On Mon, 30 Jan 2012 12:02:36 -0800 (PST), robgraham wrote:
> I'm still not convinced I understand your set-up. You say there is 'a
> gravity loop' - is this just a dump into a small radiator, or is this
> all the heat extraction from the stove ?
The load controller sits across the flow and return pipes from the
woodburner. Feed from bottom of thermal store passes through a one
way flap valve in the load controller and then down to the wood
burner. Flow back up from woodburner goes to the top of the thermal
store but there is a T into the top of the load controller. There is
a thermostatic mixer valve that starts to move at 60C (fully moved by
70C), this valve selects where the pump takes its feed water from.
Either from the flow from the woodburner (cold state) or pre the one
way valve in the feed from the thermal store (hot state). The output
from the pump is feed into the return to the woodburner after the one
way valve. Without power the one way flap valve is biased open so
there is a "normal" open loop between the woodburner and the store.
With power the +ve pressure from the pump shuts the flap valve and
circulates water to maintain the feed to the woodburner at 60C (or
above if the store bottom is hotter than 60C).
Simple enough as far as the water side is concerned. The hard bit is
the electrical control side. Don't particulary want the thing running
when the stove isn't lit but don't want to have to keep remembering
to switch it on/off either. Automagic switch on is easy, pipe stat on
the flow from woodburner set at 50C. The switch off when the stove
has died down and is no longer providing any heat is the important
one. By then the bottom of the store is probably above 60C so the
load controller circulates from the store to the woodburner and back
until the store temperature drops below 60C. And I do mean the whole
store as the woodburner goes in at the very top and out at the bottom
so store stratification goes out the window. Trouble is the backup
oil boiler cuts in when the store gets down to 65C at about 1/3 up.
This has given the installers something to think about... it should
be getting some form of differential control at some point.
> I added an oil burner to my wood burner CH system and incorporated a
> Dunsley Neutraliser to meld the output of the two sources. My
> understanding is that a thermal store is at the system neutral point and
> does much the same thing.
Yes all the flows/returns (woodburner, oil boiler, CH) end up in the
thermal store which is the neutral point. Tapping points are
different, wood burner is very top and very bottom, oil boiler hot
half way and bottom, CH flow just below the oil boiler and bottom. CW
feed for DHW goes in just above the oil boiler hot input. There is a
solar coil in the bottom as well can't remember the relationship of
the bottom tappings and that.
> What I don't recognise is the term 'load controller' - the concept of
> a thermostatic valve in a gravity feed circuit seems an anathema too.
See above its not in the gravity loop as in it doesn't control the