In message . com,
wrote:

Martin Angove wrote:
In message .com,
wrote:

Re programmable stats


Another saving with these is that they keep a more constant temp
than
bimetallic stats. If you set it to 20 it will be at 20 +/- .25 deg
C,
whereas with a bimetal you're looking at 1 deg C hysteresis or
more.

Sorry to come in late to this thread, but I've been "away" for six
months or so :-)

I'd have thought that such fine-grain control, particularly of
gas-heated wet systems would be *worse* in terms of energy efficiency
than a system with 2 or 3 degrees of hysteresis. All past advice on
this
group seems to point to the fact that boilers are most efficient when
they run for long periods, and least efficient when they short cycle
on
and off.

Hwyl!

M.

why is that?

In terms of heat loss thru walls etc, a more costant temp will lose
less heat, so the q remains how the boiler efficiency will affect it.



The difference in heat loss between (say) 19C +/- 0.25C and 19C +/- 2C
can't be that great, surely? Intuition implies it should be exactly the
same, though I doubt it is in practice. My question was about boiler
running times. Received wisdom seems to be that running the boiler for 5
or 10 minutes repeated every 15 to "top up" the heat is going to be less
efficient than running it for a solid 30 minutes every hour. Of course
I'm guessing here with the timings which will vary hugely depending on
various factors including: insulation levels and ventilation levels of
the house, amount of thermal mass inside, outside temperature, exact
placement of thermostat, temperature setpoint of heating circuit, type
of heating (i.e. rads/ufh/other), occupancy of the house and so on and
so forth.

Just curious.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... I'm an absolute, off-the-wall fanatical moderate.