Maintaining constant overnight bedroom temperature with electric heater

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.

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

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I don't know if my arithmetic is out of date but I seem to recall electricity is about 3 times the price of gas, watt for watt.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

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 ?.

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.

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.

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.

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.

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

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.

overheats

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.

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...

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

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

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. ;-)

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

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'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

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 snipped-for-privacy@spamless.invalid wrote in news: snipped-for-privacy@4ax.com:

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

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).

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.

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

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

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:

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

Indeed

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.

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