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Old 30-06-2016, 12:22   #1
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Boat Design Question -- Calorifier Capacity

A large capacity calorifier has been on my mind for a long time, for a future boat.

For endless domestic hot water, but not only -- also as a way to store engine and generator waste heat, also to store energy from shore power. To even out the demand for energy for heating water. In cold climates like where I sail, you can spend a lot of energy just heating water, which you could save if you could only store heat when it's free.

But it occurred to me today that you can't really count the capacity of the calorifier as part of the boat's fresh water capacity. Or can you? If you run out of fresh water, the full calorifier is of no direct use. Yes, you can draw it off and let it cool down in a pinch, but normal function of your water supply is stopped.

So the weight of the water inside your jumbo calorifier is largely wasted and undesirable.

Am I looking at this the wrong way? 100 liters is 100kg of water, or 220 pounds, and 100kg more than you really need is going to slow the boat down slightly. It does not replace 100 liters of main tank capacity. Maybe only if it is low enough to contribute to stability, could it be ok to have it much oversized.

Thoughts?
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Old 30-06-2016, 12:38   #2
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Re: Boat Design Question -- Calorifier Capacity

How would you keep the calorifier charged in the event of running out of water ?
Pump pressure drive heated water movement.

Hmmm, interesting question you pose !
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Old 30-06-2016, 12:41   #3
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Re: Boat Design Question -- Calorifier Capacity

Run your generator if you need hot water, install a good diesel heating system and leave the engine room door open to expell the waste heat from the genset and engine into the main cabin.

Total cost: Zero
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Old 30-06-2016, 12:50   #4
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Re: Boat Design Question -- Calorifier Capacity

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Originally Posted by Kenomac View Post
Run your generator if you need hot water, install a good diesel heating system and leave the engine room door open to expell the waste heat from the genset and engine into the main cabin.

Total cost: Zero
This is for a new boat, designed from scratch, not my present one.

What I have now is 50 liters of hot water, produced in three ways:

1. Main engine waste heat

2. 1500 watt immersion heater run by generator or shore power

3. Central heating system.

Option 1 is compromised by poor circulation, but I have bought a circulation pump which I will install soon.

That will help a lot, because now when I arrive somewhere, I have a tank full of cold water, and I have to either start the central heating or run the generator to make hot water. 1500 watts is 25% of the generator's capacity and uses a fair amount of diesel fuel, especially if there are not other significant loads to run at the same time. Likewise I hate to start the central heating system if I don't need the heat, just because I need hot water.

My next boat will have a third circulation loop for generator waste heat.

In a cold climate, heating domestic water requires a very large amount of energy, so the more you can get that energy from waste heat, the better.

When I was cruising in Florida, this question was almost irrelevant. Just go for a swim and rinse off on the transom, or shower in "cold" water. We never cared much about heating water. But up here, where the tank water may be 4 or 5 degrees C -- it's life and death.
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Old 30-06-2016, 13:21   #5
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Re: Boat Design Question -- Calorifier Capacity

You're going to burn diesel no matter what you do. You don't get something for nothing. Just run your genset, that's what it's there for. Change your batteries out for lithium and use the house batteries as the source for your stored energy. Insulate your water heater tank.
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Old 30-06-2016, 13:40   #6
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Re: Boat Design Question -- Calorifier Capacity

Storing large amounts of hot water is inefficient in terms of thermal efficiency. We also don't need endless hot water. Living aboard means we consume less not more.

We have a 6 gallon water heater which is fine for us as a liveaboard couple. And we aint camping. We currently heat from mains AC, engine and generator.

We're more interested in fitting enough solar to heat hot water. We're also interested in fitting an on demand propane water heater as we head to higher latitudes.

A large hot water system will consume too much propane and require too much solar to be viable. A large storage loop would also not let our engine or generator get up to temp quickly.

Are you planning to run a generator constantly?

