Immersion element size

[TandC]

I have an as-yet, not quite installed calorifier from SureCal.   It is a large 90lt twin-coil vertical unit, which will be sat in an insulated box in the engine bay (no, it cannot go inside the boat, no we do not have room for another smaller calorifier).

 

At the time, when I ordered it I thought that I would order a 3kw element because the only time I would be using it was when at the mooring where we have a 32mp supply.   My thinking was - go big -  as it will be the main domestic water heating source  (there is the engine, and a Webasto for central heating via the calorifier, but for the vast majority of time, it will be immersion heater). 

 

I thought if we're going to be using an immersion anyway - then go for a large element to help in getting the temperature up quicker should we go away and come back to a cold calorifier.   

 

And then when we are out and about cruising, we'd either have been moving, or if static would run the engine for a battery-top up each day and this would be the main water heating source when out and about.    And finally, we could run the Webasto to heat the calorifier, as the last option (although the Webasto is also linked to a towel rail in summer/whole heating system in winter). 

 

 

 

 

But - now, I am questioning myself...   by going for a large 3kw immersion I am not ever going to be able to run that with any surplus solar generated once batteries are charged. 

 

While a widebeam, it is unlikely to have solar panels much larger than 1.5kw (I've not got to that stage yet, but rough guesswork on available roof) - and I appreciate that in this country, we rarely get maximum available sun etc etc.   

 

I will likely be installing a MasterVolt Combi 12/3000 - so that also places a limitation on the continuous output....also, I'd need one that has the switching of a load function

 

Have I been too hasty?   Should I have opted for a smaller immersion element which could be used to heat water through excess solar?   Or, does my original thinking still stand up?!

 

 

 

 

 

 

[Jen-in-Wellies]

Ignoring losses from the cauliflower, the amount of energy required to heat the water to temperature will be the same. A lower power immersion heater will just take longer to do it. This would be more compatible with the low power, but hours of time nature of solar power on a sunny summers day, which is the only time you'd be diverting solar to water heating.

You could always drive the 3kW immersion with 120V, rather than 240V. Power is proportional to V squared, so halving the voltage means a quarter the power, or 750W. Get a dedicated 1kW 120V inverter for the cauliflower immersion and switch between that and mains 240V, when shore power is available.

[IanD]

5 minutes ago, TandC said:

I have an as-yet, not quite installed calorifier from SureCal.   It is a large 90lt twin-coil vertical unit, which will be sat in an insulated box in the engine bay (no, it cannot go inside the boat, no we do not have room for another smaller calorifier).

 

At the time, when I ordered it I thought that I would order a 3kw element because the only time I would be using it was when at the mooring where we have a 32mp supply.   My thinking was - go big -  as it will be the main domestic water heating source  (there is the engine, and a Webasto for central heating via the calorifier, but for the vast majority of time, it will be immersion heater). 

 

I thought if we're going to be using an immersion anyway - then go for a large element to help in getting the temperature up quicker should we go away and come back to a cold calorifier.   

 

And then when we are out and about cruising, we'd either have been moving, or if static would run the engine for a battery-top up each day and this would be the main water heating source when out and about.    And finally, we could run the Webasto to heat the calorifier, as the last option (although the Webasto is also linked to a towel rail in summer/whole heating system in winter). 

 

But - now, I am questioning myself...   by going for a large 3kw immersion I am not ever going to be able to run that with any surplus solar generated once batteries are charged. 

 

While a widebeam, it is unlikely to have solar panels much larger than 1.5kw (I've not got to that stage yet, but rough guesswork on available roof) - and I appreciate that in this country, we rarely get maximum available sun etc etc.   

 

I will likely be installing a MasterVolt Combi 12/3000 - so that also places a limitation on the continuous output....also, I'd need one that has the switching of a load function

 

Have I been too hasty?   Should I have opted for a smaller immersion element which could be used to heat water through excess solar?   Or, does my original thinking still stand up?!

 

 

If you want to be able to absorb all the solar power and use this to heat water, the immersion heater (and the inverter) both have to be able to absorb the panel power in full sunlight if the batteries are charged. Having the immersion bigger than this means it will have to be pulsed on and off, and needs a bigger inverter, and will put extra strain on your batteries.

