28-12-2011, 09:01 PM
Hello Alan thanks for the reply, sounds like we are talking the same lingo, I put in a similar system as you described at our last place when we first bought it, it was a Stanley wood range with just the two boiler tappings for HW, I plumbed in a couple of radiators but no one would sell me an injector tee so I made my own with a short reducer set inside a standard T piece.
In the system described in my previous post the tank stat is about two thirds down from the top of the HW tank set to run the CH pump at its setting of 55 C this in practice gives about 60-65 C at the top and approx 50 C at the bottom of the HW tank.
This is overidden when the set high temp stat on the HW flow pipe at the boiler kicks in, this stat brings in the CH pump to dump the excess heat, it is also in parallel with a manual overide switch on the chimney breast which I fitted in case of total stat failure (just a little saftey feature).
The set high temp stat contacts do close but here is a thermal delay beween the temperature of the pipe it is
fitted to and the action of the switch snapping on, I have tried increasing the tension of the stats retaining springs and also the application of a heat transfer compound.
The effect I have is similar to the action of some electric kettles insofar that the kettle sometimes boils away freely before the thermal cut out switch comes into play.
The problem behind all this is that I suspect that the HW tank is to low in relation to the boiler to enact a fast gravity flow when the the fire is initally started using dry wood, there is nothing I can do about this hieght by virtue of the layout of the house and some of it's existing support walls.
The distance from the boiler tappings to the HW tank tappings is about 1 meter, the rise/fall over that meter distance is about 160 to 170 mm the only 90 degree bends are at a distance barely an inch from the HW tank tappings and as such I do not think that they are adversly impeding any gravity flow, all primary plumbing is 28 mm with no reducers.
So I guess I am needing a fast (thermally) acting stat also with these standard Honwell style stats they have quite a high hysterysis characteristic or at least it seems so to me.
The stove itself is 9Kw into the room and 9 Kw into the CH ie: the boiler has a rated output of 9Kw however many btu's that may be.
The system works very well as I have rebuilt the house to twice thermal insulation building regulations in overall thermal loss through the building.
It's just that one little problem to resolve, all primary heating circuits and radiators have the correct inhibitors added to them in the correct dose etc.
Lawrence.
In the system described in my previous post the tank stat is about two thirds down from the top of the HW tank set to run the CH pump at its setting of 55 C this in practice gives about 60-65 C at the top and approx 50 C at the bottom of the HW tank.
This is overidden when the set high temp stat on the HW flow pipe at the boiler kicks in, this stat brings in the CH pump to dump the excess heat, it is also in parallel with a manual overide switch on the chimney breast which I fitted in case of total stat failure (just a little saftey feature).
The set high temp stat contacts do close but here is a thermal delay beween the temperature of the pipe it is
fitted to and the action of the switch snapping on, I have tried increasing the tension of the stats retaining springs and also the application of a heat transfer compound.
The effect I have is similar to the action of some electric kettles insofar that the kettle sometimes boils away freely before the thermal cut out switch comes into play.
The problem behind all this is that I suspect that the HW tank is to low in relation to the boiler to enact a fast gravity flow when the the fire is initally started using dry wood, there is nothing I can do about this hieght by virtue of the layout of the house and some of it's existing support walls.
The distance from the boiler tappings to the HW tank tappings is about 1 meter, the rise/fall over that meter distance is about 160 to 170 mm the only 90 degree bends are at a distance barely an inch from the HW tank tappings and as such I do not think that they are adversly impeding any gravity flow, all primary plumbing is 28 mm with no reducers.
So I guess I am needing a fast (thermally) acting stat also with these standard Honwell style stats they have quite a high hysterysis characteristic or at least it seems so to me.
The stove itself is 9Kw into the room and 9 Kw into the CH ie: the boiler has a rated output of 9Kw however many btu's that may be.
The system works very well as I have rebuilt the house to twice thermal insulation building regulations in overall thermal loss through the building.
It's just that one little problem to resolve, all primary heating circuits and radiators have the correct inhibitors added to them in the correct dose etc.
Lawrence.
