Hot water circuit design

[Boater Sam]

10 minutes ago, ivan&alice said:

I see - so to minimise corrosion you need:

 

1. Use only a single metal in the system

2. Avoid using steel

3. Minimise oxygen in the water (such as by avoiding fresh water)

4. Add a corrosion inhibitor to the water

5. Avoid hot water if possible

 

Is there anything else that can be done?
 

Note that my old system has 12V pumps, steel tanks, a copper calorifier and an Eberspaecher which @Tony Brooks said has an aluminium heat exchanger. So is the corrosion inhibitor the only thing keeping this system from falling apart?

Its not all that, the prime cause of corrosion is the fresh oxygenated water constantly being introduced.

Your existing is a close circuit using only the same water going round all the time, the free oxygen gets adsorbed by rust or boiled off then there is no more. 

Edited November 20, 2019 by Boater Sam

[Tony Brooks]

but corrosion of aluminium components and possibly steel can be galvanic with different metals forming a simple cell. Having copper pipes helps complete one "leg" of the galvanic circuit and thus make such corrosion worse. Steel radiators and copper cylinders have been proven to coexist happily for a reasonable working life,  especially if  inhibitor is used. Light allow less so and if I am correct (I don't know - I did say  suspect) about an aluminium hear exchanger remember Alde specifically state you must not use copper with their 3xxx series boiler.

[Chewbacka]

14 minutes ago, Boater Sam said:

Its not all that, the prime cause of corrosion is the fresh oxygenated water constantly being introduced.

Your existing is a close circuit using only the same water going round all the time, the free oxygen gets adsorbed by rust or boiled off then there is no more. 

Agree.  Earlier Ivan suggested using finrads to avoid steel rads, whilst that gets rid of the steel, it does have another problem.  To heat a boat in cold weather and to avoid excessive diesel boiler cycling you need to ideally have a ‘load’ that is the same as the boiler output, guessing about 4kW.  I seem to remember they are 300w per meter, so you would need say 10m or so.  Just something to think about.

 

I considered solar water heating, and concluded -

For hot water in hot weather it would work well, and if bright and sunny there would be plenty of solar electric to power the pump.

But I don’t want space heating in summer

 

In winter the power in the sun is too low to both heat the domestic hot water and provide space heating, so again no space heating.  Also I don’t think there will be a great deal of sun.

 

I concluded that in summer we move most days we are on the boat, so engine heats hot water, on the days we don’t move I can use the diesel boiler and solar electric to run the system.  So, for us, there was no justification for the cost of a solar water heater

Edited November 20, 2019 by Chewbacka

[MtB]

Rather like the trope about the Americans spending $millions on a Biro that will write in a gravity-free environment for their space missions, whilst the Russians used a pencil, there is an equally simple solution for Ivan.

 

Put the calorifier next to the bathroom. 

 

 

 

 

 

[jetzi]

28 minutes ago, Tony Brooks said:

solar water heating is far from conventional on a boat and as  far as that is concerned do you intend to use solar for just hot water, space heating, or both?

A couple of people on this forum ( @peterboat is one I think) have suggested diverting excess power from your solar in summer to the immersion heater. This is only for heating water in summer, and you might still need a second source of hot water. I can't see solar ever being useful for space heating, because when the sun is shining bright enough to heat the boat, you wouldn't need heating right! This would be electric only - no circulation. The solar is in fact completely optional and I might not even include it.

47 minutes ago, Tony Brooks said:

the stove only space heating via the air but I can see no reason why a stove and Eberspacher can't both use the same calorifier coil providing you fit sufficient bleed points at any air traps.

I have two stoves now, one right at the front of my 65' boat in the saloon and one right at the back in a 10 cubic metre office (yet to be installed). I got the second stove because the first stove does not sufficiently heat the rear office and I found the Eberspaecher to be similarly ineffective.

 

The stove at the back is right next to the calorifier so I thought it would be nice if I could heat water and transfer the heat around the boat a bit.

