Low down on heating an aquarium

[blacksmith37]

Let me be more constructive.
The primary heat loss from a typical aquarium is evaporation; converting liquid to vapor. For water it is 970 BTU/#. So to evapoate a gallon of water : 8.3 #/gal X 970 BTU/# X 3.4 watt hr/BTU = 27,373 watt hr/gal evaporated. It is apparent why this is the primary heat loss. ( Yes, I had to look it up because I only remember it in metric ).
Or ,136 hours(5.5 days) with a 200 watt heater to evaporate one gallon. Remember , all the heat from any filter motors and some of the heat from lights is also adding heat.
The heat from the typical strong lights used in marine aquariums requires refridgeration. I used a small fan to increase evaporation (in the summer) when I had salt tanks.

[andrewh]

Andrew, that 33 gallon is amazing!!!! I love the dimensions on it!

Thank you very much . I'm about to move this one to the living room and build a unique stand and canopy for it . Stand and canopy DIY thread to follow shortly!!!

As far as efficiency; electric resistance heating of water is as close to 100% efficient as anything in the real world. You also pick up about 100% of all the heat (wattage) from any submerged motors in filters. And a fair amount of heat from lights.
It is rare that one is increasing the temperature of an aquarium ; usually we are maintaining the temperature. But the heat wattage factors provide some idea of the factors.
To calculate the power required to maintain aquarium temperature would require some seriously difficult heat transfer/radiant loss/conduction loss/convection losses calculations :Likely worth a masters thesis in p.chem.

Yup, my thoughts exactly. There are so many variables involved the actual formula to accurately calculate the heat going into and coming out of the water would be a mile long.

Heck, you'd even have to consider the fish, plants, substrate, decor, etc. in the calculation . How much heat does a fish give off? I have no clue .

Not to mention you'll have all three heat transfer methods (conduction, convection, & radiation) in use several times throughout the final formula.

Great Post. Thanks

It's been 40 years since I took heat transfer in college so can someone refresh my memory on how to calculate the rate of heat transfer from 80f water through 3/8" glass to 75f air per square foot of surface area ?

Very welcome, I'm glad you like it.

That's a good question. I'm going to have to research it a little .

PP....


Here's what I think...

It would seem to me that there would be so many variables to consider. Your formula in a classic research or lab type environment would be fairly easy to assertain if you had no fluckuations.

But in the common household, there is always minute changes in the air/room tempetures, i.e. televisions, ovens, a/c or heating...etc...

A significant volume of water such as a 75 gallon tank that has been heated to a tempeture of say 80 degrees, might fall to 75 degrees in 8 hours in a labratory, but in a average household, it may never get to 75 due to outside influences??

That was my long winded version of I DONT KNOW....

CF

You make a good point. Even a ceiling fan above/near the tank will increase the rate at which the heat is transferred from the water through the glass to the air.

This is misleading. A 100 watt lamp is using 100 watts all the time...it's not cumulative over time. When it uses 100 watts for an hour, it uses 100 watt/hrs. Watt is the product of volts x amps, P = I x E. A 60 watt lamp operating at 120 volts has 1/2 amp current flowing through the element. It's using 60 watts all the time. Watt-hrs is also a product of watts used for time used.

Mark

A 100 watt lamp is not using 100 watts all of the time. If it was using 100 watts all the time (we'll narrow it down to say seconds), you'd have 100 watts * 60 seconds * 60 minutes = 360,000 watts per hour (a.k.a. 360 kilowatt-hours).

To calculate the wattage at a given second would look like this:
100 watts/60 minutes/60 seconds = .027 watts/second = 1.67 watts/minute.

watts and watts per hour are interchangeable units. Any time you see a wattage rating (60 watt light bulb for example) that rating is based on a 1 hour time frame.

A 60 watt light bulb @ 120V = .5 amps, but if you turn on the bulb for 1 second then turn the bulb back off you did not consume 60 watts of energy; you consumed 60w/60m/60s = .0167 watts of energy. To have a wattage value you have to have a time frame (standard is 1 hour) or it's not a true value.

Another way for me to say this would be: you cannot have watts without having a time frame associated. Watts = watts per hour (same with BTUs: BTUs = BTUs per hour).

