Boiler stove setup

[Stuart84]

I have a Yeoman boiler stove connected to a buffer tank in a closed circuit. The stove only heats the water in the buffer tank.
My boiler outlet passes through a coil within the buffer tank.
I was wondering if this is correctly set up?
Or should the return to my boiler pass through the buffer tank, reheating the returning water thus reducing the temperature difference between outlet and return causing the boiler to fire less frequently when CH & DHW is demanded.

 

[oldbutnotdead]

What a very ambiguous post.
First off, do you have 2 heat sources (usual setup is solid fuel and gas or oil boiler) or just the one.
Second, Yeoman make all sorts of stoves- is yours gas, oil, wood, what?

 

[Stuart84]

The stove is multi fuel and the back boiler of the stove heats water in a buffer tank.
Our gas boiler outlet pipework goes through the buffer tank (coil within the buffer tank) therefore our CH & DHW does not directly draw the heated water from the buffer tank.

 

[oldbutnotdead]

Odd setup. So all you are using the buffer tank for is as a preheater for the water in the main heating system.
If the multifuel stove is running then you'll get convection in the store and some heat transfer to the coil (any idea what rating the coil is? Is it at the top or bottom of the store?)
When the stove is not running you won't get much convection circulation in the store so quite quickly the water next to the coil will cool off (especially if the coil is at the bottom) so the boiler will have to chime in. Of course the boiler now has to heat the store as well as the rads and dhw cylinder.
Its an odd setup and i suspect not very efficient. It is more conventional for the heating to run directly from the store (with stove direct and gasboiler direct or indirect) and you can use a coil in the store for mains pressure dhw (if the coil is big enough-30kw minimum).

 

[Stuart84]

Yes we think it’s an odd setup too, even though the installers assured it was correct. Subsequently they have gone out of business so cannot get them back to fix.
The bypass pressure valve constantly releases causing very loud bangs.
Our CH is a pressurised system therefore cannot feed the stove straight in to the CH pipework.
Our buffer tank is 100L but doesn’t detail the rating of the coil within.
Would a larger buffer tank and having the coil within the buffer tank attached to the boiler return pipework make the setup more efficient?

 

[oldbutnotdead]

Not really, if you did it that way you'd get even less transfer from buffer tank to heating (but the gas boiler would heat the buffer more quickly).
100l isn't much of a store, if you had a larger store (200 or 300 litre) it would be worth looking at changing the heating & dhw to open vented and connect it to the store.
Which PRV is constantly releasing- gas boiler or woodburner/buffer?

 

[Stuart84]

The prv for the wood burner keeps releasing. Think it’s because the buffer tank can’t lose the heat quick enough even with the CH & DHW on.
I don’t want the gas boiler to heat the buffer, I was hoping the heated water within the buffer (from wood burner) would be transferred to the returning water, used for CH & DHW, going into the boiler (increasing its temperature) meaning boiler wouldn’t have to work as hard to reheat the water going back out to the CH & DHW system.

 

[oldbutnotdead]

Hopefully the valve that is releasing is pressure and temperature (most of them seem to do that combination). Is there a small header tank for the buffer and is there a heat loss radiator for the woodburner? I have a horrid suspicion that your installers intended the buffer tank to act as the heat loss- which obviously isn't working very effectively.

Useful test for you- read the gas meter, run the gas boiler only for a heating cycle (say your normal evening run of 4pm-11pm), read the gas meter again, note external temperature. Next day, read gas meter, run your normal heating cycle with woodburner, read meter again at the end of the night. Note external temperature. Compare the 2 gas readings, see if there's any significant difference (I don't think there will be)

If the coil in the tank was in the return line only then yes you'd get some thermal transfer back into the boiler- (subject to the limits earlier described) and yes it might be more effective than trying to heat already hot water (the temperature difference should be higher). Of course if the buffer tank is colder than the return then the boiler will be making up the difference (thermal transfer works both ways). Problem with trying to heat the coil from the buffer tank is internal circulation (or lack of) within the buffer- you'll get much better energy transfer by directly connecting.

Question- do you get your wood (or whatever) that you burn in the woodburner for free or do you pay for it?

 

[Stuart84]

I get wood for free, but have to pay for the smokeless coal.
There is a header tank in the loft to keep the stove & buffer tank at a constant level.
Thanks I’ll compare gas readings. I’ve a feeling I’ve been paying to heat a tank of water that’s not doing anything.

 

[oldbutnotdead]

Yeah, you'll not be getting much return from that buffer tank and if it is the only heatsink connected to the woodburner it isn't surprising the overtemp valve keeps blowing off.

Since you're getting fuel free it is probably worth you looking at keeping the woodburner connected to the heating system-either just using the buffer as a low loss header or go for a bigger one as a themal store. If you look at the links below this thread there's a useful one which should help explain how to make it worth the effort