On Fri, 27 Nov 2020 16:28:24 +0000, T i m wrote:

On Fri, 27 Nov 2020 13:55:42 +0000, Caecilius
wrote:

snip

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).

snip

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.

Thinking on, isn't the hysteresis partly a function of using a
convection heater, over say an oil filled rad?

A convection heater has no thermal mass and being 2kW gives a large
burst of heat, reaches stat temp, and very quickly cools down again.
If the same 2kW heater was in the form of an oil filled rad you would
get the same heating efficiency but with a lower hysteresis, simply
because of the heater design?

I think it's more to do with the difference between the mechanical
thermostat switch-on and switch-off temperatures. Last winter I
monitored the temperature and the graph looked like a sawtooth - can't
remember what the min/max spread was, but I think it was a couple of
degrees.

I'm thinking that either controlling the output power with something
like a dimmer circuit (chopping the AC waveform) or switching faster
with a solid-state relay or triac would solve that problem.

Also, have you tried it on 1kW OOI? We prefer to have a lower power
heater that runs a slower duty cycle for partly the reason you are
trying to minimise.

I don't know how easily your 2kW convector can cope but if it's more
than adequate, even in the worst conditions and better, can also cope
easily when switched to 1KW (assuming it can be), you might find you
can get away with a 600W flat panel oil filled rad and be even closer
to your desired destination 'naturally'?

It only uses around 1KWh overnight at the moment (I've got a
power-measuring device in the stack-o-plugs). As it's on for six
hours (midnight to six am), that means it's only on for around 8% of
the time. So I think it's more than adequate, and a 1KW would
certainly work.

We use one of these in the lounge:


https://www.coopersofstortford.co.uk...lled-radiator/

It's more that capable at getting the room up to temp fairly quickly
and keeping it there ... and it's much better than one of the more
upright oil filled rads we have because it's radiating surface area
better matches it's energy output (so it's doesn't 'overheat').

It's a bit big though/

Also less chance of it setting the house on fire if something falls
onto it when it's unattended?

Yes, that's true.

Cheers, T i m