 

52 minutes ago, Tony Brooks said:

If you ensure at least one calorifier coil has a decent bore then the stove could circulate by gravity, especially if its the top coil of a vertical calorifier.

Would you then have the stove the only thing on that top coil?

 

54 minutes ago, Tony Brooks said:

The  Eberspacher is pumped so both should co-exist as long as you turned the Eberspacher off before it potentially overheated from the stove and cut out.

I'm unsure about this - are you saying to have the stove and Eberspaecher on the same circuit? Would they share a coil (i.e. Eber and stove in parallel) or share a circuit (i.e. in series)?

 

56 minutes ago, Tony Brooks said:

Anything is possible but as electricity is often the thing boats are most short of I would have thought that minimising the number of pumps running for long periods was of some importance.

Yes I definitely would rather not have any pumps at all, but I'm also being realistic with my expectations when it comes to how well a DIY gravity circulation would work, especially if it gets cold and we want to circulate the water a lot faster - I'd like to be able to circulate with a pump if I wanted to.

 

58 minutes ago, Tony Brooks said:

Forget solar hot water and it all becomes a lot simpler. If you do go Lithium batteries then once they are well enough charged why not switch the solar electricity to a 12V immersion heater. That way you get space for an extra solar galvanic panel.

Yes forget solar hot water. I only meant to use a 12V immersion heater as an excess load dump for any excess solar electricity. But this can be left off entirely - it will only be useful in summer and I will usually have enough hot water then anyway.

[jetzi]

48 minutes ago, Chewbacka said:

Agree.  Earlier Ivan suggested using finrads to avoid steel rads, whilst that gets rid of the steel, it does have another problem.  To heat a boat in cold weather and to avoid excessive diesel boiler cycling you need to ideally have a ‘load’ that is the same as the boiler output, guessing about 4kW.  I seem to remember they are 300w per meter, so you would need say 10m or so.  Just something to think about.

Thanks - yes good to keep in mind that you want to match the heat output to the heat input.

 

49 minutes ago, Chewbacka said:

I concluded that in summer we move most days we are on the boat, so engine heats hot water, on the days we don’t move I can use the diesel boiler and solar electric to run the system.  So, for us, there was no justification for the cost of a solar water heater

Agreed - it's more of a place to dump excess solar energy than anything else. The cost of adding immersion heater to an already eyewateringly expensive calorifier is not really significant. I may well just add it to the spec and not plug it in.

 

28 minutes ago, Mike the Boilerman said:

Rather like the trope about the Americans spending $millions on a Biro that will write in a gravity-free environment for their space missions, whilst the Russians used a pencil, there is an equally simple solution for Ivan.

 

Put the calorifier next to the bathroom.

The bit that I'm not articulating well is that there are TWO problems - space heating and water heating.

[Tony Brooks]

4 minutes ago, ivan&alice said:

A couple of people on this forum ( @peterboat is one I think) have suggested diverting excess power from your solar in summer to the immersion heater. This is only for heating water in summer, and you might still need a second source of hot water. I can't see solar ever being useful for space heating, because when the sun is shining bright enough to heat the boat, you wouldn't need heating right! This would be electric only - no circulation. The solar is in fact completely optional and I might not even include it.

I have two stoves now, one right at the front of my 65' boat in the saloon and one right at the back in a 10 cubic metre office (yet to be installed). I got the second stove because the first stove does not sufficiently heat the rear office and I found the Eberspaecher to be similarly ineffective.

 

The stove at the back is right next to the calorifier so I thought it would be nice if I could heat water and transfer the heat around the boat a bit.

 

Would you then have the stove the only thing on that top coil?

 

I'm unsure about this - are you saying to have the stove and Eberspaecher on the same circuit? Would they share a coil (i.e. Eber and stove in parallel) or share a circuit (i.e. in series)?

 

Yes I definitely would rather not have any pumps at all, but I'm also being realistic with my expectations when it comes to how well a DIY gravity circulation would work, especially if it gets cold and we want to circulate the water a lot faster - I'd like to be able to circulate with a pump if I wanted to.

