Heating With Waste Heat

[Dockhead]

Originally Posted by Kenomac

Do you have a diesel heat system comparable to a Webasto forced hot air unit? If not, it's the answer to your problem. Uses very little diesel and heats the entire cabin in a few minutes. We don't even use our heat pump/ac unit any longer.

I don't understand why your engine doesn't heat your hot water tank. We always have loads of hot water for hours after we anchor for showers, dishes etc., then the generator will heat an additional 14 gallons in just 30 minutes while we cook dinner and charge the batteries. I assume your set up is similar? Most of the time here in Sardegna, we sail everywhere and rarely use the engine. Still, our generator is able to provide ample hot water after even 30 minutes of run time.

Ken

Eberspacher diesel-fired hydronic system -- it's like yours except instead of heating air, it heats a water/glycol mix which is circulated to fan coils or radiators. It works just like a hydronic furnace at home, except that the furnace is a compact, 24 volt, truck-type heater.

Yes, my calorifier has a loop from the main engine and is supposed to be heated by it. It worked last year, but this year it apparently had an air lock
in it which prevented coolant from circulating from the main engine.

Ah, you have a 50 liter calorifier, lucky dog. I had one, too, until it started leaking. Those were the days -- whole boat load of people could take hot showers on one hot tank, and it stayed hot for a good 24 hours once it was heated up well.

I had a hell of a time replacing it, and ended up with only 32 liters, which lasts proportionately less, and which doesn't hold the heat more than maybe 10 hours. A piping hot tank at bedtime is only barely warm enough for showers in the morning.

On the plus side, I did increase the size of the immersion heater to 1500 watts in the new calorifier, which means I can make usable hot (or warm) water fairly quickly with electricity.

[Dockhead]

Thanks everyone for all the wonderful advice. It's amazing how powerful the collective brain of CF is

After considering the amazing array of different solutions suggested here, I think I may try to get the waste heat into the main hydronic circuit. Here's the way I see it:

1. Cut into the existing engine heat loop and install air bleed valves to solve the existing problem.

2. Install a water-to-water heat exchanger in that circuit.

3. Tap into the generator fresh water cooling circuit (how?) and install another water-to-water heat exchanger there, with a short loop to the genset.

4. Cut into the supply side of the hydronic system and divert that flow through the two heat exchangers mentioned above.

5. Install a switch to allow me to switch on circulation of the hydronic system independent of the Eberspacher furnace.


That way, as long as either the main engine or genset is running, and the circulation pump for the hydronic system is on, waste heat will be dumped into that system and I can space heat and heat water with it.

Notice that I left out any direct connection between genset and calorifier -- I thought about it a long time, and I think the genset makes so much waste heat (7.9kW at full load) that it doesn't really matter that I'm heating up the whole hydronic system just to make hot water, in case I don't need the space heating (which is fairly rare).

What do y'all think about that? I think it's reasonably simple and shouldn't be terribly difficult or expensive to do. It will be fantastic to have all this heat on tap whenever an engine is running.

Here are my questions:

1. Can I just run the hydronic loop through the furnace with the furnace switched off? or do I need to bypass it?

2. Can I just run the furnace's circulation pump separately when I have a different heat source going, and leave the furnace turned off? Or do I need a separate circulation pump?

3. Do I need a separate circulation pump in the engine loop? Despite the fairly long hose runs (about 4 meters each way, I would think), the circulation -- when it works -- seems fine for heating water. But the heat exchanger will add resistance.

4. Do I need another circulation pump in the hydronic loop? And how does it work when you have two pumps in the same loop -- must they always run simultaneously, or can water flow through a stopped pump? Or is this generally a bad idea?

5. Any tips for tapping into the genset to make a loop for it? I guess I will just imitate the way its done on the main engine, but I will have to have fittings welded up, I think. I presume that the standard genset fresh water pump will be ok for getting coolant through the short loop to the heat exchanger -- right? The genset has a Yanmar 1000cc three-cylinder 3TNE74 which runs at a constant 1500RPM.

6. Is it right to plumb the heat exchangers into the supply side of the hydronic loop? If I ever thought that I would use the Eberspacher while either genset or main engine runs, I would plumb it into the return side, so the Eber will be finishing off heating of the coolant, but I can't see how there would ever be any point to running the Eber when a diesel engine is going, so long as the heat exchangers are properly sized and circulation is adequate. But if I'm wrong -- the whole thing will not work this way, if I ever want the Eber to run simultaneously, because the Eber will get the cold return water directly and will run at full blast, so that no heat is absorbed from engine or genset. What do y'all think?