[jonathanA]

I have a 55L surecal with the 1KW immersion and it does take a long time to heat up from cold on its own. I think you will be glad of a 3Kw immersion on your larger cauliflower on those occasions when you need it heat up from cold or when you want lots of and/or long showers. 

 

There are alternative ways of controlling the power sent to the immersion heater that our resident expert on everything has not mentioned using triacs or thyristors for instance  - think the biscuits describes his way on a  lithium battery thread somewhere (can't find it now) .  At home I use an iboost device which diverts excess solar PV power to my 3KW immersion. basically it uses a variable DC voltage to use up all the spare solar power rather than export it to the grid. Obviously thats not a solution that would work on board (sadly). 

 

are your batteries LA or Lithium? 

Edited October 23, 2023 by jonathanA
correction to lithium thread that I can't find !

[IanD]

1 hour ago, jonathanA said:

I have a 55L surecal with the 1KW immersion and it does take a long time to heat up from cold on its own. I think you will be glad of a 3Kw immersion on your larger cauliflower on those occasions when you need it heat up from cold or when you want lots of and/or long showers. 

 

There are alternative ways of controlling the power sent to the immersion heater that our resident expert on everything has not mentioned using triacs or thyristors for instance  - think the biscuits describes his way on a  lithium battery thread somewhere (can't find it now) .  At home I use an iboost device which diverts excess solar PV power to my 3KW immersion. basically it uses a variable DC voltage to use up all the spare solar power rather than export it to the grid. Obviously thats not a solution that would work on board (sadly). 

 

are your batteries LA or Lithium? 

You could put a power control device between the inverter and immersion but this may react badly with the inverter. A dual-element immersion heater would be the easiest solution, but these all seem to be too big, typically 2kW+2.8kW.

[nicknorman]

I would go for a 1kw heater, as we did. If you are on shore power, the thing can be left on all the time (it will have a thermostat) and so it won't matter too much that it takes a long time to heat up from cold. And in fact it probably won't take long to get some hot water - the hot water rises to the top and so after not very long, there will be some hot water for washing up etc. With a 1kw heater you can reasonably run it from the inverter/batteries if you have surplus battery power. And at some point you may be on something other than a 32A supply which will mean that you can have the immersion on and still have plenty of mains power to spare for other things.

[ditchcrawler]

40 minutes ago, nicknorman said:

I would go for a 1kw heater, as we did. If you are on shore power, the thing can be left on all the time (it will have a thermostat) and so it won't matter too much that it takes a long time to heat up from cold. And in fact it probably won't take long to get some hot water - the hot water rises to the top and so after not very long, there will be some hot water for washing up etc. With a 1kw heater you can reasonably run it from the inverter/batteries if you have surplus battery power. And at some point you may be on something other than a 32A supply which will mean that you can have the immersion on and still have plenty of mains power to spare for other things.

That makes a lot of sense

[blackrose]

Yes as Gordon Brown once famously said "I agree with Nick"

 

But I'd also install an immersion heater timer. Leaving an immersion heater on all the time will use more electricity than having it come on twice a day for 3 hours for example. It's a myth that it's the same or as some think leaving it on all the time uses less energy.

 

Also I've switched on my 1kW immersion on a sunny day from the batteries/inverter, using 910w of solar panels to supplement the draw. I left it on for a couple of hours without a problem until my 60l calorifier was hot and my 450Ah of batteries went down to about 60% SOC, but there was enough sunshine to get them fully charged again afterwards. However, it's not something I'd make a habit of doing and I'd be very careful if doing it. You must have good battery monitoring equipment.

 

The other option is a 12v immersion running directly from the MPPT controller but then you're talking about a 300w immersion heater and the limitations make it problematic.

Edited October 23, 2023 by blackrose

[nicknorman]

40 minutes ago, blackrose said:

 

But I'd also install an immersion heater timer. Leaving an immersion heater on all the time will use more electricity than having it come on twice a day for 3 hours for example. It's a myth that it's the same or as some think leaving it on all the time uses less energy.

 

It definitely doesn’t use less energy! But it may not use much more, depending on how well insulated it is. If it is perfectly insulated then it won’t use more energy to leave it on permanently. But of course a calorifier is not perfectly insulated and so keeping it on all the time (water at the max temperature and hence max heat loss) will use more energy. But maybe not by much, if the calorifier is well insulated.

