Caecilius wrote in
:

On Fri, 27 Nov 2020 18:00:48 +0000 (UTC), Peter Burke
wrote:

Caecilius wrote in
m:

In a similar application I found my 2kw convectors had 2 paralleled
elements and disconnected one to make them 1kW only and less agressive
in their heat output.

You're the second person who's mentioned de-rating a 2KW heater. I
initially thought this was pointless, but perhaps it would help reduce
overshoot.

Yes, I think it will soften that leading edge and reduce overshoot making
the controller's task easier.

For control, honeywell have been forcing P+I control and multiple
switching cycles per hour on us in their room stats for years (wearing
out over cycled zone controls in the process).

I assume P+I is like a PID controller without the derivative term?
What's "multiple switching cycles per hour" mean? The DT90E datasheet
shows a "Cycle rate" parameter with a default of 6 and possible values
of 3,6,9 or 12 so presumably that's cycles per hour, but the datasheet
doesn't explain what that really means.

You can specify a 1.5 to 3 degree proportional temperature range and once
in that zone it will control on and off periods in proportion to the
temperature error. The cycles option will break an hour down into the
requisite number of on/off cycles and control the on and off time in within
the cycle in proportion to the temperature error. eg, if on 6 (10min)
cycles and the controller has determined a 20% duty cycle is required then
it will be on for 2mins and off for 8. More cycles means more wear and tear
on the relay (in your case) or relay + zone controls (valves) in my case
which is why I am not keen on these types of cycling controls where
motorised valves are in use (mine lasted on average only a couple of
years).

Their programmable stats (eliminating the time switch) are a bit
overpriced but this one has all the P+I, default 6 cycles per hour
(programmable up to 12 if desired) and is 8A rated (selectable prog
option) so will direct switch. The mag assisted batt powered internal
relay should be quiet enough.

36.50 is not that bad, but I note this comment on the screwfix site:

"I have marked it down on performance as the "click" when it turns on
and off can be heard all over the house"

So maybe not that quiet.

That is rather annoying and I have to say that setting the programmable
load setting to 8A can only make that worse (they will use a higher current
pulse to change the relay over more forcefully and reduce the risk of
arcing a the higher load which will likely be noisier).

More work for you but a workaround may be to remote sense the temperature,
snip the temp sensor (it's generally a bead thermistor) off the thermostat
board, extend the wiring to the bedroom and have the noisy stat elsewhere.
I have modified my wired stats to remote sense and cat5 cable works fine as
a low cost twisted pair connection. I was prepared to filter the signal at
the board but it hasn't proved necessary. The sensors ar generally stood
off the board quite a way to keep then in free air and so there is plenty
of lead length to play for. You'd also then have to feed the switched mains
back in of course, not great.

Ventilated sensor enclosures are readily available eg.

https://www.ecproducts.co.uk/product...-10k4a1-te-ra/

They're often cheaper with a thermistor fitted (which may not match yours
so best to swap) or are available empty. Can't remember where I sourced
mine.


Sorry this has moved away from being a simple off the shelf solution that I
had intended.