Will this work?

[thelonious]

Hi,

 

Can I pick the brains of the boat building folks here?

 

I've been trying to decide the best way to set up the heating & hot water systems for my new boat.

 

The tricky bit is trying to effectively connect three heat sources (engine, diesel heater and back boiler) so they heat both the hot water and the radiators.

 

The solution I have come up with uses a well-insulated twin-coil cylinder both as a source of hot water and as a heat exchanger. Something like the 'thermal store' approach you see with solar set-ups.

 

You can see my proposed set up here: Proposed heating setup (PDF)

 

It LOOKS like a quite elegant solution, but it may have a major flaw! A virtual pint to anyone who can spot one.

 

One potential problem that I have already noticed is that running the engine and the stove at the same time could actually heat up the water exiting the engine, putting more strain on the skin tank. But only if the water in the cylinder is hotter than the water leaving the engine, which is unlikely I think.

 

Thanks,

 

Theo

[David Schweizer]

I have a twin source heating system on my boat using a single coil calorifier, this means that the engine, gas boiler, and radiators all use the same water. To prevent the water from the boiler heating the engine there is a non-return valve in the flow pipe from the engine to the calorifier, it has been ther 25 years and still does it's job. Of course if the engine and bolier are on at the same time, the boiler's thermostat turns the gas off if the engine water heat exceeds that of the boiler.

 

Not quite the same as you are proposing, but non return valves do work and are quite commonplace in boat heating systems.

Edited December 8, 2007 by David Schweizer

[chris w]

Theo

 

Your diesel heater will probably need a larger heatsink than just the calorifier or it will shut down very quickly. You may need to put the towel rail, at least, directly connected to the diesel heater. (What make is the heater by the way?)

 

Chris

Edited December 8, 2007 by chris w

[Yoda]

Theo, I can see a few problems with your system.

 

Looking at the pdf it appears that the back boiler will be heated by the engine or the diesel heater due to the heat exchanger being coupled to both. Effectivly your system would have to heat all you system first. There is no way to heat the rads from the engine or diesel heater, directly. They should be your heatsink.

 

I will look again in the morning.

[dacaB]

As I currently understand it your circulation pump will need to run whenever the SF is alight, will you be able to cope with that power drain.

 

Until we are shot down in flames, our plan is to keep things simple/conventional.

 

Engine heats bathroom rad and calorifier. Diesel heater, 4 rads and calorifier. SF seperate. If the SF is central even better.

[thelonious]

Thanks for your helpful replies everyone, I like this forum!

 

TheoYour diesel heater will probably need a larger heatsink than just the calorifier or it will shut down very quickly. You may need to put the towel rail, at least, directly connected to the diesel heater. (What make is the heater by the way?)Chris

 

Hi Chris,

 

If the manual heating switch is turned off, then yes, the diesel heater will quickly heat the cylinder then shut down. This is intentional and allows you to get hot water quickly in the summer when you fancy a shower.

 

But if the heating switch is on, once the cylinder gets hot the the circulation pump on the rad circuit will kick in and start to take heat away from the cylinder to the radiators. Hopefully, it will do this fast enough to keep the diesel boiler alight. Most diesel heaters seem to have an automatic high and low setting, but I have to confess I'm not sure if they will switch off entirely once a certain temperature is reached. Anyone know?

 

I haven't chosen a heater yet, but the Webasco ones seem significantly cheaper than the Eberspacers. Anyone know if they are equally good?

 

Theo

 

As I currently understand it your circulation pump will need to run whenever the SF is alight, will you be able to cope with that power drain. Until we are shot down in flames, our plan is to keep things simple/conventional.Engine heats bathroom rad and calorifier. Diesel heater, 4 rads and calorifier. SF seperate. If the SF is central even better.

 

Yes that's true, the pump will have to run whenever the stove is hot enough to prevent boiling. There are some nice 'magnetic' 12V circulation pumps out there that consume as little as 11W which should be fine. I'm planning to have around 200W of solar panels connected to the battery bank.

