simonfraser
Well-Known Member
12A for an hour is possible and would give enough for a quick shower ?
warm water off 12V
- Thread starter simonfraser
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Bobc
Well-Known Member
That's 12 Amps, for an hour just for that?
Run the engine for an hour. You'll end up having the run the engine anyway to re-charge the batteries.
Run the engine for an hour. You'll end up having the run the engine anyway to re-charge the batteries.
Wing Mark
Well-Known Member
I seem to recall, the heat capacity of water is 4.2 KJ per degree per kg
So you could work out how may Wh will warm how many litres how much.
So you could work out how may Wh will warm how many litres how much.
PaulRainbow
Well-Known Member
12V x 12A = 144W and the tank is 12 gallons (US) or 45 litres.
My calorifier is 30 litres and is fitted with a 240V, 1Kw element. In 1 hour, from cold, it's warm, not hot.
I think you'd get more hot water from a solar shower in the Summer.
I'd imaging running the engine for 15-20 mins would be enough for at least a warm shower, maybe more and you get the batteries charged up as a bonus.
My calorifier is 30 litres and is fitted with a 240V, 1Kw element. In 1 hour, from cold, it's warm, not hot.
I think you'd get more hot water from a solar shower in the Summer.
I'd imaging running the engine for 15-20 mins would be enough for at least a warm shower, maybe more and you get the batteries charged up as a bonus.
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geem
Well-Known Member
Is your calorifier vertical or horizontal?
PaulRainbow
Well-Known Member
cherod
N/A
every one just seems to assume that everyone else has a colorifier 
cherod
N/A
good, depending on your battery bank .
noelex
Well-Known Member
Thanks for the link.
Providing you have a reasonable sized lead acid (or medium sized lithium bank) with a decent sized inverter, you can just heat the water up in an electric kettle. In theory this should be at least as efficient. Despite the poorer insulation, there is little time for the hot water to lose heat to the surroundings and this is likely to make up for the capacity loss experienced by lead acid batteries at higher discharge rates (and there is almost no such loss with lithium).
However, if you have a solar array, a low power heating unit can often make use of excess solar power that would otherwise be thrown away.
Also, pre-mixing shower water to the correct temperature in a container produces an excellent boat shower, much better than a traditional marine shower, as the water temperature stays perfect and there is no water loss. The biggest advantage is that it can used at anchor even after many days in the same spot without running the engine.
We have an inbuilt shower like this installed on our boat, similar to concept shown near the end of video, but with a proper shower rose and marine pump etc. The insulated box is built in. It delivers fantastic showers and the heating method can be electric, propane, diesel, solar, or even a mix of energy sources depending on which is most suitable. We have used this system for 14 years full time cruising and it is mystery why it is not used more frequently.
Providing you have a reasonable sized lead acid (or medium sized lithium bank) with a decent sized inverter, you can just heat the water up in an electric kettle. In theory this should be at least as efficient. Despite the poorer insulation, there is little time for the hot water to lose heat to the surroundings and this is likely to make up for the capacity loss experienced by lead acid batteries at higher discharge rates (and there is almost no such loss with lithium).
However, if you have a solar array, a low power heating unit can often make use of excess solar power that would otherwise be thrown away.
Also, pre-mixing shower water to the correct temperature in a container produces an excellent boat shower, much better than a traditional marine shower, as the water temperature stays perfect and there is no water loss. The biggest advantage is that it can used at anchor even after many days in the same spot without running the engine.
We have an inbuilt shower like this installed on our boat, similar to concept shown near the end of video, but with a proper shower rose and marine pump etc. The insulated box is built in. It delivers fantastic showers and the heating method can be electric, propane, diesel, solar, or even a mix of energy sources depending on which is most suitable. We have used this system for 14 years full time cruising and it is mystery why it is not used more frequently.
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Wing Mark
Well-Known Member
Looks like I'm buying a boat without one.every one just seems to assume that everyone else has a colorifier
Pricey are they not, for a small stainless can and some tubing?
I imagine 'warming ' water instead of heating it properly carries a risk of Legionella and other nasties?
ChromeDome
Well-Known Member
The most common version is a water heater with both 240v heating element and connection to coolant flow from the engine. Hence heat from engine when running and shore power in the marina. Both sources, even modest immersion heaters (to respect current limitations in shore power supply), will make the water plenty hot for germs to be elliminated.