In the example you gave: W=VA the 'W' is watts per hour. Watts per hour = voltage * amperage ;)

Let me be more constructive.
The primary heat loss from a typical aquarium is evaporation; converting liquid to vapor. For water it is 970 BTU/#. So to evapoate a gallon of water : 8.3 #/gal X 970 BTU/# X 3.4 watt hr/BTU = 27,373 watt hr/gal evaporated. It is apparent why this is the primary heat loss. ( Yes, I had to look it up because I only remember it in metric ).
Or ,136 hours(5.5 days) with a 200 watt heater to evaporate one gallon. Remember , all the heat from any filter motors and some of the heat from lights is also adding heat.
The heat from the typical strong lights used in marine aquariums requires refridgeration. I used a small fan to increase evaporation (in the summer) when I had salt tanks.

Hmmm, I don't see the air humidity as a variable; wouldn't that play a factor in how much/fast the water is evaporated?

10% humidity @ 75*F will evap water faster than 90% humidity @ 75*F, right? Because the air at 90% is already saturated with water vapor and can only hold 10% more before you get rain (or more accurately water condensation). I'm asking because I'm not quite sure.








(Just in general - I'm not going to pretend to know everything I'm just trying to use a little math to show were some of these "rule" values come from. I could very well be wrong in my calculations and assumptions, so use this info at your own risk)

[blacksmith37]

The humidity, air velocity, etc effect the rate of evaporation but not the amount of heat required. So ,if you work for Fermilab or CERN you could put 27,373 watt hr of energy into a gallon of water in one second to vaporize it ; or with a covered 5 gal aquarium it may require a year to evaporate a gallon , but the energy would still be 27,373 watt hr.
I have been taking my own post to heart, nearly none of my tanks are covered and my total evaporation has been about 2 gal/week . So , I have been busy finding and washing tank covers. Keeping in mind that the windmill and cap&trade scams are going to about triple electric costs to us in the next couple years.

[wesleydnunder]

A 100 watt lamp is not using 100 watts all of the time. If it was using 100 watts all the time (we'll narrow it down to say seconds), you'd have 100 watts * 60 seconds * 60 minutes = 360,000 watts per hour (a.k.a. 360 kilowatt-hours).

Wrong again. There is no time component in Ohm' Law. After it uses 100 watts for 1 hour you have a hundred watt-hours, or .1 KWH. When you turn on the switch, the current in the circuit is instantaneous, or close enough to it ( speed of light ). The watthour and the watthour meter were invented by the power companies to be able the measure and charge for usage.

To calculate the wattage at a given second would look like this:
100 watts/60 minutes/60 seconds = .027 watts/second = 1.67 watts/minute.

The formula for power is P=I x E, or W= V x A if you prefer.
120 volts x .5 amps = 60 watts. Put an amprobe on the conductor of a lit 60 watt lamp and it has half an amp flowing through it. Test the voltage across the lamp and you'll read 120 volts rms. In your example above, either current or voltage would have to be drastically reduced. They aren't.

watts and watts per hour are interchangeable units. Any time you see a wattage rating (60 watt light bulb for example) that rating is based on a 1 hour time frame.

Watt and Watthour are not and have never been, nor will ever be, interchangeable.

A 60 watt light bulb @ 120V = .5 amps, but if you turn on the bulb for 1 second then turn the bulb back off you did not consume 60 watts of energy; you consumed 60w/60m/60s = .0167 watts of energy. To have a wattage value you have to have a time frame (standard is 1 hour) or it's not a true value.

Wrong again. During that second, which was reduced, voltage or current?
For .0167 W to be correct either voltage or current, or both, would have to be drastically reduced.
P=.0167W, E=120v, I=? P=I x E, so, I=P/E, I=.0167W/120V, I=.0001319A?, 131.9 microamps? hardly -- Lets check voltage --
P=.0167W, I=.5A, E=? P=I x E, so E=P/I, E=.0167W/.5A = .0334V,
33.4 millivolts? you're battin' a thousand here

Another way for me to say this would be: you cannot have watts without having a time frame associated. Watts = watts per hour (same with BTUs: BTUs = BTUs per hour).

Ever study Ohm's Law?

In the example you gave: W=VA the 'W' is watts per hour. Watts per hour = voltage * amperage

Nice try...but still incorrect.
Watt is the unit of measurement for power. There is no time factor in the formula. It's not watt per second, watt per minute or watt per hour. It's not watt per anything, it's just watts.

In the formula W = V x A, W is NOT watts per hour, it's just watts.

Andrew, I have an AAS in Electronic Technology, a State of Texas Master Electrician's license and I taught Electron theory in post secondary and proprietary degree programs for five years. I know something about this subject.

