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.

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?

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.

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

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

is one example I found.


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


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



--
Ideas are more powerful than guns. We would not let our enemies have
guns, why should we let them have ideas?

Josef Stalin

On 27/11/2020 13:55, Caecilius wrote:
I'm sure I can't be
the only person who want a constant overnight bedroom temperature
without running the main house heating.

I've experimented by turning the central heating off overnight and it
doesn't seem to reduce gas consumption much. It seems to mean that the
house is horribly cold for the first hour of the day and the heating
never switches off all morning and most of the afternoon. I think the
thermal momentum of a brick building and its contents must mean that
cooling down and warming up take an inconvenient amount of time.

Bill

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

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

snip

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.

Or have both functions (clock / stat) combined?

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.

https://www.timeguard.com/products/c...r-time-control

I'm not sure the actual switch is silent though but it is very quiet.

The problem you might have is getting the heater itself to stay on
without it's overtemp or main stat cycling, even though the remote
timer / stat is calling for heat?

I did buy some mains level PWM power controllers with the intention of
mating them with an Arduino and remote thermostats (one on the heater
and one in the room) so that I could manage the power to a small oil
filled rad (that couldn't dissipate it's heat energy fast enough so
would modulate on it's overtemp stat) and manage the room temp both
silently and more accurately (no temperature overshoot etc).

Not gotrountuit yet of course ... ;-(

Cheers, T i m

On Fri, 27 Nov 2020 15:10:00 +0000, williamwright
wrote:

On 27/11/2020 13:55, Caecilius wrote:
I'm sure I can't be
the only person who want a constant overnight bedroom temperature
without running the main house heating.

I've experimented by turning the central heating off overnight and it
doesn't seem to reduce gas consumption much. It seems to mean that the
house is horribly cold for the first hour of the day and the heating
never switches off all morning and most of the afternoon. I think the
thermal momentum of a brick building and its contents must mean that
cooling down and warming up take an inconvenient amount of time.

Bill

You don't have my gas bill!

I like my house, but it's expensive to heat, and having the CH off
overnight makes a big difference. Having it come on again at 6.00am
means its warm enough by the time I get up.

I need to do other things to reduce my energy consumption like replace
the Aga with something from the 21st century and bring my EPC rating
up from it's currently dire E rating. But for now I'm trying to live
comfortably while working through the various improvements.

On Fri, 27 Nov 2020 15:15:13 +0000, T i m wrote:

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

snip

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.

Or have both functions (clock / stat) combined?

Yes, no reason not to combine the two functions. But that's not
essential.


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.

https://www.timeguard.com/products/c...r-time-control

I'm not sure the actual switch is silent though but it is very quiet.

It's probably an improvement on the WW2 era bimetalic strip that my
convection heater uses, but I suspect it's still a relay inside and it
probably has a fairly high hysterisis to preserve contact life.
Unfortunately the data sheet doesn't give much information about the
switching method or the operating parameters.

The problem you might have is getting the heater itself to stay on
without it's overtemp or main stat cycling, even though the remote
timer / stat is calling for heat?

I don't think that will be a problem. If I set the thermostat on the
convection heater to, say, 25C then it shouldn't activate unless the
room is unpleasantly hot. And if the internal overtemp operates then
there's something badly wrong.

I did buy some mains level PWM power controllers with the intention of
mating them with an Arduino and remote thermostats (one on the heater
and one in the room) so that I could manage the power to a small oil
filled rad (that couldn't dissipate it's heat energy fast enough so
would modulate on it's overtemp stat) and manage the room temp both
silently and more accurately (no temperature overshoot etc).

Not gotrountuit yet of course ... ;-(

We've all been there with arduino/pi things I think. I know I have.

Cheers, T i m

On Fri, 27 Nov 2020 15:28:48 +0000, Caecilius
wrote:

snip

Or have both functions (clock / stat) combined?

Yes, no reason not to combine the two functions. But that's not
essential.