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Old 30-06-2016, 14:03   #7
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Re: Boat Design Question -- Calorifier Capacity

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Originally Posted by leftbrainstuff View Post
Storing large amounts of hot water is inefficient in terms of thermal efficiency. We also don't need endless hot water. Living aboard means we consume less not more.

We have a 6 gallon water heater which is fine for us as a liveaboard couple. And we aint camping. We currently heat from mains AC, engine and generator.

We're more interested in fitting enough solar to heat hot water. We're also interested in fitting an on demand propane water heater as we head to higher latitudes.

A large hot water system will consume too much propane and require too much solar to be viable. A large storage loop would also not let our engine or generator get up to temp quickly.

Are you planning to run a generator constantly?
All excellent points.
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Old 30-06-2016, 14:21   #8
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Re: Boat Design Question -- Calorifier Capacity

Quote:
Originally Posted by leftbrainstuff View Post
Storing large amounts of hot water is inefficient in terms of thermal efficiency. We also don't need endless hot water. Living aboard means we consume less not more.

We have a 6 gallon water heater which is fine for us as a liveaboard couple. And we aint camping. We currently heat from mains AC, engine and generator.

We're more interested in fitting enough solar to heat hot water. We're also interested in fitting an on demand propane water heater as we head to higher latitudes.

A large hot water system will consume too much propane and require too much solar to be viable. A large storage loop would also not let our engine or generator get up to temp quickly.

Are you planning to run a generator constantly?

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The main reason for having large hot water storage capacity is to store waste heat. If you can store a day's worth of hot water, then you never need to burn anything to make hot water, because you run the generator at least once a day anyway to generate electricity, and heat the whole tank with the waste heat from the generator's fresh water cooling circuit, for free. That's the point.

For your case, I strongly recommend not using a propane heater. This device is hard to mount outside of the main hull volume, and inside the main hull volume it violates ABYC and in any case is dangerous. Plus it's more expensive than diesel fuel per kW/H of heat produced, and when you get to cold latitudes where the tank water will be much colder, the amount of energy you have to expend to make domestic hot water goes up tremendously. I can't even imagine what it would cost me, to heat all the hot water we use on board, with propane. 6 gallons may be plenty in mild climates, where you mix the hot water with tank water at 15 or 20 degrees, but if the tank water is 5 degrees, then you will need three times as much of it to make a comfortable shower. 6 gallons of hot water will not get two people clean, up North, much less two people plus a load of dishes to wash.

If you're going to higher latitudes, then good space heating is also absolutely essential. Diesel fired hydronic heating will make your domestic hot water as well as do your space heating. Worth thinking about.
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Old 30-06-2016, 22:29   #9
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Re: Boat Design Question -- Calorifier Capacity

DH I think you are thinking about it from the wrong angle.

For starters, it's not 100kg of dead weight. Do you think about your current boats 50L of hot water as 50kg of dead weight? probably not, until now perhaps. You are only adding 50kg more than you have on your current boat and for where you cruise, the hot water is probably worth it's weight in gold.

What water capacity are you dreaming about and will you have a watermaker? If you are so worried about the weight of the extra warm water, reduce the water tanks by the same amount. If you are not planning a water maker, get one and reduce your capacity even more.

Why not connect the generators cooling system to the Calorifier, then you will heat up the water whenever you charge anything by the generator. If you have a large water heater and generate power daily, unless you use excessive amounts of hot water, then you will just be topping up the heat.

I just installed a new C-warm Calorifier and I noticed in the install manual that some models include 2 sets of inlet/outlet coils, so its something readily available.

You could also design your boat to have baltic and extended cruising water tanks. In the baltic you run the boat half empty and use the watermaker to refill those tanks generating hot water whilst you are at it. Then when you are planning to be a long way from anywhere and you want the extra water as backup, you fill the other tanks.
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Old 01-07-2016, 01:09   #10
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Re: Boat Design Question -- Calorifier Capacity

For arctic cruising I'd install a loop of engine cooling into diesel tanks. Having warm +30deg diesel in the tanks is much more saved waste energy than a warm water tank.

