Using the Circuit Breaker as an On-Off Switch

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I have a friend who just moved to the US from the UK. He went from a Victorian house with a gas (I think) tankless heating system to a modern apartment with an electric water heater tank; a new situation for him. He is responsible for the apartment utility bills.
He is frugal by nature and is used to having his domestic hot water system on a timer. I doubt it would be practical to put a timer on the apartment's water heater for the time he'll be there (and the apartment management might not like the modification), but he has asked me whether he should turn off the water heater when he leaves for work, and I wasn't sure of the answer.
My first thought was that he won't save much electricity -- it's not especially hot water (set to child-safe temps by management, I assume) and it's in an under-stair closet near the center of the building, so it's not leaking a lot of heat to cold outdoors -- I think it might be served well enough by wrapping the tank in an insulating blanket and wrapping the short exposed length of pipe.
But I also began to wonder whether a circuit-breaker switch is designed to hold up being switched on and off a couple of times a day, every day. Any trouble liable to result from him using the circuit breaker to turn off the water heater on a daily basis?
Thanks.
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It may end up costing him more to overcome the temperature swings than to just leave it hot. It is also false economy to cool and heat some units and subject them to expansion and contraction over time, although the swings are minimal compared to a boiler.
Using the breaker as a switch is not a good idea either. It servers a purpose and it was designed to be a protection device, not a switch. Yes, I've seen it done often in industrial setting where breakers do control lighting.
The added insulation may help, especially if it is an older unit. The newer ones are more efficient.
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That's another issue. I can think of several ways an electric water heater can fail. I suppose temperature cycling might be one. But operating time at full temperature might be another. (Hot water is more reactive than cold water.)
But in this case, the capital expense is the landlord's but the operating expense is the tenants.

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That is nonsense. The water heater will always use less electricity if you let it cool down. Admittedly, the difference might be irrelevantly small. Think about it this way: If the unit is being kept hot, it needs to use energy to overcome the leakage of energy. This leakage is probably heating the house or basement around the water heater. But if you let it cool down, it will always leak less energy. Admittedly, if you let it cool down, you will eventually (when you heat it back up) have to use a lot of energy at once to bring it back up to temperature; but still less than if you had kept it at higher temperature.
Remember: In temperature swings, there is no friction. Getting the heater back up to temperature costs as much energy as the heater released when the temperature went down. Where did the heater release the energy to? Into the leakage - while the power was off. If we had kept the heater on, we would have had to pay for leakage. But there was less leakage (due to the lower temperature as the heater cooled down), so we have a small net gain.
There is an interesting counter-argument: It could be that the water heater is effectively heating the house. So if you let it cool down, then the house will get colder, which will then cause you to require more heating to keep the house comfortable. If the house heating were electrical, and you had a perfect thermostat on the house, this additional expense would exactly cancel the saving at the water heater. With other forms of heating, and in particular in warm weather, this can go either way.

True, but maybe irrelevant (there are other effects that counteract this effect - for example it doesn't corrode as fast as when it is cold, and the thermostat doesn't have to switch off and on as often while the heater is off). Can't tell whether this is a good or a bad effect.

Some breakers are rates as switches. Some are not. Some are rated to switch only resistive loads, while some are rated also for inductive loads (which may or may not include lighting loads, looking at fluorescents). Look at the Square D catalog (just as an example), and you will find a wide variety of breakers.
The garden-variety breakers installed in residences are TYPICALLY BUT NOT ALWAYS rated for switching duty. But two-pole (or 240V breakers) are TYPICALLY NOT rated for switching duty. Again, for example an look at the Square D catalog, and look for HOM120 breaker (a garden-variety 20A single-pole circuit breaker, the cheapest one you can get from Square D). The footnotes to it say:
a UL Listed as SWD (switching duty) rated. Suitable for switching 120 Vac fluorescent lighting loads. b UL Listed as HACR type for use with air conditioning, heating and refrigeration equipment having motor group combinations and marked for use with HACR type circuit breakers.
The 2-pole 30A breaker (which is what one would typically use for a water heater) does NOT have footnote A.