 

As far as I know, a pump is the only option for back boilers if you are not using a 'gravity' circuit - probably not feasible due to the length required. And I don't like the large amount of high-flow pipework that would need to be on show.

 

I take your point about complexity though, it may well be overcomplicated. But I do find that the solid fuel burner usually produces far more heat than you actually need, so connecting it to the hot water system is very attractive. In an insulated cylinder, the water should stay hot overnight for the morning shower.

 

Theo, I can see a few problems with your system.Looking at the pdf it appears that the back boiler will be heated by the engine or the diesel heater due to the heat exchanger being coupled to both. Effectivly your system would have to heat all you system first. There is no way to heat the rads from the engine or diesel heater, directly. They should be your heatsink. I will look again in the morning.

 

Yes, indeed it will! But I think this is OK - the back boiler should just function as another radiator on the system.

 

It looks like a lack of heat capacity in the engine/diesel boiler circuit might be a problem. It doesn't matter for the engine, as the skin tank will take the excess heat. But the diesel heater might be unhappy just with the cylinder coil when in 'summer' mode (see above).

 

Theo

 

Keep them coming!

Edited December 8, 2007 by thelonious

[smileypete]

It LOOKS like a quite elegant solution, but it may have a major flaw! A virtual pint to anyone who can spot one.

 

Maybe a better way to approach it would be 'What do people have already which works for them, and how? What are the benefits and disadvantages of these existing systems'

 

cheers,

Pete.

[thelonious]

Maybe a better way to approach it would be 'What do people have already which works for them, and how? What are the benefits and disadvantages of these existing systems'

 

cheers,

Pete.

 

I've got a pretty good idea of the way narrowboat heating systems are normally set up, but I haven't seen any that can heat either just the water (summer) or the water and the radiators (winter) from any one of their heat sources. This would mean no gas boiler needed for hot water - that's what I'm aiming at.

 

If it won't work that's fine, I can go to a more tried and tested set up, but there's no harm in trying.

 

Theo

[blackrose]

Theo

 

Your diesel heater will probably need a larger heatsink than just the calorifier or it will shut down very quickly. You may need to put the towel rail, at least, directly connected to the diesel heater. (What make is the heater by the way?)

 

Chris

 

Yes, also if you switch on the diesel heater, your indirect system via the calorifier means it could take quite a while for the rads to get hot (assuming the stove isn't alight), because you have to heat the whole cylinder before the rads will warm up.

 

Personally, I only really use my diesel heater as my secondary cabin heating source. I usually switch it on for an hour as soon as I come back to a cold boat and the rads get hot in about 10 mins while I'm making a fire & waiting for the stove to heat up. With your indirect system you wouldn't be able to do this because your stove would probably heat the rads before your diesel heater does. So although you'll get hot water fairly quickly, your system doesn't allow you to heat the boat quickly which in my opinion is more important.

 

Perhaps I'm just basing my opinion on my big 10kw solid fuel stove which takes quite a long time to get hot - I know smaller stoves like Squirrels heat up much quicker.

 

Nice diagram by the way!

Edited December 8, 2007 by blackrose

[thelonious]

Yes - good point!

 

The cylinder would need to be small enough to heat up fast, but still big enough for a shower.

 

From experience, showers seem to use 25-30 litres a go. Though at about 40C, quite a lot would be coming from the cold supply.

 

For the sake of argument, say I had a 30 litre cylinder. To get it from stone cold (~10C) to hot enough for the rads (~60C) with a 4kW heater would take (60-10)*30*4200 / 4000 = 1575 seconds, or nearly half an hour. Damn.

 

Though as I live aboard, it would rarely be starting from stone cold.

 

Hmmm, needs more thought.

 

Just to liven things up, has anyone thought about or tried evacuated-tube solar water heating? Eco-nomical for example do them amazingly cheaply.

 

I've done several installations on houses, but never seen one on a boat before!