 

Yes forget solar hot water. I only meant to use a 12V immersion heater as an excess load dump for any excess solar electricity. But this can be left off entirely - it will only be useful in summer and I will usually have enough hot water then anyway.

 

1. The Eber and stove could share the same coil as long as you ensure the stove never causes the Eber overheat cut out to function. You would also tend to loose Eber heat up the chimney when the stove is not running. I would fit them in paralleled because with series you WOULD loose heat up the chimney when the stove is not alight.

 

2. Having the stove at the front of the boat makes gravity circulation at under gunwale height potentially a bit more problematic depending upon how far bow up the boat sits but I can see no reason a gravity system will not work well as long as you observe levels. I would fit a gravity system to the top calorifier coil if the calorifier is higher than the stove and on my gravity circulated gas boiler the 22mm top coil worked will but it did have 28mm pipes feeding it, as should the rest of a gravity system. I would use the stove at the back for heating the radiators and calorifier.

 

3. I don't understand the but about having to circulate water faster when it gets cold. You need to put more heat into the water and basically as the ambient temperature drops a gravity system will circulate faster at any given heat input. Its simply not an issue give proper pipe runs. The greater the difference between the outlet and return temperature the faster a gravity system will circulate but it will never get so fast the water does not have enough time in the boiler to heat up enough - unlike some pumped stove systems.

[Chewbacka]

1 minute ago, Tony Brooks said:

 

1. The Eber and stove could share the same coil as long as you ensure the stove never causes the Eber overheat cut out to function. You would also tend to loose Eber heat up the chimney when the stove is not running. I would fit them in paralleled because with series you WOULD loose heat up the chimney when the stove is not alight.

 

 

It might be worth asking Eber as on a vehicle the hot engine coolant passes through the Eber when the engine is running, though your stove may run hotter than spec, so I would ask them what the limit is and what happens if you exceed it. Mounting them in parallel will need to ensure careful balancing, otherwise the water may not split 50/50 and cause one or other to over heat.  Better to keep it simple......

[MtB]

7 minutes ago, ivan&alice said:

The bit that I'm not articulating well is that there are TWO problems - space heating and water heating.

 

Well I've fixed one of them for you with a beautifully elegant solution, haven't I !

[jetzi]

3 minutes ago, Tony Brooks said:

Having the stove at the front of the boat makes gravity circulation at under gunwale height potentially a bit more problematic depending upon how far bow up the boat sits

The stove at the front doesn't have a backboiler. The stove with the backboiler will be mounted directly underneath the calorifier.

 

6 minutes ago, Tony Brooks said:

1. The Eber and stove could share the same coil as long as you ensure the stove never causes the Eber overheat cut out to function. You would also tend to loose Eber heat up the chimney when the stove is not running. I would fit them in paralleled because with series you WOULD loose heat up the chimney when the stove is not alight.

This seems like good news because it would mean that I wouldn't need to pay for a third coil.

 

3 minutes ago, Tony Brooks said:

3. I don't understand the but about having to circulate water faster when it gets cold. You need to put more heat into the water and basically as the ambient temperature drops a gravity system will circulate faster at any given heat input. Its simply not an issue give proper pipe runs. The greater the difference between the outlet and return temperature the faster a gravity system will circulate but it will never get so fast the water does not have enough time in the boiler to heat up enough - unlike some pumped stove systems.

This sounds quite promising then - it sounds like you are quite confident that the gravity system will work?

 

I figured that circulating the water faster would cause a higher output from the rads, which you would want when it was cold, but that might be incorrect?

2 minutes ago, Chewbacka said:

It might be worth asking Eber as on a vehicle the hot engine coolant passes through the Eber when the engine is running, though your stove may run hotter than spec, so I would ask them what the limit is and what happens if you exceed it. Mounting them in parallel will need to ensure careful balancing, otherwise the water may not split 50/50 and cause one or other to over heat.  Better to keep it simple......

Simple as in rather use two coils?

 

Just now, Mike the Boilerman said:

 

Well I've fixed one of them for you with a beautifully elegant solution, haven't I !

