Integrated hydronic heating diagram - opinions?

Discussion in 'Boat Design' started by antonkov, Jan 8, 2014.

  1. MoePorter
    Joined: Nov 2012
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    Location: Oakland,CA

    MoePorter Junior Member

    The mixing valve is for safety - if you scavenge heat from the engine or use a Webasto/Espar you can see water temps in your system well above 130f (55c).

    Espar's D5 claim to hold your coolant temp between 149F (65c) & 176F. In my system I don't see temps above 135F (57c) in the manifolds or hoses - but it's mounted in a truck frame beneath a camper so there are temp losses in the (insulated) hose runs and heat exchangers. Just pointing out the potential heat levels in these systems...
    My valving & manifolds are all copper as I was worried about those temps - sure was a $$ choice & maybe not necessary - but easy to make...

    Mine is valved to heat the engine coolant in sub zero conditions & works great. I can't see the need in a Vancouver based boat though - both engine & batteries are within the boat envelope which is "heated" by the ocean water temp - plus plumbing the engine involves multiple potential coolant leaks sometime in the future.

    I've had good luck with these water to air heat exchangers and muffin fans if you want to save yourself some $ and can design the installation customization. The muffin fans are cheap & quiet but you have to make sure you have plenty of free air flow. It would be much easier just to go with a HeaterCraft but they are louder...


    http://www.newegg.com/Product/Product.aspx?Item=N82E16835226013
    http://www.brazetek.com/products/details/45/15/finned-coil-water-to-air-heat-exchangers/12x12-finned-coil-water-to-air-heat-exchanger

    Also I used CM10 Johnson Pumps for the circulation duties.
    http://www.spx.com/en/johnson-pump-marine/pd-mp-marine-circulation-pumps-cm10-cm30-cm90/

    Not sure why you want to make your own water heater wouldn't one of these work?
    http://www.fisheriessupply.com/seaward-products-seaward-water-heaters-with-front-connections

    I have a 5gal insulated tank in my system that just holds heated coolant so the Espar doesn't cycle on/off too much. There is a suggested minimum amount of system coolant so figure that in as well...

    These systems are a real parts puzzle & then to get all the parts to fit in a boat is a challenge so I suggest lots of design effort. Design a plan for bleeding the system of air from the outset...Moe
     
  2. John Perry
    Joined: Nov 2003
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    Location: UK

    John Perry Senior Member

    With regard to engine pre-heating, I am probably being stupid here, and maybe I dont know much about engine cooling systems, but I am wondering how you pump water through a cold engine that is not running? I would have thought that in that situation the engine thermostat is closed to the external cooling circuit so that the engine driven pump can circulate water through the engine when the engine starts but without water flowing to the external circuit. I thought the engine thermostat probably would not start to open until the water temperature in the engine reaches some point in excess of 90C.

    I guess you are going to need to add isolating valves to your diagram for maintenance purposes, also perhaps three port mixing/diverting valves to control temperatures in the various circuits. I am sure you dont want water at close to engine coolant temperatures going to taps and showers.

    On my boat the hot water system is just a camping stove and a pan of water!
     
  3. MoePorter
    Joined: Nov 2012
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    Location: Oakland,CA

    MoePorter Junior Member

    The simplest way I could figure it was to put a heat exchanger and pump in line on an external engine coolant hose. The Espar/Webasto heats the engines coolant enough to raise the block temp from 14F (-10c) to about 65F (20c) in about 45 minutes. So really you just get the oil thin enough to give the cold batteries a shot at spinning the engine enough to start...
    The pump mentioned doesn't restrict normal coolant flow in the heater hoses enough to notice.
    You can plumb the Espar/Webasto directly into the engine coolant circuit but with a complex cabin/fresh h2o heating system you end up with too many possible engine coolant leaks for my taste.
    One side benefit is the ability to run the Espar/Webasto side of the system through the engine heat exchanger to heat the cabin with scavenged engine heat. That's the only good reason I can think of to involve the engine coolant system in a boat installation.Moe
     
  4. antonkov
    Joined: Mar 2010
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    Location: Vancouver,BC

    antonkov Junior Member

    That's how I envisioned that. That's why there is a heat exchanger with an auxiliary pump, which normally wouldn't be needed when engine is running and pumping the coolant with the built-in pump.
    However, agree with the thermostat remark. Unless the thermostat is opened heat will not reach inside the engine block. Hmm..., so how they do it? I know they do coz met this "heating engine" feature in the wishlists of many.

    I am not trying to complicate or re-invent things here, just capturing various suggestions on the heating system. Thought it may be costly/challenging/not worth to add or retrofit an existing boat, but if planned before the build, it can be done with much less pain and with good benefits in the long run.
     
  5. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    You can make that very complicated, with thermostats or even motorized valves.
    Car makers keep it simple and connect the heater as a bypass to the engine circuit BEFORE the thermostat. The hoses are tiny compared to the rest of the cooling system, the 14W pump on the heater provides further flow restriction when it isn't running.
     
  6. John Perry
    Joined: Nov 2003
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    John Perry Senior Member

    Yes, of course that's right CDK, you could circulate a small flow of preheating water via the cab heater connection that comes off the block on the engine side of the thermostat. Marine engines in the size range the OP is considering are likely to have a suitable connection being based on automotive requirements.

    I should have remembered this since years ago I was asked to design a system for heating domestic hot water from a couple of sea water cooled gensets. But once you are retired, past projects soon seem to become distant memories! - perhaps CDK does not find that so.

    For that particular project we did first consider taking engine coolant from the normal cab heater connection. The engine manufacturer, Cummins I think, was helpful in advising how much heat could be extracted that way and it was nowhere near enough. So we had to take heat from the main external engine cooling circuit. If the OP needs to take a lot of heat from the engine he may need to do the same, in which case he might need to use the cab heater connection to circulate warm water for preheating in addition to connecting into the main cooling circuit for waste heat recovery.

    So, the next thought was to put a cooling water to domestic water heat exchanger in series and upstream of the cooling water to seawater heat exchanger (as shown in the OP's diagram). Doing the sums we realised that would also not recover enough heat, the customer wanted to be able to transfer pretty well all the heat available in the engine cooling circuit to the domestic hot water system. With the heat exchangers in series, that is not possible since the water will always leave the domestic water heat exchanger at a temperature well above seawater temperature, so the sea water heat exchanger will always grab a large part of the total heat available from the engine. So, in the end we had to have cooling water to domestic water heat exchangers connected in parallel with the cooling water to sea water heat exchangers and motorised three port control valves that could switch up to the whole flow between the alternative heat exchangers. That introduced an anxiety that if the motorised valve failed the wrong way when there was a low demand for domestic hot water the engine might not get cooled and the genset would shut down, which was unacceptable. So we had to find a hydraulically operated valve with a hydraulic system that included an accumulator backup and which was designed to give a very high probablilty that any failure would cause the valve to move to full seawater cooling. We did also consider heat recovery from the exhausts, that also seemed to have its problems.

    I note that it is also possible to preheat an engine using electric heaters either in the cooling circuit (block heaters) or in the oil sump, but that may not help if the object of the exercise is to save the battery when starting the engine.
     

  7. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    For me it's not much different. I sometimes think my memory has been selectively wiped or overwritten. Some ideas can be dug up from beneath a layer of dust, others seem lost forever.
    I have a complicated central heating system of my own design, with 3 heat sources and hot water storage, documented in detail, yet whenever something malfunctions I have to study hard to understand it.
     
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