Backyard Aquaponics
A place to discuss aquaponics

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Has anyone actually tried the emergency practice of shoving an AIR-PUMP in a freezer and pumping freezing air to the tank - and so get the temperature down for trout..

It's logical, that it has to work..

May not be the most economical, but hardly any worse than a proper chiller..
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Air pump has to get the air from somewhere, what would it do in a sealed freezer? Freezers don't bring in air do they?

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No - Not a serious problem..

You will have to wedge the line under the seal and this will leave a gap either side of the tube..

I have nothing to lose as it's a throw away fridge that stores the bulk Fush Food..

No - no issue there - just wondering if anyone has actually done it..

There is no point passing the tube thru the freezer as water will immediately condense and then freeze and block (with disastrous results)..

I'm in the process of converting a silly portable Air-Cond to a proper chiller, but that will take some time for special SS tube to arrive..
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Sorry BuiDoi but that will do absolutely nothing to change the water temp. Much like all cooling or heating options its the grow beds and water surface that disperse the hot or cold rendering almost every option useless. Unless your prepared to spend $$$$ which in most backyard situations outweighs the cost of the fish.

Seasonal fish choices is the smartest decision you can make.

So - "Absolutely Nothing" is surely not quite correct..

Others have declared that a significant cause in raising the water temperature, is the air that is pumped through it.. So it's questionable to say COLD will not lower that temperature, OR hold it at an acceptable level, in the least..

My special "Cold Tank" is insulated and protected from ALL direct sun.. The GB above is heavily involved with growth, and so LITTLE sunlight will heat the bed..


Seasonable Fush Choice is obvious, but having excess PV Solar Power, I can afford to waste some electricity on cooling, even if it's in an amateuristic way, of cooling the AIR..

It MUST have an effect and I assume that thus far - no one has tried it..

So Charlie, if you have not heard of it B4, then I suspect that I will be reporting on the results, if this heat-wave does affect Sydney..
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I'll disagree with absolutely nothing.

I'll say not enough cooling to measure.

And I don't know what pump you have, but mine pumps out a lot of heat when in use, and it usually hot to the touch., you could just put it outside the freezer and have an inlet valve connected though.

If you really want to cool them, I'd grab an evaporative cooler, something like this:
http://www.ebay.com.au/itm/Evaporative- ... 23444eebcd

And hook it into the AP water. But I think scale will play a big factor there.

Like Charlie says, it will have minimal effect on the water temperature, unless you are pumping vast amounts of air through your system from a freezer with a large amount of readily available cool air. I'm sure I posted some calculations in another thread about this sort of thing, but since water has thousands of times less specific heat capacity than water and is a poor conductor, you wont change the water temperature much.
How many litres per hour is your air pump? How many litres of water in your system?

Cooling ability of a freezer- a few hundred watts if you're lucky, and how much of that cooling capacity do you think the air pump can utilise? Not anywhere near all of it I'd suggest. Heat gain in my AP system on a hot day is over 25kWh, ie over 2.5kW continuous for 10 hours. Yours will no doubt be a bit less, but it will still be significant.

Yep agree with the heat capacity. A way to think of it is how you can open the oven and put your hand in and not get burnt but if you touch the wall of the cake tin (high heat capacity) you do. You can touch a cake and it doesn't burn. If you could do the opposite to one of those evacuated tube solar hot water system it would be good.

The other thing to consider is that using solar power to convert to electric power and then use that to power mechanical means (fridge) to cool another mechanical device (pump) is going through a whole set of energy loss.

Having said that I am in sydney too and worried about tomorrow

From experience, I can tell you that circulating water through a freezer to cool something down doesn't work. The freezer does not have enough cooling capacity to do anything. So if it doesn't work using water as the transfer medium, air certainly isn't going to work.

Here's what does work. Take a window air conditioner apart. Get an insulated cooler. Place the cooling coil of the air conditioner (the part the air would normally blow over) inside the cooler. Fill the cooler up with a glycol/water mixture. The glycol lowers the freezing point. Then, turn on the Air conditioner and use a pump to circulate the glycol mixture through tubing in the fish tank. Voila! A chiller unit.

note 1: Make sure you use propylene glycol. Regular anti-freeze is ethylene glycol which is toxic to humans and animals. Here in the states I've had good luck finding propylene glycol in RV shops for winterizing.

Note 2: No way to guarantee how well this will work for you. Your mileage/kilometerage may vary.

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Interesting thoughts.
Thanks Gordon.. ever the mathematician with the right observations..

Only thought on the cooling power of the freezer, .... COP.... a 300W compressor will be producing more like 1000W of cooling potential..
But that will never alter the ability to get sufficient heat transfer.. Air to Water
Looking at trying a 30L pump... Now that would stir things up..

The medium term plan is to bend up a serpentine of 10mm Stainless tube and connect it as the Air-Conds evaporator ..

I had thought of the Glycol thing.. but don't like adding yet another circulating pump to a PEX tube

The full idea with the freezer/AirPump, is to have the pump inside and even then, run the air through an old finned evaporator to ensure the compression heat is dissipated..
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http://www.aliexpress.com/item/10-Plate ... 58955.html

Were I looking at using a heat transfer intermediate... I would like to consider something like this...
I would just like to know exactly how it is built inside..

Boy there is some good stuff now available at realistic prices..
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we have played around with running a venturi air hose to suck air from an esky full of ice and heshan bags. We noticed a half decent drop in water temp and also the fish became more active with the extra 'cool' air as well

I was going to set this up again last recently with the warmer days we have had but tried other methods and managed to keep everything in check... just!!!

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and I just had a look on the compliance plate of the DIMPLEX portable A/C
800W consumption.... 3600W cooling = COP > 4
Fridges don't have to indicate their cooling ratio, but it is most fair to assume similar.. ie 4
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The slightly lossy (as in the water I was cooling was not perfectly insulated) test I did on a 24VDC fridge unit indicated an actual COP of about 1.

depending on how far your freezer is away from you fish tank all gains in cooling will be lost via heat transfer from the air line on the way to the tank, if you are only after the cooling as a means to get you through a hot day or two and not for long term use i would say the effort and expense would not outweigh simply using ice, I Keep about 20L worth of frozen water bottles in the freezer of my drinks fridge to deal with ocasional hot days, this also has the advantage of keeping my drinks fridge cooler during periods of heavy use and saves on power consumption.