This is EXCELLENT advice. We put a "heater blanket" (special pre-made encapsulated fiberglas insulation) around our heater (which was admittedly outdoors), and it saved about $10 per month.
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My ballpark estimates by doing same power cycling concluded that energy saved per day was about one shower of heat. That is heat expended every day to maintain hot water heater at 120 degrees. Again, these were only ball park numbers.
Ralph Becker-Szendy wrote:

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Robert E. Lewis wrote:
[...]

We turned off lights with circuit breakers daily at the bookstore where I worked all the way through college. No problems.
I'd encourage your friend to try this for a month and then try leaving it on for a month and compare, though. I doubt he'll save much money turning it off, and it may even be more expensive.
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may? its a sure thing it will be more expensive doing this on a daily basis. basic physics dictate this.
randy
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turn the heater off. But the difference will probably be trivial. No, I will not argue physics with you; if it is not obvious to you, you don't know enough to grasp it. (though I will give you a hint; heat loss is proportional to the difference in temperature)
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go back to community college and finish your degree...
randy
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xrongor wrote:

Just so you don't think that it's only one person picking on you Randy, I also firmly believe you are wrong about that point.
Now, instead of your just flinging insults, why don't you give us all your technical reasoning involving "basic physics" please.
Jeff
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flinging insults. i think 'i wont bother to explain to you' is an insult.
lets start with a simple question. one that comes up from time to time in trivia games. which freezes faster, hot water or cold water?
randy

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xrongor wrote:

I presume you want to start with two equal sized wooden buckets filled to the same level, one with hot water and the other with cold, set outside, no covers on 'em, on a day where the air temperature is below 32F. Right?
The wood provides some insulation between the cold air and the water, delaying heat loss through that path. The hot water will evaporate faster than the cold and leave the "hot" bucket with less water in it.
If things are tweaked right, you can find starting water temperatures and an air temperature which will result in the water remaining in the "hot" bucket freezing first.
Now, pray tell, where are you going with this? The fellow's water heater isn't open to the air, so evaporation won't be a factor.
Next?
Jeff
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<...snipped...>

That sounds pretty cool. Can you give a specific example (temperatures, quantities, etc.) where this will happen?
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Lawrence Wasserman wrote:

I got the pun..A good one too...
************************************
There's no simple answer to your question because there are LOTS of factors which must be considered, IIRC they all contribute to the "Mpemba effect" which ex[lains why hot water freeze faster than cold.
I'm just a flatfooted EE who forgot most of the physics I learned years ago, but Googling "hot water freezes faster than cold" will get you a day's worth of reading on the subject.
This URL I particularly like 'cause it's part of the "Marilyn is Wrong" series. (Marilyn vos Savant, that is.) It has a lot of links to other sites on the subject:
http://www.wiskit.com/marilyn/freezing.html
This URL will give you more than you wanted to know and choke you with details and references:
http://math.ucr.edu/home/baez/physics/General/hot_water.html
Hey, I just noticed the /baez/ in that URL. A few backwards steps will reveal that it's John Baez, a physicist at University of California, Riverside, who is a relative of Joan Baez, the entertainer. I had the pleasure of knowing Joan briefly in the 1950s around the time she began her career by singing in Harvard Square coffee houses. Her father was a physicist at Harvahd back then.
Enough already?
Jeff
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Hot water :-)
OK, so I admit it, in nearly all cases cold water will freeze faster. Look at the limiting case: Take some water that is just about frozen (say it is at 0.001 degrees C, and yes I know that the freezing point of garden-variety water is not exactly 0 degrees). This water will freeze very quickly.
But there is a case where hot water will actually freeze first. This is one of the homework problems in "The Flying Circuis of Physics". I think it only works if you use an open cup of water with insulated sides, cool it with very cold air, and make sure there is strong air flow across the surface of the water (or something like this, look it up in the book, it was about 20 years ago that I read this). I think the trick to reproducing this at home is to use an otherwise empty frost-free freezer.
If I remember right (and this is a big if), I think it has to do with evaporation: The hot water will evaporate very quickly in this situation. So by the time you get to near freezing, there is a lot less water left, and at that point the somewhat empty cup (formerly full of hot water) will actually win over the full cup (which started out as cold water). I think this also doesn't work if you start with really hot and really cold water (then the really cold water will actually win the race); it works better with really hot and lukewarm water.
There are other tricks you can play. For example, put the water into an aluminum pan, and put both pans down on a non-frost-free freezer. In this case the hot one might freeze first. Why? Because it melted through the ice underneath, and the aluminum pan ended being in contact with the cold pipes in the shelf, whereas the cold water pan sat on top of ice (a pretty good insulator). This trick only works because non-frost-free freezers typically are covered in thick layers of ice.
There is even tricks you can play with density of water and layering, causing warmer water to hide somewhere (in a layer of water, I think it requires having part of the water below 4deg C, where the density inverts), thereby delaying the freezing because the cold can't get to it as fast.
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xrongor wrote:

