May sound daft, but how does an immersion heater work?

[ericmark]

I had a problem, so looked up the part number of the thermostat, a TS-220 sorry for mirror image, and on looking it says 7 inches long, but my tank must be near to 4 foot tall, so it is only measuring the temperature of a small amount of the tank. The reset had popped and the temperature was set too high, so lowered temperature and reset.

The iboost+ then started to heat my water at nearly full output, but not for long, very soon it said

which basic means the thermostat has turned off and so immersion is open circuit, if there is no spare power it says

then I found the iboost+ turning on again latter and it said something like

not the full 3 kW but some lower amount, I assume the water has been moved in the tank allowing it to re-start heating it, not sure if the lower amount due to how much solar available or if there is some software which tell iboost+ to reduce how much it heats if it was on not long before?

However I am not sure how an immersion heats the tank, OK read about the Irish Willis system, but don't think I could trust a Welsh plumber to fit that, I have a simple immersion in the top of tank, and a hot coil further down, so how does the immersion heat the tank? Does it only heat top 7 inches, or do thermals slowly move the water allowing although slowly the whole tank to be heated?

I would think the peak

is where the tank was reheating due to it having tripped before and my resetting the cutout, not sure about other peaks, it says it has used 0.70 kWh today (actually says "saved today") but when I run the central heating to heat the water it runs for around 20 minutes at 21 kW which equals 7.00 kWh not 0.70 kWh, OK some losses in the pipe work, but we are looking at 10 times the energy used.

So what is going on? Has it been for the last 4 years since moving hear I have been using too much energy to keep water warm?

Also the boiler ran once every other day, set to run for ½ hour, but would cut out after 20 minutes, and water would stay warm over the 48 hours, but when the over temp trip opened within a day water was cold.

I have only once run a bath since moving here, and unlikely I will return to bathing instead of showering even if a bath costs less, due to being heated with solar, but shower uses too much power to be supplied by solar, at least all by solar. But I do wonder if using the immersion heater if I could fill a bath? Can't try it would upset wife as she has stuff stored in the bath, her e-bike is in one.

So comments welcome, I am willing to learn, although think the Welsh plumbers are too tick to fit a Willis system.

 

[DetlefSchmitz]

Without reading every word of the above; you probably need to know that an immersion only heats water at the same height or above. They are fitted at the top of tanks to allow you to heat a small amount of water in an emergency. If you want to use spare free energy you need an immersion at the bottom of the tank.

 

[foxhole]

Hottest water is always at top , where else would you put a thermostat?

 

[DetlefSchmitz]

Hottest water is always at top , where else would you put a thermostat?

At the bottom of the amount of water you wish to heat.

 

[foxhole]

At the bottom of the amount of water you wish to heat.

The bottoms cold , so impossible .

 

[DetlefSchmitz]

The bottoms cold , so impossible .

It should go without saying that you also put the element down there.

 

[foxhole]

It should go without saying that you also put the element down there.

Yes , and the hot water rises to top .

 

[ericmark]

As said Willis is answer, but not sure how much water circulates in a cistern? Does is slowly work its way down, I know water most dense at 4ºC so at the bottom of any large mass of water it is 4ºC, but there must be other factors, the water entering and leaving must cause some movement, pictures show a gradual change in temperature stratification is not as a hard dividing layer, I think the name for the layer of mixture is called thermocline, but how much can heat in water move by conduction? Even if that conduction is the copper wall.

I would have thought a element in the centre would cause the centre water to rise, cool slightly from the sides of the cylinder and then drop down the outside.

However the question is how much, and does the about of lets call is stirring of the water vary with the amount of energy put into the water. If the water is heated with 250 watt or 2500 watt what amount of water will they both heat?

 

[JohnW2]

Hottest water is always at top , where else would you put a thermostat?

At the bottom of the amount of water you wish to heat.

The bottoms cold , so impossible .

As Detlef then wrote ....

It should go without saying that you also put the element down there.

...but you then went on to write ...

Yes , and the hot water rises to top .