7. Any tips for sizing the heat exchangers? Don't I need to know the velocity of the water flows? I don't think I have any way of knowing or measuring that uzzled:

[Dockhead]

One last question: My engine fresh water system works at a very constant 80C. The genset at 70C. Are these temps any problem for the hydronic loop? If there is a lot of heat being produced and little being consumed, the temperature in the hydronic loop will converge with temp of the heat source. Is that ok, or do I need some kind of thermostatic cutoff?

[Dockhead]

This is my furnace, by the way:

http://www.esparofmichigan.com/cmsAd...Hydronic10.pdf

Hydronic 10 Specifications
Heat output (±10%) 9.5 kW (32,400 BTU/hr) - Boost
7.5 kW (25,600 BTU/hr) - High
3.2 kW (10,900 BTU/hr) - Medium
1.5 kW (5,100 BTU/hr) - Low
Current draw (±10%) 12Volt 24Volt
10.4 - Boost - 5.2 amps
6.3 - High - 3.2 amps
3.5 - Medium - 1.8 amps
2.9 - Low - 1.5 amps
Fuel consumption (±10%) 1.2 l/hr (0.32 USgal/hr) Boost
0.9 l/hr (0.24 USgal/hr) High
0.40 l/hr (0.11 USgal/hr) Medium
0.18 l/hr (0.05 USgal/hr) Low
Operating Voltage Range
Minimum Voltage 10 V (20V on 24 volt systems)
Maximum Voltage 15 V (30 V on 24 volt systems)
Coolant pump flow (±10%) 1400 Litre/hr
370 U.S. Gal/hr
Coolant Temperature Range (±5%) 68-85°C (154-185°F)
Overheat coolant temperature shutdown (±5%) 115°C (240°F)
Weight 6.5 kg. (14.3 lbs.)

[Arthur Garfield]

With a calorifier,upon closer examination you will often find they are inadequately insulated ! Additional insulation will greatly enhance higher temp holding time.

I dump ALL heat,via heat exchanger (S) into 300gl.fresh water tank.This is then used used through calorifier(for showers),calorifier (for overall inside heating).
I closely watch tank volume.

[Jd1]

Originally Posted by Dockhead

3. Tap into the generator fresh water cooling circuit (how?) and install another water-to-water heat exchanger there, with a short loop to the genset.

What do y'all think about that?

I would tap into the cooling circuit after the thermostat as the hot water leaves the generator and before it enters into the radiator.

This is exactly how I would do it!

Here are my questions:

1. Can I just run the hydronic loop through the furnace with the furnace switched off? or do I need to bypass it?

2. Can I just run the furnace's circulation pump separately when I have a different heat source going, and leave the furnace turned off? Or do I need a separate circulation pump?

3. Do I need a separate circulation pump in the engine loop? Despite the fairly long hose runs (about 4 meters each way, I would think), the circulation -- when it works -- seems fine for heating water. But the heat exchanger will add resistance.

4. Do I need another circulation pump in the hydronic loop? And how does it work when you have two pumps in the same loop -- must they always run simultaneously, or can water flow through a stopped pump? Or is this generally a bad idea?

5. Any tips for tapping into the genset to make a loop for it? I guess I will just imitate the way its done on the main engine, but I will have to have fittings welded up, I think. I presume that the standard genset fresh water pump will be ok for getting coolant through the short loop to the heat exchanger -- right? The genset has a Yanmar 1000cc three-cylinder 3TNE74 which runs at a constant 1500RPM.

6. Is it right to plumb the heat exchangers into the supply side of the hydronic loop? If I ever thought that I would use the Eberspacher while either genset or main engine runs, I would plumb it into the return side, so the Eber will be finishing off heating of the coolant, but I can't see how there would ever be any point to running the Eber when a diesel engine is going, so long as the heat exchangers are properly sized and circulation is adequate. But if I'm wrong -- the whole thing will not work this way, if I ever want the Eber to run simultaneously, because the Eber will get the cold return water directly and will run at full blast, so that no heat is absorbed from engine or genset. What do y'all think?

7. Any tips for sizing the heat exchangers? Don't I need to know the velocity of the water flows? I don't think I have any way of knowing or measuring that uzzled:

1) I don't know about your specific boiler but mine has the pump separate from the actual boiler and there is no problem running the pump when the boiler is not running. If you think about it, the boiler only fires when the water is cold. When the water exceeds the set top temperature,the boiler shuts down and the water still continues to circulate.
Another way of thinking - the boiler is basically an air to water heat exchanger and I can't see any reason why circulating water on one side of a heat exchanger could be bad.

