Domestic heat and water with three inputs

[ramblin]

I'm busy trying to get to the bottom of what a narrow boat build would entail so my head is swimming with info - in particular heating options!

 

Ideally the hot water tank and/or radiators could be heated from the engine, a stove or an auxilliary diesel burner, however the plans i have found tend to use the engine on one calorifier coil and the stove / diesel heater on the radiator loop to calorifier which i dont think is as flexible.

 

The engine would be used when cruising or charging batteries (maybe assisted by solar panel), the multifuel stove would provide primary source of hot water and space heating, and a diesel burner would provide a backup/fast heat. It would be good if any of the pimaries could be fed to either the hot tank or the radiators using a 3-way motorised valve. Please see diagram below of what im thinking, which im sure needs tweaking if not scrapping completely! Is the basic principle of what im geting at workable?

 

[The Bagdad Boatman (waits)]

one danger to watch out for is that any heater may raise the temperature of the water by X degrees not to a specific temp. so hot water in boiling water out..

[MtB]

Numpty edit

Edited October 25, 2016 by Mike the Boilerman

[ramblin]

one danger to watch out for is that any heater may raise the temperature of the water by X degrees not to a specific temp. so hot water in boiling water out..

 

Hi, thanks... I was wondering what would happen if stove was running and either the three way is in off position or the heat exchangers start to boil on the secondary side! The primary PRV would vent steam but as it's pressurised there will be nothing to replenish the loop once its cooled down again. The only way around this i can think of would be to either have a low pressure sensing pump to keep the primary at design pressure with fresh water if it drops, or to use a four port back boiler with an emergency heat dump loop going to the skin tank, though if the radiator loop is on whenever the stove is then maybe this wouldnt be necessary? It might even be possible to wire this into the back boiler pump to ensure the radiator heat exchanger is always active whenever the stove is running.

Edited October 25, 2016 by ramblin

[peterboat]

KISS worked for me when I wanted three sources of heat to to combine and then heat water and radiators.

[Slim]

As someone who has fitted a 55' narrowboat out from a bare shell I know the hours of entertainment and pleasure one gets from planning such a venture.

 

Having said that I would caution you very strongly (from experience) against making things anywhere near so complex. I strongly suspect that several of your ideas would simply not deliver. One example is the S/F fire producing enough heat without melting anyone within it's vicinity. Another factor would be that an installation needs to be accessible for maintenance/repair. Failures do occur.

 

I could go on at length about what I did both good and bad

 

Anyway, best of luck with your venture and remember, any estimate of how long it will take should be doubled or tripled.

 

 

Frank

[ramblin]

KISS worked for me when I wanted three sources of heat to to combine and then heat water and radiators.

 

KISS? I tried google!

 

As someone who has fitted a 55' narrowboat out from a bare shell I know the hours of entertainment and pleasure one gets from planning such a venture.

 

Having said that I would caution you very strongly (from experience) against making things anywhere near so complex. I strongly suspect that several of your ideas would simply not deliver. One example is the S/F fire producing enough heat without melting anyone within it's vicinity. Another factor would be that an installation needs to be accessible for maintenance/repair. Failures do occur.

 

I could go on at length about what I did both good and bad

 

Anyway, best of luck with your venture and remember, any estimate of how long it will take should be doubled or tripled.

 

 

Frank

 

Thanks for words of wisdom frank. I'm just trying to get my head around what is involved here so just pitching a long one really!

 

I had never considered that the MF stove might not produce enough heat, but legionella risk did cross my mind! Is this really a problem because i figured it would at least help to get the water up to temp and the rad loop could spread some heat to the far end of boat?

 

On the legionella point, what is normal practice for ensuring water gets up to safe temperature (70deg i think) on a NB?

 

Is there a standard way of achieving this or is it a case of compromising - I can see it would be relatively simple to have the engine linked to one calorifier coil and put the stove/rads on the other loop but dont see how an auxilliary heater could be introduced to this setup? Maybe like a thermal store type of system if such a thing is available at NB scale?

Edited October 25, 2016 by ramblin

[WotEver]

KISS - Keep It Simple Stupid

 

I guess you already know that triple coil calorifiers are available?

Edited October 25, 2016 by WotEver

[ramblin]

KISS - Keep It Simple Stupid

 

I guess you already know that triple coil calorifiers are available?

Haha thanks for clarifying I thought it was some techy acronym!

 

Nope, all I could see on chandlery sites was single and double so with 3 coil should I put engine on one, stove/rad loop on two and the diesel heater on three? Maybe valves could be used to direct stove heat to either rads or tank though there would be no way to get quick rad heat from the diesel burner.

[David Mack]

Solid fuel stove should have a header tank with a cold feed pipe to the lowest point near the boiler inlet and a vent pipe which rises continuously from the boiler outlet to discharge over the header tank. Otherwise what hapens if the water in the back boiler boils?

 

A multi coil calorifier enables you to heat water from a pressurised engine cooling circuit and an unpressurised back boiler circuit.