[NB Alnwick]

I can see lots of advantages in connecting all heat sources together. One especially is that in the depths of Winter, if the engine can be heated from the back boiler it will certainly protect it from frost and make starting much easier - by warming the engine prior to running you will also save fuel and reduce cylinder wear . . .

[chris w]

From experience, showers seem to use 25-30 litres a go. Though at about 40C, quite a lot would be coming from the cold supply.

 

For the sake of argument, say I had a 30 litre cylinder. To get it from stone cold (~10C) to hot enough for the rads (~60C) with a 4kW heater would take (60-10)*30*4200 / 4000 = 1575 seconds, or nearly half an hour. Damn.

 

Theo

 

You're also forgetting two other parameters in your calculations.

 

1. It's the heat output of the coil NOT the boiler that you should be using in your calculations. This may only be a KW or so not 4KW. It is linked to the rate of water flow through the coil and, thereby, the temperature drop across the coil.

 

2. You are assuming 100% efficiency and the actual efficiency will be probably 20-25% below the ideal.

 

Ergo, your times will be much extended from your calculation.

 

Chris

[smileypete]

I've got a pretty good idea of the way narrowboat heating systems are normally set up, but I haven't seen any that can heat either just the water (summer) or the water and the radiators (winter) from any one of their heat sources. This would mean no gas boiler needed for hot water - that's what I'm aiming at.

 

If it won't work that's fine, I can go to a more tried and tested set up, but there's no harm in trying.

 

I'd try to set it up so

 

The engine, OR the diesel heater, OR the back boiler

 

can directly heat...

 

The radiators AND/OR the calorifier.

 

 

This would need...

 

Appropriate non return valves for the 3 heat sources, probably swing check valves.

 

A 3 port valve or equivalent for the heat destination, probably a 3 way 'T' port ball valve.

 

 

Bear in mind that 12v circulation pumps can't cope at all well with airlocks, so the system should ideally be self bleeding of air.

 

Also ball valves to isolate the different heat sources/sinks without needing to drain the whole system.

 

 

Edit:

 

Another thing well worth having is for the back boiler to heat the radiators through convection, so you don't NEED 12v to have the stove going.

 

Edit2:

 

I could post a little sketch later if that's any help.

 

cheers,

Pete.

Edited December 8, 2007 by smileypete

[Yoda]

Lots of very good advice on this subject.

 

One thing that concerns me is that water for shower etc does not need to be heated above 45 degrees C and there are mineral problems when you heat the water up too much. On the radiator side, the water wants to be around 90 degrees C and the difference is not possible with your system.

[chris w]

But you don't want 60 litres of 45degC water in a calorifier for showers and washing-up etc. You want to heat the water up as high as is practicable and then dilute say 50/50 with cold water to give you, effectively, 120litres of shower and washing water.

 

Chris

Edited December 8, 2007 by chris w

[thelonious]

But you don't want 60 litres of 45degC water in a calorifier for showers and washing-up etc. You want to heat the water up as high as is practicable and then dilute say 50/50 with cold water to give you, effectively, 120litres of shower and washing water.Chris

 

Chris - I think you've found the achillies heel.

 

If the transfer of heat between the coils and the hot water is not efficient, it's not going to work at all. 1kw is not enough to keep the diesel heater even turned on, and the efficiency will drop even more as the water in the cylinder gets hotter.

 

Looks like the only sensible approach is to put the cylinder and the rads in series in order to make best use of the heat source.Here is another design: Heating Design 2

 

This is simpler, in that there is only one pump, one circuit and a single coil cylinder.The engine and the diesel heater will heat the radiators before the cylinder, and the back boiler will do the opposite. This is all fine.

 

However, there's no way to prevent the back boiler getting heated by the engine or diesel heater. It's not safe to fit a cut-off valve in case someone lights the fire with the valve shut - big bang or at least lots of steam! On the plus side this will act as the required heat sink, but in the height of summer when I just want hot water it will be a pain.

 

There is the possibility of fitting a solar heating circuit to the second coil for summer use, which could be done at a later date.

 

Thanks for all the great feedback.

