Cold saltwater

[Caryl]

I like to have a coldwater tank set up with inhabitants from local rockpools but the room gets too hot in summer. Does anyone know of a cheap way to keep a tank cool? With the tank needing to be below at least 15 degs C. and the room staying above 28 degs C. it is difficult.

We tried floating 3 litre bottles of ice but it was time consuming replacing them and the freezer was running non-stop trying to keep up!

[peet]

Hey Carol, have you considered purchasing a small gas/electric camping/beer fridge. Then cut a hole in the door andplace your filter box, or a good number of coils of piping inside, then using an insulating wrap around the piping and hole in the door run the pipes back into the tank.

I have been working on the idea of a similar tank myself, been having a lot of fun trying to design a tipping PVC plastic gutter to provide wave action. Thinking of running water into the off-balance gutter above the tank, once it reaches a certain volume the gutter will tip pouring water into the rock pool.

Hope that helps a little

Peet

[Caryl]

Yes we did try the pipes through a fridge trick. It didn't work as it could not cool the water down enough. I found a number of articles on the net which said the same thing too. Shows they were right!

Living in sunny Marlborough, keeping tanks cool in summer can be difficult. When the room temperature gets up to 34 and never drops below 28, even at night, expecting a fridge to drop the water temp to 15 or lower is a bit much to ask.

[Warren]

If the tank is not too big, try using a stainless steel coil in the filter or tank. Pass cold tap water through the coil. I have routed my house supply through the coil and since I use a lot of RO water, the water in the coil is always changing. You will not get down to 15'C, but I have acheived 17'C no problem and I'm from Hawkes Bay where my room temperature is usually 28'C minimum, rising to 40'C on a really hot sunny day.

The problem with using a beer fridge is getting the surface area of the exchange system large enough. A fridge only runs at about 4'C leaving only 11'C differential cooling. You will need a very large surface area (like that of a car radiator) and blow the cold air from the fridge over it. Also, the fridge is not actually designed to extract all that much energy from the water. A better method is to get an old air conditioner and modify one side to be an imersion coil. All the gas will escape during the process of course and it will need to be refilled. This system works really well, and is just about capable of feezing your tank if you want. The thermostat works really well too as the temperature range we are targeting is standard for the air conditioner (must be electronic however - not bimetal).

[peet]

Hey Warren,my parents live in the Hawkes Bay so I know how hot it gets, what I was wondering is if the water is only running through the stainless steel coil when a tap is running or is it before your hot water cylinder? (what I mean is how do you get a constant flow throught the coil) Also where in the bay do oyu collect specimens for a rockpool tank and what is the best fish shop in the area for tropical fish and plants

Cheers Peet

[Warren]

Hi Peet,

I use a RO unit, so I have a constant flow of water going through my cooling coil. (Ssshh! don't tell anyone, - but it uses about 750L a day!!) This is more than enough to keep the temperature down in all my tanks.

The easiest place to collect specimens is Harding road, just down from the Hot Chick.

Most of the other places that are really good are Reserves, and you're not allowed to take anything. If you know anyone who is into diving, Pania reef, and even Town reef have some really nice specimens.

The best fish shop for plants and fish is hard to say. Animalz is trying really hard, and can usually get most things if they are available. Their selection of plants is getting pretty good. The other shops have some of the less popular and rare fish in from time to time. The best thing to do is visit them all regularly to show them you are 'fish nuts', then they get to know you and you'll get a more personal service. Once that is established they are much more keen to help you with your unusual (and unreasonable if you are me) requests.

[Caryl]

A new public aquarium has just opened in Picton and Grant and I went for a look. It is really neat, not up to Napier's size or money naturally, but good in its own right. It has made us keen to set up a local rock pool aquarium again so we are seriously thinking of buying a hideously expensive proper cooling system. Does anyone know of any companies selling them here? I am not too sure what their proper name is so can't look up the Net. I guess if I put "Aquarium water cooling systems" it might start me somewhere.