It will. As a result, the 'height' of heated body of water (measured from the top of the cylinder) will gradually get greater, and will eventually reach the point where it goes all the way down to the level of the immersion (and thermostat), and when the temp at the bottom of that mass of heated water (i.e. at the location of the immersion+thermostat) reaches the set threshold of the thermostat, the thermostat will turn the immersion off. The temp at the top of the tank will then be a bit higher than the thermostat's 'set' temp.

I'm not sure why we are having this discussion, since all electrical immersions have an integral thermostat, so both will be at the same position within the cylinder - so , in relation to "Hottest water is always at top , where else would you put a thermostat?", unless the immersion is at the top of the cylinder (which never will be the case for a 'main' immersion) the thermostat will not be 'at the top'.

Kind Regards, John

 

[ericmark]

Immersion is at the top, I remember at one point you could get twin immersions one long and one short, and one could select bath or sink, the iboost+ installation manual does show two immersion heaters as an option but states one immersion is more popular. Can't see how one could fit two unless tank designed for it, but with cold water this morning, and 7.9 kWh exported it has only used 0.7 kWh of power to heat the water, this explains why the water did not stop hot very long.

Also noted comments about DC and the RCBO feeding the immersion is type AC.

 

[JohnW2]

Immersion is at the top,

In that case, it wil never heat more than a small amount of water - water below the immersion will never get appreciably heated, because the thermostat at the top will switch off the element as soon as the water at the top is 'up to temp'.

I remember at one point you could get twin immersions one long and one short, ...

One still can. For example ...

.... Can't see how one could fit two unless tank designed for it, ...

All of my DHW cylinders are 'designed for it' - with provision for one ('long') immersion inserted into the top, and another near the bottom on one side. These days, it seems more common to have just the top position available, but with the possibility of using a 'dual' element one, as above.

Also noted comments about DC and the RCBO feeding the immersion is type AC.

'DC components' created by an immersion heater element ??

Kind Regards, John

 

[flameport]

on looking it says 7 inches long, but my tank must be near to 4 foot tall, so it is only measuring the temperature of a small amount of the tank. The reset had popped and the temperature was set too high, so lowered temperature and reset.

If the reset has operated, the thermostat has failed and will need to be replaced.
If you only have a short heater in there, get a longer one installed which will heat most of the cylinder rather than a tiny section at the top.

 

[ericmark]

'DC components' created by an immersion heater element ??

The output from the Solar iBoost+ is modulated DC and cannot be measured with an AC Voltmeter.

The question is do I get another immersion heater installed? I will pick up a new thermostat next time in town, as @flameport says if failed once may fail again even if temperature now turned down a bit. Until solar fitted the immersion was for emergency only, so never really used.

But not withdrawn the thermostat and tested, possible the pocket is longer, and wrong one fitted? Which is why I started the thread, if the immersion is longer than the thermostat then it can heat water lower down over the temperature of the cut out before the thermostat turns off, so could trip the cut out due to wrong one being fitted or could it?

It has been some 30 plus years since I have lived in a house with a hot water tank, and the ability to use an immersion heater. I have read about the Willis system, but never seen it in use, I know the idea is it heats the top of the tank first and slowly heats further and further down the tank, and that it is promoted as being ideal for solar so if I need to alter the system would it be worth moving to the Willis system? Maybe a holiday to Belfast and make inquiries while there? Always wanted to return there want to visit the museums in Holywood. And see how Bangor has changed.

But I am an electrician not a heating engineer or plumber, and I am also new to solar power, and the question is would the changes pay for them selves? This is the hard bit, OK on theroy longer immersion or external immersion may heat more water, but I rarely have a bath, so will having more hot water really help?

 

[DetlefSchmitz]

It seems to me you have already bought solar panels, an inverter, a battery storage system with some form of islanding controller, and an iBoost to make use of your free energy, and you are now asking whether it is worth the money to buy the correct immersion heater to make the energy savings work. Seems like a no-brainer to me.

 

[JohnW2]

The output from the Solar iBoost+ is modulated DC and cannot be measured with an AC Voltmeter.

Do you have any idea what that means? Are they talking about non-sinusoidal AC, or what?

The question is do I get another immersion heater installed?

As has been said, in the context of the entire project (and it's high cost0 that question would seem to be a no-brainer.

Kind Regards, John