Plumbing in a back boiler

[Fuel__2001]

I'm asking this because I don't know.

 

Do you have to have an open vent in a solid fuel system because you have to take precautions against the water boiling? I know we accidentally boiled our domestic system twice when we had a Franco-Belge stove in our previous house. The volume of steam will be far greater than the normal expansion of the water.

 

Richard

 

Have a read of this

 

http://www.boilerstoves.co.uk/vented-or-pressurised.html

 

What im suggesting is something in between - where, the sealed header tank creates pressurise, has the ability to expand but will also vent when it reaches a certain pressure.

[sharpness]

As does an Eberspacher header tank with a built in pressure relief valve. The sealed header tank helps prevent oxygen from in atmosphere from being absorbed into the coolant, with the potential to cause corrosion within the system. The free space (air gap) within the header tank allows for the expansion of the coolant when in normal operating mode.

 

Mike

It really doesn't matter, you stick to your sealed tank & I'll stick to my open vent but I'll accept that the Eber experts may know better than me. I really cant see the "oxygen from the atmosphere being absorbed into the coolant" argument though. I'm no chemist or physicist but how? why? how much? Theres only 12 square inches of water surface & I've got water (with antifreeze) as my coolant, not silica gel.

As I have said in other posts, I'm a simple bloke, I like to keep things simple and to me, the open vent is simplest & works perfectly well.

Steve

[Doorman]

As I have said in other posts, I'm a simple bloke, I like to keep things simple and to me, the open vent is simplest & works perfectly well.

Steve

 

That makes two of us!

Edited January 14, 2011 by Doorman

[sharpness]

That makes two of us!

Its a bit early for a pint but

 

Steve

[Fuel__2001]

I think i'll have myself one of these its far to early for

[smileypete]

Have a read of this

 

http://www.boilerstoves.co.uk/vented-or-pressurised.html

 

What im suggesting is something in between - where, the sealed header tank creates pressurise, has the ability to expand but will also vent when it reaches a certain pressure.

But it also goes on to say:

 

'Very few stoves are suited to pressurised systems - make very sure that your stove is suitable if you intend to link it to a pressurised system. Most stove boilers are not designed to be under the higher pressure found in a pressurised system.'

 

So at the very least it would be right to get the definitive answer from the back boiler manufacturer.

 

But I'd be very surprised if any of the stove back boilers used in boats are designed to run pressurised.

 

cheers,

Pete.

Edited January 14, 2011 by smileypete

[Doorman]

But it also goes on to say:

 

'Very few stoves are suited to pressurised systems - make very sure that your stove is suitable if you intend to link it to a pressurised system. Most stove boilers are not designed to be under the higher pressure found in a pressurised system.'

 

So at the very least it would be right to get the definitive answer from the back boiler manufacturer.

 

But I'd be very surprised if any of the stove back boilers used in boats are designed to run pressurised.cheers,

Pete.

 

I would agree, that's why we run our system not as one that is pre-pressurised, but one that has a closed header tank with a built in PRV in the cap, there's a definite difference.

 

When consulting with Morso, their technical department did not see a problem with this!

 

Mike

[Doorman]

As there are concerns regarding the potential

for a back boiler on a solid fuel stove to

boil dry, I've provided a simple design that

would help avoid this possible situation.

 

 

The drawing shows the use of an automobile type

relay. I've included this for simplicity, as I

prefer to use the type available from Maplins.

With these relays, there are provisions to

include a light, or, an audible alarm in the

circuit as an extra feature.

 

The use of the non-return valve is to prevent

any potential back-flow of the antifreeze mixture

from entering the fresh water supply. The restrictor

valve would ensure a steady replenishment of water

without the possibility of pressurising the coolant,

to the same level as the domestic cold water on the

boat.

 

I have already used a similar design to this on the

header tank for the engine coolant. This ensures that

in the event of a leaking hose/connection while the

engine is running, the coolant level is maintained. It

also alerts me (vai an audible alarm) that there is a

problem in the coolant circuit.

