Most efficient way to boil water on a boat

[ur2slo]

And there off!!!!

[MarkSF]

Did you mean "they're off"?

[thinwater]

If the OP has 500W solar, whether the batteries are even affected is questionable. 1-cup immersion heaters typically draw 200W; the only effect would be to slow charging! The pots are typically more power-hungry (1500W), but I don't know what he has or how they vary.

[a64pilot]

OK, you guys are saying that electric resistance heating is nearly 100% efficient and is the most efficient way to heat water right?
Then how can a vapor cycle compressor system be up to 70% more efficient than a resistance heater?

GeoSpring Hybrid-Electric Heat-Pump Hot Water Heater | GE Appliances

[sailorchic34]

Originally Posted by SSgtPitt

And there's no such thing as a "hot water heater". if the water is hot, you don't need to heat it.

Oh dear me.

One sometimes wants to heat hot water hotter. So you CAN have a hot water heater, be it a desuperheater, deaerator, a booster heater in a commercial dishwash application (taking 140 degree F hot water and heating it to 180 degree F) I could go on and on about a fair amount of other process loads.

One (ok, me because I'm evil) could even argue that in order to keep hot water hot you need a heater to do it. Viola... A hot water heater. One could arque even more that water in a noncrystalline state requires heat to liquefy it. So all the water we float boats with is technically hot water being over 32 degrees F (0C) as is drinking water. Cold water, we call ICE.

Boy, we can tell that winter is arriving in the northern hemisphere.

[ur2slo]

Originally Posted by sailorchic34

Oh dear me.

Boy, we can tell that winter is arriving in the northern hemisphere.

"Rainy days and rainy nights"

Seriously tho, if I'm at the upper latitudes and I have (X) amount of sail cloth to utilize, how much rainwater could I expect to collect, get tepid so I can wash my thong , with $1.22 in ducats?

It gets cold up did way............

[ur2slo]

Originally Posted by MarkSF

Did you mean "they're off"?

ur quik.......

[sailorchic34]

Originally Posted by a64pilot

OK, you guys are saying that electric resistance heating is nearly 100% efficient and is the most efficient way to heat water right?
Then how can a vapor cycle compressor system be up to 70% more efficient than a resistance heater?

GeoSpring Hybrid-Electric Heat-Pump Hot Water Heater | GE Appliances

They are sort of kind of technically correct in that an immersion resistive electic heating element is in and of it's self near 100% efficient. That is a Kw input gives you almost a Kw output into the fluid That overlooks the 85% steam boiler used to make steam to drive a steam turbine (37% eff) and then transmitting the electric power over HT wires with a 40% loss.

So in one way heating with electric is 100 percent efficient, but from a prime heating source it's 18.8 percent ish efficient. That is of the fuel burned at the power plant only 18.8% of the energy makes it to the end user. Which makes propane and OK solar pretty efficient.

Myself they all work at roughly the same cost per heating. Lets go sailing, inless your on the east coast of the USA.

[Dockhead]

Originally Posted by lordgeoff

It's easy to carry a seasons supply of gas. Cheap and always ready.. . .

Lucky guy. I blow through a 4.5kg bottle of gas in less than a month if I have people on board and people are baking as well as cooking.

It's a problem every year since I spend 4 months out of every year cruising in countries which use different gas bottles to the ones available here.

[Dockhead]

Originally Posted by a64pilot

OK, you guys are saying that electric resistance heating is nearly 100% efficient and is the most efficient way to heat water right?
Then how can a vapor cycle compressor system be up to 70% more efficient than a resistance heater?

GeoSpring Hybrid-Electric Heat-Pump Hot Water Heater | GE Appliances

Because vapor cycle compressor systems (heat pumps) are MOVING heat, not making it. It looks like magic, getting 20kW of heat but only using 3kW of electrical power, but it's possible with a heat pump.

Electrical resistance merely converts electrical power to heat energy. Put in 3kW of electrical power and you get 3kW of heat out of it.

As I wrote above, it is ONLY 100% efficient when you're starting with electrical power. It is far less efficient if you start with diesel, and burn that to make mechanical power, and then turn a generator with that to make electrical power, before running the kettle.

Since non-turbo diesel engines are maybe 30% efficient, and good AC generators are maybe, what, 75% efficient? It means that maybe 20% or so if the heat in the diesel fuel makes it into your tea cup.

But since over here propane is 5x more expensive than diesel fuel per BTU or kW/h, that will give you just about the same cost EVEN if you had a 100% efficient stove-top kettle, which doesn't exist.

But this is a purely theoretical discussion; no one is going to choose one or the other based on the tiny cost for heating up a half liter of water.


For the record, no one said electrical heating is the "most efficient". It depends on how you define "efficient". If you are starting with a fossil fuel, then electrical heat will generally not be the most efficient in terms of what % of the heat you start out with in the fuel, gets into your tea cup. If you had a really good stovetop kettle, you would surely do better taking the heat from burning fossil fuel directly. Even if you are starting with electrical power, then electrical resistance heat (as you pointed out) might not be the most efficient use of it to heat water. Depending on the temperature of the medium for warming the evaporator, a heat pump may be many times more efficient.

[Tayana42]

Okay, it's much more efficient for me to stop reading this thread and go make myself a cup of coffee...if I can still figure out how to boil water.


S/V B'Shert

[a64pilot]

Originally Posted by Dockhead

Because vapor cycle compressor systems (heat pumps) are MOVING heat, not making it. It looks like magic, getting 20kW of heat but only using 3kW of electrical power, but it's possible with a heat pump.

That is exactly it, and to be truthful I knew that, but still electric resistance heating is not the most efficient way to heat with electricity, or houses wouldn't have heat pumps .
If like you do have enough battery bank to use your electricity this way, do so and have a way to full recharge nearly every cycle.
You and I have generators, when our banks hit X SOC, we crank our gennies and re-charge. Most I bet don't, and it's my understanding that most banks are slowly being murdered by chronic undercharging, if that is true, then I think for most people the best thing is to not pull an amp out of their bank if they can avoid it.

Myself, I use electricity to freeze water, except for morning coffee, I can't think of heating it for a drink, but my goal is to try to stay in warm climes.

[a64pilot]

Originally Posted by Dockhead

For the record, no one said electrical heating is the "most efficient".

Title of the thread is?

[sailorchic34]

Originally Posted by Dockhead

But since over here propane is 5x more expensive than diesel fuel per BTU or kW/h, that will give you just about the same cost EVEN if you had a 100% efficient stove-top kettle, which doesn't exist.

Diesel does offer more BTU's per gallon or liter then propane. Roughly 31% more. In the US, propane, in California anyway, is $3.50 a gallon and diesel is somewhere between $2.70 to $3.60 a gallon depending on where you buy it. So, propane is not that bad here.

[a64pilot]

My propane cost is nothing, I bet I spend more on fish bait.

But I concede that is not always the case, and I bet it's more than anything a case of looking at hundreds of gallons of propane, but not having a way to put it in your bottle that is the worst issue.