Unconventional heating arrangement - but would it work?

[agg221]

We have a small boat so everything is more on the caravan scale rather than boat scale, ie compact and multi-purpose. That is except for the lump that is the Kelvin J2, which gets honoured with more space than the children have between them! The layout is back cabin (7'), engine room (8'), small shower/toilet, open galley/saloon with dinette/bed (~12').

At present, there is a compact single coil calorifer run off the engine and an Epping stove right at the back, and that's it for heating/hot water.

We will retain a solid fuel stove, but are looking at heating/hot water solutions which are easier to use to give uniform heat throughout the boat and hot water. Also, because this boat is for leisure, using solid fuel only makes it a bit tricky to shut down at the end of the last day. Because of the extremely compact size, a Refleks diesel heater looks very promising, due to the zero stand-off needed from non-flammable materials, and the ability to run a copper coil for a heating/hot water system. There is a route that can be used to allow a gravity fed system, running round to the calorifer and the back cabin. However, the unconventional bit, is there any particular reason why I can't plumb it in series with the engine cooling loop?

Running the stove but not the engine, e.g. overnight, the engine would then act as a heat sink which would help achieve uniform background heating throughout the boat since it is in the middle, and would be pre-heated which would aid starting in the morning. During the day, the engine would provide enough heat without the Refleks, so the stove could be shut down and the heating system would be driven by the engine water pump. Both would share the common header tank.

So far as I can see, all I would need is a valved bypass for the engine water pump, to switch between gravity fed and pumped, and a couple of small twin pipe finned radiators, one for each end. Fault conditions I can think of are:

1. Forgetting to open the bypass valve when firing up the stove and the engine stopped. Outcome - should not cause a problem as the stove shares a common header tank.
2. On a hot summer's day, turning off the whole heating loop and forgetting to turn it on again before starting the stove. Outcome - controlled by a thermostatic cut-out at the stove hot water outlet.
3. Forgetting to close the bypass valve when starting the engine. Cooling efficiency may drop slightly, due to back-flow, unless a one-way check valve is installed (are these available?)

So the question is, is the above feasible, have I missed something or is there a better, equally compact system that can be installed using mostly what I already have?

 

Alec

[Tony Brooks]

In no particular order:

 

2. Solid fuel stoves in boat sizes do not normally have any overheat cutout. So unless the Epping has been converted to run on oil, it won't have an overheat cutout. Even if it did, there is every chance that you would boil the water and expel it from the header tank.

 

Is the Kelvn tank/heat exchanger cooled, or direct raw water cooled and does it run unpressurised, unlike modern engines?

 

3. Both flap and spring type one way valves are available.

[agg221]

9 minutes ago, Tony Brooks said:

In no particular order:

 

2. Solid fuel stoves in boat sizes do not normally have any overheat cutout. So unless the Epping has been converted to run on oil, it won't have an overheat cutout. Even if it did, there is every chance that you would boil the water and expel it from the header tank.

 

Is the Kelvn tank/heat exchanger cooled, or direct raw water cooled and does it run unpressurised, unlike modern engines?

 

3. Both flap and spring type one way valves are available.

Thanks Tony,

 

The solid fuel stove will not have a back-boiler - just be a source of heat independent of the water heating system. It is the Refleks oil stove which will have the hot water coil and the thermal cut-out to the oil supply. This system is available.

 

The Kelvin is heat exchanger cooled. It is unpressurised beyond the 1.5m or so from the unsealed header tank. The water currently circulates through the engine and calorifer and then, when up to temperature, a thermostat opens which circulates through a keel cooling loop.

 

The use of a one way valve should completely remove the risk of 3. Flap is probably the best option for very low pressures?

 

Alec

Edited October 7, 2021 by agg221

[Tony Brooks]

3 minutes ago, agg221 said:

Thanks Tony,

 

The solid fuel stove will not have a back-boiler - just be a source of heat independent of the water heating system. It is the Refleks oil stove which will have the hot water coil and the thermal cut-out to the oil supply. This system is available.

 

The Kelvin is heat exchanger cooled. It is unpressurised beyond the 1.5m or so from the unsealed header tank. The water currently circulates through the engine and calorifer and then, when up to temperature, a thermostat opens which circulates through a keel cooling loop.

 

The use of a one way valve should completely remove the risk of 3. Flap is probably the best option for very low pressures?

 

Alec

 

If the Reflecks overheat is a real water temperature cut out and not a fire valve, that should be fine.

 

As long as the engine cooling circuit is not pressurised there is no reason it can not be linked to an open vented heating coil, but you will have to watch the levels of the heating and engine header tanks. Both need to be pretty much the same height.

[Tracy D'arth]

The only question I would raise to your obviously well thought out idea is that you are increasing the total water capacity and you will have to cope with more expansion. 

Gravity flap valve would be preferable but I would try it without first, keep it simple.

I cannot find a figure for the heat output of a Kelvin J2 cast iron radiator but it will be substantial!  

[agg221]

Thanks Both, it sounds like I haven't made any glaring errors so it's worth doing.