 

Mike

Edited January 15, 2011 by Doorman

[smileypete]

I would agree, that's why we run our system not as one that is pre-pressurised, but one that has a closed header tank with a built in PRV in the cap, there's a definite difference.

If the back boiler goes over 100°C then the system will pressurise and the water in the back boiler be heated over 100°C, maybe up to 125°C.

 

If there's a sudden pressure drop, like the back boiler fractures or a hose comes off or a joint comes apart anywhere in the system, this will create quantities of 'flash steam'

 

'Flash steam occupies many times the volume of water from which it forms. For example, flash steam created by hot condensate flowing from 15 PSIG to an atmospheric pressure will have nearly 1,600 times the volume of the high pressure hot water.'

 

Not only a very large volume of scalding hot steam but also a large amount of scalding hot water and antifreeze could spray out under pressure. Not something I'd like anyone to suffer in the confines of a boat.

 

 

When consulting with Morso, their technical department did not see a problem with this!

I think I'd like to see it from them in black and white in their words, even so I wouldn't allow a back boiler to run under pressure under any circumstances.

 

cheers,

Pete.

[Doorman]

If the back boiler goes over 100°C then the system will pressurise and the water in the back boiler be heated over 100°C, maybe up to 125°C.

 

If there's a sudden pressure drop, like the back boiler fractures or a hose comes off or a joint comes apart anywhere in the system, this will create quantities of 'flash steam'

 

'Flash steam occupies many times the volume of water from which it forms. For example, flash steam created by hot condensate flowing from 15 PSIG to an atmospheric pressure will have nearly 1,600 times the volume of the high pressure hot water.'

 

Not only a very large volume of scalding hot steam but also a large amount of scalding hot water and antifreeze could spray out under pressure. Not something I'd like anyone to suffer in the confines of a boat.

 

 

 

I think I'd like to see it from them in black and white in their words, even so I wouldn't allow a back boiler to run under pressure under any circumstances.

 

cheers,

Pete.

 

Hi Pete,

 

Your concerns are justifiable if there are no safety devices incorporated within the system and if anyone were to be fool enough to install such a flawed design on a boat, or, anywhere else for that matter.

 

Also, the related article regarding flash steam indicates the potential dangers if this situation occurs. The fact that our C/H system incorporates not one, but two safety valves, ie., one on the flow outlet on the boiler and one in the header tank (cap) to avoid such a catastrophe, indicates that this potential hazard has been accounted for.

 

I can list numerous instances where there is potential for life threatening occurrences, some on board a narrow boat and many elsewhere. Fortunately, experience has taught mankind how to avoid such disasters by adding features that help correct or temper the effects of any potential shortcomings.

 

Clearly, we are at odds with each other on this subject and although I respect your point of view, I remain satisfied that we have a safe and controllable duel heat source on board our narrow boat.

 

Mike

[sharpness]

If there's a sudden pressure drop, like the back boiler fractures or a hose comes off or a joint comes apart anywhere in the system,

 

 

or a safety valve lifts?? or an expansion tank cap lifts??

 

Steve

[smileypete]

or a safety valve lifts?? or an expansion tank cap lifts??

In the end I think it's best to seek the advice of a competent, time served heating engineer with relevant experience and qualifications in back boiler heating systems.

 

If they think it's a bad idea to have a back boiler served by header tank sealed in any way, then... it most definitely is. Would you not agree?

 

cheers,

Pete.

Edited January 19, 2011 by smileypete

[sharpness]

In the end I think it's best to seek the advice of a competent, time served heating engineer with relevant experience and qualifications in back boiler heating systems.

 

If they think it's a bad idea to have a back boiler served by header tank sealed in any way, then... it most definitely is. Would you not agree?

 

cheers,

Pete.

 

I am none of those - a competent, time served heating engineer with relevant experience and qualifications in back boiler heating systems. It just seems unwise to me, and more to the point in my case, uneccesarily complicated so I wholeheartedly agree.

 

Steve

[Doorman]

I had hoped that my last post would have brought closure to this thread but apparently not.