[TandC]

Well thanks folks - in some ways, I am glad I asked because it's been annoying me...  and the nagging feeling was that I should have gone for the 1kw all along.  ALthough now I have the worrying task of swapping the factory-fitted 3kw for a smaller one. Plus £90 wasted... hey ho.  

 

I guess as long as a smaller one is the same length, it will still heat the whole tank fully - just take longer to  do so?   Which as you've said is not really an issue for when on shorepower.  

 

The other option is to run the engine briefly i guess if we're really desperate to heat the water quickly from cold to give it some extra oomph.  And realistically, it's only a few times a year when we go on holiday or wotnot that we'd be turning off the hot water to allow it to go cold.

 

And if it opens up the option of harvesting a bit of solar-powered hot water then that appeals....  

 

Next question - for a 1kw immersion, what would the recommended inverter be - to allow a continuous draw for a 1kw immersion plus a bit on top so we can still run a 240v fridge/freezer, a few power sockets etc for normal devices (not a kettle or iron or anything powerful).

 

Our power usage is very low when on batteries - we just run a 240v fridge with freezer box.  No TV, no washing machine, just a few chargers and wotnot. 

 

 

[Alan de Enfield]

9 minutes ago, TandC said:

Next question - for a 1kw immersion,

 

Just remember that a 1kw heater element will be drawing 100Ah out of the batteries (via the inverter)

[TandC]

1 minute ago, Alan de Enfield said:

 

Just remember that a 1kw heater element will be drawing 100Ah out of the batteries (via the inverter)

Yep - appreciate that it would be probably not be worth running the batteries down for hot water.  

 

I need to investigate with MasterVolt how configure-able the solar charger is - it states in their limited bumpf that it is possible to set the system up so that once battery bank is fully charged it can be used to switch a water heater load on - and presumably to switch it off again at set values.   

 

Also, it's likely we would be onboard (sunbathing!) if we were to use the solar to heat water - monitoring the battery SOC, considering the weather and sticking it on for a few hours where possible, manually. 

 

Also with MasterVolt - their 12v/2000 versus 12v/3000 CombiMasters state no difference between their standby power draw - should we believe that?   If they really are close enough in their power consumption, aside from the physical size differences, why not go for the larger capacity?

[nicknorman]

19 minutes ago, TandC said:

Well thanks folks - in some ways, I am glad I asked because it's been annoying me...  and the nagging feeling was that I should have gone for the 1kw all along.  ALthough now I have the worrying task of swapping the factory-fitted 3kw for a smaller one. Plus £90 wasted... hey ho.  

 

I guess as long as a smaller one is the same length, it will still heat the whole tank fully - just take longer to  do so?   Which as you've said is not really an issue for when on shorepower.  

 

The other option is to run the engine briefly i guess if we're really desperate to heat the water quickly from cold to give it some extra oomph.  And realistically, it's only a few times a year when we go on holiday or wotnot that we'd be turning off the hot water to allow it to go cold.

 

And if it opens up the option of harvesting a bit of solar-powered hot water then that appeals....  

 

Next question - for a 1kw immersion, what would the recommended inverter be - to allow a continuous draw for a 1kw immersion plus a bit on top so we can still run a 240v fridge/freezer, a few power sockets etc for normal devices (not a kettle or iron or anything powerful).

 

Our power usage is very low when on batteries - we just run a 240v fridge with freezer box.  No TV, no washing machine, just a few chargers and wotnot. 

 

A fridge has a high transient power demand momentarily when the thermostat kicks in. The exact answer depends on the fridge and the inverter’s transient supply capability, but I’d go for a 3000va inverter if it were me.

2 minutes ago, TandC said:

Yep - appreciate that it would be probably not be worth running the batteries down for hot water.  

 

I need to investigate with MasterVolt how configure-able the solar charger is - it states in their limited bumpf that it is possible to set the system up so that once battery bank is fully charged it can be used to switch a water heater load on - and presumably to switch it off again at set values.   

 

Also, it's likely we would be onboard (sunbathing!) if we were to use the solar to heat water - monitoring the battery SOC, considering the weather and sticking it on for a few hours where possible, manually. 

