric shock won't be pleasant to the axies or to you. Always safety first.

I highly suggest against using any ethylene glycol based coolants. While a drip or two will not bother your car or computer, it would be fatal for aquatic animals. Have you had a go at the cooling articles on Caudata Culture? There may be some ideas there you would be able to work with.

Thanks for the input.
Consider this:
All the fittings that have a possibility of leaking or coming loose are not above or in the tank. The copper pipe is a single piece and so it won't leak unless it corrodes which is another thing I'll have to look into. If the system leaked, the worst case scenario is that I'd have a mess on my hands to clean up - the drips would be outside of the tank
http://img42.image shack.us/img42/6351/64444807.png

I'm not 100% sure but I read somewhere that copper is poisonous to axolotls so dont know if copper pipe in water will contaminate the water . As i say not 100% sure but maybe worth investigating

Well that's going to be a show stopper. Looking at thermal conductivity values the other options are diamond, silver, gold, and aluminium. I don't think any of these come in pipes like copper does.

I saw some chillers but now can't find them again - that had hoses hooked up to spirals that I presume were put inside the tank. Do these have a name? Might be able to get some ideas for materials from those.

Copper is definitely toxic to amphibians, with caudates being especially sensitive. I have been giving this issue quite a bit of thought today and I think I have come up with a solution you may find helpful. Given you are not attempting extremely cold temperatures, why not build an external heat exchanger?

Basically, you could construct a silicone a box on the back of the tank, external side, near the top of the water line. You could utilize your peltier or liquid cooling system to cool water in the box. The thermal transfer through the tank glass would be sufficient (if the cooling box was big enough) to cool the tank water. It would increase efficiency at the waterline, since cold water sinks and warm water rises, thus possibly helping with thermal transfer AND increasing circulation in the tank. You could easily build the box out of acrylic and silicone it directly to the exterior glass. It could even be insulated with Styrofoam. This set-up would be well hidden, not take away tank water volume, and be cheap to build. It would also completely isolate the cooling system from the water your pets are actually living in, thus eliminate risks of copper toxicity or glycol poisoning. (If I have not described this idea adequately, let me know in this thread and I will post up some sketches..)

Hmmm - I think I understand. Like my initial idea but having a liquid (water) medium between the glass and the cooling apparatus? There is a guy I know who can laser cut and fold acrylic sheet (perspex) for what I'm guessing is a reasonable price, definitely not anymore expensive than the cost of copper pipe.

Something else I've considered is putting the 'chiller' in line with the power filter I have. It has fittings for barbs like this that can go onto the power filters water outlet-
http://www.over- clock.co.uk/acatalog/adapthalfinbarb.jpg
I could fix a hose to that that goes to the peltier apparatus, and then a hose to come back to the tank. That way I still only have one pump making noise. I hope my diagram makes sense:
http://img412.image shack.us/img412/6885/40740335.png
This way there is no glass for heat to conduct through, only the medium between the peltier and the water. Which begs the question what to make that out of? I don't want to risk the water being contaminated with traces of copper...

Also, would you mind just clarifying what you mean by 'heat exchanger'? In my experience it's pretty synonymous with a radiator - but that wouldn't work here since that is used to cool down an object to ambient temperature rather than reduce it to sub-ambient.

Thanks for the input

A heat exchanger is any object that conveys a change in temperature between two conveying mediums while still pyhsically seperated. You are correct in thinking of a radiator. Or the compressor coils on a refrigerator. Or the core of a liquid cooling system for a CPU.

In this case both mediums are water kept separate by glass. To really boil your brain:
Are you cooling the tank with this method or is the tank warming the cooller box?
Thermodynamics is kind of cool...no pun intended...:grin:

Well I'd be lying if I said I wasn't a nerd Physics is my best subject :rollseyes:

Well with the above you have 2 peltier modules constantly being cold - however they're being heated by the water being pumped into them yak yak yak resulting in the water in the tank being colder - since the peltiers are continually running maintaining the sub-ambient temperature. I'm toying with the idea of not having a medium between the peltier and the water... maybe have an acryllic tunnel with the cold-side of the peltiers sitting inside and glued down on the top with some sort of super-glue like adhesive (You Americans have JB-weld etc. I believe.) Making a sealed container will be tedious but I can get all the acryllic pre-cut, I'd just need to learn to use a silicon gun, glue some water tubing barbs on and seal them on tight and presto. Having to order the peltiers from HK means I'll have to wait 2-3 weeks before any real progress, but I'm pretty keen on the idea even if it only drops the tank temperature only a few degrees. I can possibly get to work on readying a PSU and design some containers... which won't be a heat exchanger as such

Sounds to me like a solid plan. I look forward to seeing the final product!

