Heating With Waste Heat

[Dockhead]

I’ve been trying to figure out how to properly use waste heat from my engine and genset for a couple of years already, and still haven’t figured out the right solution.

The thing is this – My home port is above 50 degrees N, and I spent last summer mostly above 60. Those are pretty high latitudes. I sail year around. That means I sail a lot in cold weather, so I am constantly needing heat. Above 60N, you may need heat even in the middle of the summer. I have a pretty good central heating system – a 10kW Eberspacher (Espar) hydronic furnace which makes hot water and does space heating through three fan coils. But I don’t like to run it constantly – for one thing, it consumes diesel fuel, for another, it is a somewhat high maintenance piece of equipment, thirdly – it uses electrical power, and my boat lives on a mid-river mooring with no shore power.

When I’m at anchor or on my mooring in the winter time, I find myself heating water with electrical power from my generator, and even using electrical space heaters, just because the genset is running anyway. Which is a stupid, inefficient way to do it, even though the generator is running anyway to charge batts. And all the while, the generator is just dumping 10kw or 20kW of heat into the ocean

My calorifier has two loops in it – one from the central heating, one from the engine. I’ve had the engine loop working before, but lately I haven’t been able to get it to work. It seems to get an air lock which is hard to get rid of. The hoses have to curve up over a point higher than the point at which they attach to the engine – I guess that’s the problem. When this is not working, I find myself in the stupid situation of arriving at an anchorage with the whole crew desperately wanting a hot shower, and there is no hot water even though the engine has just been running

So I want to solve all this somehow this winter. I thought and thought about putting in heat exchangers to transfer waste heat from both main engine and generator to the central heating circuit. Then, if I could wire up the pump to run independently from the Eberspacher, I could run the central heating system and heat water off waste heat from either engine or genset. This is a really elegant solution from a functional point of view, but I balked a bit at the complexity – all the hoses, heat exchangers, pumps, etc., etc.
So now I’m thinking about something simpler which might also be reasonably effective. I’m just not sure it will work, so I will be interested in expert opinions from here. What if I do the following:

1. Buy one of those bus heaters and put it in under my companionway stairs, and plumb it into the existing engine-to-calorifier loop.

2. Put a circulation pump in that loop.

3. Put some kind of device – some kind of header tank maybe – into the high point of the hoses, so I can get the air out.

4. Create a new loop from the generator fresh water circuit, and plumb that into the engine-to-calorifier loop using diverter valves, so that I can switch the valves and put heat into the loop from either engine or generator, depending on which one is being used.

I like the fact that with this variant, there will be much less plumbing and less hoses – very little more hose than what I have now. I like the fact that the bus heater is simple and separate from the existing central heating system. What I don’t understand is whether it is acceptable to mix the coolant from two engines – from main engine, and genset, which will happen with this scheme. I use the same coolant in both engine and genset, and change them religiously every two years, so maybe there’s nothing wrong with commingling the coolant? What do you guys think?

Or does someone have a better scheme than either of these?

As always, grateful for sage advice.

[weavis]

Originally Posted by Dockhead

Or does someone have a better scheme than either of these?

As always, grateful for sage advice.

Buy the Gunboat.. Im ready.........

[Dockhead]

Originally Posted by weavis

Buy the Gunboat.. Im ready.........

And that solves my waste heat problem . . . . how?

[jackdale]

I was going suggest a hydronic system, but ...

[weavis]

Originally Posted by Dockhead

And that solves my waste heat problem . . . . how?

Great heating/water system on the Gunboat............

[Stu Jackson]

3. Put some kind of device – some kind of header tank maybe – into the high point of the hoses, so I can get the air out.

What you really need on that loop, on both high points, is what is called an automatic air vent. They occur regularly in all hydronic building systems with water in pipes. Go see an HVAC vendor and ask for two of 'em.

Here's what one of our skippers did, along the lines you're thinking:

Cabin Heater - C34

[IdoraKeeper]

Open the door to the engine compartment and get a big fan?

[Dsanduril]

Dockhead,

you could try these:

http://www.spirotech.co.uk/_media/en...wq9YcRtx3PATp2

We use them on hot water/hot glycol systems and they work a treat. Not too expensive, available in brass or 316SS and rated to anywhere from 110C to 200C (which would be steam in a water system)

I do recommend hooking up a hose to the vent side and plumbing it to a drain so that if it decides to dribble it has a place to go...