 

I read with interest that neither of you appear to hold qualifications on this subject and up until this point, I felt that there was no need for me to justify my comments with neither qualifications, or, experience but here goes.

 

Qualifications: Mechanical Engineer

 

Experience: 23 years in industrial plant engineering, including maintenance in a plant heating system of a 450,000 sq ft factory (high pressure hot water).

 

Maintenance of hydraulic plant, operating at and above 375 bar.

 

Maintenance of Industrial gas powered ovens.

 

Maintenance of Robotic systems also involving hydraulic powered actuators.

 

Maintenance of High pressure paint feed and control systems.

 

11 years as owner of an industrial door company, whereby I was responsible for the design and installation of industrial and commercial doors, some of which measured 6m x 6m and weighed 3 tonnes.

 

These are just some of the applications that I have been involved in during my working life time.

 

So, although reluctant to 'blow my own trumpet', I felt it necessary to make an exception in this case and illustrate that I have quite a substantial amount of experience in the world of mechanical engineering, including heat transfer systems.

 

It is from this experience, where safety is paramount in design, that I have included in my own central heating system, two safety features, as described previously.

 

I hope that this thread can be concluded now with an appreciation of each others opinions, based upon their relevant knowledge.

 

Mike

Edited January 20, 2011 by Doorman

[smileypete]

I had hoped that my last post would have brought closure to this thread but apparently not.

 

I read with interest that neither of you appear to hold qualifications on this subject and up until this point, I felt that there was no need for me to justify my comments with neither qualifications, or, experience but here goes.

 

So please tell us, why exactly would you run a back boiler from a header tank that's sealed in some way?

 

I don't doubt your qualifications and experience, but I would still defer to a competent time served heating engineer with relevant experience and qualifications in back boiler heating systems.

 

cheers,

Pete.

Edited January 20, 2011 by smileypete

[Doorman]

It is from this experience, where safety is paramount in design, that I have included in my own central heating system, two safety features, as described previously.

 

I hope that this thread can be concluded now with an appreciation of each others opinions, based upon their relevant knowledge.

 

Mike

 

I've re-quoted this section of what I'd hoped to be my final comment on this topic, just in case you may have missed it...!

 

Mike

[sharpness]

I hope that this thread can be concluded now with an appreciation of each others opinions, based upon their relevant knowledge.

 

Mike

I have no problem atall with your system, nor any need to know your qualifications, you carry on chief. With your qualifications & experience I'm sure you'll make it work.

My only questions with it based on no qualifications other than life are

1 Why have pressure where none is needed. As far as I understand it, schoolboy physics, is that pressure is only needed to raise the boiling point of the water, as in an engine cooling system. Surely it shouldnt be that hot. If I am wrong please explain to me.

2 why does it need to be so unnecessarily complicated (other than to cope with the pressure), far to much to go wrong, it wouldn't suit me.

Closed as far as I am concerned.

Steve

[Fuel__2001]

ENOUGH please, i appreciate everyones input on the vented, closed and pressure relief systems that have been discussed on this thread.

 

I have the information i need to make a decision based on the information from here and elsewhere, i thank you all for the banter and input. People will agree and disagree on the merits of whats best and thats what makes for great discussion.

 

The last piece of the jigsaw which you'll be pleased to know doesn't relate to the type of system im using, is shopping for a 'pipe stat'

 

The pipe stats ive seen are for 240v or are they also able to work from 12v supply?

[nb Innisfree]

Surely even open vented back boilers run under pressure if the header tank is several floors high, 4 storeys at, say, 10'each = 40' = approx 18psi at floor level back boiler.

[RLWP]

Surely even open vented back boilers run under pressure if the header tank is several floors high, 4 storeys at, say, 10'each = 40' = approx 18psi at floor level back boiler.

 

Yes, that's true. However they have the advantage of a full bore open tube for steam to escape from in the event of the solid fuel fire running away and boiling the water. That's very different to the small passage ways in a car-radiator cap

 

Richard

[Doorman]

 

The last piece of the jigsaw which you'll be pleased to know doesn't relate to the type of system im using, is shopping for a 'pipe stat'

 

The pipe stats ive seen are for 240v or are they also able to work from 12v supply?

