Rayburn Plumbing - Newbie help needed.

[FunkyFox]

Hi all,

I'm installing a Rayburn 212 SFW on a narrowboat for heating and hot water. I've played around with a few plumbing layouts, the latest one is shown below ( just checked the preview and it's not very clear but I can email if needed ). Not being an expert plumber I'd really appreciate some pointers and feedback as I've still got some niggling worries abour whether or not it will work.



The first worry is that the hot water output is considerably more that I'll need. The Rayburn install guide says that normal operation will produce around 100 gals of hot water per day, probably about 50 more than I'll need! So.. what to do with all that extra heat? They suggets a 'A towel rail of not more than 0.5m2 heating surface' which leads on to the next worry...

What to do with the (possible) excess heat. I've read somewhere that a heat leak radiator should have somewhere between 25-30% the nominal boiler output. For a 2.2kw Rayburn that would be about 500w give or take which is not in itself a problem but fa more than the powel rail suggested by the mfrs. I am also struggling with how to connect it. In the diagram I've connected it in parallel with the rtn pipe, reasoning that if the return flow is hotter than the radiator then it should thermosyphon on its own and get rid of any excess heat. I'm guessing it would be more efficient to put it in series in terms of dumping the excess heat since all water would be forced to flow through the radiator regardless, however all of the radiators I've found are 22mm pipe vs the 28mm (1inch) pipes specified for the Rayburn. This would severely restrict the flow which is why I've opted for a parallel connection.. any thoughts?

I've seen various layouts on other sites showing complex systems of pumps, pipe stats and changover valves, but given the probability of a pump failure (or more likely a flat battery on a boat) these are really a no go. This, in addition to the 'more heat than needed' makes me worry abou the thing boilng over / boiling dry.

If anyone has any suggestions then I'd really appreciate them!

For info I've posted links to the Rayburn and cylinder specs below.

http://www.rayburn-web.co.uk/Prodin...FW/Ray 200 212 SFW inst 12-09 EINS 514406.pdf

400 x 1500 172 litre thermal store at Swithenbanks Alternative Energy | Grid Tie Inverters | Solar Photovoltaic

Thanks,

Jeff

 

[Bartdude]

First of all have you considered the safety implications of fitting a continuously burning solid fuel appliance on a boat?,are you going to be living on it?

Rayburns figures of 100 gallons of hot water over 24 hours is a lot of hot water and if you can't use that then there will be a lot of extra heat generated.A well insulated thermal store will overheat I think and coupled with an uncontrolled heat source I'm not sure it's suitable in your situation. How does the coil from the engine fit in to the plan?

A heat leak radiator of 0.5kw is normal for a Rayburn 212(or Royal as it used to be called).In this case a bigger rad would help.It would have to be connected in the usual way,ideally with the flow in the top of the rad and the return out the bottom(opposite side)to obtain good gravity circulation. It wouldn't work the way you have put it on your diagram. A normal radiator with 1/2" connections is fine,15mm pipework teed into the 28mm primary pipes will work perfectly well.

I think the other methods of control that you refer to will be for heating systems and combining different heat sources,that's not applicable to this type of system.The 212 is designed for cooking and hot water only,no pumps or thermostats etc.

There's a lot of weight there too,the Rayburn and thermal store when full will be over 500kg,so that's an issue.

I see there is a pumped cold water supply,how is that fed?

 

[FunkyFox]

Thanks Bartdude,

Strting with the easy one, the weight isn't really a problem. Narrowboats generally carry a few tonnes of ballast, so some of this is simply removed and the rest redistributed to compensate for the extra weight of the heating system. The cold feed is pumped from a 120 gallon tank with a pressure of about 1.7 bar and there's also an accumulator tank in there somewhere rated to 4 bar which would cope with any limited expansion in the tanks coils. The coil from the engine simply pumps waste heat from the engine when it's running, acting like a second heat source and the output isn't huge.

As you say, one possible solution might be to use a larger radiator. Although it's unlikely to need to dump the entire boiler outpupt it seems better to be safe than sorry in a case like this, so is adding a radiator with 2kw capacity a possible solution? Also, most heat outputs for radiators are quoted at delta 40, as the temperature goes up then so will the heat output but is there a way to calculate this?

I've toyed with using a few lengths of finrad (google it if you're not familiar) to create a big enough heat dump. It's pretty ugly stuff but with a bit of paint might look quite minimalist?

Your input is much appreciated,

Jeff

ps.. re safety implications of solid fuel.. you'd be hard pressed to find a narrowboat without a wood burning stove, most of which also have back boilers. It sounds scary but reported problems with them are rare and mostly caused by a lack of common sense!

 

[FunkyFox]

Ok..

Here's an updated diagram. I've upped the size of the read to be around 1kw and teed off the flow pipe before it gets to the cylinder and am hoping I can remove the top and bottom valve connectors on the rad to reduce the restrictions and also stop anyone turning it off!



I'm hoping...

1) that when the cylinder is cold, then since the flow keeps rising beyond the radiator tee then most of the hot water will continue to rise past the rad and end up in the tank where it's most useful. (swept tee or ordinary tee... ?)

2) as the tank heats up then the thermosyphon through the tank will reduce and gradually more and more of the hot water will divert through the rad to dump the excess heat.