[Warren]

Hi Caryl,

You may find it a lot cheaper to get a standard air-conditioner modified. I have inquired about that option here. It is possible to replace the cooling radiator side of the air-conditioner with a coil you can put into the tank. I was going to use a stainless steel one for freshwater. Should also work ok in a marine setup if you can get a grade of stainless that is non-toxic to marine's and will work with the air-con.

I will be using a modified air-con soon. I now need 3000W in winter just to keep my tanks warm. It is costing $250/month just to heat them. The air-con will drop this to about $80/month (payback about 18 months on the savings). You should be able to get by with a very small unit (I am heating / cooling 9000 Liters of water).

I will let you know how I get on.

PS: The beauty of an air-con is it can heat and cool!

[Caryl]

Are you saying an air conditioner is cheaper to buy than a cooler or will be cheaper to run, or both? Running costs are important as I have no intention of paying anything near your monthly bills! Mind you, I am only going to be cooling a 4ft tank which is a few less litres than you have.

PS. Answer my email please

[Warren]

An air conditioner will cost more to buy, but work more efficiently than a cooler unit.

The cooler unit will be quite a bit cheaper to set up, but will cost more to run.

The running cost difference for a 4 foot tank is likely to be very small. The difference in cost between a cooler and an air-con on a 4 foot system is likely to take years to pay back based on the difference in running cost.

If you can get the cooling system out of a refrigerated display unit it would work really well. You could pick one of these up second hand quite easily. You would have to check the thermostat to make sure it can go up to 8-14'C. These units usually have a cooling pipe that runs under the display tray. It can be easily removed and reshaped with some care. This unit is ideal as you do not have to let the gas out and get it replaced later. The pipe however is likely to be copper. You cannot therefore let it come into contact with the water. It would have to go under the tanks or under the pond liner.

Air-con units are perfect for tropicals as their temperature range is typically 16-35'C and tropicals fall right in the middle.

[Pegasus]

Hi Peoples,

I'm not into cooling water as of yet, but have you thought of an air con from a car, there should be heaps knocking around the wreckers yards, and the cost would be a lot lower, although it would be 12volt and need a tranny.

[Ira]

A car's AC wouldn't be 12 volt. They run off the belt on the engine. You might be able to rig up reasonable sized electric motor and connect it to the compressor. NOt sure about the rest of what would need done.

[Pegasus]

I was referring to the fan and such internal units being 12v Ira, not the compressor, but as you say, you would probably need a grunty motor to drive it, so there possibly wouldn't be a saving. Don't really know the energy it would take to run one of these as I've only ever seen them insitu, and even then didn't take much notice.

On the other hand, it may only have to run for short periods each day. Just a thought

[Bruce]

Hi Caryl

We have a Refridgeration Expert come and work for us on a weekly basis so will get any ideas from him for you, he might even have something suitable kicking around

Please correct me if I am wrong

250 litres, ccoled to 15 degrees C

And of course no copper to be in contact with the water

Cheers

/Bruce

[Ira]

Why no copper in contact with the water? Such a tiny amount would dissolve in the water, even if it is a little toxic, it wouldn't have any effect. Lots of plumbing is copper, I believe.

[Caryl]

Any help you can give would be appreciated Bruce. It will be around 250 - 300 litres, depending on how many rocks we fill it with. Anywhere from 10 - 15 degrees would suit but not higher on a prolonged basis.

Ira, it will be saltwater, which is corrosive to copper.

[Bruce]

Hi Caryl

Spoke to our resident fridgey at length today,

He recommended the following

Air Conditioners are NOT suitable as they have a range where the work in and 10-15 degrees is not within that range, Air conditioners work between 17 and 27 degrees not any lower or higher than this, even replacing the refrigerent with a low end type would not be successful in this case.

