I tend to agree with you. I think there might be a substantial improvement in a thermo-siphon system, but there will be negligible differences otherwise.
Something one could perhaps look at: The Americans tend to favour an upright tank. I’ve seen models with a second element lower down, precisely because the concentration towards the top of the tank actually limits the volume of available hot water.
Edit: Of course Phil replied at the same time as me and basically said the same thing: With the vertical tank, you sometimes need a second element. But that could be a good thing.
Yeah, but outside the standing loss, which we know to be around 2kWh a day, it is close to being a closed system. For most people, the bulk of the energy used will be proportional to the amount of hot water they use.
Which is a debate I’ve had numerous times with proponents of “geyser timers”. Geyser timers save a portion of the standing loss, because it allows the tank to remain cooler for a larger part of the day, thereby reducing the standing loss (according to Newton’s law of cooling). But by how much? IT cannot be more than 2kWh per day, by definition. And it won’t even get anywhere close to it… literally cents in a day, not enough to pay for the device by the time it fails.
Edit: Though again I must hasten to add, that in a thermosiphon system or a retrofit system, the timer is a must-have. You want the tank COLD in the morning so the sun has cold water to work with.
I wanted to mount my geyser vertical, but the plumber said they had issues with the heatpump not liking the vertical geysers that much.
The vertical vs horisontal area is for standing loss. If the water is moving (inflow from usage, or heat/solar pump) that will mix more of the water inside the tank.
I did not do that well with thermodynamics at university, so I would rather leave the formulas for others to explain.
But if this only has to do with introducing cold water, this would just impact the time that you can shower hot, right?
The loss to the air around the geyser should relate to the surface area of the geyser and the difference in temperature inside the geyser vs outside?
I understand the latter to be “standing loss”. If I put more cold water into my geyser, I need to heat it at some point. The energy to heat it isn’t “lost” as long as I use that cold water. After my geyser ran its course, the whole thing should be at 55 degree surely?
Ps. I might be giving away that I didn’t study any physics at university.
That is like saying other than it isn’t, it actually is.
Of course, but that is not the topic of discussion.
Oh, we do, do we? This is actually the topic of this discussion that is controversial.
We are discussing efficiency, so we are not discussing the energy used to heat water, but the losses associated with heating and storing that hot water.
From an energy loss viewpoint, this statement is flawed.
The bulk of losses will be more proportional to the amount of water we actually heat, not the amount of water we actually use.
This is an important distinction see my bath/sink element example above.
An electrical element vertical geyser far more efficient if a lesser amount of water is used.
So the vertical geyser wins there.
But that is not the only place a vertical geyser wins, as many people have already pointed out the area of the stratification in a horizontal geyser is far larger than a vertical geyser.
That means that the cold water in a horizontal geyser will absorb energy faster than it will in a vertical through that greater contact area.
If the cold water in the horizontal is warmer than in the vertical, the horizontal’s delta T to the ambient outside in its colder part, will be greater and it will lose more energy. (This is why the closed/open system distinction is important).
Your argument that the energy is still in that cold water and you just have to add top up electrical energy doesn’t’ hold. The horizontal geyser will actually lose more energy than its vertical counterpart.
It depend on your usage.
If you have a geyser full of hot water at 4pm and you don’t use any hot water until tomorrow morning when you want to shower, then yes it is only loss to the outside air.
But in reality this does not happen as people want to wash their hands in warm water, was dishes and some sower at night. All this introduce cold water into your geyser.
Well, perhaps not… but in South Africa there are regulations around that sort of thing. For a 200-liter tank it is slightly above 2kWh, for a 150-liter tank slightly below. If you don’t insulate the piping properly, then of course it is worse. Etc etc. I find 2kWh to be a good “rule of thumb”.
And I’m not really arguing that the vertical geyser isn’t more efficient. I’m saying it comes with caveats (stratification causing a small amount of immediately usable hot water for example), and the savings is probably not a significant amount. Though of course I don’t mind being proven wrong
So to aid my understanding, does it boil down to the cold water you introduce to a geyser heating up quicker in a horisontal geyser, and then lose that energy to the ambient? But won’t the converse then also hold true: That the hot water in the horisonal geyser would cool down more (after cold water is introduced) and therefore lose less to the ambient air?
Seems difficult to say that one is better than the other, because it seems to depend on how much cold water you introduce unless I’m missing something,
I have never seen anything that quantifies the losses, so there no debate there. There are also practical reasons why a horizontal geyser may be a person’s choice. I used to have vertical geysers in my ceiling space in SA, which through time have all been changed to horizontals at ground level. I found ease of access and maintenance to outweigh any energy savings.
Fair comment. However, that is where the thermostat will kick in and maintain the hot side temp, so the delta on the hot side should be very similar in both.
Well, the one thing I avoid, even if it costs me money, is the wife having to take a cold(er) shower. So efficiency is all good and well.
Phil is right, even if perhaps a tad pedantic, that energy use is proportional to water heated and not water used. Sure. But if you make sure that everyone gets a hot shower, then that is the same thing. I mean it doesn’t take a genius to realise that if I take a cold shower every evening, then I’ll be saving 25% on hot water I don’t have to (re)heat, but that is hardly something I feel like doing
In the end, inputs indeed equal outputs. Some of the outputs are just unwelcome… we want to minimise them. Energy in = Energy used (for showers) + energy lost (through uninsulated pipes, standing loss, etc). If we assume the household doesn’t change any habits, then the discussion centers around reducing the losses.
Does an upright tank decrease losses? Yes. By enough to make it meaningful? That I would like to see
This is always a game of tackling the lowest hanging fruit first and the geyser may not be it.
No, doubt where I am there are as well, hence the style of geyser we have here.
I don’t know if the differences are meaningful, as I have said my choice of mount is influenced more by my growing age, than an energy-saving.
I suppose for governments to try to regulate these things it must have a made a difference to someone, somewhere at one time.
It is also nice to know though, if the choice made no difference in terms of anything else, there can be a difference.
apologies for throwing in something else, I have a 200 litre horizontal geyser ( 2 kW element )that i heat mostly with solar pv/inverter, thermostat set to 70 degrees, the timer switches on at 10 am ( by that time solar production is around 2000 watts ), depending on how much hot water gets used, might take 6 up 13 kwh to reach back up to 70 degrees. The aim is to reduce grid usage, am i doing the best thing or not.
Oh wait, maybe this is where I misunderstand. I thought my horisontal geyser’s element is at the bottom (like a kettle), where the cold water should be? Doesn’t an electric geyser still use the “thermocycle” type principle to heat the cold water at the bottom?
If it only heats the hot water, surely it’ll take a very long time to heat the whole geyser because you will rely on heat transfer from the hot to cold water to heat the cold water?
Interesting. Well as far as I am aware both my (horisonal) geysers take their elements at the bottom.
As an aside, something I recently realised and found fascinating is that a really important feature of water is that it becomes less dense (apparently below 4 degrees) just before it freezes. Which is why lakes only freeze at the top (and not from the bottom up). Quite important for life to exist!
