Going green(er) with a Viessmann 200W (& heating efficiency home improvements)

Screwdriva

Following the success of our heating gas saving measures, we've decided to install polypipe underfloor heating on the ground floor of our semi-detached, paired with a new 19kW Viessman 100-W compact heat only boiler.  

Reasons for going with Viessman boiler are:

1) Ability of the boiler to modulate down to < 3 kW (1:10 modulation ratio), which is quite incredible! 
2) Weather compensation 
3) Load compensation via Nest 
4) Hot water prioritization
5) 10 year warranty for a relatively well made German boiler that is H2 compatible. 

Absolutely nothing wrong with our 5 year old Worcester Bosch 18Ri heat only boiler but it cannot achieve this level of theoretical efficiency, as it lacks the above functionality. We also looked at air source heat pumps but came away feeling that these are simply too nascent a technology today. 

Here is the episode of the completed project. Heating efficiency gains will be shared in the coming winter.

https://www.youtube.com/watch?v=UHD_-i5ulms

michaels

WE have a 10 year old 19kwh 200-w, similar but I think only modulates down to 4kwh , hasn't been great tbh, seems to use more gas than you would expect and not as reliable as we would have hoped (fine until the 5 year warranty ran out but then pretty dodgy)

Reed_Richards

1)  I bought an Atag gas boiler in 1998 which could modulate down very low.
2)  Likewise it had weather compensation and load compensation.  This was 24 years ago
3)  Load Compensation via Opentherm.  Any Opentherm-compatible controller should do weather and load compensation.  You'll need the right wiring though, not what you have at present.
4)  Are there really boilers that don't prioritise hot water?
5)  A 10 year warranty is good.  I would be very surprised if you see any H2 in the next 10 years and you may find that you have to pay for the mod. that makes it work.

Screwdriva

Reed_Richards said:

1)  I bought an Atag gas boiler in 1998 which could modulate down very low.
2)  Likewise it had weather compensation and load compensation.  This was 24 years ago
3)  Load Compensation via Opentherm.  Any Opentherm-compatible controller should do weather and load compensation.  You'll need the right wiring though, not what you have at present.
4)  Are there really boilers that don't prioritise hot water?
5)  A 10 year warranty is good.  I would be very surprised if you see any H2 in the next 10 years and you may find that you have to pay for the mod. that makes it work.

Didn't realize that condensing boilers have been around that long! Thanks for sharing! 

QrizB

Screwdriva said:

Absolutely nothing wrong with our 5 year old Worcester Bosch 18Ri heat only boiler but it cannot achieve this level of theoretical efficiency, as it lacks the above functionality.

Not wishing to be a gloomster, but it seems a lot of work and expense to save maybe 5% on your annual gas consumption.

(That's just my wet-finger estimate; your current boiler should be 85-90% efficient and so there's not much room for improvement.)

coffeehound

Screwdriva said:

1) Ability of the boiler to modulate down to < 2kW (1:10 modulation ratio), which is quite incredible! 

Hi @Screwdriva, do you have a ref to this figure?  Looking at Viessman's info, they just quote a minimum figure of 2.9 - 3.2 kW, dependant on flow temperature.  In comparison, your WB has a quoted minimum output of 5.54 kW, so yes the Viessman can go significantly lower.

Beyond that, they are pretty similar in efficiency figures.  Your WB is quoted at 86.9% efficiency for a high flow temperature, and 97.6% at 30 ℃ return temperature.

The 100-W is quoted as 88.2% and 98.0% in comparison, so maybe a 1.3% improvement at best.

I saw you mention low flow temperature in your other thread.  Are you heating the DHW tank using the immersion heater or renewables rather than with the boiler?

Screwdriva

QrizB said:

Not wishing to be a gloomster, but it seems a lot of work and expense to save maybe 5% on your annual gas consumption.

No worries - all feedback is useful. To be fair, my installer was transparent about this and said that it'll be around 10% improvement given the existing Greenstar boilers lack all the above efficiency measures + the greater surface area of the underfloor heating. 

We're hoping the underfloor heating will increase comfort levels substantially for us as we're currently "under-radiated".

ed110220

QrizB said:

Screwdriva said:

Absolutely nothing wrong with our 5 year old Worcester Bosch 18Ri heat only boiler but it cannot achieve this level of theoretical efficiency, as it lacks the above functionality.

Not wishing to be a gloomster, but it seems a lot of work and expense to save maybe 5% on your annual gas consumption.

(That's just my wet-finger estimate; your current boiler should be 85-90% efficient and so there's not much room for improvement.)

Sorry to pile in on the negativity but I'd also question installing a new gas boiler when it's technology that's being phased out. Maybe if your previous one failed and a heat pump isn't for you right now, but I wouldn't want to be replacing one newish gas boiler with another when it's likely to be legacy technology soon.

Magnitio

Have you looked at electric boilers?

QrizB

Magnitio said:

Have you looked at electric boilers?

Mostly on this forum we look at them and then run screaming in the other direction!

Magnitio

QrizB said:

Magnitio said:

Have you looked at electric boilers?

Mostly on this forum we look at them and then run screaming in the other direction!

But there are some interesting new developments such as this:

https://tepeo.com/thezeb

Not sure I would want to be an early adopter, but I quite like the concept.