water heating

[gracyf]

Hi all

can anybody help me on the matter of water heating

I have 3 ways to heat water

1. By running the engine which is highly affective when under way or moving but seems over kill when moored and noisy and anti social on a summers da.

2.webasto dieselthermo top which seems to warm the water but not fantastically when the heating is on but I am somewhat cautious to run with all the rads turned off with the exception of the towel rad(presume this to be the bypass rad) which gets very hot when this is run alone ia this ok or should I shut this off as wells or not do at all.

3. And finally when the sun is out the 165w solar panel and mppt reg can recharge the batterys and3 x 100amp batterys by say noon meaning it is doing noting the rest of the day if I was to run the 1kw240v immersion through the victron inverter at say 90% ?efficient to heat the water would this be feasable or would it empty the batteries which from what I have read should only be cycled down to 50%.

Your thoughts. Would be interesting

Regards and thanks in advance

[Titus]

I've had a similar problem and after much trial and error I found that the best way when not travelling is to run the engine, inverter on and immersion heater on for 15/20 minutes, enough hot water for at least a couple of showers,

(I wouldn't try the immersion heater on without running the engine at the same time)

 

Dave

[Alan de Enfield]

gracyf, on 15 Jun 2014 - 1:47 PM, said:gracyf, on 15 Jun 2014 - 1:47 PM, said:

3. And finally when the sun is out the 165w solar panel and mppt reg can recharge the batterys and3 x 100amp batterys by say noon meaning it is doing noting the rest of the day if I was to run the 1kw240v immersion through the victron inverter at say 90% ?efficient to heat the water would this be feasable or would it empty the batteries which from what I have read should only be cycled down to 50%.

 

 

One hours use of the Immersion heater would take 100 amps out of the batteries, 2 hours = 200Ah

How long does your immersion need to be on to get hot/hot water from 'cold' ?

 

Unless your batteries are brand new then you are probably not getting 100 amps out of them - possibly down to 80 amps ??? (3 x 80 = 240)

 

The 100 amps used (in an hour) by the immersion heater is going to use a huge percentage of that available.

 

Running the engine to replace (part) of the 'amps used' whilst the immersion is running seems a waste of time - if you run the engine you'll get hot water anyway,

 

Personally (other opinions are available) I wouldn't use the immersion - after heating the water you may not have enough solar to replace it before the sun sets.

Edited June 15, 2014 by Alan de Enfield

[Tony Brooks]

However a large alternator running close to flat out to supply the immersion heater would load the engine so that would allow the engine to dump more heat into the calorifier in addition to the immersion heater. I can see little wrong with this idea as long as the alternator can cover the immersion heater load plus a little.

[jelunga]

However a large alternator running close to flat out to supply the immersion heater would load the engine so that would allow the engine to dump more heat into the calorifier in addition to the immersion heater. I can see little wrong with this idea as long as the alternator can cover the immersion heater load plus a little.

I agree. My MC42 takes agesto warm up on no load so would take hrs to get any hot domestic. But using my 1kW immersion through the inverter with engine running not knly geats the water in about 45 mjns but akso gets a good load ti warm engine up quicker which then contributes to domestic water heating.

I have a twin alternatir set up, but even so the SOC on smartgahge drops from 100 to about 85%. But whether that is just a smartgauge feature or a real drop I am not sure.

[bottle]

1Kw supplied via an inverter supplied by batteries (12v), means a 100amp load on the batteries.

 

Conservative estimate that it will take 30 minutes to heat calorifier, that is 50 amp.hrs.

 

Battery bank of 200 amp.hrs, starting at 100% SOC (perfect batteries), assuming 50% rule, that is half you usable amp.hrs or a drop from 100% to 75% SOC.

[Tony Brooks]

1Kw supplied via an inverter supplied by batteries (12v), means a 100amp load on the batteries.

 

Conservative estimate that it will take 30 minutes to heat calorifier, that is 50 amp.hrs.

 

Battery bank of 200 amp.hrs, starting at 100% SOC (perfect batteries), assuming 50% rule, that is half you usable amp.hrs or a drop from 100% to 75% SOC.

 

But the suggestion was that the OP uses his ALTERNATOR output to feed the immersion, not the batteries although I accept it would need to en a big alternator, say 130 to 150 amp job for it to work. No good trying it with a 50 amp output.

[Henhouse]

None of these methods are particularly efficient ways of producing hot water.

 

If you are needing just a small quantity for washing up etc, I would be boiling a kettle on the gas cooker.

 

If you want to use the calorifier / immersion heater, then consider a portable generator which will output 240V.

 

Personally I think that to be preferable to running an expensive boat engine, or taking a large load from your battery bank.