Prices vary. An exapmle:
Quick Nautic Boiler B3 20L 1200w Water Heater Calorifier
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Minerva
Well-Known Member
12v and 12A for an hour is 144watts.
Assuming; a 10l water vessel, a starting temperature of 12'C (water from the cold tap temperature), 100% efficient heating and zero heat transfer from the body of water being heated to a) the vessel containing the water and b) the wider environment we can calculate the following;
After an hour you will end up with a water temp of around 23'C.
If you drop the volume of water down to 5l then you may expect a temperature of around 32'C.
In short, yes you *technically* could heat the water but would be a cold shower. Further more the longer you leave the system to heat the water and the warmer the water gets, the more you will lose through heat loss to the environment and you would reach a max ceiling temperature fairly quickly where heat loss is equal to heat input.
Assuming; a 10l water vessel, a starting temperature of 12'C (water from the cold tap temperature), 100% efficient heating and zero heat transfer from the body of water being heated to a) the vessel containing the water and b) the wider environment we can calculate the following;
After an hour you will end up with a water temp of around 23'C.
If you drop the volume of water down to 5l then you may expect a temperature of around 32'C.
In short, yes you *technically* could heat the water but would be a cold shower. Further more the longer you leave the system to heat the water and the warmer the water gets, the more you will lose through heat loss to the environment and you would reach a max ceiling temperature fairly quickly where heat loss is equal to heat input.
geem
Well-Known Member
Just noticed a typo in my previous post, the element is 240V, not 24V
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Vertical calorifiers work better. If you are running them at limited watts or limited heating time a vertical calorifier will stratify such that you will get hot water at the top of the calorifier where the draw off connection is. 1/2hr with our vertical 27 litre calorifier and 1200w immersion heater provides enough hot water for two showers and the washing up
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PaulRainbow
Well-Known Member
No room for a vertical one. If i'm on shore power i don't mind how long it takes, it's hot enough in a short enough time for a shower. If i'm at sea the engine will heat it quickly, but, to be honest, i'm not bothered, i can have a strip wash with a kettle full of water.
geem
Well-Known Member
I was pointing out that the heat up to time to get some useful output is far shorter with a vertical calorifier due to the benefits of stratification. That why asked what you had. Obviously the time you quote for heat up only relates to a horizontal calorifier not a vertical one
Minerva
Well-Known Member
Stratification is a thing on a domestic (stationary) water tank, there will be significantly more mixing going on with a sailing boat, or even one rocking at anchor so I'd expect a far more uniform temperature
geem
Well-Known Member
Sat at anchor the stratification is significant. We know as we make full use of it. We heat hot water from our solar panels. 300w for two hours with the starting temperature at circa 17degC. Two showers and washing up. Friends swapped their horizontal calorifier for a vertical one so they could do the same as us. Fortunately they found somebody who wanted their larger horizontal calorifier so straight swap. They now make hot water from solar when previously they couldn't.
AntarcticPilot
Well-Known Member
Basically, you've got 144 watts for an hour. As far as I can make out, and assuming no losses (big assumption!) you could raise the temperature of 5 litres of water by about 25 degrees C, or 10 litres by 12.5 degrees C.
Using the waste heat from the engine is probably more efficient. And if you're charging your batteries using solar cells, then a black bag in the sun would also be more efficient.
Using the waste heat from the engine is probably more efficient. And if you're charging your batteries using solar cells, then a black bag in the sun would also be more efficient.
geem
Well-Known Member
Yep, efficiency of solar only about 17% but if you have it spare once the batteries are on float then using it to heat domestic hot water is great.
We use a solar hot water collector in the Caribbean but here in Portugal the air temperature isn't high enough. The wind cools the bag. It's also a bit chilly in the evening to use a solar shower. Putting the heat directly in to the insulated calorifier during the day means you can shower later in the evening
William_H
Well-Known Member
I would imagine a far more efficient way to take the chill off shower water with 12v heating might be to have an element in the shower head. So only water actually used is heated. A small container ie 1 litre with heating element and thermostat to turn off the current when set water temp is reached ie when water is turned off. This way you conserve not just electricity but water also. Or perhaps a foot operated valve for water flow with switch connected. I imagine you would need a lot more current than 12amps but then for a lot shorter time. Interesting to figure the water flow min. needed and watts needed to raise temp perhaps 10 degrees.