On Fri, 27 Nov 2020 14:40:57 +0000, The Natural Philosopher
wrote:

On 27/11/2020 13:55, Caecilius wrote:
I've got a large house with gas central heating which I use during the
day. It gets cold overnight in the bedroom though, so I use a 2KW
electric convection heater with the thermostat set to about 18 C on a
timeclock which switches on between midnight and six am (boiler comes
on again at six).

This was a great improvement last winter, and it only uses one or two
KWh overnight which must be cheaper than heating the whole house with
gas.

This year I want to improve the solution to keep the temperature more
constant (there's a big hysteresis on the convection heater
thermostat) and remove the bimetallic thermostat clicking noise.

I think I want electronic switching to remove the clicking noise and
allow a lower hysteresis plus an external temperature sensor. Maybe
something that's closer to a temperature controlled dimmer switch
instead of a standard bimetallic thermostat.

My plan is to put this temperature controller between the timeclock
and the heater, and set the heater thermostat to something like 25C as
a fail-safe.

Has anyone found or built something like this? I'm sure I can't be
the only person who want a constant overnight bedroom temperature
without running the main house heating.

Mmm. Raspberry Pi with a solid state relay, real time clock and
temperature sensor?

I could certainly do that, although I'd probably use an arduino rather
than a pi because it's a very simple task that doesn't need a general
purpose OS.

To be honest in most control situations its as good to have a
hysteresis and longer cycle time on the element as to have a modulated
in real time electricity supply.

That's an interesting view - I'd assumed that "dimming" the heater by
chopping the waveform would be the way to go, but I guess it ends up
making no difference if the hysterisis is low enough. Something like
0.5C would be unnoticible.

So I would go solid sate, and push the hysteresis down, rather than go
dimmer.

http://sustainablebuildingmaterials....ble-thermostat

is one example I found.

Thanks for that link: although the 0.2A capacity means it won't work
with a 2KW heater there may be similar units available that do what I
want.

I think the takeaway is solid-state switching plus low hysteresis.

Or you would use a wireless stat and put the receiver in a soundproof box.

Possibly. Sounds a bit more complex and heath-robinson that I need
though.

Or suffer from Hives...I am sure they do something

Not sure how a hive would help TBH