Help with Evohome / Opentherm / Intergas

[The EVOHOME Shop]

This is probably the first time I have seen a company admit, in writing, to a problem that doesn't exist?

I was saying earlier, manufacturers like to pedal their own controls. Intergas are no different...

[paulockenden]

It not called a proportional band either. Its a 'control bandwidth'...

I'll get my coat...

I only called it a proportional band because some dudes who work for a company beginning with H used that terminology....

[DBMandrake]

I only called it a proportional band because some dudes who work for a company beginning with H used that terminology....

Never mind what Honeywell do or don't call it, the HR92's are PID (proportional integral differential) controllers, "proportional band" is standard nomenclature for PID controllers for the region of operation where the output is at least partly proportional to the input:

https://en.wikipedia.org/wiki/PID_controller

"Tuning a control loop is the adjustment of its control parameters (proportional band/gain, integral gain/reset, derivative gain/rate) to the optimum values for the desired control response."

In a PID system one of the tuning parameters is the width of the proportional band - outside this range the output is either fully on (full heat demand in our case) or fully off. Inside the proportional band there will be a partial output that is somewhere between fully off and fully on, and will be proportional in some way to the input (and also past history of the input for the integral term) depending on the tuning of the other parameters.

In Evohome the proportional band is not user adjustable and is probably fixed in width, and I have seen +/- 1.5 degrees quoted by Honeywell guys on at least one occasion, and that does seem to agree with my own anecdotal measurements. I have not taken any detailed measurements to confirm whether it is exactly +/- 1.5 degrees though, as that would be quite tedious and time consuming, and require an HGI80 to do properly.

I doubt that it's only +/- 1 degree as the system as a whole would hardly ever be in the proportional band if that was the case as it would be difficult to keep all rooms within +/- 1 degrees the majority of the time unless the scheduled temperatures of the rooms stay the same most of the day, and people don't travel between rooms opening and closing doors in their wake...

Quibbling over the name of the proportional band is a bit silly though - we all know what it means.

[HenGus]

I am still none the wiser. A none problem has been resolved, but Dan states that when Override is elected Evohome 'drops its knickers and panics' but that this is normal operation. For the sake of my sanity, could someone from Honeywell take 5 minutes to describe how Evohome was actually designed to work under Opentherm control?

[Dan_Robinson]

Remember, the hr92 are not OpenTherm, a few exert their own control authority over their radiator. As well as giving information to the base unit which acts in the boiler.

[G4RHL]

Damn, how do you edit typo's?

Go back to your own posting and there is usual an edit option.

[Dan_Robinson]

Can't see it on my mobile.

[Dan_Robinson]

Just seem to delete my own posts :lol:

[The EVOHOME Shop]

Never mind what Honeywell do or don't call it, the HR92's are PID (proportional integral differential) controllers, "proportional band" is standard nomenclature for PID controllers for the region of operation where the output is at least partly proportional to the input:

https://en.wikipedia.org/wiki/PID_controller

"Tuning a control loop is the adjustment of its control parameters (proportional band/gain, integral gain/reset, derivative gain/rate) to the optimum values for the desired control response."

In a PID system one of the tuning parameters is the width of the proportional band - outside this range the output is either fully on (full heat demand in our case) or fully off. Inside the proportional band there will be a partial output that is somewhere between fully off and fully on, and will be proportional in some way to the input (and also past history of the input for the integral term) depending on the tuning of the other parameters.

In Evohome the proportional band is not user adjustable and is probably fixed in width, and I have seen +/- 1.5 degrees quoted by Honeywell guys on at least one occasion, and that does seem to agree with my own anecdotal measurements. I have not taken any detailed measurements to confirm whether it is exactly +/- 1.5 degrees though, as that would be quite tedious and time consuming, and require an HGI80 to do properly.

I doubt that it's only +/- 1 degree as the system as a whole would hardly ever be in the proportional band if that was the case as it would be difficult to keep all rooms within +/- 1 degrees the majority of the time unless the scheduled temperatures of the rooms stay the same most of the day, and people don't travel between rooms opening and closing doors in their wake...

Quibbling over the name of the proportional band is a bit silly though - we all know what it means.

The evohome system is using fuzzy logic and Honeywell control algorithms. I was told on several occasions this is not TPI control when using Honeywell to Honeywell technology (such as the Honeywell chip inside the ECO RF) or a bus connection like OpenTherm.

From what I have read and understood, a fuzzy logic control system can be implemented without PI algorithms, just as long as the process is not 'dumb' (i.e. just an ON/OFF switch controlling a fixed output heat source). The control bandwidth is then defined by the software and the fuzzy logic is told to keep it within that parameter by changing the control environment (closing TRV's and reducing boiler setpoint - the main features I have witnessed in multi zone evohome and OpenTherm).

There is no point second guessing about this 'control bandwidth' tolerance either - it is plus or minus 1 degrees C on setpoint which was confirmed by Honeywell at my meeting on Monday.

[blowlamp]

The evohome system is using fuzzy logic and Honeywell control algorithms. I was told on several occasions this is not TPI control when using Honeywell to Honeywell technology (such as the Honeywell chip inside the ECO RF) or a bus connection like OpenTherm.

From what I have read and understood, a fuzzy logic control system can be implemented without PI algorithms, just as long as the process is not 'dumb' (i.e. just an ON/OFF switch controlling a fixed output heat source). The control bandwidth is then defined by the software and the fuzzy logic is told to keep it within that parameter by changing the control environment (closing TRV's and reducing boiler setpoint - the main features I have witnessed in multi zone evohome and OpenTherm).

There is no point second guessing about this 'control bandwidth' tolerance either - it is plus or minus 1 degrees C on setpoint which was confirmed by Honeywell at my meeting on Monday.

So up until the ± 1°C band is reached throughout all zones, Evohome/OpenTherm acts in a similar manner to an on/off thermostat, only modulating the gas valve in an analogue way once within that band?

[top brake]

Intergas thought that there was an issue. Their reply dated December 2016:

Many thanks for your email.

There is no resolution date for the issue with the Eco PCB at present, we are still awaiting any news on that sorry.

We have no release date for the Extreme boilers but I have been assured that they will be opentherm compatible. As soon as we have a release date for these boilers we will let everyone know.

Regards

xxxx xxxx
Technical Support Engineer



Intergas Heating Ltd
Unit 94, Bay 1 Vantage Point
The Pensnett Estate
Kingswinford
West Midlands
DY6 7FS

Wires crossed I think. I think that answer refers to the fact that you cannot pair evohome to eco rf internal wireless receiver. And you still can't. You need to use Opentherm bridge

[top brake]

I'll write a fresh thread sometime to clear up all these misconceptions, or maybe we can do a webinar.
I'm surprised that there is so much fascination with how evohome works rather than just being happy that it does work

[paulockenden]

I think that answer refers to the fact that you cannot pair evohome to eco rf internal wireless receiver.

I wish someone had said that about a million posts ago! ;-)

[top brake]

I wish someone had said that about a million posts ago! ;-)

You only had to ask me Paul 👍

[top brake]

The issue with these forums is that it is hard to communicate truth and rumours repeated often enough become defacto. I have taken several steps back over the last year for various reasons (including growing a new tibia) but I'm happy to answer straightforward questions. I started a thread the other day with this intent but it quickly snowballed into another hard to follow one like all the others