To fellow boxers: Sorry for this hijack. I felt this complete misunderstanding and misrepresentation of basic electricity should be corrected.

Mark

[thekarens]

Mark, you have just made me feel so under educated...... I think I'll go find a book to read

J/K................it was all Greek to me. I'm more of a they send me a bill, I complain kind of gal

[PhishPhreek]

OK - I tweeked it a little bit. Let me know if I missed something. 8^D

The General Rule – Your heater should be 3-5 watts per gallon (20g tank ~ 100W heater)

Hope this helps explain the science and math behind the scenes a bit

You've probably heard of BTUs (British Thermal Units) which is a measurement of heat transfer. It takes 1 BTU to heat one pound of water 1*F. There are approximately 8 pound of water in 1 gallon of water. So it takes 8 BTUs to raise 1 gallon of water by 1*F.

1 BTU = 1# water ^ 1*F
1 watt = 3.42 BTUs, so you need 0.29 (call it .3) watts per gallon per 1*F increase.
8# = 1 gallon = 8 BTU
2.34 watts per 1 gallon of water
time frame = 8 hours (how fast you want to make the change)

As an example take a 100 gallon tank. Going from 72*F (room temp) to 82*F (desired water temp) would required:
100 gal X 10*F X 2.34 watts per gal / 8 hours = 292 watts or 3 watts per gallon.

The above “class room examples” do not allow for "wind" blowing across the surface of the water nor over the sided of the glass (like a ceiling fan or AC vent). Generally you can double the number you get to account for heat loss and other factors that will increase the wattage needed to reach the desired water temp in a timely manner.

[andrewh]

Wrong again. There is no time component in Ohm' Law. After it uses 100 watts for 1 hour you have a hundred watt-hours, or .1 KWH. When you turn on the switch, the current in the circuit is instantaneous, or close enough to it ( speed of light ). The watthour and the watthour meter were invented by the power companies to be able the measure and charge for usage.

Ohm's Law has 3 components: I = V/R
I = Current in amperes
V = Volts
R = Resistance in ohms (also known as volts per ampere)

Ohm's Law states: The current within a conductor between two points has a proportional relationship with the voltage across those points and has an inverse relationship with the resistance between the two points.

Ampere = measure of the amount of electric charge passing through a point per unit of time.

Charge = quantity of electricity carried in 1 second with a current of one ampere.

Volts = The potential difference across a conductor when a current of one ampere dissipates one watt of power.

Watt = one joule of energy per second

Joule = work preformed to produce one watt continuously for one second

Resistance = watt equals voltage * amps also equals voltage squared divided by ohms also equals amps squared * ohms


Seems there is "time" all over Ohm's law, as well as, Joule's Law and almost every other definition for explaining work potential or measuring work (as in horsepower). Work accomplished over period of time.

The formula for power is P=I x E, or W= V x A if you prefer.
120 volts x .5 amps = 60 watts. Put an amprobe on the conductor of a lit 60 watt lamp and it has half an amp flowing through it. Test the voltage across the lamp and you'll read 120 volts rms. In your example above, either current or voltage would have to be drastically reduced. They aren't.

The amperage is per unit of time as well as watt, so if you use 120 volts at 60 watts for one hour, you've consumed .5 amperes over that time period.

Are you trying to tell me that if you use 120 volts at 60 watts for one hour you'll consume 1800 amperes (.5 amps * 60 seconds * 60 minutes)? That would be a total energy consumption of 216,000 watts over 1 hour.

That's absurd. That would be the equivalent of a 60 watt light bulb using 216 kWh, so if you left that bulb on all day (24h) for 1 month (30 days) your electric bill would be: 216kWh * 24 * 30 * $0.136 per kWh (charges from the electric company) = $21,150.72 not including the other electrical devices in your house.

If you have a 60 watt light bulb turned on for 1 second, then 2 seconds, then three seconds all the way to 1 hour, the electric company is not going to charge you 60 watts * 60 seconds * 60 minutes = 216,000 watthours worth of electricity, they're going to charge you for 60 watts of electricity. because that is what you used for that one hour with that light bulb.

Every time you use 60watts they charge you for it, so if you were using 60 watts per second they would charge you for 60w * 60s * 60m = 216,000 watts per that one hour of usage since they bill in hours (kWh to be exact).

Watt and Watthour are not and have never been, nor will ever be, interchangeable.

