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Old 25-09-2014, 10:35   #46
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I believe there's no such thing as a stupid question.

We thought about this, which indeed would greatly simplify everything.

But the calorifier coils probably won't pass more than a couple of kW, which is not enough to heat the whole boat.
That does give me an idea, however. If I could commingle coolant of main engine and genset, I could get by with one instead of two heat exchangers, and greatly simplify the plumbing.

The cooling systems would not be connected, but when switched over, coolant in the calorifier loop left over from, say, the main engine would wind up in the genset. Since I use the same mix in both and change them regularly, I don't really see why this would be a problem.
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Old 25-09-2014, 10:41   #47
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Re: Heating With Waste Heat

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For the sake of simplicity I would just put a heat exchanger big enough to be placed directly in the primary loop of the engine cooling. You can allway turn of the pump if it get's too hot..
The danger is the added pressure drop that the second heat exchanger would add to the system. That would effect the peak GPM (LPM) rate a bit, more so as the unit fouled.

Far safer to have a side arm heat exchanger with a small DC pump. That way engine cooling is not compromised
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Old 25-09-2014, 10:51   #48
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Originally Posted by sailorchic34 View Post

The danger is the added pressure drop that the second heat exchanger would add to the system. That would effect the peak GPM (LPM) rate a bit, more so as the unit fouled.

Far safer to have a side arm heat exchanger with a small DC pump. That way engine cooling is not compromised
I would just use the existing calorifier loop. That's a "sidearm" (branch?) isn't it? I would just splice the heat exchanger right into the existing hose.
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Old 25-09-2014, 10:52   #49
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Re: Heating With Waste Heat

Quote:
Originally Posted by Dockhead View Post
That does give me an idea, however. If I could commingle coolant of main engine and genset, I could get by with one instead of two heat exchangers, and greatly simplify the plumbing.

The cooling systems would not be connected, but when switched over, coolant in the calorifier loop left over from, say, the main engine would wind up in the genset. Since I use the same mix in both and change them regularly, I don't really see why this would be a problem.
IMHO, it is best to keep them as separate as possible. Just a gut feeling though.
'Greatly simplifying' ??? If one cut of the hydronic loop and attaching two clamps causes you great anguish or if $200 is prohibitively expensive for you then there are other issues to be considered.
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Old 25-09-2014, 10:55   #50
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Re: Heating With Waste Heat

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Great stuff -- thanks!! Yes, I was worried about adding head to the engine fresh water circuit -- but AFAIK, this diverted flow for heating is an extra loop, so if there is too much head, there just won't be flow in the loop -- correct? It won't interfere with engine cooling? I would not want to risk that.
Correct, provided the side arm pump is sized for a smaller flow rate then the engine cooling pump. Really you want a DC pump for about 6 GPM. This will match the 30MBH ish of the 10kW boiler you currently have. This will be less GPM then the engine produces which is what we want.

This is called a primary/secondary system, which allows the primary loop to do it's thing without the secondary loop messing with the flow dynamics

Keeping it side stream pretty much negates any loss of flow or capacity to the engine cooling loop.

On delta T between engine loop and hydronic loop. As you surmised, there must be a temperature differential between the sides of the heat exchanger. Otherwise, no heat is transferred. Realistically your looking at a hydronic side temperature of about 75C with the engine at 80C. Still well within the hydronic loop design range so all will be well.
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Old 25-09-2014, 10:57   #51
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IMHO, it is best to keep them as separate as possible. Just a gut feeling though.
'Greatly simplifying' ??? If one cut of the hydronic loop and attaching two clamps causes you great anguish or if $200 is prohibitively expensive for you then there are other issues to be considered.
It's not really the money, but a lot more clutter with a lot of extra hoses and finding space for one more heat exchanger.
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Old 25-09-2014, 11:07   #52
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Re: Heating With Waste Heat

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I would just use the existing calorifier loop. That's a "sidearm" (branch?) isn't it? I would just splice the heat exchanger right into the existing hose.
This will work up to a point. With 1/2" or 3/4" hose your limited by flow rate So you might get 2 GPM through 1/2, probably a bit less as rubber hose has really high pressure drops. Maybe 4 GPM through 3/4" hose.

The smaller hose will probably only give about 3 ish kW of heat. Why 1" hose/loop and a DC pump is what you need to get the full 10kW of heat

2 GPM would give you about 10,000 BTU"S (3 ish KW), 4 GPM about 20K BTU or 6KW. In order to get 10kw of heat to match the hydronic boiler, you need a flow rate of about 6 GPM through the heat exchanger with a 10 degree F delta T. In theory, 4 GPM might work with a higher delta T,say 15-18 degree's F. But that puts the loop temp down around 60 degrees C, which may effect heat transfer through the fan coils.

In other words, the air temp out of the fan coils would be cooler. The hydronic heating system is designed for 70-80 degree C and about a 5 degree C delta T (which is pretty standard).
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Old 25-09-2014, 11:24   #53
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Re: Heating With Waste Heat

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Originally Posted by Dockhead View Post
I believe there's no such thing as a stupid question.

