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

Reed_Richards

Will you need to balance the radiators now?

Screwdriva

michaels said:

Wow - your display gives a lot more info than our 10 year old one.

Be really interested to see if you find that curve is steep enough to maintain a constant interior temp when it gets colder outside as ours is a lot steeper - I guess it depends on insulation and emitter power.

It is so good when it just works - ours did for the first 6 years but since then seems to have developed restricted flow through the heat exchanger (despite having a filter device).  When the boiler modulates down, so does the pump and this reduces the flow too much so not enough heat 'leaves' the boiler quickly enough and it cycles on and off.  Works fine when providing more heat when the outside temp is lower or doing the hot water as the pump ramps back up and the flow is sufficient.  We had the heat exchanger flushed once, that helped for a while, apparently replacing it is uneconomic

Did you power flush your system prior to installation and every 3-5 years? I think that's a must do as Viessmann is the only company that does not require a filter to be installed in its installation instructions. 

I agree - it's amazing to just leave it on and enjoy a comfortable home knowing you're consuming half as much gas as we did a year ago. When compared to a heat pump we nearly purchased, assuming a SCOP of 4.5, which we can now verify is achievable, we would have saved £350 per annum over the V200 .  But it would have cost us ~£6K extra, or 17 years to recover this. 

Reed_Richards said:

Will you need to balance the radiators now?

Balanced. Currently running flow temperature < 37 degrees @ 11.5% modulation, so they're pretty much set up for maximized surface area.  

Reed_Richards

Screwdriva said:

Reed_Richards said:

Will you need to balance the radiators now?

Balanced. Currently running flow temperature < 37 degrees @ 11.5% modulation, so they're pretty much set up for maximized surface area.  

By "balanced" I meant adjusting the flow rates through the radiators so all the rooms warm up at a similar rate.  On reflection, it probably hasn't been cold enough to do that yet.  Do your radiators have TRVs?

Screwdriva

Reed_Richards said:

By "balanced" I meant adjusting the flow rates through the radiators so all the rooms warm up at a similar rate.  On reflection, it probably hasn't been cold enough to do that yet.  Do your radiators have TRVs?

Yes, all balanced and all have TRVs. You'll remember that the rads were upsized during installation of the boiler - the increase in comfort despite the flow temperature can only be described as truly remarkable. 

Screwdriva

A remarkable 49.7% measured reduction in gas use compared to 11/21. Some of that is down to the 2 degree warmer average temperature this month, and some to the efficiency improvements made (UFH, triple glazing in a bedroom, upsized radiators). The Viessmann 200-W has consistently modulated itself down to a constant 2.2 kWh output on most days, rarely exceeding 4 kWh, while keeping both zones very comfortable (The old Worcester Bosch Greenstar's lowest possible output was 5.5 kWh).

Safe to say, this has exceeded all expectations, essentially negating most of the impact from the energy price increases. 

Nov 21 - 2584 kWh  - Avg London temperature -   8.9 C
Nov 22 - 1300 kWh  - Avg London temperature - 10.9 C 

michaels

Nov 21 3341 kwh
Nov 22 1715 kwh

Same boiler, just warmer air temps and being more careful with usage due to the high prices.

How is your (compared to us) flat curve doing at keeping the internal temperature constant when it gets and stays colder outside like the last couple of days?

BUFF

Nov 21 518kWh
Nov 22  44kWh

No changes to boiler, controls or house fabric.
Haven't had the heating on yet this Autumn ... 

michaels

BUFF said:

Nov 21 518kWh
Nov 22  44kWh

No changes to boiler, controls or house fabric.
Haven't had the heating on yet this Autumn ... 

I'm hoping very much that you have an electric shower...

Screwdriva

michaels said:

Nov 21 3341 kwh
Nov 22 1715 kwh

Same boiler, just warmer air temps and being more careful with usage due to the high prices.

How is your (compared to us) flat curve doing at keeping the internal temperature constant when it gets and stays colder outside like the last couple of days?

Same boiler? As in a V200-W?

The temperature (flow temperature) is modulated by the external temperature sensor. When it gets colder outside, it simply adjusts this upwards by a few %. That said, it has yet to generate more than than 3kW consistently. The range, even at 5 degrees temperature, has been between 2.2-3 kW. 

What the above numbers don't show is the drastically improved comfort levels experienced. Gone are the days of dreading going downstairs for fear of getting "purple toes". BUFF said:

Haven't had the heating on yet this Autumn ... 

We were able to hold off till heating last month but once the internal temperature drops below 17 degrees, the boiler will always fire up.

michaels

Screwdriva said:

michaels said:

Nov 21 3341 kwh
Nov 22 1715 kwh

Same boiler, just warmer air temps and being more careful with usage due to the high prices.

How is your (compared to us) flat curve doing at keeping the internal temperature constant when it gets and stays colder outside like the last couple of days?

Same boiler? As in a V200-W?

The temperature (flow temperature) is modulated by the external temperature sensor. When it gets colder outside, it simply adjusts this upwards by a few %. That said, it has yet to generate more than than 3kW consistently. The range, even at 5 degrees temperature, has been between 2.2-3 kW. 

What the above numbers don't show is the drastically improved comfort levels experienced. Gone are the days of dreading going downstairs for fear of getting "purple toes". BUFF said:

Haven't had the heating on yet this Autumn ... 

We were able to hold off till heating last month but once the internal temperature drops below 17 degrees, the boiler will always fire up.

A 200 system boiler but 11 years old now.  Our curve gradient is 1.6 - ie outside temp goes down by one degree, return temp needs to go up by 1.6 to maintain the fixed interior temp.  You showed us earlier that your slope is 1.0 which I guess suggests your insulation is better and/or your emitters are bigger.  I was just wondering if you were finding that slope was working for you now the temps were getting colder or whether you might need to tweak it a bit steeper?