Using Waste Heat

[Kenomac]

Originally Posted by Dockhead

That wouldn't work on my boat -- big blowers circulate a lot of air through the engine room, and there's no heat.

Do you run the electric engine fan all the time while motoring? One delivery captain did that on our boat right up until he burned out the fan motor. I've been advised by Oyster and several mechanics, that the engine fan is really only to be used if the engine is being run while the boat is stationary or to vent off waste heat upon arrival at the anchorage or dock.

[goboatingnow]

Originally Posted by Kenomac

Do you run the electric engine fan all the time while motoring? One delivery captain did that on our boat right up until he burned out the fan motor. I've been advised by Oyster and several mechanics, that the engine fan is really only to be used if the engine is being run while the boat is stationary or to vent off waste heat upon arrival at the anchorage or dock.

Many boats now have full time engine room fans.

[Dockhead]

Originally Posted by Kenomac

Do you run the electric engine fan all the time while motoring? One delivery captain did that on our boat right up until he burned out the fan motor. I've been advised by Oyster and several mechanics, that the engine fan is really only to be used if the engine is being run while the boat is stationary or to vent off waste heat upon arrival at the anchorage or dock.

Ken, I bet you've got more than one fan there, and that whatever you are switching on and off is not the only ventilation you have. It's hard to believe that Oyster would advise you to not ventilate your engine room.

My engine room blowers are heavy-duty commercial type units which will outlast the boat. They are on a thermostatic control which is automatically switched on when either main engine or genset are running.

One blows in and the other blows out, and I believe that a well-ventilated engine room is a really good thing, so I would not try to shut them down, nor would I advise you to. There are many reasons why you need lots of air down there. Remember, your engine space is inside the main hull volume. Anything (fumes, blow-by, etc.) which doesn't get blown out somehow ends up inside your boat. For another thing, all kinds of devices in your engine room can be damaged or life shortened by heat. For yet another thing, diesel engines need lots of fresh, cool air. If they encounter any resistance in breathing, or if they breathe hot air, their efficiency falls off dramatically.

[Kenomac]

Thanks, I'll look into the engine fan issue again. It just seems odd and bassackwards that the delivery captain used the engine fan 100% of the time, ran the boat at only 6 knots for over a thousand miles and burned up the engine fan and the turbo. Subsequently over the past two four month cruising seasons, we've run the boat over the same distance... probably more without the fan and have had no problems.

There's probably more to do with the fact that we rev the engine at least once every hour for several minutes which keeps it running cool and carbon free and he neglected to do that. We'll begin using the fan again. Do you know of specific issues with diesels involving increased efficiency running at lower temperatures? Why do truckers routinely place covers over their radiators when running the trucks in low temperature environments?

[Yeti]

Originally Posted by Kenomac

Do you know of specific issues with diesels involving increased efficiency running at lower temperatures? Why do truckers routinely place covers over their radiators when running the trucks in low temperature environments?

While I'm not an expert, I did work in Antarctica for parts of two years. In cold environments people cover up the radiator a bit so that the engine gets warmer quickly and stays warmer. The heater loop stays warmer etc....

As far as cold air vs. warm air, I imagine it could be a air density thing. Warmer air being less dense than cold air. I'm not sure our little diesels are that picky but I could be wrong.

[tanglewood]

I designed (with a lot of help) a diesel fired hydronic heating system for our boat. It includes a heat exchanger like you are contemplating. The engine coolant loop that circulates through the hot water tank also passes through a heat exchanger. In the heat exchanger, it imparts heat into the hydronic heat loops. The controls have a selector switch for Diesel heat (the boiler) or engine heat. I know, both are diesel powered, but I think you get what the position mean. In the engine heat position, all the controls and circulator pump operate as normal, but the boiler is locked out and all heat is drawn off the main engine. It is all waste heat otherwise destine to dump in the ocean, so there is truely zero fuel cost to heat the boat this way. So far it works great, but I think the coldest we have been in while cruising is about 40F.