Yes indeed! The calorifier is only a few metres away from the bathroom, so it's not as much of a problem as I'm making out. My solution may not be conventional, but provided it works (which I'm not at all certain it will), it certainly seems elegant and simple to me since it only has one pipe run.

[Tony Brooks]

7 minutes ago, Chewbacka said:

It might be worth asking Eber as on a vehicle the hot engine coolant passes through the Eber when the engine is running, though your stove may run hotter than spec, so I would ask them what the limit is and what happens if you exceed it. Mounting them in parallel will need to ensure careful balancing, otherwise the water may not split 50/50 and cause one or other to over heat.  Better to keep it simple......

The way I see it the only reason the have both an Eber and stove is to get a fast warm up while the stove gets going so as long as the Eber is shut down once the stove is alight I can't see a problem with a parallel system. Also as the Eber is pumped then the Eberr output pipe could be lead low and then up to where it joins the stoves gravity system. This should prevent the chances of the stove gravity circulating through the Eber.

Edited November 20, 2019 by Tony Brooks

[jetzi]

I've updated the diagram to clarify some of the points, showing that the whole hot water system is only copper and plastic. Since most fresh water systems are copper I can't believe that this would be an issue for corrosion.

 

The three coils in the calorifier are completely independent, though I'm not sure what metals are inside the heat sources - the backboiler is stainless steel and the Eberspaecher may have an aluminium heat exchanger. I presume the engine is steel. However all three of these circuits would of course have corrosion inhibitors inside them.

 

Forget solar - it is only an optional immersion heating element inside the calorifier.

 

[Tony Brooks]

6 minutes ago, ivan&alice said:

The stove at the front doesn't have a backboiler. The stove with the backboiler will be mounted directly underneath the calorifier.

 

This seems like good news because it would mean that I wouldn't need to pay for a third coil.

 

This sounds quite promising then - it sounds like you are quite confident that the gravity system will work?

 

I figured that circulating the water faster would cause a higher output from the rads, which you would want when it was cold, but that might be incorrect?

With Gravity it all depends on relative heights so as long as the calorifier coil is a bit higher than the stove outlet then you should get circulation providing you have the pipes large enough. I think my top coil was only a couple of inches or so above the boiler outlet and it was next to the calorifier.

 

I think the circulation speed thing is incorrect. When its cold you need to put more heat into the water, if you do not the radiators will simply run cooler so you need to think about the back boiler output. In fact if you circulate too fast (which a gravity system can not)  the water will not be in the boiler long enough to absorb sufficient heat so the rads do not get as hot as they may with slower circulation. However a correctly installed gravity circulation will sort all that out for you automatically. Too low an output back boiler or too low a fire and the radiators will simply not get as warm.

 

If you do go for two heat  sources into one coil just make sure the expansion tank is large enough.

 

Also if this is to be a new install don't skimp on bleed points at all points at high level. I would suggest at the top pie at the extreme front of the boat, at the top of the up pipe from the boiler unless there is a vent pipe to the expansion tank there and at the top coil inlet on the calorifier.

 

Also install a valve so you can isolate the Eber for the radiators yet use it to heat the domestic water. You may never use it but its  a backup in case of summer engine failure.

 

[jetzi]

10 minutes ago, Tony Brooks said:

With Gravity it all depends on relative heights so as long as the calorifier coil is a bit higher than the stove outlet then you should get circulation providing you have the pipes large enough. I think my top coil was only a couple of inches or so above the boiler outlet and it was next to the calorifier.

Is higher better? I would like to mount the stove as low as possible and the calorifier as high as possible (for layout and practical reasons). It is a new install yes so I can use whatever pipes make sense. 28mm for both the coils and the pipe runs?

 

My main concern with the gravity system is that I will need very long pipe runs as I'm thinking of getting the length required by making S bends in the pipework for the rads. I realise that this could resist the flow of the water though. However, given that the rads job is to lose heat, perhaps this will provide the motive force to move the water around?

