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

[ericmark]

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.

OK I see your point. Since buying the system they have said my battery is not big enough, by 11 pm most days it is discharged to the amount set when on grid, there is a lower amount should the grid supply fail. So on grid failure I have 7% of 3.5 kWh to keep freezers and central heating running until the sun comes out.

So 10% of the battery is normally not used. So I want to use solar rather than give it to the grid at 9 p per unit, so in real terms gain 29 p per unit if I use it rather than export it as I pay 38 p for electric from the grid.

Well as far as iboost+ goes really saving oil rather than electric so hard to put a figure on that.

However now I have removed the times that the oil boiler runs to heat my DHW, to switch it back on manually not something I am likely to do. Wash hands in cold water is more likely.

So now really stuck with the iboost+ but as to if a new immersion would pay for itself not so sure, (or indecisive) hence my questions, aimed at other who have preceded me in stalling solar panels. Ask me in a years time and I will have the answers, but as it stands, not a clue if worth some upgrade.

Had the reset not tripped I would have weighted, and decided best option in a years time, but the trip worries me, and I really need to replace the thermostat, so just thermostat, or immersion and thermostat?

So I need to get my head around how an immersion heater works. Today 0.46 kWh has been used to get tank up to temperature set. If I now get three dull days, will I still have hot water on day 3? If the answer is yes, then existing system is good enough, in summer unlikely to get more than 3 dull days, in winter central heating running so not an issue.

Since it tripped out, I don't know if it lasted three days. The iboost+ shows kWh saved, which translated to kWh used to heat water, but I have no idea when it tripped.

I have clearly spent a lot of money around £11k and want a return, still not sure if it was all worth it, but a rough calculation on extra batteries and it seems unlikely to be worth it. Changing life style as to when dish washer, washing machine, and tumble dryer started likely worth the change.

As to waiting until 10 am for first cup of coffee, forget that. But as it stands 3.7 kWh exported today, this grid today shows how I have exported energy which it would have been better if I had used. But 38 - 9 = 29 p a unit wasted by exporting. Seems unlikely I will export enough to make using more to heat water worth while.

 

[eveares]

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.

Or install a pump to circulate the water from the top of the tank to the bottom of the tank. (Or circulate from bottom to top.)

 

[JohnW2]

Or install a pump to circulate the water from the top of the tank to the bottom of the tank. (Or circulate from bottom to top.)

One could do that, although I've never heard of it done in a domestic DHW system, probably since it would be pretty 'unsatisfactory' ...

.... if one achieved good 'mixing' of all the water in the cylinder by the method you suggest, one would have to wait until the entire tank had heated up to target temp before one could draw reasonably hot water from the top, and then once drew off some of the hot hot water, the temperature of drawn water would immediately start falling - which is really the opposite of what one wants, and the opposite of what is achieved without such forced mixing, Convection is our friend in this situation.

Kind Regards, John

 

[ericmark]

Or install a pump to circulate the water from the top of the tank to the bottom of the tank. (Or circulate from bottom to top.)

Sounds good at first reading, but then one has to consider the work involved doing that compared with installing the Willis system, and the Willis on the face of it seems better, however not talked to a single person with it installed, seems good on the face of it, but who would I find to fit it, who knows what they are doing?

How would it work in combination with the iboost+? And today we could not even satisfy the homes demand at midday, so how much would the system save?

The other point is soon I will be turning on the central heating, two things, one the hot coil will cause circulation, and two it will also be heating the DHW. Hence my question, I have no idea as a new solar panel user what they will do on average.

7th of September the panels went on line, 12th the iboost+ fitted, and 14th the UPS fitted, 26th the immersion thermostat over temp found tripped, not a clue when it tripped, the water was too hot so turned the thermostat down when reset the trip. We have had some good and bad days, but also days when solar not running all day due to work being done, and also the iboost+ to start with was turning on when it should not have, the increase in off set 100 watt to 200 watt seems to have cured that.

However it means I have not really been able to test the system well. And also my wife has been ill, so I was chief cook and bottle washer, so washer, dryer, dish washer have not been used as normal, and my daughter has been staying in the flat so also using power when it would not normally be used.

So rather a poor test to date. And it seems likely it will be next year before we really know what will be required.

My main aim at the moment is to reduce the back ground use. At 360 watt as shown here

It is too high to over night without discharging battery to limit by 11 pm. Freezers seem to be using around 120 watt, TV is around another 120 watt, lights all LED, so we are using double what we should be using as back ground load. I am slowly moving around the house with the three energy monitors to try to work out where it's going. I am wondering about wife's PC and printer, but we emptied part of loft for the solar equipment which then never went in the loft anyway, but means can't reach things in the office. Will need to get to things soon as batteries will need changing in the TRV heads.

 

[Risteard]

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 View attachment 315059stratification 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?

I have a Willis heater here. They're still reasonably common, though not so much in new installations.

