Material/Media to prolong water cooling.

[BFG]

Hello fellow Reefers!

I have been trying to find a way to lower the cost of cooling my reef tank. I am at a stage where I am designing a new tank as an upgrade and it will not exceed 1000 litre. Currently, I am using a Mitsubishi Starmex aircon compressor with a drop in coil in the sump tank. This equipment is the main electrical drain in my setup.

My idea is to use a small capacity chiller, a 1/10 hp maybe, to chill a smaller container of liquid. This container ( unknown right now but may be a off the shelf spare tank or something similar ) will be placed in the sump to passively cool the water of my tank and it Will Not be connected nor will it mix with the tank water. The temperature I'll be aiming for my new tank is about 26 degree celsius.

My question to fellow reefer is, is there a methodology or media or something that I could add into this container to prolong the length of time the water stay cool before the chiller is activated when the water temperature in this container rise. This container will be connected to a chiller via a water pump. I have come up with 2 ideas right now, just a guess. 1 is to have a higher salinity in this container or packing about 90 percent of this volume of water with sponge.

Anybody has any better ideas? Sorry for the wall of text. Thanks for reading!

 

[Timfish]

Evaporative cooling works wonders. Small 12 vdc muffin fans can do quite a bit to reduce the work you chiller has to do. I also know a lot of aquarists here in central Texas put their chillers outside so their house AC doesn't have to deal with the heat.

 

[Subsea]

Thermodynamics 101:
When 1 pound of water evaporates, 1000 BTU of cooling takes place during the phase change from liquid to vapor.

A medium sized oak tree will evaporate 100 gallons each day. If you do the math, that would equate to 800,000 BTU's of cooling.

I operate 10,000 gallons of macro growout under a greenhouse in the Texas Hill Country near Austin. With 100 degree days and 2000 PAR sunlight I maintain water temperature below 80 degrees. Two 1/2 HP exhaust fans move 10,000 CFM of hot dry air across the water surface of a 20' by 12' tank and evaporate that same 100 GPD. If I used refrigeration cooling, it would take a 7 ton (about 7 HP) unit to keep up with the heat load.

1 HP of evaporative cooling outperforms 7 HP of refrigeration.

On an inside 55G tank with 400W of MH, a 7.6W 12VDC muffin fan maintains water temperature below 75 degrees. When the fan goes off with the lights, the water temperature rises to 77 degrees.

 

[ca1ore]

I had a baffling conversation with a LFS owner many years ago who was trying to sell me a lifeguard filter module system. He noted that I'd be able to get away with a much smaller heater because it would only have to heat the small volume inside the heater module. Right! ..... wrong! Tank still contains the same amount of water and still loses (or gains) the same amount of heat regardless of where you put the heater. Afraid the same thing applies whether you place the chiller probe in an 'open' area or within a smaller water volume.

Evaporative cooling can be vey effective, though that effectiveness is attenuated by the relative humidity of the surrounding air (whish is why it is a popular choice for house A/C in dry areas like parts of Texas and Arizona). Years ago I built a large plexiglass box containing bioballs through which I trickled water and pumped in a ton of air. I was able to effect cooling of about 4 degrees, with a commensurate increase in evaporation rates, but the high humidity here in the Northeast did not allow me to completely chuck the refrigeration unit.

 

[Subsea]

Central cooling remidies that situation for most people. Attention to water make up is the biggest issue. On the 55G tank referenced above, evaporation rates approach 5 GPD.

Here in Austin. this past month sees morning humidities approaching 90%. With afternoon temperatures reaching 100+ plus degrees, the humidity drops to 35%. Before I committed to building a 20' by 40' greenhouse with a 10,000 gallon macro growout system, I studied on what greenhouse fish farmers did in Florida with high humidities all the time. They relied on evaporative cooling to maintain temperatures at or below the dew point during summer weather. The OP in Singapore would have Florida type of weather. Even though he did not say it, I suspect he has refrigeration cooling in his fish tank room.

 

[ca1ore]

Central cooling remidies that situation for most people.

It's all about trade-offs I suppose. When I ran my aforementioned evaporative cooler, I kept it outside so as not to put 5 gallons of water into my house air, but you are right that not everyone would do that.

 

[disc1]

This won't work, regardless of whether you put the coil in the sump or put the coil in another tank in the sump, the chiller still has to move the same amount of heat. That's basic thermodynamics.

 

[Subsea]

It's all about trade-offs I suppose. When I ran my aforementioned evaporative cooler, I kept it outside so as not to put 5 gallons of water into my house air, but you are right that not everyone would do that.

The water vapor that is removed by central air conditioning is called latent heat by AC technicians. It easily is 70% of the heat load on central AC systems. Your central unit would easily be 5 times as efficient as reef type chillers at removing this heat load.

 

[Decadence]

Get yourself an automotive A/C condenser from the junkyard and a nice long section of titanium tubing. Bend the tubing into a grid layout with a large surface area to stick into your sump and plumb it to the condenser with a pump. Nothing but titanium should tough the water and all connections should be made far from the sump. You can fill it with a mix of water an automotive coolant. Place a small fan on the condenser and have that and a pump come on when the temperature gets above your set point. You should be able to cool a very large reef this way.

Other options for a large reef would be geothermal or a coil of tap water.

 

[Epicreefer]

Placing a boundary like the glass or even worse acrylic of the smaller tank between your chiller and main tank will just cause issues. Your chiller will turn on and off more frequently because it can chill this volume of water very fast, then the heat moves from your main tank to the small chilled tank and the chiller restarts. This is called short cycling and it is bad for electric motors. If you just chilled the main tank then it would probably run 5x as long, but only turn on 1/5 as often. The less frequent it turns on the better for motor life. On the other side you don't necessarily want the chiller running 24/7. For chillers it is best to follow manufacturers recommendations and use an inline chiller, not a drop in chiller. If you are running LEDs then you can probably push the recommendation 20% or so. To reduce chiller running cost try using high efficiency lights and external pumps that are air cooled. Running a lower room temp will just raise youac bill. Evaporative cooling is a good option if that will work for you.

 

[Randy Holmes-Farley]

David is right that you cannot get any more cooling capacity from the chiller by material selection. You could get more capacity from a cold solution by incorporating certain salts that may undergo dissolution with uptake of heat, but all that does is give the secondary containment more capacity, it does not increase the integrated overall rate of cooling of the tank.

FWIW, I use tap water running through a coil of plastic tubing in my sump to cool my tank. The flow is controlled by a solenoid that is switched by a temperature controller. The water then runs out to the yard to water plants.

This only works, however, if the tap water is cooler than the tank water (which it always is here).

 

[BFG]

Thank you all for the insight. I guess I will continue to use my chiller.