Edited October 25, 2016 by David Mack

[ramblin]

Hi david,

 

The layout that im thinking around would not work with a gravity back boiler system (the stove would just be on the wrong side of the boat!!!) though i'm not sure how much of a drawback a pumped system is. Anyhow when i drew diagram with pumped inputs a header tank didn't seem to work (it seemed like it would just cycle the header tank water), hence the extra expansion vessel and pressure relief valve on the primary side. This seems safe and shouldnt over heat during normal operation as the hot tank or rads would be dissipating heat, though if it did vent steam it would need to be manually topped up.

 

Can this arrangement just be swapped for header tank? I guess as long as the header tank is at a greater static head than is dropped in the primary loop then it should be ok since water always seeks the easiest path!

 

Actually i just noticed that the rad loop would blow up when it heated up so definitely not good!!!

Edited October 25, 2016 by ramblin

[springy]

The engine must run a pressurised cooling system and should be able to dump its heat directly to the skin tank,

although a second automotive type thermostat can be used to make the calorifier more efficient, the exchanger/calorifier

circuit acts as an "alternative loop" in the external cooling circuit of the engine.

The main cooling circuit should not have any valves capable of being "shut off"

 

Multi coil calorifier is the way to go, if triple is not available, I'm sure it could be done with a twin - engine (pressurised)

on one coil, MF Stove/ diesel heater (unpressurised) on the other (we have a domestic system which does exactly this,

combining a MF Stove and an electric CH boiler as dual sources for the hot water and central heating).

 

springy

[ramblin]

Hi Springy,

 

Thanks for advise. I will probably be initially cheapskating a small car diesel engine so it definitely wont have a separate thermostat pump on it. Can such an engine be run through a single coil on the calorifier assuming no valves? Maybe over-cooling the engine would be a problem here, is so a thermostatic bypass valve (with no off position!) could get around this?

 

Anyway it looks like the prospect of charging batteries while heating the radiators from the engine is one i should just let go of! Is this a completely lost cause?

 

Chris

Edited October 25, 2016 by ramblin

[WotEver]

Hi Springy,

 

Thanks for advise. I will probably be initially cheapskating a small car diesel engine so it definitely wont have a separate thermostat pump on it. Can such an engine be run through a single coil on the calorifier assuming no valves? Maybe over-cooling the engine would be a problem here, is so a thermostatic bypass valve (with no off position!) could get around this?

 

Anyway it looks like the prospect of charging batteries while heating the radiators from the engine is one i should just let go of! Is this a completely lost cause?

 

Chris

No problem with over-cooling the engine. That's what the engine thermostat is for. The calorifier in the heater circuit will be no kind of cooling load.

 

Every time the engine is running you'll be charging the batteries - why do you think otherwise?

[DHutch]

In farm houses I know, with several heat sources; range/stove/oil and various outputs, they just have a small mixing tank, for get its formal name if I ever knew it, but about a foot in dia and 6inch in height, with tank fittings in a circle round top and bottom of the side. All heat sources leave the bottom and return to the top, all rad loops leave the top and return at the bottom. No valves, just switch the pumps with thermostates/timers.

 

 

Daniel

[Scholar Gypsy]

In addition to some of the points above, I personally think it is quite important that the primary engine cooling circuit is as simple & self contained as possible, and uses a heat exchanger to transfer heat to eg a radiator circuit.

 

The reason I say that is to minimize the number of places where a leak would cause the engine cooling to fail and so the engine to stop, probably as you are approaching a weir or in the middle of a tunnel. With your set up the engine coolant also circulates around the stove and the diesel heater, though not around the radiators.

[ramblin]

Thanks all... there's a long way to go here and your comments are really useful!

 

No problem with over-cooling the engine. That's what the engine thermostat is for. The calorifier in the heater circuit will be no kind of cooling load.

Every time the engine is running you'll be charging the batteries - why do you think otherwise?

 

Ok cool, i thought that the thermostat just turned on the radiator fan! But it actually bypasses the engine coolant channels until the engine is up to temperature so presumably the coolant can simply be passed through a calorifier coil then the skin tank, asssuming pressure drop is acceptable, and the thermostat will keep engine temp correct?

 

I realise batteries will be charging when engine is running and estimate around 3kW of waste heat while ticking over to charge batteries (based on transit alternator torque curve and 30% efficiency). Obviously it would be good if this could be directed to at least the calorifier but it would be awesome if it could be circulated around the radiator loop if possible. My original thoughts were along these lines but it seems the 3-way valve that selected betweeen calorifier and radiator heat exchanger would be dangerous. Maybe this could be fixed by adding a pressure relief bypass loop so that the coolant path cannot get blocked?

 

In farm houses I know, with several heat sources; range/stove/oil and various outputs, they just have a small mixing tank, for get its formal name if I ever knew it, but about a foot in dia and 6inch in height, with tank fittings in a circle round top and bottom of the side. All heat sources leave the bottom and return to the top, all rad loops leave the top and return at the bottom. No valves, just switch the pumps with thermostates/timers.