 

Surprising that there is no data for Kelvins as radiators - there is probably plenty for their use as boat anchors though!

 

Alec

[David Mack]

I take it that your engine room has the same level of insulation as the rest of the cabin. My Big Woolwich engine room has uninsulated steel cabin and hull, and ill-fitting side doors that allow wind and rain in. An engine radiator as you suggest would waste a lot of heat!

[dmr]

Essentially you are planning to use the engine as a radiator and heat store?

Nice idea and I have thought about something similar but all considered its probably easier just to put a little radiator in the engine room.

 

The engine will hold heat for a few hours but not all night. In winter we run ours (a mere JD3) 5:30 till 8 and its still a little warm at midnight but not the next morning.

Are there any direct metal connections between engine and boat that will let all the heat escape?

A Kelvin J is a precious thing that needs looking after so you need to be 100% sure that no mistakes or failures can compromise the cooling system, this would include preventing the engine from getting up to temperature which would likely do it no good at all.

[Detling]

1 hour ago, dmr said:

 

A Kelvin J is a precious thing that needs looking after so you need to be 100% sure that no mistakes or failures can compromise the cooling system, this would include preventing the engine from getting up to temperature which would likely do it no good at all.

Maybe a restrictor valve to the boat bit when the engine is running, I have a heat exchanger from my modern engine to the boats radiators and whilst fine when running at cruising speed, at Tick over as well as in a flight of locks I need to reduce the heat transfer to keep the engine temperature high enough.

[agg221]

15 minutes ago, dmr said:

Essentially you are planning to use the engine as a radiator and heat store?

Nice idea and I have thought about something similar but all considered its probably easier just to put a little radiator in the engine room.

 

The engine will hold heat for a few hours but not all night. In winter we run ours (a mere JD3) 5:30 till 8 and its still a little warm at midnight but not the next morning.

Are there any direct metal connections between engine and boat that will let all the heat escape?

A Kelvin J is a precious thing that needs looking after so you need to be 100% sure that no mistakes or failures can compromise the cooling system, this would include preventing the engine from getting up to temperature which would likely do it no good at all.

Yes, that's correct, I am thinking of using the engine as a radiator and heat store. Not holding heat overnight is not an issue - if it's cold enough to need the heating on we will have the Refleks running, so it will continue to remain warm. This is generally regarded as a good thing to reduce wear anyway; in fact some modern vehicles have a Webasto type heater installed for that purpose.

 

Good thought on the heat losses through the engine bed. The cooling pathway does not specifically run that way, but it could result in heat loss through conduction via the lower half of the crank case.

 

Equally good thoughts from you and Detling that the system needs to ensure the engine runs at temperature. I'll have to think through the various scenarios and make sure that any valves/controls are automated so far as possible to deal with the complete logic tree of possible scenarios. In practice, the Refleks will be installed initially without the hot water outlet as I am going to have to custom build it. That will give me a chance to understand how much heat output I am really dealing with and how it behaves in the heat flow around the boat.

 

Alec

 

 

 

[dmr]

11 minutes ago, Detling said:

Maybe a restrictor valve to the boat bit when the engine is running, I have a heat exchanger from my modern engine to the boats radiators and whilst fine when running at cruising speed, at Tick over as well as in a flight of locks I need to reduce the heat transfer to keep the engine temperature high enough.

 

A good temperature gauge would be essential to keep an eye on things.

A heat exchanger is an extra complication but a good idea, this will require another pump.

I don't like the idea of the engine sharing the central heating water, but not sure exactly why.

When we got our boat it had a complicated valve system so that the radiators could run off either the engine or Alde. After fitting a temperature gauge I now know that the engine never gets hot when charging batteries (unless I use the immersion heater via the TravelPower) so I suspect the engine spent all its winters running very cold.

The engine was also very very sick with bore wear (I replaced it). This was possibly due to some accident with the previous owners but it is also possible that the cold running was the cause.

[dmr]

13 minutes ago, agg221 said:

Yes, that's correct, I am thinking of using the engine as a radiator and heat store. Not holding heat overnight is not an issue - if it's cold enough to need the heating on we will have the Refleks running, so it will continue to remain warm. This is generally regarded as a good thing to reduce wear anyway; in fact some modern vehicles have a Webasto type heater installed for that purpose.

 

Good thought on the heat losses through the engine bed. The cooling pathway does not specifically run that way, but it could result in heat loss through conduction via the lower half of the crank case.

 

Equally good thoughts from you and Detling that the system needs to ensure the engine runs at temperature. I'll have to think through the various scenarios and make sure that any valves/controls are automated so far as possible to deal with the complete logic tree of possible scenarios. In practice, the Refleks will be installed initially without the hot water outlet as I am going to have to custom build it. That will give me a chance to understand how much heat output I am really dealing with and how it behaves in the heat flow around the boat.

 

Alec

 

 

 

 

My engine (in its industrial version) has provision for an electric heater for very cold starting. If we ever got a winter/home  mooring with a hook up I would think about using the engine as a big electric radiator. A simple electric heater on the wall would be neater and more efficient but I rather like the idea of a nice warm engine.