It just stopped there being a 'tree' of plugin things. ;-)


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.

https://www.timeguard.com/products/c...r-time-control

I'm not sure the actual switch is silent though but it is very quiet.

It's probably an improvement on the WW2 era bimetalic strip that my
convection heater uses,

Quite, the overtemp stats in the little (600W) oil filled rads are
particularly noisy (in an otherwise quiet bedroom).

but I suspect it's still a relay inside and it
probably has a fairly high hysterisis to preserve contact life.

Yes, that sounds right (from the discrete 'Click' you can just hear
now and again).

Unfortunately the data sheet doesn't give much information about the
switching method or the operating parameters.

No, it is a pretty basic piece of kit but it's what's right in front
of me now and in it's second season of use.

The problem you might have is getting the heater itself to stay on
without it's overtemp or main stat cycling, even though the remote
timer / stat is calling for heat?

I don't think that will be a problem. If I set the thermostat on the
convection heater to, say, 25C then it shouldn't activate unless the
room is unpleasantly hot.

No, it *shouldn't* and being a convector, might not.

And if the internal overtemp operates then
there's something badly wrong.

Well, that's how I treated the functionality of the (several) oil
filled rads I have here but it's how they work nonetheless.

Even the 600W ones can generate more heat than they can dissipate and
so do 'overheat' and then cycle on their overtemp stats, way before
they may have reached the temp set by the main thermostat. I even
considered (and may well try this year) or rigging up two sockets on
an extension lead and wiring two of the 600W heaters in series so they
become two x 300W heaters. Set one stat on Max and then use the other
to manage the actual room temp.

I did buy some mains level PWM power controllers with the intention of
mating them with an Arduino and remote thermostats (one on the heater
and one in the room) so that I could manage the power to a small oil
filled rad (that couldn't dissipate it's heat energy fast enough so
would modulate on it's overtemp stat) and manage the room temp both
silently and more accurately (no temperature overshoot etc).

Not gotrountuit yet of course ... ;-(

We've all been there with arduino/pi things I think.

I just had a look on eBay and there are quite a few choices of 2kW
opto coupled module that should be very easy to interface. An Arduino
Nano, a Dallas I2C external temperature probe and a few lines of code
and you should be able to do what you need.

Mount it all in a plastic double box (like a trailing lead) with a
double pole switch on one side and 13A socket on the other and with
the stat coming out though a rubber grommet to somewhere suitable in
the room and you should be good to go (if you are ok with the coding).
;-)

I know I have.

I was sorting though some electronicy stuff earlier and came across an
ESP32 with external SIM card reader that was part of a project I was
playing with previously. That has built in BT and WiFi so you might
even be able to use one of those and set / adjust the required temp
with an App! ;-)

Cheers, T i m

Caecilius wrote:
On Fri, 27 Nov 2020 15:10:00 +0000, williamwright
wrote:

On 27/11/2020 13:55, Caecilius wrote:
I'm sure I can't be
the only person who want a constant overnight bedroom temperature
without running the main house heating.

I've experimented by turning the central heating off overnight and it
doesn't seem to reduce gas consumption much. It seems to mean that the
house is horribly cold for the first hour of the day and the heating
never switches off all morning and most of the afternoon. I think the
thermal momentum of a brick building and its contents must mean that
cooling down and warming up take an inconvenient amount of time.

Bill

You don't have my gas bill!

I like my house, but it's expensive to heat, and having the CH off
overnight makes a big difference. Having it come on again at 6.00am
means its warm enough by the time I get up.

I think ours is similar. ... and gas isn't cheaper off-peak,
especially ours as it's LPG in a big tank.

We tend to have the gas CH on when there are a lot of rooms in use and
use electricity for quick short term top-ups and in bath and shower
rooms etc.

--
Chris Green
·

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?

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'?

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').

