On Fri, 27 Nov 2020 16:48:19 +0000, Caecilius
wrote:

snip

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.

That's a big part of course, especially if it's physically in the
heater itself.

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.

But the thing is the speed of the temperature increasing in the room
versus the thermostats chance to monitor / react to same. Imagine
putting a 10kW heater in there and how hot it would get before the
thermostat had chance to do anything about it?

The closer you match the heat losses from the room to the heat being
applied to it the smaller the chance of wide temperature swings?

I'm thinking that either controlling the output power with something
like a dimmer circuit (chopping the AC waveform)

Yes, I think that would work ...

or switching faster
with a solid-state relay or triac would solve that problem.

Or better still, actually 'hold' the temperature at whatever you want
using PWM rather than Bang-bang?

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

Ok, suggesting that 1kW (or even less) should be ok (and obviously,
less hysteresis).

(I've got a
power-measuring device in the stack-o-plugs).

LOL!

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.

Agreed.

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/

Well yes, it's fairly long but not 'big' as such, as long as you can
find somewhere to position it. Under a window maybe?

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

Yes, that's true.

If you are a good coder (especially in C) maybe you could make the
solution we and I'm sure (as you say) many others are waiting for!?
;-)

Or even if you didn't want to do so commercially (not everyone can
handle being a millionaire g) maybe it could be put on the net as
one of those d-i-y walkthroughs?

Arduino Mini, 2kW opto coupled PWM controller, Dallas I2C thermocouple
and a cheapo 5V wall wart ... I'd build one. ;-)

Cheers, T i m