My Viessman boiler journey

[JohnMo]

1 hour ago, marshian said:

That is an excellent result but maybe way outside the abilities of most people

It really needs to made to work simply, but it's letting me map an flow average temp and effects based on OAT and flow temp. Straight WC is the answer but due to weather, have no (safe) access to reinstall the OAT sensor.

[marshian]

21 hours ago, John Carroll said:

 

If you can believe the below, then any run time of more than 3 minutes per cycle has a negligible effect on boiler efficiency.

 

Sorry meant to also say it does show that there is an impact on efficiency until 60 mins of run time (OK so it's the outer edge of a bell curve) IMO it's still over 1% (but less than 2%) loss at a 3 min run time which is why I like to set the system up to minimise cycling as much as possibe

[John Carroll]

2 hours ago, marshian said:

 

Sorry meant to also say it does show that there is an impact on efficiency until 60 mins of run time (OK so it's the outer edge of a bell curve) IMO it's still over 1% (but less than 2%) loss at a 3 min run time which is why I like to set the system up to minimise cycling as much as possibe

Honeywell don't pay much attention to these findings since their Evohome continuously cycles the boiler and even smart roomstats with TPI? control do similar.

[marshian]

25 minutes ago, John Carroll said:

Honeywell don't pay much attention to these findings since their Evohome continuously cycles the boiler and even smart roomstats with TPI? control do similar.

 

It's a conversation being carried out elsewhere on here - Smart is not always "smart" sometimes it's pretty (expletive deleted)ing dumb

[JohnMo]

9 hours ago, John Carroll said:

Evohome continuously cycles the boiler

Is that running Opentherm or on/off?

[John Carroll]

Sorry John,

Don't know as I just read a lot about Evohome in Automated Home.

[JohnMo]

On 04/01/2025 at 21:38, John Carroll said:

 

If you can believe the below, then any run time of more than 3 minutes per cycle has a negligible effect on boiler efficiency.

Not sure how accurate that graph is in real terms. Believe it covers the boiler in isolation from a full system. System effects on efficiency are very different depending on system volume and type of heating (radiators, fan coils or UFH). When you fire up a boiler you have to heat the boiler metal work, interconnected pipes, the water within, then the radiators or floor, before any useful work is actually completed.

 

A boiler running in a small loop, doing no useful work, my loose 12% efficiency on a 30 second run, but you wouldn't have a warm house, so real efficiency is zero.

 

Trouble with most on/off control, is most boilers run full load to get to set point ASAP, so a short run is just full load, then off, so you have zero chance of utilising part load modulation efficiency gains, which comes from prolonged running, or something like Opentherm telling the boiler to slow down work less hard.

 

Believe are also many differences in Opentherm on how hard it allows the boiler to run, Honeywell is run it hard to keep run time short, while Tado is run it slow and long - could be wrong?