complex dual fuel central heating questions

[exon16m]

Hi

Thought I would try and run this past you lot.

I have a conventional oil vented central heating system. I am installing a wood burner with back boiler. It is in an bungalow so only a low height water loop.

I have a fitting kit with heat exchanger from the maker of the burner that bridges the two vented circulation loops.


I have run 28mm pipes from the pre and post boiler pipes to the heat exchanger.

The initial plan was the resistance of the 30m loop back through the loft to the heat exchanger would mean when the oil is on and burner not, the system would flow as before.


When the burner is on it will suckling up from the cold return and pass it back to the other side of the outflow from the oil boiler.


Since doing this i have contemplated having a check valve in the loop so that when the wood burners pump is on it does not need the current pump to be in to prevent back flow.

my questions:

1) how much will a check valve restrict flow in the conventional loop. Is this a better option or is the dual pump a better method? (I assume it does it reduce the diameter of the pjpe)

2) I have had to run pipes up and over a joist in the attic with a shallow inverted u. will this create an airlock and does it need a air release tap the system here?

I will get a picture up to make this explanation make sense in a bit

 

[MeldrewsMate]

Please will you also re-read your post and insert/delete words as appropriate to make it legible?

 

[exon16m]

 

[exon16m]

Hope that makes it easier to understand?

 

[Norcon]

What your doing is probably similar to Systemlinks heat genie...
http://www.systemlink.ie/products-59/heat-genie.html

 

[MeldrewsMate]

Hope that makes it easier to understand?

A picture, even drawn by a four year old, paints a thousand words....and it IS a good picture!

That may work, the output from the log burner to the heat exchanger will probably need a pump, but only set on a low setting.
I suggest the heat exchanger on the boiler side has a pump and zone valve installed to prevent heat leaking from the boiler side to the log burner (when not lit) and to effectively take heat away from the heat exchanger to the rads when in use.

As you mentioned, the high points will need to be vented.

 

[Norcon]

That picture might as well have been drawn by a four old. No offence.
Basics like vent and cold feed wrong.

I'd suggest the OP studies the link I gave.

 

[exon16m]

What your doing is probably similar to Systemlinks heat genie...
http://www.systemlink.ie/products-59/heat-genie.html[/QUOTE]

Yes just like that. Although with far fewer pumps

 

[exon16m]

That picture might as well have been drawn by a four old. No offence.
Basics like vent and cold feed wrong.

I'd suggest the OP studies the link I gave.

That is how the system is can you explain what you mean please, I hope it's my drawing not the house that is done wrong. I think I see what you mean old refill to pre heating side and expansion on post heater side. (mine is genuinely as per my picture)


With this system do you think you would get much flow via the wood burner loop when not in use given it is nearly 35m long horizontal goes uphill and has many bends to make having an electric valve worth it? I wanted to minimise any potential points that could fail and cause the wood burner loop to over heat.

So I will need two of these on the section over the joist?

http://www.jtmplumbing.co.uk/compression-40/valves-41/automatic-air-vent-7152.htm

 

[Norcon]

3 pumps on your schematic.
Only an extra one with this...
http://www.systemlink.ie/images/stories/systemlink/Schematics/ME00112010.pdf

You can do the 2 pipe take off or the 4.
With a system like that you lose the troublesome zone valves.

 

[Norcon]

If the distance between your solid fuel stove and oil boiler/hot water cylinder is 35m then the heat genie will be a better method.

 

[Corgigrouch]

Oh My!..... Why are folk determined to overcomplicate something that could be so simple and reliable.... made from off the shelf stuff... Where is the DHW cylinder?

When that quench valve operates where will all the water go?

 

[MeldrewsMate]

With this system do you think you would get much flow via the wood burner loop when not in use given it is nearly 35m long horizontal goes uphill and has many bends to make having an electric valve worth it? I wanted to minimise any potential points that could fail and cause the wood burner loop to over heat.

The ZV goes on the boiler supplied loop as this water would be pumped along your 35m of lovely heat transmitting pipework....insulated or not, that's heat you're paying for, and gas that my kids (and yours) would like in 20 odd years please.

Be carefull with AAVs, they can also let air in if put in a low pressure location. Manual vents are OK though.

If your sketch is accurate then you need to move one of the boiler to HE pipes to the output side of the pump or you will depress the boiler output temperature with the return water after it has gone through your loft mounted HE.


....and anyway, shouldn't you be in bed by now? It's school/nursery tomorrow. I'll send dad up to read you a story.

 

[exon16m]

Oh My!..... Why are folk determined to overcomplicate something that could be so simple and reliable.... made from off the shelf stuff... Where is the DHW cylinder?

When that quench valve operates where will all the water go?

It is an off the shelf kit. From the maker of the boiler.

The dhw is on a loop with an automated valve from the out and return part of the diagram.

The quench valve discharges into an external drain as the wood burner would overheat if it was not there and the heat for some reason was unable to be lost

 

[exon16m]

With this system do you think you would get much flow via the wood burner loop when not in use given it is nearly 35m long horizontal goes uphill and has many bends to make having an electric valve worth it? I wanted to minimise any potential points that could fail and cause the wood burner loop to over heat.

The ZV goes on the boiler supplied loop as this water would be pumped along your 35m of lovely heat transmitting pipework....insulated or not, that's heat you're paying for, and gas that my kids (and yours) would like in 20 odd years please.

Be carefull with AAVs, they can also let air in if put in a low pressure location. Manual vents are OK though.

If your sketch is accurate then you need to move one of the boiler to HE pipes to the output side of the pump or you will depress the boiler output temperature with the return water after it has gone through your loft mounted HE.


....and anyway, shouldn't you be in bed by now? It's school/nursery tomorrow. I'll send dad up to read you a story.

Lol thanks... I guess I could have drawn it not on the back of an envelope and taken a little more time.

I will see if I can make a better one today.

Depressing the boiler you mean I would have a "short circuit" missing the boiler without a automated valve to close this loop.

The check valve question. Do they significantly affect flow it would be nice to have one to prevent back flow via boiler when wood burner is heating without needing to have a third pump running.