 

[JohnW2]

Sounds good at first reading, but then one has to consider the work involved doing that compared with installing the Willis system, and the Willis on the face of it seems better,

That wouldn't surprise me since, as I wrote to eveares, I think that his idea of using a pump (or some other method) to mix the contents of the cylinder would not be very satisfactory/convenient, and certainly would not be very efficient of 'cost-effective'. ...

• With the usual system (no pump/mixing), one only has to heat a small amount of water up to 'target temp' (which doesn't take very long) in order to be able to draw water at that temp from the top of the cylinder, and the temp of what one was drawing would remain close to the 'target temp' until all of the heated water had been drawn.
• In contrast, with 'mixing', one would have to heat the entire contents of the cylinder to 'target temp' (and wait until that had been achieved) before one could draw off any water at that temp, and the temp of what one was drawing would be falling from the very start.

Kind Regards, John

 

[ericmark]

I have a Willis heater here. They're still reasonably common, though not so much in new installations.

I should have realised, location says it all. Would love to hear how well it works in practice. Why it never made its way across to the mainland I don't know.

I think down to the skill of the installers! I noted when we moved to modulating gas boilers which could gain the latent heat from flue gases the installers did not seem to change their ways, may be it's down to working with lead, they are Plumbers after all, possible had an effect on them?

 

[SpecialK]

Put a longer immersion in the tank if it will fit? This time of year you will have less excess for the immersion. Does the iboost offer dual output? You could use the other output to a simple oil filled rad?

I have sent 906kWh to my immersion so far this year! Either excess solar or using free agile time slots.

360W background is fairly high if you don't have any high draw items running. Mine is about 250W and thats with a server consuming 115W. I have managed to get the fridge to use less electric by pulling it away from the wall and turning the temps up by a degree each.

 

[ericmark]

Dish washer run so that was a high user, but today battery just 50% charged, so immersion unlikely to get anything today. Seems likely a longer immersion will help, but maybe at this point I should just wait and see what happens in the coming months?

 

[SpecialK]

Dish washer run so that was a high user, but today battery just 50% charged, so immersion unlikely to get anything today. Seems likely a longer immersion will help, but maybe at this point I should just wait and see what happens in the coming months?

Find a cheapy second hand oil rad (not a smart one) and wire that in for the winter? If the boiler is firing for heating it may as well heat the hot water for now.
Sort the immersion for March next year when the weather picks back up and you will have excess for the immersion.

 

[JohnW2]

..... today battery just 50% charged, so immersion unlikely to get anything today. Seems likely a longer immersion will help, but maybe at this point I should just wait and see what happens in the coming months?

If (assuming I understand correctly) what you currently have is just a short immersion near the top of your cylinder, that was never intended to, and never will, result in a significant amount of electrically-heated water - so, to achieve that, you will have no option other than to install a longer immersion (from the top) [ or a short one near the bottom of the cylinder, if your has provision for that (which I don't think it does) ]

However, as has been said, that's probably not an immediate high priority at present, since I suspect that you're not going to get a lot of solar/batter-heated water during the Winter months.

Kind Regards, John

 

[ericmark]

It does seem I am in the in-between time, where the CH is not running but the solar is not enough to heat water. Come March when CH is turning off again we will need to assess if the solar as is will satisfy our needs, not worth swapping the immersion for a couple of months a year when neither solar or CH is enough.

Two days on the run with low solar will mean we run out of DHW, but how often will that happen when CH not running?

 

[JohnW2]

It does seem I am in the in-between time, where the CH is not running but the solar is not enough to heat water.

As I said, even if it were mid-Summer and very sunny, your 'top' immersion would not be able to heat enough water for your needs.

Two days on the run with low solar will mean we run out of DHW, but how often will that happen when CH not running?

As above, getting enough DHW heated will always require that you have a longer/lower immersion than at present, regardless of the amount of sun and other loads.

Kind Regards, John

 

[SpecialK]

It does seem I am in the in-between time, where the CH is not running but the solar is not enough to heat water. Come March when CH is turning off again we will need to assess if the solar as is will satisfy our needs, not worth swapping the immersion for a couple of months a year when neither solar or CH is enough.

Two days on the run with low solar will mean we run out of DHW, but how often will that happen when CH not running?

Today was rubbish for solar - predicted at 12kWh and made 10.2kWh. Sat (28kWh) and Sun (23kWh) are meant to be good. It should bump a load in to the hot water tank once the battery is full...

 

[Risteard]

I should have realised, location says it all. Would love to hear how well it works in practice. Why it never made its way across to the mainland I don't know.

I think down to the skill of the installers! I noted when we moved to modulating gas boilers which could gain the latent heat from flue gases the installers did not seem to change their ways, may be it's down to working with lead, they are Plumbers after all, possible had an effect on them?

It works really well. I'm not sure why they're so uncommon in Britain. However ever since I had my hot water cylinder replaced a few years ago it just doesn't hold the heat the same way.