Rayburn solid fuel DHW installation advice

[Slavo]

Hello,

Currently installing the DHW parts for a Rayburn 216SFW boiler (Solid Fuel).

Using the installation manuals and Document G / Document J of the building regulations I still cannot find answers to some queries I have.

It is a gravity system on 28mm, <6M flow & return lengths.
210L vented indirect cylinder.

1: Is there a minimum F&E tank size?

2: Is there a specific material the F&E tank must be constructed of?

3: What is the minimum static head for the Primary circuit?
All I can establish is that it is to be sufficient to prevent sub atmospheric pressure at highest point when pump is in operation.

4: I have been told that the vent pipe must rise continually with no joints. Is this correct? This is currently infeasible if the cylinder remains in the location of the existing (vented, direct) cylinder whose vent travels nearly 10m (never dropping but some parts very close to horizontal as it moves around the room).

Any advice would be greatly appreciated!

 

[Norcon]

Its usually beyond a diyers capability to fit these and is one area where the black arts of plumbing can be applied.
Hi-Lo stats needed and injector T. AVTA cooling valve on the heat leak rad optional!
When applied properly it will give you hot water and heating without any electricity. And of course cooking in your case.
If your current plumbing is wrong then its needs modifying to suit.

 

[Slavo]

Hello and thank you for taking the time to reply, it is greatly appreciated.

Just for clarification, an injector T is only required for a pumped heating system, which would require the Hi-Lo stats and electricity, you would then only get heating from the heat sink radiator should the power fail. I'm initially looking only to provide DHW and cooking from the system. The heating must wait until I complete the stove and back boiler for full integration with that, which is to feed the majority of radiators in the house.

I didn't list every detail within the system as this was not required for answering my questions, however, I have a tank thermostat to be linked to a normally closed 2-port valve and will be fitting a temperature / pressure relief valve (only one of these is required but belts & braces for an uncontrollable heat source).

I have good advice for the minimum static head, so no longer need to know this, it just needs to be above the cylinder.

Thanks again for the advice regarding the AVTA cooling valves, I shall investigate these. I like how they don't require power in order to work! I need to be 100% confident that they are safe and if they do fail, fail open. I was always under the impression that heat sink radiators had to have 'always open' valves that cannot be closed (for obvious reasons).

 

[Richardthe3rd]

Forgive my ignorance, but what is the output to water from the appliance?? Is it solely designed for DHW or does it do CH also?? Yes as said it is a bit of a dark art, with pipe gradiants etc...not many of young pups or course cowboys on here would be able to use a 28mm bending machine & form gradiants required for a SF system.

 

[Norcon]

How will you energise the cylinder thermostat?

If the avta valve fails it will likely be due to the phial charge escaping and it will fail closed shutting down the coolant supply. But that's rare and won't result in a melt down causing you to evacuate your home. (laff out loud)
And not critical as the cold feed and vent will take over.
The main reason for fitting this valve is to give priority to the HW.

The heat leak rad should have no valves fitted and be piped direct if you fit an avta!
A by-pass is also required to provide heat to the phial and of course allow the return stat to be triggered.

 

[Corgigrouch]

Norcon, how do you propose to connect a heat dump valve without a cooling coil in the boiler?

 

[Slavo]

Hi Richardthe3rd, the output to water is 5KW. It is designed such that it can be used solely for DHW or both DHW and CH, in both situations there must be a gravity-fed heatsink radiator. Are you able to share any of this "dark art" or your expertise?

Norton, the cylinder thermostat will be energised by mains electricity, should it fail, the motorised 2-port valve will assume its normally closed state and the flow will be entirely diverted through the heat sink radiator.

 

[Norcon]

You'll need to be careful with the wiring. If you follow the MI's (page 4)
http://tinyurl.com/ld4yu2r

...they have shown the low limit stat with the possibility to be isolated.
Then the cylinder stat becomes the high limit stat and when triggered will cause greater delay on heat up. From cold start you want the low limit stat being the workhorse.
No need for time clocks and room stats on these appliances imo. Only causing complications.
They also show no heat leak rad! When we had one of these in our old gaffe we just turned on the hot tap when it boiled. The vent pipe went out through the roof.
It has about the same output as a Stanley Tara which I find will heat three 1.8kw rads with ease.