[bottle]

Tony

 

Yes, agreed I was just trying to give an idea as to how much (amps) a 1Kw load needs from a 12v supply.

 

His question three for instance running the immersion heater from 165 watts of solar power, implies that he thinks this would be enough.

 

I think Henhouse (post #8) is correct and is what I would advise but of course running the engine to heat the water would also charge the batteries (a little) if the immersion heater was not ON

[adam1uk]

Turn the radiators off (except the towel rail, which probably can't be turned off anyway) and run the Webasto. That's what they're for.

 

When we had a share boat with a Webasto, the central heating circuit had a valve to shut off all the rads in one go, so only the water was heated. Our current boat has an Eberspacher, and in the summer it heats the water without the rads.

[peterboat]

My last boat had an Alde gas heater in summer turned a lever and it just heated water worked well. My new boat has 1500ah of batteries and 1k of solar if the sun shines lol I put the immersion on for an hour for hot water it does the job otherwise I turn on the engine with the immersion on as others has said it loads the engine so heats water quicker

 

peter

[Grace and Favour]

1Kw supplied via an inverter supplied by batteries (12v), means a 100amp load on the batteries.

 

Conservative estimate that it will take 30 minutes to heat calorifier, that is 50 amp.hrs.

 

Battery bank of 200 amp.hrs, starting at 100% SOC (perfect batteries), assuming 50% rule, that is half you usable amp.hrs or a drop from 100% to 75% SOC.

Another way of looking at it

If the OP has a 55Ltr cauliflower, at an ambient temperature of 17C, and wishes to raise it to 60C, then it will take the sole use of a 1Kw immersion 2.75 hours.

[matty40s]

Another way of looking at it

If the OP has a 55Ltr cauliflower, at an ambient temperature of 17C, and wishes to raise it to 60C, then it will take the sole use of a 1Kw immersion 2.75 hours.

How many kw to heat a 70l cabbage??

[Grace and Favour]

How many kw to heat a 70l cabbage??

it would take a 1Kw heater 3.5Hrs to heat a 70L cabbage (assuming, of course, that the cabbage was well insulated!)

[Staarek]

Hi all

can anybody help me on the matter of water heating

I have 3 ways to heat water

1. By running the engine which is highly affective when under way or moving but seems over kill when moored and noisy and anti social on a summers da.

2.webasto dieselthermo top which seems to warm the water but not fantastically when the heating is on but I am somewhat cautious to run with all the rads turned off with the exception of the towel rad(presume this to be the bypass rad) which gets very hot when this is run alone ia this ok or should I shut this off as wells or not do at all.

3. And finally when the sun is out the 165w solar panel and mppt reg can recharge the batterys and3 x 100amp batterys by say noon meaning it is doing noting the rest of the day if I was to run the 1kw240v immersion through the victron inverter at say 90% ?efficient to heat the water would this be feasable or would it empty the batteries which from what I have read should only be cycled down to 50%.

Your thoughts. Would be interesting

Regards and thanks in advance

 

I'm about to replace my 1kw immersion heater for smaller, 500w unit. I've got 1200w of solar & 1200ah battery bank. My daily usage is about 100-150ah and in recent weather my setup is capable of producing around 250ah/day. Till now I was leaving dehumidifier on, as the battery bank was at 100% SOC by noon. It will take longer with 500w element but the panels should cope easier with covering 50amps power demand than 100amps. I will keep you updated how (if) it works.

 

Another way of looking at it

If the OP has a 55Ltr cauliflower, at an ambient temperature of 17C, and wishes to raise it to 60C, then it will take the sole use of a 1Kw immersion 2.75 hours.

 

How do you calculate this? Is there a formula? Thanks

[Bodkin]

Turn the radiators off (except the towel rail, which probably can't be turned off anyway) and run the Webasto. That's what they're for.

 

When we had a share boat with a Webasto, the central heating circuit had a valve to shut off all the rads in one go, so only the water was heated. Our current boat has an Eberspacher, and in the summer it heats the water without the rads.

 

Just like the OP, we are trying to come up with a solution to get hot water without running the engine. We are increasing our solar bank (from 200 watts to 695) and have an immersion which we wondered whether we could run using the solar only.

 

We also have Webasto central heating but did not know that it is possible to use it for hot water only. Are all set up's likely to be like this or in some cases would we need to switch off all the radiators to achieve the desired effect?

 

If there is a valve on our Webasto, where would it be located - in/on the engine, near the radiator tank or near the motor that runs the CH? And what does it look like - if anyone has any pictures that would be brilliant.

 

Thanks in advance.

[RLWP]

 

Does anyone heat water directly using solar? its a pretty simple system yet it seems uncommon on boats

 

Richard

[Jambo]

I ordered a 500W immersion heater from Sure Cal to heat our hot water during summer.