 

 

Daniel

 

Hi dutch, i think this is basically how a thermal store works except it has an internal coil for domestic hot water, though these are usually large. will definitely research.

 

In addition to some of the points above, I personally think it is quite important that the primary engine cooling circuit is as simple & self contained as possible, and uses a heat exchanger to transfer heat to eg a radiator circuit.

 

The reason I say that is to minimize the number of places where a leak would cause the engine cooling to fail and so the engine to stop, probably as you are approaching a weir or in the middle of a tunnel. With your set up the engine coolant also circulates around the stove and the diesel heater, though not around the radiators.

 

I was hoping the heat exchanger would essentially isolate the coolant and heating system so the engine can jsut do its thing and if the radiator pump detected available heat it would grab it before it winds up in the canal! Yes i think this is bad design but the check valves on each should prevent circulation from one source to another. I think the problem would be running engine coolant through the stove and diesel heater maybe!

Edited October 26, 2016 by ramblin

[DHutch]

Hi dutch, i think this is basically how a thermal store works except it has an internal coil for domestic hot water, though these are usually large. will definitely research.

 

Yes, I guess it is in effect a really small thermal store, such as to have no real storage capacity.

 

My surprise when I first saw it was quite how small, particularly short, it was. In the application I saw it was compact enough to fit within the profile of the floor joists with only one joist removed and braced around.

 

The temerature gradiatent from top to bottom was impressive.

 

 

Daniel

[OldGoat]

ramblin, on 25 Oct 2016 - 10:28 PM, said:

Hi Springy,

 

Thanks for advise. I will probably be initially cheapskating a small car diesel engine so it definitely wont have a separate thermostat pump on it. Can such an engine be run through a single coil on the calorifier assuming no valves? Maybe over-cooling the engine would be a problem here, is so a thermostatic bypass valve (with no off position!) could get around this?

 

Anyway it looks like the prospect of charging batteries while heating the radiators from the engine is one i should just let go of! Is this a completely lost cause?

 

Chris

 

Automotive diesel engine are NOT the way to go (apart from the old BMC1500 and these are so long in the tooth - so not sensible). You can't just bung an engine in, you have to consider the gearbox fitting, reduction ratio and so on. Also you really need to have a water cooled manifold to keep the engine bay temperature down. It also adds to the heat output for your water heating...

 

If you're going to spend good money on the other elements of heating and charging batteries - then why cheapen it with an unsuitable engine.

 

Others will, hopefully expand on these topics....

[WotEver]

 

Yes, I guess it is in effect a really small thermal store, such as to have no real storage capacity.

 

My surprise when I first saw it was quite how small, particularly short, it was. In the application I saw it was compact enough to fit within the profile of the floor joists with only one joist removed and braced around.

 

The temerature gradiatent from top to bottom was impressive.

 

 

Daniel

Isn't it simply a heat exchanger?

 

Many new houses now have forced air ventilation systems which also has a heat exchanger for the fresh air.

[DHutch]

Isn't it simply a heat exchanger?

 

In effect yes, but as there are various types, I have tried explain in more detail.

 

A conventional water-water (or air-water for that matter) heat exchanger would typically be a cross-flow plate/tube exchanger without mixing of the fluids.

 

In this case as far as I am aware all of the 'loops' coming in and out of the unit where open to freely intercommunicate.

 

 

Daniel

[WotEver]

 

In this case as far as I am aware all of the 'loops' coming in and out of the unit where open to freely intercommunicate.

 

 

Daniel

I can't see how that would work... oh well.

[ramblin]

 

In effect yes, but as there are various types, I have tried explain in more detail.

 

A conventional water-water (or air-water for that matter) heat exchanger would typically be a cross-flow plate/tube exchanger without mixing of the fluids.

 

In this case as far as I am aware all of the 'loops' coming in and out of the unit where open to freely intercommunicate.

 

 

Daniel

 

Hmm, it sounds interesting... thermal stores are designed to maximise the temparature gradient with baffles to stop mixing, etc. The mixer tank sounds like the opposite... if there was suction at the top rad feed and pressure at the bottom rad return, while there was also suction at the bottom engine feed and positive pressure at the top outlet then the flow would tend to go from the radiator return to the engine feed, back to the tank then out of the radiator feed. Though the flow could wind up so the rad loop and engine loop become less entangled presumably depending on temps, pressures and tank geometry.

 

So far google hasnt turned up anything on what it is called though!

[DHutch]

I can't see how that would work... oh well.

 

I too was surprised by the performance obtained from such a limited volume, however the principle of heat rising is fairly known.

 

There may well be some baffles inside it to reduced mixing of the tank, but assuming the top remains hot (supply for rads, delivery from heat source) and the bottom remains cool (return from rads, supply to heat source) then you have a system. A cross between a conventional manifold, and a modern thermal store.

 

At which point the engine (or more likely, a heat exchange with the engine loop) simply becomes a heat source, inconjuction with further cooling provision or otherwise.

 

 

Daniel

[Iain_S]

I assume the system DHutch is talking about didn't have a pump, and worked by convection alone.