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Old 03-18-2008, 10:12 PM   #1
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Heating Question for a 15 gallon tank.

Hi, this might seem fairly trivial to you guys, but hear me out.

I'm a member of a student Mechanical Engineering group for my Thermodynamics course, and we are tasked with designing a heating system for a 15 gallon tank. The heater is required to keep the tank at 78 degrees +-1degree, and the tank is going to be put outside for the purposes of our exam(where the temperature could be as low as 30 degrees F).

Here's the issue. While we have a good idea as to how much heat we are actually going to need, the issue is if we should sort of rig up a heater, or if we should go with an off the shelf. I myself, being an ME(as well as the rest of my group), have very limited experience in programming microcontrollers to actually control a heater(control systems are the domain of EE's typically). I was wondering if you guys might know of any brands of heaters that have automatic controls that can't give us this kind of accuracy. I know the pumping and circulation of the water is going to be an issue, but that's something that we feel we can easily address.

We've got a budget of 200 bucks, and of course we're also required to create a pump for the purpose of recirculating the water. Don't worry, there aren't going to be fish in the tank, it's purely an exercise in eastimating heat conduction from the tank, etc. So if any of you guys might know of a good product that is capable of keeping water temps very consistent, could you please let me know. I figure who better to ask, then people who spend a lot of money, and who have a lot of practical experience working with these kinds of systems.

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Old 03-18-2008, 11:40 PM   #2
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Just installed one of these on my tank this past weekend...

Johnson A419ABC-1C 120/240V Single Stage Temperature Control - The

Setpoint at 79 degrees, differential at 1 degree. The literature makes it seem like it's actually a 2 degree differential, but the short story is that it isn't. Tank has remained stable between 78 and 79 for the last 4 days. Just turn the heater thermostat up (cranked mine up to 86 deg) and let the controller do it's job.

Takes a little DIY wiring, but if I can handle it (another Mech Engr!) then I'm sure you folks can!

[Edit: regarding the recirculation pump... unless they absolutely want you to pump water out of the tank and back in, I'd just go with a standard submersible aquarium heater with a MaxiJet powerhead in the tank to provide some circulation so your tank heats more evenly. The controller I listed, a 100W heater, and a MaxiJet should run you just over $100 or so... maybe $120.]

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Old 03-19-2008, 01:02 AM   #3
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Yeah, we need to recirculate the water with pump. As far as heaters go, what brand would you recommend for this task? I'm thinking to be safe we need something that's a bit overkill for a typical 15 gallon tank, since it has to keep the 78 degree temp for over an hour(all while outside where it might be in the high 30's) . We're given about an hour and half to get the water warmed up, then we need to keep the water at 78.

The idea behind the simulation is for a "petstore" sidewalk sale lol(Like that'd happen in the upper peninsula of michigan at the start of april). We need to set up a heating system that can keep the fish from being killed or stressed by the cold outside environment. To get an A, we need to hold it to within +- 1.5 degrees(which is probably isn't too difficult to shoot for).

As far as flowrates are concerned, I myself am in favor of a low flowrate for the heat(the heater is NOT in the tank, but in the recirculating pipe with the pump, it's a design requirement). I figure it would be more gradual in heating up the tank, but once we got it to the optimum temp, the temperature probably wouldn't fluctuate as much(plus I figure if this were acquarium actually had fish in it, it probably wouldn't be a good idea to to recirculating the tank water ever 30 seconds).

The only thing that is sort of the big question at least from my view, is getting consistent heat throughout the tank. I believe that our instructor is going to take an "average" from multiple locations as a means of determining the tank temperature, and I was wondering what ways you guys might have to solve that problem(this would be a non issue if it were indoors, but because it might be windy, one side of the tank will lose more heat than the other). We were leaning towards a waterwheel or something in order keep the water stirred up, and hopefully help keep any temperature variation small. What tips do you guys have for dealing with that issue(this is probably more commonly experienced by people with fish ponds and the like).
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Old 03-19-2008, 10:35 AM   #4
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Ah... missed that "tank is outisde" deal. You'll definitely need more than a 100W heater like I was envisioning. Guess that's where your equations will come into play! For your application, heater brand probably doesn't come into play since short-term reliability really isn't an issue with any of them. I would recommend that you get one with a light that shows when the heater is on. Seems like troubleshooting would be easier. Marineland's Visitherm Deluxe comes to mind.

If you have to put the heater in the recirculation pipe, then I'd agree with you... a low flowrate will give the water more time in contact with the heater. And you're right, if you have a lid on the tank (which I'd recommend), your heat loss won't be as much as you'd think it would be.

If you put a powerhead in the tank itself, that will even out the temp of the water in the tank by recirculating the water within the tank itself. Something like this...

Aquarium powerhead/water pump: Maxi-Jet Powerhead/Pumps provide vital water movement

Also... on that temperature controller, you can also buy a pre-wired version. And if you do use it, just be aware that the temp probe on it isn't waterproof. You'll have to seal it up using silicone sealant or something.

[Edit: They also make these...

Hydor ETH In-Line Heaters

...which may be better suited to your application.]
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15 gallon, 5 gallon, eat, eating, heating, tan

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