3) the flow rate through the rad + dissipation in the connecting pipework should be sufficient to dump all excess heat under almost all conditions. Worst case scenario is starting to cook (ie rayburn at high output) with an already hot tank. In this case I'm likely to get a VERY hot radiator?

Any thoughts welcome.

Jeff

 

[Bartdude]

Hi Jeff

I assumed that the boat has a wooden floor,that was why I mentioned the weight. I don't know much about the construction of these boats though,so I'll leave that side of things to you!

Judging from your reply I don't think the engine coil is going to cause problems.The thermal store you have is 172 litres and Rayburns recommended cylinder size is 140,but I've seen all sizes fitted in houses and overheating problems are usually caused by an undersized cylinder,also some systems don't have a heat leak at all which compound the problem.

Regarding the radiator size,I would be inclined to size it around 0.5-0.75kw.If you fit a single panel rad it can always be upgraded to a double panel if needed.My radiator chart lists temperatures at 50 and 60C,using the 60 scale a 600x600 single panel would suffice.I don't think it's necessary to calculate the size at a higher temperature.Obviously,no thermostatic valve to be fitted!

The thermal store is of a good size and coupled with the heat leak rad I wouldn't expect boiling to occur,there's no surefire way to be certain until you try it though. The store should have a safety relief valve which must discharge outside,the ball valve in the feed and expansion tank must have a copper float,the overflow must be copper too.I don't think the finrad would be required.

I suppose there are lots of narrowboats with some kind of stove fitted,I'm not sure what regulations apply to the fitting but I guess the things to pay attention to are plinth/hearth and distance to combustible materials,but then that goes for a house install too. I did have to repair a Rayburn that was fitted in a yacht once,it was moored in Brixham harbour, but narrowboats are new to me!

Hope that helps.

 

[FunkyFox]

Thanks again,

The floor is mainly wood supported on steel bearers but I'm adding an extra bit of steel framing under the rayburn which I'm lining with quarry tiles... hopefully no problems!

On your suggestion I'm going to try for a rad near the upper end (0.75kw). In your opinion would the second diagram fit the bill, and also would it be best to use normal tees or a swept tees for the branch to the rad. I'm still a bit concerned about the flow restriction.

Thanks for all you help on this.

 

[Bartdude]

The quarry tiles need to extend at least 300mm from the front of the cooker too,to catch any sparks that may fall when you re-fuel.

Normal tees will be fine,don't worry about any flow restriction,with the flow entering at the top it will work really well. The key with gravity circulation pipework is to have the flow rising to the radiator tee,the heat is doing the work,just give it a clear run. If the pipework is straight like your diagram you'll be fine. If gravity pipework is properly installed it can be surprising how quickly it can move around the system. Not every system needs to be pumped and pressurised!!

Do you have a photo?

Edit: I don't think you will need the vent pipe at the top of the flow pipe,that should be built into the thermal store,check the MIs though.

 

[FunkyFox]

Thanks, I think I'm almost there!

Sorry no photos, the boat isn't even built yet!

I'll keep ypu posted.

Cheers,

Jeff

 

[thefreereed]

Hello FunkyFox,

Did you get this all working in the end?

I'm considering something for my narrowboat self build. It will be a 50-57 footer. Do you think I'll need 2 rads?

 

[FunkyFox]

Hi thefreereed..

Yep, it's all in and working, pretty much 'as is' in the diagram I posted, so concept proved I guess.

As to whether or not you'll 'need' 2 rads.. depends on what you mean by 'need'.. in terms of dissipating the excess heat I'd say probably just the one would be fine. I ran it for most of last winter with no rads at all and only once did the thing boil, but I guess it also depends how exposed your pipework is and also how long.. If it's about heating the boat then possibly but again depends on your layout, but to be honest the aga itself seems to heat most of the boat on it's own..

A few other things to think about ff you're considering this, firstly the draw through the chimney.. all the standard ones seem to be fairly miniscule so you mat have to get one custom made (I got one made at 30 inches, plus a stubby one for cruising) and they ain't cheap! Second, if you are considering putting in a second rad then you might want to put a small pump i too (after the first heat leak rad!!) since the boat is likely to slope naturally from front to back and without it it's difficult to get enough of a rise on the pipework to get the water to thermo-syphon efficiently..

I don't have much more wisdom on the subject but if you're struggling then give me a shout.. I remember being completely lost this time last year!

Good luck!

 

[thefreereed]

Thank you so much for replying.

When you say 30 inches for the chimney I take it you mean 30 inches above the top of the boat?

I'm planning on having the heat source nearer the stern, as the boat will naturally sit back a bit towards engine. This should help with the rise of the pipes.

I guess I can try the 2 rads and if it doesn't work add a pump later. Trying to keep electrical consumption to absolute minimum. 2 rads would be good for my layout.

I'm also considering diesel powered alternative such as mikuni or bubble as I've heard they're very reliable (compared to Eberspacher and others). Less waste/dust but not as cosy as a wood burner of course. Nice to use big supply of diesel on boat, and no need for coal/wood storage. Pros and cons of both.

Anyway all in planning stages at the moment. I hopefully will order hull next Summer and will do fit out in my garden!

Just ordered my Kregg jig so will practice with it in my house doing various projects.