Is a triple coil calorifier overkill?

[baronbradders]

I have been pondering the heating design for our new boat and am still undecided which route to follow.

 

As far as I can see the main options are:-

 

Diesel boiler i.e. Webasto.

Engine heating

Immersion heater

Solid fuel backboiler.

 

All appear to have their own benefits depending on the situation. (and the associated drawbacks).

 

The boat will be a liveaboard and there will be times when we are cruising but I imagine most of our time will be spent moored up.

 

The ideal for me would to have the engine provide hot water when cruising, the back boiler during the winter, the webasto for convenience during the summer or if needed in the mornings before the fire is stoked and/or if away from a shore supply and the immersion for when hooked up.

 

I have found a website that will supply a triple coil tank for an additional £50+VAT so in theory I could have all the systems installed and pick which ever one is needed at the time.

 

Has anyone tried this and if so do you think it's worthwhile going to the extra expense?

[ChrisPy]

if you have 3 sources of hot water apart from the immersion, it is the logical way to go.

only you can decide if it is worth £50 to dispense with the valves needed to manage the system with one or two coils.

I would go for it.

[blackrose]

I'm in favour of as many independant systems on liveaboard boats as possible within reason. I have hot water from engine & diesel heater to the calorifier, plus an immersion. I'll also have a gas hot water heater as soon as I get around to installing the gas.

 

Bear in mind that thermocycling (the circulation of hot water by convection), works best through large bore pipes, so if you want hot water from your solid fuel stove's backboiler you'll probably need a pump to get it through the narrow coils of the calorifier efficiently. I've heard people on the forum say they've done it without a pump but I've never seen it for myself so I don't know how they did it. My backboiler just feeds a couple of radiators - no pump.

 

The disadvantage of a pumped backboiler system is of course that it constantly draws power from the batteries when the stove gets up to temperature - albeit a small current draw. Some people use thermostats to control the pump and others do it manually with a switch. The other thing is that if the pump malfunctions you can't really light the stove because you don't want static boiling water to overheat and possibly crack your backboiler. So if you do go for a pumped system I would install the pump with a gate valve on either side and I would always have a spare pump onboard, so that when it breaks in the middle of winter it can be easily replaced without draining the whole system.

Edited October 14, 2007 by blackrose

[ChrisPy]

The other thing is that if the pump malfunctions you can't really light the stove because you don't want static boiling water to overheat and possibly crack your backboiler.

Mike, is that a realistic risk? Your back boiler circuit should have pressure relief - mine has a vertical vent pipe directly above the back boiler so any slugs of steam that may be generated go straight out the roof.

[blackrose]

Mike, is that a realistic risk? Your back boiler circuit should have pressure relief - mine has a vertical vent pipe directly above the back boiler so any slugs of steam that may be generated go straight out the roof.

 

I don't know, perhaps I was wrong. Nevertheless, I still think it's a good idea to have a gate valve either side of the pump, just for ease of changing it.

 

Mine is an open system with a header tank Ting off from the highest point about 2m from the backboiler, but I've got 28mm pipes coming out of the backboiler and continuing on the main runs, so the hot water is always going to circulate on it's own. What happens if a pumped system is using 15mm pipes (or even smaller if feeding a calorifier) and the pump breaks? Is it still ok to keep the fire going if the hot water can't circulate and radiate that heat?

Edited October 14, 2007 by blackrose

[pagan witch]

Given the small additional price then I'd go for it if I had a third heat source.

 

We have 3 mains systems on board - shore line, inverter, gen set, the normal 2 heating systems - engine and eber and 2 lighting systems - mains and 12v

 

The more indpendant options you can realistically have the better in my view.

 

Not able to comment on the overheating back boiler as I understand both viewpoints being given here but have no practical knowledge of the subject, this is in my view time for me to shut my mouth and open my ears.

[wonderdust]

I don't know, perhaps I was wrong. Nevertheless, I still think it's a good idea to have a gate valve either side of the pump, just for ease of changing it.

 

Mine is an open system with a header tank Ting off from the highest point about 2m from the backboiler, but I've got 28mm pipes coming out of the backboiler and continuing on the main runs, so the hot water is always going to circulate on it's own. What happens if a pumped system is using 15mm pipes (or even smaller if feeding a calorifier) and the pump breaks? Is it still ok to keep the fire going if the hot water can't circulate and radiate that heat?

