Posted by: @jaynieq

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Thankfully this weather is rare. How’s your usage looking..?

About 70kWh in the last 24 hours, OAT hovering between 2 and 4 degrees. Ouch...!

To put things in perspective, I have plotted weekly and full monthly kWh use since I had the full monitoring setup. Midwinter is hugely expensive, but at other times it is a lot less so: 

Note Spring 2023 includes a period when I tried turning off weather compensation (if I recall, on advice from the professionals...and, in my defence, I was still learning) and using a fixed flow temp, and I learnt my lesson. Compare that Spring to Spring 2024. The OATs were probably a bit less in Spring 2023 compared to Spring 2024, but not different enough to explain the higher usage in Spring 2023.  

Posted by: @jaynieq

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Senso - yes

TRV - yes, radbots

Other thermostat - external air temp

Other heating timer - water thermostat

Wifi interface - yes

myVaillant app - yes but not playing today

Buffer tank - unsure but will send pic later

Occupied - continually as both retired

Elec tariff - still on previous fixed with Octopus as still waiting for DOA

Mother board - see pic

Oil consumption - approx 2000 litres per annum 

Flow temp - not sure if this was included in design info but will confirm asap 

I saw you just posted some new pics.  One questuon about those:

Do you know - Is the big tank just a DHW tank, I think probably so (300l)?, but its just possible that there is an integral buffer tank (I dont think so).  I presume that this is the only tank.

Oil consumption equates to 20000kWh per year, very similar to my gas consumption, so I think its likely the losses of our house are similar, about 7-8kW.  11kW is probably an over estimate (but that's fairly normal).  Dont worry about it.

Your consumption over the past couple of days is not very different to mine.  When its cold its a double whammy, the house loses more heat and the heat pump is less efficient.  In very round terms that means that you can expect to use ~3x as much electricity when its 0 outside as you will use when its 7-8 outside.  With your oil boiler this ratio would have been nearer 2.  The good news is that when its 7+ outside your heat pump will be a lot cheaper to run.  I reckon Im on track to come in at the same price as gas or a little cheaper

You can probably do better on tariff. 

• If you dont have an EV then any OVO tarrif plus their heat pump add on is a much better bet (15p for all the leccy you use for your heat pump).  I dont think this tarriff can survive for long, but while its there....  Your MyVaillant needs to be working, I dont know if you need a smart meter.
• If you have an EV then EON NextDrive 5 is pretty good, its essentially economy 7, about 10% more per unit from 7am-midnight, and about one quarter between midnight and 7am.  This requires a smart meter
• If you want to stick with Octopus then Cosy is probably as good as any
• If you dont have a smart meter your options are probably limited to a fixed tarrif or economy 7.  

If the only other thermostat is the external air temp monitor then thats good.

The radbots are a bit of a concern.  If these are on all rads then thats definitely not good, unless they are turned up well above the design temp.  If they are only on a minority of rads not so concerning.  Can you advise?

From what you have said so far I dont think you are a mile away (credit to your installer) and nor should you be expecting horrendous bills, but there almost certainly improvements to be had particularly around the WC (and, as I mention above, tarriff.

In the absence of the MyVaillant app can you post the following from the sensocomfort

From Information - Energy data:

• All the figures under Environmental yield
• All the figures under Power consumption

The ratio (environmental yield + power consumption)/power consumption is the COP and should be between 3 and 4

from Settings - Installer Level - Installation configuration - circuit 1

• the value against 'heat curve'  (BTW this is where you adjust the WC).
• the value against 'target flow temperature
• the value against 'room temp mod'

I wouldnt change anything in installer settings yet.

Its worth reading the Sensocomfort manual section 2.12  this explains how Vaillant go about WC and how you change it.  The latter is far more user friendly than many, once you get your head around the concept.

Sorry for all the questions but its very difficult to provide suggestions without knowing a bit about the system.  I think there is a good chance its going to come down to something as simple as set most of the radbots high, turn the WC curve down until the house is just warm enough, leave for a while.  

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BTW (in case you dont yet know) weather compensation (WC) adjusts the flow temperature according to the outside air temperature (OAT).  For the past 20 years this method of control has been common on boilers and heat pumps in several countries in mainland Europe, notably Germany and NL, but for some unknown reason we didn't adopt it.  As a result (albeit slightly indirectly) many have been paying 10% more for their heating than they needed to, and enjoying poorer levels of comfort as well.

Anyway now its here and a good thing to.  The basic aim is that the system adjusts the flow temperature to be as low as possible so that the output of the emitters just matches the loss from the house.  The principal driver of the latter is OAT hence why that is used as the reference. 

This may at first seem a bit counterintuitive, since its indoor temperature that we care about.  However there is a problem using IAT as the control parameter, namely that your house (and therefore the IAT) takes a very long time to respond and, in the time that it takes to respond, the conditions can change.  Delays and changes in the characteristics of control loops cause instability (there is a whole branch of engineering, control theory, dedicated to this with some pretty hairy maths).  By using the OAT as the principal driver the system knows in advance what is going to happen and can thus adjust for it with much less instability.

The other advantage of WC is that, because the loss and energy supply just balance, emitters are all (or almost all) of the time at a much lower FT, rather than switching on and off frequently on a thermostat.  This results in reduced temperature variations with time and reduced temperature gradients.  Furthermore both boilers but more particularly heat pumps are more efficient if run in this 'slow and low' way.