I get a bit nervous with peltier chillers in general. One side of the plate hits sub zero fast and often freezes up. This is good. The tricky part is how to remove the heat from the hot side of the plate. I worked on a few Peltier effect cooled RADAR a few years back. we ultimately dumped the plates for liquid and air cooling as the Peltiers were overkill.

Be very selective in the adhesive you choose. It is probably worth while to get a small aluminum plate to affix to the tank and then use CPU thermal transfer paste to ensure good contact. For the hot side of the plate I bet an off the shelf CPU cooler with fan would work well depending on the DC voltage through the plate and the temperature it reaches peak.

I have given a lot of thought to it. For a TIM (Thermal interface material) I was just going to buy an el cheapo $3 30g tube from a shop in HK called dealextreme(.com), I only have a little bit of good CPU stuff here... it costs about $9 for a 5g tube so I'd rather leave that for CPU's And the 'user reviews' on the site are favourable for it - even though they're pretty much team stupid. It's not an ahesive though - for that I'll use bolts and pressure mount it.

I'll get around the enthusiast PC forums and get some cheap CPU heatsinks and fans - ones for older systems still work fine but often just don't mount on new gear so I should be able to get something decent there.

Though I think you've missed a bit of my idea - Though going through the glass might work, I'm really not to happy with how efficient it would be. See here, external chilling inline with the power filter which doubles as a pump for the chiller -
http://img412.image shack.us/img412/6885/40740335.png
This also beats the need for a strong adhesive that is also a good TIM - it doesn't need to hold the peltier to glass AND some weight from a heatsink.

I'll get to on a diagram on how I'd like to construct it.

By using an ATX PSU from a PC, I can easily buy a few switches and readily change them between 12v and 5v (I think - Most PSU's won't have enough power on the 5v rails for a 90w peltier - resistor phun times ensue). So if my chiller had 2 peltiers, then I could effectively have a few different temperature levels. 12-12, 5-5, 12-5...off-12 off-5.

Thanks for the input

Brilliant!

schnappy said:

I have given a lot of thought to it. For a TIM (Thermal interface material) I was just going to buy an el cheapo $3 30g tube from a shop in HK called dealextreme(.com), I only have a little bit of good CPU stuff here... it costs about $9 for a 5g tube so I'd rather leave that for CPU's And the 'user reviews' on the site are favourable for it - even though they're pretty much team stupid. It's not an ahesive though - for that I'll use bolts and pressure mount it.

I'll get around the enthusiast PC forums and get some cheap CPU heatsinks and fans - ones for older systems still work fine but often just don't mount on new gear so I should be able to get something decent there.

Though I think you've missed a bit of my idea - Though going through the glass might work, I'm really not to happy with how efficient it would be. See here, external chilling inline with the power filter which doubles as a pump for the chiller -
http://img412.image shack.us/img412/6885/40740335.png
This also beats the need for a strong adhesive that is also a good TIM - it doesn't need to hold the peltier to glass AND some weight from a heatsink.

I'll get to on a diagram on how I'd like to construct it.

By using an ATX PSU from a PC, I can easily buy a few switches and readily change them between 12v and 5v (I think - Most PSU's won't have enough power on the 5v rails for a 90w peltier - resistor phun times ensue). So if my chiller had 2 peltiers, then I could effectively have a few different temperature levels. 12-12, 5-5, 12-5...off-12 off-5.

Thanks for the input

Click to expand...

A diagram for the visually inclined would be much appreciated! There is much vested interest in your idea!

http://img23.image shack.us/img23/1300/chillercopy.png

Zing. By the time I buy the acrylic, cut the holes for the hoses (barbs maybe) and for the TEC's and fracture all the acrylic probably be much cheaper to have it all laser cut - it's nothing intricate. There is a guy in Brisbane who I'd think would do it very cheaply from his off cuts, but he's in Japan for another week and a half I think.