 

14 minutes ago, Tony Brooks said:

I think the circulation speed thing is incorrect. When its cold you need to put more heat into the water, if you do not the radiators will simply run cooler so you need to think about the back boiler output. In fact if you circulate too fast (which a gravity system can not)  the water will not be in the boiler long enough to absorb sufficient heat so the rads do not get as hot as they may with slower circulation. However a correctly installed gravity circulation will sort all that out for you automatically. Too low an output back boiler or too low a fire and the radiators will simply not get as warm.

This sounds really appealing. The hotter the gravity system, the faster the water circulates and thus the slower it heats - so it is self-limiting.

 

I guess I am just not confident that a self-designed gravity system will work well. But perhaps I need to have more faith? If it does work well I wouldn't need a motor at all.

 

16 minutes ago, Tony Brooks said:

If you do go for two heat  sources into one coil just make sure the expansion tank is large enough.

Is the expansion tank on the coil circuit? I have imagined it on the fresh hot water circuit. Or do you need one on each?

 

17 minutes ago, Tony Brooks said:

Also if this is to be a new install don't skimp on bleed points at all points at high level. I would suggest at the top pie at the extreme front of the boat, at the top of the up pipe from the boiler unless there is a vent pipe to the expansion tank there and at the top coil inlet on the calorifier.

 

Also install a valve so you can isolate the Eber for the radiators yet use it to heat the domestic water. You may never use it but its  a backup in case of summer engine failure.

Good advice, thank you! It is a new build yes. I will make sure that I put in plenty of bleed points and isolation valves. A lot of the reasoning behind all this is to create as much redundancy as possible.

[Tony Brooks]

51 minutes ago, ivan&alice said:

I've updated the diagram to clarify some of the points, showing that the whole hot water system is only copper and plastic. Since most fresh water systems are copper I can't believe that this would be an issue for corrosion.

 

The three coils in the calorifier are completely independent, though I'm not sure what metals are inside the heat sources - the backboiler is stainless steel and the Eberspaecher may have an aluminium heat exchanger. I presume the engine is steel. However all three of these circuits would of course have corrosion inhibitors inside them.

 

Forget solar - it is only an optional immersion heating element inside the calorifier.

 

 

That diagram still makes no sense.

 

The water inside the calorifically (not the coils) is for domestic (tap) use only and conventionally does not go anywhere near the central heating system

 

The Eber and back boiler input conventionally would have the radiator in parallel with them so the boiler and/or the Eber can heat both the rads and hot domestic water. It is basically two separate circuits:-

 

1. Domestic hot water provided bu the body of the calorifier that is heated by one or more coils. There is no connection between the coil water and domestic water bar heat transfer through pipe walls.

 

2. Sources to heat the domestic water in the calorifier via a coil or coils in the calorifier with  the calorifier coil appearing to whatever heat source as just another heat sink or in other words a radiator. These heat sources will require some form of header or expansion tank but its different to the one of the domestic hot water.

 

Here is a diagram for domestic hot water showing the coils from other heat sources.

 

 

 

I will now see if I have a diagram for a stove heated central heating and will add later if I find one.

 

Here it is but be aware there are options so is not definitive

 

 

You see two totally separate systems but all using a calorifier in one way of another.

Edited November 20, 2019 by Tony Brooks

[Tacet]

The domestic (hot) water and the (hot) water circulating through the radiators, boilers etc need to be separate.  Apart from the corrosion issues in the various heating-side fittings caused by fresh, oxygenated water passing through,  the hot water at the taps is liable to be errr.... not hot.....as it will be cooled by passing through the rads, even if it next passes through the heat boiler/eberspacher just before arriving at the taps.  If/when everything is running flat out, it may be OK, but not when ticking-over. I suppose you could try to prevent over-circulation by putting a engine-type thermostat or other control to keep the water hot at the taps.  But basically, much better to keep the circuits separate.