 

I was generally finding that running a 1kW immersion heater was hitting the batteries a little harder than I would have liked, even with 1kW of PV on the roof. It's ok when it's very sunny and we're getting 750W+ out of the panels but if there's any cloud it was depleting the batteries and then if it's cloudy in the afternoon you don't have a full battery going into the night.

 

A 500W immersion heater means that even on a partially sunny day we can heat the water and still keep the batteries nicely topped up. It's worth noting that a good long heat of the water in the calorifier to get it up to 60 degrees periodically is a good idea to inhibit Legionella.

 

When we're back into winter we'll swap back to a 1kW immersion heater.

 

I'm keen to investigate the potential for solar water heating using evacuated tubes or a flat plate collector as it's far more efficient.

[Staarek]

I ordered a 500W immersion heater from Sure Cal to heat our hot water during summer.

 

I was generally finding that running a 1kW immersion heater was hitting the batteries a little harder than I would have liked, even with 1kW of PV on the roof. It's ok when it's very sunny and we're getting 750W+ out of the panels but if there's any cloud it was depleting the batteries and then if it's cloudy in the afternoon you don't have a full battery going into the night.

 

A 500W immersion heater means that even on a partially sunny day we can heat the water and still keep the batteries nicely topped up. It's worth noting that a good long heat of the water in the calorifier to get it up to 60 degrees periodically is a good idea to inhibit Legionella.

 

When we're back into winter we'll swap back to a 1kW immersion heater.

 

I'm keen to investigate the potential for solar water heating using evacuated tubes or a flat plate collector as it's far more efficient.

 

This is exactly what I'm going to do. How long does it take to heat up the water to lets say 50'C? (more or less) with 500W immersion?

[Alan de Enfield]

 

This is exactly what I'm going to do. How long does it take to heat up the water to lets say 50'C? (more or less) with 500W immersion?

 

17^oC - 60^oC in a 55litre calorifier will be 5.5 hours (and use 275Ah)

[Staarek]

 

17^oC - 60^oC in a 55litre calorifier will be 5.5 hours (and use 275Ah)

 

Wow, that's is quite a bit, both time wise and ah.

[adam1uk]

We also have Webasto central heating but did not know that it is possible to use it for hot water only. Are all set up's likely to be like this or in some cases would we need to switch off all the radiators to achieve the desired effect?

 

If there is a valve on our Webasto, where would it be located - in/on the engine, near the radiator tank or near the motor that runs the CH? And what does it look like - if anyone has any pictures that would be brilliant.

 

Thanks in advance.

The valve was just in the pipe running to the radiators. Turning off your radiators would be just as good -- that's all we do with our Eberspacher.

[Alan de Enfield]

 

Wow, that's is quite a bit, both time wise and ah.

Heating water uses a fixed amount of Joules.

It doesnt matter if you use 100 watts or 1kw, or 3kw heating a set amount of water over a set increase in temperature will use exactly the same 'energy', the difference is the time taken.

 

So for a 55 litre calorifier, it doesnt matter if you use a 3kw, a 1kw or a 500w immersion heater they will all take the same 'amount' out of the batteries.

 

Many years ago I had a small 'immersion' heater that you plugged into the car cigarette lighter socked and then put the element into a cup of water (so you could make a cup of tea on the 'go')

I could go from Nottingham to Birmingham and it still wouldn't be much more than luke-warm

[Staarek]

Heating water uses a fixed amount of Joules.

It doesnt matter if you use 100 watts or 1kw, or 3kw heating a set amount of water over a set increase in temperature will use exactly the same 'energy', the difference is the time taken.

 

So for a 55 litre calorifier, it doesnt matter if you use a 3kw, a 1kw or a 500w immersion heater they will all take the same 'amount' out of the batteries.

 

Many years ago I had a small 'immersion' heater that you plugged into the car cigarette lighter socked and then put the element into a cup of water (so you could make a cup of tea on the 'go')

I could go from Nottingham to Birmingham and it still wouldn't be much more than luke-warm

 

Interesting stuff, thanks Alan.

[RLWP]

Heating water uses a fixed amount of Joules.

It doesnt matter if you use 100 watts or 1kw, or 3kw heating a set amount of water over a set increase in temperature will use exactly the same 'energy', the difference is the time taken.

 

So for a 55 litre calorifier, it doesnt matter if you use a 3kw, a 1kw or a 500w immersion heater they will all take the same 'amount' out of the batteries.

 

 

Succinct and accurate, although this does assume no heat loss from the calorifier. If you add that in, the smaller heater takes longer, meaning more time for heat to be lost and therefore uses more energy. The extreme example would be a 1W heater which wouldn't keep up with the heat loss and so would drain the batteries to no effect

 

Richard