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

Reed_Richards

"Advanced Weather Compensation"?  I have seen that term used to describe Weather Compensation" and "Load Compensation" but these are actually separate things (and my Atag gas boiler bought in 1998 could do both).  There is an interesting article on Low Temperature Heating Systems here: https://www.heatgeek.com/benefits-of-low-temprature-heating-systems/ .  As usual with Heat Geek it is OTT  but if the chart of boiler efficiency against return water temperature is to be believed you need the return water to be at about 15 C to achieve your 98% efficiency in which case you certainly do need Weather Compensation.

Edit:  another reference with the same diagram: https://www.purmo.com/au/clever/guide-the-increasing-use-of-low-temperature-water-systems.htm   

Screwdriva

Reed_Richards said:

"Advanced Weather Compensation"?

https://viessmanndirect.co.uk/files/8e57dbc7-8a10-4065-bcc6-a27700ee752a/weather_comp.pdf

Seems like a more intuitive use of weather and room temperature inputs to me. Only available on the 200-W.

BUFF

Screwdriva said:

Reed_Richards said:

Screwdriva said:

...Given the 200-W can modulate below 2kW in theory and has advanced weather compensation and is more efficient and combined with the increase in radiator surface area + UFH, I'm quite optimistic we will see a real world savings % in the double digits over an already efficiency setup. 

I think you may be being over optimistic and double-counting some of the beneficial features.  The best you can achieve with a gas boiler is 100% efficiency.  Your old boiler, operated at 50/30 might well have achieved >90% efficiency.  If the new one has a SCOP of 0.98 (i.e. 98% efficiency) then that is probably because it has all the other features and faculties you list; they are necessities to the performance, not extras.

You may be right on my level of optimism. What is clear is that the Viessmann boiler has a superior modulation ratio and advanced weather compensation, which my Greenstar 18Ri boiler does not. Installing UFH and increasing radiator surface area are additional improvements proven to improve low flow temperature heating.

I'll be sure to report back with real world consumption numbers.

You will have to bear in mind when comparing future system consumption to present system/this year consumption that this has been an unusually mild winter (at least in Glasgow) - my gas consumption is down ~30%.

Reed_Richards

Screwdriva said:

https://viessmanndirect.co.uk/files/8e57dbc7-8a10-4065-bcc6-a27700ee752a/weather_comp.pdf

Seems like a more intuitive use of weather and room temperature inputs to me. Only available on the 200-W.

Strangely there is no mention of Load Compensation and I cannot see an indication  that this function is performed.  If your desired room temperature is say 21 C and the actual temperature is 18 C then you want the boiler to work quite hard.  But when the actual temperature approaches the desired temperature , say 20.9 C, you want the boiler to modulate its output right down so it maintains just enough output to get to 21 C then maintain a steady temperature.  This will give you a boiler flow temperature that is completely stable (for as long as the outside temperature remains the same). 

Screwdriva

BUFF said:

You will have to bear in mind when comparing future system consumption to present system/this year consumption that this has been an unusually mild winter (at least in Glasgow) - my gas consumption is down ~30%.

Yes, of course. In the thread I've linked, I compare only months with near identical average temperatures. 

Reed_Richards

The top chart (from your referenced document) makes no sense and the bottom one worries me because you never appear to achieve the steady boiler flow temperature that Load Compensation would give you.

ABrass

Reed_Richards said:

The top chart (from your referenced document) makes no sense and the bottom one worries me because you never appear to achieve the steady boiler flow temperature that Load Compensation would give you.

Perfect weather compensation wouldn't give you a steady boiler temperature, it would increase and decrease to match the rate of heat loss, which in turn would vary because of external temperature.

The graphs are a bit silly, Apparently before you have weather compensation you like 10 degree rooms but afterwards you punch it up to 20.

Cardew

I have weather compensation on my Viessmann 100 boiler - so not advanced weather compensation.

I wonder how much it actually saves? Viessmann state UP TO 15% but of course 'up to' covers a saving of 0.0001%!!

Screwdriva

This is the most thorough review of the boiler I could find. 

https://www.heatgeek.com/viessmann-vitodens-200-boiler-review/

Reed_Richards

they also offer external controls and room sensors in the form of the Vitotrol 200 and Vitotrol 300. These both give the optimum solution of placing a room influence % on your weather compensated control.

It looks like you would need the Vitrotrol 300A to give you control over your upstairs and downstairs zones and the ability to program and control your hot water.  Any other controller and you might be in difficulty because:

 there is an Opentherm module available opening it up to third-party controls. However, this module is hard to obtain in the UK and is not supported by Viessmann UK.