[Kenomac]

Put your time, money and energy into installing diesel heat. It's awesome. Or, just run the heat pump based heating system you already have off your waste electricity coming off the alternator and leave the engine room door open. It's kind of the same thing.

[Dockhead]

Originally Posted by Kenomac

Put your time, money and energy into installing diesel heat. It's awesome. Or, just run the heat pump based heating system you already have off your waste electricity coming off the alternator and leave the engine room door open. It's kind of the same thing.

Ken! Read the OP! I already have diesel heat. And I don't have a heat pump.

As I wrote, diesel hydronic heat is, of course, awesome, but not a total solution.

[SV Lift]

I don't see anything wrong with combining the hot water circuits, but you are right to install diverter valves and that sounds like a pain to switch back and forth. An extra advantage would be being able to preheat the engine by running the generator or heater if it is really cold out. An oil circulator would be even sweeter.

My keep it simple approach was just to add a bus heater between the engine and the hot water tank. It works fantastic. <$300 and heats the whole boat whenever the engine is running. Without the fan running, it barely puts out heat so I don't bother bypassing it, even in summer.

PS- yes, install air purge valves at the high points

[Stu Jackson]

Originally Posted by Stu Jackson

Here's what one of our skippers did, along the lines you're thinking:

Cabin Heater - C34

Yes, this is essentially a bus heater.

[sailorchic34]

I think what you want to do is put your waste heat in the hydronic's loop. Just connect the engine loop and generator loop to the hydronic loop and connect the hydronic loop to the water heater. Then add a pump connected to the water heater t-stat (via relay). This pump and the hydronic pump will run when water heater calls for heat.

So either the engine, or genny or the diesel boiler will be firing puting heat into the loop. Assuming all have a 13 psi/ one bar pressure rating, no heat exchanger is needed. You would need to add antifreeze to the heating loop, but that's a minor cost.

This saves a heat exchanger pump and controls and allows either heater, engine or genny to provide heating to calorifier or space heating.

I've attached a simple sketch showing the piping arrangement. The engine thermostats will prevent back flow through the engines or between the engines. The diesel heater also acts as a decouple point between the engine water pumps and hydronic electric pump..

You will want to add a ball valve at the high point of the system to add anti freeze to the system and to act as an air vent. The engine coolant overflow tank will act as a expansion tank. A bit O wiring to work out between the two or three thermostats. Actually if you added a thermostat (surface mounted) to the calorifier you could get rid of the relay at the water heater.

it needs a bit O work for the electrical side, to isolate the hydronic pump from the diesel heater (added relay) and probably a switch to turn the pump on when engine or genney is running.

[estarzinger]

On this front, I have:

HEATER CRAFT MARINE HEAT HEATERS

simple, inexpensive, lasted 16 years now.

They do have bigger ones:

BUS HEATERS

[sailorchic34]

A few more thoughts on my sketch. My original assumption is that only one heat generator would be operational at one point. If you have need to run the engine and generator at the same time , route the genny hoses to the hydronic loop separate. That will prevent things from getting a bit wonky. I'm pretty sure it would be fine in either case, but direct connecting the genny to the hydronic loop separate from the engine, decouples the engine and genny water pumps.

Plus you would want a double throw relay for the hydronic pump so it still runs with the diesel boiler off and a DPST switch which locks out the heater, when the switch is in the engine running position. Any any case you would not want to run the diesel boiler with either the engine or genny running. There should be a temp sensor on the boiler, but if there is not the DPST switch would prevent all from running at the same time.

What I've shown is a simple primary secondary heating system. This is one of the things I use to get paid for, though on a much larger scale.

BTW the connection of the calorifier to the hydronic loop with side arm pump, is shown correctly. The pump would prevent the calorifier from overheating from the engine loops. Though if you don't mind 180 degree water loose the pump and connect the calorifier return to the hydronic return.

BTW2, you don't want to connect the genny lines to the existing engine lines to the calorifier as the engine driven pumps are not then decoupled and could effect the other engine cooling flows depending on rpm's. Connecting both engine heating lines to the hydronic loop, decouples the engine pumps via the diesel heater, which is not running with either or both engines running.

Probably clear as mud...