 

Also with MasterVolt - their 12v/2000 versus 12v/3000 CombiMasters state no difference between their standby power draw - should we believe that?   If they really are close enough in their power consumption, aside from the physical size differences, why not go for the larger capacity?

With Li batteries you wouldn’t flinch at running them down somewhat with a 1kw immersion. We do that sometimes. With lead acid, maybe not.

 

The new Mastervolt Combis do seem to have a rather high quiescent power drain, much higher than our 10 year old Mastervolt 12/2500/100 which is 9w (around 0.75A). Victron Combis seem to be better for quiescent power consumption these days.

[ditchcrawler]

4 minutes ago, nicknorman said:

A fridge has a high transient power demand momentarily when the thermostat kicks in. The exact answer depends on the fridge and the inverter’s transient supply capability, but I’d go for a 3000va inverter if it were me.

I have a 1500 Mastervolt and it starts the fridge fine with any other load I gave on, Induction hop, grill, kettle, coffee machine etc.

[TandC]

Should have said - for now, i think we'll stick with hte lead acids and see how we get on with them, by the time they collapse, we can rethink - consider the new market options which in 3 or 4 years i expect will have come down in price a fair bit 

 

The online stuff says 10w for energy saver mode consumpton, and 30w for  battery no load consumption, this for both the 12/2000 and the 12/3000.

 

Not really sure what the difference is between those two modes? 

(this is a taking a bit of diversion away from teh immersion heater but all helpful stuff all the same !!)

 

[nicknorman]

10 hours ago, TandC said:

Should have said - for now, i think we'll stick with hte lead acids and see how we get on with them, by the time they collapse, we can rethink - consider the new market options which in 3 or 4 years i expect will have come down in price a fair bit 

 

The online stuff says 10w for energy saver mode consumpton, and 30w for  battery no load consumption, this for both the 12/2000 and the 12/3000.

 

Not really sure what the difference is between those two modes? 

(this is a taking a bit of diversion away from teh immersion heater but all helpful stuff all the same !!)

 

Energy saving mode is typically some sniffer mode where the inverter is shut down and momentarily fires up every 10 seconds or so. If it finds a load connected, it stays on. If no load connected, it shuts down again.

 

The problem is that some devices present insufficient load to keep the inverter on, such as timers/clocks associated with some devices, maybe phone chargers etc. A fancy fridge that doesn’t have a mechanical thermostat might be a problem. And of course once the threshold is breached and the inverter stays on to supply a small load, you still have the higher power drain of the “normal” mode. For this reason I tend not to give energy saving mode consumption any priority, I just look at the normal mode consumption, and 30w is quite a lot, 2.5A or so, which is 60Ah over 24 hours.

 

A Victron 3000va Combi is 20w which is high compared to the 9w of our Mastervolt, but respresents 38Ah per day - better than 60Ah!

Edited October 24, 2023 by nicknorman

[Onewheeler]

Whatever power immersion you buy, remember that it should be a marine type. If I remember correctly (I'm sure someone will correct me otherwise, I made a mental note at the time as I was thinking of fitting an external immersion), domestic immersions have a secondary over-temperature thermostat which will trip at something like 70 C and need manually resetting. A marine immersion has a secondary thermostat which trips at a higher temperature to cope with engine heating (will it auto-reset?)

[TandC]

Really appreciate that NIck - that clarifies things a lot.  

 

8 hours ago, Onewheeler said:

Whatever power immersion you buy, remember that it should be a marine type. If I remember correctly (I'm sure someone will correct me otherwise, I made a mental note at the time as I was thinking of fitting an external immersion), domestic immersions have a secondary over-temperature thermostat which will trip at something like 70 C and need manually resetting. A marine immersion has a secondary thermostat which trips at a higher temperature to cope with engine heating (will it auto-reset?)

Yep - it's a SureCal supplied marine immersion. 

[blackrose]

12 hours ago, nicknorman said:

It definitely doesn’t use less energy! But it may not use much more, depending on how well insulated it is. If it is perfectly insulated then it won’t use more energy to leave it on permanently. But of course a calorifier is not perfectly insulated and so keeping it on all the time (water at the max temperature and hence max heat loss) will use more energy. But maybe not by much, if the calorifier is well insulated.