The only way to go would be a Glycol Heat exchange system and here are the prices (These are off the top of his head and within $50 each way)

Glycol Pump $600

Stainless Steel Heat Exchange $1100

Controller Thermostat $500

Wiring-Plumbing $300-400

Labour & Sheetmetal Work $400-$500

Total Cost Around $3000 Give or Take

There is nothing that he is aware of that is off the shelf and a reasonable price

Hope this helps in some way, at least you know you can discount the Aircon option

Cheers

/Bruce

[Ira]

I wonder how he meant, not suitable? If he's a professional to him not suitable might have meant for a high price, high load system. I have heard of people using jury rigged air conditioners and similar equipment...You'd really only need something sucking about 300 watts max out of the water, so even if the AC isn't working very efficiently because it's out of its temperature range it should be able to handle that. An actual aquarium chiller would cost less than 3000, I think.

[Bruce]

Not suitable means that they will not work effectivley at all, 99% of the available models will NOT cool down to the desired levels at all, well at least not without giving themselves a very expensive hernia within a very short time frame.

Normal A/C units are filled with R22 refrigerant this will not boil (Yes thats right Boil) at anything below 15 degrees C, by the time you add 2 degrees C on for heat loss you end up with the minimum cooling for this gas

Hope this helps

Cheers

/Bruce

[Caryl]

It is my understanding that proper aquarium coolers are available around $1,000 but I don't know where to get one (plus I don't have $1,000 lying around at the moment. Must go check my Kachingo tickets!)

Thanks for finding all that out for me Bruce. If, I mean WHEN, I finally get this tank up and running I will tell you what I ended up with.

[Ira]

Hmmm, I'm sure I remember reading that car ACs are designed to have the air leaving the AC unit at somewhere a few degrees above freezing. Might be wrong though.

[Cpt. Copepod]

Try a beer cooler - they are marine grade stainless steel, pubs and breweries dispose of them every few years, even if they are working. You may be able to pick one up for next to nothing.

[Warren]

You could try peltier devices. These are neat electronic coolers. You pass a current through them, - one side gets cold and the other side gets hot. All you have to do is connect the cold side to the water and heatsink the hot side to get rid of the energy.

The down side is that it takes as much electrical energy to cool as the amount of energy removed. This means you have double the power loss in the heatsink, ie 300Watts Electrical Energy in, 300W Heat Energy removed from the water, and 600W Heat Energy Dissipated in the heatsink. You have to size the heatsink just right so you get the correct delta T across the peltier device.

It would cost about $200 for 300Watts of Peltier devices + you need a 300W 12VDC Supply. Its a feasable option, has no moving parts and is almost affordable.

I have used this method on smaller tanks and it works really well. It is best used for heating where you get a 2:1 energy gain.

The other bonus with peltier devices is they are bidirrectional, ie reverse the polarity and they heat instead of cool.

[Ira]

I actually looked at using peltiers. The problem is that, just like all other cooling devices, the greater the difference in temperature between in this case, the water and the heat sink the less cooling. The prices I saw it was somewhere around $200 US for a 300W peltier and if I remember right assuming a really good heatsink on the hot side you'd only be drawing out something like 100watts or less. So, you'd need 3 to get 300 watts.

[Warren]

At the moment the largest available peltier device is about 125Watts as a single device (available through Ohm Co in Japan - It is a Fuji device). You have to connect a group of them together on a larger surface to get more power.

I use these devices in my work so I know what I am talking about. I design this type of equipment regularly. Beleive me to remove 300watts of energy there will be 600watts or more energy coming out the hot-side. The heatsink needs to be relatively large and fan cooled to keep the delta T to a minimum (less than 35'C is good). If your ambient is 35'C and you want 10'C in the water the heatsink max temperature is 45'C. You only have 10'C of heatsink rise above the ambient. It is quite possible. I use a range of heatsinks that have thermal resistances of less than 0.01'C/watt. These are used to dissipate 2500W with only 25'C delta T.

A more practically sized peltier device is the 50watt version. These are priced at about $35.00 each. Six will therefore cost $210.00. They are available from a company in Christchurch.

It is a fairly cheap cooling option compared to many others. It requires no plumbing and no tradesman to install it. It may be a little difficult for everyone to impliment on their own, but with a little help and guidance it would be no problem.

The power supply is the hardest part!