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

Cheers, T i m

On Fri, 27 Nov 2020 15:59:50 +0000, T i m wrote:

On Fri, 27 Nov 2020 15:28:48 +0000, Caecilius
wrote:

[snip]

And if the internal overtemp operates then
there's something badly wrong.

Well, that's how I treated the functionality of the (several) oil
filled rads I have here but it's how they work nonetheless.

Even the 600W ones can generate more heat than they can dissipate and
so do 'overheat' and then cycle on their overtemp stats, way before
they may have reached the temp set by the main thermostat. I even
considered (and may well try this year) or rigging up two sockets on
an extension lead and wiring two of the 600W heaters in series so they
become two x 300W heaters. Set one stat on Max and then use the other
to manage the actual room temp.

That's useful information. I was considering replacing the convector
heater with a oil-filled rad to smooth the output by increasing
thermal mass, but I don't think I'll bother now if that's how they
work.


I did buy some mains level PWM power controllers with the intention of
mating them with an Arduino and remote thermostats (one on the heater
and one in the room) so that I could manage the power to a small oil
filled rad (that couldn't dissipate it's heat energy fast enough so
would modulate on it's overtemp stat) and manage the room temp both
silently and more accurately (no temperature overshoot etc).

Not gotrountuit yet of course ... ;-(

We've all been there with arduino/pi things I think.

I just had a look on eBay and there are quite a few choices of 2kW
opto coupled module that should be very easy to interface. An Arduino
Nano, a Dallas I2C external temperature probe and a few lines of code
and you should be able to do what you need.

Mount it all in a plastic double box (like a trailing lead) with a
double pole switch on one side and 13A socket on the other and with
the stat coming out though a rubber grommet to somewhere suitable in
the room and you should be good to go (if you are ok with the coding).
;-)

Yes, I'm fine with coding - I used to be a software engineer in the
1980s so I'm comfortable with C.

I'm still hoping there's a neater pre-built solution though. I would
hope that solid-state switching add-on thermostats would be common - I
can't be the only person with this use case.

I know I have.

I was sorting though some electronicy stuff earlier and came across an
ESP32 with external SIM card reader that was part of a project I was
playing with previously. That has built in BT and WiFi so you might
even be able to use one of those and set / adjust the required temp
with an App! ;-)

This is the sort of thing I like to play around with, but don't want
to integrate into "production" equipment around the house that I want
other family members to be able to use.

Cheers, T i m

Caecilius wrote:
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.

If you don't mind DIYing a case, there are PID controllers, eg:

https://www.ebay.co.uk/itm/REX-C100-...t/363129928297
(they're all clones of clones of clones)

I wouldn't trust the SSR with 40A but 8A mains should be ok.

I don't know if the thermocouples would be accurate enough - quite a
difference in +/- 2C for room temperature. You might be able to manually
offset it (ie ask 20C and get 22, so ask for 18C instead).

The advantage of PID is that it should aim to keep wherever you place the
thermocouple at a constant temperature - it'll 'learn' the dynamics of the
room and the heater to avoid peaks and troughs as it overheats and then
overcools.

Theo

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

On 27 Nov 2020 16:43:09 +0000 (GMT), Theo
wrote:

Caecilius wrote:
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.

If you don't mind DIYing a case, there are PID controllers, eg:

https://www.ebay.co.uk/itm/REX-C100-...t/363129928297
(they're all clones of clones of clones)

That's interesting. PID control might be a bit OTT for my
application, but it's cheap enough.

I wouldn't trust the SSR with 40A but 8A mains should be ok.

Yes, I've seen enough big Clive videos to know how optimistic these
ratings are. But as you say a 2KW pure resitive load should be well
within it's capabilities.

I don't know if the thermocouples would be accurate enough - quite a
difference in +/- 2C for room temperature. You might be able to manually
offset it (ie ask 20C and get 22, so ask for 18C instead).

I'd hope that there's something with a smaller temp range (0 - 1300 C
looks like it's designed for a kiln) and an associated increase in
accuracy. I'd like something like 0.5 C or maybe even 0.1 C if
possible.