2) Same pump assuming it is outside the boiler. The reason I say that is because repair parts for a boiler specific pump might be expensive whereas a common pump that is separate is easy to replace. If you have a built in pump for some reason, make sure it isn't a positive displacement type pump which would not let water flow if the pump is not running (an impeller type pump will let the water circulate even if i is not running)

3) no

4) the hydronic loop is powered by the pump that is currently part of your furnace install. There is a slight chance that the current pump isn't powerful enough for the extra back pressure in the loop but I would not worry about it unless it turns out that there are issues. You can run pumps in series or in parallel to your hearts content if they are impeller pumps.

5) already answered above. I don't know what your current setup is like but usually the radiator or other cooling device is separate from the engine itself and connected via hoses - no welding or other stuff require.

6) the heat exchangers need to be in the cold side of the boiler.

7) that is the hardest question of all ... take a wild guess and then double it
The actual capacity of the heat exchanger required is a function of flow rate, input temperature of both sides of the exchanger and desired output temperatures on both sides of the exchanger. Unfortunately I can not be more specific. I do however have another suggestion .....
My boat uses a standard tube and shell type heat exchanger. They are big, bulky, ugly and horrendously expensive. I often wondered why I don't see "Brazed Plate Heat Exchangers" in these situations. They are much more compact and a fraction of the size. I can suggest Stainless Steel Copper Brazed Flat Plate Heat Exchangers as source. As a general start point for sizing, assume that 33% of your diesel engines energy usage ends up in the cooling system (same for the generator) so that gives you an idea of how many BTU you need to get rid off and the heat exchangers are rated in BTU. I would double the BTU capacity if I was using a brazed plate heat exchanger. There is no down side other than cost and that is not a real big factor in these units.

Hope that gives you a start on things!

[W3GAC]

I don't have an expert recommendation, but I use my boat all year as well, although down at 42 degree latitude. As engineer, I like the idea of a separate 'bus heater' core for main & gen coolant for free heat when running either. This keeps overall system complexity low and promotes simpler troubleshooting when main/ gen issues happen. Assume your boat is well insulated, especially ceiling. Over the years I've added insulation on inside hull and thicker carpet pads... big difference. I only use my V-birth for storage and added an insulated door allowing me to close it off most of the time which dropped my heat loss almost 50%. I'm a 46' ketch and I get by with a 16,000 btu diesel heater running about mid btu capability during wake hours and low btu sleeping. My Winter outside temps range from usual night lows of 28 degrees and day highs of mid 40s. Bad wx however lows can be single-digit and highs in teens. I can still maintain 70+ but usually just put on a thick sweater and let inside temps sag to 65ish.

[AnchorageGuy]

Originally Posted by Dockhead

One last question: My engine fresh water system works at a very constant 80C. The genset at 70C. Are these temps any problem for the hydronic loop? If there is a lot of heat being produced and little being consumed, the temperature in the hydronic loop will converge with temp of the heat source. Is that ok, or do I need some kind of thermostatic cutoff?

That should be no problem as long as the hoses and components are designed to withstand those temps for long periods of time. Chuck

[DeepFrz]

There are brushless DC motor powered blowers available from some of the hydronic heater manufacturer. They claim that they are almost silent. I don't have a link for you but shouldn't be hard to find. Maybe contact your Ebespacher (sp?) dealer near you.

[sailorchic34]

Thanks Dockhead for the tech info on the heating system and genset.

So your heating system is designed for a 10 degree delta T (F). Which is cool.

First, I think the hot water circ pump is fine to use for connecting to secondary heat exchangers at the genny and main engine. The trick with the engine driven cooling pumps is they are low head pumps. So they don't have lots of head to push through a heat exchanger.

The main engine is too large a heat load for your heating loop and clorifier, so just using the 3/4" lines that go to the colorifier and using the colorifier as a small heat exchanger is still possible. Its tricky to divert a small flow rate off the engine cooling loop and doing it full flow would make a pretty large heat exchanger that you could only use 1/3 of the heat from anyway.