 

Try this company for your pipe stat. It will also work with 12v dc as well as 230v a/c.

 

Clicky

 

Chief Engineer Mike

Edited January 21, 2011 by Doorman

[Doorman]

1 Why have pressure where none is needed. As far as I understand it, schoolboy physics, is that pressure is only needed to raise the boiling point of the water, as in an engine cooling system. Surely it shouldnt be that hot. If I am wrong please explain to me.

2 why does it need to be so unnecessarily complicated (other than to cope with the pressure), far to much to go wrong, it wouldn't suit me.

Closed as far as I am concerned.

Steve

 

Hi Steve,

 

In answer to your questions.

 

1. Initially, the system is not under pressure, it is not like a pressurised central heating system where an accumulator vessel is used to pre-charge the circuit up to say; 2 bar. It runs at atmospheric pressure, 1 bar at sea level. The only time there will be any increase in pressure will be when the coolant expands. The air gap in the header tank accommodates this expansion. If, say under extreme conditions and the stove is allowed to overheat, the water will expand further and the relief valve in the header tank will operate, thus relieving the circuit of the unwanted pressure.

 

2. If you recall the drawing of our C/H system, it was relatively simple in design with no directional control valves incorporated. It has now been in operation for more than 13 months

and requires very little maintenance, other than a common sense approach in controlling the air intake to the stove.

 

My main concern with a multi-fuel stove is not the potential to create super-heated steam, but the fire risk involved with the effects of Pyrolysis. But that's another subject entirely!

 

Mike

[smileypete]

Surely even open vented back boilers run under pressure if the header tank is several floors high, 4 storeys at, say, 10'each = 40' = approx 18psi at floor level back boiler.

 

I think this website puts it pretty well:

 

'With the growing demand we are also seeing a rise in the number of systems that have been installed dangerously, and without a though for the safety measures that must be followed when using a fuel that cannot be turned off with the flick of a switch. In this guide we wish to clarify the basic restrictions that must be considered when designing a wood burning system, and to cover the methods we employ to design a fully integrated and safe system, while still following the cardinal rules...

 

• 
   
  
• A wood burner must be part of a vented water system, with an uninterrupted path to atmosphere.
  
• The system must ensure all heat generated to water is removed from the heater (and system) without reliance upon electrical power, the operation of pumps or human intervention. i.e. the system water must not reach 100°C under any circumstances.'
   
  

Edit: After covering the above, the next area to consider may be how best to combine pumped radiator(s) and calorifier with the gravity fed heat dump radiator(s) and back boiler...

 

cheers,

Pete.

Edited January 21, 2011 by smileypete

[Doorman]

I think this website puts it pretty well:

 

'With the growing demand we are also seeing a rise in the number of systems that have been installed dangerously, and without a though for the safety measures that must be followed when using a fuel that cannot be turned off with the flick of a switch. In this guide we wish to clarify the basic restrictions that must be considered when designing a wood burning system, and to cover the methods we employ to design a fully integrated and safe system, while still following the cardinal rules...

 

• 
   
  
• A wood burner must be part of a vented water system, with an uninterrupted path to atmosphere.
  
• The system must ensure all heat generated to water is removed from the heater (and system) without reliance upon electrical power, the operation of pumps or human intervention. i.e. the system water must not reach 100°C under any circumstances.'
   
  

Edit: After covering the above, the next area to consider may be how best to combine pumped radiator(s) and calorifier with the gravity fed heat dump radiator(s) and back boiler...

 

cheers,

Pete.

 

Does this mean that I have to find a buyer for my Morso...?

 

CE Mike

[sharpness]

Hi Steve,

But that's another subject entirely!

 

Mike

We wont go there then!!!!

I understand the what but not the why. I dont even have a back boiler (on the boat but have had at home). I would like to put one in one day but it will be open vented if I do.

I'm happy to agree to differ and looking forward to some weather when we dont need the heating on. Any chance??

 

Cheers

 

Steve