You're avoiding the question because you are beginning to see how wrong you are, and you don't have the balls to admit it.
Best regards, Bob
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On Thu, 28 Oct 2004 15:31:45 -0600 "xrongor" used 28 lines of text to write in newsgroup: alt.home.repair

Randy,
Could you explain the "basic physics" principals used to calculate your observation? I would think you need specific information about the size and thermal resistance of the water heater, and it's heater coil power consumption to make a statement like that. You would also need to know the ambient temperature in the apartment, and the temperature of the incoming cold water. It would also help to know where the thermostat is set.
-Graham
Remove the 'snails' from my email
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save energy as long as the heating element only has one setting and the water in the heater is free to circulate normally. You can create artificial conditions where the heat must diffuse slowly and the like, but with a real heater turning the power off will always save energy.
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why?
assuming the water will not reach room temperature in the time the heater is off (in which case you would clearly save money) from a power/energy standpoint whats the difference between operating it in a mode where it turns on and off with in 1 degree of its setting, or 5 degrees, or allowing it to cool down 20 degrees before it turns on? whatever you saved by not turning it on earlier, has to be paid again on the way back up. the way i see it the difference is that the lower you let it drop before turning back on, the more thermal inertia to overcome hence it will be more costly to operate it by letting it cool down 20 degrees than it would be to just keep it at the higher temperature.
you dont agree i take it... the only way i can see it would be cheaper is if there is some energy lost in the act of cycling the thermostat from on to off, or in initially 'charging' the coils or something like that. in which case fewer cycles would be cheaper...
randy
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ok randy here's the answer

absolutely correct, you've got part of the answer

no, the energy lost during the cool down is the only energy that needs to be replaced. Your thermal inertia concept is flawed if you think there is a extra penalty for letting the temp fall further.
If the tank cools 20 degs & it takes 10000 btu's to bring it back up to temp; then it will only take twice that energy 20000 btu's if the tank is allowed to fall 40 degs.
The small (if not trivial) energy savings is had because a cooler tank (one that is closer to room temp) looses less enery than a hotter tank. If the tank lost all its heat (fell to room temp) it would stop loosing heat to the environment.
Electrical water heaters typically are well insulated & loose heat rather slowly. The only energy saved during the "off period" would be the energy consumed in the cycling (if any) that would have occured to "maintain" temp during the day.
By your logic I wouldn't save any energy if I turned the thing off for a week because "I had to make up all that thermal inertia"?
A cooler house (or water heater) looses less heat to the surroundings.
That's why I turn the heater WAY down when I'm away from the mountain cabin :)
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