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Old 09-03-2014, 04:14 PM   #41
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Dickinson stoves and Trident submarines use convective water heating as well.
True. If it makes one feel better, Grunfos makes a nice little circ pump in whatever voltage you want.

I wonder how big the pump is that moves the Gulf Stream?
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Old 09-03-2014, 04:27 PM   #42
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I do not know, but the sun pumps out a lot of power. If your engine room is at 190 degrees your convection idea would be good. My engine room is about 120 after running all day and I suspect that even with no heat source other than heat soak from the environment my water heater would be at about 120. Its well insulated and would probably maintain that for several hours. That would be "convection". If you ran your exhaust thru your water heater that would be convection. But you will not get enough energy transfer thru static fluid to effect any useable gain. Passive energy flow on a small basis being what it is.
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Old 09-03-2014, 04:28 PM   #43
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Why use the secondary loop at all? Why not just use a water heater without a heating loop and just pass the hot water through the sekamp heat exchanger? Then you could bypass the secondary glycol loop, expansion tank, etc. You also wouldn't have to worry about pressurizing and purging the secondary loop with glycol at all.
Trying to visualize what you're asking. Is it why not run the cold water directly through the engine heat exchanger before it goes to the tank? If so, it is because the exchange rate won't be sufficient to extract much heat if the water is moving, and if it is not, then the volume actually heated would be minimal. I'm probably misunderstanding what you're saying....

The reason convection works is because while the initial movement of heated water from the engine exchanger to the loop in the hot water tank is pretty slow, as the water in the loop goes up in temperature, the rate of heat transfer from that water to the fresh water in the tank also increases, which makes the convection run quicker. It isn't as fast as it would be with a pump, but the point is to extract the heat, not have it move quickly through the water tank. I assume a pump would increase the efficiency of the system but I don't think enough to make much material difference in what comes out the faucet. But like I said, if you want a pump, install a pump. Won't hurt anything even if not needed.

In the greenhouse biz, we started using regular solenoid water valves for hydronic systems, but these passed enough heat through convection that the floors of the greenhouse (where the heating tubes were) would always be hot. We had to go to electric ball valves to interrupt this flow. I doubt the water was moving very quickly, but it was moving fast enough to make the floors hot.
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Old 09-03-2014, 04:31 PM   #44
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The key phrase here being "the water was moving".
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Old 09-03-2014, 04:46 PM   #45
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It seems to me that adding an additional heat exchanger to make hot water is just extra equipment to buy, install and maintain. And another point of possible failure. Running the engine coolant through the water heater is simple and effective. It's also safe. It's possible for it to fail but this is very uncommon.
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Old 09-03-2014, 04:54 PM   #46
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We have kept the engine/hot water heater loop closed since day one. Somehow the water stays quite hot. I guess it's "Magic."
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Old 09-03-2014, 04:56 PM   #47
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It works. Its worked since the first engine was installed in a boat. Its reliable, does anyone have any first hand knowledge of a water heater poisoning anyone or destroying an engine ? If you can drink the current engine coolant your taste buds are not your "buds". It will make you very ill but not kill you. Even if your heater takes a $hit it will most likely push the coolant out of your engine and replace it with fresh water. Not catastrophic. Surely on an engine room check you will catch this. I just dont see any reason to try to improve on this system. Except for meteors.
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Old 09-03-2014, 05:52 PM   #48
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It works. Its worked since the first engine was installed in a boat. Its reliable, does anyone have any first hand knowledge of a water heater poisoning anyone or destroying an engine ? If you can drink the current engine coolant your taste buds are not your "buds". It will make you very ill but not kill you. Even if your heater takes a $hit it will most likely push the coolant out of your engine and replace it with fresh water. Not catastrophic. Surely on an engine room check you will catch this. I just dont see any reason to try to improve on this system. Except for meteors.
It's hardly an attempt to improve on a system, but a recognition that there is not necessarily a single system for all applications. On my vessel, rather than running engine coolant 24 feet in a loop to the location of the water heater, I chose to keep engine critical functions in the ER where I can see them by using a non pressurized loop through an exchanger. I have no idea why you've taken this all so personally, but perhaps you have never worked on a boat where the water heater wasn't close to the engine?

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No need for a seperate expansion tank on the engine side. An expansion tank is a good idea on the house water side.
Just for the sake of accuracy, you are incorrect and you do need an expansion tank if the added volume of the coolant in the added loop is more than 3 or 4 quarts, or if the water heater is above the pressure relief cap on the engine. Spy's reference to Volvo recommendations on this is one example that at least some manufacturers would also disagree with you.
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Old 09-03-2014, 06:03 PM   #49
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Some people inherently do things the hard way. Your water heater would work just as well, perhaps better with just the 24 feet of hose between the engine and the water heater. If the distance concerns you, buy higher quality hose. You might want to bundle and insulate it to minimize heat loss.
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Old 09-03-2014, 06:38 PM   #50
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Trying to visualize what you're asking. Is it why not run the cold water directly through the engine heat exchanger before it goes to the tank? If so, it is because the exchange rate won't be sufficient to extract much heat if the water is moving, and if it is not, then the volume actually heated would be minimal. I'm probably misunderstanding what you're saying.....
No. I mean eliminate the HX in the water heater altogether and have the water in the water heater circulate (supply and return) from the water heater to your seakamp HX (and back to the water heater). IE; a water heater without a heat exchanger.