The advantage of PID is that it should aim to keep wherever you place the
thermocouple at a constant temperature - it'll 'learn' the dynamics of the
room and the heater to avoid peaks and troughs as it overheats and then
overcools.

I'm surprised that a PID controller uses a simple SSR output. I would
have thought that a "dimmer" type circuit using a triac for switching
would be better for that.

Theo

On 11/27/2020 02:55 PM, 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.

Have a look at triac datasheets.
For the 2kw heater you'll need a rather large one. (18 amps? BTA20 maybe)
and a heatsink.
Not all triacs are insulated,

as to how to drive them... you'll need some power supply, xfrmr or resistive.
and generate pulses or pulse train with correct timing.
There are application notes.

Microchip AN958
Low-Cost Electric Range Control Using a Triac
(very much what you want)

ST has a lot of appnotes. search their website.

On semi
AN1048/D (Snubber networks)
HBD855/D (Thyristor Theory and Design Considerations) Handbook, large
There's a zero point switch shown on pg 137. supposedly there's IC versions.


OTOH
There are perfectly fine thermostats and heaters available
wot utilize triacs. maybe get one of those.

On Fri, 27 Nov 2020 16:33:27 +0000, Caecilius
wrote:

snip

I was considering replacing the convector
heater with a oil-filled rad to smooth the output by increasing
thermal mass, but I don't think I'll bother now if that's how they
work.

That's how some of the cheaper ones work yes. We are currently running
a more traditional upright oil-filled rad (on 1kW) here in the lounge
(with the external timer stat) and it's fine. The point being it's
surface area is better matched to it's output power so it works
'properly'. ;-)

snip

Mount it all in a plastic double box (like a trailing lead) with a
double pole switch on one side and 13A socket on the other and with
the stat coming out though a rubber grommet to somewhere suitable in
the room and you should be good to go (if you are ok with the coding).
;-)

Yes, I'm fine with coding - I used to be a software engineer in the
1980s so I'm comfortable with C.

I'm still hoping there's a neater pre-built solution though. I would
hope that solid-state switching add-on thermostats would be common - I
can't be the only person with this use case.

That's *exactly* what I thought when I was looking for the same a
couple of years ago and I couldn't find one then. ;-(

I was sorting though some electronicy stuff earlier and came across an
ESP32 with external SIM card reader that was part of a project I was
playing with previously. That has built in BT and WiFi so you might
even be able to use one of those and set / adjust the required temp
with an App! ;-)

This is the sort of thing I like to play around with, but don't want
to integrate into "production" equipment around the house that I want
other family members to be able to use.

Understood. That's why something even 'preset' at whatever temperature
you consider reasonable might be a good solution, or add reading the
value of a pot to the project and make it fully adjustable. ;-)

Cheers, T i m

p.s. On these little (and they are pretty small) 450W oil filled rads
I was also going to fit one of the PWM modules inside the unit to
limit the power to something they could actually radiate!

Caecilius wrote:
That's interesting. PID control might be a bit OTT for my
application, but it's cheap enough.

Might come in handy for other things too. I put one in a case to control
the soldering oven, but it gets borrowed for other things.

I'd hope that there's something with a smaller temp range (0 - 1300 C
looks like it's designed for a kiln) and an associated increase in
accuracy. I'd like something like 0.5 C or maybe even 0.1 C if
possible.

You might be able to change the thermocouple type - not sure if there's a
setting for that (it'll depend on which clone it is).

I'm surprised that a PID controller uses a simple SSR output. I would
have thought that a "dimmer" type circuit using a triac for switching
would be better for that.

I don't think it matters - the thermal mass is such that giving a blast of 2
seconds on / 2 seconds off is just as good as 50/50 duty cycle at 50Hz - and
less buzzing.

Theo

Caecilius wrote in
:


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.

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.

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).