[poiu]

Originally Posted by Kenomac

Do you run the electric engine fan all the time while motoring? One delivery captain did that on our boat right up until he burned out the fan motor. I've been advised by Oyster and several mechanics, that the engine fan is really only to be used if the engine is being run while the boat is stationary or to vent off waste heat upon arrival at the anchorage or dock.

It depends on the size and design of the openings to the engine room as to what extra fan power is needed.

The engine needs a given flow of air for combustion, which is pretty substantial and it needs to be at a low temperature (under 60 deg C). The cooler the better for power and efficiency. As the engine sucks air in for its own operation it is also ventilating the engine room.

My engine room is naturally well ventilated and is very happy without the fans running. I suspect yours will be so too. I notice no difference to power when they do run and only a small reduction in engine room air temperatures of about 10deg. Say from 50deg C at worst to 40 deg C. I leave the fans off unless I am working in the engine room under power. They are noisy, consume a lot of amps and don't do much.

When the engine is shut down you can feel rather a large flow of air coming through the external vents, drawn by the temperature/pressure difference. The fans don't add an awful lot to that flow. It takes two days at anchor to cool the engine room fully! That's when it can be useful to open the engine room door, but I wouldn't want to do it whilst the engine was potentially pumping out CO and CO2 fumes.

[Kenomac]

Thanks Poiu,

We're currently doing and experiencing the same situation regarding engine cooling and air temperature inside the engine compartment. Air temp seems to be around 50 degrees C while running inside the compartment with excellent air flow without the additional high powered fan running.

Ken

[DeepFrz]

Ken, here is a good reason to reduce the airflow through a radiator and engine space.

Tonight

Clear. Local blowing snow late this evening. Wind north 30 km/h gusting to 50 becoming light overnight. Low minus 30. Extreme wind chill minus 40.
Saturday

Sunny. Wind up to 15 km/h. High minus 25. Wind chill minus 41 in the morning and minus 33 in the afternoon.
Saturday night

Increasing cloudiness. Light snow beginning after midnight. Wind becoming south 20 km/h near midnight. Temperature steady near minus 25. Wind chill minus 37.

I bet you don't experience those temps. on your boat.

[Lepke]

I have a hydronic system based on an oil fired boiler and baseboard type radiators. It was installed when diesel was about 20¢/gallon. I am in the process of replacing the baseboards with marine heaters similar to the ones in other replies. I found the forced air heated a cold boat much faster than the baseboards. 30 minutes vs several hours. None of the original circulation lines were insulated and I had a large heat loss from the boiler to distant heaters. Insulation makes a big difference.
As to waste heat - my boiler has a copper coil in the top of the boiler that heats a 50 gallon electric hot water tank if the boiler is hot. Both mains were modified to send 175° engine water thru the boiler by turning a few valves. Most engines have a in and out port that can be used for a heater. Mains and generators of mine have these. By diverting the water with valves into the circulation system the engine fresh water pump pushes enough water thru the boiler to heat it to about 170°. I don't need an auxiliary pump. Each new heater is a zone with a valve controlled by a thermostat. The zone valves are closed unless there is a call for heat. The engine water just goes thru the boiler unless there is a heat call. Then the boiler circulation pump also pushes water. It works better having the engine water enter the boiler top and return from the bottom. Opposite normal circulation. But this way I get heat as soon as the engine is warm and hot water will flow to the heaters even if the boiler is still cold. I only have 1 engine heating the boiler at a time in case of some plumbing accident. I don't want both mains w/o water.
I also have a pellet stove with a coil that heats the boiler and a diesel stove with a coil that can heat the hot water tank. Most of the time I have the boiler oil burner disconnected, but use the control circuit for the thermostats. In the winter I use the pellet stove to heat the whole boat via the boiler.
I had to redo the fresh water plumbing and added a return line and small pump that allows me to get hot water to a remote sink or shower without dumping fresh water down the drain. The cool water in the supply line is returned to the hot water tank where normally incoming cold water replaces hot water being used.
With a little thought, all of this can be controlled with solenoid valves and relays.