Guess I should have been more specific. When you see the wattage rating on a light bulb, that rating is watts/hour. So when calculating the wattage for lighting using the manufacture's wattage rating printed on the package or bulb itself, watts and watts/hour are interchangeable. The watts/hour is a lighting industry standard unless it is specifically stated otherwise (as in watts/second or watts/minute, watts/year, etc.).

Most other electrical device manufactures (an electric aquarium heater for example) also list their product's wattage rating in watts/hour so that it is easy for people to calculate how much that device will cost them on their electric bill. Again, the watt/hour is an industry standard, but not all manufacturers use it.

Wrong again. During that second, which was reduced, voltage or current?
For .0167 W to be correct either voltage or current, or both, would have to be drastically reduced.
P=.0167W, E=120v, I=? P=I x E, so, I=P/E, I=.0167W/120V, I=.0001319A?, 131.9 microamps? hardly -- Lets check voltage --
P=.0167W, I=.5A, E=? P=I x E, so E=P/I, E=.0167W/.5A = .0334V,
33.4 millivolts? you're battin' a thousand here

See above for explanation.

Ever study Ohm's Law?

Nice try...but still incorrect.
Watt is the unit of measurement for power. There is no time factor in the formula. It's not watt per second, watt per minute or watt per hour. It's not watt per anything, it's just watts.

In the formula W = V x A, W is NOT watts per hour, it's just watts.

I beg to differ. Watts are joules per second. Joules are work accomplished over time.

There is most definitely a time associated.

Andrew, I have an AAS in Electronic Technology, a State of Texas Master Electrician's license and I taught Electron theory in post secondary and proprietary degree programs for five years. I know something about this subject.

To fellow boxers: Sorry for this hijack. I felt this complete misunderstanding and misrepresentation of basic electricity should be corrected.

Mark

I'm not going to pretend that I know everything, and I do not mean any disrespect towards you personally.

I will conclude: it doesn't matter per the original post contents (or even the overall purpose of this thread). I didn't start this thread to debate electrical terms & definitions, so we can take this to PM if you like or move on.

Basally, most will need 3-5 watts worth of heater per gallon to maintain the temp. But there are still exceptions to this conclusion as well. There are so many variables to calculate that nailing down a "do this and it will always work" regarding aquarium heaters isn't practical.

[thekarens]

Hmmm my 200w heater is keeping my 90g tank at 85 degrees. It must not have read the rules.

Mark, it appears your education was for not

Yes, sarcasm was implied.

[wesleydnunder]

Hmmm my 200w heater is keeping my 90g tank at 85 degrees. It must not have read the rules.

Mark, it appears your education was for not

Yes, sarcasm was implied.

I know Karen. I guess I wasted most of my life doing this--lol.


OK Andrew, one last try. Maybe you'll believe this guy. Please pay attention to the distinction between watts and watt hours:

http://michaelbluejay.com/electricity/cost.html

I'll shut up about this now...the horse is still dead.

Mark

[andrewh]

Mark, thank you for link!!!! Definitely helped me see where I was going wrong. Thanks for not giving up, appreciate it!

Someone toss me a towel so I can wipe this egg off my face . On DFWfb, I'd be "in the corner" - so off I go .

The 35 miles per hour analogy make the light bulb click for me (lol pun intended). Don't know why I was making it so hard. Pretty simple really (don't think we have a foot in mouth smillie do we?).

Deleting my replies seemed like it would mess up the thread (leaving new comers scratching their heads), so hopefully crossing through it will keep folks from using this bad info, but can still follow the entire thread .

[blacksmith37]

Just to kick the dead horse again: You can repeat the discussion in metric , which tends to be easier to work with. One calorie = one gram of water X one degree C. G = cc = ml ( more or less ,at 68F). One caution , the calories on food labels are different from real calories by an order of magnitude( 10 X).

[wesleydnunder]

Mark, thank you for link!!!! Definitely helped me see where I was going wrong. Thanks for not giving up, appreciate it!

Someone toss me a towel so I can wipe this egg off my face . On DFWfb, I'd be "in the corner" - so off I go .

The 35 miles per hour analogy make the light bulb click for me (lol pun intended). Don't know why I was making it so hard. Pretty simple really (don't think we have a foot in mouth smillie do we?).

Deleting my replies seemed like it would mess up the thread (leaving new comers scratching their heads), so hopefully crossing through it will keep folks from using this bad info, but can still follow the entire thread .

No worries, mate. Glad to help.

Mark