Hi-Lo stats is the way to go the same as the woodwarm set up here on page 17....
http://tinyurl.com/6xcte8y

To incorporate the zone valve with an avta valve on the heat leak rad I would fit an off delay relay energised from the low limit stat satisfied terminal set for about an hour energising the cylinder stat.
A manual by-pass is required to let this operate as the gravity circuit must perform a loop.
That way its automatic and not dependant on a timer being functional and prevents on/off cycling of the mv.

The other option without an avta is a timer.

 

[oilhead]

Shouldn't your 2 port be to the heat sink, and be normally open, energised closed so that when the cylinder overheats, the valve will open and put excess to the heat sink?

 

[Richardthe3rd]

Hi Richardthe3rd, the output to water is 5KW. It is designed such that it can be used solely for DHW or both DHW and CH, in both situations there must be a gravity-fed heatsink radiator. Are you able to share any of this "dark art" or your expertise?

Norton, the cylinder thermostat will be energised by mains electricity, should it fail, the motorised 2-port valve will assume its normally closed state and the flow will be entirely diverted through the heat sink radiator.

5KW is not a lot for central heating??!! In fact it'll be daft to have a complex control system on an appliance that small. The typical HW/CH layout on the MIs don't even show a heat leak. A standard immersion heater produces 3KW, that gives you an indication of the output of the your appliance.

Gravity circulation is not really something a daftyDIYer should tackle.

 

[Slavo]

Norcon, I totally agree! Whilst they mention the heat leak radiator in the text, I think it's madness that it is only a "should" be fitted if the primary pipes flow/return pipes are <7M.

This is why I seek advice from those who are experienced and not rely upon their destructions.

Oilhead, I think I understand your point in that the DHW would heat up more quickly and prevent unwanted heat loss through the heatsink radiator during times the cylinder is low temp, however, can I be confident that the heat sink radiator will draw enough heat such that I don't scald myself under the hot tap? I feel that both cylinder valve (normally closed) and valve to the heatsink (normally open) energised by the cylinder valve is the best way to go.

This in my opinion is, as Norcon states, the best arrangement for the CH pump.

(sorry I realise I have used heatleak/sink interchangeably).


Can anyone tell me whether or not it is acceptable to have soldered joints (couplers and elbows between pipes) on the vent?

 

[Slavo]

<edited, can't be bothered with negativity>

 

[Corgigrouch]

Can anyone tell me whether or not it is acceptable to have soldered joints (couplers and elbows between pipes) on the vent?

Yes of course you can.

In reply to your earlier question the feed and expansion tank must be made of heat resistant material to BS4213...Must be able to withstand boiling water for 500 hours without going floppy..... In short GRP, copper or stainless

Place a normally open valve on the branch that feeds the cylinder so that the flow to the heat leak (10% of the output of the stove minimum) or vent is never closed off..

Dicky is right that designing a gravity flow system can be tricky if the pipework run is complex but as long as the cylinder is virtually directly above the stove then it should be pretty straight forward..

Ignore Norcon, he's mad..

 

[Norcon]

This is the setup I have. Put your name on it. LoL
http://s27.postimg.org/4fhf3wykz/Slavo_Images_002.jpg

Works well though I'm finding it collecting some air.
You'll notice the injector valve with an extra tapping, so I'll pipe that to the return side of the pump with a gate valve fitted and see what happens. Hope to have the cylinder fitted shortly.

Thermal integrations deploy the avta....
http://www.heatweb.com/Wood/circ1.gif
Though I was fitting them on complex commercial heat recovery systems long before I noticed them on internet websites.

And very cleverly deployed here by HWAM stoves on page 41..
http://www.deanforge.co.uk/content/doc/lib/622/Hwam_Stoves.pdf

 

[Nige F]

there must be a gravity-fed heatsink radiator. .

That will need 3/4 inch tappings minimum to work on gravity circuit