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.

https://www.screwfix.com/p/honeywell-home-dt90e/41365

Instructions downloadable from the spec tab of that page for a preview.

Could save a bit of faff in rolling your own.

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

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

Caecilius wrote in
:


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.

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.

I certainly don't need anywhere near 2KW as the duty cycle is below
10%.

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.

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.


https://www.screwfix.com/p/honeywell-home-dt90e/41365

Instructions downloadable from the spec tab of that page for a preview.

Could save a bit of faff in rolling your own.

On 27/11/2020 19:04, Caecilius wrote:
On Fri, 27 Nov 2020 18:00:48 +0000 (UTC), Peter Burke
wrote:

Caecilius wrote in
:


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.

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.

I certainly don't need anywhere near 2KW as the duty cycle is below
10%.

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.

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.


https://www.screwfix.com/p/honeywell-home-dt90e/41365

Instructions downloadable from the spec tab of that page for a preview.

Could save a bit of faff in rolling your own.

If you consistently only need 200/300 watts per hour then a cheap
option would be to just use a couple low power ceramic heat "lamps"
rated at 100 watts each and forget about a thermostat. The amount saved
in capital would pay go along way towards offsetting any excess power
being used.
Of course you then dont have a nice DIY project to keep you busy !!

On Fri, 27 Nov 2020 19:17:42 +0000, Robert
wrote:

[snip]

If you consistently only need 200/300 watts per hour then a cheap
option would be to just use a couple low power ceramic heat "lamps"
rated at 100 watts each and forget about a thermostat. The amount saved
in capital would pay go along way towards offsetting any excess power
being used.

That's around the wattage I need at the moment, but it will vary with
the outside temperature so I don't think a fixed wattage solution will
work.

Of course you then dont have a nice DIY project to keep you busy !!

That's true - I find the journey just as interesting as the
destination. Thankfully my wife doesn't read usenet!

On 13:55 27 Nov 2020, Caecilius said:

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.

If you can't find anything along those lines, then a low power
oil-filled electric heater might do the job. You could leave it on
all night or, alternatively, if you use the stat it wouldn't trip as
frquently as a convection heater.

I don't know if my arithmetic is out of date but I seem to recall
electricity is about 3 times the price of gas, watt for watt.

If so then heating one room overnight with electricity might cost
the same as heating 3 with gas. Someone is bound to correct me if
I've gone wrong.

On 27/11/2020 15:19, Caecilius wrote:
On Fri, 27 Nov 2020 15:10:00 +0000, williamwright
wrote:

On 27/11/2020 13:55, Caecilius wrote:
I'm sure I can't be
the only person who want a constant overnight bedroom temperature
without running the main house heating.

I've experimented by turning the central heating off overnight and it
doesn't seem to reduce gas consumption much. It seems to mean that the
house is horribly cold for the first hour of the day and the heating
never switches off all morning and most of the afternoon. I think the
thermal momentum of a brick building and its contents must mean that
cooling down and warming up take an inconvenient amount of time.

Bill

You don't have my gas bill!

I like my house, but it's expensive to heat, and having the CH off
overnight makes a big difference. Having it come on again at 6.00am
means its warm enough by the time I get up.

I need to do other things to reduce my energy consumption like replace
the Aga with something from the 21st century and bring my EPC rating
up from it's currently dire E rating. But for now I'm trying to live
comfortably while working through the various improvements.


Why keep the bedroom 'warm' when you could have an overblanket on all
night and you would be just as warm. That's what I do.

Is there really not anything you can do to reduce the heatloss ?.
What construction is your house ?. Solid walls, cavity, wattle & daub,
Aberdeen granite ?.

On 27/11/2020 18:00, Peter Burke wrote:
Caecilius wrote in
:


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.

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.

All the 2 and 3KW heaters that I have ever seen have a switch that
allows it to function as a 1KW , 2KW or 3KW heater. I have three
and all have this switch, including the cheapo £15 2KW job from a
supermarket.