As far as convection and the confusion within the thread, perhaps you mean to use the term thermosiphon instead of convection?
Thermosiphon - Wikipedia, the free encyclopedia
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Old 09-03-2014, 08:17 PM   #51
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No. I mean eliminate the HX in the water heater altogether and have the water in the water heater circulate (supply and return) from the water heater to your seakamp HX (and back to the water heater). IE; a water heater without a heat exchanger.

As far as convection and the confusion within the thread, perhaps you mean to use the term thermosiphon instead of convection?
Thermosiphon - Wikipedia, the free encyclopedia
Duh, now I get it. That's a circulating loop like I have in my house, and they work fine - you would just be circulating through an exchanger. You just tee off the hot water out, through the exchanger, then return to tee into the cold water supply to the heater.

That said, I can't see how this is an improvement on just using the exchanger loop that always comes with a marine water heater. The question of whether you use the exchanger at the engine is again, your preference for keeping the cooling system the health of your engine depends on all where you can see it, which would not matter much if the water heater is in the engine room. If it is located elsewhere in the boat, then having an engine critical system with a lot of extra hose in it you can't see doesn't seem particularly prudent. You still need an expansion tank if the water heater is above the pressure cap on the engine, or you have more than a gallon of coolant in the loop.

Great find on the thermosiphon - thanks! That certainly does look like the correct term, and as the article points out, this is a very common way of getting water to move around from cold to hot. I didn't realize they used to cool automobile engines this way.
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Old 09-03-2014, 09:31 PM   #52
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The old automotive or industrial term would be "percolate". With 24 feet of hose it aint gonna work.
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Old 09-03-2014, 09:40 PM   #53
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The old automotive or industrial term would be "percolate". With 24 feet of hose it aint gonna work.
Sorry, Newton, but the longer the hose, the better.

And it works just fine.
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Old 09-03-2014, 10:44 PM   #54
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There has to be some height difference somewhere to make natural circ work. Not much but enough difference in fluid densities between the hot and cold legs to make the fluid move. The hot water rising or cold water falling or both is the driving force. If the HX and hoses are horizontal, you get very little d/p.
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Old 09-03-2014, 10:56 PM   #55
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Carl..
Kulas just doesn't understand the principal behind the thermosiphon.. It does work.. we do it all the time in homes for a recirc line back to the water heater.. the key in homes is to have slope up to the farthest fixture.. and slope down to the point it returns to the heat source.. we also add a check valve so it doesn't pull cold water from the bottom of the heater when a large demand device ( soaking tubs are the worst ) needs hot water. Sometimes because of layout it is impossible to get it to work.. then we add a Grunfoss pump on a timer.
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Old 09-03-2014, 11:05 PM   #56
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There has to be some height difference somewhere to make natural circ work. Not much but enough difference in fluid densities between the hot and cold legs to make the fluid move. The hot water rising or cold water falling or both is the driving force. If the HX and hoses are horizontal, you get very little d/p.
You are quite right, and that should have been mentioned, thank you. In my case the heater is 10' above the exchanger, so it works a charm.
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Old 09-03-2014, 11:07 PM   #57
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Carl..
Kulas just doesn't understand the principal behind the thermosiphon.. It does work.. we do it all the time in homes for a recirc line back to the water heater.. the key in homes is to have slope up to the farthest fixture.. and slope down to the point it returns to the heat source.. we also add a check valve so it doesn't pull cold water from the bottom of the heater when a large demand device ( soaking tubs are the worst ) needs hot water. Sometimes because of layout it is impossible to get it to work.. then we add a Grunfoss pump on a timer.
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Yes, we had to install a little Grunfos on our circ loop for that reason - the top of the tank was above first floor faucets.
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Old 09-03-2014, 11:12 PM   #58
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You are quite right, and that should have been mentioned, thank you. In my case the heater is 10' above the exchanger, so it works a charm.
10' is huge. You could probably distill saltwater too!
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Old 09-03-2014, 11:23 PM   #59
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10' is huge. You could probably distill saltwater too!
Well, that would compete for space with my other distillation operation....
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Old 09-03-2014, 11:26 PM   #60
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I'm calling BS on this. On a boat anyway. You will not move enough energy (heat) along a 12 foot length of hose in static (nonmoving) coolant to affect any useable heat transfer. Not gonna happen. And yes I do understand convection but you just cant move that much energy thru water to do the job required. Possibly if you had 190 degrees at the source for 12 hours you could affect a modest heat transfer to the house water. I still dont know why you would go this route, except for avoiding meteors. Disclaimer, I have been wrong before, even once today. The debate is enjoyable !!!
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