 

But surely if leaving an immersion heater switched on all the time uses ANY more energy (which we know it does) then it's beneficial to fit a timer? It may not use much more energy on a single day, but over the course of a year there will be a significant difference. So not fitting a timer just doesn't make any sense - unless you like wasting money. 

[nicknorman]

25 minutes ago, blackrose said:

 

But surely if leaving an immersion heater switched on all the time uses ANY more energy (which we know it does) then it's beneficial to fit a timer? It may not use much more energy on a single day, but over the course of a year there will be a significant difference. So not fitting a timer just doesn't make any sense - unless you like wasting money. 

 

The extra energy comes from heat lost through the insulation, which is proportional to the difference in temperature of the water to that of the ambient air. So for example an immersion set to 80C on a timer whereby it is on for 1/2 the time, will likely use more electricity than an always-on immersion set to 60C.

 

It’s certainly true though that for the same temperature setting, the timer will reduce consumption simply because the water spends some time at a lower temperature and hence there is less heat loss. By how much depends on how well insulated it is.

 

A timer makes more sense if your life is on a schedule ie you are out at work 9 to 5. Have it come on in the early morning, go off at 8, back on at 4, off at 10pm or whatever. If you life is more random because you are retired or work from home, the timer is less useful. We are in the latter group and don’t have a timer, but I did take to turning the immersion off manually over night etc when electricity prices rose, but I don’t think it made a huge difference because most of the energy is dumped into the canal when you pull the basin plug / have a shower etc. The additional bit lost through the insulation is a small %.

[Tracy D'arth]

31 minutes ago, nicknorman said:

The extra energy comes from heat lost through the insulation, which is proportional to the difference in temperature of the water to that of the ambient air. So for example an immersion set to 80C on a timer whereby it is on for 1/2 the time, will likely use more electricity than an always-on immersion set to 60C.

 

It’s certainly true though that for the same temperature setting, the timer will reduce consumption simply because the water spends some time at a lower temperature and hence there is less heat loss. By how much depends on how well insulated it is.

 

A timer makes more sense if your life is on a schedule ie you are out at work 9 to 5. Have it come on in the early morning, go off at 8, back on at 4, off at 10pm or whatever. If you life is more random because you are retired or work from home, the timer is less useful. We are in the latter group and don’t have a timer, but I did take to turning the immersion off manually over night etc when electricity prices rose, but I don’t think it made a huge difference because most of the energy is dumped into the canal when you pull the basin plug / have a shower etc. The additional bit lost through the insulation is a small %.

And then you have to consider the energy used by the timer 24-7.

[GUMPY]

A timer is a must with a time of use tariff, preferably one that can be set remotely.

You really wouldn't want to be using electricity in the peak periods.

See below for the variance, it is different every day.

 

[TandC]

Here's another question on the same sort of topic...

 

Is there a "smart" timer controller that can also be used with a smartphone app?

 

That way, it would be possible to turn on the immersion heater remotely (this being for when on shoreline power and with the onboard wi-fi router on). 

 

Surely such a gizmo must exist? 

3 minutes ago, GUMPY said:

A timer is a must with a time of use tariff, preferably one that can be set remotely.

You really wouldn't want to be using electricity in the peak periods.

See below for the variance, it is different every day.

 

 

This is a good consideration too.   Up until now, I have never really shopped around for electric supply on our shoreline - I've been with Octopus for years and years now.   Our electric usage is really quite low (current boat is gas for water heating, so 240v is just the other domestic use, we work full time away from the boat etc etc).

 

But, with the new boat - and being reliant on the 240v immersion for all hot water - that will up our usage a fair bit I expect and so may be worth looking into those tariffs where you're incentivised away from the peak periods etc. 

[nicknorman]

If you have onboard wifi you could just use a smart plug, and have a 13A plug on the end of the immersion cable. 13A fine for 1kw but maybe a bit tight for 3kw. The ones I use at home are the TCP ones from Screwfix, £16.32 for one. They have been faultless so far.

https://www.screwfix.com/p/tcp-wissinwuk-13a-smart-plug-white/231hk

Edited October 24, 2023 by nicknorman

[jonathanA]

There is a 2Kw immersion heater if memory serves that might be a reasonable compromise.  its a shame they dont do a dual power version 1 + 1  or  1 +2 KW something like that.   they clearly do a dual 12v+240v version....