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).

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.

https://www.screwfix.com/p/honeywell-home-dt90e/41365

Instructions downloadable from the spec tab of that page for a preview.

Could save a bit of faff in rolling your own.

On Fri, 27 Nov 2020 15:59:50 +0000, T i m wrote:

I just had a look on eBay and there are quite a few choices of 2kW
opto coupled module that should be very easy to interface. An Arduino
Nano, a Dallas I2C external temperature probe and a few lines of code
and you should be able to do what you need.

KISS - solid state relay instead of PWM module. 1-Wire temperature
sensor and Arduino to generate the PWM to drive the relay directly
using a PID(*) control algorithm based on measured temp.

(*) Proportional Integral Derivative.
https://en.wikipedia.org/wiki/PID_controller

--
Cheers
Dave.

On Fri, 27 Nov 2020 19:56:11 +0000, Andrew
wrote:

On 27/11/2020 15:19, Caecilius wrote:
On Fri, 27 Nov 2020 15:10:00 +0000, williamwright
wrote:

On 27/11/2020 13:55, Caecilius wrote:
I'm sure I can't be
the only person who want a constant overnight bedroom temperature
without running the main house heating.

I've experimented by turning the central heating off overnight and it
doesn't seem to reduce gas consumption much. It seems to mean that the
house is horribly cold for the first hour of the day and the heating
never switches off all morning and most of the afternoon. I think the
thermal momentum of a brick building and its contents must mean that
cooling down and warming up take an inconvenient amount of time.

Bill

You don't have my gas bill!

I like my house, but it's expensive to heat, and having the CH off
overnight makes a big difference. Having it come on again at 6.00am
means its warm enough by the time I get up.

I need to do other things to reduce my energy consumption like replace
the Aga with something from the 21st century and bring my EPC rating
up from it's currently dire E rating. But for now I'm trying to live
comfortably while working through the various improvements.


Why keep the bedroom 'warm' when you could have an overblanket on all
night and you would be just as warm. That's what I do.

I don't like my head getting cold, so I prefer a warm room. But by
"warm" I mean around 18 C, so just "not cool" really.

Is there really not anything you can do to reduce the heatloss ?.
What construction is your house ?. Solid walls, cavity, wattle & daub,
Aberdeen granite ?.

It's a large 1930s house with traditional brick breeze block
construction. Total floor area about 315 square metres. The kitchen
is heated with an Aga and the rest of the house is heated with two gas
boilers installed in parallel (weird I know).

I did a lot of work on it this year, but I still need to sort out the
heating and insulation. But that's a project for next year after
winter - I'll probably be on the group again when I start that project
as there's a lot to do.

Just checked my EPC cert, and it's 38 (F) (not E as I previously
thought) which is even worse that I thought.

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.


I seem to be in a minority here but the whole idea of maintaining a
constant bedroom temperature strikes me as odd. Get a thicker duvet or an
electric blanket that can be left on. Being warm under a duvet but having
cool air to breathe just feels right to me.

Tim

--
Please don't feed the trolls

On Fri, 27 Nov 2020 19:49:06 GMT, Pamela
wrote:

On 13:55 27 Nov 2020, Caecilius said:

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.

If you can't find anything along those lines, then a low power
oil-filled electric heater might do the job. You could leave it on
all night or, alternatively, if you use the stat it wouldn't trip as
frquently as a convection heater.

I don't know if my arithmetic is out of date but I seem to recall
electricity is about 3 times the price of gas, watt for watt.

If so then heating one room overnight with electricity might cost
the same as heating 3 with gas. Someone is bound to correct me if
I've gone wrong.

The bedroom area is only about 6.5% of the house area, so the
difference would need to be much greater than 3:1.

I've measured the overnight consumption of the electric heater, and
it's just under 1KWh at the moment which seems quite reasonable to me.