 

If you wish to avoid wasting (cold) water in running the taps until the water hot water arrives from the cylinder, a circulatory system on the domestic side will work.  Personally, I would see the complexities and down-sides as too great to be worth it.  Obviously you will need to double up pipe runs and provide a pump.   The heat losses from the pipe runs will warm the boat - which may be fine, but unless you have a heat source working, you will soon cool the whole domestic system and have no hot water the taps.  So the pump would need to be controlled somehow for times when you are tied up, with a nice hot cylinder of water but no need for space heating.

 

I can't really see why bronze fittings etc would be any more necessary on a circulated system.  It is true that the fresh water will be oxygenated and without inhibitors (unlike  the heating side) - but it is not so very different from the usual system where cold water is pumped.  Yes - there will be a constant flow and yes - it will be hot water too.  But you will not be introducing more oxygen, in fact it will be less.

 

 

 

 

[nb Innisfree]

2 hours ago, Mike the Boilerman said:

Rather like the trope about the Americans spending $millions on a Biro that will write in a gravity-free environment for their space missions, whilst the Russians used a pencil, there is an equally simple solution for Ivan.

 

Put the calorifier next to the bathroom. 

 

 

 

 

 

Urban myth, there never was a need for a special ballpoint pen as they work OK in zero g. 

[nb Innisfree]

15 hours ago, ivan&alice said:

No, I'm talking about recirculation. Basically instead of having a pipe that comes out of your hot water cylinder and ends in a tap, you have a circuit that leaves the top of the cylinder, circuits around the house and then rejoins at the bottom of the cylinder. Taps are then spurs off of this circuit.

 

Sometimes this is achieved with a pump, but it can also be done with gravity, by insulating the top pipes and not insulating the return pipes. This does cost a bit of heat. The water doesn't have to move very fast for this to work.

 

Hotels often used to recirculate DHW and used a bronze version of a CH pump, perhaps they are still available, could be activated for a few seconds prior to turning hot tap on? 

Edited November 20, 2019 by nb Innisfree

[cuthound]

6 hours ago, Boater Sam said:

Pray tell me where you will buy a bronze 12v DC pump from?

 

Years ago there were copper radiators/towel rails made for use on direct hot water systems when back boilers were common. The back boilers were also copper or glass lined cast iron and they still corroded eventually Hot water full of fresh oxygen in a mixed metal system will cause galvanic corrosion like you would not believe possible.

 

And whenever you fill up in a hard water area, the hot water will deposit limescale so the heating will get less and less effective as the pipes scale up.

[jetzi]

3 hours ago, Tony Brooks said:

The water inside the calorifically (not the coils) is for domestic (tap) use only and conventionally does not go anywhere near the central heating system

Yes, I'm aware that this is a break in convention. I'm questioning why they need to be separate? If they are together it's half as many pipes and it means hot water recirculates for free.

 

The first diagram is pretty much how my old system worked before it died, except the coil B for the central heating also includes an Eberspaecher.

 

I don't understand the second diagram around where the stove is. It looks like there are three pipes out of the back boiler? Which way does the water flow in those pipes?

Here is a diagram for what I (think) is the conventional way of installing three heat sources - please correct me if I'm wrong? The green pipe would be if I wanted to install a hot water recirculation system (which I don't think I would bother with if I was going to do this the conventional way).

 

 

2 hours ago, Tacet said:

 the hot water at the taps is liable to be errr.... not hot.....as it will be cooled by passing through the rads

No, if you refer to the original diagram, the water from the rad outlets doesn't up in the tap, but in the bottom of the calorifier. They are on the same circuit, but the water in the tap is directly from the top of the calorifier so is just as hot as in a "conventional" system.

 

8 minutes ago, cuthound said:

And whenever you fill up in a hard water area, the hot water will deposit limescale so the heating will get less and less effective as the pipes scale up.

I think this is a fair point. Doesn't it take a really long time for normal hot tap pipes to scale up? The same water will be circulating most of the time, it only gets replaced when the hot tap is run. It's not like it's a constant stream of fresh water. But yes, point about scale is noted.

