cynic wrote:

I can see that it would be in defensible as it is using equipment in a
way for which it isn't designed but unsafe? After all it's using 0.6 the
voltage and current it was designed for.

AJH

I just did a fag packet calculation to check your power per element
and you are closely correct.

I just rounded 1 over root 3 by a bit.


The only thing I can see that you have
not mentioned is temperature control but for a three phase unit I
would expect it to be via a separate thermostat and contactor in the
supply. The coil voltage may be 400(415) and would require a coil
change.
Are the ends of the elements not accessible to split the delta at all?

It doesn't look like it, just 3 bolted terminals under the exterior cover. I
thought the temperature control would just be a bimetallic contact as in a
domestic immersion but if you're right then this is a worry. The system has
2 pressure relief valves (both set at 4 bar yet one is 3 storeys and 12m
below the other) and automatic water make up so little chance of damage.

There's 3tonne of water to heat so little chance of boiling.



The question remains is 2 kW going to be enough for a meaningful
contribution or would it be a waste of time anyway?

Maybe a waste of time but I imagine the occupants would be grateful of
something just to take the chill off. The worst heat demand is some
600kWhr/day and this is for DHW and space heating.

The stupid thing about the arrangement is that the top of the tank is not
reserved for DHW so the underfloor loop destroys stratification and lowers
the whole tank to one temperature when things go bad.

Finally if it takes three days for spares for the wood burner to
arrive what is the cost of downtime and it may be worth keeping a set
of common parts on stock.

The woodburner costs about 10 times as much as a condensing gas boiler. The
latest failure was a small stainless steel part in the fire box distorting
and then heat radiating onto some connector blocks in the grate area. The
silicon wires held up but the plastic connectors and plastic grate motor
cover melted. The new firebox is 500 quid, I have fitted one sent down by
an old friend from Scotland but it still took from the fault reported on
Friday to my deciding what needed doing on Sunday to being up and running
on Tuesday as I live 2 hours away and have work commitments. The new parts
will take 2 weeks but yes they should be kept in stock.

I replaced the connectors with porcelain ones and will consider fitting an
Aga fire stop valve to the control the feed auger.

Four years ago I asked for some sort of webserver to be used to flag up
faults as the 3 tonnes of water will keep the place going from hot to 25C
for 8hours at worst case. If they dedicated the top of the thermal store to
maintain DHW it would be much longer before the floor slabs were cold.

BTW when the load of each flat was calculated use of CRT televisions was
expected, presumably modern electronics waste less power as heat as the
system struggles.

AJH