 

My system sounds very similar to yours no pressure valve just a header tank 28mm finned rads and about 3mts of 15mm pipe to a house rad, calorifier, johnsons pump switched by pipe themo with gate valves either side. Last winter the pump stopped working 15 yrs old so not to bad, anyway the system started gurggle and bank very loudly the other half was on the stern in a flash!

The only place the steam could escape was the header tank situated about 2mts away only action was to throw wet newspapers on the fire and to close all the vents on the door to try and cool the fire down to stop the boiling of the water.

Now i do not know if it is the way my system is installed be it the 15mm pipes, calorifier or the restriction of the pump but my system will not work using thermocycling it has to have the pump running.

Edited October 14, 2007 by wonderdust

[blackrose]

My system sounds very similar to yours no pressure valve just a header tank 28mm finned rads and about 3mts of 15mm pipe to a house rad, calorifier, johnsons pump switched by pipe themo with gate valves either side.

I think our systems are fundamentally different in that yours utilises a pump but mine doesn't.

 

Now i do not know if it is the way my system is installed be it the 15mm pipes, calorifier or the restriction of the pump but my system will not work using thermocycling it has to have the pump running.

It's probably all of the above. Your system wasn't designed to circulate hot water by convection, whereas when I built mine I made great efforts to ensure that there were as few restrictions as possible in the system - using wide bore pipe and even going so far as to use 2 x 135 degree elbows in the main run to achieve right angled joints, rather than simply using 90 degree elbows.

 

Pumped systems are fine but the pump has to working.

Edited October 14, 2007 by blackrose

[baronbradders]

The website quotes the main coil as being 28mm. From the look of the website they can supply a boiler with any size connections or coil that is required. They are mainly designed for solar heating systems which throws up another possibilty!

 

http://www.lowimpact.org/acatalog/twin_and...0_diameter.html

[blackrose]

The website quotes the main coil as being 28mm. From the look of the website they can supply a boiler with any size connections or coil that is required. They are mainly designed for solar heating systems which throws up another possibilty!

 

http://www.lowimpact.org/acatalog/twin_and...0_diameter.html

 

I always thought that calorifier coils were a lot thinner than that, but if that is the case perhaps you can run it on thermocycling as long as the calorifier's not too far away from the backboiler. You've got to decide whether you want a pump or not as that will influence the design of the system. If you do a search you'll find there are some older threads on the forum about designing a system to run on thermocycling.

[ChrisPy]

I always thought that calorifier coils were a lot thinner than that, ...............................

it says 'boiler coil 28mm, solar coil 16.5mm' whatever that means

[GUMPY]

The website quotes the main coil as being 28mm. From the look of the website they can supply a boiler with any size connections or coil that is required. They are mainly designed for solar heating systems which throws up another possibilty!

 

http://www.lowimpact.org/acatalog/twin_and...0_diameter.html

 

Be warned that Calorifiers for marine use are not the same as domestic.

They need to have a higher working pressure and domestic ones can split if used.

 

Check the pressure rating on anything you buy, I know of at least one that has "bulged" to fit the space that its located in its only the walls that have stopped it splitting.

 

Julian

Edited October 15, 2007 by idleness

[blackrose]

Be warned that Calorifiers for marine use are not the same as domestic.

They need to have a higher working pressure....

 

Presumably because it has to be able to deal with the hot water pressure in the engine and not just domestic hot water pressure?

[GUMPY]

Presumably because it has to be able to deal with the hot water pressure in the engine and not just domestic hot water pressure?

Its the working pressure of the system that has caused the one that I know of to bulge. It has no connection to the engine just a Somy boiler.

It was fed from a tank on the roof by gravity much as domestic ones used to be done, as soon as it was connected to a waterpump at 30PSI it started to bulge.

In theory 30PSI is only 2.07 bar and most domestics have PRV set at 3.0bar ( 43.5PSI) however the cylynders are not designed to work at that pressure just survive it in the event of a failure of the system.

 

Julian

[Dave Hannigan]

Its the working pressure of the system that has caused the one that I know of to bulge. It has no connection to the engine just a Somy boiler.

It was fed from a tank on the roof by gravity much as domestic ones used to be done, as soon as it was connected to a waterpump at 30PSI it started to bulge.