On Fri, 27 Nov 2020 16:59:36 +0000, Caecilius wrote:

The advantage of PID is that it should aim to keep wherever you
place
the thermocouple at a constant temperature - it'll 'learn' the
dynamics
of the room and the heater to avoid peaks and troughs as it
overheats
and then overcools.

Get the three control variables and it should run flat out until it
starts to approach the target temp then it'll throttle back to hit
the target temp with no overshoot. It'll then hold the temp there as
required, possibly very finely.

I'm surprised that a PID controller uses a simple SSR output. I would
have thought that a "dimmer" type circuit using a triac for switching
would be better for that.

A SSR can be driven with a PWM signal, you have to be a bit careful
with the underlying pulse frequency otherwise the PWM waveform beats
with the 50 Hz mains meaning the power delivered varies at the beat
frequency at some settings. Looks like the pump speed controller I
have runs at 3 Hz.

What do you think is in a SSR? B-)

I guess you could drive a triac directly, some how. You'd have to
provide the isolation, zero crossing stuff etc...

--
Cheers
Dave.

Some older Belling three bar fires used a dimmer idea. I still have one, but
I cannot say it was that successful as the thermostatic bit was inside the
heater and hence not really seeing the real room temp. You really need a
remote sensor. I was not convinced either of the efficiency of dimmed
elements of the type seen in bathroom fires when quite dim, indeed, it was
all to easy to forget it was on as they were too dim to see some of the
time. I saw it as a bit of a gimmick.
Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Caecilius" wrote in message
...
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.

On 27 Nov 2020 20:54:32 GMT, Tim+ wrote:

I seem to be in a minority here but the whole idea of maintaining a
constant bedroom temperature strikes me as odd. Get a thicker duvet or an
electric blanket that can be left on. Being warm under a duvet but having
cool air to breathe just feels right to me.

No, I think I'm in the minority judging by the absense of commercial
solutions!

On Fri, 27 Nov 2020 20:28:26 +0000 (GMT), "Dave Liquorice"
wrote:

On Fri, 27 Nov 2020 15:59:50 +0000, T i m wrote:

I just had a look on eBay and there are quite a few choices of 2kW
opto coupled module that should be very easy to interface. An Arduino
Nano, a Dallas I2C external temperature probe and a few lines of code
and you should be able to do what you need.

KISS - solid state relay instead of PWM module. 1-Wire temperature
sensor and Arduino to generate the PWM to drive the relay directly
using a PID(*) control algorithm based on measured temp.

Well, apart from the relay instead of the SSR, it's pretty much the
same thing isn't it, well, other than the programming is more
complicated. ;-)

(*) Proportional Integral Derivative.
https://en.wikipedia.org/wiki/PID_controller

I was thinking you could (if it became necessary) to just
progressively reduce the PWM ratio every degree you got nearer the
target temp from a few away. Given the idea was the OP might get
better results using a lower powered and possibly oil filled rad, the
chances of any overshoot should be minimised in any case ... and he
was going to do the coding himself. ;-)

Cheers, T i m

On 27/11/2020 15:19, Caecilius wrote:

I've experimented by turning the central heating off overnight and it
doesn't seem to reduce gas consumption much. It seems to mean that the
house is horribly cold for the first hour of the day and the heating
never switches off all morning and most of the afternoon. I think the
thermal momentum of a brick building and its contents must mean that
cooling down and warming up take an inconvenient amount of time.

Bill

You don't have my gas bill!

Mine is £1,560 per year. (Sort of inverted willy waving there!)

The size of the gas bill is irrelevant to what I said anyway, which is
that in my experience (of this house only) turning the heating off at
night seems to make very little difference. It could be because with no
comings and goings and no wondows open the heating doesn't come on all
that much at night.

I like my house, but it's expensive to heat, and having the CH off
overnight makes a big difference. Having it come on again at 6.00am
means its warm enough by the time I get up.