Other option for main engine is tee off the hose to the engine heat exchanger from the water pump twice with two inline tees spaced 6" apart. The branch size needs to be one inch. That hose gets longer of course. Then put a 6-8 GPM DC pump in line and connect the suction to the tee closest to the engine pump. This pumps through the heat exchanger (small brazed plate and frame heat exchanger with 1" connections, available from amazon

http://www.amazon.com/Plate-Brazed-H...DJ8A884SR8E6RE)

and returns to the second in line tee before the engine heat exchanger. This gives a side arm arrangement, that will not effect engine water pump and heat exchanger performance.

This would work for the genny too. Very safe as no additional head is added to the engine pumps which is pretty important. The plate heat exchanger is a tad oversized to keep the pressure drop low.

As far as the temperatures go. The heating loop is pretty much an 80C system which is very standard, even in the commercial world. So the boiler, engine and genny temperatures are close enough that they will play well together.

Assuming that there is no tempering valve on the return side of the heater and with 80 degree C there should not be, Then you can just circulate the water through the boiler (switched off). No damage will be done.

You'll want a single throw double pole switch to transfer power and keep the boiler off if the engine(s) are on

I would connect the engine(s) brazed plate and frame heat exchangers to the return line prior to the boiler. So the return would run through the two plate and frames and then to the boiler.

PM me if your unclear about the pump and tee arrangement at the engines.

[TeddyDiver]

Originally Posted by sailorchic34

The main engine is too large a heat load for your heating loop and clorifier, so just using the 3/4" lines that go to the colorifier and using the colorifier as a small heat exchanger is still possible. Its tricky to divert a small flow rate off the engine cooling loop and doing it full flow would make a pretty large heat exchanger that you could only use 1/3 of the heat from anyway.

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..

[Dockhead]

Originally Posted by TeddyDiver

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..

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.

[Dockhead]

Originally Posted by sailorchic34

Thanks Dockhead for the tech info on the heating system and genset.

So your heating system is designed for a 10 degree delta T (F). Which is cool.

First, I think the hot water circ pump is fine to use for connecting to secondary heat exchangers at the genny and main engine. The trick with the engine driven cooling pumps is they are low head pumps. So they don't have lots of head to push through a heat exchanger.

The main engine is too large a heat load for your heating loop and clorifier, so just using the 3/4" lines that go to the colorifier and using the colorifier as a small heat exchanger is still possible. Its tricky to divert a small flow rate off the engine cooling loop and doing it full flow would make a pretty large heat exchanger that you could only use 1/3 of the heat from anyway.

Other option for main engine is tee off the hose to the engine heat exchanger from the water pump twice with two inline tees spaced 6" apart. The branch size needs to be one inch. That hose gets longer of course. Then put a 6-8 GPM DC pump in line and connect the suction to the tee closest to the engine pump. This pumps through the heat exchanger (small brazed plate and frame heat exchanger with 1" connections, available from amazon

20 Plate 5"x12" Brazed Plate Heat Exchanger [1" MPT] w/ Insulation Kit - Heaters Water Heaters - Amazon.com)

and returns to the second in line tee before the engine heat exchanger. This gives a side arm arrangement, that will not effect engine water pump and heat exchanger performance.

This would work for the genny too. Very safe as no additional head is added to the engine pumps which is pretty important. The plate heat exchanger is a tad oversized to keep the pressure drop low.

As far as the temperatures go. The heating loop is pretty much an 80C system which is very standard, even in the commercial world. So the boiler, engine and genny temperatures are close enough that they will play well together.

Assuming that there is no tempering valve on the return side of the heater and with 80 degree C there should not be, Then you can just circulate the water through the boiler (switched off). No damage will be done.

You'll want a single throw double pole switch to transfer power and keep the boiler off if the engine(s) are on

I would connect the engine(s) brazed plate and frame heat exchangers to the return line prior to the boiler. So the return would run through the two plate and frames and then to the boiler.

PM me if your unclear about the pump and tee arrangement at the engines.

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.

[a64pilot]

I'll admit to not reading through the whole thing, and this may be a stupid question if so I apologize, but I'm thinking of keeping it simple.
Right now your engine heats the water in your hot water heater I assume, why not just plumb your Hydronic system into your hot water heater, or maybe easier and simpler a bus heater into your hot water heater?

[Dockhead]

Originally Posted by a64pilot

I'll admit to not reading through the whole thing, and this may be a stupid question if so I apologize, but I'm thinking of keeping it simple.
Right now your engine heats the water in your hot water heater I assume, why not just plumb your Hydronic system into your hot water heater, or maybe easier and simpler a bus heater into your hot water heater?

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.