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

70sbudgie

Screwdriva said:

An early preview of what to expect this winter perhaps? August was the first month the cylinder immersion heater wasn't used (given Agile Outgoing prices.) The follow are the actual measured consumption figures YoY:

August 2021 - 20 metre units/ 640 kWh used for DHW
August 2022 - 13 metre units/ 415 kWh used for DHW

Consumption patterns were largely the same. The only variable was pipe lagging. It's clear the Viessmann 200-W has yielded gas consumption savings of ~35% for DHW. If my maths is correct, at the new price cap tariff, this would translate to a savings of £400 per annum for hot water.

Have these figures changed your expectations of the CH savings?

Screwdriva

70sbudgie said:

Have these figures changed your expectations of the CH savings?

Very difficult to compare DHW savings to CH but I will say we did not expect the actual savings to exceed ~20% as a best case. If you scroll back to the first page, you’ll find these actual numbers fly in the face of the opinions shared by the gloomier lot!

Our goal was similar in that we wanted to delay our heat pump purchase to allow for technological advancement, while saving as much gas as possible. The video shared highlights of what was done to make our home "heat pump ready".

To summarize, we installed:

T22 double radiators (the largest size we could accommodate)
Wet UFH with XPS 25mm floor insulation
Triple glazing
V200-W boiler

We are currently aiming for the near impossible EPC A rating but will likely miss it.

I will continue to post monthly consumption data to ensure consistency but it is safe to say that our installer is pleasantly surprised by these numbers. 

70sbudgie

I've just watched the video. It's great. I will be digging out my boiler manual and looking at my UFH manifold again.

Last weekend I stood and stared at pipework, but couldn't get my head around what I was looking at. My boiler and hot water tank are right next to each other, so I should be able to trace from one to the other! 

Did your plumber balance your new (configuration of) radiators for you or is that part of the joy to come?

Screwdriva

70sbudgie said:

Did your plumber balance your new (configuration of) radiators for you or is that part of the joy to come?

He's a great plumber. And yes, he flushed and balanced everything. 

Screwdriva

September 2021 - 19 metre units/ 596 kWh used for DHW
September 2022 - 16 metre units/ 509 kWh used for DHW

15% gas savings YoY in September despite an 21% increase in DHW usage over August.

Alnat1

Sep 2021 155.85kWh
Sep 2022 83.46kWh (not including today)

45% gas savings in September

Didn't spend anything, simply turned boiler temperature down and heated for less time 

Screwdriva

Alnat1 said:

Sep 2021 155.85kWh
Sep 2022 83.46kWh (not including today)

45% gas savings in September

Didn't spend anything, simply turned boiler temperature down and heated for less time 

We are yet to turn on heating. Savings are primarily for DHW so far. Central heating savings, if any, will be reflected Nov onwards

Screwdriva

October 2021 - 1006 kWh used -> Average temperature in London 13.6 degrees Celsius
October 2022 -   489 kWh used -> Average temperature in London 14.7 degrees Celsius.

The warmer weather & improvements in insulation have helped us avoid using our heating system so far. That said, our gas consumption remains much lower than expected. It is likely next month's update will include gas consumption for heating and DHW. 

Screwdriva

Yesterday was the first day of heating. Within 15 minutes of activation, the radiator circuit (9 rads) achieved flow temperatures which settled at a remarkable 37 degrees. The V200 boiler modulated itself down to 11.6% and stayed there for hours. That's  ~2.2 kWh, which is an unbelievable 60% reduction in gas consumption when compared to the Greenstar boiler it replaced (5.5 kWh peak modulation). 

The now oversized T22 radiators and UFH (flow temp <30 degrees) continue to keep the house very comfortable, which came as a pleasant surprise given we are used to high temperature, hot radiator on/off heating. 

michaels

Screwdriva said:

Yesterday was the first day of heating. Within 15 minutes of activation, the radiator circuit (9 rads) achieved flow temperatures which settled at a remarkable 37 degrees. The V200 boiler modulated itself down to 11.6% and stayed there for hours. By my maths, that's < 2.2 kWh, which is a significant reduction in gas consumption. 

The now oversized T22 radiators and UFH (flow temp <30 degrees) continue to keep the house very comfortable, which came as a pleasant surprise given we are used to high temperature, hot radiator on/off heating. 

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