We thought about this, which indeed would greatly simplify everything.

But the calorifier coils probably won't pass more than a couple of kW, which is not enough to heat the whole boat.
OK, then why not bypass the engine heat exchanger entirely? A small automobile radiator with a good electric fan will keep your engine cool, of course you still need the water pump">raw water pump putting in water into the exhaust, but two three way valves and you can bypass the heat exchanger and put all the engine heat in the boat.

All that other stuff for me is just too complicated as I'm no Engineer, just a dumb mechanic.
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Old 25-09-2014, 12:32   #54
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Re: Heating With Waste Heat

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OK, then why not bypass the engine heat exchanger entirely? A small automobile radiator with a good electric fan will keep your engine cool, of course you still need the raw water pump putting in water into the exhaust, but two three way valves and you can bypass the heat exchanger and put all the engine heat in the boat.

All that other stuff for me is just too complicated as I'm no Engineer, just a dumb mechanic.

Dockhead already has an impressive heating system with three fan coils (another name for a radiator), one per cabin plus the colorifier loop. So he just needs a better method to transfer heat to his hydronic loop from the engine.

A single fan coil (radiator/bus heater)will not evenly distribute heat about his big boat.

I figure it will cost about $1000 for two heat exchangers (one per engine), two 12V 6 GPM pumps and a bit of hose or pex, or copper pipe.

Myself I would recommend doing the generator loop first as I'm guessing the boat spends more time at anchor then under main engine power.
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Old 25-09-2014, 13:44   #55
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Quote:
Originally Posted by sailorchic34 View Post

Dockhead already has an impressive heating system with three fan coils (another name for a radiator), one per cabin plus the colorifier loop. So he just needs a better method to transfer heat to his hydronic loop from the engine.

A single fan coil (radiator/bus heater)will not evenly distribute heat about his big boat.

I figure it will cost about $1000 for two heat exchangers (one per engine), two 12V 6 GPM pumps and a bit of hose or pex, or copper pipe.

Myself I would recommend doing the generator loop first as I'm guessing the boat spends more time at anchor then under main engine power.
How about something like this?

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Can the flow through 3/4" hose be improved much with a pump?
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Old 25-09-2014, 14:36   #56
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Re: Heating With Waste Heat

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Yes, but I'm struggling to see the problem with too much heat from the main engine. I'm not an engineer, but heat won't be transferred if there's no delta T -- not so? So the hydronic loop will take on heat only until it reaches 80C, then it will stay there, right? No matter how much heat the main engine puts out, it can't raise the temperature in the hydronic loop higher than the temperature in its own cooling system. That seems all good to me, or what am I missing?

Now that I read the specs (duh) and see that the system is designed for up 68C to 85C, I think constant 80C should be very good -- you modulate heat in the cabin with the fan coils like you're supposed to. Main engine seems like an ideal heat source for this system, to me, since you don't have to modulate it to conserve fuel, like you do the Eberspacher.
Right on spot, and about what I thought too but didn't obviously succeed to write..
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Old 25-09-2014, 14:45   #57
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Re: Heating With Waste Heat

There is a limit to how much flow you can get through a hose of a given size before it becomes uneconomical.

For inside hose diameters you get the following for 5 GPM

1/2" = 66 feet of head per 100 feet
5/8" = 22 feet of head per 100 feet
3/4" = 9.2 feet of head per 100 feet
1" = 2.2 feet of heat

With a heat exchanger (~12') valves(~2 each) and hose your looking at a pressure drop for the system of about ~20 feet at 5 GPM, so say 25' at 6 gpm with 5/8" inside diameter. That falls to 17 feet at 3/4" and 14 feet at 1". These are approximate as temperature and glycol % will effect friction loss.

So you have to select a pump that will give you 6 GPM at either 17 or 14 feet of head (or 25 feet for 5/8") depending on hose size you select. Odds are this will be about what your hydronic pump is sized for. So more pressure drop means the pump needs to be larger.

When connecting the hose to the engine, Don't do it as you would for the colorifier. Doing so with a DC pump in series flow with the engine pump could adversely effect engine cooling performance. Take the supply and return off the same hose that goes to the engine heat exchanger. This decouples the DC pump from the engine cooling circuit and does not effect engine cooling flow rate.
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Old 25-09-2014, 14:51   #58
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Re: Heating With Waste Heat

How I would..
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Old 25-09-2014, 15:10   #59
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Re: Heating With Waste Heat

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The danger is the added pressure drop that the second heat exchanger would add to the system. That would effect the peak GPM (LPM) rate a bit, more so as the unit fouled.
That's why I said big enough..
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Old 25-09-2014, 15:17   #60
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Re: Heating With Waste Heat

System Info | International Thermal Research
This automated flow diagram may help you visualize the system.
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