In theory 30PSI is only 2.07 bar and most domestics have PRV set at 3.0bar ( 43.5PSI) however the cylynders are not designed to work at that pressure just survive it in the event of a failure of the system.

 

Most domestic calorifiers are designed to work on open vented systems and therefore do not have a PRV but are protected by having an open vent to atmosphere and are designed to work from a max static head of water which, from memory, is 10m or 1 bar.

 

The domestic type to compare with marine is the unvented cylinder, which have a PRV usually, from memory again, set at 6 bar to cope with incoming mains pressure.

[Trilby Tim]

if you have 3 sources of hot water apart from the immersion, it is the logical way to go.

only you can decide if it is worth £50 to dispense with the valves needed to manage the system with one or two coils.

I would go for it.

I know I'm resurrecting an old thread, but I'm interested in this. Is there anyway to connect both engine and stove to the same coil on the calorifier and choose between them with valves? The engine is a pressurised system, but can the stove back boiler also be pressurised?

[DHutch]

If i was pairing, i would pair the diesal heater with the squiral, as they would both want to use the same radiators anyway i would say?

- Mind you, theres an argument for attaching the engine to the rads too... Although its nice to get the stove in if you are boating in the cold!

 

 

Daniel

[Trilby Tim]

I was thinking of using the calorifier as a sort of heat exchanger. Putting heat in through one coil (engine and stove, no diesel heater planned yet) and taking it out for heating through the other coil. With a thermostat to stop circulation through the heating circuit if the temperature in calorifier drops below some point so we don't end up with cold water.

[colin stone]

I was thinking of using the calorifier as a sort of heat exchanger. Putting heat in through one coil (engine and stove, no diesel heater planned yet) and taking it out for heating through the other coil. With a thermostat to stop circulation through the heating circuit if the temperature in calorifier drops below some point so we don't end up with cold water.

 

I thought of that but was told that calorifiers did not work well trying to achieve a heat transfer function.

 

Rather than engine heat just supplying a calorifier coil, I fitted a Bowman tubular heat exchanger in the CH circuit so that the engine heats the whole CH system, radiators and calorifier, still using the engine calorifier connections. An engine probably generates more waste heat than a dedicated CH boiler.

Edited May 6, 2009 by colin stone

[Smelly]

We used an Lport valve to switch between calorfiers and the same could be used to switch feeds, however the first time you forget to switch them when you light the fire... kablooey unless there's a gravity system to dispel the heat.

 

We've got dedicated circuits for engine/backboiler and much prefer it that way. I've one spare coil for the solar panel I intend one day to buy...

[Tony Brooks]

If i was pairing, i would pair the diesal heater with the squiral, as they would both want to use the same radiators anyway i would say?

- Mind you, theres an argument for attaching the engine to the rads too... Although its nice to get the stove in if you are boating in the cold!

 

 

Daniel

 

 

Yeh - isn't it called a condenser?

[Theo]

While people's minds are on the subject I would be interested in why it is necessary to have more than one coil. I have a twin coil calorifier but only use one of them. I have paralleled Mikuni, Engine, Bathroom rad and living room rad and can choose to use the Mikuni to heat any or all of those, including preheating the engine if I feel like it. Or I can use engine heat instead of the Mikuni. Why complicate matters?

 

Nick

[Smelly]

While people's minds are on the subject I would be interested in why it is necessary to have more than one coil. I have a twin coil calorifier but only use one of them. I have paralleled Mikuni, Engine, Bathroom rad and living room rad and can choose to use the Mikuni to heat any or all of those, including preheating the engine if I feel like it. Or I can use engine heat instead of the Mikuni. Why complicate matters?

 

Nick

 

When you introduce a backboiler it becomes a different game...

[Trilby Tim]

Can a back boiler be used as part of a pressurised system? It would still have an expansion bottle and an overflow to vent through if the pressure gets too high.

[Smelly]

Can a back boiler be used as part of a pressurised system? It would still have an expansion bottle and an overflow to vent through if the pressure gets too high.

 

It's been done and Chris Pink would be a good person to ask about the technicalities, however you'd have to be quick as amongst the new stove installation guidelines -which if you search for "don't complain"- you might find-; banning pressurised systems running from fires is one of the less draconian measures that are mooted. They're not law yet and whether you'd keep any transitional protection is subject to debate.