You can 'layer on' other variables to tweak the flow temperature, and some heat pumps, including Vaillant, make this possible natively.  Third party systems like Homely take this one step further and factor in varying cost due to ToU tariffs and other things.  However, even with these more sophisticated tweaks, the basic control mechanism remains weather compensation.  Many people find that operating on pure WC gives excellent results, others layer on some tweaks.  This is a bit house and person dependent.

That’s amazing, thank you @JamesPa for being so generous with your time and knowledge. I’ll take the evening to re-read and digest and try to get the myVaillant to load… Hope I’m ok to respond in the morning? 

I’m not as expert as James but we have Vaillant and are happy with the heat level and wince a bit at the cost when it’s this cold

So you ought to be warm enough so that’s the thing to get right and then you can trade off as you need

What temperature do you want your house to be and what is it in degrees C?

Where is your Sensocomfort box located?

Posted by: @judith

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I’m not as expert as James

Whoa, how do you know that?  I've only had my heat pump for just over a month!

Hi, I think partly the problem is the immediate feedback that the electricity meter provides, versus the oil boiler where (I presume) you just get the bill at the end of the year. This is then somewhat compounded by the fact that you got your heat pump in the coldest week of the year so far. 
if we try to calculate what the oil would have cost it hopefully looks a bit better:

as your heat loss is about 9kw, a full day at your design temp would have cost:

9kwh*24h/80% efficiency/10kwh/l*0.70£/l=£15.75

the heat pump should cost:

9kwh*24h/300% efficiency*0.25£/kwh=£18.00

So that looks not too bad and will even itself out when the “warmer” weather comes around and the efficiency goes over to 400%. 
Did your solar install include a battery? If yes octopus cozy or similar can be used to reduce charge in the cheap periods and thus halve your electricity cost  

and yes definitely set up the heat curve and open all the trvs to optimise the system and get it working well , as the others said  

Posted by: @adrian

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9kwh*24h/80% efficiency/10kwh/l*0.70£/l=£15.75

Slight side track. Genuine question. Why 10kWh for the boiler equation?

Posted by: @editor

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Posted by: @adrian

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9kwh*24h/80% efficiency/10kwh/l*0.70£/l=£15.75

Slight side track. Genuine question. Why 10kWh for the boiler equation?

 

it’s because there are 10kwh hiding in every Liter of oil. 

Posted by: @adrian

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it’s because there are 10kwh hiding in every Liter of oil. 

Which is one reason why fossil fuels are successful.  A lead acid battery as used in a car might store 1kWh in about 8l, one 80th of the volumetric energy density (the mass energy density is even more in favour of oil).  Burning oil is very space and mass efficient.

Its also the reason why eating too much oil (it doesn't have to be heating oil, most oils are similarly high in energy density) is likely to make you fat!

Oil is simultaneously wonderful and horrific, on several levels.

Posted by: @jamespa

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Oil is simultaneously wonderful and horrific, on several levels.

Which is why I always found HVO to be an intriguing alternative for home heating, but with the obscene levies imposed on it, it’s not financially viable.

@jaynieq 

We have similar situation in that Matt's (son) MS and other conditions "qualified" our house for ECO4.

1890 cottage. solid brick walls. single glazing. double burner oil fired range providing heating, DHW and cooking. open log fire. single story adapted extension for Matt (double glazed etc)

Our install included internal wall insulation. It should have included 12 solar panels but the surveyor got it wrong and only 9 would fit. 

Now in our second winter and, especially with current weather the running cost IS scary ! Your installer doesn't sound good, although I think that is an area that falls down with the ECO scheme. They seem to be under more time pressure. Ours where, all being subbies on fixed rate for the job with responsibility being passed back to the main contractor. I was/am lucky in being ex engineer (not heating) so was able to extract a fair bit of info during the install to supplement the meagre setup info provided. This forum helped massively all the same.

Overall, despite our dwelling being "wrong" for an ASHP install, and with Matt's non functioning internal body temperature control which precludes "proper/normal/most efficient" control, we ARE a worthwhile amount better off than before (even though I'll easily beat your £50/wk this month 😐) 

I suspect/hope that once you have a handle on controlling your system and are past winter conditions it will look better.

Edit. I make as much use of Octopus Cosy tariff as I can.

I can't make 24hr running the best option here .........my wife insists the bathroom being in 19c during waking hours. It has a relatively large glass (single glazed) area and as outside temps drop the heat loss overnight is such that, so far, I am unable to find a setting that gives overall better efficiency running lower constant system temp than running it a bit higher and being off between 10pm and 6am

@jamespa good morning. Please don’t apologise for all the questions! I’m sorry that I’m slow in responding. It’s down to a combination of daily grandma duties and a frightening lack of tech knowledge! 

The tank on the pic is a 300l DHW. We questioned why such a large tank was needed in a house with no bath tubs and were told it was needed for the system to operate efficiently..(?)

Radbots - are on all but one radiator. We have  x 13. The one without, we were told, was to ‘balance the system’

Im working on the info needed from the Senso panel but am finding it tricky to work with. I will get there in the end. 

The myVaillant saga continues as we don’t have a QR code and suspect that may be with our installer who registered the product on our behalf. I have been trying to contact the installer for 3 hours this morning but they are not answering their phone. I’ve also sent my query to Vaillant and am waiting for their response.. 

Thank you for your time and patience 🙏