 

Theo

 

Lots of very good advice on this subject.One thing that concerns me is that water for shower etc does not need to be heated above 45 degrees C and there are mineral problems when you heat the water up too much. On the radiator side, the water wants to be around 90 degrees C and the difference is not possible with your system.

 

I was thinking of fitting a thermostatic mixer where the hot water leaves the cylinder to regulate the maximum temperature of the hot water to the taps down to 40 or so. I just left it off the drawing because it was getting messy.

 

This does not solve the mineral issue though. Very hard water around here too.

 

Theo

Edited December 8, 2007 by thelonious

[thelonious]

Another thing well worth having is for the back boiler to heat the radiators through convection, so you don't NEED 12v to have the stove going.

 

I could post a little sketch later if that's any help.

 

cheers,

Pete.

 

Hi Pete,

 

A convection circuit certainly has its attractions - simplicity and no electricity required.

 

But there are problems with having a calorifier on the same circuit. It might drain all the heat out of the cylinder when the stove is cold. And if the cylinder is hot, it might not circulate at all. I don't think it would have the 'go' to push open an non return valve either.

 

Plus you need massive pipes, which are hard to conceal, they seem tricky to set up, and the length of the boat (60') might be a problem. I'm not sure whether you could set up a secondary heat source to heat the rads.

 

This is becoming one of those open-source design projects I keep hearing about!

 

Theo

[Yoda]

I would definately have a solar heater in circuit to raise the base level of heating required. On a lot of days it will give you all the hot water you need.

[blackrose]

I would definately have a solar heater in circuit to raise the base level of heating required. On a lot of days it will give you all the hot water you need.

 

Do you have any info on these please - e.g. models and how they are fitted?

[smileypete]

Hi Pete,

 

A convection circuit certainly has its attractions - simplicity and no electricity required.

 

But there are problems with having a calorifier on the same circuit. It might drain all the heat out of the cylinder when the stove is cold. And if the cylinder is hot, it might not circulate at all. I don't think it would have the 'go' to push open an non return valve either.

 

Plus you need massive pipes, which are hard to conceal, they seem tricky to set up, and the length of the boat (60') might be a problem. I'm not sure whether you could set up a secondary heat source to heat the rads.

 

This is becoming one of those open-source design projects I keep hearing about!

Hi,

 

Have thought about this a bit this afternoon .

 

What I'd ideally have is a big radiator(s) in the saloon fed from the back boiler by convection, using massive pipes.

 

Then I'd have a pumped circuit that taps in to the pipes right next to/across the back boiler. This circuit would feed the other rads and/or the calorifier with normal sized pipes.

 

The above means the massive pipes would only need to run a short distance, yet you wouldn't be absolutely dependent on the circulation pump to be able to run the stove.

 

Also the pump need only run when there is a need to heat the other rads/calorifier.

 

By arranging the pipes in the pumped circuit correctly, problems with back convection from the calorifier could be avoided.

 

The pump itself could be controlled by a switch or pipe thermostat, so it stops pumping when the stove starts cooling down.

 

When the pump is running, most of the water will take the path of least resistance though the backboiler, instead of through the big radiator, so most of the heat will be diverted to the other rads/calorifier.

 

If the convection circuit has it's own header tank and can be isolated from the pumped circuit, the stove can still be run when the pumped circuit is being worked on.

 

cheers,

Pete.

[Endeavour]

Hi Pete

 

Just re-reading this interesting thread.

 

Have you finally decided on a configuration? If so, is it too early to say how successfully it works?

[smileypete]

Hi Pete

 

Just re-reading this interesting thread.

 

Have you finally decided on a configuration? If so, is it too early to say how successfully it works?

 

I haven't done this myself but just suggested how I'd go about it.

 

With plumbing I try to make things adaptable as poss using a fairly common range of bits, then buy a few extra bits for doing the more tricky things differently by way of a backup.

 

A read through the catalogues from Screwfix and BES (www.bes.co.uk) give some idea what wierd and wonderful bits can be had, in addition to the boaty plumbing ones.

 

cheers,

Pete.