Weather Compensation for CH?

[JonE]

Baxi offer an In-Flue Outdoor Sensor (IFOS) which is clipped into the flue of a compatible boiler to sense temperature of incoming air and is wired to PCB so as to vary CH circulation temperature according to outdoor temperature.

Given that the house is usually occupied all day for most days but that conscientious manual intervention to adjust flow temperature is unlikely, is it a no-brainer to install an IFOS with a new boiler or a pointless gimmick?

As an aside, I recognise that the boiler has to be configured for the presence of an IFOS before my intended (OpenTherm compatible) portable RF thermostat/programmer's receiver is connected to the (OpenTherm compatible) boiler but idly wonder about the consequences of the IFOS failing (especially if it does so silently). Please note that an internet-dependent 'smart' controller is quite deliberately not being contemplated so that aspect is outside scope of my enquiry.

Cheers!

[scotview]

Baxi offer an In-Flue Outdoor Sensor (IFOS) which is clipped into the flue of a compatible boiler.

Cheers!

The problem with this is that your boiler will have probably been grossly oversized at installation, which kind of defeats the purpose of this type of modulation.

[Lootman]

You probably won't like this answer but I think it is adding complexity for little return. I would not do it for much the same reason as I would not use a so-called "smart" thermostat like a Nest. All too clever by three quarters.

I don't care what the outside temperature is, only the indoor temperature. I set the heating for 20 during the day and 16 at night. There is an "away" setting that switches on heat for an hour a day when we are not at home, to stop the pipes from freezing.

If I am cold I turn the heat up. If I am hot I turn it down. That and an on-off switch is all the technology I need.

[Boots]

I have a neural network, heuristic, amino acid based processor to dynamically monitor ambient conditions, and all predicted future events and adjust the heating controls minute by minute.

I married her 20 years ago.

[88V8]

Baxi offer an In-Flue Outdoor Sensor (IFOS) which is clipped into the flue of a compatible boiler to sense temperature of incoming air and is wired to PCB so as to vary CH circulation temperature according to outdoor temperature.....a pointless gimmick?

It would be useful if one were trying to heat the garden.

V8

[swill453]

I have a neural network, heuristic, amino acid based processor to dynamically monitor ambient conditions, and all predicted future events and adjust the heating controls minute by minute.

You'd think modern AI would have learned how a thermostat works...

Scott.

[BullDog]

Baxi offer an In-Flue Outdoor Sensor (IFOS) which is clipped into the flue of a compatible boiler to sense temperature of incoming air and is wired to PCB so as to vary CH circulation temperature according to outdoor temperature.

Given that the house is usually occupied all day for most days but that conscientious manual intervention to adjust flow temperature is unlikely, is it a no-brainer to install an IFOS with a new boiler or a pointless gimmick?

As an aside, I recognise that the boiler has to be configured for the presence of an IFOS before my intended (OpenTherm compatible) portable RF thermostat/programmer's receiver is connected to the (OpenTherm compatible) boiler but idly wonder about the consequences of the IFOS failing (especially if it does so silently). Please note that an internet-dependent 'smart' controller is quite deliberately not being contemplated so that aspect is outside scope of my enquiry.

Cheers!

Ignore the luddites would be my attitude. I see no downside to what you propose for weather compensation. Regarding a faulty temperature sensor, you could check it out, but I expect open therm would ignore a temperature sensor fault and act like the weather compensation input just wasn't there. If it tightens the control of the boiler modulation a little and has no effect on home comfort then there's no downside that I can see to having weather compensation installed with the new boiler. It might save a couple of per cent on gas consumption without effecting personal comfort. I'd go for it myself if installing a new modulating open therm boiler.

[jaizan]

Allegedly better controllers are not always as good as claimed.

Mine supposedly has a PI controller to prevent temperature overshoot. Supposedly.

In practice, it's terrible at that.
It faffs around and at times, it switches the heating on, runs for as little as 2 seconds and then switches off.
Then, if heating from more than 2C below the target temperature, there's still a big overshoot when it gets to temperature. It simply doesn't do what it claims.

I was going to switch to a similar model from another established brand, but I read a customer review which described exactly the same problem I have. Although he provided a far more complete description.

The way I make mine work is to predict when it will start to overshoot, then program the temperature at that time 0.5C lower.

I also do "weather compensation", as the thermostat is set to 20C at 6:00 am and 21C at 6:30 AM. So if the room is colder, it starts half an hour earlier. That's the one thing that does seem to work.

[servodude]

Allegedly better controllers are not always as good as claimed.

Mine supposedly has a PI controller to prevent temperature overshoot. Supposedly.

In practice, it's terrible at that.
It faffs around and at times, it switches the heating on, runs for as little as 2 seconds and then switches off.
Then, if heating from more than 2C below the target temperature, there's still a big overshoot when it gets to temperature. It simply doesn't do what it claims.

I was going to switch to a similar model from another established brand, but I read a customer review which described exactly the same problem I have. Although he provided a far more complete description.

The way I make mine work is to predict when it will start to overshoot, then program the temperature at that time 0.5C lower.

I also do "weather compensation", as the thermostat is set to 20C at 6:00 am and 21C at 6:30 AM. So if the room is colder, it starts half an hour earlier. That's the one thing that does seem to work.

While you can tune a PI controller to get a pretty decent response to be controlling overshoot really needs the D
P(roportional) - for transients (speed of response)
I(ntegral) - for removing steady state error
D(erivative) - for tuning overshoot

The main problem with control of temperature of something are the time lags between the energy being applied to the heating element, that heating up and the transfer of heat to whatever you want to control

What you're doing with the set points in time is probably as good as you can do in a home situation

[servodude]

I have a neural network, heuristic, amino acid based processor to dynamically monitor ambient conditions, and all predicted future events and adjust the heating controls minute by minute.

You'd think modern AI would have learned how a thermostat works...

Scott.

I believe they come out the factory configured with the algorithm:

is the radiator hot to touch? - no: turn up the thermostat

[DrFfybes]

Allegedly better controllers are not always as good as claimed.

Mine supposedly has a PI controller to prevent temperature overshoot. Supposedly.

In practice, it's terrible at that.
[...]
The way I make mine work is to predict when it will start to overshoot, then program the temperature at that time 0.5C lower.

I've come to the conclusion that's they way of most of these 'smart' control systems - they work fine in a closed controlled well insulated testbed, but out in the real world with opening doors and windows and heat sources walking between rooms things are not quite as good. Our timer has a 'holiday' mode so you can make it come back on just before you get home. In reality by the time we've unpacked and made a cuppa the rads are hot anyway. Then again the installer said there was no point in insulating the pipes to the rads - we have over 100m pipework in our place, 22, 15, and 10mm. Some of the distant rads had a 15C drop before the water reached them, now reduced to under 5C

I also do "weather compensation", as the thermostat is set to 20C at 6:00 am and 21C at 6:30 AM. So if the room is colder, it starts half an hour earlier. That's the one thing that does seem to work.

Now that is brilliant - probably the first practical use of a programmable stat I've come across. Apart from the 6am bit

Paul

[jaizan]

I'm slightly tempted to programme an Arduino ESP 32 to control my central heating.

I've done data logging to thingspeak, plus power logging.
Also one that sets a beeper off if the kitchen extractor fan is not used when cooking, useful for student tenants....!

So that's most of the know how for a programmable thermostat. The only remaining bit of code to plagiarise is for a real time clock, which I presume it can get off the internet.