I need to do other things to reduce my energy consumption like replace
the Aga with something from the 21st century and bring my EPC rating
up from it's currently dire E rating. But for now I'm trying to live
comfortably while working through the various improvements.


I'm irritated by the fact the fairly new double glazing units seem to
let draughts in, in a few places, and I haven't been able to figure out
how to adjust them.

The thing I've done that made the biggest difference was making sure all
the doors in the basement were kept shut. The basement isn't heated but
it's obvious that draughts come in through the doors and then go though
crevices in the ceiling into the middle floor rooms.

Bill

On Sat, 28 Nov 2020 02:00:20 +0000, williamwright
wrote:

snip

I'm irritated by the fact the fairly new double glazing units seem to
let draughts in, in a few places, and I haven't been able to figure out
how to adjust them.

Yup, we live perfectly well in houses with gaps and draughts and have
no issues. Then we hermetically seal them and suffer black mould. So
then we fit non-closeable trickle vents in our double glazed units and
are forced to have non-closeable airbricks to avoid the problems we
never had in the first place?

As for changing all the air in the house every few hours ...

Cheers, T i m

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.

On 27/11/2020 13:55:42, 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.

Some thermostats have an "accelerator" heating resistor next to the
bimetallic strip. This reduces the hysteresis and make it more PWM based.

If you want accurate control then you're in the realms of PID control
and something like this:

https://www.amazon.co.uk/Hilitand-In.../dp/B07HJ5GQ2L

I have used similar controllers in kiln applications where ramp and soak
functions are required.

On 28 Nov 2020 at 15:20:39 GMT, "Pamela" wrote:

On 20:58 27 Nov 2020, Caecilius said:

On Fri, 27 Nov 2020 19:49:06 GMT, Pamela
wrote:

On 13:55 27 Nov 2020, Caecilius said:

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.

If you can't find anything along those lines, then a low power
oil-filled electric heater might do the job. You could leave it
on all night or, alternatively, if you use the stat it wouldn't
trip as frquently as a convection heater.

I don't know if my arithmetic is out of date but I seem to recall
electricity is about 3 times the price of gas, watt for watt.

If so then heating one room overnight with electricity might cost
the same as heating 3 with gas. Someone is bound to correct me if
I've gone wrong.

Yep I'd agree, taking into account the relative efficiency.



The bedroom area is only about 6.5% of the house area, so the
difference would need to be much greater than 3:1.

I've measured the overnight consumption of the electric heater,
and it's just under 1KWh at the moment which seems quite
reasonable to me.

Are you sure because 1 kWh seems very little for heating a room
overnight. It equates to a "one bar" fire left on for an hour which
wouldn't heat my room much.

Perhaps that room needs only the slightest amount of additional
heating

Indeed

--
Cheers, Rob

On Sat, 28 Nov 2020 15:20:39 GMT, Pamela
wrote:

snip

I've measured the overnight consumption of the electric heater,
and it's just under 1KWh at the moment which seems quite
reasonable to me.

Are you sure because 1 kWh seems very little for heating a room
overnight. It equates to a "one bar" fire left on for an hour which
wouldn't heat my room much.

We only have a 1kW oil filled rad in this lounge atm, the current
temperature is 23 DegC and the heater is off most of the time?

Before we were testing the (3,2,1KW in 1KW mode) upright oil filled
rad the 600W long, low slim one also worked perfectly.

Perhaps that room needs only the slightest amount of additional
heating

Victorian cottage here with solid 9" brick walls so not very good
thermally but the oil filled rad in the bedroom (with few other heat
sources, like TV's and computers) can be held at 'comfortable quite
easily as well.

Cheers, T i m

Caecilius used his keyboard to write :
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).

Could you not arrange a single zone to be on for that bedroom, use a
wireless thermostat and take the thermostat up to bed with you?

I have to ask why your house/bedroom becomes so very cold during the
night? I usually run the general house temperature at 20/21 C and with
no heat input, on a freezing night, my indoor temperature rarely falls
below 19C before next morning.