Changing Yanmar 2gm20 to freshwater cooling

Discussion in 'Diesel Engines' started by skatun, Apr 20, 2020.

  1. skatun
    Joined: Sep 2010
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    Location: Aachen

    skatun Junior Member

    We have a sailboat with a 2gm20 in it. This produces heat and currently this is wasted, as well as having saltwater running through the engine is not ideal, the engine runs at uneven temperature an a little bit to cold. So we have been thinking for while to change to it to freshwater cooled, but what really made this interesting was the addition of the HVAC on board. The air quality aboard has increased dramatically, but now we also have a pipes and duct running on both sides of the boat to distrubute air. So why not use these pipes to feed hot air from the enginge by adding a radiator to it. So we made up a schematic as seen in the attachment and would like some feedback on it. The original saltwater pump is there in the event of not enough cooling from hvac and in case the circulation pump fails. I think it might be hard to rebuild the saltwater pump so that it can be turned on or off right?

    The HVAC in the diagram is actually one unit consiting of Heeat Exchanger, filter and fan for both extract and supply air, but is listed as seperated unit in the diagram.

    Im not sure the second Heat Exchanger is needed, it is basically there to cool the inlet air with saltwater on summer days without running the engine.

    Any feedback on the topic and schematic would be great. Also if someone knows what kind of connectors goes to yanmar original control panel it would be great. Because with this rebuild it makes sense to make a new control panel but it would be nice to read out oil pressure and RPM from the engine. So my idea was to just hook up to the original connectors and keep the old control panel in case I screw up something or I figure out the new system does not work as desired. I know I could always get some extension cables, but the original is freaking expensive and hence it would be nice to just get the connectors instead. So if anyone knows what those square connectors are called it would be awesome.
     

    Attached Files:

  2. Lepke
    Joined: Sep 2015
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    Location: Oregon to Alaska

    Lepke Junior Member

    When you switch to fw cooled, the thermostat can be changed to a higher temp about 110° to 125°C and the engine will run more efficiently. Old thermostat is probably about 100°C or lower. The higher temp will give more heat and maybe allow for the sw pump to run as normal. An electric clutch added to the sw pump will turn it off, but you still need adequate water flow in the wet exhaust. Turning the sw pump on and off with a clutch might cause belt problems at higher engine speeds.
    Joint ac/heat systems usually run the fan at a higher speed for ac. Going thru 2 exchangers will slow the air flow. I have a hydronic system with with a marine (car like) air/water heater in each area. It uses a boiler and chiller. In the summer the boiler is bypassed and in the winter the chiller is bypassed. Same water either hot or cold. When cruising, the engine coolant heats the boiler.
    When you switch to fw cooled, you want to get all the salt out of the engine. Probably flush it a couple times with something like Barnacle Buster. You probably should ad a zinc in the sw system so your exchanger doesn't get eaten. Usually with a tee somewhere in your plumbing and all metal bonded together.
    The schematic was a little too busy for me.
    A simpler system would be an air/water heater where you need the heat and 2 waterlines to and from the engine. Water leaves the hottest part of the system (usually before the exchanger) and returns after the exchanger. Valves to isolate the heater in case of a leak. Add a sw electric pump, a couple more valves and switch the heater from hot to cold. Flushing with fw before returning to coolant side.
     
  3. skatun
    Joined: Sep 2010
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    Location: Aachen

    skatun Junior Member

    It is way lower than 100C, because it is depending on load and RPM. I have order a thermocouple for it, so I can log it. I will give zou guys some data on it as soon as I have it.

    What amount is that?

    That was what I figured out as well, hence my idea was to just keep it running but just bypass the flow back to ocean. But some more thinking, why not just take the belt off and keep it at hand? It takes like 2 minute to reinstall when needed.

    Since the engine is practically air cooled(with the hvac and losses through pipes and water boiler) the failure mode will be that the hvac can not cool the engine enough, i.e running at high load for longer times. This will never be a dangerous situation because then you can always slow down. The other failure mode is that the circulation pump fails, then you need to quickly change to salt water cooling again by swapping valves over to the saltwater pump. Then when safe, you need to replace the pump, flush the system .. And in the unlikely event that both electric pumps fails at same time, you need to stop the motor for a minute and put on the belt. But to save time and not have to move 1 hose on the engine (from electric to engine driven pump) we can have 3 way valve to save this time.

    Good Point!

    The question is how big the Air/FW and the SW/FW heat exchanger needs to be. I have this one laying around, but I am unsure how much heat will be transferred to air with that one. I can always install more if needed. Quite some heat will be lost in pipes and in the water boiler I assume.
     
  4. Lepke
    Joined: Sep 2015
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    Location: Oregon to Alaska

    Lepke Junior Member

    The best system is the simplest, with the fewest components. That's why I think a system like a car has is the best. The small radiator linked is way too small for much heat or cooling. About like a tiny electric heater. Image is marine heaters I use in my hydronic system. The ones shown are 12kw. A smaller one is 7kw 235x290 with a core about 50mm thick. You also could use radiators. On my powerboat, 83' 2 heated decks, was originally configured with radiators. The move to forced air heated the boat 4x faster from unheated in below freezing weather. It's more efficient to move heated water than heated air. My water lines are insulated and the hull is insulated. With a series of valves, I can use the engine heat from my mains for the hydronic heat, but the sw system is stock. In cold weather my Detroit mains supply about 30kw of heat. Your engine may provide about 5kw of heat.

    You're a sailboat with 2 modes of movement, but the engine is also a piece of safety equipment and need to be 100% reliable for those unknown emergencies. 12V pumps are less reliable than a belt driven pump. Usually because of low voltage with the motor eventually burning itself out. And you probably need a flow of at least 20lpm to ensure cooling and reasonable exhaust temps. I'd use the electric pump just for the sw cooling on hot days. Heaters.JPG
     
  5. skatun
    Joined: Sep 2010
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    Location: Aachen

    skatun Junior Member

    That's why I have triple reduancy, only last stage will require some quick manual work..

    But one option is to use the original belt driven pump as the circulation pump and electric salt water pump, and if you get a leakage in the circulation loop with some valves put it back to running saltwater in engine.

    So a radiator of around 1.5L should be enough for my setup if we consider losses in water heater and pipes as well.
     
  6. brendan gardam
    Joined: Feb 2020
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    Location: east gippsland australia

    brendan gardam Senior Member

    where do get your numbers from. salt water thermostats are 63c or lower otherwise you would have a salted block in no time. freshwater systems normally run an 80c thermostat.
     
  7. Lepke
    Joined: Sep 2015
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    Location: Oregon to Alaska

    Lepke Junior Member

    In the US, sw cooled thermostats are about 140°-160°F (if memory serves) about 100°C or under. Diesels have better combustion efficiency at 180°-210°F, about 82°- 100°C so I read the table wrong. I don't work in the metric system unless forced. I've noticed yacht throw away engines run lower thermostats, I assumed to limit warranty exposure on less well maintained engines.
     

  8. brendan gardam
    Joined: Feb 2020
    Posts: 368
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    Location: east gippsland australia

    brendan gardam Senior Member

    the low temp thermostats stop saltwater cooled blocks getting salt build up in the water jackets . you will find the same in all saltwater cooled engines. even outboards.
     
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