 

3 hours ago, ivan&alice said:

Is higher better? I would like to mount the stove as low as possible and the calorifier as high as possible (for layout and practical reasons). It is a new install yes so I can use whatever pipes make sense. 28mm for both the coils and the pipe runs?

 

My main concern with the gravity system is that I will need very long pipe runs as I'm thinking of getting the length required by making S bends in the pipework for the rads. I realise that this could resist the flow of the water though. However, given that the rads job is to lose heat, perhaps this will provide the motive force to move the water around?

I don't think anyone saw the above question, and this is relevant to both a conventional gravity system and my wacky idea, so I'd really like some advice on this!

[MtB]

6 minutes ago, ivan&alice said:

I don't think anyone saw the above question, and this is relevant to both a conventional gravity system and my wacky idea, so I'd really like some advice on this!

 

The motive force for 'gravity' circulation comes from the fact that hot water is less dense than cool water so the cool water is attracted by gravity more towards the bottom of the circuit than the hot water in that circuit. So the motive force is a function of the dt in the system, not the length of the pipe runs. The flow rate around the circuit driven by this tiny motive force is roughly inversely proportional to the circuit 'effective length', and roughly proportional to the size of pipes used. 

 

 

[stegra]

Your second diagram still includes an nvr. The only type of nvr that might work in a gravity circuit is a clack valve positioned horizontally. Your third diagram includes a tap above the radiators; I assume this was an oversight. 

 

A back boiler on solid fuel stove needs extra precautions in case of boiling as the heat can't be switched off. Normally there is a dedicated radiator to act as a heat sink on a purely gravity circuit. If the calorifier circuit is pumped then an injector tee might be used to direct the flow away from the heat sink except when overheating. It seems your plan is for the calorifier circuit to be gravity and for the radiators/taps to be gravity. This is a slow way of moving the heat if the calorifier gets too hot. There are thermally controlled devices that allow cold water into the system in case of overheating but I think they require 240v.

[Tony Brooks]

13 minutes ago, stegra said:

Your second diagram still includes an nvr. The only type of nvr that might work in a gravity circuit is a clack valve positioned horizontally. Your third diagram includes a tap above the radiators; I assume this was an oversight. 

 

A back boiler on solid fuel stove needs extra precautions in case of boiling as the heat can't be switched off. Normally there is a dedicated radiator to act as a heat sink on a purely gravity circuit. If the calorifier circuit is pumped then an injector tee might be used to direct the flow away from the heat sink except when overheating. It seems your plan is for the calorifier circuit to be gravity and for the radiators/taps to be gravity. This is a slow way of moving the heat if the calorifier gets too hot. There are thermally controlled devices that allow cold water into the system in case of overheating but I think they require 240v.

Why should the calorifier get too hot? It can't get any hotter then the heat source. If the stove boiled there would be panic stations to get the stove out, the noise alone would be enough to ensure it. I can't see even a boiling stove causing the calorifier to boil, especially as that is a pressurised system with a consequentially higher boiling point. An over-hot calorifer is normally dealt with by a thermostatic mixing valve on the outlet side.

 

My gravity system was not particularly slow at moving heat about once the heat source was up to temperature.

 

The NRV is shown in the pressure fed part of the system so the pump will ensure it opens , just as it does an all the other domestic water systems on boats. The green (gravity circulated) pipe rejoins the system after the NRV. It is still in my view an idiot concept.

 

 

[David Mack]

1 hour ago, ivan&alice said:

 

Here is a diagram for what I (think) is the conventional way of installing three heat sources - please correct me if I'm wrong?

 

 

You have the calorifier coil and radiators in series.  That means that the radiators won't get warm until the calorifier is well on its way to working temperature. And also you can't heat water from the eberspacher or back bolier without also eventually heating the radiators. Put the calorifier coil in parallel with the rads with control valves and you can have independent control of water and space heating.

[WotEver]

6 hours ago, nb Innisfree said:

Urban myth, there never was a need for a special ballpoint pen as they work OK in zero g. 

Equally incorrect. 
 

https://www.scientificamerican.com/article/fact-or-fiction-nasa-spen/