BR Teddy
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Old 01-07-2016, 01:42   #11
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Re: Boat Design Question -- Calorifier Capacity

Quote:
Originally Posted by hoppy View Post
DH I think you are thinking about it from the wrong angle.

For starters, it's not 100kg of dead weight. Do you think about your current boats 50L of hot water as 50kg of dead weight? probably not, until now perhaps. You are only adding 50kg more than you have on your current boat and for where you cruise, the hot water is probably worth it's weight in gold.

What water capacity are you dreaming about and will you have a watermaker? If you are so worried about the weight of the extra warm water, reduce the water tanks by the same amount. If you are not planning a water maker, get one and reduce your capacity even more.

Why not connect the generators cooling system to the Calorifier, then you will heat up the water whenever you charge anything by the generator. If you have a large water heater and generate power daily, unless you use excessive amounts of hot water, then you will just be topping up the heat.

I just installed a new C-warm Calorifier and I noticed in the install manual that some models include 2 sets of inlet/outlet coils, so its something readily available.

You could also design your boat to have baltic and extended cruising water tanks. In the baltic you run the boat half empty and use the watermaker to refill those tanks generating hot water whilst you are at it. Then when you are planning to be a long way from anywhere and you want the extra water as backup, you fill the other tanks.
It's practically the first line in the design brief, and mentioned above, that I will be heating domestic hot water with generator waste heat, besides engine waste heat.


Reducing the main tanks by the extra capacity of the calorifier was always what I had in mind, and why before yesterday I never worried about the weight of the extra water. The subject of this thread actually is whether or not you can count it that way, or not. The more I think about it, the more convinced I am that you can't count calorifier capacity as part of your total fresh water capacity. In a survival situation (broken down watermaker) of course you could get and use that water, but for practical purposes I think it doesn't count. That's because every time you draw a liter out of the calorifier, a liter is drawn out of the main tank to replace it. When there's nothing more in the main tank, you're out of water for practical purposes, even if your calorifier is full. Back to the drawing board.

I had thought that a couple-three hundred liters would be nice, but I think it's going to need to be more like one hundred, unless the designers can find a really low spot where the extra water will contribute to stability.


As to total water capacity -- I now have 1000 liters, and no watermaker. I would probably not want to have a lot less than this, even with a watermaker. My father was a real water nazi on his boat, and I swore I would always have plenty of fresh water on my own boat, and never oppress the poor crew, who just want to be clean, the way he did
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Old 01-07-2016, 01:53   #12
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Re: Boat Design Question -- Calorifier Capacity

Quote:
Originally Posted by TeddyDiver View Post
For arctic cruising I'd install a loop of engine cooling into diesel tanks. Having warm +30deg diesel in the tanks is much more saved waste energy than a warm water tank.

BR Teddy
One doesn't exclude the other.

In cold places (even where I am now, we need space heating 12 months a year), it hurts you to dump all that heat right into the sea.
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Old 01-07-2016, 02:21   #13
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Re: Boat Design Question -- Calorifier Capacity

Dockhead, are you perhaps overthinking the impact of 100 litres? With a 60+ footer there should be no problem finding a spot for this lowish and central. The size of the unit is merely about 47 cm cubed.

Also, I don't see why the volume it can't be treated as part of your water capacity. Your last 100 litres would only ever be considered emergency water anyway, wouldn't it? This just makes the emergency water a little less accessible. If you can't top it up, then I think you have more things to worry about than cooling the hot water down to drink it.

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Old 01-07-2016, 03:39   #14
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Re: Boat Design Question -- Calorifier Capacity

Install two Spectra watermakers, then you won't need to worry about the watermaker not working.
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Old 01-07-2016, 09:05   #15
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Re: Boat Design Question -- Calorifier Capacity

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Install two Spectra watermakers, then you won't need to worry about the watermaker not working.
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