Energy Efficiency: Big vs. Small Heaters

[wpeterson]

We have a large 300w heater in our 90 gallon tank, which has enough power to raise the temperature quickly but draws a lot of current (~ 2 amps). It doesn't turn on very frequently, but when it does it runs briefly and turns off.

Is it more efficient to have a big heater running less often, but with more current? Or is it more efficient to have a smaller heater running for longer periods of time?

I'm tempted to turn this heater down to a fail-safe level, maybe 2 degress below my target and add a 200w or smaller heater set at the target level. Would that provide any benefits?

 

[this is me]

I always chose the multiple heaters over one powerful one.
For one thing, it provide redundancy. Second, multiple heaters provide more surface area of heating which can lead to more efficiency. If I can get a plate heater instead of a stick, I would get it.
Hmmmm...maybe it'll be my new invention.

 

[reef87]

Two 100w is better. That way if one fails you have the other to backup.


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[dz6t]

I always chose the multiple heaters over one powerful one.
For one thing, it provide redundancy. Second, multiple heaters provide more surface area of heating which can lead to more efficiency. If I can get a plate heater instead of a stick, I would get it.
Hmmmm...maybe it'll be my new invention.

people put heat mat under their tank.

 

[dz6t]

Two 100w is better. That way if one fails you have the other to backup.


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+1, also, if one stuck on and it has less chance to cook the tank

 

[Jim Tansey]

The power required to raise a given quantity of water "x" degrees is the same regardless of the heater size, assuming the heater has the capacity to reach and maintain the desired temperature. A point might be made that the smaller heater will not tend to overshoot the control point as much but even then most of that energy is stored in the water the result being it will take a little longer to reach the "cold" setpoint". That being said a heater properly sized to the tank and environment will provide the most even heat.

Jim

 

[wpeterson]

I run the main 300W heater on our Apex controller, so I have a failsafe for stuck heaters and alarming on temperature ranges.

I may turn the 300W heater down to 77deg from 78 and add a 100W heater set to 78. This should allow the smaller heater to run more often with less output but over a longer period of time, which should draw less current. It sounds like the overall wattage used to heat the water should be the same despite how it's quantized (ie: less time for 300W heater heating more per unit, or more time with less heat per unit from 100W).

Isn't there some loss due to inefficiency? Is it the same efficiency between a 100W and 300W heater?

I also have a hot-swap 300W heater as a replacement if the main one fails, but I don't have it in the tank. The goal there is to have a fresh heater for when this one fails, which will be caught by the controller.

 

[wpeterson]

The reason I mention current is because I rent a house with terrible wiring. The genius who wired it put every single outlet in the entire house on a single 15amp breaker. So spikes in current draw from any one source can easily overload the entire house

In that case, having a small heater coming on earlier (at say 78) and a larger heater as a backup (at say 76/77) should allow me to draw less current by heating the tank more slowly.

 

[Jim Tansey]

I always chose the multiple heaters over one powerful one.
For one thing, it provide redundancy. Second, multiple heaters provide more surface area of heating which can lead to more efficiency. If I can get a plate heater instead of a stick, I would get it.
Hmmmm...maybe it'll be my new invention.

You got me thinking about "more efficiency" that would say more total heat energy is absorbed by the tank by the flat heater as opposed to a round one, even if your flat one had a lot more surface area its temperature per unit of surface area would be lower but the energy transferred would be the same and the efficiency the same I THINK. Now if you were to bring the water to the boiling point you have a whole different kettle of fish, then I would buy your large area heater.

Jim

 

[this is me]

I don't have a degree in thermal dynamic so I could be totally wrong. But just putting on my engineering hat on.
If you have an area of 10"x10", if you put a stick heater with a diameter of 1", even if the C/A(temperature per area) is higher, the heat has to transfer throughout the entire 10"x10" area. If you have a plate that cover the whole area, even if the C/A is lower, there's would be no heat loss in getting the heat to where you want. It makes sense to me but again, I'm not a thermal expert.

 

[dz6t]

Due to the high water flow go through heaters in reef tank, energy efficiency is almost the same for large and small heaters.
If all you have is a 15amp breaker, you got an issue. sorry man, you got to change the wiring. I have eight 20AMP breaker installed.

 

[wpeterson]

Due to the high water flow go through heaters in reef tank, energy efficiency is almost the same for large and small heaters.
If all you have is a 15amp breaker, you got an issue. sorry man, you got to change the wiring.

I absolutely would if I could. We're stuck with this until we buy a house back in the Boston area and escape the west coast. The housing stock in Silicon Valley is as low-quality as it is overpriced :-/

 

[this is me]

Due to the high water flow go through heaters in reef tank, energy efficiency is almost the same for large and small heaters.

Yes, it maybe true. But the principle is still better to use larger surface area heaters.

 

[Jim Tansey]

I don't have a degree in thermal dynamic so I could be totally wrong. But just putting on my engineering hat on.
If you have an area of 10"x10", if you put a stick heater with a diameter of 1", even if the C/A(temperature per area) is higher, the heat has to transfer throughout the entire 10"x10" area. If you have a plate that cover the whole area, even if the C/A is lower, there's would be no heat loss in getting the heat to where you want. It makes sense to me but again, I'm not a thermal expert.

I think you can forget the heat transfer aspect with the moving water virtually all the heat energy is rapidly absorbed by the water and we come down to the basics EFFICIENCY= OUTPUT/INPUT.

Jim

 

[dz6t]

I absolutely would if I could. We're stuck with this until we buy a house back in the Boston area and escape the west coast. The housing stock in Silicon Valley is as low-quality as it is overpriced :-/

do you miss the snow and the shoveling?

 

[this is me]

I think you can forget the heat transfer aspect with the moving water virtually all the heat energy is rapidly absorbed by the water and we come down to the basics EFFICIENCY= OUTPUT/INPUT.

Jim

Yes, you're right. I'm just thinking technically.

 

[delta]

Yes heat it fast and shut off. If you under size the heater that is when you will wast a ton of energy. Aquarium heaters are inefficient, nothing you can do but size them correctly.

 

[wpeterson]

do you miss the snow and the shoveling?

I don't miss that, but I sure do miss finding great frags in your tanks. Coral prices are ridiculous out here and I haven't been able to find as many nice pieces as we did in the Boston area.