Nicolas Boretos wrote:

Hi all,

Calling from Greece here.
Managed to install an olive kernel boiler last week and need to pick
your collective minds regarding temp control.
Boiler will be feeding floor heating, undertile, and AFAIU, need to keep
the temp between ~ 45-25 centigrade to avoid lifting tiles, cracks etc.

Currently the system has a simple thermostat that controls the leadscrew
feeder under the hopper as well as the fan blower (they are wired in
parallel). When it reaches temp. the system goes off for a while.
Another thermostat controls the water circulator.

Olive kernel boilers here are typically run without much concern given
to efficiency because olive kernel is quite cheap, and when they are
installed "on-grid", electrical consumption is not a concern. People
usually turn them on in November and off in April, and many keep the
"windows open.." I would not be surprised if this was how the coal
burners were run in the UK...

I live off-grid, and my main problem is that the leadscrew drive system
has a gearbox, and sucks down ~ 20 amps (@12v) off my battery bank, with
no load, and with the simple on-off control, the leadscrew (burner) is
mostly on. The thermostat has only a few degress hysterises, so the
boiler comes back on ~42 degrees...

What I'd like to do is have the burner "sleep", and come back on when
water in the return line reaches ~ 25 degrees instead. This is not
considering lags, etc...

Anyone have any ideas on doing this in an easy way, outside of using an
programmable boiler controller..dont need the expense, nor the hassle. I
wonder if they make thermostats with adjustable hysterises-differential?

One not so smart option is to use a programmable timer here, the octal
plug type, that has adjustable TIMEon, TIMEoff, but this does not take
into consideration temperature, the thermostat is simply wired in series
with it and the motor/blower...


I must be missing something, as I don't see the problem.

You set the main thermostat to 25 degrees. You use a second
thermostat,connected to the supply *after* the main stat and
set to 45 degrees, to power a relay with contacts across the
25 degree stat.

Initially, both stats are closed and the 25 deg stat is
shorted by the relay. The temp will rise until the 25 stat
opens. No problem, the supply is maintained by the relay
contacts.
The temperature will rise until the 45 stat opens. This
opens the relay, the 25 stat is already open - so no power
then goes to the load or the 45deg stat or its relay.

Only when the temp has fallen to 25 deg will the main stat
close, restarting the cycle.

HTH
Sue