[wooden head]

With my boat the diesel stove (old school lump of cast iron) is set up with coils as is my water heater. By tying the engine, stove, and water heater together with a couple of heater boxes I can heat the boat with gas diesel or electric, I can use the stove or engine to heat water on the hook or traveling. And I can preheat my engine for easier starts not that she needs it but cold starts are what wears engines. Now I just need a pre- oiler.

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[Dockhead]

Originally Posted by tanglewood

I designed (with a lot of help) a diesel fired hydronic heating system for our boat. It includes a heat exchanger like you are contemplating. The engine coolant loop that circulates through the hot water tank also passes through a heat exchanger. In the heat exchanger, it imparts heat into the hydronic heat loops. The controls have a selector switch for Diesel heat (the boiler) or engine heat. I know, both are diesel powered, but I think you get what the position mean. In the engine heat position, all the controls and circulator pump operate as normal, but the boiler is locked out and all heat is drawn off the main engine. It is all waste heat otherwise destine to dump in the ocean, so there is truely zero fuel cost to heat the boat this way. So far it works great, but I think the coldest we have been in while cruising is about 40F.

Very interesting. Of course, with a power boat, you have a far larger main engine, used more often, but the principles apply nevertheless.

Do you have a diagram you could post?

Do you bypass the diesel furnace or pump water through it, when you're running off the main engine?

Do you use the standard hydronic circulation pump, or do you have an alternate one to use when running off the engine?

[Dockhead]

After some thought on this, I have come to some conclusions.

I don't want to unnecessarily complicate an already complicated vessel.

All this waste heat sounds great in theory, but in practice it's worth less. For example, getting heat from the genset just means I could shut down my furnace for a couple of hours while the genset is running -- big deal. Likewise, with hot water made from the genset -- I have abundant power when the genset is running (it's rated for continuous prime power production at 6.5kW), so I can switch on the immersion heater, and the total incremental cost of fuel for doing so will never, however long I live, add up to the cost of putting in a heat exchanger, pump, etc.

On the other hand, waste heat from the main engine is great -- arrive at an anchorage with a tank full of hot water -- priceless. Blast a bus heater while motoring in cold, rainy weather -- ditto.

So I've just decided to do this -- splice into the existing engine-calorifier loop a bleeding/filling port, to deal with the air lock issues. Install a big (6kW or so) bus heater under my companionway steps, plumbed into the main engine-calorifier loop.

Observe this for effective circulation and add a pump if necessary. Cheap and simple.

Some day, perhaps, I will put in a second bus heater powered by the genset. The second bus heater will be cheaper than the appropriate heat exchanger, not to mention the engineering and fiddling required. If I ever replace the calorifier (again), I'll order one with THREE loops (yes, such things are made) -- one for central heat, one for main engine, one for genset. But that last is not a priority.

Thanks to everone for the good advice, especially on bus heaters.

[wooden head]

Sounds like a good plan. I have one last request in modifying any water heating system please make sure all loops are over presure protected. RE; t&p valve on waterheater, presure vent cap on engine loop etc. When adding valves keep in mind every heating source must not be valved off from relief. Explosion hazzard if you're lucky no one gets hurt you just blow a hole in the hull.

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[carstenb]

Dockhead - why make this so complicated?

You already have an engine waste heat exchanger - it is called a hot water heater.

Simply buy another hot water heater (a 40 liter costs maybe £300) and plumb it in just like your current water heater.

Now take the fresh water outlet and plumb that to your towel rack (and perhaps a small radiator or two somewhere else).

now plumb the fresh water coming back from the towel rack into the inlet side of the water heater so you have a closed loop system.

If you also hook the electric heater side up to your inverter, then you have warm towels even when your engine hasn't been running for several days.

Finally you could (quite simply and at very little cost) rig a set of electrically operated valves in front and back of this supplementary water heater so you could shunt the hot water into your regular hot water system (this way the gals would have a lot more hot water to shower in - extra brownie points)

For a low () hourly wage, I will plumb this system up for you